Photoacoustic devices and systems

Abstract

Photoacoustic devices and systems are disclosed. A user device may include a light source system including one or more light sources; a receiver system including one or more receivers configured to detect acoustic signals generated based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least portion of the user.

Description

PHOTOACOUSTIC DEVICES AND SYSTEMSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority from Indian Provisional Application No. 202341062837, entitled “PHOTO ACOUSTIC DEVICES AND SYSTEMS” and filed on September 19, 2023, which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] This disclosure relates generally to photoacoustic devices and systems.DESCRIPTION OF RELATED TECHNOLOGY

[0003] 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 push is partly a result of the limitations in the usability of traditional measuring devices for continuous, noninvasive and ambulatory 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

[0004] 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.

[0005] In one aspect of the present disclosure, a user device is disclosed. In some embodiments, the user device may include: a light source system including one or more light sources; a receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a secondacoustic characteristic corresponding to an acoustic characteristic the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least portion of the user.

[0006] In another aspect of the present disclosure, a method for monitoring a physiological parameter of a user using a photoacoustic device is disclosed. In some embodiments, the method may include: causing transmission of optical signals via one or more waveguides from a light source system of the photoacoustic device toward a portion of a user proximate a receiver system of the photoacoustic device, the receiver system disposed remotely from the light source system without direct contact therewith, the photoacoustic device comprising: the light source system including one or more light sources; the receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least portion of the user; receiving, from the receiver system, information regarding the acoustic signals detected by the one or more receivers; and determining the physiological parameter of the user based on the information regarding the acoustic signals.

[0007] In another aspect of the present disclosure, an apparatus is disclosed. In some embodiments, the apparatus may include: light source means for transmitting light, the light source means comprising one or more light sources; receiver means for detecting acoustic signals generated by a target object based on optical signals from the light source means, the receiver means comprising one or more receiver elements; interface means contactable by a user, the interface means comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the receiver means, the interface means comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to anacoustic characteristic of the receiver means; and waveguide means for transmitting the optical signals from the one or more light sources to the at least portion of the user, the waveguide means comprising one or more waveguides at least partially embedded in the interface layer.

[0008] In another aspect of the present invention, a non-transitory computer-readable apparatus is disclosed. In some embodiments, the non-transitory computer-readable apparatus may include a storage medium, the storage medium comprising a plurality of instructions configured to, when executed by a control system, cause a photoacoustic device to: cause transmission of optical signals via one or more waveguides from a light source system of the photoacoustic device toward a portion of a user proximate a receiver system of the photoacoustic device, the receiver system disposed remotely from the light source system without direct contact therewith, the photoacoustic device comprising: the light source system including one or more light sources; the receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least portion of the user; receive, from the receiver system, information regarding the acoustic signals detected by the one or more receivers; and determine the physiological parameter of the user based on the information regarding the acoustic signals.

[0009] 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 of the following figures may not be drawn to scale.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 shows an example of a blood pressure monitoring device based on photoacoustic plethysmography, which may be referred to herein as PAPG.

[0011] Figure 2 is a block diagram that shows example components of an apparatus according to some disclosed implementations.

[0012] Figures 3A - 3C show examples of graded portions or graded layers of an interface of the apparatus of Figure 2, according to some disclosed implementations.

[0013] Figures 4A - 4C show example configurations of an interface, a receiver element of a receiver system, and an optical waveguide of a photoacoustic apparatus, according to some disclosed implementations.

[0014] Figures 4D - 4F show example configurations of the interface, the receiver element of a receiver system, and multiple optical waveguides of the photoacoustic apparatus, according to some disclosed implementations.

[0015] Figures 5A and 5B show example implementations of receiver elements of a receiver system, according to some disclosed implementations.

[0016] Figure 6 shows an example configuration of a photoacoustic apparatus, according to some disclosed implementations.

[0017] Figure 7 is a flow diagram of a method for monitoring a physiological parameter of a user, according to some disclosed implementations.

[0018] Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0019] The following description is directed to certain implementations for the purposes of describing various aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein can be applied in a multitude of different ways. Some of the concepts and examples provided in this disclosure are especially applicable to blood pressure monitoring applications or monitoring of other physiological parameters. However, some implementations also may be applicable to other types of biological sensing applications, as well as to other fluidflow systems. The described implementations may be implemented in any device, apparatus, or system that includes an apparatus as disclosed herein. In addition, it is contemplated that the described implementations may be included in or associated with a variety of electronic devices such as, but not limited to: mobile telephones, multimedia Internet enabled cellular telephones, mobile television receivers, wireless devices, smartphones, smart cards, wearable devices such as bracelets, armbands, wristbands, rings, headbands, patches, chest bands, anklets, etc., Bluetooth® devices, personal data assistants (PDAs), wireless electronic mail receivers, hand-held or portable computers, netbooks, notebooks, smartbooks, tablets, printers, copiers, scanners, facsimile devices, global positioning system (GPS) receivers / navigators, cameras, digital media players, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, auto displays (including odometer and speedometer displays, etc.), cockpit controls and / or displays, camera view displays (such as the display of a rear view camera in a vehicle), architectural structures, microwaves, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable memory chips, washers, dryers, washer / dryers, parking meters, automobile doors, Internet of Things (loT) devices, etc. Thus, the teachings are not intended to be limited to the specific implementations depicted and described with reference to the drawings; rather, the teachings have wide applicability as will be readily apparent to persons having ordinary skill in the art.

[0020] Non-invasive health monitoring devices, such as photoacoustic plethysmography (PAPG)-based devices, have various potential advantages over more invasive health monitoring devices such as cuff-based or catheter-based blood pressure measurement devices. However, it has proven to be difficult to design satisfactory compact, wearable PAPG-based devices. Some wearable PAPG-based devices may include a platen for transmitting both light and acoustic signals. The platen should be optically transparent and should ideally have an acoustic impedance that closely matches that of human skin. The requirement of optically transparent platen materials may result in sub-optimal sound transmission characteristics. The use of a platen may also limit the number of independent light sources that can be used for collecting data, due to space constraints. Wearable PAPG-based devices having a single light source location, or fewlight source locations may not be optimal, at least in part because alignment with a target — such as an artery — may be challenging.

[0021] Some disclosed devices described herein include an interface, a light source system and an ultrasonic receiver system. Some such devices may not include a rigid platen. According to some implementations, the interface may be a physical, flexible interface constructed of one or more of suitable materials having a desired property or properties (e.g., an acoustic property such as acoustic impedance, softness of the material). In some implementations, the interface may be a flexible interface that can contact a target object that may be proximate to or contact the interface. There may be salient differences between such an interface and a platen. In some implementations, the light source system may be configured to direct light using one or more optical waveguides (e.g., optical fibers) configured to direct light toward a target object. According to some implementations, the interface may have an outer surface, or a layer on the outer surface, with an acoustic impedance that is configured to approximate the acoustic impedance of human skin. Such outer surface may have a contact portion that is contactable by a user or a body part of the user (e.g., finger, wrist). In some examples, the optical waveguide(s) may be embedded in one or more acoustic matching layers that are configured to bring the light transmitted by the optical waveguide(s) very close to tissue. The outer surface and / or other parts of the interface may be compliant, pliable, flexible, or otherwise at least partially conforming to the shape and contours of the body part of the user. In some implementations, the interface may have a surface proximate the ultrasonic receiver system, or a layer on the surface proximate the ultrasonic receiver system, with an acoustic impedance that is configured to approximate the acoustic impedance of the ultrasonic receiver system.

[0022] Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. V arious disclosed configurations include PAPG-capable devices that utilize flexible material such that the devices are worn to obtain and evaluate measurements, e.g., cardiac measurements, via photoacoustic means. According to some examples, the optical waveguide(s) may be configured to provide light at various lateral distances along a target, such as an artery. In some such examples, an array of receiver elements may be configured to receive ultrasonic waves caused by photoacoustic responses within human tissue caused by light from the optical waveguide(s). Such implementations allow thecollection of multi-point information with respect to blood pressure, pulse wave velocity, depth discrimination, heart rate etc. Acoustic impedance matching layers may mitigate unwanted reflections of acoustic waves, thereby mitigating noise. Some disclosed devices include impedance matching layers having a relatively lower acoustic attenuation — as compared with commonly-used platen materials — that can improve the signal-to-noise ratio (SNR).

[0023] Figure 1 shows an example of a blood pressure monitoring device based on photoacoustic plethysmography, which may be referred to herein as PAPG. Figure 1 shows the same examples of arteries, veins, arterioles, venules and capillaries inside a body part, which is a finger 115 in this example. In some examples, the light source shown in Figure 1 may be coupled to a light source system (not shown) that is disposed remotely from the body part (e.g., finger 1 15). In some implementations, the light source may be an opening of an optical fiber or other waveguide. Such an opening may also be connected to an opening of an interface that is contactable with the body part. In some embodiments, the light source system may include one or more LEDs, one or more laser diodes, etc. In this example, the light source has transmitted light (in some examples, green, red, and / or near-infrared (NIR) light) that has penetrated the tissues of the finger 115 in an illuminated zone.

[0024] In the example shown in Figure 1, blood vessels (and components of the blood itself) are heated by the incident light from the light source and are emitting acoustic waves 102. In this example, the emitted acoustic waves 102 include ultrasonic waves. According to this implementation, the acoustic wave emissions 102 are being detected by an ultrasonic receiver, which is a piezoelectric receiver in this example. Photoacoustic emissions 102 from the illuminated tissues, detected by the piezoelectric receiver, may be used to detect volumetric changes in the blood of the illuminated zone of the finger 115 that correspond to physiological data within the illuminated tissues of finger 115, such as heart rate waveforms. Although some of the tissue areas shown to be illuminated are offset from those shown to be producing photoacoustic emissions 102, this is merely for illustrative convenience. It will be appreciated that that the illuminated tissues will actually be those producing photoacoustic emissions. Moreover, it will be appreciated that the maximum levels of photoacoustic emissions will often be produced along the same axis as the maximum levels of illumination. In some examples, the ultrasonicreceiver may be an instance of the receiver system 202 that is described below with reference to Figure 2.

