Photoacoustic device and system

Abstract

An apparatus may include a platen, a light source system, and an ultrasonic receiver system. The light source system may be configured to provide light to a target object on an outer surface of the platen. The light source system may be configured to direct light along a first axis oriented at a first angle relative to an outer surface of the platen. The ultrasonic receiver system may be configured to receive ultrasonic waves generated by a target object in response to light from the light source system. The ultrasonic receiver system may include one or more receiver elements located in a receiver plane. The normal to the receiver plane may be oriented along a second axis at a second angle relative to the outer surface of the platen. The first angle may be different than the second angle.

Description

[0001] Priority Claim

[0002] This application claims priority to U.S. Patent Application No. 18 / 069,859, filed December 21, 2022, entitled "Photoacoustic Device and System", which is hereby incorporated by reference in its entirety for all purposes.

[0003] Cross - Reference to Related Applications

[0004] This application is related to U.S. Patent Application No. 18 / 069,901, entitled "Photoacoustic Device and System Comprising One or More Optical Waveguide Components" (Attorney Docket No. 2300761 / QUALP591US), U.S. Patent Application No. 18 / 069,877, entitled "Semi - Compact Photoacoustic Device and System" (Attorney Docket No. 2205722U1 / QUALP580AUS), U.S. Patent Application No. 18 / 069,882, entitled "Semi - Compact Photoacoustic Device and System" (Attorney Docket No. 2205722U2 / QUALP580BUS), U.S. Patent Application No. 18 / 069,885, entitled "Semi - Compact Photoacoustic Device and System" (Attorney Docket No. 2205722U3 / QUALP580CUS), U.S. Patent Application No. 18 / 069,888, entitled "Semi - Compact Photoacoustic Device and System" (Attorney Docket No. 2205722U4 / QUALP580DUS), and U.S. Patent Application No. 18 / 069,893, entitled "Semi - Compact Photoacoustic Device and System" (Attorney Docket No. 2205722U5 / QUALP580EUS), all of which are hereby incorporated by reference in their entireties for all purposes. Technical Field

[0005] This disclosure generally relates to photoacoustic devices and systems. Background Art

[0006] A variety of different sensing technologies and algorithms are being implemented in devices for various biometric and biomedical applications, including health and wellness monitoring. This drive is, in part, a result of the limitations in the availability of traditional measurement devices for continuous, non - invasive, and mobile monitoring. Some such devices are or include photoacoustic devices. Although some previously deployed photoacoustic devices and systems can provide acceptable results, improved photoacoustic devices and systems would be desirable. Summary of the Invention

[0007] The systems, methods, and devices of this disclosure each have several aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

[0008] One innovative aspect of the subject matter described in this disclosure can be implemented in a device. The device can include a platen, a light source system, and a receiver system. The receiver system can be or can include an ultrasonic receiver system. In some embodiments, a mobile device (such as a wearable device, a cellular phone, etc.) can be or can include at least a portion of the device.

[0009] The light source system can be configured to provide light to a target object on an outer surface of the platen. The light source system can be configured to direct light along a first axis oriented at a first angle relative to the outer surface of the platen.

[0010] The ultrasonic receiver system can be configured to receive ultrasonic waves generated by the target object in response to light from the light source system. The ultrasonic receiver system can include one or more receiver elements located in a receiver plane. A normal of the receiver plane can be oriented along a second axis at a second angle relative to the outer surface of the platen.

[0011] In some examples, the second angle can be approximately 90 degrees. In some alternative examples, the second angle can be in the range from 20 degrees to 50 degrees.

[0012] According to some examples, at least a portion of the platen can be configured to direct ultrasonic waves generated by the target object along a third axis that is at a third angle relative to the outer surface of the platen. In some examples, the third axis can be parallel to or substantially parallel to the second axis. In some examples, the third angle can be different from the first angle.

[0013] In some examples, the light source system can include one or more light directing elements configured to direct light from the light source system toward the target object along the first axis. In some such examples, the one or more light directing elements can include a diffraction grating. In some examples, the one or more light directing elements can include a lens.

[0014] According to some examples, the light source system can include a light source system surface having a normal parallel to or substantially parallel to the first axis. In some such examples, a light source of the light source system is located on the light source system surface.

[0015] In some examples, a first platen portion located between the light source system and the outer surface of the platen can have a first platen portion thickness that is less than a second platen portion thickness of a second platen portion located between at least one receiver element of the ultrasonic receiver system and the outer surface of the platen. In some alternative examples, a first platen portion located between the light source system and the outer surface of the platen can have a first platen portion thickness that is greater than a second platen portion thickness of a second platen portion located between at least one receiver element of the ultrasonic receiver system and the outer surface of the platen.

[0016] According to some examples, the device may include an acoustic waveguide configured to direct ultrasonic waves towards at least one receiver element of an ultrasonic receiver system. In some examples, a first distance that light from a light source system travels through the platen may be less than a second distance that ultrasonic waves travel through the platen and reach at least one receiver element of the ultrasonic receiver system. According to some examples, the platen may include a recessed area configured to receive a finger.

[0017] In some examples, a portion of the platen configured to receive light from a light source system may also be configured to reflect ultrasonic waves generated by a target object towards at least one receiver element of the ultrasonic receiver system. In some such examples, a first distance that light from the light source system travels through the platen portion to the target object may be less than a second distance that ultrasonic waves travel from the platen portion to at least one receiver element of the ultrasonic receiver system.

[0018] According to some examples, a first axis may be perpendicular or substantially perpendicular to an outer surface. At least a portion of the platen may be configured to direct ultrasonic waves generated by a target object along a third axis that is at a third angle relative to the outer surface of the platen. In some examples, a second axis may be parallel or substantially parallel to the third axis. In some examples, the first angle may be different from the third angle. In some such examples, a first portion of the platen may be configured to direct a first portion of ultrasonic waves generated by a target object along the third axis, and a second portion of the platen may be configured to direct a second portion of ultrasonic waves generated by a target object along a fourth axis that is at a fourth angle relative to the outer surface. According to some examples, the third angle may be different from the first angle and the fourth angle.

[0019] In some examples, the ultrasonic receiver system may include a first receiver element located in a first receiver plane that is substantially perpendicular to the third axis. In some such examples, the ultrasonic receiver system may include a second receiver element located in a second receiver plane that is substantially perpendicular to the fourth axis.

[0020] According to some examples, at least a portion of the platen may be configured to direct ultrasonic waves generated by a target object along a third axis that is at a third angle relative to the outer surface of the platen. In some such examples, the third axis may be perpendicular or substantially perpendicular to the outer surface. In some examples, a second axis may be parallel or substantially parallel to the third axis. In some examples, the first angle may be different from the third angle. According to some examples, the light source system may include a first light source portion and a second light source portion, the first light source portion being configured to direct a first light towards the target object along the first axis, and the second light source portion being configured to direct a second light towards the target object along a fourth axis that is at a fourth angle relative to the outer surface of the platen. In some such examples, the third angle may be different from the first angle and the fourth angle.

[0021] In some examples, the device may include sound insulation material located between at least a portion of the light source system and the ultrasonic receiver system. According to some examples, the device may include electromagnetic noise suppression material proximate to at least a portion of the ultrasonic receiver system, proximate to conductive material attached to at least a portion of the ultrasonic receiver system, or a combination thereof.

[0022] According to some examples, the device may be configured to attach to a person's wrist. In some such examples, the light source system may be configured to provide light to one or more arteries within the person's wrist. In some examples, the light source system may be configured to provide light to one or more arteries within the person's finger.

[0023] According to some examples, the platen, the light source system, or a combination thereof may be configured to deliver light in the range of 400 to 1000 nanometers. In some examples, the light source system may be configured to provide light pulses having a pulse width in the range of 50 to 500 nanoseconds.

[0024] In some examples, at least a portion of the ultrasonic receiver system may include a composite piezoelectric material. According to some examples, at least a portion of the ultrasonic receiver system may include a conductive layer, a first piezoelectric layer proximate to a first side of the conductive layer, and a second piezoelectric layer proximate to a second side of the conductive layer. In some such examples, the first piezoelectric layer and the second piezoelectric layer may include a piezoelectric copolymer, a piezoelectric composite, or a combination thereof. In some examples, the device may include a first electrically grounded layer portion and a second electrically grounded layer portion. In some such examples, the first piezoelectric layer may be located between the first electrically grounded layer portion and the conductive layer, and the second piezoelectric layer may be located between the second electrically grounded layer portion and the conductive layer.

[0025] According to some examples, at least a portion of the platen may have an acoustic impedance configured to approximate the acoustic impedance of the material near that portion of the platen. In some examples, the outer surface of the platen or a layer located on the outer surface of the platen may have an acoustic impedance configured to approximate the acoustic impedance of a person's skin. In some examples, the device may include one or more mirror layers configured to reflect light away from one or more portions of the ultrasonic receiver system.

[0026] In some examples, the device may include a layer located between the platen and the one or more receiver elements. The acoustic impedance of the layer may be within the acoustic impedance range between the acoustic impedance of the platen and the acoustic impedance of the one or more receiver elements.

[0027] According to some examples, the device may include one or more antireflection layers. In some such examples, at least one of the one or more antireflection layers may be positioned proximate an outer surface of the platen. As used herein, "antireflection" refers to light. In other words, an antireflection layer is a layer configured to reduce or inhibit reflection of light.

[0028] In some examples, at least a portion of the platen may include an acoustic lens system. In some such examples, the acoustic lens system may include a spherical lens, a cylindrical lens, or both. According to some examples, the acoustic lens system may be positioned on the outer surface of the platen or positioned proximate the outer surface of the platen.

[0029] According to some examples, the device may include one or more optical waveguides. In some such examples, at least a portion of one of the one or more optical waveguides may be located within a portion of the platen.

[0030] In some embodiments, the device may include a control system. The control system may include one or more general single-chip or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or combinations thereof. According to some examples, the control system may be configured to control a light source system to emit light and to receive a signal from an ultrasonic receiver corresponding to ultrasonic waves generated by a target object. In some such examples, the control system may be configured to identify a vascular signal from the ultrasonic receiver, the vascular signal corresponding to ultrasonic waves generated by blood within a blood vessel of the target object, ultrasonic waves generated by one or more blood vessel walls, or a combination thereof. In some such examples, the control system may be configured to estimate one or more cardiac characteristics at least in part based on the vascular signal.

[0031] Additional innovative aspects of the subject matter described in this disclosure can be implemented in a method. The method may include controlling, by a control system, a light source system to emit light. The method may include receiving, by the control system, a signal from an ultrasonic receiver corresponding to ultrasonic waves generated by a target object. The method may include identifying, by the control system, a vascular signal from the ultrasonic receiver, the vascular signal corresponding to ultrasonic waves generated by blood within a blood vessel of the target object, ultrasonic waves generated by one or more blood vessel walls, or a combination thereof. In some such examples, the method may include estimating, by the control system, one or more cardiac characteristics at least in part based on the vascular signal.

[0032] Some or all of the methods described herein may be performed by one or more devices according to instructions (such as software) stored on a non - transitory medium. Such a non - transitory medium may include storage devices such as those described herein, including but not limited to random access memory (RAM) devices, read - only memory (ROM) devices, and the like. Thus, some innovative aspects of the subject matter described in this disclosure can be implemented on one or more non - transitory media having software stored thereon. The software may include instructions for controlling one or more devices to perform one or more of the disclosed methods.

[0033] According to some such examples, the method may include controlling a light source system to emit light through a control system. The method may include receiving, through the control system, a signal from an ultrasonic receiver corresponding to ultrasonic waves generated by a target object. The method may include identifying, through the control system, a vascular signal from the ultrasonic receiver, the vascular signal corresponding to ultrasonic waves generated by blood within blood vessels of the target object, ultrasonic waves generated by one or more blood vessel walls, or a combination thereof. In some such examples, the method may include estimating, through the control system, one or more cardiac characteristics based at least in part on the vascular signal.

[0034] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. Note that the relative dimensions in the figures below may not be drawn to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Shows an example of a blood pressure monitoring device based on photoplethysmography (PPG).

[0036] Figure 2 Shows an example of a blood pressure monitoring device based on photoacoustic plethysmography (which may be referred to herein as PAPG).

[0037] Figure 3 Is a block diagram showing example components of a device according to some disclosed implementations.

[0038] Figure 4A Shows example components of a device according to some disclosed implementations.

[0039] Figure 4B Shows example components of a device according to some disclosed implementations.

[0040] Figure 5 Shows example components of an alternative device according to some disclosed implementations.

[0041] Figure 6 Shows example components of an alternative device according to some additional disclosed implementations.

[0042] Figure 7 Illustrates example components of an alternative device according to some disclosed embodiments.

[0043] Figure 8 、 9 and 10 illustrate example components of a device according to some alternative embodiments.

[0044] Fig.11 Illustrates example components of a device according to some additional embodiments.

[0045] Fig.12 Illustrates example components of a device according to some additional embodiments.

[0046] Fig.13 Illustrates example components of a device according to some additional embodiments.

[0047] Fig.14 Illustrates example components of a device according to some additional embodiments.

[0048] Fig.15 Illustrates example components of a device according to some additional embodiments.

[0049] Fig.16 Illustrates example components of a device according to some additional embodiments.

[0050] Fig.17 Illustrates example components of a device according to some additional embodiments.

[0051] Fig.18 Illustrates example components of a device according to some additional embodiments.

[0052] Fig.19 Illustrates example components of a device according to some additional embodiments.

[0053] Fig. 20 Illustrates example components of a device part according to some additional embodiments.

[0054] Fig.21 Illustrates example components of a device part according to some embodiments.

[0055] Fig. 22 Illustrates example components of a device part according to some alternative embodiments.

[0056] Fig.23 Is a flowchart that illustrates examples of some disclosed operations.

[0057] Fig.24 Illustrates that can be according to Fig.23Examples of heart rate waveform (HRW) features extracted by some embodiments of the method.

[0058] Fig.25 Shows an example of a device that can be used in a system for estimating blood pressure based at least in part on pulse transit time (PTT).

[0059] Fig.26 Shows a schematic cross-sectional side view of a portion of an artery through which a pulse is propagating.

[0060] Fig.27A Shows an example of a wearable monitoring device designed to be worn on the wrist according to some embodiments.

[0061] Fig.27B Shows an example of a wearable monitoring device designed to be worn on a finger according to some embodiments.

[0062] Fig.27C Shows an example of a wearable monitoring device designed to be located on an earplug according to some embodiments.

[0063] Like reference numerals and names in the various figures represent like elements. Detailed Description

[0064] For purposes of describing aspects of the present disclosure, the following description is directed to certain embodiments. However, those of ordinary skill in the art will readily recognize that the teachings herein can be applied in many different ways. Some of the concepts and examples provided in the present disclosure are particularly applicable to blood pressure monitoring applications. However, some embodiments can also be applicable to other types of biosensing applications, as well as other fluid flow systems. The described embodiments can be implemented in any apparatus, device, or system that includes a device as disclosed herein. Additionally, it is contemplated that the described embodiments can be included in or associated with various electronic devices, such as but not limited to: mobile phones, cellular phones supporting multimedia Internet, mobile TV receivers, wireless devices, smart phones, smart cards, wearable devices such as bracelets, armbands, wristbands, rings, headbands, patches, etc., Bluetooth devices, personal data assistants (PDAs), wireless email receivers, handheld or portable computers, netbooks, notebooks, smartbooks, tablet computers, printers, copiers, scanners, fax devices, global positioning system (GPS) receivers / navigators, cameras, digital media players, gaming consoles, watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, automotive displays (including odometer and speedometer displays, etc.), cockpit controls and / or displays, camera viewing displays (such as the display of a rearview camera in a vehicle), building structures, microwave ovens, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable storage chips, washing machines, dryers, washer / dryers, parking meters, vehicle doors, autonomous or semi-autonomous vehicles, drones, Internet of Things (IoT) devices, etc. Thus, the teachings are not intended to be limited to the specific embodiments depicted and described with reference to the drawings; rather, the teachings have broad applicability, which will be apparent to those of ordinary skill in the art.

