Ultrasonic fingerprint sensor with low-frequency vibration source

Abstract

An apparatus may include an ultrasonic sensor system, a low-frequency vibration source, and a control system. The ultrasonic sensor system may include an ultrasonic receiver and an ultrasonic transmitter, wherein the ultrasonic receiver and the ultrasonic transmitter are configured to transmit ultrasonic waves in a first frequency range (e.g., 1 MHz to 30 MHz). The low-frequency vibration source may be configured to generate low-frequency vibrations in a second frequency range (e.g., 5 Hz to 2000 Hz). The control system may be configured to synchronize the generation of the first low-frequency vibrations with the transmission of the first ultrasonic waves.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 896,520, filed on September 5, 2019, entitled “ULTRASONIC FINGERPRINT SENSOR WITH LOW-FREQUENCY VIBRATION SOURCE,” which is incorporated herein by reference. This application also claims priority to U.S. Patent Application No. 16 / 751,820, filed on January 24, 2020, entitled “ULTRASONIC FINGERPRINT SENSOR WITH LOW-FREQUENCY VIBRATION SOURCE,” and U.S. Patent Application No. 16 / 751,849, filed on January 24, 2020, entitled “ULTRASONIC FINGERPRINT SENSOR WITH LOW-FREQUENCY VIBRATION SOURCE,” both of which are incorporated herein by reference for all purposes. Technical Field

[0003] The present disclosure generally relates to ultrasonic sensor systems and methods of using such systems. Background Art

[0004] Ultrasonic fingerprint sensors have been included in devices such as smartphones, cash machines, and cars for user authentication. Although some existing ultrasonic fingerprint sensors can provide satisfactory performance, improved ultrasonic fingerprint sensors are desired. Summary of the Invention

[0005] The systems, methods and devices of the present disclosure each have several innovative aspects, no single aspect of which is solely responsible for the desirable attributes disclosed herein.

[0006] One innovative aspect of the subject matter described in this disclosure can be implemented in a device. The device can include an ultrasonic sensor system and a control system configured to communicate with the ultrasonic sensor system. In some examples, at least a portion of the control system can be coupled to the ultrasonic sensor system. In some embodiments, a mobile device can be or include the device. For example, a mobile device can include the device disclosed herein. In some examples, the device can include a pressure plate.

[0007] According to some examples, an ultrasonic sensor system includes an ultrasonic receiver and an ultrasonic transmitter, each configured to transmit ultrasonic waves in the range of 1 MHz to 30 MHz. In some examples, the ultrasonic transceiver layer may include an ultrasonic transmitter and an ultrasonic receiver. The ultrasonic transmitter disclosed herein may be referred to as a "transmitting component" or a "component for transmitting ultrasonic waves." The ultrasonic receiver disclosed herein may be referred to as a "receiving component" or a "component for receiving ultrasonic waves."

[0008] In some embodiments, the apparatus includes a low-frequency vibration source. According to some examples, the ultrasonic sensor system can be configured to function as a low-frequency vibration source. A single device can include a low-frequency vibration source and an ultrasonic transmitter. However, in some instances, the low-frequency vibration source can be a separate device, such as a tactile device or a speaker. In some embodiments, the low-frequency vibration source can be configured to generate low-frequency vibrations in the range of 5 Hz to 2000 Hz. In some examples, the low-frequency vibration source can be or can include a piezoelectric actuator, an eccentric rotating mass, and / or a linear resonant actuator. The low-frequency vibration source disclosed herein can be referred to as a "generating component" or a "component for generating low-frequency vibrations."

[0009] 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 a combination thereof. According to some examples, the control system may be configured to control the ultrasonic transmitter for transmitting the first ultrasonic wave and to control the low-frequency vibration source for generating the first low-frequency vibration. The control system disclosed herein or a portion thereof may be referred to as a "control component."

[0010] In some embodiments, the control system can be configured to synchronize the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave. In some embodiments, synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave can involve controlling the low-frequency vibration source for generation of the first low-frequency vibration during a first time interval, and controlling the ultrasonic transmitter for transmission of the first ultrasonic wave during a second time interval, the second time interval being subsequent to the first time interval. However, in some embodiments, synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave can involve controlling the low-frequency vibration source for generation of the first low-frequency vibration during the first time interval, and controlling the ultrasonic transmitter for transmission of the first ultrasonic wave during the second time interval, the second time interval at least partially coinciding with the first time interval.