[0025] One important difference between an optical technique such as a photoplethysmography (PPG)-based system the PAPG-based method of Figure 1 is that the acoustic waves shown in Figure 1 travel much more slowly than the reflected light waves involved in PPG. Accordingly, depth discrimination based on the arrival times of the acoustic waves shown in Figure 1 is possible, whereas depth discrimination based on the arrival times of the light waves in PPG may not be possible. This depth discrimination allows some disclosed implementations to isolate acoustic waves received from the different blood vessels.

[0026] According to some such examples, such depth discrimination allows artery heart rate waveforms to be distinguished from vein heart rate waveforms and other heart rate waveforms. Therefore, blood pressure estimation based on depth-discriminated PAPG methods can be substantially more accurate than blood pressure estimation based on PPG-based methods.Example PAPG Apparatus

[0027] Figure 2 is a block diagram that shows example components of an apparatus according to some disclosed implementations. In this example, the apparatus 200 includes an interface 201, a receiver system 202, a light source system 204, and a waveguide system 205. Although the light source system 204 and the waveguide system 205 are shown as separate elements in Figure 2, in some instances the waveguide system 205 may be described as being part of the light source system 204. Some implementations of the apparatus 200 may include a control system 206, an interface system 208, a noise reduction system 210, or combinations thereof.

[0028] Various examples of the interface 201 and various configurations of light source systems 204 and receiver systems 202 are disclosed herein. Some examples are described in more detail below.

[0029] In some implementations in which the receiver system 202 includes an ultrasonic receiver system, the interface 201 may be an interface having a contact portion configured to make contact with a body part of a user such as the finger 115 shown in Figure 1.

[0030] In some embodiments, the light source system 204 may include one or more light sources that may be disposed remotely from the interface 201 and / or the receiver system 202. As will be described elsewhere herein, in some example implementations, some or all of the one or more light sources may be disposed substantially opposite to the interface 201 and / or the receiver system 202. In some example implementations, some or all of the one or more light sources may be disposed at or along an axis that is angled relative to a central axis associated with the interface 201 and / or the receiver system 202. To illustrate with an example, in an apparatus 200 implemented as a wearable device such as a wristband or a ring, the interface 201 and / or the receiver system 202 may be disposed at a bottom portion of the wearable device, while the one or more light sources may be disposed at a top portion opposite to the bottom portion, or along the sides of the wearable device. As will be discussed further, light may travel via one or more optical waveguides of a waveguide system 205 toward a target object (e.g., body part, tissue of interest) that is proximate to the interface 201 and / or the receiver system 202, and can cause generation of ultrasonic waves (e.g., 102) by the target object. The one or more optical waveguides may be optical fibers, for example.

[0031] According to some examples, the interface 201 may include different portions, which may have varying thicknesses, depending on the particular implementation. In some examples, the interface 201 may include a first portion residing between the light source system 204 and the outer surface of the interface 201. In some examples, the first portion may have a first portion thickness that is less than a second portion thickness of a second portion residing between at least one receiver element of the receiver system 202 and the outer surface of the interface 201. In some such examples, the first portion may be configured to receive light from the light source system 204 and may also be configured to reflect the ultrasonic waves generated by the target object towards at least one receiver element of the receiver system 202. However, in some examples, a first portion residing between the light source system 204 and the outer surface of the interface 201 may have a first portion thickness that is greater than a second portion residing between at least one receiver element of the receiver system 202 and the outer surface of the interface 201.

[0032] In some embodiments, the interface 201 may be made of a flexible material and include one or more of the different portions (e.g., layers) having a specific acoustic property (e.g., acoustic impedance). In certain implementations, a first layer of theinterface 201 which has the contact portion may be a material having an acoustic impedance that is at, approximately, or within a range of the acoustic impedance of human skin (1.5 MRayls) or muscle (1.71 MRayls). For instance, the first layer or a portion thereof may be polyethylene, which has an acoustic impedance of 1.73 MRayls. In different implementations, the first layer may possess an acoustic impedance that is within a range within the acoustic impedance of human skin. As but one example range, the acoustic impedance of the first layer may be between 1.5 and 2.0 MRayls to facilitate the approximation or matching of acoustic impedance. Hence, in some example implementations, a material having an acoustic impedance within such a range, such as low-density polyethylene having an acoustic impedance of 1.79 MRayls, styrene butadiene (or its rubber derivatives) having an acoustic impedance of 1.95 MRayls, ethyl vinyl acetate with 18% acetate having an acoustic impedance of 1.69 MRayls, or ethyl vinyl acetate with 28% acetate having an acoustic impedance of 1.60 MRayls, may be used in the first layer of the interface 201 contacting the user’s skin. Unlike platens, which are typically rigid, the material of the interface 201 may be compliant, pliable, flexible, or otherwise conforming to the shape and contours of the body part of the user, e.g., at the finger 115, wrist, waist, etc.

[0033] In some implementations, the interface 201 may have a second layer having a surface proximate (e.g., contacting) the receiver system 202, the second layer being a material with an acoustic impedance that is configured to approximate the acoustic impedance of the receiver system 202, similar to the first layer approximating an acoustic property of skin. One example range of values of acoustic impedance associated with the receiver system 202 may be 2 - 10 MRayls.

[0034] In some implementations, more than two layers may be present in the interface 201. For example, the interface 201 may include two layers proximate the body part of the user and a layer proximate the receiver system 202. In some cases, the two layers proximate the body part of the user may be different materials that approximate the acoustic impedance of the body part, e.g., polyethylene (acoustic impedance of 1.73 MRayls) and low-density polyethylene (acoustic impedance of 1.79 MRayls). This type of graded configuration may introduce a gradual change in the acoustic properties or impedances, where they progressively match that of the skin or body part and that of the receiver system 202, advantageously minimizing loss of acoustic energy across the interface 201 and increasing efficiency of acoustic wave transmission.

[0035] Figure 3A is an example of graded portions or graded layers of the interface 201 of the apparatus 200, according to some disclosed implementations. In this example, a first layer 301a is disposed adjacent (e.g., over) a second layer 301b. The first layer 301a may possess a first acoustic property such as the acoustic impedance of a first material, e.g., polyethylene). The first layer 301a may have a contact portion that interfaces with a body part of a user. The second layer 301b may possess a second acoustic property such as the acoustic impedance of a second material, e.g., low-density polyethylene. In some variants of this example, the second acoustic property of the second layer 301b may be closer to or better approximate the acoustic impedance of a receiver or receiver element 302. The receiver element 302 may be an example of a receiver element of the receiver system 202. In some variants, the first acoustic property of the first layer 301a may be closer to or better approximate the acoustic impedance of the target object, e.g., skin (1.5), muscle (1.71), fat (1.34), blood (1.65), or other body parts.

[0036] Figure 3B is another example of graded portions or graded layers of the interface 201 of the apparatus 200, according to some disclosed implementations. In this example, a first layer 301a, a second layer 301b, and a third layer 301c may be disposed adjacent to one another. Similar to the example of Figure 3 A, each of these layers may possess respective acoustic properties.

[0037] In some configurations, at least one layer may be removable, appliable or replaceable. A role of this type of layer may be to act as an interface between skin and an optical waveguide. This helps to protect the soft skin from potentially sharp edges of waveguides as well as protect the waveguide from environmental contaminants such as dust, liquids, etc. Hence, this protective layer may be a topmost layer (e.g., first layer 301a) in some configurations. Such a layer may be a transparent polymer film or tape with useful optical and acoustic transmission properties. An example of this layer may be a thin polymer film constructed of a clear and flexible material, at least a portion of which having a sticky or tacky property, similar to screen protectors for user devices. Such a tacky polymer film may have an acoustic impedance closely matching that of skin (approximately 1.5 MRayls), or in some instances, acoustic impedance closely matching that of an adjacent layer (e.g., second layer 301b or third layer 301c). In some configurations, this type of layer may not be removable and be permanently fixed to an adjacent layer or the receiver element 302.

[0038] Figure 3C is another example of graded portions or graded layers of the interface 201 of the apparatus 200, according to some disclosed implementations. In this example, the property of the interface layer 301 may be even more granular than the example of Figure 3B, having numerous layers or portions that have a gradually increasing or decreasing acoustic impedance. In some implementations, the interface layer 301 may instead be one material having progressively varying acoustic impedance, which may be due to the material being more or less dense over the thickness of the layer 301.

[0039] In some implementations, the first layer 301a of the interface 201 or a contact portion thereof may include a coating substance. In some cases, the coating substance can be a transparent polymer tape or film, which may be removable or appliable. Such a coating substance may serve as a protective layer (e.g., such as that discussed above) and / or further facilitate the transition of the acoustic characteristics between the body part and the layers.

[0040] As a general approach, a material of the layer(s) of the interface 201 may be selected according to the following equation (Eqn. 1) representing a reflection coefficient r for an acoustic wave traveling through or interacting with the interface 201:

[0041] In Eqn. 1, Zi represents an impedance of a first material, Z2 represents an impedance of a second material, EH represents a root-mean-square amplitude of the electric field of an incident acoustic wave, and Eirrepresents an amplitude of the electric field of a reflected acoustic wave. Reflection coefficient T is the ratio of Eir to EH.

[0042] In an example configuration of the interface 201, if Zi = 1.5 (skin), and Z2 = 1.73 (polyethylene), T is approximately 7.1%, so 92.9% of the acoustic energy can be transmitted through the interface 201. In another example configuration of the interface 201, if Zi = 1.71 (muscle), and Z2 = 1.79 (low-density polyethylene), T is approximately 2.3%, so 97.7% of the acoustic energy can be transmitted through the interface 201. Similar determinations of transmission efficiency may be made with respect to additional layers, e.g., graded matching layers. Lower reflection coefficient T can result in higher acoustic transmission efficiency and higher signal quality (e.g., higher signal-to-noise ratio (SNR)), based on selection of materials having higher transmission efficiency.