[0065] Compared to more invasive health monitoring devices such as cuff-based or catheter-based blood pressure measurement devices, non-invasive health monitoring devices such as photoacoustic plethysmography (PAPG)-based devices have various potential advantages. However, it has proven difficult to design a satisfactory compact or semi-compact PAPG-based device. (Some "semi-compact" devices can have a length in the range of 5.0 mm to 40 mm. Some semi-compact devices can have a length in the range of 6.0 mm 2 to 50 mm 2The cross-sectional area within the range of. A "compact" device is smaller than a semi-compact device. For example, some semi-compact devices recently developed by the present assignee to mitigate spurious signals such as electromagnetic interference (EMI) signals, signals from reflected light, and signals from reflected sound waves can be too large to be conveniently deployed in wearable devices such as watches, patches, or earbuds.

[0066] Some disclosed devices include a platen, a light source system, and an ultrasonic receiver system. According to some embodiments, the light source system can be configured to direct light along a first axis that is oriented at a first angle with respect to an outer surface of the platen on which a target object can be placed. In some such embodiments, the normal of the receiver plane can be oriented along a second axis that is at a second angle with respect to the outer surface of the platen. In some embodiments, the platen can include an anti-reflection layer, a mirror layer, or a combination thereof. According to some embodiments, the platen can have an outer surface or a layer on the outer surface that has an acoustic impedance configured to be close to the acoustic impedance of human skin. In some embodiments, the platen can have a surface proximate to the ultrasonic receiver system, or a layer on the surface proximate to the ultrasonic receiver system, that has an acoustic impedance configured to be close to the acoustic impedance of the ultrasonic receiver system.

[0067] Particular embodiments of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages. Various disclosed configurations include devices with PAPG functionality that are compact enough to reside in wearable devices. In some embodiments that include an anti-reflection layer, a mirror layer, or a combination thereof, these elements can be configured to reduce the amount of light from the light source system received by the ultrasonic receiver system, thereby mitigating noise. The acoustic impedance matching layer can mitigate unwanted reflections of sound waves, thereby mitigating another type of noise.

[0068] Figure 1 An example of a photoplethysmography (PPG)-based blood pressure monitoring device is shown. Figure 1 Examples of arteries, veins, arterioles, venules, and capillaries (including those within finger 115) of the circulatory system are shown. In Figure 1 In the example shown, an electrocardiogram (ECG) sensor has detected a proximal arterial pulse near the heart 116. Some examples of the measurement of arterial pulse transit time (PTT) based on the arterial pulse measured by two sensors are described below, where in some embodiments one of the two sensors can be an ECG sensor.

[0069] According to Figure 1In the example shown, a light source including one or more lasers or light-emitting diodes (LEDs) has emitted light (in some examples, green light, red light, and / or near-infrared (NIR) light), which has penetrated the tissue in the illumination area of finger 115. The reflections from this tissue detected by a photodetector can be used to detect the change in blood volume in the illuminated area of finger 115, which corresponds to a heart rate waveform.

[0070] As Figure 1 shown in heart rate waveform diagram 118, the capillary heart rate waveform 119 has a different shape and is phase-shifted relative to the arterial heart rate waveform 117. In this simple example, the detected heart rate waveform 121 is a combination of the capillary heart rate waveform 119 and the arterial heart rate waveform 117. In some cases, the response of one or more other blood vessels can also be part of the heart rate waveform 121 detected by a PPG-based blood pressure monitoring device. PPG-based blood pressure monitoring devices are not optimal because PPG superimposes data corresponding to the blood volumes of all illuminated blood vessels, each of which exhibits a different and time-shifted change in blood volume. Nevertheless, there are many deployed PPG-based blood pressure monitoring devices.

[0071] Figure 2 An example of a blood pressure monitoring device based on photoacoustic plethysmography, which may be referred to herein as PAPG, is shown. Figure 2 Shown Figure 1 is the same example of arteries, veins, arterioles, venules, and capillaries within finger 115 shown in Figure 2 In some examples, the light source shown can be or can include one or more LEDs, one or more laser diodes, etc. In this example, as Figure 1 shown in

[0072] In Figure 2In the example shown, the blood vessels (and the components of the blood itself) are heated by incident light from a light source and emit sound waves. In this example, the emitted sound waves include ultrasonic waves. According to this embodiment, the sound wave emission is detected by an ultrasonic receiver, which in this example is a piezoelectric receiver. The photoacoustic emission from the irradiated tissue detected by the piezoelectric receiver can be used to detect the blood volume change corresponding to the heart rate waveform in the irradiated area of the finger 115. Although some of the tissue areas shown as irradiated deviate from the tissue areas shown as generating photoacoustic emission, this is merely for illustrative convenience. It will be understood that the irradiated tissue will actually be the tissue that generates photoacoustic emission. In addition, it will be understood that the maximum level of photoacoustic emission will generally be generated along the same axis as the maximum level of illumination. In some examples, the ultrasonic receiver can be the case of the receiver system 302 described below with reference to Figure 3 The receiver system 302 described below with reference to

[0073] Figure 1 An important difference between the PPG-based system of Figure 2 And the PAPG-based method of Figure 2 Is that the sound waves shown in Figure 1 Propagate much slower than the reflected light waves shown in Figure 2 Therefore, depth discrimination based on the arrival time of the sound waves shown in Figure 1 Is possible, while depth discrimination based on the arrival time of the light waves shown in

[0074] This depth discrimination allows some of the disclosed embodiments to separate the sound waves received from different blood vessels. According to some such examples, such depth discrimination allows the arterial heart rate waveform to be distinguished from the venous heart rate waveform and other heart rate waveforms. Therefore, blood pressure estimation based on the depth discrimination PAPG method can be much more accurate than blood pressure estimation based on the PPG-based method.

[0075] Figure 3 Is a block diagram showing example components of a device according to some disclosed embodiments. In this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. Some embodiments of the device 300 may include a control system 306, an interface system 308, a noise reduction system 310, or a combination thereof.

[0076] Various examples of the platen 301 and various configurations of the light source system 304 and the receiver system 302 are disclosed herein. Some examples are described in more detail below with reference to FIGS. 4-19.

[0077] In some embodiments where the receiver system 302 includes an ultrasonic receiver system, the platen 301 may be configured to increase the intensity of ultrasonic energy received by at least a portion of the ultrasonic receiver system. In some such embodiments, the platen 301 may include an acoustic waveguide. According to some embodiments, the platen 301 may include an acoustic lens system. The acoustic lens system may be positioned, for example, on the outer surface of the platen 301 or positioned adjacent to the outer surface of the platen 301. The acoustic lens system may include, for example, a spherical lens or a cylindrical lens. In some such examples, the outer surface of the platen 301 may include a recess having a shape corresponding to a portion of a sphere, a portion of a cylinder, or both. According to some examples, at least a portion of the ultrasonic receiver system may provide an acoustic focusing function. For example, at least a portion of the ultrasonic receiver system may be located on a curved surface.

[0078] According to some examples, the platen 301, the light source system 304, or a combination thereof may be configured to deliver at least some of the light from the light source system along a first axis or substantially along a first axis to the outer surface of the platen (or to a target object on or near the outer surface), the first axis being oriented at a first angle with respect to the outer surface of the platen. In this regard, "substantially along the first axis" may mean within an angular range of plus or minus 10 degrees of the first axis, within an angular range of plus or minus 15 degrees of the first axis, within an angular range of plus or minus 20 degrees of the first axis, within an angular range of plus or minus 25 degrees of the first axis, within an angular range of plus or minus 30 degrees of the first axis, or within another such angular range.

[0079] In some examples, the light source system 304 may include a light source system surface having a normal parallel or substantially parallel to the first axis. In some such examples, the light source of the light source system may be positioned on the light source system surface or positioned adjacent to the light source system surface.

[0080] According to some examples, the receiver system 302 may include one or more receiver elements located in a receiver plane. The normal of the receiver plane may be oriented along a second axis or substantially along a second axis, the second axis being at a second angle with respect to the outer surface of the platen. In this regard, "substantially along the second axis" may mean within an angular range of plus or minus 10 degrees of the second axis, within an angular range of plus or minus 15 degrees of the second axis, within an angular range of plus or minus 20 degrees of the second axis, within an angular range of plus or minus 25 degrees of the second axis, within an angular range of plus or minus 30 degrees of the second axis, or within another such angular range. According to some examples, the second axis may be parallel to the first axis. However, in some examples, the second angle may be different from the first angle.

[0081] In some examples, at least a portion of the platen 301 can be configured to transmit at least some of the ultrasonic waves generated by the target object along a third axis or substantially along the third axis, where the third axis is at a third angle relative to the outer surface of the platen. According to some examples, the third axis can be parallel to the second axis.

[0082] According to some examples, the platen 301 can include different portions that can have different thicknesses, orientations, etc. according to a particular implementation. In some examples, the platen 301 can include a first platen portion located between the light source system and the outer surface of the platen. In some examples, the first platen portion can have a first platen portion thickness that can be less than the second platen portion thickness of a second platen portion located between at least one receiver element of the receiver system 302 and the outer surface of the platen. In some such examples, the first platen portion can be configured to receive light from the light source system and can also be configured to reflect ultrasonic waves generated by the target object toward at least one receiver element of the receiver system. However, in some examples, the first platen portion located between the light source system and the outer surface of the platen can have a greater first platen portion thickness than the second platen portion located between at least one receiver element of the receiver system 302 and the outer surface of the platen.

[0083] According to some examples, the platen 301 (or another part of the device) can include one or more anti-reflection layers. In some examples, the one or more anti-reflection layers can be located on one or more outer surfaces of the platen 301 or positioned proximate to one or more outer surfaces of the platen 301.

[0084] In some examples, at least a portion of the outer surface of the platen 301 can have an acoustic impedance that is configured to approximate the acoustic impedance of human skin. This portion of the outer surface of the platen 301 can be, for example, the portion configured to receive a target object such as a human finger. (As used herein, the terms "finger" and "digit" can be used interchangeably such that the thumb is an example of a finger.) The typical range of the acoustic impedance of human skin is 1.53 - 1.680 MRayl. In some examples, at least the outer surface of the platen 301 can have an acoustic impedance in the range of 1.4 - 1.8 MRayl or in the range of 1.5 - 1.7 MRayl.

[0085] Alternatively, or additionally, in some examples, at least the outer surface of the platen 301 can be configured to conform to the surface of human skin. In some such examples, at least the outer surface of the platen 301 can have material properties similar to those of putty or chewing gum.

[0086] In some examples, at least a portion of the platen 301 can have an acoustic impedance that is configured to approximate the acoustic impedance of one or more receiver elements of the receiver system 302. According to some examples, a layer located between the platen 301 and the one or more receiver elements can have an acoustic impedance that is configured to approximate the acoustic impedance of the one or more receiver elements. Alternatively, or additionally, in some examples, a layer located between the platen 301 and the one or more receiver elements can have an acoustic impedance within an acoustic impedance range between the acoustic impedance of the platen and the acoustic impedance of the one or more receiver elements.

[0087] Various examples of the receiver system 302 are disclosed herein, some of which can include an ultrasonic receiver system, an optical receiver system, or a combination thereof. In some embodiments that include an ultrasonic receiver system, an ultrasonic receiver and an ultrasonic transmitter can be incorporated in an ultrasonic transceiver. In some examples, the receiver system 302 can include a piezoelectric receiver layer, such as a PVDF polymer layer or a PVDF-TrFE copolymer layer. In some embodiments, a single piezoelectric layer can be used as an ultrasonic receiver. In some embodiments, additional piezoelectric materials, such as aluminum nitride (AlN) or lead zirconate titanate (PZT), can be used in the piezoelectric layer. In some examples, the receiver system 302 can include an array of ultrasonic transducer elements, such as an array of piezoelectric micromachined ultrasonic transducers (PMUTs), an array of capacitive micromachined ultrasonic transducers (CMUTs), etc. In some such examples, the piezoelectric receiver layer, a PMUT element in a single-layer array of PMUTs, or a CMUT element in a single-layer array of CMUTs can be used as both an ultrasonic transmitter and an ultrasonic receiver. According to some examples, the receiver system 302 can be or can include an ultrasonic receiver array. In some examples, the device 300 can include one or more independent ultrasonic transmitter elements. In some such examples, the ultrasonic transmitter can include an ultrasonic plane wave generator.

[0088] In some examples, the light source system 304 can include one or more light-emitting diodes. In some embodiments, the light source system 304 can include one or more laser diodes. According to some embodiments, the light source system 304 can include one or more vertical-cavity surface-emitting lasers (VCSELs). In some embodiments, the light source system 304 can include one or more edge-emitting lasers. In some embodiments, the light source system can include one or more neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers.

[0089] According to some examples, the light source system 304 may include one or more light guiding elements configured to direct light from the light source system toward a target object along a first axis. In some examples, the one or more light guiding elements may include at least one diffraction grating. Alternatively, or additionally, the one or more light guiding elements may include at least one lens.

[0090] In some examples, the light source system 304 may be configured to emit light within one or more wavelength ranges. In some examples, the light source system 304 may be configured to emit light within a wavelength range of 500 to 600 nanometers (nm). According to some examples, the light source system 304 may be configured to emit light within a wavelength range of 800 to 950 nm. Considering factors such as skin reflectivity, energy density, absorption coefficients of blood and various tissues, and skin safety limits, one or both of these wavelength ranges may be suitable for various use cases. For example, both the wavelength range of 500 nm to 600 nm and the wavelength range of 800 nm to 950 nm may be suitable for obtaining a photoacoustic response from relatively small, shallow blood vessels (such as blood vessels having a diameter of about 0.5 mm and a depth in the range of 0.5 mm to 1.5 mm, such as blood vessels that can be found in a finger). For example, the wavelength range of 800 to 950 nm may be suitable for obtaining a photoacoustic response from relatively large, deep blood vessels (such as blood vessels having a diameter of about 2.0 mm and a depth in the range of 2 mm to 3 mm, such as blood vessels that can be found in an adult wrist).

[0091] According to specific embodiments, the light source system 304 may include various types of drive circuitry. In some disclosed embodiments, the light source system 304 may include at least one multi-junction laser diode, which may generate less noise than a single-junction laser diode. In some examples, the light source system 304 may include a drive circuit (also referred to herein as drive circuitry) configured to cause the light source system to emit light pulses with a pulse width in the range of 3 nanoseconds to 1000 nanoseconds. According to some examples, the light source system 304 may include a drive circuit configured to cause the light source system to emit light pulses with a pulse repetition frequency in the range of 1 kilohertz to 100 kilohertz.

[0092] In some embodiments, the device (e.g., the receiver system 302, the light source system 304, or both) may include one or more sound-absorbing layers, sound-insulating materials, light-absorbing materials, light-reflecting materials, or combinations thereof. In some examples, the sound-insulating material may be located between at least a portion of the light source system 304 and the receiver system 302. In some examples, the device (e.g., the receiver system 302, the light source system 304, or both) may include one or more electromagnetic shielding transmission lines. In some such examples, the one or more electromagnetic shielding transmission lines may be configured to reduce electromagnetic interference received by the receiver system 302 from the light source system 304.

