Multiple-frequency ultrasonic sensor system

Abstract

An ultrasonic sensor system may include: an ultrasonic transceiver layer, a thin-film transistor (TFT) layer adjacent to a first side of the ultrasonic transceiver layer, a frequency splitting layer adjacent to a second side of the ultrasonic transceiver layer, and a high-impedance layer adjacent to the frequency splitting layer. The frequency splitting layer may reside between the ultrasonic transceiver layer and the high-impedance layer. The high-impedance layer may have a higher acoustic impedance than the frequency splitting layer.

Description

Technical Field

[0001] This application claims priority to U.S. Patent Application No. 16 / 946,717, filed July 1, 2020, entitled “MULTIPLE-FREQUENCY ULTRASONIC SENSOR SYSTEM,” which is incorporated herein by reference for all purposes.

[0002] This disclosure generally relates to sensor devices and related methods, including but not limited to ultrasonic sensor systems and methods for using such systems. Prior Technology

[0003] Biometric identification can be an important feature for controlling access to devices, etc. Many existing products include some type of biometric identification. While some existing biometric identification technologies offer satisfactory performance, improvements in methods and devices are still desired. Summary of the Invention

[0004] The systems, methods, and apparatuses disclosed herein each have several innovative aspects, and no single aspect is solely responsible for the desired properties disclosed herein.

[0005] One inventive aspect of the subject matter described in this disclosure can be implemented in a device. In some implementations, the device includes an ultrasonic sensing system. In some such implementations, the ultrasonic sensing system includes: an ultrasonic transceiver layer, a thin-film transistor (TFT) layer adjacent to a first side of the ultrasonic transceiver layer, a frequency splitting layer adjacent to a second side of the ultrasonic transceiver layer, and a high-impedance layer adjacent to the frequency splitting layer. In some such examples, the frequency splitting layer resides between the ultrasonic transceiver layer and the high-impedance layer. In some such examples, the high-impedance layer has a higher acoustic impedance than the frequency splitting layer. According to some examples, the high-impedance layer may be or may include high-impedance ink. In some instances, the device may reside within a mobile device.

[0006] In some examples, the TFT layer may have a thickness ranging from 50 micrometers to 1000 micrometers. According to some examples, the TFT layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and a second thickness in the high-frequency region of the ultrasonic sensor system. In some examples, the ultrasonic transceiver layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and wherein the ultrasonic transceiver layer may have a second thickness in the high-frequency region of the ultrasonic sensor system. According to some implementations, the ultrasonic transceiver layer may have first to Nth thicknesses in first to Nth regions of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

[0007] In some examples, the ultrasonic sensor system may include a conductive layer residing between the ultrasonic transceiver layer and the high-impedance layer. The conductive layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and a second thickness in the high-frequency region of the ultrasonic sensor system. According to some such examples, the conductive layer may have first to Nth thicknesses in first to Nth regions of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

[0008] According to some implementations, an ultrasonic sensor system may include an adhesive layer residing between an ultrasonic transceiver layer and a high-impedance layer. In some such examples, the adhesive layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and the adhesive layer may have a second thickness in the high-frequency region of the ultrasonic sensor system. In some instances, the adhesive layer may have first to Nth thicknesses in first to Nth regions of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

[0009] According to some examples, the frequency splitting layer may be or may include a material having a lower acoustic impedance than glass. In some examples, the frequency splitting layer may be or may include one or more of plastic or polyethylene terephthalate.

[0010] In some examples, the device may include a control system. The control system may include one or more general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or combinations thereof.

[0011] According to some examples, the control system can be configured to control the ultrasonic transceiver layer to emit ultrasonic waves. In some instances, a first portion of the ultrasonic waves may be emitted through the TFT layer in a first direction. In some examples, the first portion of the ultrasonic waves may include a first peak frequency. According to some examples, the control system can be configured to receive from the ultrasonic transceiver layer a first signal corresponding to the reflection of the first portion of the ultrasonic waves from the surface of a portion of a target object located on the outer surface of the device. In some examples, the control system can be configured to perform an authentication procedure at least partially based on the first signal. According to some examples, the control system can be configured to obtain fingerprint data based on a portion of the first signal received within a time interval that corresponds to a fingerprint.

[0012] In some examples, the second portion of the ultrasound wave may be emitted in a second direction through a frequency splitting layer. In some such examples, the frequency splitting layer and the high-impedance layer may be configured such that the reflected second portion of the ultrasound wave includes a second peak frequency lower than the first peak frequency. According to some examples, the control system may be configured to receive from the ultrasound transceiver layer a second signal corresponding to the reflection of the second portion of the ultrasound wave from the interior of a portion of the target object, and to perform an authentication procedure at least in part based on the second signal. According to some examples, the second signal may include subepidermal information corresponding to the reflection of the second portion of the ultrasound wave received from that portion of the target object within a time interval, corresponding to a subepidermal region.

[0013] According to some examples, the first peak frequency can be in the range of 10 MHz to 20 MHz. According to some implementations, the second peak frequency can be in the range of 1 MHz to 10 MHz. In some examples, the frequency splitting layer can have a thickness corresponding to a quarter wavelength at the second peak frequency.

[0014] In some examples, the device may include an adhesive layer residing between the high-impedance layer and the ultrasonic transceiver layer. According to some examples, the device may include a silver ink layer residing between a second side of the high-impedance layer and the ultrasonic transceiver layer. In some examples, the device may include a display stack adjacent to the TFT layer. In some such examples, the TFT layer may reside between the ultrasonic transceiver layer and the display stack.

[0015] Other inventive aspects of the subject matter described in this disclosure can be implemented in a device. In some implementations, the device includes an ultrasonic sensing system. In some such implementations, the ultrasonic sensing system includes: an ultrasonic transceiver layer, a thin-film transistor (TFT) layer adjacent to a first side of the ultrasonic transceiver layer, and a high-impedance layer in a first region adjacent to a second side of the ultrasonic transceiver layer. In some such examples, the high-impedance layer has a higher acoustic impedance than the adjacent layer. In some implementations, the first region corresponds to a low-frequency region of the ultrasonic sensing system. According to some examples, the high-impedance layer may be or may include high-impedance ink. In some such examples, the high-impedance ink may serve as an acoustic layer and as a conductive layer. In some instances, the device may reside within a mobile device.

[0016] In some implementations, the high-impedance layer may not be adjacent to the second region of the ultrasonic transceiver layer. In some such examples, the second region may correspond to the high-frequency region of the ultrasonic sensor system.

[0017] In some examples, the TFT layer may have a thickness ranging from 50 micrometers to 1000 micrometers. According to some examples, the TFT layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and a second thickness in the high-frequency region of the ultrasonic sensor system. In some examples, the ultrasonic transceiver layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and wherein the ultrasonic transceiver layer may have a second thickness in the high-frequency region of the ultrasonic sensor system. According to some implementations, the ultrasonic transceiver layer may have first to Nth thicknesses in first to Nth regions of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

[0018] In some examples, the ultrasonic sensor system may include a conductive layer residing between the ultrasonic transceiver layer and the high-impedance layer. The conductive layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and a second thickness in the high-frequency region of the ultrasonic sensor system. According to some such examples, the conductive layer may have first to Nth thicknesses in first to Nth regions of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

[0019] According to some implementations, an ultrasonic sensor system may include an adhesive layer residing between an ultrasonic transceiver layer and a high-impedance layer. In some such examples, the adhesive layer may have a first thickness in the low-frequency region of the ultrasonic sensor system, and the adhesive layer may have a second thickness in the high-frequency region of the ultrasonic sensor system. In some instances, the adhesive layer may have first to Nth thicknesses in first to Nth regions of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

[0020] According to some implementations, the device may include a backing layer. In some examples, a high-impedance layer may reside between the backing layer and the ultrasonic transceiver layer. In some examples, the backing layer may have a first thickness in a low-frequency region and a second thickness in a high-frequency region. In some examples, the backing layer may have a first to Nth thickness in a first to Nth region of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies. In some instances, the high-impedance layer may have a higher acoustic impedance than the backing layer. According to some implementations, the device may include a conductive layer residing between a first region on a second side of the high-impedance layer and the ultrasonic transceiver layer.

[0021] In some implementations, the device may include a conductive layer residing between the ultrasonic transceiver layer and the high-impedance layer. In some examples, the conductive layer may have a first thickness in the low-frequency region of the ultrasonic sensor system and a second thickness in the high-frequency region of the ultrasonic sensor system. In some instances, the conductive layer may have a first to an Nth thickness in a first to an Nth region of the ultrasonic sensor system. Each of the first to Nth regions may correspond to one of the first to Nth peak frequencies.

[0022] In some examples, the high-impedance layer may be adjacent to a first region of the ultrasonic transceiver layer. In some implementations, the device may include a light source system configured to induce photoacoustic emission in a target object. In some implementations, the device may include a display stack adjacent to the TFT layer. In some such examples, the TFT layer may reside between the ultrasonic transceiver layer and the display stack.

[0023] In some examples, the device may include a control system. The control system may include one or more general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or combinations thereof.