[0043] Advantageously, according to embodiments herein, it is not necessary to use a platen to implement PAPG-based methods. While platens generally have rigid and inflexible surfaces, the interface 201 disclosed herein may not be so rigid. Using an embedded optical fiber or waveguide allows for a broader choice of polymers as matching layers which best match the acoustic impedance of a user (e.g., skin) with low attenuation. For example, it becomes feasible to construct the interface 201 and the apparatus 200 using a flexible material, for example, polyethylene. Furthermore, acoustic attenuation layers, and positioning and quantity of components (e.g., light sources, receiver elements), can be optimized without constraints such as shape and size of the apparatus 200. The apparatus 200 can thus be implemented and operated as a user-conformal wearable device (wristband, ring, bracelet, anklet, etc.). Implementations and variations thereof will be described in more detail below. In such a wearable device, the interface 201 can enable direct contact with tissue of interest, e.g., near blood vessels, in order to obtain and evaluate photoacoustic signals (e.g., emitted acoustic waves 102). Hence, the apparatus 200 can be a user-friendly, lightweight, compact or semi-compact, and portable device for enhanced, consistent monitoring of physiological parameters, such as blood pressure.

[0044] According to some examples, the interface 201 (or another portion of the apparatus 200) may include one or more anti-reflective layers. In some examples, one or more anti-reflective layers may reside on, or proximate, one or more outer surfaces of the interface 201.

[0045] In some examples, at least a portion of the outer surface of the interface 201 may have an acoustic impedance that is configured to approximate an acoustic impedance of human skin. The portion of the outer surface of the interface 201 may, for example, be a portion that is configured to receive a target object, such as a human digit or other appendage. (As used herein, the terms “finger” and “digit” may be used interchangeably, such that a thumb is one example of a finger.) A typical range of acoustic impedances for human skin is 1.53-1.680 MRayls. In some examples, at least an outer surface of the interface 201 may have an acoustic impedance that is in the range of 1.4-1.8 MRayls, or in the range of 1.5- 1.7 MRayls.

[0046] Alternatively, or additionally, in some examples at least an outer surface of the interface 201 may be configured to conform to a surface of human skin. In fact, the apparatus 200 may be substantially formed with material that can conform to the surfaceof human skin. In some such examples, at least an outer surface of the interface 201 may have material properties like those of putty or chewing gum.

[0047] In some examples, at least a portion of the interface 201 have an acoustic impedance that is configured to approximate an acoustic impedance of one or more, or a plurality of, receiver elements of the receiver system 202. According to some examples, a layer residing between the interface 201 and one or more receiver elements may have an acoustic impedance that is configured to approximate an acoustic impedance of the one or more receiver elements. Alternatively, or additionally, in some examples a layer residing between the interface 201 and one or more receiver elements may have an acoustic impedance that is in an acoustic impedance range between an acoustic impedance of the platen and an acoustic impedance of the one or more receiver elements.

[0048] Various examples of receiver systems 202 are disclosed herein, some of which may include ultrasonic receiver systems, optical receiver systems, or combinations thereof. In some implementations that include an ultrasonic receiver system, the ultrasonic receiver and an ultrasonic transmitter may be combined in an ultrasonic transceiver. In some examples, the receiver system 202 may include a piezoelectric receiver layer, such as a layer of PVDF polymer or a layer of PVDF-TrFE copolymer. In some implementations, a single piezoelectric layer may serve as an ultrasonic receiver. In some implementations, other piezoelectric materials may be used in the piezoelectric layer, such as aluminum nitride (AIN) or lead zirconate titanate (PZT). The receiver system 202 may, in some examples, 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, a piezoelectric receiver layer, PMUT elements in a single-layer array of PMUTs, or CMUT elements in a single-layer array of CMUTs, may be used as ultrasonic transmitters as well as ultrasonic receivers. According to some examples, the receiver system 202 may be, or may include, an ultrasonic receiver array. In some examples, the apparatus 200 may include one or more separate ultrasonic transmitter elements. In some such examples, the ultrasonic transmitter(s) may include an ultrasonic plane-wave generator.

[0049] The light source system 204 may, in some examples, include one or more light-emitting diodes. In some implementations, the light source system 204 may include one or more laser diodes. According to some implementations, the light source system204 may include one or more vertical-cavity surface-emitting lasers (VCSELs). In some implementations, the light source system 204 may include one or more edge-emitting lasers. In some implementations, the light source system may include one or more neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers.

[0050] According to some examples, the light source system 204 may include one or more light-directing elements configured to direct light from the light source system towards the target object along the first axis. In some examples, the one or more lightdirecting elements may include at least one diffraction grating. Alternatively, or additionally, the one or more light-directing elements may include at least one lens.

[0051] The light source system 204 may, in some examples, be configured to transmit light in one or more wavelength ranges. In some examples, the light source system 304 may configured for transmitting light in a wavelength range of 500 to 600 nanometers (nm). According to some examples, the light source system 304 may configured for transmitting light in a wavelength range of 800 to 950 nm. In view of factors such as skin reflectance, fluence, the 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, the wavelength ranges of 500 nm to 600 nm and of 800 to 950 nm may both be suitable for obtaining photoacoustic responses from relatively smaller, shallower blood vessels, such as blood vessels having diameters of approximately 0.5 mm and depths in the range of 0.5 mm to 1.5 mm, such as may be found in a finger. The wavelength range of 800 to 950 nm may, for example, be suitable for obtaining photoacoustic responses from relatively larger, deeper blood vessels, such as blood vessels having diameters of approximately 2.0 mm and depths in the range of 2 mm to 3 mm, such as may be found in an adult wrist.

[0052] The light source system 204 may include various types of drive circuitry, depending on the particular implementation. In some disclosed implementations, the light source system 204 may include at least one multi-junction laser diode, which may produce less noise than single-junction laser diodes. In some examples, the light source system 204 may include a drive circuit (also referred to herein as drive circuitry) configured to cause the light source system to emit pulses of light at pulse widths in a range from 3 nanoseconds to 1000 nanoseconds. According to some examples, the light source system 204 may include a drive circuit configured to cause the light source system to emit pulses of light at pulse repetition frequencies in a range from 1 kilohertz to 100 kilohertz.

[0053] In some implementations, at least portions of the apparatus 200 (for example, the receiver system 202, the light source system 204, or both) may include one or more sound-absorbing layers, acoustic isolation material, light- absorbing material, lightreflecting material, or combinations thereof. In some examples, acoustic isolation material may reside between the light source system 204 and at least a portion of the receiver system 202. In some examples, at least portions of the apparatus 200 (for example, the receiver system 202, the light source system 204, or both) may include one or more electromagnetically shielded transmission wires. In some such examples, the one or more electromagnetically shielded transmission wires may be configured to reduce electromagnetic interference from the light source system 204 that is received by the receiver system 202.

[0054] In some implementations, the light source system 204 may be configured for emitting various wavelengths of light, which may be selectable to trigger acoustic wave emissions primarily from a particular type of material. For example, because the hemoglobin in blood absorbs near-infrared light very strongly, in some implementations the light source system 204 may be configured for emitting one or more wavelengths of light in the near-infrared range, in order to trigger acoustic wave emissions from hemoglobin. However, in some examples, the control system 206 may control the wavelength(s) of light emitted by the light source system 204 to preferentially induce acoustic waves in blood vessels, other soft tissue, and / or bones. For example, an infrared (IR) light-emitting diode LED may be selected and a short pulse of IR light emitted to illuminate a portion of a target object and generate acoustic wave emissions that are then detected by the receiver system 202. In another example, an IR LED and a red LED or other color such as green, blue, white or ultraviolet (UV) may be selected and a short pulse of light emitted from each light source in turn with ultrasonic images obtained after light has been emitted from each light source. In other implementations, one or more light sources of different wavelengths may be fired in turn or simultaneously to generate acoustic emissions that may be detected by the ultrasonic receiver. Image data from the ultrasonic receiver that is obtained with light sources of different wavelengths and at different depths (e.g., varying RGDs) into the target object may be combined to determine the location and type of material in the target object. Image contrast may occur as materials in the body generally absorb light at different wavelengths differently. As materials in the body absorb light at a specific wavelength, they may heat differentiallyand generate acoustic wave emissions with sufficiently short pulses of light having sufficient intensities. Depth contrast may be obtained with light of different wavelengths and / or intensities at each selected wavelength. That is, successive images may be obtained at a fixed RGD (which may correspond with a fixed depth into the target object) with varying light intensities and wavelengths to detect materials and their locations within a target object. For example, hemoglobin, blood glucose or blood oxygen within a blood vessel inside a target object such as a finger may be detected photoacoustically.

[0055] According to some implementations, the light source system 204 may be configured for emitting a light pulse with a pulse width less than about 100 nanoseconds, hi some implementations, the light pulse may have a pulse width between about 10 nanoseconds and about 500 nanoseconds or more. According to some examples, the light source system may be configured for emitting a plurality of light pulses at a pulse repetition frequency between 10 Hz and 100 kHz. Alternatively, or additionally, in some implementations the light source system 204 may be configured for emitting a plurality of light pulses at a pulse repetition frequency between about 1 MHz and about 100 MHz. Alternatively, or additionally, in some implementations the light source system 204 may be configured for emitting 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 may correspond to an acoustic resonant frequency of the ultrasonic receiver and the substrate. For example, a set of four or more light pulses may be emitted from the light source system 204 at a frequency that corresponds with the resonant frequency of a resonant acoustic cavity in the sensor stack, allowing a build-up of the received ultrasonic waves and a higher resultant signal strength. In some implementations, filtered light or light sources with specific wavelengths for detecting selected materials may be included with the light source system 204. In some implementations, the light source system 204 may contain light sources such as red, green and blue LEDs of a display that may be augmented with light sources of other wavelengths (such as IR and / or UV) and with light sources of higher optical power. For example, high-power laser diodes or electronic flash units (e.g., an LED or xenon flash unit) with or without filters may be used for short-term illumination of the target object.