[0093] In some embodiments, the light source system 304 may be configured to emit light of various wavelengths that may be optionally used to trigger acoustic wave emission primarily from a particular type of material. For example, since hemoglobin in blood strongly absorbs near-infrared light, in some embodiments, to trigger acoustic wave emission from hemoglobin, the light source system 304 may be configured to emit one or more wavelengths of light in the near-infrared range. However, in some examples, the control system 306 may control the wavelength of the light emitted by the light source system 304 to preferentially induce acoustic waves in blood vessels, additional soft tissues, and / or bones. For example, an infrared (IR) light-emitting diode (LED) may be selected, and short pulses of IR light may be emitted to illuminate a portion of the target object and generate acoustic wave emission, which is then detected by the receiver system 302. In another example, an IR LED and a red LED or other colors such as green, blue, white, or ultraviolet (UV) may be selected, and short pulses of light may be sequentially emitted from each light source, and ultrasonic images may be obtained after light is emitted from each light source. In additional embodiments, one or more light sources of different wavelengths may be activated sequentially or simultaneously to generate acoustic emissions that can be detected by an ultrasonic receiver. Image data from the ultrasonic receiver obtained using light sources of different wavelengths and at different depths (e.g., varying RGDs) in the target object may be combined to determine the location and type of materials in the target object. Since materials in the body typically absorb different wavelengths of light differently, image contrast may occur. Since materials in the body absorb specific wavelengths of light, they may, using light of a short enough pulse with sufficient intensity, heat differently and generate acoustic wave emission. By using different wavelengths and / or different intensities at each selected wavelength of light, depth contrast may be obtained. That is, continuous images may be obtained at a fixed RGD (which may correspond to a fixed depth within the target object) using varying light intensities and wavelengths to detect materials and their locations within the target object. For example, hemoglobin, blood glucose, or blood oxygen in blood vessels within a target object such as a finger may be photoacoustically detected.

[0094] According to some embodiments, the light source system 304 can be configured to emit light pulses having a pulse width of less than about 100 nanoseconds. In some embodiments, the light pulses can have a pulse width between about 10 nanoseconds and about 500 nanoseconds or greater. According to some examples, the light source system can be configured to emit a plurality of light pulses at a pulse repetition frequency between 10 Hz and 100 kHz. Alternatively, or additionally, in some embodiments, the light source system 304 can be configured to emit a plurality of light pulses at a pulse repetition frequency between about 1 MHz and about 100 MHz. Alternatively, or additionally, in some embodiments, the light source system 304 can be configured to emit a plurality of light pulses at a pulse repetition frequency between about 10 Hz and about 1 MHz. In some examples, the pulse repetition frequency of the light pulses can correspond to the acoustic resonance frequency of the ultrasonic receiver and the substrate. For example, a set of four or more light pulses can be emitted from the light source system 304 at a frequency corresponding to the resonance frequency of a resonant acoustic cavity in the sensor stack, which allows for the accumulation of the received ultrasonic waves and a higher final signal intensity. In some embodiments, the light source system 304 can include a filtered light or light source having a specific wavelength for detecting a selected material. In some embodiments, the light source system can include light sources such as red LEDs, green LEDs, and blue LEDs of a display, which can be enhanced with light sources of other wavelengths (such as IR and / or UV) and with light sources of higher optical power. For example, a high-power laser diode or an electronic flash unit (such as an LED or a xenon flash unit), with or without a filter, can be used for short-term illumination of the target object.

[0095] The control system 306 can include one or more general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or combinations thereof. The control system 306 can also include one or more storage devices (and / or be configured to communicate with the one or more storage devices) such as one or more random access memory (RAM) devices, read-only memory (ROM) devices, etc. Thus, the device 300 can have a storage system that includes one or more storage devices, although Figure 3 the storage system is not shown. The control system 306 can be configured to receive and process data from the receiver system 302, as described below. If the device 300 includes an ultrasonic transmitter, the control system 306 can be configured to control the ultrasonic transmitter. In some embodiments, the functions of the control system 306 can be split between one or more controllers or processors (such as a dedicated sensor controller and an application processor of a mobile device).

[0096] In some examples, the control system 306 can be configured to control the light source system 304 to emit light toward a target object on an outer surface of the platen 301. In some such examples, the control system 306 can be configured to receive a signal from the ultrasonic receiver system 302 that corresponds to ultrasonic waves generated by the target object in response to the light from the light source system 304. In some examples, the control system 306 can be configured to identify one or more vascular signals from the ultrasonic receiver system, such as arterial signals or venous signals. In some such examples, the one or more arterial signals or venous signals can be or can include one or more vascular wall signals corresponding to ultrasonic waves generated by one or more arterial walls or venous walls of the target object. In some such examples, the one or more arterial signals or venous signals can be or can include one or more arterial blood signals corresponding to ultrasonic waves generated by blood within an artery of the target object, or one or more venous blood signals corresponding to ultrasonic waves generated by blood within a vein of the target object. In some examples, the control system 306 can be configured to estimate one or more cardiac characteristics based at least in part on one or more arterial signals, on one or more venous signals, or on a combination thereof. According to some examples, the cardiac characteristic can be or can include blood pressure.

[0097] Some embodiments of the device 300 can include an interface system 308. In some examples, the interface system 308 can include a wireless interface system. In some embodiments, the interface system 308 can include a user interface system, one or more network interfaces, one or more interfaces between the control system 306 and a storage system, and / or one or more interfaces between the control system 306 and one or more external device interfaces (e.g., ports or application processors), or a combination thereof. According to some examples in which the interface system 308 is present and includes a user interface system, the user interface system can include a microphone system, a speaker system, a haptic feedback system, a voice command system, one or more displays, or a combination thereof. According to some examples, the interface system 308 can include a touch sensor system, a gesture sensor system, or a combination thereof. The touch sensor system (if present) can be or can include a resistive touch sensor system, a surface capacitive touch sensor system, a projected capacitive touch sensor system, a surface acoustic wave touch sensor system, an infrared touch sensor system, any other suitable type of touch sensor system, or a combination thereof.

[0098] In some examples, the interface system 308 may include a force sensor system. The force sensor system, if present, may be or may include a piezoresistive sensor, a capacitive sensor, a thin film sensor (such as a polymer-based thin film sensor), other types of suitable force sensors, or a combination thereof. If the force sensor system includes a piezoresistive sensor, the piezoresistive sensor may include silicon, metal, polysilicon, glass, or a combination thereof. In some embodiments, the ultrasonic fingerprint sensor and the force sensor system may be mechanically coupled. In some such examples, the force sensor system may be integrated into the circuitry of the ultrasonic fingerprint sensor. In some examples, the interface system 308 may include an optical sensor system, one or more cameras, or a combination thereof.

[0099] According to some examples, the device 300 may include a noise reduction system 310. For example, the noise reduction system 310 may include one or more mirrors configured to reflect light from the light source system 304 away from the receiver system 302. In some embodiments, the noise reduction system 310 may include one or more sound-absorbing layers, sound-insulating materials, light-absorbing materials, light-reflecting materials, or a combination thereof. In some examples, the noise reduction system 310 may include a sound-insulating material that may be located between at least a portion of the receiver system 302 and the light source system 304, on at least a portion of the receiver system 302, or a combination thereof. In some examples, the noise reduction system 310 may include one or more electromagnetic shielding transmission lines. In some such examples, the one or more electromagnetic shielding transmission lines may be configured to reduce electromagnetic interference received by the receiver system 302 from the circuitry of the light source system 304, the receiver system circuitry, or a combination thereof.

[0100] The device 300 can be used in a variety of different environments, many examples of which are disclosed herein. For example, in some embodiments, a mobile device may include the device 300. In some such examples, the mobile device may be a smart phone. In some embodiments, a wearable device may include the device 300. The wearable device may be, for example, a bracelet, an armband, a wristband, a watch, a ring, a headband, or a patch.

[0101] Figure 4A Exemplary components of a device according to some disclosed embodiments are shown. As with other figures provided herein, Figure 1 likewise, Figure 4A the number, type, and arrangement of the elements shown are shown only as examples. In this example, the device 300 is Figure 3 an example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger 115, a wrist, and the like.

[0102] According to this example, the light source system 304 includes a light emitting portion 304a and a lens 304b. The light emitting portion 304a may include, for example, one or more light emitting diodes, one or more laser diodes, one or more VCSELs, one or more edge emitting lasers, one or more neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, or a combination thereof. In this example, the lens 304b is configured to focus the light 403 emitted by the light emitting portion 304a into a relatively small cross-sectional area, which increases the intensity of the light 403 received by a target object (such as finger 115) on the outer surface 408a. Although Figure 4A it is shown that there is a gap between the light emitting portion 304a and the lens 304b, the light emitting portion 304a and the lens 304b are generally disposed close to each other.

[0103] In this example, the platen 301 includes a platen portion 301a and a platen portion 301b. According to this example, the platen portion 301a has a thickness t1, which is less than the thickness T1 of the platen portion 301b. In this example, the platen portion 301a includes a surface 408b, which is configured to receive the light 403 from the light source system 304. Although Figure 4A it is shown that there is a gap between the light source system 304 and the surface 408b, in some examples, the light source system 304 is disposed close to the surface 408b without a gap. According to this example, the platen portion 301a is configured to direct the light 403 from the light source system 304 toward the outer surface 408a and toward a target object (if any) on the outer surface 408a.

[0104] According to this example, the platen 301 (more specifically, the platen portion 301a) and the light source system 304 are configured to convey the light 403 from the light source system 304 to the outer surface 408a of the platen 301 along a first axis or substantially along a first axis, and the first axis is oriented at a first angle with respect to the outer surface 408a. In Figure 4A it, the axis 405a is an example of the first axis, and the angle Θ1 is an example of the first angle. In this regard, "substantially along the first axis" or "substantially parallel to the first axis" may mean within an angular range of plus or minus 10 degrees of the first axis, within an angular range of plus or minus 15 degrees of the first axis, within an angular range of plus or minus 20 degrees of the first axis, within an angular range of plus or minus 25 degrees of the first axis, within an angular range of plus or minus 30 degrees of the first axis, or within another such angular range. According to this example, the axis 405a is perpendicular to the surface 408b.

[0105] In this example, the receiver system 302 (which is an ultrasonic receiver system in this embodiment) is located near the surface 408c of the platen 301 (more specifically, the platen portion 301b). According to this example, the receiver system 302 is located in a receiver plane 410 oriented parallel to the surface 408c. In this example, the normal of the receiver plane 410 is oriented along a second axis that is oriented at a second angle relative to the outer surface 408a. The second axis in this example is the axis 405b. In Figure 4A , the angle Θ2 is an example of the second angle. In this example, the receiver plane 410 is parallel to the outer surface 408a, and thus the angle Θ2 is 90 degrees.

[0106] According to this example, the platen 301 (more specifically, the platen portion 301b) is configured to direct acoustic waves (including photoacoustic waves PA) emitted by a target object on the outer surface 408a towards the receiver system 302. In this example, the platen 301 (more specifically, the platen portion 301b) is configured to transmit acoustic waves (including but not limited to ultrasonic waves) generated by a target object on the outer surface 408a towards the receiver system 302 along a third axis or substantially along a third axis. The third axis is oriented at a third angle relative to the outer surface 408a. In Figure 4A , the axis 405c is an example of the third axis, and the angle Θ3 is an example of the third angle. In this regard, "substantially along the third axis" or "substantially parallel to the third axis" can mean within an angular range of plus or minus 10 degrees of the third axis, within an angular range of plus or minus 15 degrees of the third axis, within an angular range of plus or minus 20 degrees of the third axis, within an angular range of plus or minus 25 degrees of the third axis, within an angular range of plus or minus 30 degrees of the third axis, or within another such angular range. According to this example, the platen portion 301b is shown to transmit arterial photoacoustic waves PA substantially along the axis 405c. In this example, the second axis is parallel to or substantially parallel to the third axis (e.g., within plus or minus 5 degrees of parallel, within plus or minus 10 degrees of parallel, within plus or minus 15 degrees of parallel, within plus or minus 20 degrees of parallel, etc.).

[0107] In this example, the third axis is not parallel to the first axis, but instead is separated from the first axis by an angle (Θ3 - Θ1). In some examples, the angle (Θ3 - Θ1) can be in the range of 20 degrees to 60 degrees. According to some alternative examples, the third axis can be parallel to the first axis. However, in some alternative examples, the first axis can be parallel to or substantially parallel to (e.g., within plus or minus 5 degrees of parallel, within plus or minus 10 degrees of parallel, within plus or minus 15 degrees of parallel, within plus or minus 20 degrees of parallel, etc.) the third axis.

[0108] In some examples, the first axis, the second axis, and the third axis can be defined by a coordinate system relative to the device 300 or a part thereof. In Figure 4A In the example shown, the Cartesian coordinate system is shown as being defined relative to the outer surface 408a of the platen 301.

[0109] In this example, the axis 405d is parallel to the outer surface 408a. The angle Θ4 is shown between the axis 405d and the surface 408b, which indicates that the angle between the surface 408b and the outer surface 408a is also Θ4. According to this example, Θ4 = Θ3 - Θ1.

[0110] In some embodiments, the platen 301 (e.g., at least a portion of the platen portion 301b) may include an acoustic waveguide. In some such embodiments, the platen portion 301b may be configured to transmit ultrasonic waves generated by a target object on the outer surface 408a towards the receiver system 302 via the acoustic waveguide.

[0111] According to some examples, the platen 301 may include one or more anti - reflection layers. In some examples, the one or more anti - reflection layers may be located on the platen 301 or positioned close to the platen 301, such as on or close to the outer surface 408a.

[0112] Figure 4B Exemplary components of a device according to some disclosed embodiments are shown. As with other figures provided herein, Figure 1 likewise, Figure 4B the number, type, and arrangement of the elements shown are presented only as examples. In this example, the device 300 is Figure 3 an example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger 115.

[0113] Figure 4B Many of the elements of the device 300 shown are substantially the same as Figure 4A the elements shown. Accordingly, the unchanged elements are not described here. In Figure 4B the example shown, the platen portion 301a includes an optical waveguide 415. In some cases, a hole may be formed in the platen portion 301a, and an optical waveguide that may include one or more optical fibers may be inserted into the hole. According to some additional examples, the platen portion 301a may be fabricated to include the optical waveguide 415. In some alternative examples, the optical waveguide 415 may be configured to direct light to a region of the outer surface 408a that is closer to the central portion of the receiver system 302, such as the region 420 shown in FIG. 4. Although additional disclosed embodiments may be shown without the optical waveguide 415, these disclosed embodiments (including but not limited to Figure 4A and 5Alternative versions (such as those shown in -19) may include one or more optical waveguides 415, or one or more optical waveguides of another type.

[0114] Figure 5 Exemplary components of an alternative device according to some disclosed embodiments are shown. As with other figures provided herein, Figure 1 likewise, Figure 5 the number, type, and arrangement of the elements shown in are shown only by way of example. In this example, device 300 is Figure 3 an example of the device 300 shown. According to this example, device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger, wrist, etc.

[0115] According to this example, the light source system 304 includes a light-emitting portion 304a and a lens 304b. In this example, the lens 304b is configured to focus the light 403 emitted by the light-emitting portion 304a into a relatively small cross-sectional area, which increases the intensity of the light 403 received by the target object (such as finger 115) on the outer surface 408a. Although Figure 5 the light-emitting portion 304a and the lens 304b are shown separated by a gap, the light-emitting portion 304a and the lens 304b are typically disposed in close proximity to each other.

[0116] In this example, the platen 301 includes a platen portion 301a and a platen portion 301b. In this example, the platen portion 301a includes a surface 408b, which is configured to receive the light 403 from the light source system 304. Although Figure 5 the light source system 304 is shown separated from the surface 408b by a gap, in some examples, the light source system 304 may be disposed in close proximity to the surface 408b without a gap. According to this example, the platen portion 301a is configured to direct the light 403 from the light source system 304 toward the outer surface 408a and toward the target object (if any) on the outer surface 408a.