[0024] According to some examples, the control system can be configured to control the ultrasonic transceiver layer to emit ultrasonic waves. In some instances, a first portion of the ultrasonic waves may be emitted through the TFT layer in a first direction. In some examples, the first portion of the ultrasonic waves may include a first peak frequency. According to some examples, the control system can be configured to receive from the ultrasonic transceiver layer a first signal corresponding to the reflection of the first portion of the ultrasonic waves from the surface of a portion of a target object located on the outer surface of the device. In some examples, the control system can be configured to perform an authentication procedure at least partially based on the first signal. According to some examples, the control system can be configured to obtain fingerprint data based on a portion of the first signal received within a time interval that corresponds to a fingerprint.

[0025] In some examples, the second portion of the ultrasound wave may be emitted in a second direction through a frequency splitting layer. In some such examples, the frequency splitting layer and the high-impedance layer may be configured such that the reflected second portion of the ultrasound wave includes a second peak frequency lower than the first peak frequency. According to some examples, the control system may be configured to receive from the ultrasound transceiver layer a second signal corresponding to the reflection of the second portion of the ultrasound wave from the interior of a portion of the target object, and to perform an authentication procedure at least in part based on the second signal. According to some examples, the second signal may include subepidermal information corresponding to the reflection of the second portion of the ultrasound wave received from that portion of the target object within a time interval, corresponding to a subepidermal region.

[0026] Other inventive aspects of the subject matter described in this disclosure can be implemented in a method for controlling an ultrasonic sensor system. In some examples, the method involves controlling an ultrasonic transceiver layer to emit ultrasonic waves. In some instances, a first portion of the ultrasonic wave is emitted in a first direction through a thin-film transistor (TFT) layer. In some instances, the first portion of the ultrasonic wave includes a first peak frequency. In some instances, a second portion of the ultrasonic wave is emitted in a second direction through a frequency splitting layer to reach a high-impedance layer. In some instances, the frequency splitting layer and the high-impedance layer are configured such that the reflected second portion of the ultrasonic wave includes a second peak frequency lower than the first peak frequency.

[0027] In some examples, the method involves receiving from the ultrasonic transceiver layer a first signal corresponding to the reflection of a first portion of ultrasound from a surface of a portion of a target object located on an outer surface of a device including the ultrasonic sensor system. In some examples, the method involves receiving from the ultrasonic transceiver layer a second signal corresponding to the reflection of a second portion of ultrasound from an interior of a portion of the target object. In some examples, the method involves performing an authentication procedure at least partially based on the first and second signals.

[0028] According to some examples, the method may involve obtaining fingerprint data based on a portion of a first signal received within a time interval that corresponds to a fingerprint. According to some examples, the second signal may include subepidermal information corresponding to reflections of a second ultrasound wave received from that portion of a target object within a time interval that correspond to a subepidermal region.

[0029] Other inventive aspects of the subject matter described in this disclosure can be implemented in a method for controlling an ultrasonic sensor system. In some examples, the method involves controlling an ultrasonic transceiver layer to emit ultrasonic waves, a first portion of which is emitted in a first direction through a thin-film transistor (TFT) layer, the first portion of which includes a first peak frequency. In some examples, a second portion of the ultrasonic waves is emitted in a second direction toward a high-impedance layer. In some examples, the high-impedance layer and one or more layers between the high-impedance layer and the ultrasonic transceiver layer are configured such that the reflected second portion of the ultrasonic waves includes a second peak frequency lower than the first peak frequency.

[0030] In some examples, the method involves receiving from an ultrasonic transceiver layer a first signal corresponding to reflection from a surface of a portion of a target object, representing a first portion of an ultrasonic wave, from an outer surface of a device including the ultrasonic sensor system. In some examples, the method involves receiving from an ultrasonic transceiver layer a second signal corresponding to reflection from an interior portion of the target object, representing a second portion of an ultrasonic wave. In some examples, the method involves performing an authentication procedure at least partially based on the first and second signals. In some examples, the method may involve obtaining fingerprint data based on a portion of the first signal received within a time interval that corresponds to a fingerprint. In some examples, the second signal may include subepidermal information corresponding to reflection from that portion of the target object, within a time interval, of a second ultrasonic wave that corresponds to a subepidermal region.

[0031] Some or all of the operations, functions, and / or methods described herein may be executed by one or more devices according to instructions (e.g., software) stored on one or more non-transitory media. Such non-transitory media may include memory devices such as those described herein, including but not limited to random access memory (RAM) devices, read-only memory (ROM) devices, etc. Accordingly, some innovative aspects of the subject matter described herein may be implemented in one or more non-transitory media on which software is stored.

[0032] For example, the software may include instructions for controlling one or more devices to perform a method of controlling an ultrasonic sensor system. In some examples, the method involves controlling an ultrasonic transceiver layer to emit ultrasonic waves. In some instances, a first portion of the ultrasonic waves is emitted in a first direction through a thin-film transistor (TFT) layer. In some instances, the first portion of the ultrasonic waves includes a first peak frequency. In some instances, a second portion of the ultrasonic waves is emitted in a second direction through a frequency splitting layer to reach a high-impedance layer. In some instances, the frequency splitting layer and the high-impedance layer are configured such that the reflected second portion of the ultrasonic waves includes a second peak frequency lower than the first peak frequency.

[0033] In some examples, the method involves receiving from the ultrasonic transceiver layer a first signal corresponding to the reflection of a first portion of ultrasound from a surface of a portion of a target object located on an outer surface of a device including the ultrasonic sensor system. In some examples, the method involves receiving from the ultrasonic transceiver layer a second signal corresponding to the reflection of a second portion of ultrasound from an interior of a portion of the target object. In some examples, the method involves performing an authentication procedure at least partially based on the first and second signals.

[0034] According to some examples, the method may involve obtaining fingerprint data based on a portion of a first signal received within a time interval that corresponds to a fingerprint. According to some examples, the second signal may include subepidermal information corresponding to reflections of a second ultrasound wave received from that portion of a target object within a time interval that correspond to a subepidermal region.

[0035] In some examples, the method involves controlling an ultrasonic transceiver layer to emit ultrasonic waves, a first portion of which is emitted in a first direction through a thin-film transistor (TFT) layer, the first portion of which includes a first peak frequency. In some examples, a second portion of the ultrasonic waves is emitted in a second direction toward a high-impedance layer. In some examples, the high-impedance layer and one or more layers between the high-impedance layer and the ultrasonic transceiver layer are configured such that the reflected second portion of the ultrasonic waves includes a second peak frequency lower than the first peak frequency.

[0036] In some examples, the method involves receiving from an ultrasonic transceiver layer a first signal corresponding to reflection from a surface of a portion of a target object, representing a first portion of an ultrasonic wave, from an outer surface of a device including the ultrasonic sensor system. In some examples, the method involves receiving from an ultrasonic transceiver layer a second signal corresponding to reflection from an interior portion of the target object, representing a second portion of an ultrasonic wave. In some examples, the method involves performing an authentication procedure at least partially based on the first and second signals. In some examples, the method may involve obtaining fingerprint data based on a portion of the first signal received within a time interval that corresponds to a fingerprint. In some examples, the second signal may include subepidermal information corresponding to reflection from that portion of the target object, within a time interval, of a second ultrasonic wave that corresponds to a subepidermal region. Simple Explanation of the Diagram

[0037] Details of one or more implementations of the subject matter described in this specification are set forth in the drawings and the following description. Other features, aspects, and advantages will become apparent from this description, the drawings, and the claims. It should be noted that the relative dimensions in the following drawings may not be drawn to scale. Similar reference numerals and names in the various drawings indicate similar elements.

[0038] Figure 1A shows an example of subepidermal features.

[0039] Figure 1B is a block diagram showing example components of a device implemented according to some disclosed content.

[0040] Figure 2 shows example components of a device implemented according to some of the disclosed content.

[0041] Figures 3A and 3B are graphs of the Δ signal strength relative to the thickness of the frequency splitter based on two examples.

[0042] Figure 4 shows example components of a device implemented according to some of the disclosed content.

[0043] Figures 5 and 6 show example components of a device based on some alternative implementations.

[0044] Figure 7 shows example components of a device implemented according to some alternative methods.

[0045] Figure 8A shows an implementation where the TFT layer has two different thicknesses.

[0046] Figure 8B shows an implementation where the conductive layer adjacent to the ultrasonic transceiver layer has two different thicknesses.

[0047] Figure 9A shows an implementation where the ultrasonic transceiver layer has two different thicknesses.

[0048] Figure 9B shows an implementation where the high-resistivity layer has two different thicknesses.

[0049] Figure 10A shows an implementation where the backing layer has two different thicknesses.

[0050] Figure 10B shows an implementation where the epoxy resin film has two different thicknesses.

[0051] Figure 11 is a flowchart providing an example of operation according to some of the disclosed methods.

[0052] Figure 12 is another flowchart providing an example of operation according to some of the disclosed methods.