[0056] The control system 206 may include one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logicdevices, discrete gates or transistor logic, discrete hardware components, or combinations thereof. The control system 206 also may include (and / or be configured for communication with) one or more memory devices, such as one or more random access memory (RAM) devices, read-only memory (ROM) devices, etc. Accordingly, the apparatus 200 may have a memory system that includes one or more memory devices, though the memory system is not shown in Figure 2. The control system 206 may be configured for receiving and processing data from the receiver system 202, e.g., as described below. If the apparatus 200 includes an ultrasonic transmitter, the control system 206 may be configured for controlling the ultrasonic transmitter. In some implementations, functionality of the control system 206 may be partitioned between one or more controllers or processors, such as a dedicated sensor controller and an applications processor of a mobile device.

[0057] In some examples, the control system 206 may be communicatively coupled to the light source system 204 and configured to control the light source system 204 to emit light towards a target object on an outer surface of the interface 201. In some such examples, the control system 206 may be configured to receive signals from the ultrasonic receiver system 202 corresponding to the ultrasonic waves generated by the target object responsive to the light from the light source system 204. In some examples, the control system 206 may be configured to identify one or more blood vessel signals, such as arterial signals or vein signals, from the ultrasonic receiver system. In some such examples, the one or more arterial signals or vein signals may be, or may include, one or more blood vessel wall signals corresponding to ultrasonic waves generated by one or more arterial walls or vein walls of the target object. In some such examples, the one or more arterial signals or vein signals may be, or may 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 vein blood signals corresponding to ultrasonic waves generated by blood within a vein of the target object. In some examples, the control system 206 may be configured to determine or estimate one or more physiological parameters or cardiac features based, at least in part, on one or more arterial signals, on one or more vein signals, or on combinations thereof. According to some examples, the cardiac features may be, or may include, blood pressure.

[0058] In further examples, the control system 206 may be communicatively coupled to the receiver system 202. The control system 206 may be configured to select at leastone of a plurality of receiver elements of the receiver system 202. Such selected receiver element(s) may correspond to the best signals from multiple receiver elements. In some embodiments, the selection of the at least one receiver element may be based on information regarding detected acoustic signals (e.g., arterial signals or vein signals) from the plurality of receivers. For example, signal quality or signal strength (based, e.g., on signal-to-noise ratio (SNR)) of some signals may be relatively higher than some others or above a prescribed threshold or percentile, which may indicate the best signals. In some implementations, the control system 206 may also be configured to, based on the information regarding detected acoustic signals, determine or estimate at least one characteristic of the blood vessels such as pulse wave velocity (indicative of arterial stiffness), arterial dimensions, or both.

[0059] Some implementations of the apparatus 200 may include an interface system 208. In some examples, the interface system 208 may include a wireless interface system. In some implementations, the interface system 208 may include a user interface system, one or more network interfaces, one or more interfaces between the control system 206 and a memory system and / or one or more interfaces between the control system 206 and one or more external device interfaces (e.g., ports or applications processors), or combinations thereof. According to some examples in which the interface system 208 is present and includes a user interface system, the user interface system may include a microphone system, a loudspeaker system, a haptic feedback system, a voice command system, one or more displays, or combinations thereof. According to some examples, the interface system 208 may include a touch sensor system, a gesture sensor system, or a combination thereof. The touch sensor system (if present) may be, or may 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 combinations thereof.

[0060] In some examples, the interface system 208 may include a force sensor system. The force sensor system (if present) may be, or may include, a piezo-resistive sensor, a capacitive sensor, a thin film sensor (for example, a polymer-based thin film sensor), another type of suitable force sensor, or combinations thereof. If the force sensor system includes a piezo-resistive sensor, the piezo-resistive sensor may include silicon, metal, polysilicon, glass, or combinations thereof. An ultrasonic fingerprint sensor and a forcesensor system may, in some implementations, be mechanically coupled. In some such examples, the force sensor system may be integrated into circuitry of the ultrasonic fingerprint sensor. In some examples, the interface system 208 may include an optical sensor system, one or more cameras, or a combination thereof.

[0061] According to some examples, the apparatus 200 may include a noise reduction system 210. For example, the noise reduction system 210 may include one or more mirrors that are configured to reflect light from the light source system 204 away from the receiver system 202. In some implementations, the noise reduction system 210 may include one or more sound-absorbing layers, acoustic isolation material, light-absorbing material, light-reflecting material, or combinations thereof. In some examples, the noise reduction system 210 may include acoustic isolation material, which may reside between the light source system 204 and at least a portion of the receiver system 202, on at least a portion of the receiver system 202, or combinations thereof. In some examples, the noise reduction system 210 may include one or more electromagnetically shielded transmission wires. In some such examples, the one or more electromagnetically shielded transmission wires may be configured to reduce electromagnetic interference from circuitry of the light source system 204, receiver system circuitry, or combinations thereof, that is received by the receiver system 202.

[0062] The apparatus 200 may be used in a variety of different contexts, many examples of which are disclosed herein. For example, in some implementations a mobile device may include the apparatus 200. In some such examples, the mobile device may be a smart phone. In some implementations, a wearable device may include the apparatus 200. The wearable device may, for example, be a bracelet, an armband, a wristband, a watch, a ring, a headband or a patch.Example Configurations of PAPG Apparatus

[0063] Figure 4A shows an example configuration of an interface 401, a receiver element 402 of a receiver system, and an optical waveguide 404 of a photoacoustic apparatus, according to some disclosed implementations. The photoacoustic apparatus may be an example of the apparatus 200, and may be configured to perform PAPG-based methods as described herein. The interface 401 may be an example of the interface 201 and may be constructed to be flexible and compliant with a body part 415 or other appendage of a user. The receiver system may be an example of the receiver system 202.The receiver element 402 may be an example of the receiver element 302. The receiver element 402 may be embedded at least partially in the interface 401. The interface 401 may be made of one or more materials having an acoustic property, as described with respect to the interface 201 and the receiver system 202. The acoustic property may be acoustic impedance that approximates that of the interface 201 or a portion thereof, the receiver system 202 or a portion thereof, and / or at least a portion the body part 415.

[0064] Referring to the Figure 4 A example, it can be seen that the interface 401 is disposed adjacent the receiver element 402. In some implementations, the waveguide 404 may be coupled to a light source system (not shown) on one end, embedded at least partially in the interface 401, and terminate at the other end at an opening 406 of the interface 401. The waveguide 404 does not protrude into human skin, but rather, may abut or end at the skin of the body part 415. In some instances, the waveguide 404 and the skin may be separated by a thin polymer film, such as the protective layer discussed above. In some implementations, the waveguide 404 may possess a degree of slack within the interface 401 so as to allow for adjustability. Consider a use scenario in which the photoacoustic apparatus is implemented as a wearable device such as a flexible wristband or ring. Since at least a portion (e.g., the interface 201) of the wristband or ring may be made of relatively flexible material, at least the portion of the wristband or ring (or the whole wristband or ring) may stretch apart or open to some degree when wearing or attempting to wear the wristband or ring, and shrink to its original shape when manual pressure is removed. This may help to conformally apply pressure to tissue of the user. In some implementations, the waveguide 404 may extend adjacent to the receiver element 402 or be built into (e.g., extend via a hole or opening of) the receiver element 402.

[0065] According to various implementations, the opening 406 may be covered with a transparent material, covered with a material of the interface 401, or exposed to the exterior of the photoacoustic apparatus. In some implementations, the opening 406 may terminate at a protrusion from the interface 401. Physical protrusions may further aid in directing the light toward a target object, or offer tactile indications to the user as to where the light is being emitted or should be emitted. Myriad variations will be apparent to those with ordinary skill in the relevant arts. Optical waveguides embedded in acoustic matching layers can also bring the light very close to tissue. When the body part 415 of the user contacts the interface 401, light that is transmitted via the waveguide 404 from the light source system of the photoacoustic apparatus may be directed toward a targetportion of interest, such as one or more blood vessels in the body part 415. In some embodiments, the light source system and one or more light sources thereof may be disposed remotely from the receiver element 402 and / or the receiver system.

[0066] In some embodiments, the waveguide 404 may be an optical fiber. Advantageously, the flexible construction of the interface 201 and its layers can enable the waveguide 404 to be embedded in the interface 201 at any angle. Further, a small area of irradiation provided by the waveguide 404 helps reduce signal noise. In some scenarios, this reduction of signal noise includes reduction of background acoustic signals (e.g., those induced by light interacting with tissue and organs that are not of interest). As discussed throughout this disclosure, optically non-transparent materials with desirable acoustic transmission characteristics may be used as interface materials to accomplish this. Further, having the waveguide 404 at an angle can help improve detection of acoustic signals generated and received responsive to the light by allowing for a clean acoustic path to the receiver element 402. The receiver element 402 may be communicatively coupled to a control system of the photoacoustic apparatus, and may be configured to send the acoustic signals to the control system. In the Figure 4A example, the waveguide 404 is angled (at 0) with respect to a surface of the interface 201, or more specifically, angled with respect to a top layer (contactable with the body part 415) of the interface 201. Other angles and approaches may be possible, as indicated by the dotted lines representing possible waveguide configurations, including one that extends adjacent to (or through) the receiver element 402, one that is curved, and one that has a comer.

[0067] Figure 4B shows such an example configuration of the interface 401, the receiver element 402 of a receiver system, and the optical waveguide 404 of the photoacoustic apparatus, according to some disclosed implementations. Here, the configuration of the components of the photoacoustic apparatus are identical to that of Figure 4A, except the waveguide 404 is angled substantially parallel or lateral to the interface 201 or a surface of the interface 201.