[0117] According to this example, the platen portion 301a and the light source system 304 are configured to transmit the light 403 from the light source system 304 to the outer surface 408a of the platen 301 along a first axis or substantially along a first axis, the first axis being oriented at a first angle with respect to the outer surface 408a. The first axis and the first angle may correspond to Figure 4A the axis 405a and the angle Θ1 shown.

[0118] In this example, the receiver system 302 is located in the receiver plane 410 near the surface 408c of the platen portion 301b, and the receiver plane 410 is oriented parallel to the surface 408c. In this example, the normal of the receiver plane 410 is oriented along a second axis, and the second axis is oriented at a second angle relative to the outer surface 408a. The second axis and the second angle may correspond to Figure 4A the axis 405b and the angle Θ2 shown. According to this example, the platen portion 301b is configured to direct sound waves (including photoacoustic waves PA) emitted by a target object on the outer surface 408a toward the receiver system 302 along a third axis or substantially along the third axis, and the third axis is oriented at a third angle relative to the outer surface 408a. The third axis and the third angle may correspond to Figure 4A the axis 405c and the angle Θ3 shown.

[0119] In these examples, the relative orientations of the surfaces 408a, 408b, and 408c, the first axis, the second axis, and the third axis, the receiver plane 410, and the light source system 304 are as Figure 4A shown, with one exception: Figure 4A the platen portion 301b shown is much thicker than Figure 5 the platen portion 301b shown. Figure 4A The platen portion 301b of Figure 5 has a thickness T1, and the thickness T1 may be in the range of 7 mm to 15 mm in some examples, while

[0120] Figure 6 shows an example component of an alternative device according to some additional disclosed embodiments. Like other figures provided herein, Figure 1 the number, type, and arrangement of the elements shown in Figure 6 are shown only as examples. In this example, the device 300 is Figure 3 an example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger, a wrist, etc. According to this example, the platen portion 301a has a thickness t2, which is greater than the thickness T3 of the platen portion 301b.

[0121] According to this example, the light source system 304 and the receiver system 302 are configured substantially as shown in FIGS. 4 and 5. In Figure 6In the example shown, the relative orientations of the surfaces 408a, 408b, and 408c, the first axis, the second axis, and the third axis, the receiver plane 410, and the light source system 304 are as referenced Figure 5 as described, with one exception: Figure 5 The platen portion 301a shown is much thicker than Figure 6 the platen portion 301a shown. Figure 5 The platen portion 301a of has a thickness t1, which in some examples can be in the range of 7 mm to 15 mm, while Figure 6 the platen portion 301a shown in has a thickness t2, which in some examples can be in the range of 6 mm to 12 mm. In this example, the thickness T3 of the platen portion 301b is in the range of 3 mm to 7 mm, for example 5 mm. According to this example, the width W of the surface 408c is in the range of 5 mm to 10 mm, for example 7 or 8 mm.

[0122] Figure 7 FIG. shows example components of an alternative device according to some disclosed embodiments. As with other figures provided herein, Figure 1 the number, type, and arrangement of the elements shown in Figure 7 are shown only as examples. In this example, the device 300 is Figure 3 an example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger, a wrist, etc. According to this example, the platen portion 301a has a thickness t2, which is greater than the thickness T3 of the platen portion 301b.

[0123] According to this example, the light source system 304 and the receiver system 302 are configured substantially as shown in FIGS. 4 - 6. In Figure 7 the example shown, the relative orientations of the surfaces 408a, 408b, and 408c, the first axis, the second axis, and the third axis, the receiver plane 410, and the light source system 304 are as Figure 6 shown, with one exception: In Figure 7 the example shown, the device 300 includes an acoustic waveguide 702 between the surface 408c and the receiver system 302.

[0124] Figure 8 、 9 and 10 show example components of a device according to some alternative embodiments. As with other figures provided herein, Figure 1 the number, type, and arrangement of the elements shown in Figure 8-10 are shown only as examples. In each of these examples, the device 300 is Figure 3An example of the device 300 is shown. According to these examples, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In these examples, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger, a wrist, etc.

[0125] According to Figure 8-10 the examples shown, the light source system 304 is not attached to the platen 301. Although Figure 8 or Fig. 9 not shown in, but in some examples, the light source system 304 may include a lens 304b. In Figure 8 and 9 the examples shown, the light emitting portion 304a and the light source circuit system 304c are both located on the light source system surface 304d, and the normal of the light source system surface 304d corresponds to the axis 805. In these examples, the axis 805 is parallel to or substantially parallel to the axis 405a. Although Figure 8 or Fig. 9 not shown in, but in some examples, the light source system 304 may include a lens 304b. In Figure 8 and 9 the examples shown, the light source system surface 304d is attached to the support structure 810 and is configured to cause the light emitting portion 304a to emit at least some of the light 403 along the axis 405a, and the axis 405a is at an angle Θ1 with respect to the outer surface 408a.

[0126] According to some examples, the support structure 810 may include a sound insulating material such as a sound absorbing material, which is configured to at least partially suppress the sound waves that may be generated by the light source circuit system 304c. In some such examples, at least a portion of the support structure 810 may be configured to at least partially decouple the sound energy generated by the light source circuit system 304c from the platen 301 and the receiver system 302.

[0127] In Fig.10 the examples shown, the light emitting portion 304a and the light source circuit system 304c are both located on a portion of the support structure 810 that is parallel to or substantially parallel to the outer surface 408a. Therefore, many of the light 403 from the light emitting portion 304a are directly emitted toward the outer surface 408a. However, in Fig.10 the examples shown, the light source system 304 includes a light guiding element 304e, and the light guiding element 304e is configured to re - guide at least some of the light 403 along the axis 405a. In some examples, the light guiding element 304e may be or may include a diffraction grating.

[0128] In Figure 8-10In the example shown, the receiver system 302 includes a receiver portion 302a, a backer 302b, a mirror layer 302c, a noise absorption layer 302d, receiver system circuitry 302e, and a connector 302f. The receiver portion 302a may include a piezoelectric material such as a piezoelectric copolymer, a piezoelectric composite, etc. Some detailed examples are described below with reference to Figure 20-22 Description.

[0129] According to some examples, the noise absorption layer 302d may include a light-blocking material (such as a light-absorbing material), a sound-absorbing material, or a combination thereof. In some examples, the noise absorption layer 302d may include an optical and acoustic isolation foam.

[0130] In these examples, the mirror layer 302c is configured to reflect light (including but not limited to light from the light source system 304 reflected from the outer surface 408a) away from the receiver portion 302a. According to some examples, an anti-reflection material may be located on or proximate to the outer surface 408a.

[0131] In Figure 8-10 the example shown, the receiver system circuitry 302e is located on the support structure 810 and is not directly attached to the platen 301 or the receiver portion 302a. Such a configuration helps to shield the receiver portion 302a from noise generated by the receiver system circuitry 302e. In these examples, the connector 302f is configured to electrically connect the receiver system circuitry 302e to the receiver portion 302a. According to some examples, the connector 302f may include a conductive material insulated by an electromagnetic noise suppression material. Such examples can at least partially isolate the receiver portion 302a from electromagnetic noise generated by the receiver system circuitry 302e. The electromagnetic noise suppression material, the noise absorption layer 302d, and the mirror layer 302c may be regarded as Figure 3 components of the noise reduction system 310.

[0132] According to these examples, the receiver system 302 includes a backing layer 302b. The backing layer 302b may be configured to suppress at least some acoustic artifacts and may provide a relatively higher signal-to-noise ratio (SNR) compared to a receiver system 302 lacking a backing layer. In these examples, the thicknesses T6 ( Figure 8 shown in) of the receiver portion 302a, the backer 302b, the mirror layer 302c, and the noise absorption layer 302d may be in the range of 5 mm to 10 mm, and most of which (such as 5 mm to 7 mm) may correspond to the thickness of the backing layer 302b. Thus, including such a relatively thick backing layer 302b can improve the SNR but may increase the total device thickness in some embodiments.

[0133] In Figure 8and 10 In the example shown, the surface 408b of the platen 301 is parallel or substantially parallel to the surface 304d of the light source system. In these examples, the surface 408b is perpendicular or substantially perpendicular to the axis 405a. Thus, in these examples, the platen portion 301a has a thickness ranging from T4 to T5, the latter of which can range from 1 mm to 3 mm. However, in Fig. 9 the example shown, each of the platen portions 301a and 301b has a thickness of T4, which in some cases can range from 3 mm to 7 mm.

[0134] Fig.11 An example component of a device according to some additional embodiments is shown. As with other figures provided herein Figure 1 likewise Fig.11 the number, type, and arrangement of the elements shown are presented only as examples. In this example, the device 300 is Figure 3 an example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger 115, a wrist, etc.

[0135] According to this example, the light source system 304 is located on the surface 408b of the platen 301 that is parallel or substantially parallel to the outer surface 408a. Thus, in this example, the angle Θ1 between the axis 405a and the outer surface 408a is 90 degrees or approximately 90 degrees (such as within + / - 10 degrees, within + / - 15 degrees, within + / - 20 degrees, etc.). In this example, the receiver system 302 is located on the surface 408c of the platen 301, and the surface 408c is not parallel or substantially parallel to the outer surface 408a. Instead, the surface 408c and the receiver plane 410 are angled with respect to the outer surface 408a such that the axis 405b (perpendicular to the receiver plane 410) is oriented at an angle Θ2 with respect to the outer surface 408a, and the angle Θ2 is less than 90 degrees.

[0136] Such an embodiment has the potential advantage that most of the light 403 reflected from the outer surface 408a can be reflected back towards the light source system 304 rather than towards the receiver system 302. According to some examples, to further mitigate such reflections, the platen 301 may include one or more anti-reflection layers. In some examples, one or more anti-reflection layers may be located on the platen 301 or positioned close to the platen 301, such as on the outer surface 408a or close to the outer surface 408a.

[0137] It can be observed that Fig.11 the embodiment shown in Figure 4A is similar to that shown in, except that Fig.11 The receiver system 302 of Figure 4A is located outside the location where the light source system 304 of Fig.11 is located. Another difference is that in Figure 4A , the surfaces 408b and 408c are at an angle to each other but are continuous: there is no sudden decrease in the thickness of the platen 301 from the surface 408c to the surface 408b as shown in

[0138] Fig.12 shows example components of a device according to some additional embodiments. As with other figures provided herein, Figure 1 the Fig.12 number, type, and arrangement of the elements shown in Figure 3 are shown only by way of example. In this example, the device 300 is an example of the device 300 shown in

[0139] It can be observed that Fig.12 the embodiment shown in Fig.11 is similar to the embodiment shown in Fig.12 , except that in

[0140] in Fig.11 and 12 , the light source system 304 is located on a surface 408b of the platen 301 that is not parallel or not substantially parallel to the outer surface 408a. Instead, both the angle Θ1 and the angle Θ2 are less than 90 degrees. In some examples, the angle Θ1 and the angle Θ2 can be equal or approximately equal (such as within + / - 10 degrees, within + / - 15 degrees, within + / - 20 degrees, etc.).

[0140] In Fig.11 and 12 , the outer surface 408a is shown as being in a plane. In some alternative embodiments, the outer surface 408a can be in more than one plane. According to some such embodiments, a portion of the outer surface 408a can be in a plane parallel or substantially parallel to Fig.11 or Fig.12 the surface 408c. Alternatively or additionally, in some examples, a portion of the outer surface 408a can be in a plane parallel or substantially parallel to Fig.12 the surface 408b.

[0141] Fig.13 shows example components of a device according to some additional embodiments. As with other figures provided herein, Figure 1 the Fig.13 number, type, and arrangement of the elements shown in Figure 3An example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a wrist 1315, a finger, etc.

[0142] According to this example, the light source system 304 is located on the surface 408b of the platen 301 that is parallel to or substantially parallel to the outer surface 408a. Thus, in this example, the angle Θ1 between the axis 405a and the outer surface 408a is 90 degrees or approximately 90 degrees (such as within + / - 10 degrees, within + / - 15 degrees, within + / - 20 degrees, etc.). Here, the light source system 304 is configured to provide light to the outer surface 408a (and to the target object on the outer surface 408a, if any) via the platen portion 301a.

[0143] In this example, the receiver system 302 includes receiver system components 302A and 302B. According to this example, the receiver system component 302A is located on the surface 408c1 of the platen 301, and the receiver system component 302B is located on the surface 408c2 of the platen 301. In this example, the surfaces 408c1 and 408c2 are not parallel to or not substantially parallel to the outer surface 408a. Instead, the surface 408c1 and the corresponding receiver plane 410a are at an angle with respect to the outer surface 408a such that the axis 405b1 (perpendicular to the receiver plane 410a) is oriented at an angle Θ2a less than 90 degrees with respect to the outer surface 408a. Similarly, the surface 408c2 and the corresponding receiver plane 410b are at an angle with respect to the outer surface 408a such that the axis 405b2 (perpendicular to the receiver plane 410b) is oriented at an angle Θ2b less than 90 degrees with respect to the outer surface 408a. In some examples, the absolute value of the angle Θ2a may be equal to or substantially equal to the absolute value of the angle Θ2b.

[0144] In this example, the light 403 induces photoacoustic waves PA1 and PA2 in the artery 1307. According to this example, at least a portion of the photoacoustic wave PA1 propagates along the axis 405c1 in the platen portion 301b1, and the axis 405c1 is at an angle Θ3a with respect to the outer surface 408a. In this example, at least a portion of the photoacoustic wave PA2 propagates along the axis 405c2 in the platen portion 301b2, and the axis 405c2 is at an angle Θ3b with respect to the outer surface 408a.

[0145] It can be observed that Fig.13 the illustrated embodiment is similar to Fig.11 the illustrated embodiment, except that instead of having a single receiver system 302 as shown in Fig.11 the illustration, Fig.13The embodiments include, among other things, receiver system components 302A and 302B.

[0146] such as Fig.13 Embodiments such as the illustrated embodiment have the potential advantage that much of the light 403 reflected from the outer surface 408a can be reflected back towards the light source system 304 rather than towards the receiver system component 302A or the receiver system component 302B. According to some examples, to further mitigate such reflections, the platen 301 may include one or more anti-reflection layers. In some examples, one or more anti-reflection layers may be located on the platen 301 or positioned proximate to the platen 301, such as on the outer surface 408a or proximate to the outer surface 408a. Similar to Fig.13 Another potential advantage of embodiments such as the illustrated embodiment is that, compared to Fig.11 the single receiver system 302 as shown, more photoacoustic waves emitted by the target object can be captured due to the presence of multiple receiver system components.

[0147] Fig.14 Exemplary components of a device according to some additional embodiments are shown. As with other figures provided herein, Figure 1 likewise, Fig.14 the number, type, and arrangement of the elements shown in [figure number] are shown only by way of example. In this example, the device 300 is Figure 3 an example of the device 300 as shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger 115, a wrist, etc.

[0148] According to this example, the receiver system 302 is located on a surface 408c of the platen 301 that is parallel to or substantially parallel to the outer surface 408a. Thus, in this example, the angle Θ2 between the axis 405b (perpendicular to the receiver plane 410) and the outer surface 408a is 90 degrees or approximately 90 degrees (e.g., within + / - 10 degrees, within + / - 15 degrees, within + / - 20 degrees, etc.).

[0149] Here, the light source system 304 includes light source system components 304A and 304B. The light source system components 304A and 304B are configured to provide light 403a and 403b to the outer surface 408a (and the target object on the outer surface 408a, if any) via the platen portions 301a1 and 301a2. According to this example, at least some of the light 403a propagates substantially parallel to the axis 405a1, which is at an angle Θ1a with respect to the outer surface 408a, and at least some of the light 403b propagates substantially parallel to the axis 405a2, which is at an angle Θ1b with respect to the outer surface 408a. In some examples, the absolute value of the angle Θ1a may be equal to or substantially equal to the absolute value of the angle Θ1b.