[0053] Figure 13 typically depicts various aspects of a 4×4 pixel array of sensor pixels used in an ultrasonic sensor system. Implementation

[0054] The following description is directed to certain implementations in an attempt to describe the innovative aspects of this disclosure. However, those skilled in the art will readily recognize that the teachings herein can be applied in many different ways. The described implementations can be implemented in any device, apparatus, or system, including biometric systems as disclosed herein. Furthermore, it is contemplated that the described implementations can be included in or associated with a variety of electronic devices, such as, but not limited to: mobile phones, internet-enabled multimedia cellular phones, mobile TV receivers, wireless devices, smartphones, smart cards, wearable devices (such as wristbands, armbands, wrist straps, rings, headbands, patches, etc.), Bluetooth® devices, personal digital assistants (PDAs), wireless email receivers, handheld or portable computers, laptops, notebook computers, smart laptops, tablets, printers, copiers, scanners, fax machines, GPS receivers / navigators, cameras, digital multimedia players (such as MP3 players), camcorders, game consoles, wristwatches, clocks, calculators, television monitors, and more. Panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, automotive displays (including odometer and speedometer displays), cockpit controls and / or displays, camera image displays (such as rearview camera displays in vehicles), electronic photographs, electronic billboards or signs, projectors, building structures, microwave ovens, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable storage chips, washing machines, dryers, washer / dryer units, parking timers, packages (such as in electromechanical systems (EMS) applications, including microelectromechanical systems (MEMS) applications, and non-EMS applications), aesthetic structures (such as image displays on a piece of jewelry or clothing), and various EMS devices. The teachings herein can also be used in applications such as, but not limited to, electronic switching devices, radio frequency filters, sensors, accelerometers, gyroscopes, motion sensing devices, magnetometers, inertial components for consumer electronic devices, components for consumer electronic products, steering wheels or other automotive components, variable capacitors, liquid crystal devices, electrophoresis equipment, drive schemes, manufacturing processes, and electronic test equipment. Therefore, these teachings are not intended to be limited to the implementations depicted in the diagrams, but have broad applicability, as will be obvious to those skilled in the art.

[0055] Many existing products (including, but not limited to, mobile phones) are configured for fingerprint-based authentication. However, even high-end mobile phone manufacturers have successfully compromised their fingerprint-based authentication systems shortly after product launch. In some instances, counterfeiting can involve using finger-like objects that form the fingerprint pattern of a legitimate user on their outer surface, including silicone rubber, polyvinyl acetate (white glue), gelatin, glycerin, etc. In some cases, hackers can form the fingerprint pattern of a legitimate user over or across the finger sleeve or part of the finger sleeve.

[0056] Authentication methods based at least in part on subepidermal features are more reliable than those based solely on fingerprints, partly because subepidermal features are more difficult to forge. Figure 1A shows an example of a subepidermal feature. As used herein, the term "subepidermal feature" can refer to any tissue layer located beneath the epidermis 100, including the dermis, papillary layer, reticular layer, subcutaneous tissue, etc., and any blood vessels, lymphatic vessels, sweat glands, hair follicles, dermal papillae, fat lobules, etc., that may be present in these tissue layers. Accordingly, subepidermal features may also include features not shown in Figure 1A, such as muscle tissue, bone material, etc.

[0057] Accordingly, some of the disclosed implementations can be configured to perform authentication methods that are at least partially based on subepidermal features. Some such implementations may include an ultrasound sensor system capable of acquiring image data from the epidermis, such as fingerprint image data, and image data corresponding to subepidermal features. Data received from the ultrasound sensor system may be referred to herein as "ultrasound image data," "image data," etc., although the data is typically received from the ultrasound sensor system in the form of electrical signals. Accordingly, such image data need not be perceptible to humans as images without additional processing.

[0058] Designing an ultrasonic sensor system suitable for imaging both fingerprints and subcutaneous features can be challenging. For example, relatively high frequencies (e.g., 10 MHz or higher) are suitable for fingerprint imaging, while relatively low frequencies (e.g., below 10 MHz) are suitable for imaging subcutaneous features. If the ultrasonic sensor system is configured to emit both high-frequency and low-frequency ultrasound, it can lead to crosstalk.

[0059] Some disclosed devices include an ultrasonic sensing system configured to emit ultrasound at two or more peak frequencies. In some examples, the ultrasonic sensing system may include: an ultrasonic transceiver layer, a thin-film transistor (TFT) layer on or near a first side of the ultrasonic transceiver layer, a high-impedance layer, and a frequency splitting layer between a second side of the ultrasonic transceiver layer and the high-impedance layer. In some examples, the frequency splitting layer may be configured to allow relatively lower frequencies suitable for imaging subepidermal features to pass through. In some such examples, the frequency splitting layer may be configured to suppress relatively higher frequencies suitable for fingerprint imaging. However, some implementations do not include a frequency splitting layer. In some examples, the TFT layer may reside between the ultrasonic transceiver layer and a display.

[0060] In some examples, ultrasound waves emitted directly from the ultrasound transceiver layer have relatively high peak frequencies suitable for fingerprint imaging. According to some such examples, ultrasound waves reflected from the high-impedance layer have relatively low frequencies suitable for imaging subepidermal features. In some implementations, ultrasound waves are emitted through a frequency-splitting layer and then reflected from the high-impedance layer. In some implementations, one or more of the layers in the ultrasound sensor system may have a first thickness in the low-frequency region of the ultrasound sensor system and a second thickness in the high-frequency region of the ultrasound sensor system. The second thickness may be less than the first thickness. In some examples, one or more of the layers in the ultrasound sensor system may have first to Nth thicknesses in the first to Nth regions of the ultrasound sensor system. Each of these thicknesses may correspond to a different peak frequency of the corresponding region of the ultrasound sensor system.

[0061] Specific implementations of the subject matter described in this disclosure may be implemented to achieve one or more of the following potential advantages. In some examples, an ultrasound sensor system may be configured to emit ultrasound at two or more peak frequencies. For example, an ultrasound sensor system may be configured to emit ultrasound with a relatively high peak frequency suitable for fingerprint imaging and ultrasound with a relatively low frequency suitable for imaging subepidermal features. In some examples, the same ultrasound transceiver layer may be used to generate both the higher and lower peak frequencies.

[0062] Figure 1B is a block diagram illustrating example components of a device according to some disclosed implementations. As with other disclosed implementations, the number, type, and arrangement of elements shown in Figure 1B are presented merely as examples. Although not shown in Figure 1B, device 100 may include other components such as a cover glass, one or more conductive layers (such as conductive ink layers), one or more adhesive layers, etc. Some examples are described below.

[0063] According to this example, device 100 includes an ultrasonic sensor system. In this implementation, device 100 includes an ultrasonic transceiver layer 101, a thin-film transistor (TFT) layer 102, a selective frequency splitting layer 103, and a high-impedance layer 105. The frequency splitting layer 103 may reside between the ultrasonic transceiver layer 101 and the high-impedance layer 105, if present. In this example, the ultrasonic transceiver layer 101 can serve as both an ultrasonic transmitter and an ultrasonic receiver. According to some implementations, the ultrasonic transceiver layer 101 may be a single piezoelectric layer, while in other implementations, the ultrasonic transceiver layer 101 may be a multilayer piezoelectric structure or an array of such structures.

[0064] For example, in some implementations, the ultrasonic transceiver layer 101 may include a piezoelectric layer, such as a PVDF polymer layer or a PVDF-TrFE copolymer layer. In some implementations, other piezoelectric materials, such as aluminum nitride (AlN) or lead zirconate titanate (PZT), may be used in the ultrasonic transceiver layer 101. Some alternative implementations may include separate ultrasonic transmitter and ultrasonic receiver layers.

[0065] In some examples, the ultrasonic transceiver layer 101 may include an array of ultrasonic transducer elements, such as a piezoelectric micromechanical ultrasonic transducer (PMUT) array, a capacitive micromechanical ultrasonic transducer (CMUT) array, etc. In some such examples, a piezoelectric receiver layer, PMUT elements in a single-layer PMUT array, or CMUT elements in a single-layer CMUT array may be used as both an ultrasonic transmitter and an ultrasonic receiver.

[0066] In some examples, the ultrasonic transceiver layer 101 may have a first thickness in the low-frequency region of the ultrasonic sensor system and a second thickness in the high-frequency region of the ultrasonic sensor system. For example, the ultrasonic transceiver layer 101 may be thicker in the low-frequency region and thinner in the high-frequency region. According to some implementations, the first thickness may be between 5 micrometers and 20 micrometers. In some such implementations, the second thickness may be between 1 micrometer and 10 micrometers. In some examples, the ultrasonic transceiver layer 101 may have a first to an Nth thickness in a first to an Nth region of the ultrasonic sensor system. Each of these thicknesses may correspond to a different peak frequency of the corresponding region of the ultrasonic sensor system.

[0067] The TFT layer 102 can be a type of metal-oxide-semiconductor field-effect transistor (MOSFET) fabricated by depositing an effective semiconductor thin film layer, a dielectric layer, and metal contacts on a substrate. In some examples, the substrate is a non-conductive material, such as glass. According to some implementations, the TFT layer 102 can have a thickness ranging from 50 micrometers to 400 micrometers. In some examples, the TFT layer 102 can have a first thickness in the low-frequency region of the ultrasonic sensor system and a second thickness in the high-frequency region of the ultrasonic sensor system. For example, the TFT layer 102 can be thicker in the low-frequency region and thinner in the high-frequency region. According to some implementations, the first thickness is between 250 micrometers and 400 micrometers. In some such implementations, the second thickness is between 50 micrometers and 250 micrometers. In some examples, the TFT layer 102 can have a first to an Nth thickness in the first to Nth regions of the ultrasonic sensor system. Each of these thicknesses can correspond to a different peak frequency of the corresponding region of the ultrasonic sensor system.