[0068] Figure 4C shows another example configuration of the interface 401, the receiver element 402 of a receiver system, and the optical waveguide 404 of the photoacoustic apparatus, according to some disclosed implementations. Here, the receiver element 402 may be disposed adjacent to the interface 401 but in a different location compared to the examples of Figures 4 A and 4B. Since the waveguide 404 can be angled in any convenient fashion, the location of the receiver element 402 is also capable of beingin any convenient location. This can be useful for small form factors and chassis for semicompact and compact devices such as a wearable device.

[0069] Figure 4D shows an example configuration of the interface 401, the receiver element 402 of a receiver system, and multiple optical waveguides 404a, 404b of the photoacoustic apparatus, according to some disclosed implementations. Similar to the example of Figures 4B and 4C, this example shows substantially horizontal optical waveguides 404a, 404b coming from different directions toward an opening 406 of the interface 401, embedded in the interface 401 and directed to the body part 415 of a user.

[0070] Figure 4E shows an example configuration of the interface 401, the receiver element 402 of a receiver system, and multiple optical waveguides 404a, 404b of the photoacoustic apparatus, according to some disclosed implementations. Here, the waveguides 404a, 404b approach from the same side (left side of Figure 4E). It can also be seen that multiple receiver elements 402a, 402b are included in the apparatus. Each of these receiver elements 402a, 402b could detect acoustic signals generate as a result of light interacting with the body part 415. It will be appreciated that the receiver elements 402a, 402b may not necessarily correspond to specific ones of the optical waveguides 404a, 404b. That is, either receiver element 402a or 402b may be configured to detect acoustic signals generated as a result of light coming from either of optical waveguide 404a or 404b. However, the receiver elements 402a, 402b and the optical waveguides 404a, 404b may be positioned such that receipt of the acoustic signals is optimized for least noise (e.g., high SNR) or highest detectability (e.g., clear path or line of sight to the body part 415). For instance, it can be seen in Figure 4E that having the receiver elements 402a, 402b on one side (right side) can create space for optical waveguides 404a, 404b to come in from the other side (left side).

[0071] Figure 4F shows an example configuration of the interface 401, multiple receiver elements 402a, 402b of a receiver system, and multiple optical waveguides 404a, 404b of the photoacoustic apparatus, according to some disclosed implementations. As shown, a body part of the user (e.g., finger 415) may be pressed against the interface 401. A non-cross-sectional view is shown for variety in illustration and perspective, and to show that optical waveguides and receiver elements may be oriented in different ways, e.g., orthogonal to the orientation of optical waveguides and positions of receiver elements shown thus far (e.g., in Figures 4 A - 4E). Moreover, optical waveguides 404a, 404b need not be straight and linear such as those shown in Figures 4A - 4E. Opticalfibers may be embedded and oriented in a way similar to electrical cables in relatively loose configurations, e.g., to accommodate the positioning of openings and components of the photoacoustic apparatus such as receiver elements 402a, 402b. Finger 415 may have a target object such as a blood vessel 416. Light emitted from openings 406 of the optical waveguides 404a, 404b may interact with the blood vessel 416 and cause acoustic signals to be generated by the target object and sent toward the receiver elements 402a, 402b of the receiver system.

[0072] Although two receiver elements 402a, 402b and two optical waveguides 404a, 404b are shown, in no way is it intended to imply that each optical waveguide has a corresponding receiver element. For example, one receiver element, three or more receiver elements, one waveguide, or three or more waveguides may be present for the photoacoustic apparatus of Figure 4F to emit optical signals and receive acoustic signals. However, with more receiver elements or more waveguides, selection of signals may become more optimal (e.g., less noisy), as will now be explained.

[0073] It can thus be seen that many different light launch configurations are possible for different purposes. For example, vertical launches, angled launches, and / or horizontal launches would be possible as illustrated in Figures 4A - 4F. Multi-point information with respect to at least one characteristic of the body part 415 can be obtained from multiple waveguides, multiple receiver elements, and / or multiple light sources. Such characteristic may be blood pressure, heart rate, pulse wave velocity (PWV, a measure of arterial stiffness), arterial dimensions, or another cardiac feature. Moreover, as alluded to above, using PAPG methods to obtain acoustic signals can enable enhanced depth discrimination over PPG methods. At least one characteristic associated with one or more blood vessels of the body part 415 such as blood pressure, PWV, heart rate, etc. can thereby be characterized and monitored. According to some approaches, the angle of the waveguide 404, or a given waveguide of multiple waveguides 404a, 404b, can be selected based on the noise or signal quality (e.g., SNR) and / or detectability or line of sight to the received acoustic signal.

[0074] Further, having multiple waveguides and / or angles allows optimization of signals from a single wavelength. That is, multiple waveguides can transmit light having the same wavelength, at different times (e.g., time-shifted pulses) in some cases to distinguish the light signals, and the waveguide(s) that are able to provide light that result in the least noise or highest detectability may be selected or given a higher weight forcontinued or future light transmission. See also discussion relating to delay-and-sum beamforming below. In some cases, having multiple waveguides and / or angles allows easier implementation of multiple wavelengths. That is, light signals having different wavelengths may be transmitted via different waveguides. In some cases, multiple channels for different optical waveguides and fibers can be designed, where these waveguides may carry light from different sources (which may generate or provide light signals having single or multiple wavelengths) and launch this light at different points in the target object.

[0075] Figure 5A shows an example of an ultrasonic receiver element array of a receiver system, which can be used with implementations disclosed herein. In this example, the array of ultrasonic receiver elements 502 is a two-dimensional (areal) array of ultrasonic receiver elements. According to this example, the array of ultrasonic receiver elements 502 is arranged in a square having six (6) active ultrasonic receiver elements 515 on each side and a total of 36 active ultrasonic receiver elements 515. As with other disclosed examples, the type, number, size and arrangement of elements shown in Figure 5A and described herein are merely examples. For example, alternative examples of two- dimensional arrays of ultrasonic receiver elements may be arranged in a different shape, such as a non-square rectangular shape, a hexagonal shape, etc. Some alternative examples of two-dimensional arrays of ultrasonic receiver elements may include a different number of active ultrasonic receiver elements 515, such as 16, 20, 25, 30, 32, 36, 40, 48, etc.

[0076] Figure 5B shows another example of an ultrasonic receiver element array of a receiver system, which can be used with implementations disclosed herein. In this example, the array of ultrasonic receiver elements 504 is a linear array of ultrasonic receiver elements. According to this example, the array of ultrasonic receiver elements 502 is arranged in a line having six (6) active ultrasonic receiver elements 515.

[0077] In some implementations, an ultrasonic receiver element array may be an array of arrays. For example, the array may be a linear or two-dimensional array of two- dimensional arrays of ultrasonic receiver elements 502. As another example, the array may be a linear or two-dimensional array of linear arrays of ultrasonic receiver elements 504.

[0078] Having multiple receiver elements is advantageous for the disclosed implementations as it does not require precise positioning of a body part or target object of interest relative to receiver elements. A user could, for instance, put on a wearable photoacoustic device in any orientation or location along a wrist or finger and still be able to monitor physiological parameters because the ubiquity of receiver elements (and / or other components such as waveguides) allows PAPG methods described herein to be performed with the wrist or finger, and in some implementations, result in selection of an optimal or best receiver element or waveguide for determining the physiological parameters as described elsewhere herein.

[0079] In some cases, it is also possible to implement a delay-and-sum beamforming process with multiple receiver elements. More specifically, a delay could be applied to an ultrasonic receiver signal by performing a correlation operation on input ultrasonic receiver signals. For example, a control system may perform a correlation operation on first and second ultrasonic different receiver signals, and may determine that by applying a first time shift to the first ultrasonic receiver signal, the first ultrasonic receiver signal would be strongly correlated with a third ultrasonic receiver signal. Similarly, the control system may perform a correlation operation on second and third ultrasonic receiver signals, and may determine that by applying a second time shift to the second ultrasonic receiver signal, the second ultrasonic receiver signal would be strongly correlated with the third ultrasonic receiver signal. According to this example, the control system may be configured to sum the first time-shifted ultrasonic receiver signal, the second time-shifted ultrasonic receiver signal, and the third ultrasonic receiver signal, producing a summed signal. The amplitude of the summed signal may be greater than the amplitude of any one of the first, second, or third ultrasonic receiver signal. In some instances, the signal-to- noise ratio (SNR) of the summed signal may be greater than the SNR of any of the first, second, or third ultrasonic receiver signal. Hence, cleaner and less noisy signals may be obtained by using multiple receiver elements.

[0080] Figure 6 shows an example configuration of a photoacoustic apparatus 600, according to some disclosed implementations. The photoacoustic apparatus 600 may be an example of apparatus 200. As noted elsewhere herein, the photoacoustic apparatus 600 may be implemented and operated as a wearable device, such as a ring, watch, wristband, waistband, etc. For example, the photoacoustic apparatus 600 may be a watch that can fit around a wrist of a user, or it may be a ring that can fit around a finger of the user. Thebody part of the user may be associated with a target object or tissue of interest, e.g., where blood vessels are located. The photoacoustic apparatus 600 may thus perform PAPG-based techniques as discussed above to monitor physiological parameters such as blood pressure, heart rate, PWV, arterial dimensions, or other cardiac features.