[0150] In this example, the light 403 induces photoacoustic waves PA in the blood vessel 407. According to this example, at least a portion of the photoacoustic waves PA propagates along the axis 405c in the platen portion 301b, which is at an angle Θ3 with respect to the outer surface 408a.

[0151] It can be observed that Fig.14 the illustrated embodiment is similar to Fig.13 the illustrated embodiment, except that, instead of having a single light source system 304 and two receiver system components as Fig.13 illustrated, Fig.14 the embodiment includes a single receiver system 302 and light source system components 304A and 302B.

[0152] Compared with the embodiment including only a single light source system, an embodiment such as Fig.14 the illustrated embodiment has the potential advantage that additional light energy can be provided to the target object. Another potential advantage of an embodiment similar to Fig.14 the illustrated embodiment is that additional light paths into the target object can be provided. For example, in Fig.14 the illustrated example, the path of the light 403a is more favorable for irradiating the blood vessel 407 than the path of the light 403b.

[0153] Fig.15 An example component of a device according to some additional embodiments is shown. As with other figures provided herein, Figure 1 the number, type, and arrangement of the elements shown in Fig.15 are shown only as examples. In this example, the device 300 is Figure 3 an example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger 115 or the like.

[0154] According to this example, the receiver system 302 is located on a surface 408c of the platen 301 that is parallel to or substantially parallel to the outer surface 408a. Thus, in this example, the angle Θ2 between the axis 405b (perpendicular to the receiver plane 410) and the outer surface 408a is 90 degrees or approximately 90 degrees (such as within + / - 5 degrees, within + / - 10 degrees, within + / - 15 degrees, within + / - 20 degrees, etc.).

[0155] Here, the light source system 304 includes a light source system component 304A and a light source system component 302B. In this example, the light source system component 304A is coupled to the surface 408b1 and is configured to provide light 403a to a target object (if any) on the outer surface 408a via the platen portion 301a1 and the outer surface A. In this example, the light source system component 304B is coupled to the surface 408b2 and is configured to provide light 403b to a target object (if any) on the outer surface 408a via the platen portion 301a2 and the outer surface B. In some examples, the target object may be in contact with the outer surface A, the outer surface B, or both.

[0156] According to this example, at least some of the light 403a propagates substantially parallel to the axis 405a1, which is parallel to or substantially parallel to the outer surface 408a and perpendicular to or substantially perpendicular to the outer surface A. In this example, at least some of the light 403b propagates substantially parallel to the axis 405a2, which is parallel to or substantially parallel to the outer surface 408a and perpendicular to or substantially perpendicular to the outer surface B. In this example, the light 403a propagates in a direction opposite to the direction in which the light 403b propagates.

[0157] In this example, the light 403a, the light 403b, or a combination thereof causes photoacoustic waves PA in the blood vessel 407. According to this example, at least a portion of the photoacoustic waves PA propagates along the axis 405c in the platen portion 301b, and the axis 405c is at an angle Θ3 with respect to the outer surface 408a. In this example, the angle Θ3 is 90 degrees, or approximately 90 degrees.

[0158] It can be observed that Fig.15 the illustrated embodiment is similar to Fig.14 the illustrated embodiment, except that the outer surface of the platen 301 has a different configuration and the light source system components 304A and 302B are shown to be arranged at different angles. Fig.14 the outer surface 408a of the illustrated platen 301 that is configured to receive the target object is substantially in a single plane; while Fig.15 the recessed area 1505 of the platen 301 is shown, and the recessed area 1505 includes the outer surface 408a and the outer surfaces A and B, which are configured to receive the target object. Fig.15The platen configuration shown allows light 403a and 403b to be provided along the same plane in opposite directions.

[0159] Compared to embodiments that include only a single light source system, such as Fig.14 and 15 the embodiments shown have the potential advantage of being able to provide additional light energy to the target object. Similar to Fig.14 and 15 another potential advantage of embodiments such as those shown is that they can provide additional light paths into the target object. Compared to the example shown in Fig.14 the example shown in Fig.15 provides a further potential advantage in that relatively less reflected light generated by light 403a and 403b may reach the receiver system 302.

[0160] Fig.16 Exemplary components of a device according to some additional embodiments are shown. As with other figures provided herein, Figure 1 the number, type, and arrangement of the elements shown in Fig.16 are shown only by way of example. In this example, device 300 is Figure 3 an example of the device 300 shown. According to this example, device 300 includes a platen 301, a receiver system 302, and a light source system 304.

[0161] In this example, the platen 301 includes a recessed area 1605 that contains outer surfaces 408a1 and 408a2, which are configured to receive a target object, such as a finger 115, etc. According to this example, outer surface 408a1 is perpendicular or substantially perpendicular to outer surface 408a2. However, in some alternative examples, outer surface 408a1 may be oriented at an angle greater than or less than 90 degrees relative to outer surface 408a2. In this example, outer surface 408a2 is at an angle Θ4 with respect to outer surface 408a3.

[0162] According to this example, the light source system 304 is coupled to a surface 408b of the platen 301, which in this example is parallel or substantially parallel to outer surface 408a1. In some alternative embodiments, the light source system 304 may be close to surface 408b but not coupled to surface 408b. In some alternative embodiments, surface 408b may not be parallel or not substantially parallel to outer surface 408a1. In this example, the light source system 304 is configured to provide light 403 to a target object (if any) on outer surface 408a1 via platen portion 301a. According to this example, at least some of light 403 propagates substantially parallel to axis 405a, which is perpendicular or substantially perpendicular to surface 408b and outer surface 408a1, and is at an angle Θ5 with respect to outer surface 408a3.

[0163] According to this example, the receiver system 302 is located on a surface 408c of the platen 301 that is parallel to or substantially parallel to the receiver plane 410. In this example, light 403 induces photoacoustic wave PA in the blood vessel 407. According to this example, at least a portion of the photoacoustic wave PA propagates in the platen portion 301b parallel to or substantially parallel to the axis 405c, which in this example is parallel to or substantially parallel to the axis 405b and the outer surface 408a3.

[0164] Such as Fig.16 Embodiments such as the illustrated embodiment have the potential advantage that relatively little reflected light may reach the receiver system 302, in part because the target object can shield the receiver system 302 from at least some of the reflected light.

[0165] Fig.17 Illustrates example components of a device according to some additional embodiments. As with other figures provided herein Figure 1 likewise, Fig.17 the number, type, and arrangement of the elements shown are shown only by way of example. In this example, the device 300 is Figure 3 an example of the device 300 shown. According to this example, the device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger 115, a wrist, etc.

[0166] It can be observed that in Fig.17 the illustrated embodiment, the light source system 304 is located on a surface 408b of the platen 301 that is not parallel or not substantially parallel to the outer surface 408a. In some alternative embodiments, the light source system 304 may be adjacent to the surface 408b but not coupled to the surface 408b. In this example, the light source system 304 is configured to provide light 403 to a target object (if any) on the outer surface 408a via the platen portion 301a. According to this example, at least some of the light 403 propagates substantially parallel to the axis 405a, which is perpendicular or substantially perpendicular to the surface 408b and at an angle Θ1 with respect to the outer surface 408a.

[0167] Furthermore, in Fig.17 the illustrated embodiment, the receiver system 302 is located on a surface 408c of the platen 301 that is not parallel or not substantially parallel to the outer surface 408a. In this example, the receiver system 302 includes a receiver portion 302a and a backing portion 302b. Here, the receiver plane 410 is parallel to or substantially parallel to the surface 408c. The axis 405b perpendicular to the receiver plane 410 forms an angle Θ2 with the outer surface 408a.

[0168] In this example, light 403 causes photoacoustic wave PA in blood vessel 407. According to this example, at least a part of the photoacoustic wave PA propagates in platen portion 301b parallel to or substantially parallel to axis 405c, and axis 405c is parallel to or substantially parallel to axis 405b. In this example, axis 405c forms an angle Θ3 with outer surface 408a.

[0169] In Fig.17 , outer surface 408a is shown as being in a single plane. In some alternative embodiments, the outer surface of platen 301 configured to receive a target object may be in more than one plane, such as as shown in Fig.15 or Fig.16 . According to some such embodiments, a part of outer surface 408a may be in a plane parallel to or substantially parallel to surface 408c of Fig.17 . Alternatively or additionally, a part of outer surface 408a may be in a plane parallel to or substantially parallel to surface 408b of Fig.17 .

[0170] Fig.18 FIG. shows an example component of a device according to some additional embodiments. As with other figures provided herein, Figure 1 the number, type, and arrangement of the elements shown in Fig.18 are shown only as examples. In this example, device 300 is an example of the device 300 shown in Figure 3 . According to this example, device 300 includes platen 301, receiver system 302, and light source system 304. In this example, outer surface 408a of platen 301 is configured to receive a target object, such as finger 115, wrist, etc.

[0171] It can be observed that in the embodiment shown in Fig.18 , light source system 304 is configured to emit at least some of light 403 through surface 408b along axis 405a toward outer surface 408a (and the target object on outer surface 408a, if any). In some alternative embodiments, light source system 304 may be coupled to surface 408b. In this example, light source system 304 is configured to provide light 403 to the target object (if any) on outer surface 408a via platen portions 301a, 301b. According to this example, axis 405a is perpendicular to or substantially perpendicular to outer surface 408a.

[0172] In this example, light 403 induces photoacoustic wave PA in blood vessel 407. According to this example, at least a portion of the photoacoustic wave PA propagates in platen portions 301a, 301b parallel to or substantially parallel to axis 405a. According to this example, device 300 includes acoustic waveguide 1805. Here, acoustic waveguide 1805 is configured to direct the photoacoustic wave PA (which includes ultrasonic waves in this example) towards receiver system 302 (which is or includes an ultrasonic receiver system in this example).

[0173] According to this example, acoustic waveguide 1805 includes platen portions 301b2 and 301b3. In this example, platen portion 301b3 includes interface 1810, and interface 1810 is configured to reflect acoustic waves, such as photoacoustic wave PA. According to this example, platen portion 301b3 includes interface 1810 having a high acoustic impedance contrast. In some such examples, the high acoustic impedance contrast can be caused by air 1815 within region 1815. For example, if platen portions 301b2 and 301b3 are additionally made of a solid material such as acrylic, then the air / solid material interface 1810 will have a high acoustic impedance contrast.

[0174] In Fig.18 the illustrated embodiment, receiver system 302 is located on surface 408c of platen 301 that is not parallel to or not substantially parallel to outer surface 408a. Here, receiver plane 410 is parallel to or substantially parallel to surface 408c. In this example, axis 405b perpendicular to receiver plane 410 is parallel to or substantially parallel to outer surface 408a. In an alternative embodiment, axis 405b may not be parallel to or not substantially parallel to outer surface 408a.

[0175] In this example, receiver system 302 is or includes an ultrasonic receiver system. According to this example, receiver system 302 includes receiver portion 302a and backing portion 302b. As noted elsewhere herein, and as Fig.17 illustrated, backing portion 302b can be beneficial for SNR improvement, but will significantly increase the overall thickness of receiver system 302. Thus, positioning receiver plane 410 of relatively thick receiver system 302 including backing portion 302b such that receiver plane 410 is perpendicular to or substantially perpendicular to outer surface 408a can advantageously reduce the overall thickness of device 300 (e.g., the thickness along axis 405a). In other words, positioning axis 405b of receiver system 302 including backing portion 302b such that axis 405b is parallel to or substantially parallel to outer surface 408a can advantageously reduce the overall thickness of device 300. According to this example, acoustic waveguide 1805 allows receiver system 302 to be positioned in this orientation or a similar orientation by redirecting at least some of the photoacoustic wave PA along axis 405b.

[0176] Fig.19 Illustrate example components of a device according to some additional embodiments. As with other appendices provided herein Figure 1 likewise Fig.19 the number, type, and arrangement of the elements shown are presented only as examples. In this example, device 300 is Figure 3 an example of the device 300 shown. According to this example, device 300 includes a platen 301, a receiver system 302, and a light source system 304. In this example, the outer surface 408a of the platen 301 is configured to receive a target object, such as a finger 115, a wrist, etc.

[0177] In Fig.19 the illustrated embodiment, the light source system 304 is configured to emit at least some of the light 403 through the surface 408b along the axis 405a toward the outer surface 408a (and the target object, if any, on the outer surface 408a). According to some embodiments, the light source system 304 may be disposed on a light source system surface, such as Figure 8 and 9 the light source system surface 304d shown. In some alternative embodiments, the light source system 304 may be coupled to the platen 301, for example, to the surface 408b. In this example, the light source system 304 is configured to provide the light 403 to the target object (if any) on the outer surface 408a via the platen portions 301a, 301b1. According to this example, the axis 405a is at an angle Θ1 with respect to the outer surface 408a.

[0178] In this example, the light 403 induces photoacoustic waves PA in the blood vessel 407. According to this example, at least a portion of the photoacoustic waves PA propagates in the platen portion 301b2 parallel to or substantially parallel to the axis 405a. According to this example, the platen 301 includes an acoustic waveguide 1805. Here, the acoustic waveguide 1805 is configured to direct the photoacoustic waves PA (which include ultrasonic waves in this example) toward the receiver system 302.

[0179] According to this example, the acoustic waveguide 1805 includes the platen portions 301b2 and 301b3. In this example, the surface 408b includes an interface configured to reflect the photoacoustic waves PA. According to this example, the surface 408b corresponds to an interface with a high acoustic impedance contrast. In this example, the high acoustic impedance contrast is caused by the air outside the surface 408b. In this example, the platen portions 301a, 301b1 are made of a solid material such as acrylic. Thus, as Fig.18 in the example shown

[0180] In Fig.19In the illustrated embodiment, the receiver system 302 is located on a surface 408c of the platen 301 that is not parallel or not substantially parallel to the outer surface 408a. Here, the receiver plane 410 is parallel or substantially parallel to the surface 408c. In this example, an axis 405b that is perpendicular to the receiver plane 410 is parallel or substantially parallel to the outer surface 408a. In additional embodiments, the axis 405b may not be parallel or not substantially parallel to the outer surface 408a.

[0181] In this example, the receiver system 302 is or includes an ultrasonic receiver system. According to this example, the receiver system 302 includes a receiver portion 302a and a backing portion 302b. As noted elsewhere herein, the backing portion 302b can be beneficial for SNR improvement but can significantly increase the overall thickness of the receiver system 302. Thus, Fig.19 positioning the receiver system 302 as shown can advantageously reduce the overall thickness of the device 300. According to this example, the configuration of the platen 301 forms an acoustic waveguide 1805 and allows the receiver system 302 to be positioned in this orientation or a similar orientation.

[0182] In one non - limiting example, dimension A can be 4 mm, dimension B can be 1 mm, dimension C can be 3 mm, dimension D can be 10 mm, and angle α can be 135 degrees. Additional embodiments of the platen 301 may have additional configurations, additional dimensions, etc.

[0183] Fig. 20 Illustrative example components of a portion of a device according to some additional embodiments. As with other figures provided herein, Figure 1 likewise, Fig. 20 the number, type, and arrangement of the elements shown are presented only as an example. In this example, a portion of the device 300 is shown, and the device 300 is Figure 3 an example of the device 300 shown. According to this example, Fig. 20 the portion of the device 300 shown includes the platen 301 and the receiver system 302.

[0184] According to this example, the platen 301 is connected to the receiver system 302 via a conductive double - sided tape (DST) 2001 and conductive ink 2003. In some examples, the conductive DST 2001 may include a copper layer. The conductive ink 2003 can include, for example, silver particles, carbon particles, or a combination thereof, which are linked to each other by a solvent.