[0068] In some examples, the frequency splitting layer 103 may comprise polyethylene terephthalate (PET). In other examples, the frequency splitting layer 103 may comprise a pressure-sensitive adhesive, plastic spacers, and / or a metal strip, such as a copper strip. In some implementations, the frequency splitting layer 103 may have a relatively lower acoustic impedance than the glass and / or high-impedance layer 105. In some implementations, the frequency splitting layer 103 may be configured to suppress relatively high-frequency ultrasound suitable for fingerprint imaging. According to some such implementations, the relatively high-frequency ultrasound may be emitted by the ultrasonic transceiver layer 101 and may include a peak frequency referred to herein as a “first peak frequency.” The first peak frequency may, for example, be in the range of 10 MHz to 20 MHz.

[0069] In some examples, the frequency splitting layer 103 can be configured to allow relatively low-frequency ultrasound waves suitable for imaging subepidermal features to pass through. According to some such implementations, the relatively low-frequency ultrasound waves can be reflected by the high-impedance layer 105 and can include a frequency referred to herein as the "second peak frequency." The second peak frequency can, for example, be in the range of 1 MHz to 10 MHz.

[0070] In some implementations, the frequency splitting layer 103 may have a relatively lower acoustic impedance than the high-impedance layer 105. According to some examples, the frequency splitting layer 103 may have a thickness corresponding to an odd multiple of a quarter wavelength at the second peak frequency.

[0071] In some examples, the frequency splitting layer 103 may have a first thickness in the low-frequency region of the ultrasound sensor system and a second thickness in the high-frequency region of the ultrasound sensor system. For example, the frequency splitting layer 103 may be thicker in the low-frequency region and thinner in the high-frequency region. According to some implementations, the first thickness may be between 50 micrometers and 100 micrometers. In some such implementations, the second thickness may be between 0 micrometers and 50 micrometers. In some examples, the frequency splitting layer 103 may have a first to an Nth thickness in the first to Nth regions of the ultrasound sensor system. Each of these thicknesses may correspond to a different peak frequency of the corresponding region of the ultrasound sensor system.

[0072] The high-resistivity layer 105 may be or may include one or more materials having a relatively high acoustic impedance, such as metals (e.g., copper or tungsten), metal oxides (e.g., zinc oxide (ZnO)), etc. In some examples, the high-resistivity layer 105 may be or may include 3M™ Scotch-Weld™ epoxy potting compound DP270. According to some examples, the high-resistivity layer 105 may be or may include one or more commercially available high-resistivity inks. In some implementations, the high-resistivity ink may include an ink particle density higher than that typically used in commercially available inks. In some such examples, the high-resistivity layer 105 may be deposited on an adjacent layer using a screen printing process or an inkjet process. According to some implementations, the high-resistivity layer 105 may be conductive.

[0073] In some examples, device 100 may include interface system 107, control system 109, and / or display system 111. In some implementations, TFT layer 102 may reside adjacent to display system 111, for example, beneath display system 111. In some implementations, the selective display system 111 may be or may include a light-emitting diode (LED) display, such as an organic light-emitting diode (OLED) display.

[0074] Control system 109 may include one or more general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or combinations thereof. Control system 109 may also include one or more memory devices (and / or be configured to communicate with one or more memory devices), such as one or more random access memory (RAM) devices, read-only memory (ROM) devices, etc. Accordingly, device 100 may have a memory system including one or more storage devices, although such memory system is not shown in FIG. 1B. Control system 109 may be able to receive and process data from ultrasonic transceiver layer 101, as described below, for example. In some implementations, the functionality of control system 109 may be divided among one or more controllers or processors, such as between a dedicated sensor controller and an application processor for a mobile device.

[0075] Some implementations of device 100 may include interface system 107. In some examples, the interface system may include a wireless interface system. In some implementations, the interface system may include a user interface system, one or more network interfaces, one or more interfaces between the control system 109 and the memory system, and / or one or more interfaces between the control system 109 and one or more external device interfaces (e.g., ports or application processors).

[0076] Interface system 107 may be configured to provide communication between the components of device 100 (which may include wired or wireless communication, such as electrical communication, radio communication, etc.). In some such examples, interface system 107 may be configured to provide communication between control system 109 and ultrasonic receiver layer 101. According to some such examples, a portion of interface system 107 may couple at least a portion of control system 109 to ultrasonic receiver layer 101, for example, via a conductive material.

[0077] According to some examples, interface system 107 may be configured to provide communication between device 100 and other devices and / or humans. In some such examples, interface system 107 may include one or more user interfaces. In some examples, interface system 107 may include one or more network interfaces and / or one or more external device interfaces (such as one or more Universal Serial Bus (USB) interfaces). In some implementations, device 100 may include a memory system. In some examples, interface system 107 may include at least one interface between control system 109 and memory system.

[0078] In some examples, device 100 may include a selective light source system 113. In some such examples, the selective light source system 113 may be configured to emit light suitable for inducing photoacoustic emission in a target object. According to some such examples, the selective light source system 113 may include one or more light-emitting diodes, such as laser diodes.

[0079] Device 100 can be used in a variety of different contexts, many of which are disclosed herein. For example, in some implementations, a mobile device (such as a cellular phone, smartphone, tablet, laptop computer (e.g., a laptop touchpad)) may include at least a portion of device 100. In some implementations, a wearable device may include at least a portion of device 100. For example, a wearable device may be a watch, bracelet, armband, wristband, ring, headband, or patch. In some implementations, control system 109 may reside in more than one device. For example, a portion of control system 109 may reside in a wearable device, while another portion of control system 109 may reside in another device (such as a mobile device (e.g., a smartphone or tablet computer) and / or a server). In some such examples, interface system 107 may also reside in more than one device.

[0080] Figure 2 illustrates example components of a device according to some of the disclosed implementations. As with other disclosed implementations, the types, numbers, and arrangements of the elements, as well as the dimensions of the elements, are merely examples. According to this example, device 100 is configured to perform at least some of the methods disclosed herein. In this example, display 111 is an OLED display and is attached to TFT layer 102 via adhesive layer 201.

[0081] According to this implementation, the TFT layer 102 is coupled to at least a portion of the control system 109 and one side of the ultrasonic transceiver layer 101 via a portion of the interface system 107, the portion of which includes a conductive material. In this implementation, the ultrasonic transceiver layer 101 includes one or more piezoelectric copolymers. In this example, the interface system 107 also includes a conductive layer 203, which provides conductivity between a portion of the control system 109 and the other side of the ultrasonic transceiver layer 101.

[0082] In this example, epoxy resin film 205 couples conductive layer 203 to frequency splitting layer 103, which in this example is coupled to high impedance layer 105. In this implementation, frequency splitting layer 103 has a relatively lower acoustic impedance than high impedance layer 105. According to some examples, frequency splitting layer 103 has an acoustic impedance that is about 20% lower than that of high impedance layer 105. In some such implementations, frequency splitting layer 103 may have a thickness corresponding to a quarter wavelength (or an odd multiple of a quarter wavelength) at the second peak frequency of the ultrasound emitted by device 100.

[0083] In this example, the high-resistivity layer 105 is a copper backing layer. In some implementations, the copper backing layer has a thickness in the range of 100 micrometers to 200 micrometers.

[0084] In this example, device 100 is configured to perform at least some of the methods disclosed herein. In this example, control system 109 is configured to control ultrasonic transceiver layer 101 to emit ultrasonic waves. According to this example, a first portion 213 of the ultrasonic wave is emitted through TFT layer 102 in a first direction. In this implementation, the first portion 213 of the ultrasonic wave corresponds to a first peak frequency. In some implementations, the first peak frequency may be, for example, in the range of 10 MHz to 20 MHz. In the example shown in FIG. 2, the first peak frequency is 12 MHz. Arrow 214 corresponds to the reflection of the first portion 213 of the ultrasonic wave from the surface of a portion of a target object 207 located on the outer surface of device 100. In this example, the target object 207 is a finger. (As used herein, the term "finger" can refer to any finger, including the thumb. Accordingly, a thumbprint will be considered a type of "fingerprint.")

[0085] In this example, the control system 109 is configured to receive from the ultrasonic transceiver layer 101 a first signal corresponding to the reflection 214 of a first portion of an ultrasonic wave from the surface of a portion of a target object. In some examples, the control system 109 is configured to obtain fingerprint data based on a portion of the first signal received within a time interval corresponding to a fingerprint. This time interval can be measured, for example, relative to the time the first ultrasonic wave was emitted. Obtaining fingerprint data may, for example, involve extracting a first target object feature from the first signal via the control system. The first target object feature may, for example, include fingerprint features. According to some examples, fingerprint features may include fingerprint details, key points, and / or sweat pores. In some examples, fingerprint features may include ridge termination information, ridge bifurcation information, short ridge information, ridge flow information, island information, branch information, triangle information, core information, etc.

[0086] In some examples, the control system 109 may be configured to perform an authentication procedure at least in part based on a first signal. In some such examples, the control system 109 may be configured to perform an authentication procedure at least in part based on fingerprint features. According to some examples, the control system 109 may be configured to compare fingerprint features with the fingerprint features of an authorized user. For example, the fingerprint features of the authorized user may have already been received during a previous registration procedure.