[0081] In some embodiments, the photoacoustic apparatus 600 may include a user interface 602, a wearable structure 604, a light source system (having at least one light source 606), a receiver system (having one or more receiver elements such as receiver elements 609a - 609n), an interface 610, and a waveguide system 612. In some implementations, the user interface 602 may include a face (e.g., that of a watch), a display screen, a touch screen, and / or a physical control (e.g., dial, switch). In some implementations, the user interface 602 may be part of a housing 601, which may house other components, e.g., memory, storage, control system 206, and / or interface system 208. In some implementations, the wearable structure 604 may include straps or a pliable band so as to form a ring- like shape (e.g., circular, elliptical, one or more straps that overlap each other). The interface 610 is incorporated into the wearable structure 604 and may have contact portions that can make contact with a body part of a user. In some implementations, contact portions may be facing inward toward an open space 618 surrounded by the wearable structure 604. However, in certain implementations, contact portions may also face outwardly, in which case interface 610 may also include an outer surface of the wearable structure 604. The interface 610 may be an example of the interface 201. Hence, in some implementations, the material of at least a portion of the interface 610 may be flexible, pliable, or otherwise compliant to the shape of the body part. For example, at least the inner surface of the wearable structure 604 may be made of flexible material to accommodate the user’s body part in a comfortable manner. The inner surface may include the first layer 301 a, for instance, which as discussed above may be made of a relatively soft material, e.g., a polymer such as polyethylene. In another example, the entirety of the wearable structure 604 may be made of flexible material. In some implementations, the receiver system may include one or more receiver elements 609a - 609n. At least some of one or more light sources (one of which is shown as light source 606) may be located near a portion (e.g., proximate to area 614) of the photoacoustic apparatus 600 which is substantially opposite to one or more receiver elements and proximate to where the housing 601 or the user interface 602 is located. In some contexts, receiver elements 609a - 609c may be considered to be substantiallyopposite to area 614. In some contexts, receiver element 609d may be considered to be substantially opposite to area 614. In some contexts, receiver element 609n may be considered to be substantially opposite to area 614. Advantageously, the light source system and the receiver system being at least partly separated in location and / or located on substantially opposite areas of the photoacoustic apparatus 600 rather than proximate to each other allows flexibility in placement of such components, and allows waveguides to emit a small area of irradiation to reduce background noise and provide a pointed source of light toward targets of interest in the user. There is another potential advantage of having the light source system (e.g., circuitry associated with the light source 606) on the opposite side of the receiver system (e.g., one or more of receiver elements 609a - 609n). More specifically, the light source system circuitry can be a significant source of noise, so having human tissue (a user's arm, finger, etc.) in between the light source system and the receiver system in the open space 618 (where the user’s body part can be inserted), including some conductive material, can significantly cut down the received noise. In some cases, one or more receiver elements 609a - 609n may be embedded in and located along the wearable structure 604 (e.g., areas 616, 617). In this context, a component being located “along the wearable structure” may mean being in any radial location of the circumference of the wearable structure 604. In some implementations, the light source system may include one or more light sources 606. At least some of the one or more light sources may be located proximate or within the housing 601, e.g., proximate to area 614 and / or embedded in and located along the wearable structure 604 (e.g., areas 616, 617). In some cases, one or more light sources may be located proximate to one or more of the receiver elements 609a - 609n; in such cases, intensity of the light emission may be stronger than if light were transmitted via a longer optical waveguide from, e.g., the housing 601. Similar to the receiver element arrays of Figures 5A and 5B, the one or more light sources may be arranged in a two-dimensional or linear array, or an array of arrays. In some implementations, the waveguide system 612 may include one or more optical waveguides, such as optical fibers, as well as one or more waveguide terminations that end at the interface 610 and are configured to be close to a user’s tissue and to deliver light to the tissue. One waveguide is shown for simplicity of illustration. However, it can be seen in this example that individual waveguides can branch out toward different portions of the wearable structure 604. The one or more optical waveguides may be coupled to the one or more light sources, be embedded in and extend along thewearable structure 604, and terminate at openings at the interface 610. Seven waveguide terminations are illustrated, three examples of which are labeled 620a - 620c, five example of which are located proximate receiver elements 609a - 609n (one of which is waveguide termination 620b). However, there may be more or fewer waveguide terminations in different configurations. There does not need to be a one-to-one relationship between the number of waveguide terminations and the receiver elements. The waveguide terminations also do not all need be in the same location relative to the receiver elements and the receiver elements. The openings of the waveguide terminations may face inwardly toward the open space 618 surrounded by the wearable structure 604. Such openings may be examples of the opening 406 described above. Light 622 transmitted from the one or more light sources may be emitted from an opening and interact with a target object (e.g., blood vessel), generating acoustic signals 624 from the target object. Acoustic signals may be received by one or more receiver elements 609a - 609n. According to the example configuration of a photoacoustic apparatus 600, light may be launched substantially vertically relative to a surface the interface 610 from a single waveguide or optical fiber, depending on the configuration and direction of the waveguide, and acoustic signals may be received at a single receiver element (similar to one or more configurations shown in Figure 4A). In some scenarios, this process may occur depending on waveguide angles and / or receiver element position(s) according to, e.g., the example configurations of Figures 4A - 4F. Note that the quantities of light sources, receiver elements, and waveguides may not necessarily correspond to one another. For instance, there may be fewer waveguides than light sources and vice versa. There may be fewer light sources than receiver elements and vice versa. There may be fewer waveguides than receiver elements and vice versa.

[0082] In some embodiments, a control system may be another component of the photoacoustic apparatus 600. For example, the housing 601 may house the control system. In other embodiments, the control system may be separately disposed from the photoacoustic apparatus 600. The control system here may be an example of control system 206 and may be configured to perform various operations and applications relating to the operation of the photoacoustic apparatus 600. In some implementations, the control system may be configured to select the best location for monitoring a physiological parameter, e.g., blood pressure, heart rate. To accomplish this, the control system may determine the noise and / or detectability associated with various acoustic signals that aregenerated as a result of light emitted toward the target object (e.g., blood vessel) via the one or more waveguides of the waveguide system 612, and detected by one or more receiver elements 609a - 609n of the receiver system. Noise may be determined based on signal strength and / or signal quality (e.g., SNR) of the acoustic signals. Detectability may relate to whether there is a clear path or line of sight to the target object, which may also be a function of noise.

[0083] In some embodiments, the photoacoustic apparatus 600 may include multiple receiver elements 609a - 609n. Five (5) receiver elements 609a - 609n are shown to be placed in example locations in Figure 6. Some may be more clustered than others, such as those in area 616 (receiver elements 609a - 609c). These receiver elements may be embedded in and arranged along the wearable structure 604 (e.g., in areas 616, 617) in an array such as that shown in Figures 5A and 5B, in separate individual locations along the wearable structure 604, or as arrays each in a respective location along the wearable structure 604. The arrangement of the receiver elements may be such that the receiver elements are close to potential target objects and likely areas of interest of the user’s body part (e.g., bottom of wrist, finger). As explained with respect to Figures 4A - 4F, waveguides may launch light from the light source system (e.g., from at least one light source 606) toward the openings at any angle relative to a surface of the interface 610.

[0084] Based on the structure of the example photoacoustic apparatus 600 described above, the embodiments and implementations of apparatus described herein may be capable of securing the target body part or tissue of interest and obtaining the best acoustic signal despite movement of the user’s body part or appendage. In some other example implementations, the photoacoustic apparatus 600 may be or include a cuff that is constructed to apply pressure uniformly around an appendage, such as the user’s arm. Signal data quality can thereby be improved.Example Method

[0085] Figure 7 is a flow diagram of a method 700 for monitoring a physiological parameter of a user using a photoacoustic device, according to some disclosed implementations. Structure for performing the functionality illustrated in one or more of the blocks shown in Figure 7 may be performed by hardware and / or software components of a computerized apparatus or system (which may be implemented as a wearable device in some embodiments). Components of such apparatus or system may include, forexample, one or more sensors, one or more light sources, one or more receiver elements, one or more optical waveguides, one or more control systems (including one or more processors), one or more memory, and / or one or more computer-readable apparatus including a storage medium storing computer-readable and / or computer-executable instructions that are configured to, when executed by the control system, cause the control system, one or more processors, or the apparatus to perform operations represented by blocks below. Example components of the apparatus are illustrated in Figure 2, which are described in more detail above.

[0086] The blocks of Figure 7 may, for example, be performed by the apparatus 200 of Figure 2 or by a similar apparatus, or a component thereof (e.g., a control system). As with other methods disclosed herein, the method outlined in Figure 7 may include more or fewer blocks than indicated. Moreover, the blocks of methods disclosed herein are not necessarily performed in the order indicated. In some instances, one or more of the blocks shown in Figure 7 may be performed concurrently.

[0087] At block 710, the method 700 may include causing transmission of optical signals via one or more waveguides from a light source system of the photoacoustic device toward a portion of a user proximate a receiver system of the photoacoustic device, the receiver system disposed remotely from the light source system without direct contact therewith, the receiver system configured to detect acoustic signals generated based on the optical signals. The receiver system may include one or more receiver elements or arrays thereof. The light source system may include one or more light sources or arrays thereof.

[0088] In some embodiments, the photoacoustic device may include: the light source system including one or more light sources; the receiver system including one or more receivers configured to detect acoustic signals generated based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic the one or more receivers; a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the user; or a combination thereof.

[0089] In some embodiments, the apparatus may further include a wearable structure, the wearable structure securable to the user and comprising the light source system, the receiver system, the interface layer, and the waveguide system.

[0090] In some embodiments, the apparatus may be a wearable user device. The light source system may be disposed at a first portion of the user device, and at least one of the one or more receivers may be disposed at a second portion of the user device; the first portion and the second portion may be positioned such that at least the portion of the user resides between the first portion and the second portion when the user wears the user device; and at least one of the one or more waveguides may be configured to provide light from the first portion of the user device toward the second portion. Referring to Figure 6 as an example, the first portion of the user device may correspond to area 614, and the second portion of the user device may correspond to area 616.

[0091] In some embodiments, the first acoustic characteristic may include a first acoustic impedance associated with skin of the user, and the second acoustic characteristic may include a second acoustic impedance associated with the one or more receivers. In some implementations, the first acoustic impedance may be between about 1.5 and about 2.0, and the second acoustic impedance may correspond to a material of the one or more receivers. In some approaches, the first and second acoustic impedances may be selected based on Eqn. 1.

[0092] In some embodiments, the interface layer may include a matching layer having a first surface and a second surface, the first surface contactable by and configured to interface with the skin of the user, the second surface adjacent to and configured to interface with the receiver system. In some implementations, the matching layer may at least partly include a polyethylene (or polyethylene variant, such as low-density polyethylene or high-density polyethylene in some cases). Other types of materials may be used as desired, as discussed above. In some implementations, the matching layer may have progressively varying acoustic impedances between the first acoustic impedance associated with the skin of the user and the second acoustic impedance associated with the one or more receivers. In some implementations, the first surface may have the first acoustic impedance, and the second surface may have the second acoustic impedance.