[0185] In this example, the receiver system 302 includes an anisotropic conductive film (ACF) 2005, a receiver portion 302a, and receiver system circuitry 302e. An ACF is a type of adhesive surface - mount interconnection that allows conductivity only in the thickness direction. In Fig. 20In the example shown, the receiver portion 302a includes a composite piezoelectric material, such as a 1-3 composite, a 2-2 composite, a 3-3 composite, etc. According to this example, the receiver system circuitry 302e includes a flexible printed circuit 2009 and a conductive connector 2007 configured to form an electrical connection between the receiver portion 302a and the flexible printed circuit 2009.

[0186] In one non-limiting example, the conductive ink layer can have a thickness of 140 micrometers and the ACF 2005 can have a thickness of 7 micrometers. Further embodiments of the device 300 can have additional configurations, additional dimensions, etc.

[0187] Fig.21 An example component of a device portion according to some embodiments is shown. As with other figures provided herein, Figure 1 likewise, Fig.21 the number, type, and arrangement of the elements shown are presented only as examples. In this example, Fig.21 the receiver portion 302a of the receiver system 302 is shown.

[0188] According to this example, the receiver portion 302a includes a signal electrode 2105, a first layer of piezoelectric copolymer 2115a on a first side of the signal electrode 2105, a second layer of piezoelectric copolymer 2115b on a second opposite side of the signal electrode 2105, and a ground structure 2110 that surrounds the signal electrode 2105, the first layer of piezoelectric copolymer 2115a, and the second layer of piezoelectric copolymer 2115b. In this example, each of the first layer of piezoelectric copolymer 2115a and the second layer of piezoelectric copolymer 2115b is in contact with a portion of the ground structure 2110. In some examples, the signal electrode 2105, the ground structure 2110, or both can include copper or another suitable conductive material.

[0189] Fig. 22 An example component of a device portion according to some alternative embodiments is shown. As with other figures provided herein, Figure 1 likewise, Fig. 22 the number, type, and arrangement of the elements shown are presented only as examples. In this example, Fig. 22 the receiver portion 302a of the receiver system 302 is shown.

[0190] This example is similar to Fig.21 the example shown. In Fig. 22 the example shown, similar to Fig.21In an example, the receiver portion 302a includes a signal electrode 2105, a first layer of piezoelectric copolymer 2115a on a first side of the signal electrode 2105, a second layer of piezoelectric copolymer 2115b on a second opposite side of the signal electrode 2105, and a ground structure 2110 that surrounds the signal electrode 2105, the first layer of piezoelectric copolymer 2115a, and the second layer of piezoelectric copolymer 2115b.

[0191] However, in Fig. 22 the example shown, these layers of piezoelectric copolymers 2115a and 2115b do not extend from the signal electrode 2105 to the ground structure 2110. Instead, in this example, an ACF layer and a conductive layer are located between each layer of piezoelectric copolymer and each ground layer or signal electrode: an ACF layer 2205a and a conductive layer 2210a are located between the first layer of piezoelectric copolymer 2115a and the ground structure portion 2110a, an ACF layer 2205b and a conductive layer 2210b are located between the first layer of piezoelectric copolymer 2115a and the signal electrode 2105, an ACF layer 2205c and a conductive layer 2210c are located between the signal electrode 2105 and the second layer of piezoelectric copolymer 2115b, and an ACF layer 2205d and a conductive layer 2210d are located between the second layer of piezoelectric copolymer 2115b and the ground structure portion 2110b. Another minor difference is that in Fig. 22 the example shown, the ground structure 2110 includes a ground structure portion 2110a and a ground structure portion 2110b, and the ground structure portion 2110a and the ground structure portion 2110b are joined in this example by a conductive adhesive (such as silver epoxy).

[0192] In a non-limiting example, each of the ground structure portion 2110a, the signal electrode 2105, and the ground structure portion 2110b may comprise copper and each may be between 8 microns and 12 microns in thickness, each of the ACF layers 2205a–2205d may be between 5 microns and 9 microns in thickness, each of the conductive layers 2210a–2210d may comprise copper, and each of these layers of piezoelectric copolymers 2115a and 2115b may be between 300 microns and 400 microns in thickness. In some alternative examples, a piezoelectric composite layer may replace Fig. 22 these layers of piezoelectric copolymers 2115a and 2115b shown in

[0193] Fig.23 is a flowchart that shows an example of some of the disclosed operations. Fig.23 The blocks of Figure 3 (and those of other flowcharts provided herein) may be performed, for example, by Fig.23The methods outlined herein may include more or fewer blocks than those shown. Additionally, the blocks of the methods disclosed herein are not necessarily executed in the order shown. In some cases, Fig.23 one or more of the blocks shown may be executed simultaneously.

[0194] In this example, block 2305 includes controlling, by a control system, a light source system to emit light toward a target object on an outer surface of a platen or a target object proximate to the outer surface of the platen. Depending on the particular example, the target object may be a finger, a wrist, etc. According to this example, block 2310 includes receiving, by the control system, a signal from an ultrasonic receiver system, the signal corresponding to ultrasonic waves generated by the target object in response to the light emitted by the light source system.

[0195] According to this example, block 2315 includes identifying, by the control system, a vascular signal from the ultrasonic receiver system, the vascular signal corresponding to ultrasonic waves generated by blood within a blood vessel of the target object, by one or more blood vessel walls, or by a combination thereof. According to some examples, block 2315 may include identifying, by the control system, an arterial signal from the ultrasonic receiver system, the arterial signal corresponding to ultrasonic waves generated by blood within an artery of the target object, by one or more arterial walls, or by a combination thereof. For example, a vascular signal may be identified by applying a range gate delay (RGD) corresponding to a desired depth to the blood vessel. Alternatively or additionally, an arterial signal may be identified based on one or more characteristics of the photoacoustic response of the blood vessel wall, blood, or a combination thereof.

[0196] In this example, block 2320 includes estimating, by the control system, one or more cardiac characteristics based at least in part on the vascular signal. In some examples, block 2320 may include estimating blood pressure based at least in part on the vascular signal. In some such examples, block 2320 may include estimating blood pressure based at least in part on the arterial signal. According to some examples, block 2320 or additional aspects of method 2300 may include extracting and evaluating heart rate waveform (HRW) features.

[0197] Fig.24 Examples of heart rate waveform (HRW) features that may be extracted according to Fig.23 some embodiments of the method are shown. Fig.24The horizontal axis represents time and the vertical axis represents signal amplitude. The cardiac cycle is represented by the time between adjacent peaks of the HRW. The systolic time interval and the diastolic time interval of the heart are marked below the horizontal axis. During the systolic phase of the cardiac cycle, when the pulse propagates along the artery past a particular location, the arterial wall expands according to the pulse waveform and the elastic properties of the arterial wall. Associated with this expansion is a corresponding increase in the blood volume at that particular location or region, and associated with this increase in blood volume are related changes in one or more properties in that region. Conversely, during the diastolic phase of the cardiac cycle, the blood pressure in the artery decreases and the arterial wall contracts. Associated with this contraction is a corresponding decrease in the blood volume at that particular location, and associated with this decrease in blood volume are related changes in the one or more properties in that region.

[0198] Fig.24 The HRW features shown in are related to the widths of the systolic and / or diastolic portions of the HRW curve at different "heights", which are represented as percentages of the maximum amplitude. For example, the SW50 feature is the width of the systolic portion of the HRW curve at the "height" of 50% of the maximum amplitude. In some embodiments, the HRW features used for blood pressure estimation may include some or all of the SW10, SW25, SW33, SW50, SW66, SW75, DW10, DW25, DW33, DW50, DW66, and DW75 HRW features. In additional embodiments, additional HRW features may be used for blood pressure estimation. In some cases, such additional HRW features may include the sum and ratio of SW and DW at one or more "heights", such as (DW75+SW75), DW75 / SW75, (DW66+SW66), DW66 / SW66, (DW50+SW50), DW50 / SW50, (DW33+SW33), DW33 / SW33, (DW25+SW25), DW25 / SW25, and / or (DW10+SW10), DW10 / SW10. Additional embodiments may also use additional HRW features for blood pressure estimation. In some cases, such additional HRW features may include sums, differences, ratios, and / or other operations based on more than one "height", such as (DW75+SW75) / (DW50+SW50), (DW50+SW50 / (DW10+SW10), etc.

[0199] Fig.25 Shows an example of an apparatus that can be used in a system for estimating blood pressure based at least in part on pulse transit time (PTT). As with other figures provided herein Figure 1Likewise, the number, type, and arrangement of components are shown only as examples. According to this example, system 2500 includes at least two sensors. In this example, system 2500 includes at least an electrocardiogram sensor 2505 and a device 2510 configured to be mounted on the finger of a person 2501. In this example, device 2510 is or includes a device configured to perform at least some of the PAPG methods disclosed herein. For example, device 2510 may be or may include Figure 3 device 300 or a similar device.

[0200] As shown in graph 2520, PAT includes two parts, pre-ejection period (PEP, the time required to convert an electrical signal into a mechanical pumping force and isovolumetric contraction to open the aortic valve) and PTT. The starting time of PAT can be estimated based on the QRS complex - the electrical signal characteristic of ventricular electrical stimulation. As shown in graph 2520, in this example, the start of the pulse arrival time (PAT) can be calculated based on the peak of the R wave measured by electrocardiogram sensor 2505, and the end of PAT can be detected by analyzing the signal provided by device 2510. In this example, the end of PAT is assumed to correspond to the intersection between the tangent of the local minimum detected by device 2510 and the tangent of the maximum slope / first derivative of the sensor signal after the time of the minimum.

[0201] There are many known blood pressure estimation algorithms based on PTT and / or PAT, some of which are summarized in Table 1 of "Cuffless and Continuous Blood Pressure Monitoring: A Review of Methods" by Sharma, M. et al. in Technologies 2017, 5, 21 of the Multidisciplinary Digital Publishing Institute (MDPI) ("Sharma"), and are described in the corresponding text on pages 5 - 10 thereof, both of which are incorporated herein by reference.

[0202] Some previously disclosed methods include calculating blood pressure based on PTT and / or PAT measured by a sensor system including a PPG sensor according to one or more of the equations shown in Table 1 of Sharma or other known equations. As mentioned above, some disclosed PAPG-based embodiments are configured to distinguish arterial HRW from other HRW. Such embodiments may provide a more accurate measurement of PTT and / or PAT compared to PTT and / or PAT measured by a PPG sensor. Therefore, the disclosed PAPG-based embodiments can provide a more accurate blood pressure estimation, even if the blood pressure estimation is based on previously known formulas.

[0203] Other embodiments of system 2500 may not include electrocardiogram sensor 2505. In some such embodiments, the device 2515 configured to be mounted on the wrist of a person 2501 may be or may include a device configured to perform at least some of the PAPG methods disclosed herein. For example, device 2515 may be or may include Figure 2 device 200 or a similar device. According to some such examples, device 2515 may include a light source system and two or more ultrasonic receivers. One example is described below with reference to Fig.27A In some examples, device 2515 may include an ultrasonic receiver array.

[0204] In some embodiments of system 2500 that do not include electrocardiogram sensor 2505, device 2510 may include a light source system and two or more ultrasonic receivers. One example is described below with reference to Fig.27B described.

[0205] Fig.26 A cross-sectional side view schematic of a portion of artery 2600 is shown, through which pulse 2602 is propagating. Fig.26 The boxed arrows in show the direction of blood flow and pulse propagation. As schematically shown, the propagating pulse 2602 causes strain in artery wall 2604, which manifests itself in the form of an expansion (referred to as "dilation") of the diameter (and thus cross-sectional area) of the artery wall. The spatial length L of the actually propagating pulse along the artery (in the direction of blood flow) is typically comparable to the length of a limb such as the distance from the subject's shoulder to the subject's wrist or finger, and is typically less than 1 meter (m). However, the length L of the propagating pulse can vary significantly from subject to subject and, for a given subject, can vary significantly over multiple time periods depending on various factors. The spatial length L of the pulse typically decreases as the distance from the heart increases until the pulse reaches the capillaries.

[0206] As described above, some particular embodiments relate to devices, systems, and methods for estimating blood pressure or other cardiovascular characteristics based on an estimate of an arterial dilation waveform. Unless otherwise specified, the terms "estimate," "measure," "calculate," "infer," "derive," "evaluate," "determine," and "monitor" may be used interchangeably herein as appropriate. Similarly, derivatives of the roots of these terms are also used interchangeably as appropriate; for example, the terms "estimate," "measure," "calculate," "infer," and "determine" are also used interchangeably herein. In some embodiments, the pulse wave velocity (PWV) of a propagating pulse can be estimated by measuring the pulse transit time (PTT) of the pulse as it travels from a first physical location along an artery to another, more distal second physical location along the artery. It will be understood that this PTT is different from the PTT described above with reference to Fig.15 However, either version of the PTT can be used for the purpose of blood pressure estimation. Assuming that the physical distance ΔD between the first physical location and the second physical location is determinable, the PWV can be estimated as the quotient of the physical spatial distance ΔD traveled by the pulse divided by the time (PTT) taken for the pulse to travel the physical spatial distance ΔD. Generally, a first sensor located at the first physical location is used to determine the start time (also referred to herein as the "first time location") at which the pulse arrives at or propagates through the first physical location. A second sensor located at the second physical location is used to determine the end time (also referred to herein as the "second time location") at which the pulse arrives at or propagates through the second physical location and continues through the remainder of the arterial branch. In such an example, the PTT represents the time distance (or time difference) between the first time location and the second time location (start time and end time).

[0207] The fact that arterial dilation waveform measurements are performed at two different physical locations means that the estimated PWV inevitably represents an average over the entire path distance ΔD traveled by the pulse between the first physical location and the second physical location. More specifically, the PWV generally depends on several factors including blood density ρ, the stiffness E (or conversely, elasticity) of the arterial wall, arterial diameter, arterial wall thickness, and blood pressure. Since both arterial wall elasticity and the baseline resting diameter (e.g., the diameter at the end of ventricular diastole) vary significantly throughout the arterial system, the PWV estimate obtained from PTT measurements is inherently an average (averaged over the entire path length ΔD between the two locations where the measurements are made).

[0208] In traditional methods for obtaining PWV, the starting time of a pulse has been obtained at the heart using an electrocardiogram (ECG) sensor that detects electrical signals from the heart. For example, the starting time can be estimated based on the QRS complex (an electrical signal characteristic of the electrical stimulation of the ventricles). In such methods, a different sensor placed at a second location (such as a finger) is typically used to obtain the ending time of the pulse. As those of ordinary skill in the art will understand, there are many arterial discontinuities, branches, and variations along the entire path length from the heart to the finger. Along each segment of the entire path length from the heart to the finger, the PWV can change by up to or more than an order of magnitude. Therefore, PWV estimates based on such long path lengths are unreliable.

[0209] In various embodiments described herein, a PTT estimate is obtained based on measurements associated with arterial distension signals (also referred to as "arterial distension data" or more generally as "sensor data"), the arterial distension signals being obtained by each of a first arterial distension sensor 2606 and a second arterial distension sensor 2608 that are respectively proximate a first physical location and a second physical location along an artery of interest. In some particular embodiments, the first arterial distension sensor 2606 and the second arterial distension sensor 2608 are advantageously positioned proximate the first physical location and the second physical location between which arterial properties such as wall elasticity and diameter of the artery of interest can be considered or assumed to be relatively constant. Thus, the PWV calculated based on the PTT estimate is more representative of the actual PWV along a particular segment of the artery. Next, the blood pressure P estimated based on the PWV is more representative of the true blood pressure. In some embodiments, the magnitude of the distance ΔD between the first arterial distension sensor 2606 and the second arterial distension sensor 2608 (and thus, the distance between the first location and the second location along the artery) can range from about 1 centimeter (cm) to several tens of centimeters - long enough to distinguish the arrival of the pulse at the first physical location from the arrival of the pulse at the second physical location, but close enough to provide sufficient assurance of arterial consistency. In some specific embodiments, the distance ΔD between the first arterial distension sensor 2606 and the second arterial distension sensor 2608 can range from about 1 cm to about 30 cm, and in some embodiments is less than or equal to about 20 cm, and in some embodiments is less than or equal to about 10 cm, and in some specific embodiments is less than or equal to about 5 cm. In some additional embodiments, the distance ΔD between the first arterial distension sensor 2606 and the second arterial distension sensor 2608 can be less than or equal to 1 cm, such as about 0.1 cm, about 0.25 cm, about 0.5 cm, or about 0.75 cm. As a reference, a typical PWV can be about 15 meters per second (m / s). Using a mobile monitoring device in which the first arterial distension sensor 2606 and the second arterial distension sensor 2608 are separated by a distance of about 5 cm, and assuming a PWV of about 15 m / s, this implies a PTT of about 3.3 milliseconds (ms).