[0087] According to the example shown in Figure 2, a second portion 216 of the ultrasound wave is emitted in a second direction through the frequency splitting layer 103. In this example, the frequency splitting layer 103 and the high-impedance layer 105 are configured such that the reflected second portion 215 of the ultrasound wave includes a second peak frequency lower than the first peak frequency. In some implementations, the second peak frequency can be, for example, in the range of 1 MHz to 10 MHz. In the example shown in Figure 2, the second peak frequency is 6 MHz. In some examples, the second peak frequency can be in the range of ultrasound frequencies suitable for imaging subepidermal features. For example, the second peak frequency can be in the range of 1 MHz to 10 MHz. In some implementations, the second peak frequency can be in the range of 2 MHz to 7 MHz.

[0088] In the example shown in Figure 2, the control system 109 is configured to receive from the ultrasonic transceiver layer 101 a second signal corresponding to the reflection 217 of the second portion of the ultrasound from the interior of that portion of the target object. According to some such examples, the control system 109 may be configured to perform an authentication procedure at least partially based on the second signal. According to some implementations, this authentication procedure may be at least partially based on both the first and second signals.

[0089] In some implementations, the control system 109 may be configured to extract subcutaneous features from the second signal. For example, the subcutaneous features of an authorized user may have already been received during a previous registration procedure. According to some implementations, the authentication procedure may involve comparing the subcutaneous features extracted from the second signal with the subcutaneous features of the authorized user.

[0090] In some such implementations, subepidermal features may include subepidermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object within a time interval, corresponding to a subepidermal region. For example, subepidermal features may include dermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object 207. The dermal information corresponding to the dermis may have already been obtained within a time interval. The authentication process may be based at least in part on the dermal information.

[0091] Alternatively or additionally, subepidermal features may include information about other subepidermal layers, such as the papillary layer, reticular layer, subcutaneous tissue, etc., and any blood vessels, lymphatic vessels, sweat glands, hair follicles, dermal papillae, fat lobules, etc., that may be present within such tissue layers. Some examples are described above with reference to Figure 1A. However, subepidermal features may include information about subepidermal features (such as muscle tissue, bone material, etc.) not shown in Figure 1A.

[0092] In some examples, the control system 109 may be configured to control access to device 100 or to another device, at least in part, based on an authentication process. For example, in some implementations, a mobile device (such as a cellular phone) may include device 100. In some such examples, the control system 109 may be configured to control access to the mobile device, at least in part, based on an authentication process.

[0093] In some implementations, the Internet of Things (IoT) device may include device 100. For example, in some such implementations, devices intended for use in a residence, such as remote control devices (e.g., remote control devices for smart TVs), stoves, ovens, refrigerators, coffee makers, alarm systems, door locks, mailbox / package locks, thermostats, etc., may include device 100. In some such examples, the control system may be configured to control access to the IoT device, at least in part, based on an authentication process.

[0094] In alternative implementations, a vehicle (including, but not limited to, partially or fully automated vehicles), a partially or fully automated delivery vehicle, a drone, or another device typically used outside a residence may include device 100. In some such examples, the control system may be configured to control access to the vehicle, drone, etc., at least in part based on an authentication process.

[0095] In some examples, including but not limited to many IoT implementations, a layer of metal, plastic, ceramic, or polymer may be present between the outer surface of device 100 or the outer surface of a device including device 100. In such implementations, sound waves emitted toward a finger or other target, and sound waves reflected from a finger or other target, may need to pass through this metal, plastic, ceramic, or polymer layer. Ultrasound and other sound waves can be successfully emitted through, for example, a metal layer, while some other types of waves (e.g., light waves) cannot. Similarly, ultrasound and other sound waves can be successfully emitted through optically transparent plastic, ceramic, or polymer layers, while some other types of waves (such as light waves) cannot. This feature is another potential advantage of some disclosed implementations compared to devices that rely on optical or capacitive fingerprint sensors.

[0096] Figures 3A and 3B are graphs showing the Δ signal strength relative to the thickness of the frequency splitter according to two examples. In each example, the frequency splitter comprises two sections of epoxy resin. In the examples shown in Figures 3A and 3B, the Δ signal strength indicates the difference between the signal corresponding to the fingerprint ridge (shown as "R" in Figures 3A and 3B) and the signal corresponding to the fingerprint valley (shown as "V" in Figures 3A and 3B). In the example of Figure 3A, ultrasound was transmitted at 5 MHz (the example of the "second frequency"), while in the example of Figure 3B, ultrasound was transmitted at 12 MHz (the example of the "first frequency"). By comparing Figures 3A and 3B, it can be observed that the same frequency splitter thickness (10⁻⁴ m) corresponding to the high Δ signal strength used for the 5 MHz signal also significantly suppresses the 12 MHz signal.

[0097] Figure 4 illustrates example components of a device according to some of the disclosed implementations. As mentioned above, some implementations of device 100 do not include a frequency splitting layer. Figure 4 illustrates such an example. As with other disclosed implementations, the type, number, and arrangement of elements, as well as the dimensions of the elements, are merely examples. According to this example, device 100 is configured to perform at least some of the methods disclosed herein. In this example, display 111 is an OLED display and is attached to TFT layer 102 via adhesive layer 201.

[0098] According to this implementation, the TFT layer 102 is coupled to at least a portion of the control system 109 and one side of the ultrasonic transceiver layer 101 via a portion of the interface system 107, the portion of which includes a conductive material. In this implementation, the ultrasonic transceiver layer 101 includes one or more piezoelectric copolymers. In this example, the interface system 107 also includes a conductive layer 203, which provides conductivity between a portion of the control system 109 and the other side of the ultrasonic transceiver layer 101.

[0099] In this example, the epoxy resin film 205 couples the conductive layer 203 to the high impedance layer 105. In this implementation, the epoxy resin film 205 has a relatively lower acoustic impedance than the high impedance layer 105.

[0100] According to this example, device 100 includes a low-frequency region 405 and a high-frequency region 410. In this example, a high-impedance layer 105 extends across the low-frequency region 405 but does not extend across the high-frequency region 410.

[0101] In this example, device 100 is configured to perform at least some of the methods disclosed herein. In this example, control system 109 is configured to control ultrasonic transceiver layer 101 to emit ultrasonic waves. According to this example, a first portion 213 of the ultrasonic wave is emitted through TFT layer 102 in a first direction. In this implementation, the first portion 213 of the ultrasonic wave corresponds to a first peak frequency. In some implementations, the first peak frequency may be, for example, in the range of 10 MHz to 20 MHz. In the example shown in FIG. 4, the first peak frequency is 12 MHz. Arrow 214 corresponds to the reflection of the first portion of the ultrasonic wave from the surface of a portion of a target object 207 located on the outer surface of device 100. In this example, the target object 207 is a finger.

[0102] In this example, the control system 109 is configured to receive from the ultrasonic transceiver layer 101 a first signal corresponding to the reflection 214 of a first portion of an ultrasonic wave from the surface of a portion of a target object. In some examples, the control system 109 is configured to obtain fingerprint data based on a portion of the first signal received within a time interval corresponding to a fingerprint. This time interval can be measured, for example, relative to the time the first ultrasonic wave was emitted. Obtaining fingerprint data may, for example, involve extracting a first target object feature from the first signal via the control system. The first target object feature may, for example, include fingerprint features, such as those described above with reference to FIG2.

[0103] In some examples, the control system 109 may be configured to perform an authentication procedure at least in part based on a first signal. In some such examples, the control system 109 may be configured to perform an authentication procedure at least in part based on fingerprint features. According to some examples, the control system 109 may be configured to compare fingerprint features with the fingerprint features of an authorized user. For example, the fingerprint features of the authorized user may have already been received during a previous registration procedure.

[0104] According to the example shown in Figure 4, the second portion 216 of the ultrasound is emitted toward the high-impedance layer 105 in a second direction. In this implementation, the high-impedance layer in the low-frequency region 405 and the respective layers between the high-impedance layer 105 and the ultrasound transceiver layer 101 are configured such that the reflected second portion 215 of the ultrasound includes a second peak frequency lower than the first peak frequency. In some implementations, the second peak frequency may be, for example, in the range of 1 MHz to 10 MHz. In some examples, the second peak frequency may be in the range of ultrasound frequencies suitable for imaging subepidermal features. For example, the second peak frequency may be in the range of 1 MHz to 10 MHz. In some implementations, the second peak frequency may be in the range of 2 MHz to 7 MHz.

[0105] In the example shown in Figure 4, the control system 109 is configured to receive from the ultrasonic transceiver layer 101 a second signal corresponding to a reflection 217 of the second portion of the ultrasound from the interior of that portion of the target object. According to some such examples, the control system 109 may be configured to perform an authentication procedure at least in part based on the second signal.

[0106] In some implementations, the control system 109 may be configured to extract subcutaneous features from the second signal. For example, the subcutaneous features of an authorized user may have already been received during a previous registration procedure. According to some implementations, the authentication procedure may involve comparing the subcutaneous features extracted from the second signal with the subcutaneous features of the authorized user.

[0107] In some such implementations, subepidermal features may include subepidermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object within a time interval, corresponding to a subepidermal region. For example, subepidermal features may include dermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object 207. The dermal information corresponding to the dermis may have already been obtained within a time interval. The authentication process may be based at least in part on the dermal information. Alternatively or additionally, subepidermal features may include information about other subepidermal layers, such as those described above with reference to Figures 1A and 2. According to some implementations, the authentication process may be based at least in part on both the first and second signals.