[0093] In some embodiments, the apparatus may further include a control system, wherein the control system may be configured to determine the physiological parameterof the user based on the detected acoustic signal. In some implementations, the physiological parameter may include a blood pressure of the user. In other implementations, the physiological parameter may include a heart rate, a pulse wave velocity (PWV), an arterial dimension, or another cardiac feature.

[0094] In some embodiments, the receiver system may include a plurality of receivers each configured to send information regarding the detected acoustic signals to the control system; and the control system may be configured to select at least one of the plurality of receivers based on respective information received regarding the detected acoustic signals from the plurality of receivers. In some implementations, the control system may be further configured to, using the selected at least one of the plurality of receivers, estimate at least one characteristic of one or more blood vessels of at least the portion of the user. The at least one characteristic of the one or more blood vessels may include PWV (which may indicate arterial stiffness or relate to blood pressure) and / or artery dimensions.

[0095] In some embodiments, at least one of the one or more waveguides may be angled with respect to a surface of the interface layer (as illustrated in, e.g., Figures 4 A and 4E). In some embodiments, at least one of the one or more waveguides may be angled substantially parallel to a surface of the interface layer (as illustrated in, e.g., Figures 4B - 4E). In some embodiments, at least a portion of at least one of the one or more waveguides may be embedded in the interface layer in a free-form manner (as illustrated in, e.g., Figure 4F).

[0096] Means for performing functionality at block 710 may include an interface 201 , a receiver system 202 and a light source system 204, waveguide system 205, a control system 206, and / or other components of an apparatus as shown in Figure 2.

[0097] At block 720, the method 700 may include receiving, from the receiver system, information regarding the acoustic signals detected by the receiver system. Information regarding acoustic signals may include waveforms, processed information (e.g., intervals in waveforms), wave parameters (e.g., wavelength, amplitude) associated with acoustic signals from each receiver element of the receiver system.

[0098] Means for performing functionality at block 720 may include a receiver system 202 and / or other components of an apparatus as shown in Figure 2.

[0099] At block 730, the method 700 may include determining the physiological parameter of the user based on the information regarding the acoustic signals.

[0100] Means for performing functionality at block 730 may include a control system 206 and / or other components of an apparatus as shown in Figure 2.

[0101] As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an 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.

[0102] The various illustrative logics, logical blocks, modules, circuits and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. The interchangeability of hardware and software has been described generally, in terms of functionality, and illustrated in the various illustrative components, blocks, modules, circuits and processes described above. Whether such functionality is implemented in hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0103] The hardware and data processing apparatus used to implement the various illustrative logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single- 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 may be a microprocessor, or, any conventional processor, controller, microcontroller, or state machine. A processor also may be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, particular processes and methods may be performed by circuitry that is specific to a given function.

[0104] In one or more aspects, the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware, including the structures disclosed in this specification and their structural equivalents thereof, or in any combination thereof. Implementations of the subject matter described in this specification also may be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computer storage media for execution by, or to control the operation of, data processing apparatus.

[0105] If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium, such as a non- transitory medium. The processes of a method or algorithm disclosed herein may be implemented in a processor-executable software module which may reside on a computer-readable medium. Computer-readable media include both computer storage media and communication media including any medium that may be enabled to transfer a computer program from one place to another. Storage media may be any available media that may 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 may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Also, any connection may be properly termed a computer-readable medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks usually reproduce data magnetically, while discs 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 set of codes and instructions on a machine readable medium and computer-readable medium, which may be incorporated into a computer program product.

[0106] Various modifications to the implementations described in this disclosure may be readily apparent to those having ordinary skill in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the claims, the principles and the novel features disclosed herein. The word “exemplary” is used exclusively herein, if at all, to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

[0107] Certain features that are described in this specification in the context of separate implementations also may be implemented in combination in a singleimplementation. Conversely, various features that are described in the context of a single implementation also may be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0108] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0109] It will be understood that unless features in any of the particular described implementations are expressly identified as incompatible with one another or the surrounding context implies that they are mutually exclusive and not readily combinable in a complementary and / or supportive sense, the totality of this disclosure contemplates and envisions that specific features of those complementary implementations may be selectively combined to provide one or more comprehensive, but slightly different, technical solutions. It will therefore be further appreciated that the above description has been given by way of example only and that modifications in detail may be made within the scope of this disclosure.

[0110] Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the following claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scope consistent with this disclosure, the principles and the novel features disclosed herein.

[0111] Additionally, certain features that are described in this specification in the context of separate implementations also can be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation also can be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0112] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the drawings may schematically depict one more example processes in the form of a flow diagram. However, other operations that are not depicted can be incorporated in the example processes that are schematically illustrated. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. Moreover, various ones of the described and illustrated operations can itself include and collectively refer to a number of sub-operations. For example, each of the operations described above can itself involve the execution of a process or algorithm. Furthermore, various ones of the described and illustrated operations can be combined or performed in parallel in some implementations. Similarly, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations. As such, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

[0113] Implementation examples are described in the following numbered clauses:

[0114] Clause 1: A user device comprising: a light source system including one or more light sources; a receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or morelight sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least the portion of the user.

[0115] Clause 2: The user device of clause 1, further comprising a wearable structure, the wearable structure securable to the user and comprising the light source system, the receiver system, the interface layer, and the waveguide system.

[0116] Clause 3: The user device of any one of clauses 1-2 wherein the first acoustic characteristic comprises a first acoustic impedance associated with skin of the user, and the second acoustic characteristic comprises a second acoustic impedance associated with the one or more receivers.

[0117] Clause 4: The user device of any one of clauses 1-3 wherein the first acoustic impedance is between about 1.5 and about 2.0, and the second acoustic impedance corresponds to a material of the one or more receivers.

[0118] Clause 5: The user device of any one of clauses 1-4 wherein the interface layer comprises a matching layer having a first surface and a second surface, the first surface contactable by and configured to interface with the skin of the user, the second surface adjacent to and configured to interface with the receiver system.

[0119] Clause 6: The user device of any one of clauses 1-5 wherein the matching layer at least partly comprises a polyethylene.

[0120] Clause 7: The user device of any one of clauses 1-6 wherein the matching layer comprises progressively varying acoustic impedances between the first acoustic impedance associated with the skin of the user and the second acoustic impedance associated with the one or more receivers.

[0121] Clause 8: The user device of any one of clauses 1-7 wherein the first surface comprises the first acoustic impedance, and the second surface comprises the second acoustic impedance.

[0122] Clause 9: The user device of any one of clauses 1-8 further comprising a control system, wherein the control system is configured to determine a physiological parameter of the user based on the detected acoustic signals.

[0123] Clause 10: The user device of any one of clauses 1-9 wherein the physiological parameter comprises a blood pressure of the user.

[0124] Clause 11: The user device of any one of clauses 1-10 further comprising a control system, wherein: the receiver system comprises a plurality of receivers each configured to send information regarding the detected acoustic signals to the control system; and the control system is configured to select at least one of the plurality of receivers based on respective information received regarding the detected acoustic signals from the plurality of receivers.

[0125] Clause 12: The user device of any one of clauses 1-11 wherein the control system is further configured to, using the selected at least one of the plurality of receivers, estimate at least one characteristic of the target object, the target object comprising one or more blood vessels of at least the portion of the user.

[0126] Clause 13: The user device of any one of clauses 1-12 wherein at least one of the one or more waveguides is angled with respect to a surface of the interface layer.

[0127] Clause 14: The user device of any one of clauses 1-13 wherein at least one of the one or more waveguides is angled substantially parallel to a surface of the interface layer.

[0128] Clause 15: The user device of any one of clauses 1-14 wherein the light source system is disposed at a first portion of the user device, and at least one of the one or more receivers is disposed at a second portion of the user device; the first portion and the second portion are positioned such that at least the portion of the user resides between the first portion and the second portion when the user wears the user device; and at least one of the one or more waveguides is configured to provide light from the first portion of the user device toward the second portion.

[0129] Clause 16: A method for monitoring a physiological parameter of a user using a photoacoustic device, the method comprising: causing transmission of optical signals via one or more waveguides from a light source system of the photoacoustic device toward a portion of a user proximate a receiver system of the photoacoustic device, thereceiver system disposed remotely from the light source system without direct contact therewith, the photoacoustic device comprising: the light source system including one or more light sources; the receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least the portion of the user; receiving, from the receiver system, information regarding the acoustic signals detected by the one or more receivers; and determining the physiological parameter of the user based on the information regarding the acoustic signals.

[0130] Clause 17: The method of clause 16, wherein the photoacoustic device further comprises a wearable structure, the wearable structure securable to the user and comprising the light source system, the receiver system, the interface layer, and the waveguide system.

[0131] Clause 18: The method of any one of clauses 16-17 wherein the first acoustic characteristic comprises a first acoustic impedance associated with skin of the user, and the second acoustic characteristic comprises a second acoustic impedance associated with the one or more receivers.

[0132] Clause 19: The method of any one of clauses 16-18 wherein the first acoustic impedance is between about 1.5 and about 2.0, and the second acoustic impedance corresponds to a material of the one or more receivers.

[0133] Clause 20: The method of any one of clauses 16- 19 wherein the interface layer comprises a matching layer having a first surface and a second surface, the first surface contactable by and configured to interface with the skin of the user, the second surface adjacent to and configured to interface with the receiver system.

[0134] Clause 21: The method of any one of clauses 16-20 wherein the matching layer at least partly comprises a polyethylene.

[0135] Clause 22: The method of any one of clauses 16-21 wherein the matching layer comprises progressively varying acoustic impedances between the first acoustic impedance associated with the skin of the user and the second acoustic impedance associated with the one or more receivers.