[0210] The value of the magnitude of the distance ΔD between the first arterial distension sensor 2606 and the second arterial distension sensor 2608 can be pre-programmed, respectively, into a memory within the monitoring device incorporating the sensors (e.g., such as that referenced above Figure 3in the memory of the described control system 306 or in a memory configured to communicate with the control system 306). As will be understood by one of ordinary skill in the art, in such an embodiment, the spatial length L of the pulse can be greater than the distance ΔD from the first arterial dilation sensor 2606 to the second arterial dilation sensor 2608. Thus, although Fig.26 the illustrative pulse 2602 shown is shown as having a spatial length L comparable to the distance between the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608, in reality each pulse can typically have a spatial length L that is greater than, and even much greater than (e.g., approximately an order of magnitude or more greater than), the distance ΔD between the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608.

[0211] Sensing Architecture and Topology

[0212] In some embodiments of the mobile monitoring device disclosed herein, both the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 are sensors of the same sensor type. In some such embodiments, the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 are the same sensor. In such an embodiment, each of the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 applies the same sensor technology with the same sensitivity to arterial dilation signals caused by propagating pulses, and has the same time delay and sampling characteristics. In some embodiments, each of the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 is configured for photoacoustic plethysmography (PAPG) sensing, such as as disclosed elsewhere herein. Some such embodiments include a light source system and two or more ultrasonic receivers, which can be Figure 3in the case of the light source system 304 and the receiver system 302. In some embodiments, each of the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 is configured for ultrasonic sensing by means of the emission of ultrasonic signals and the reception of corresponding reflections. In some alternative embodiments, each of the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 may be configured for impedance plethysmography (IPG) sensing (also referred to as bioimpedance sensing in a biomedical context). In various embodiments, regardless of the type of sensor used, each of the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 is generally used to capture and provide arterial dilation data representing an arterial dilation signal caused by the propagation of a pulse through a portion of the artery that is disposed adjacent to each sensor. For example, the arterial dilation data may be provided to the processor in the form of a voltage signal generated or received by the sensor based on the ultrasonic signals or impedance signals sensed by the corresponding sensor.

[0213] As described above, during the systolic phase of the cardiac cycle, as the pulse propagates along the artery through a particular location, the arterial wall expands according to the pulse waveform and the elastic properties of the arterial wall. Associated with this expansion is a corresponding increase in the blood volume at that particular location or region, and associated with this increase in blood volume are related changes in one or more properties in that region. Conversely, during the diastolic phase of the cardiac cycle, the blood pressure in the artery decreases and the arterial wall contracts. Associated with this contraction is a corresponding decrease in the blood volume at that particular location, and associated with this decrease in blood volume are related changes in the one or more properties in that region.

[0214] In the case of bioimpedance sensing (or impedance plethysmography), the blood in the artery has a greater electrical conductivity than the electrical conductivity of the surrounding or nearby skin, muscle, fat, tendon, ligament, bone, lymph, or other tissues. The susceptance (and thus the dielectric constant) of the blood also differs from the susceptance (and dielectric constant) of other types of surrounding or nearby tissues. As the pulse propagates through a particular location, the corresponding increase in blood volume results in an increase in the electrical conductivity (more generally an increase in admittance, or equivalently a decrease in impedance) at that particular location. Conversely, during the diastolic phase of the cardiac cycle, the corresponding decrease in blood volume results in an increase in the resistivity (more generally an increase in impedance, or equivalently a decrease in admittance) at that particular location.

[0215] Bioimpedance sensors typically operate by applying an electrical excitation signal at an excitation carrier frequency via two or more input electrodes to a region of interest and detecting an output signal (or output signals) via two or more output electrodes. In some more specific embodiments, the electrical excitation signal is a current signal that is injected into the region of interest via the input electrodes. In some such embodiments, the output signal is a voltage signal representative of the voltage response of the tissue in the region of interest to the applied excitation signal. The detected voltage response signal is affected by the different (and in some cases time-varying) electrical properties of the various tissues through which the injected excitation current signal passes. In some embodiments in which the bioimpedance sensor is operable to monitor blood pressure, heart rate, or other cardiovascular characteristics, the detected voltage response signal is amplitude and phase modulated by the time-varying impedance (or conversely, admittance) of the underlying artery, which fluctuates in synchrony with the user's heartbeat as described above. To determine the various biological characteristics, information in the detected voltage response signal is typically demodulated from the excitation carrier frequency components using various analog or digital signal processing circuits, which may include both passive and active components.

[0216] In some examples incorporating ultrasonic sensors, the measurement of arterial dilation can include, for example, directing ultrasonic waves into a limb towards an artery via one or more ultrasonic transducers. Such ultrasonic sensors are also configured to receive reflected waves based (at least in part) on the directed waves. The reflected waves can include scattered waves, specularly reflected waves, or both scattered and specularly reflected waves. The reflected waves provide information about the arterial wall and thus about arterial dilation.

[0217] In some embodiments, regardless of the type of sensors used for the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608, both the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 can be arranged, assembled, or otherwise included within a single housing of a single mobile monitoring device. As described above, the housing and other components of the monitoring device can be configured such that when the monitoring device is secured or otherwise physically coupled to a subject, both the first arterial dilation sensor 2606 and the second arterial dilation sensor 2608 contact or are adjacent to the skin of the user at a first location and a second location, respectively, the first location and the second location being separated by a distance ΔD, and in some embodiments, the first location and the second location are along a segment of an artery, between which various arterial characteristics can be assumed to be relatively constant. In various embodiments, the housing of the mobile monitoring device is a wearable housing, or is incorporated into or integrated with a wearable housing. In some specific embodiments, the wearable housing includes (or is connected to) a physical coupling mechanism for detachable non-invasive attachment to the user. The housing can be formed using any of a variety of suitable manufacturing processes, including injection molding and vacuum forming, etc. Additionally, the housing can be made of any of a variety of suitable materials, including but not limited to plastics, metals, glass, rubber, ceramics, or combinations of these or other materials. In certain embodiments, the housing and the coupling mechanism enable full mobility use. In other words, some embodiments of the wearable monitoring device described herein are non-invasive, not body-restrictive, and generally do not limit the free unrestricted movement of the subject's arm or leg, which enables continuous or periodic monitoring of cardiovascular characteristics such as blood pressure even when the subject is moving or otherwise engaged in physical activity. Thus, the mobile monitoring device facilitates and enables long-term wearing and monitoring (e.g., for days, weeks, or a month or more without interruption) of one or more biological characteristics of interest to obtain a better picture of such characteristics over an extended duration, and generally a better picture of the health of the user.

[0218] In some embodiments, the mobile monitoring device can be placed around the user's wrist using a strap or band, similar to a watch or a fitness / activity tracker. Fig.27A An example mobile monitoring device 2700 designed to be worn on the wrist according to some embodiments is shown. In the example shown, the monitoring device 2700 includes a housing 2702 that is integrally formed with, coupled to, or otherwise integrated with a wristband 2704. In some cases, the first arterial dilation sensor 2706 and the second arterial dilation sensor 2708 can each include that described above with reference to Figure 3An example of the described ultrasonic receiver system 302 and a portion of the light source system 304. In this example, the mobile monitoring device 2700 is coupled around the wrist such that each of the first arterial dilation sensor 2706 and the second arterial dilation sensor 2708 within the housing 2702 is positioned along a segment of the radial artery 2710 (note that the sensors are typically hidden from view from the outer or external surface of the housing facing the subject when the monitoring device is coupled to the subject, but are exposed on the inner surface of the housing so that the sensors can obtain measurements from the underlying artery through the subject's skin). Also as shown, the first arterial dilation sensor 2706 and the second arterial dilation sensor 2708 are separated by a fixed distance ΔD. In some additional embodiments, the mobile monitoring device 2700 can be similarly designed or modified to be positioned around the forearm, upper arm, ankle, calf, thigh, or finger (all of which are hereinafter referred to as "limbs") using a strap or band.

[0219] Fig.27B An example mobile monitoring device 2700 designed to be worn on a finger is shown, according to some embodiments. In some cases, the first arterial dilation sensor 2706 and the second arterial dilation sensor 2708 can each include an example of the ultrasonic receiver 302 and a portion of the light source system 304 described above with reference to Figure 3 the described ultrasonic receiver 302 and a portion of the light source system 304.

[0220] In some additional embodiments, the mobile monitoring devices disclosed herein can be positioned on the area of interest of a user without the use of a strap or band. For example, the first arterial dilation sensor 2706 and the second arterial dilation sensor 2708 of the monitoring device, as well as additional components, can be encapsulated within a housing that is secured to the skin of the area of interest of the user using an adhesive or other suitable attachment mechanism (an example of a "patch" monitoring device).

[0221] Fig.27C An example mobile monitoring device 2700 designed to be located on an earbud is shown, according to some embodiments. According to this example, the mobile monitoring device 2700 is coupled to the housing of the earbud 2720. In some cases, the first arterial dilation sensor 2706 and the second arterial dilation sensor 2708 can each include an example of the ultrasonic receiver 302 and a portion of the light source system 304 described above with reference to Figure 3 the described ultrasonic receiver 302 and a portion of the light source system 304.

[0222] Implementation examples are described in the following numbered clauses:

[0223] 1. An apparatus, comprising: a platen; a light source system configured to provide light to a target object on an outer surface of the platen, wherein the light source system is configured to direct light along a first axis oriented at a first angle relative to the outer surface of the platen; and an ultrasonic receiver system configured to receive ultrasonic waves generated by the target object in response to light from the light source system, the ultrasonic receiver system including one or more receiver elements located in a receiver plane, a normal of the receiver plane being oriented along a second axis at a second angle relative to the outer surface of the platen.

[0224] 2. The apparatus according to clause 1, wherein the second angle is about 90 degrees.

[0225] 3. The apparatus according to clause 1, wherein the second angle is in the range from 20 degrees to 50 degrees.

[0226] 4. The apparatus according to any one of clauses 1 - 3, wherein at least a portion of the platen is configured to direct ultrasonic waves generated by the target object along a third axis that is at a third angle relative to the outer surface of the platen.

[0227] 5. The apparatus according to clause 4, wherein the third axis is parallel to or substantially parallel to the second axis.

[0228] 6. The apparatus according to clause 4, wherein the third angle is different from the first angle.

[0229] 7. The apparatus according to any one of clauses 1 - 6, wherein the light source system includes one or more light directing elements configured to direct light from the light source system toward the target object along the first axis.

[0230] 8. The apparatus according to clause 7, wherein the one or more light directing elements include a diffraction grating.

[0231] 9. The apparatus according to clause 7 or clause 8, wherein the one or more light directing elements include a lens.

[0232] 10. The apparatus according to any one of clauses 1 - 9, wherein the light source system includes a light source system surface having a normal parallel to or substantially parallel to the first axis, wherein a light source of the light source system is located on the light source system surface.

[0233] 11. The apparatus according to any one of clauses 1 - 10, wherein a first platen portion located between the light source system and the outer surface of the platen may have a first platen portion thickness that is less than a second platen portion thickness of a second platen portion located between at least one receiver element of the ultrasonic receiver system and the outer surface of the platen.

[0234] 12. The apparatus according to any one of clauses 1 - 11, wherein a first platen portion located between an outer surface of the light source system and the platen may have a first platen portion thickness that is greater than a second platen portion thickness of a second platen portion located between at least one receiver element of the ultrasonic receiver system and the outer surface of the platen.

[0235] 13. The apparatus according to any one of clauses 1 - 12, further comprising an acoustic waveguide configured to direct ultrasonic waves towards at least one receiver element of the ultrasonic receiver system.

[0236] 14. The apparatus according to any one of clauses 1 - 13, wherein a first distance that light from the light source system travels through the platen is less than a second distance that ultrasonic waves travel through the platen and reach at least one receiver element of the ultrasonic receiver system.

[0237] 15. The apparatus according to any one of clauses 1 - 14, wherein a platen portion configured to receive light from the light source system is also configured to reflect ultrasonic waves generated by a target object towards at least one receiver element of the ultrasonic receiver system.

[0238] 16. The apparatus according to clause 15, wherein a first distance that light from the light source system travels through the platen portion to the target object is less than a second distance that ultrasonic waves travel from the platen portion to at least one receiver element of the ultrasonic receiver system.

[0239] 17. The apparatus according to any one of clauses 1 - 16, wherein the platen includes a recessed area configured to receive a finger.

[0240] 18. The apparatus according to clause 1, wherein the first axis is perpendicular or substantially perpendicular to the outer surface.

[0241] 19. The apparatus according to clause 18, wherein at least a portion of the platen is configured to direct ultrasonic waves generated by a target object along a third axis that is at a third angle relative to the outer surface of the platen, wherein the second axis is parallel or substantially parallel to the third axis, and wherein the first angle is different from the third angle.

[0242] 20. The apparatus according to clause 19, wherein a first portion of the platen is configured to direct a first portion of ultrasonic waves generated by a target object along the third axis, and a second portion of the platen is configured to direct a second portion of ultrasonic waves generated by a target object along a fourth axis that is at a fourth angle relative to the outer surface, the third angle being different from the first angle and the fourth angle.

[0243] 21. The apparatus according to clause 20, wherein the ultrasonic receiver system comprises: a first receiver element located in a first receiver plane substantially perpendicular to the third axis; and a second receiver element located in a second receiver plane substantially perpendicular to the fourth axis.

[0244] 22. The apparatus according to any one of clauses 1-21, wherein at least a portion of the platen is configured to direct ultrasonic waves generated by a target object along a third axis that is at a third angle relative to the outer surface of the platen, and wherein the third axis is perpendicular or substantially perpendicular to the outer surface.

[0245] 23. The apparatus according to clause 22, wherein the second axis is parallel or substantially parallel to the third axis, and wherein the first angle is different from the third angle.

[0246] 24. The apparatus according to clause 23, wherein the light source system comprises: a first light source portion configured to direct a first light along the first axis towards the target object; and a second light source portion configured to direct a second light along a fourth axis that is at a fourth angle relative to the outer surface of the platen towards the target object, the third angle being different from the first angle and the fourth angle.

[0247] 25. The apparatus according to any one of clauses 1-24, further comprising sound insulating material located between at least a portion of the light source system and at least a portion of the ultrasonic receiver system.

[0248] 26. The apparatus according to any one of clauses 1-25, further comprising electromagnetic noise suppression material proximate to at least a portion of the ultrasonic receiver system, proximate to conductive material attached to at least a portion of the ultrasonic receiver system, or a combination thereof.

[0249] 27. The apparatus according to any one of clauses 1-26, wherein the apparatus is configured to be attached to a person's wrist.

[0250] 28. The apparatus according to clause 27, wherein the light source system is configured to provide light to one or more arteries within a person's wrist.

[0251] 29. The apparatus according to any one of clauses 1-26, wherein the light source system is configured to provide light to one or more arteries within a person's finger.

[0252] 30. The apparatus according to any one of clauses 1-29, wherein the platen, the light source system, or a combination thereof is configured to deliver light in the range from 400 nanometers to 1000 nanometers.