[0108] As indicated by the examples of arrows 213 and 214 in the low-frequency region 405, in this example, high-frequency fingerprint imaging can be performed in both the high-frequency region 410 and the low-frequency region 405 of the device 100.

[0109] In some examples, the control system 109 may be configured to control access to device 100 or to another device, at least in part, based on an authentication procedure. For example, in some implementations, a mobile device (such as a cellular phone) may include device 100. In some such examples, the control system 109 may be configured to control access to the mobile device, at least in part, based on an authentication procedure. The description of Figure 2 above provides additional examples of devices to which access can be controlled according to an authentication procedure.

[0110] Figures 5 and 6 illustrate example components of a device according to some alternative implementations. Figures 5 and 6 show additional examples where device 100 does not include a frequency splitting layer. As with other disclosed implementations, the types, numbers, and arrangements of elements, as well as the dimensions of elements, shown in Figures 5 and 6 are merely examples. According to these examples, device 100 is configured to perform at least some of the methods disclosed herein. In these examples, display 111 is an OLED display and is attached to TFT layer 102 via adhesive layer 201. According to these examples, control system 109 can be configured to perform the operations described above with reference to Figure 4.

[0111] The device 100 shown in Figures 5 and 6 is similar to the implementation shown in Figure 4, but each implementation has at least three significant differences. One difference is that in Figures 5 and 6, the high-impedance layer 105 extends across the area of ​​device 100 by at least the same size as the area of ​​the ultrasonic transceiver layer 101. Accordingly, the separate low-frequency region 405 and high-frequency region 410 are not present in the implementations shown in Figures 5 and 6.

[0112] Another difference is that in Figures 5 and 6, there is a backing layer 505 adjacent to the high-impedance layer 105. In some implementations, the backing layer 505 can be or may include a metal, such as copper or tungsten. Having a backing layer 505 adjacent to one side of the high-impedance layer 105 can offer several potential advantages. Some materials from which the high-impedance layer 105 can be formed (such as some high-impedance inks) may be relatively soft. Therefore, a rigid backing layer 505 can provide structural support for such relatively soft materials. Another potential advantage is that the thickness and / or acoustic impedance of the backing layer 505 can be adjusted to enhance one or more desired emission frequencies.

[0113] Another difference from the implementation shown in Figure 4 is that in Figure 5, there is no epoxy resin film 205 between the conductive layer 203 and the high-impedance layer 105. In this example, the conductive layer 203 is adjacent to one side of the high-impedance layer 105. The thickness of the high-impedance layer 107 can be optimized based on the acoustic impedance mismatch with the adjacent layer. In some examples, the high-impedance layer 105 may have a thickness in the range of 20 micrometers to 40 micrometers. This thickness range has been shown to provide good signal strength. High-density materials are preferred for the high-impedance layer 105 to provide a strong signal.

[0114] In Figure 6, neither the epoxy resin film 205 nor the conductive layer 203 of Figure 4 are present. In this example, the ultrasonic transceiver layer 101 is adjacent to one side of the high-impedance layer 105. When the high-impedance layer 105 is formed of a conductive material, the implementation of the type shown in Figure 6 can be advantageous, making a separate conductive layer 203 unnecessary.

[0115] Figure 7 shows example components of a device according to some alternative implementations. As with other disclosed implementations, the types, numbers, and arrangements of the elements, as well as the dimensions of the elements, are merely examples.

[0116] Figure 7 shows an additional example in which device 100 does not include a frequency splitting layer. As in the example shown in Figure 4, device 100 of Figure 7 includes a low-frequency region 405 and a high-frequency region 410. In this example, a high-impedance layer 105 (which in this instance comprises copper) extends across the low-frequency region 405 but does not extend across the high-frequency region 410.

[0117] In this example, display 111 is an OLED display. Here, display 111 is attached to TFT layer 102 via adhesive layer 201, which in this example includes a black copper strip. In this example, cover glass 701 covers display 111 and provides a durable outer surface. According to these examples, control system 109 can be configured to perform the operations described above with reference to FIG4.

[0118] However, the device 100 of Figure 7 also includes a light source system 113, which in this example is a high-power (e.g., 5-10 megajoules (mJ) per square centimeter (cm²)) LED. In an alternative example, the light source system 113 may be or may include a laser diode. According to this example, the light source system 113 is configured to emit light 705, which may induce photoacoustic emission 710 in a target object 207 (in this example, a finger). According to some implementations, the light source system 113 is configured to induce relatively low-frequency photoacoustic emission 710 (e.g., in the range of 1 MHz to 9 MHz) from the subcutaneous structures of the finger. In this example, a low-frequency region 405 is configured to detect the low-frequency photoacoustic emission 710.

[0119] Some alternative implementations will now be described with reference to Figures 8A through 10B. In these implementations, one or more layers in the ultrasound sensor system have a first thickness in the low-frequency region of the ultrasound sensor system and a second thickness in the high-frequency region of the ultrasound sensor system. The second thickness may be less than the first thickness. Although only two different layer thicknesses are shown in Figures 8A through 10B, some alternative implementations of each of these examples may include three or more different layer thicknesses. According to some of these implementations, one or more layers in the ultrasound sensor system may have a first to an Nth thickness in the first to Nth regions of the ultrasound sensor system. Each of these thicknesses may correspond to a different peak frequency of the corresponding region of the ultrasound sensor system.

[0120] Figure 8A illustrates an implementation where the TFT layer has two different thicknesses. The TFT layer 102 is thicker in the low-frequency region 405 of the device 100 and thinner in the high-frequency region 410 of the device 100. In some examples, the thickness in the low-frequency region 405 can be between 250 micrometers and 1000 micrometers. In some such implementations, the thickness in the high-frequency region 410 can be between 50 micrometers and 250 micrometers. In some implementations, the TFT layer 102 can be deposited at the thickness shown in the low-frequency region 405, and then the TFT layer 102 can be etched to the desired thickness in the high-frequency region 410. In some examples, the adhesion layer 201 can be conformally deposited on the TFT layer 102.

[0121] Figure 8B illustrates an implementation where the conductive layer adjacent to the ultrasonic transceiver layer has two different thicknesses. The conductive layer 203 is thicker in the low-frequency region 405 of the device 100 and thinner in the high-frequency region 410 of the device 100. According to some implementations, the conductive layer 203 may have a thickness ranging from 10 micrometers to 100 micrometers. In some implementations, the conductive layer 203 may be a conductive ink, such as silver ink. According to some such implementations, only the first layer (“Layer 1”) is deposited in the high-frequency region 410, while both the first and second layers (“Layer 2”) are deposited in the low-frequency region 405. In some examples, an epoxy film 205 may be conformally deposited on the conductive layer 203, and a high-impedance layer 105 may be conformally deposited on the epoxy film 205.

[0122] Figure 9A illustrates an implementation where the ultrasonic transceiver layer has two different thicknesses. The ultrasonic transceiver layer 101 is thicker in the low-frequency region 405 and thinner in the high-frequency region 410. In some implementations, the ultrasonic transceiver layer 101 may have a thickness ranging from 4 micrometers to 50 micrometers. According to some implementations, the thickness in the low-frequency region 405 may be between 20 micrometers and 50 micrometers. In some such implementations, the thickness in the high-frequency region 410 may be between 4 micrometers and 20 micrometers. In some implementations, the ultrasonic transceiver layer 101 may be a piezoelectric copolymer. According to some such implementations, only the first layer is deposited in the high-frequency region 410, while both the first and second layers are deposited in the low-frequency region 405. In an alternative implementation, the piezoelectric copolymer may be deposited at the thickness shown in the low-frequency region 405, and the piezoelectric copolymer in the high-frequency region 410 may be etched or dissolved to the desired thickness.

[0123] Figure 9B illustrates an implementation where the high-resistivity layer has two different thicknesses. The high-resistivity layer 105 is thicker in the low-frequency region 405 of the device 100 and thinner in the high-frequency region 410 of the device 100. In some implementations, the high-resistivity layer 105 may have a thickness ranging from 10 micrometers to 100 micrometers. In some implementations, the high-resistivity layer 105 may be a high-resistivity ink. According to some of these implementations, only the first layer (“Layer 1”) is deposited in the high-frequency region 410, while both the first and second layers (“Layer 2”) are deposited in the low-frequency region 405.

[0124] Figure 10A illustrates an implementation where the backing layer has two different thicknesses. The backing layer 505 is thicker in the low-frequency region 405 of device 100 and thinner in the high-frequency region 410 of device 100. In some implementations, the backing layer 505 may have a thickness ranging from 5 micrometers to 200 micrometers. In some implementations, the backing layer 505 may be a high-resistivity metal, such as copper or tungsten. According to some such implementations, only the first layer (“Layer 1”) is deposited in the high-frequency region 410, while both the first and second layers (“Layer 2”) are deposited in the low-frequency region 405. In other examples, the backing layer 505 may be deposited at the thickness shown in the low-frequency region 405, and the portion of the backing layer 505 residing in the high-frequency region 410 may be etched to the desired thickness.

[0125] Figure 10B illustrates an implementation where the epoxy film has two different thicknesses. The epoxy film 205 is thicker in the low-frequency region 405 and thinner in the high-frequency region 410. In some implementations, the epoxy film 205 may have a thickness ranging from 5 micrometers to 200 micrometers. In some implementations, only the first layer is deposited in the high-frequency region 410, while both the first and second layers are deposited in the low-frequency region 405.