[0136] Clause 23: The method of any one of clauses 16-22 wherein the photoacoustic device further comprises a control system, wherein the control system is configured to determine a physiological parameter of the user based on the detected acoustic signals.

[0137] Clause 24: The method of any one of clauses 16-23 wherein the physiological parameter comprises a blood pressure of the user.

[0138] Clause 25: The method of any one of clauses 16-24 wherein the photoacoustic device further comprises a control system, wherein: the receiver system comprises a plurality of receivers each configured to send information regarding the detected acoustic signals to the control system; and the control system is configured to: select at least one of the plurality of receivers based on respective information received regarding the detected acoustic signals from the plurality of receivers; and using the selected at least one of the plurality of receivers, estimate at least one characteristic of the target object, the target object comprising one or more blood vessels of at least the portion of the user.

[0139] Clause 26: The method of any one of clauses 16-25 wherein at least one of the one or more waveguides is angled with respect to a surface of the interface layer, or is angled substantially parallel to a surface of the interface layer.

[0140] Clause 27: An apparatus comprising: light source means for transmitting light, the light source means comprising one or more light sources; receiver means for detecting acoustic signals generated by a target object based on optical signals from the light source means, the receiver means comprising one or more receiver elements; interface means contactable by a user, the interface means comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the receiver means, the interface means comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the receiver means; and waveguide means for transmitting the optical signals from the one or more light sources to the at least the portion of the user, the waveguide means comprising one or more waveguides at least partially embedded in the interface means.

[0141] Clause 28: The apparatus of clause 27, wherein: the interface means comprise a matching layer having a first surface and a second surface, the first surface contactable by and configured to interface with skin of the user, the second surface adjacent to and configured to interface with the receiver means; and the first acoustic characteristic comprises a first acoustic impedance associated with the skin of the user, and the second acoustic characteristic comprises a second acoustic impedance associated with the one or more receivers, the matching layer having graded acoustic impedances that progressively change between the first acoustic impedance associated with the skin of the user and the second acoustic impedance associated with the one or more receivers.

[0142] Clause 29: The apparatus of any one of clauses 27-28 wherein at least one of the one or more waveguides is angled with respect to a surface of the interface means, or is angled substantially parallel to a surface of the interface means.

[0143] Clause 30: A non- transitory computer-readable apparatus comprising a storage medium, the storage medium comprising a plurality of instructions configured to, when executed by a control system, cause a photoacoustic device to: cause transmission of optical signals via one or more waveguides from a light source system of the photoacoustic device toward a portion of a user proximate a receiver system of the photoacoustic device, the receiver system disposed remotely from the light source system without direct contact therewith, the photoacoustic device comprising: the light source system including one or more light sources; the receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least the portion of the user; receive, from the receiver system, information regarding the acoustic signals detected by the one or more receivers; and determine a physiological parameter of the user based on the information regarding the acoustic signals.

Claims

CLAIMSWhat is claimed:

1. A user device comprising: a light source system including one or more light sources; a receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least the portion of the user.

2. The user device of claim 1, further comprising a wearable structure, the wearable structure securable to the user and comprising the light source system, the receiver system, the interface layer, and the waveguide system.

3. The user device of claim 1, wherein the first acoustic characteristic comprises a first acoustic impedance associated with skin of the user, and the second acoustic characteristic comprises a second acoustic impedance associated with the one or more receivers.

4. The user device of claim 3, wherein the first acoustic impedance is between about 1.5 and about 2.0, and the second acoustic impedance corresponds to a material of the one or more receivers.

5. The user device of claim 3, wherein the interface layer comprises a matching layer having a first surface and a second surface, the first surface contactableby and configured to interface with the skin of the user, the second surface adjacent to and configured to interface with the receiver system.

6. The user device of claim 5, wherein the matching layer at least partly comprises a polyethylene.

7. The user device of claim 5, wherein the matching layer comprises progressively varying acoustic impedances between the first acoustic impedance associated with the skin of the user and the second acoustic impedance associated with the one or more receivers.

8. The user device of claim 5, wherein: the first surface comprises the first acoustic impedance, and the second surface comprises the second acoustic impedance.

9. The user device of claim 1 , further comprising a control system, wherein the control system is configured to determine a physiological parameter of the user based on the detected acoustic signals.

10. The user device of claim 9, wherein the physiological parameter comprises a blood pressure of the user.

11. The user device of claim 1 , further comprising a control system, wherein: the receiver system comprises a plurality of receivers each configured to send information regarding the detected acoustic signals to the control system; and the control system is configured to select at least one of the plurality of receivers based on respective information received regarding the detected acoustic signals from the plurality of receivers.

12. The user device of claim 11, wherein the control system is further configured to, using the selected at least one of the plurality of receivers, estimate at least one characteristic of the target object, the target object comprising one or more blood vessels of at least the portion of the user.

13. The user device of claim 1, wherein at least one of the one or more waveguides is angled with respect to a surface of the interface layer.

14. The user device of claim 1, wherein at least one of the one or more waveguides is angled substantially parallel to a surface of the interface layer.

15. The user device of claim 1, wherein: the light source system is disposed at a first portion of the user device, and at least one of the one or more receivers is disposed at a second portion of the user device; the first portion and the second portion are positioned such that at least the portion of the user resides between the first portion and the second portion when the user wears the user device; and at least one of the one or more waveguides is configured to provide light from the first portion of the user device toward the second portion.

16. A method for monitoring a physiological parameter of a user using a photoacoustic device, the method comprising: causing transmission of optical signals via one or more waveguides from a light source system of the photoacoustic device toward a portion of a user proximate a receiver system of the photoacoustic device, the receiver system disposed remotely from the light source system without direct contact therewith, the photoacoustic device comprising: the light source system including one or more light sources; the receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the one or more receivers; anda waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least the portion of the user; receiving, from the receiver system, information regarding the acoustic signals detected by the one or more receivers; and determining the physiological parameter of the user based on the information regarding the acoustic signals.

17. The method of claim 16, wherein the photoacoustic device further comprises a wearable structure, the wearable structure securable to the user and comprising the light source system, the receiver system, the interface layer, and the waveguide system.

18. The method of claim 16, wherein the first acoustic characteristic comprises a first acoustic impedance associated with skin of the user, and the second acoustic characteristic comprises a second acoustic impedance associated with the one or more receivers.

19. The method of claim 18, wherein the first acoustic impedance is between about 1.5 and about 2.0, and the second acoustic impedance corresponds to a material of the one or more receivers.

20. The method of claim 18, wherein the interface layer comprises a matching layer having a first surface and a second surface, the first surface contactable by and configured to interface with the skin of the user, the second surface adjacent to and configured to interface with the receiver system.

21. The method of claim 20, wherein the matching layer at least partly comprises a polyethylene.

22. The method of claim 20, wherein the matching layer comprises progressively varying acoustic impedances between the first acoustic impedanceassociated with the skin of the user and the second acoustic impedance associated with the one or more receivers.

23. The method of claim 16, wherein the photoacoustic device further comprises a control system, wherein the control system is configured to determine a physiological parameter of the user based on the detected acoustic signals.

24. The method of claim 23, wherein the physiological parameter comprises a blood pressure of the user.

25. The method of claim 16, wherein the photoacoustic device further comprises a control system, wherein: the receiver system comprises a plurality of receivers each configured to send information regarding the detected acoustic signals to the control system; and the control system is configured to: select at least one of the plurality of receivers based on respective information received regarding the detected acoustic signals from the plurality of receivers; and using the selected at least one of the plurality of receivers, estimate at least one characteristic of the target object, the target object comprising one or more blood vessels of at least the portion of the user.

26. The method of claim 16, wherein at least one of the one or more waveguides is angled with respect to a surface of the interface layer, or is angled substantially parallel to a surface of the interface layer.

27. An apparatus comprising: light source means for transmitting light, the light source means comprising one or more light sources; receiver means for detecting acoustic signals generated by a target object based on optical signals from the light source means, the receiver means comprising one or more receiver elements;interface means contactable by a user, the interface means comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the receiver means, the interface means comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the receiver means; and waveguide means for transmitting the optical signals from the one or more light sources to the at least the portion of the user, the waveguide means comprising one or more waveguides at least partially embedded in the interface means.

28. The apparatus of claim 27, wherein: the interface means comprise a matching layer having a first surface and a second surface, the first surface contactable by and configured to interface with skin of the user, the second surface adjacent to and configured to interface with the receiver means; and the first acoustic characteristic comprises a first acoustic impedance associated with the skin of the user, and the second acoustic characteristic comprises a second acoustic impedance associated with the one or more receivers, the matching layer having graded acoustic impedances that progressively change between the first acoustic impedance associated with the skin of the user and the second acoustic impedance associated with the one or more receivers.

29. The apparatus of claim 27, wherein at least one of the one or more waveguides is angled with respect to a surface of the interface means, or is angled substantially parallel to a surface of the interface means.

30. A non-transitory computer-readable apparatus comprising a storage medium, the storage medium comprising a plurality of instructions configured to, when executed by a control system, cause a photoacoustic device to: cause transmission of optical signals via one or more waveguides from a light source system of the photoacoustic device toward a portion of a user proximate a receiver system of the photoacoustic device, the receiver system disposed remotely from the light source system without direct contact therewith, the photoacoustic device comprising:the light source system including one or more light sources; the receiver system including one or more receivers configured to detect acoustic signals generated by a target object based on optical signals from the one or more light sources; an interface layer contactable by a user, the interface layer comprising a flexible material configured to conform to at least a portion of the user, and adjacent to the one or more receivers, the interface layer comprising both a first acoustic characteristic corresponding to an acoustic characteristic of the user, and a second acoustic characteristic corresponding to an acoustic characteristic of the one or more receivers; and a waveguide system comprising one or more waveguides at least partially embedded in the interface layer, and configured to transmit the optical signals from the one or more light sources to the at least the portion of the user; receive, from the receiver system, information regarding the acoustic signals detected by the one or more receivers; and determine a physiological parameter of the user based on the information regarding the acoustic signals.

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