[0253] 31. The apparatus according to any one of clauses 1-30, wherein the light source system is configured to provide light pulses having a pulse width in the range from 50 nanoseconds to 500 nanoseconds.

[0254] 32. The device according to any one of clauses 1 - 31, wherein at least a part of the ultrasonic receiver system comprises a composite piezoelectric material.

[0255] 33. The device according to any one of clauses 1 - 32, wherein at least a part of the ultrasonic receiver system comprises a conductive layer, a first piezoelectric layer adjacent to a first side of the conductive layer, and a second piezoelectric layer adjacent to a second side of the conductive layer.

[0256] 34. The device according to clause 33, wherein the first piezoelectric layer and the second piezoelectric layer comprise a piezoelectric copolymer, a piezoelectric composite, or a combination thereof.

[0257] 35. The device according to clause 33, further comprising a first electrically grounded layer portion and a second electrically grounded layer portion, wherein the first piezoelectric layer is located between the first electrically grounded layer portion and the conductive layer, and the second piezoelectric layer is located between the second electrically grounded layer portion and the conductive layer.

[0258] 36. The device according to any one of clauses 1 - 35, wherein at least a part of the platen has an acoustic impedance that is configured to approximate the acoustic impedance of the material adjacent to the part of the platen.

[0259] 37. The device according to any one of clauses 1 - 36, further comprising a control system configured to: control the light source system to emit light; receive a signal from the ultrasonic receiver corresponding to the ultrasonic waves generated by the target object; identify vascular signals from the ultrasonic receiver corresponding to ultrasonic waves generated by blood within blood vessels of the target object, ultrasonic waves generated by one or more blood vessel walls, or a combination thereof; and estimate one or more cardiac characteristics based at least in part on the vascular signals.

[0260] 38. The device according to any one of clauses 1 - 37, further comprising one or more mirror layers configured to reflect light away from one or more parts of the ultrasonic receiver system.

[0261] 39. The device according to any one of clauses 1 - 38, wherein the outer surface of the platen or a layer located on the outer surface of the platen has an acoustic impedance that is configured to approximate the acoustic impedance of human skin.

[0262] 40. The device according to any one of clauses 1 - 39, further comprising a layer located between the platen and the one or more receiver elements, the acoustic impedance of which is within the acoustic impedance range between the acoustic impedance of the platen and the acoustic impedance of the one or more receiver elements.

[0263] 41. The device according to any one of clauses 1 - 40, further comprising one or more anti - reflection layers.

[0264] 42. The apparatus according to clause 41, wherein at least one of the one or more anti-reflection layers is positioned close to the outer surface of the platen.

[0265] 43. The apparatus according to any one of clauses 1-42, wherein at least a portion of the platen includes an acoustic lens system.

[0266] 44. The apparatus according to clause 43, wherein the acoustic lens system includes a spherical lens, a cylindrical lens, or both.

[0267] 45. The apparatus according to clause 43 or clause 44, wherein the acoustic lens system is positioned on the outer surface of the platen or positioned close to the outer surface of the platen.

[0268] 46. The apparatus according to any one of clauses 1-45, further comprising one or more optical waveguides.

[0269] 47. The apparatus according to clause 46, wherein at least a portion of one of the one or more optical waveguides is located in a portion of the platen.

[0270] As used herein, the phrase referring to "at least one" of a list of items means any combination of those items including a single member. For example, "at least one of a, b, or c" is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0271] The various illustrative logics, logic blocks, modules, circuits, and algorithmic processes described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or a combination of both. The interchangeability of hardware and software has been generally described in terms of functionality and has been illustrated in the various illustrative components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0272] Hardware and data processing devices for implementing the various illustrative logics, logic blocks, modules, and circuits described in connection with the aspects disclosed herein can be implemented or executed with a general-purpose single-chip or multi-chip processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof (designed to perform the functions described herein). A general-purpose processor can be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. The processor can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some embodiments, particular processes and methods can be performed by circuitry specific to a given function.

[0273] In one or more aspects, the described functionality can be implemented in hardware, digital electronic circuitry, computer software, firmware, including the structures disclosed in this specification and structural equivalents thereof, or any combination thereof. Embodiments of the subject matter described in this specification can also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on a computer storage medium for execution by, or to control the operation of, a data processing apparatus.

[0274] If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium such as a non-transitory medium or transmitted through a computer-readable medium such as a non-transitory medium. The processes of the methods or algorithms disclosed herein may be implemented as processor-executable software modules, which may reside on a computer-readable medium. The computer-readable medium includes both computer storage media and communication media, and the communication media includes any medium that can be capable of transmitting a computer program from one place to another. The storage media may be any available medium that can be accessed by a computer. By way of example and not limitation, non-transitory media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection may be properly termed a computer-readable medium. As used herein, disk and optical disks include compact disk (CD), laser disk, optical disk, digital versatile disk (DVD), floppy disk, and Blu-ray disk, where disks typically reproduce data magnetically, while optical disks reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or collection of code and instructions on a machine-readable medium and a computer-readable medium, which may be incorporated into a computer program product.

[0275] Various modifications to the embodiments described in this disclosure may be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the claims, principles, and novel features disclosed herein. The word "exemplary" is specifically used herein to mean "serving as an example, instance, or illustration," if any. Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0276] Certain features that are described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented separately or in any suitable sub-combination in multiple embodiments. Additionally, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be adapted to a sub-combination or variant of a combination.

[0277] Similarly, although operations are depicted in the drawings in a particular order, this should not be construed as requiring that such operations be performed in the particular order shown or sequentially, or that all of the illustrated operations be performed to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Additionally, the separation of various system components in the above-described embodiments should not be construed as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Further, additional embodiments are within the scope of the claims. In some cases, the acts recited in the claims can be performed in a different order and still achieve the desired result.

[0278] It should be understood that unless features in any of the particular described embodiments are explicitly identified as being incompatible with each other, or the context implies that they are mutually exclusive and not readily combinable in a complementary and / or supportive sense, the overall expectation and contemplation of the present disclosure is that specific features of these complementary embodiments can be selectively combined to provide one or more comprehensive but slightly different technical solutions. Accordingly, it will be further understood that the foregoing description is given by way of example only, and modifications in details may be made within the scope of the present disclosure.

[0279] Various modifications to the embodiments described in this disclosure may be readily apparent to those skilled in the art, and the general principles defined herein may be applied to additional embodiments without departing from the spirit or scope of the disclosure. Accordingly, the appended claims are not intended to be limited to the embodiments shown herein, but are to be accorded the widest scope consistent with the disclosure, the principles disclosed herein, and the novel features.

[0280] In addition, certain features described in separate embodiments in this specification can also be implemented in combination in a single embodiment. Conversely, various features described in a single embodiment can also be implemented separately or in any suitable sub-combination in multiple embodiments. Further, although features may be described above as acting in certain combinations and even initially claimed as such, one or more of the features in the claimed combination can in some cases be deleted from the combination, and the claimed combination can be adjusted to a sub-combination or a variant of a combination.

[0281] Similarly, although the operations are depicted in the drawings in a particular order, this should not be construed as requiring that the operations be performed in the particular order shown or sequentially, or that all of the operations shown be performed to achieve the desired result. Additionally, the drawings may schematically depict one or more example processes in the form of a flowchart. However, additional operations not depicted can be incorporated into the example processes schematically shown. For example, one or more additional operations can be performed before, after, simultaneously with, or between any of the operations shown. Further, the various operations within the operations described and shown can themselves include and generally refer to multiple sub-operations. For example, each of the operations described above can itself include the execution of a process or algorithm. Additionally, in some embodiments, the various operations within the operations described and shown can be combined or performed in parallel. Similarly, the separation of the various system components in the embodiments described above should not be construed as requiring such separation in all embodiments. Likewise, other embodiments are within the scope of the appended claims. In some cases, the acts recited in the claims can be performed in a different order and still achieve the desired result.

Claims

1. An apparatus, comprising: a platen; a light source system configured to provide light to a target object on an outer surface of the platen, wherein the light source system is configured to direct light along a first axis oriented at a first angle relative to the outer surface of the platen; and an ultrasonic receiver system configured to receive ultrasonic waves generated by the target object in response to the light from the light source system, the ultrasonic receiver system including one or more receiver elements located in a receiver plane, a normal of the receiver plane being oriented along a second axis at a second angle relative to the outer surface of the platen.

2. The apparatus according to claim 1, wherein the second angle is about 90 degrees.

3. The apparatus according to claim 1, wherein the second angle is in a range from 20 degrees to 50 degrees.

4. The apparatus according to claim 1, wherein at least a portion of the platen is configured to direct the ultrasonic waves generated by the target object along a third axis that is at a third angle relative to the outer surface of the platen.

5. The apparatus according to claim 4, wherein the third axis is parallel to or substantially parallel to the second axis.

6. The apparatus according to claim 4, wherein the third angle is different from the first angle.

7. The apparatus according to claim 1, wherein the light source system includes one or more light directing elements configured to direct light from the light source system toward the target object along the first axis.

8. The apparatus according to claim 7, wherein the one or more light directing elements include a diffraction grating.

9. The apparatus according to claim 8, wherein the one or more light directing elements include a lens.

10. The apparatus according to claim 1, wherein the light source system includes a light source system surface having a normal parallel to or substantially parallel to the first axis, wherein a light source of the light source system is located on the light source system surface.

11. The apparatus according to claim 1, wherein a first platen portion located between the light source system and the outer surface of the platen may have a first platen portion thickness that is less than a second platen portion thickness of a second platen portion located between at least one receiver element of the ultrasonic receiver system and the outer surface of the platen.

12. The apparatus according to claim 1, wherein a first platen portion located between the light source system and the outer surface of the platen may have a first platen portion thickness that is greater than a second platen portion thickness of a second platen portion located between at least one receiver element of the ultrasonic receiver system and the outer surface of the platen.

13. The apparatus according to claim 1, further comprising an acoustic waveguide configured to direct the ultrasonic waves toward at least one receiver element of the ultrasonic receiver system.

14. The device according to claim 1, wherein a first distance that the light from the light source system travels through the platen is less than a second distance that the ultrasonic wave travels through the platen and reaches at least one receiver element of the ultrasonic receiver system.

15. The device according to claim 1, wherein a portion of the platen configured to receive the light from the light source system is also configured to reflect the ultrasonic wave generated by the target object toward at least one receiver element of the ultrasonic receiver system.

16. The device according to claim 15, wherein a first distance that the light from the light source system travels through the platen portion to the target object is less than a second distance that the ultrasonic wave travels from the platen portion to the at least one receiver element of the ultrasonic receiver system.

17. The device according to claim 1, wherein the platen includes a recessed area configured to receive a finger.

18. The device according to claim 1, wherein the first axis is perpendicular or substantially perpendicular to the outer surface.

19. The device according to claim 18, wherein at least a portion of the platen is configured to direct the ultrasonic wave generated by the target object along a third axis that is at a third angle relative to the outer surface of the platen, wherein the second axis is parallel or substantially parallel to the third axis, and wherein the first angle is different from the third angle.

20. The device according to claim 19, wherein a first portion of the platen is configured to direct a first portion of the ultrasonic wave generated by the target object along the third axis, and a second portion of the platen is configured to direct a second portion of the ultrasonic wave generated by the target object along a fourth axis that is at a fourth angle relative to the outer surface, the third angle being different from the first angle and the fourth angle.

21. The device according to claim 20, wherein the ultrasonic receiver system includes: a first receiver element located in a first receiver plane that is substantially perpendicular to the third axis; and a second receiver element located in a second receiver plane that is substantially perpendicular to the fourth axis.

22. The device according to claim 1, wherein at least a portion of the platen is configured to direct the ultrasonic wave generated by the target object along a third axis that is at a third angle relative to the outer surface of the platen, and wherein the third axis is perpendicular or substantially perpendicular to the outer surface.

23. The device according to claim 22, wherein the second axis is parallel or substantially parallel to the third axis, and wherein the first angle is different from the third angle.

24. The device according to claim 23, wherein the light source system includes: a first light source portion configured to direct first light toward the target object along the first axis; and A second light source portion configured to direct second light towards the target object along a fourth axis that is at a fourth angle relative to the outer surface of the platen, the third angle being different from the first angle and the fourth angle.

25. The apparatus of claim 1, further comprising sound insulation material located between at least a portion of the light source system and at least a portion of the ultrasonic receiver system.

26. The apparatus of claim 1, further comprising electromagnetic noise suppression material proximate to at least a portion of the ultrasonic receiver system, proximate to conductive material attached to at least a portion of the ultrasonic receiver system, or a combination thereof.

27. The apparatus of claim 1, wherein the apparatus is configured to be attached to a person's wrist.

28. The apparatus of claim 27, wherein the light source system is configured to provide light to one or more arteries within a person's wrist.

29. The apparatus of claim 1, wherein the light source system is configured to provide light to one or more arteries within a person's finger.

30. The apparatus of claim 1, wherein the platen, the light source system, or a combination thereof is configured to deliver light in the range from 400 nanometers to 1000 nanometers.

31. The apparatus of claim 1, wherein the light source system is configured to provide light pulses having a pulse width in the range from 50 nanoseconds to 500 nanoseconds.

32. The apparatus of claim 1, wherein at least a portion of the ultrasonic receiver system comprises a composite piezoelectric material.

33. The apparatus of claim 1, wherein at least a portion of the ultrasonic receiver system comprises a conductive layer, a first piezoelectric layer proximate to a first side of the conductive layer, and a second piezoelectric layer proximate to a second side of the conductive layer.

34. The apparatus of claim 33, wherein the first piezoelectric layer and the second piezoelectric layer comprise a piezoelectric copolymer, a piezoelectric composite, or a combination thereof.

35. The apparatus of claim 33, further comprising a first electrically grounded layer portion and a second electrically grounded layer portion, wherein the first piezoelectric layer is located between the first electrically grounded layer portion and the conductive layer, and the second piezoelectric layer is located between the second electrically grounded layer portion and the conductive layer.

36. The apparatus of claim 1, wherein at least a portion of the platen has an acoustic impedance that is configured to approximate the acoustic impedance of the material proximate to the portion of the platen.

37. The apparatus of claim 1, further comprising a control system configured to: control the light source system to emit light; receive a signal from the ultrasonic receiver corresponding to the ultrasonic waves generated by the target object; identify vascular signals from the ultrasonic receiver corresponding to ultrasonic waves generated by blood within blood vessels of the target object, ultrasonic waves generated by one or more blood vessel walls, or a combination thereof; and estimate one or more cardiac characteristics based at least in part on the vascular signals.

38. The apparatus according to claim 1, further comprising one or more mirror layers configured to reflect light away from one or more portions of the ultrasonic receiver system.

39. The apparatus according to claim 1, wherein an outer surface of the platen or a layer located on the outer surface of the platen has an acoustic impedance configured to approximate the acoustic impedance of human skin.

40. The apparatus according to claim 1, further comprising a layer located between the platen and the one or more receiver elements, the layer having an acoustic impedance within an acoustic impedance range between the acoustic impedance of the platen and the acoustic impedance of the one or more receiver elements.

41. The apparatus according to claim 1, further comprising one or more anti-reflection layers.

42. The apparatus according to claim 41, wherein at least one of the one or more anti-reflection layers is located adjacent to the outer surface of the platen.

43. The apparatus according to claim 1, wherein at least a portion of the platen comprises an acoustic lens system.

44. The apparatus according to claim 43, wherein the acoustic lens system comprises a spherical lens, a cylindrical lens, or both.

45. The apparatus according to claim 43, wherein the acoustic lens system is located on the outer surface of the platen or adjacent to the outer surface of the platen.

46. The apparatus according to claim 1, further comprising one or more optical waveguides.

47. The apparatus according to claim 46, wherein at least a portion of one of the one or more optical waveguides is located within a portion of the platen.

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