[0126] Figure 11 is a flowchart providing examples of operation according to some of the disclosed methods. For example, the blocks in Figure 11 can be executed by the device 100 of Figure 2 or a similar device including a frequency splitting layer. As with other methods disclosed herein, the methods outlined in Figure 11 may include more or fewer blocks than indicated. Furthermore, the blocks of the methods disclosed herein are not necessarily executed in the indicated order. In some instances, one or more blocks may be executed in parallel.

[0127] In this example, block 1103 relates to controlling the ultrasonic transceiver layer to emit ultrasonic waves. According to this implementation, a first portion of the ultrasonic wave is emitted in a first direction through a thin-film transistor (TFT) layer. Here, the first portion of the ultrasonic wave corresponds to a first peak frequency. In some examples, the first peak frequency can be in the range of 10 MHz to 20 MHz. However, in other examples, the first peak frequency can include frequencies higher than 20 MHz and / or lower than 10 MHz. In this example, a second portion of the ultrasonic wave is emitted in a second direction through a frequency splitting layer to reach a high-impedance layer. In this implementation, the frequency splitting layer and the high-impedance layer are configured such that the reflected second portion of the ultrasonic wave includes a second peak frequency lower than the first peak frequency. In some examples, the second peak frequency can be in the range of 1 MHz to 10 MHz. In some implementations, the second frequency can be in the range of 2 MHz to 7 MHz.

[0128] According to this implementation, block 1105 relates to receiving from the ultrasonic transceiver layer a first signal corresponding to the reflection of a first portion of an ultrasonic wave from a surface of a portion of a target object located on the outer surface of a device including the ultrasonic sensor system. If the target object is a finger, the first signal may correspond to the reflection of the first portion of the ultrasonic wave from the surface of the finger.

[0129] In this example, block 1110 relates to receiving a second signal from the ultrasonic transceiver layer corresponding to the reflection of a second portion of the ultrasonic wave from the interior of that portion of the target object. According to this implementation, block 1115 relates to performing an authentication procedure at least in part based on the first and second signals.

[0130] According to some implementations, method 1100 may involve obtaining fingerprint data based on a portion of a first signal received within a time interval corresponding to a fingerprint. This time interval may be measured, for example, relative to the time when the first ultrasound wave was emitted. Obtaining the fingerprint data may, for example, involve extracting a first target object feature from the first signal via a control system. The first target object feature may, for example, include fingerprint features. According to some examples, fingerprint features may include fingerprint details, key points, and / or sweat pores. In some examples, fingerprint features may include ridge termination information, ridge bifurcation information, short ridge information, ridge flow information, island information, branch information, triangle information, core information, etc.

[0131] In some examples, block 1115 may involve comparing the fingerprint feature with the fingerprint feature of an authorized user. For example, the fingerprint feature of an authorized user may have already been received during a previous registration process.

[0132] In some implementations, the method may involve extracting subcutaneous features from a second signal. For example, the subcutaneous features of an authorized user may have already been received during a previous registration process. According to some implementations, the authentication process may involve comparing the subcutaneous features extracted from the second signal with the subcutaneous features of the authorized user.

[0133] In some such implementations, subepidermal features may include subepidermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object within a time interval, corresponding to a subepidermal region. For example, subepidermal features may include dermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object. The dermal information corresponding to the dermis may have already been obtained within a time interval. The authentication process may be based at least in part on the dermal information. Alternatively or additionally, subepidermal features may include information about other subepidermal layers, such as those described above with reference to Figures 1A and 2. According to some implementations, the authentication process may be based at least in part on both the first and second signals.

[0134] In some implementations, method 1100 may involve controlling access to the device or another device based at least in part on the authentication procedure.

[0135] Figure 12 is another flowchart providing an example of operation according to some of the disclosed methods. The blocks of Figure 12 can be executed, for example, by the device 100 of Figure 4 or by a similar device such as those shown in Figures 5 through 10B that does not include a frequency splitting layer. However, the blocks of Figure 12 can also be executed by the device 100 of Figure 2 or a similar device including a frequency splitting layer. As with other methods disclosed herein, the methods outlined in Figure 12 may include more or fewer blocks than indicated. Furthermore, the blocks of the methods disclosed herein are not necessarily executed in the indicated order. In some instances, one or more blocks may be executed in parallel.

[0136] In this example, block 1203 relates to controlling the ultrasonic transceiver layer to emit ultrasonic waves. According to this implementation, a first portion of the ultrasonic wave is emitted through a thin-film transistor (TFT) layer in a first direction. Here, the first portion of the ultrasonic wave corresponds to a first peak frequency. In some examples, the first peak frequency can be in the range of 10 MHz to 20 MHz. However, in other examples, the first peak frequency can include frequencies higher than 20 MHz and / or lower than 10 MHz. In this example, a second portion of the ultrasonic wave is emitted to a high-impedance layer in a second direction. In this implementation, the high-impedance layer and one or more layers between the high-impedance layer and the ultrasonic transceiver layer are configured such that the reflected second portion of the ultrasonic wave includes a second peak frequency lower than the first peak frequency. In some examples, the second peak frequency can be in the range of 1 MHz to 10 MHz. In some implementations, the second frequency can be in the range of 2 MHz to 7 MHz.

[0137] According to this implementation, block 1205 relates to receiving from the ultrasonic transceiver layer a first signal corresponding to the reflection of a first portion of an ultrasonic wave from a surface of a portion of a target object located on the outer surface of a device including the ultrasonic sensor system. If the target object is a finger, the first signal may correspond to the reflection of the first portion of the ultrasonic wave from the surface of the finger.

[0138] In this example, block 1210 relates to receiving a second signal from the ultrasonic transceiver layer corresponding to the reflection of a second portion of the ultrasonic wave from the interior of that portion of the target object. According to this implementation, block 1215 relates to performing an authentication procedure at least in part based on the first and second signals. In some implementations, method 1200 may relate to controlling access to the device or to another device, at least in part based on this authentication procedure.

[0139] According to some implementations, method 1200 may involve obtaining fingerprint data based on a portion of a first signal received within a time interval corresponding to a fingerprint. This time interval may be measured, for example, relative to the time when the first ultrasound wave was emitted. Obtaining the fingerprint data may, for example, involve extracting a first target object feature from the first signal via a control system. The first target object feature may, for example, include fingerprint features. According to some examples, fingerprint features may include fingerprint details, key points, and / or sweat pores. In some examples, fingerprint features may include ridge termination information, ridge bifurcation information, short ridge information, ridge flow information, island information, branch information, triangle information, core information, etc.

[0140] In some examples, block 1215 may involve comparing the fingerprint feature with the fingerprint feature of an authorized user. For example, the fingerprint feature of an authorized user may have already been received during a previous registration process.

[0141] In some implementations, the method may involve extracting subcutaneous features from a second signal. For example, the subcutaneous features of an authorized user may have already been received during a previous registration process. According to some implementations, the authentication process may involve comparing the subcutaneous features extracted from the second signal with the subcutaneous features of the authorized user.

[0142] In some such implementations, subepidermal features may include subepidermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object within a time interval, corresponding to a subepidermal region. For example, subepidermal features may include dermal information corresponding to the reflection of a second ultrasound wave received from that portion of the target object. The dermal information corresponding to the dermis may have already been obtained within a time interval. The authentication process may be based at least in part on the dermal information. Alternatively or additionally, subepidermal features may include information about other subepidermal layers, such as those described above with reference to Figures 1A and 2. According to some implementations, the authentication process may be based at least in part on both the first and second signals.

[0143] Figure 13 typically depicts various aspects of a 4×4 pixel array of sensor pixels for an ultrasonic sensor system. Each pixel 1334 may be associated, for example, with a local region of piezoelectric sensing material (PSM), a peak detection diode (D1), and a readout transistor (M3); many or all of these elements may be formed on or in a substrate to form pixel circuitry 1336. In practice, the local region of the piezoelectric sensing material of each pixel 1334 can convert the received ultrasonic energy into electrical charge. The peak detection diode D1 can record the maximum amount of charge detected by the local region of the piezoelectric sensing material PSM. Each column of the pixel array 1335 can then be scanned, for example, via a column selection mechanism, a gate driver, or a shift register, and the readout transistor M3 of each column can be triggered to allow the amplitude of the peak charge of each pixel 1334 to be read by additional circuitry (e.g., a multiplexer and an A / D converter). The pixel circuit 1336 may include one or more TFTs to allow gating, addressing and resetting of the pixel 1334.

[0144] Each pixel circuit 1336 provides information about a small portion of the object detected by the ultrasonic sensor system. Although the example shown in Figure 13 has a relatively coarse resolution for ease of explanation, ultrasonic sensors with resolutions on the order of 500 pixels per inch or higher can be configured with appropriately scaled structures. The detection area of ​​the ultrasonic sensor system can be selected depending on the object to be detected. For example, the detection area can range from approximately 5 mm x 5 mm for a single finger to approximately 3 inches x 3 inches for four fingers. Smaller and larger areas (including square, rectangular, and non-rectangular geometries) can be appropriately used for target objects.

[0145] As used in this article, the phrase “at least one” referring to a list of items means any combination of those items, including a single member. As an example, “at least one of a, b, or c” is intended to cover: a, b, c, ab, ac, bc, and abc.

[0146] The various explanatory logics, logic blocks, modules, circuits, and algorithms described in conjunction with the implementations disclosed herein can be implemented as electronic hardware, computer software, or a combination of both. This interchangeability between hardware and software has been generally described in terms of its functionality and is illustrated in the various explanatory components, blocks, modules, circuits, and programs described above. Whether such functionality is implemented in hardware or software depends on the specific application and the design constraints imposed on the overall system.

[0147] Hardware and data processing devices for implementing the various descriptive logics, logic blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented or executed using general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or any combination thereof. A general-purpose processor may be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors cooperating with a DSP core, or any other such configuration. In some implementations, specific programs and methods may be executed by a circuit system dedicated to a given function.

[0148] In one or more aspects, the described functionality may be implemented in hardware, digital electronic circuitry, computer software, firmware (including the structures disclosed herein and their structural equivalents), or any combination thereof. Implementation of the subject matter described herein may also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a computer storage medium for execution by a data processing device or for controlling the operation of a data processing device.

[0149] If implemented in software, the functions can be stored or transmitted as one or more instructions or codes on or via a computer-readable medium (such as a non-transitory medium). Programs of methods or algorithms disclosed herein can be implemented in processor-executable software modules that can reside on a computer-readable medium. Computer-readable media includes both computer storage media and communication media, including any media that can be implemented to transfer a computer program from one location to another. Storage media can be any available media accessible to a computer. By way of example, but not limitation, non-transitory media can include RAM, ROM, EEPROM, CD-ROM or other optical disc storage, magnetic disk storage or other magnetic storage devices, or any other media that can be used to store desired program code in the form of instructions or data structures and is accessible to a computer. Furthermore, any connection can also be appropriately referred to as computer-readable media. As used herein, "disk" and "disc" include CDs, laser discs, optical discs, DVDs, floppy disks, and Blu-ray discs, where a disk typically reproduces data magnetically and a disc optically using a laser. Combinations of these should also be included within the scope of computer-readable media. Furthermore, the operation of a method or algorithm may reside as one of codes and instructions, or any combination or set of codes and instructions, on machine-readable and computer-readable media that can be incorporated into a computer program product.

[0150] Various modifications to the implementations described in this disclosure may be apparent to those skilled in the art, and the general principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not intended to be limited to the implementations shown herein, but should be granted the broadest scope consistent with the claims, the principles and novel features disclosed herein. The term “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as superior to or better than other implementations.

[0151] Some features described in this specification in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented separately or in any suitable sub-combination in multiple implementations. Furthermore, although features may be described above as operating in certain combinations and even initially claimed in this way, one or more features from the claimed combination may be removed from that combination in some cases, and the claimed combination may be for sub-combinations or variations thereof.

[0152] Similarly, although the operations are depicted in a specific order in the diagrams, this should not be construed as requiring such operations to be performed in the indicated specific order or sequential order, or requiring the execution of all described operations to achieve the desired result. In some environments, multitasking and parallel processing may be advantageous. Furthermore, the separation of the various system components in the implementation described above should not be construed as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations also fall within the scope of the appended claims. In some cases, the actions described in the claims can be performed in a different order and still achieve the desired result.

[0153] It will be understood that, unless features in any particular described implementation are explicitly identified as incompatible with each other, or the surrounding context suggests that they are mutually exclusive and not readily combinable in a complementary and / or supporting sense, this disclosure generally 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. Therefore, it will be further appreciated that the above description is given by way of example only and may be modified in detail within the scope of this disclosure.

[0154] 100: Device 101: Ultrasonic transceiver layer 102: Thin Film Transistor (TFT) Layer 103: Frequency Splitting Layer 105: High-resistivity layer 107: Interface System 109: Control System 111: Monitor 113: Light source system 201: Adhesive layer 203: Conductive layer 205: Epoxy Resin Film 207: Target object 213: The first part of ultrasound 214: Arrow 215: The second part of the reflected ultrasound waves 216: Part Two of Ultrasound 217: Reflection of the second part of the ultrasound wave 405: Low-frequency region 410: High-frequency region 505: Backing layer 701: Cover glass 705: Light 710: Photoacoustic emission 1100: Method 1103: Steps 1105: Steps 1110: Steps 1115: Steps 1200: Method 1203: Steps 1205: Steps 1210: Steps 1215: Steps 1334: pixels 1335: pixel array 1336: Pixel Circuit

Claims

1. An ultrasonic sensor device for acquiring fingerprint data and subepidermal information, comprising: An ultrasonic sensor system includes: an ultrasonic transceiver layer; a thin-film transistor (TFT) layer coupled to a first side of the ultrasonic transceiver layer; and a high-impedance layer extending across a second side of the ultrasonic transceiver layer, wherein the high-impedance layer has a higher acoustic impedance than an adjacent layer coupled between the high-impedance layer and the ultrasonic transceiver layer, and wherein the first region corresponds to a low-frequency region of the ultrasonic sensor system, wherein the high-impedance layer does not extend across the second region of the ultrasonic transceiver layer, and wherein the second region corresponds to a high-frequency region of the ultrasonic sensor system.

2. The apparatus of claim 1, wherein the TFT layer has a first thickness in a first region of the ultrasonic sensor system, and wherein the TFT layer has a second thickness in a second region of the ultrasonic sensor system, the second region corresponding to the high-frequency region.

3. The apparatus of claim 1, wherein the TFT layer has a thickness in the range of 50 to 1000 micrometers.

4. The apparatus of claim 1, wherein the ultrasonic transceiver layer has a first thickness in the low-frequency region and a second thickness in the high-frequency region.

5. The apparatus of claim 1, wherein the ultrasonic transceiver layer has a first to Nth thickness in a first to Nth region of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

6. The apparatus of claim 1, further comprising an adhesive layer residing between the ultrasonic transceiver layer and the high impedance layer, wherein the adhesive layer has a first thickness in the low-frequency region and a second thickness in the high-frequency region.

7. The apparatus of claim 6, wherein the adhesive layer has a first to Nth thickness in a first to Nth region of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

8. The apparatus of claim 1, wherein the high-resistivity layer comprises high-resistivity ink.

9. The apparatus as claimed in claim 8, wherein the high-resistivity ink serves as both an acoustic layer and a conductive layer.

10. The apparatus of claim 1, further comprising a backing layer, wherein the high-impedance layer resides between the backing layer and the ultrasonic transceiver layer.

11. The apparatus of claim 10, wherein the backing layer has a first thickness in the low-frequency region and a second thickness in the high-frequency region.

12. The apparatus of claim 11, wherein the backing layer has a first to Nth thickness in a first to Nth region of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

13. The apparatus of claim 10, wherein the high-impedance layer has a higher acoustic impedance than the backing layer.

14. The apparatus of claim 10, further comprising a conductive layer residing between a first region on a second side of the high-impedance layer and the ultrasonic transceiver layer.

15. The apparatus of claim 1, further comprising a conductive layer residing between the ultrasonic transceiver layer and the high-impedance layer, wherein the conductive layer has a first thickness in the low-frequency region of the ultrasonic sensor system, and wherein the conductive layer has a second thickness in the high-frequency region of the ultrasonic sensor system.

16. The apparatus of claim 15, wherein the conductive layer has a first to Nth thickness in a first to Nth region of the ultrasonic sensor system, each of the first to Nth regions corresponding to one of the first to Nth peak frequencies.

17. The apparatus of claim 1, wherein the high-impedance layer is adjacent to a first region on the second side of the ultrasonic transceiver layer.

18. The apparatus of claim 1, further comprising a light source system configured to induce photoacoustic emission in a target object.

19. The apparatus of claim 1, further comprising a display stack adjacent to the TFT layer, wherein the TFT layer resides between the ultrasonic transceiver layer and the display stack.

20. The apparatus of claim 1, further comprising a control system configured to: control the ultrasonic transceiver layer to emit ultrasonic waves, a first portion of which is emitted through the TFT layer in a first direction, the first portion of which includes a first peak frequency; and receive from the ultrasonic transceiver layer a first signal corresponding to reflection of the first portion of the ultrasonic waves from a surface of a portion of a target object located on an outer surface of the apparatus.

21. The apparatus of claim 20, wherein the control system is configured to perform an authentication procedure at least in part based on the first signal.

22. The apparatus of claim 20, wherein the control system is configured to obtain fingerprint data based on a portion of the first signal received within a time interval that corresponds to a fingerprint.

23. The apparatus of claim 20, wherein the second portion of the ultrasound is emitted toward the high-impedance layer in a second direction, and wherein the high-impedance layer and one or more layers between the high-impedance layer and the ultrasound transceiver layer are configured such that the reflected second portion of the ultrasound includes a second peak frequency lower than the first peak frequency.

24. The apparatus of claim 20, wherein the control system is configured to: receive from the ultrasonic transceiver layer a second signal corresponding to the reflection of the second portion of the ultrasonic wave from the interior of the portion of the target object; and perform an authentication procedure at least in part based on the second signal.

25. The apparatus of claim 24, wherein the second signal includes subepidermal information corresponding to the reflection of a second ultrasound wave received from the portion of the target object within a time interval, corresponding to a subepidermal region.

26. The device as claimed in claim 1, wherein the device resides within a mobile device.

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