[0011] According to some examples, the control system can be configured to receive an ultrasonic receiver signal from an ultrasonic receiver. The ultrasonic receiver signal can include a signal corresponding to a reflection of a first ultrasonic wave from a target object in contact with an external surface of the device. In some such examples, the control system can be configured to perform an authentication process based at least in part on the ultrasonic receiver signal. Depending on the specific embodiment, the external surface can be a pressure plate, a display cover glass, etc.

[0012] In some examples, the control system can be configured to cause the low-frequency vibration source to generate a first low-frequency vibration in the plane of the outer surface. Alternatively or additionally, the control system can be configured to cause the low-frequency vibration source to generate a first low-frequency vibration perpendicular to the plane of the outer surface.

[0013] In some examples, the low-frequency vibration source can be configured to cause local low-frequency vibrations of only a portion of the device. In other embodiments, the low-frequency vibration source can be configured to cause global low-frequency vibrations of the entire device or substantially the entire device. In some examples, the control system can be configured to control the low-frequency vibration source to generate a single frequency. In other examples, the control system can be configured to control the low-frequency vibration source to generate multiple frequencies. In some instances, the control system can be configured to control the low-frequency vibration source to generate the low-frequency vibration continuously, for example, during a time interval. In other examples, the control system can be configured to control the low-frequency vibration source to generate the low-frequency vibration intermittently, for example, during a time interval.

[0014] In some embodiments, the control system may be configured to extract features from the ultrasonic receiver signal. The authentication process may be based at least in part on the features. In some examples, the control system may be configured to detect background noise in the ultrasonic receiver signal based at least in part on the first low-frequency vibration. In some examples, the control system may be configured to determine at least one feature quality metric. According to some such examples, the control system may be configured to use the feature quality metric as a feedback signal for a low-frequency vibration source and control the low-frequency vibration source based at least in part on the feedback signal. In some instances, the control system may be configured to determine whether the at least one feature quality metric is below a feature quality metric threshold, and if it is determined that the at least one feature quality metric is below the feature quality metric threshold, control the low-frequency vibration source to generate a second low-frequency vibration having an amplitude greater than the amplitude of the first low-frequency vibration.

[0015] As described above, in some embodiments, synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave may involve controlling a low-frequency vibration source for generation of the first low-frequency vibration during a first time interval, and controlling an ultrasonic transmitter for transmission of the first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval. Some such embodiments may involve detecting background noise in an ultrasonic receiver signal based at least in part on the first low-frequency vibration.

[0016] According to some examples, the control system may be configured to control the ultrasonic transmitter by controlling multiple instances of ultrasonic transmission during a first time interval. In some such examples, the control system may be further configured to capture multiple sets of fingerprint image data via the ultrasonic receiver during the first time interval. Each set of fingerprint image data may correspond to a reflection of an ultrasonic wave transmitted during a different instance of ultrasonic transmission from a target object.

[0017] In some examples, the control system can be further configured to extract fingerprint features from each set of fingerprint image data. In some such examples, the control system can be configured to extract background features from each set of fingerprint image data and distinguish the background features from the fingerprint features.

[0018] According to some embodiments, the control system can be further configured to perform a coherent feature detection method that involves synchronizing the times during which each set of fingerprint image data is captured by the ultrasonic receiver at the period and phase of the low-frequency vibration. In some such embodiments, the control system can be configured to multiply each set of fingerprint image data by a corresponding weighting factor from a plurality of weighting factors to generate a weighted fingerprint image data value. For example, each weighting factor can correspond to the phase of the low-frequency vibration.

[0019] In some such embodiments, the control system can be configured to sum the weighted fingerprint image data values ​​to obtain a plurality of pixel-by-pixel correlations with the low-frequency vibrations. According to some examples, the control system can be configured to determine the absolute value of each pixel-by-pixel correlation, compare each absolute value to a threshold, and generate a binarization mask based on the comparison of each absolute value to the threshold. For example, the binarization mask can indicate edges of one or more of the fingerprint features. In some such examples, the control system can be configured to use the binarization mask to reject one or more of the background features.

[0020] According to some embodiments, the control system can be configured to perform an incoherent feature detection method in which the time during which the fingerprint image is captured is independent of the period and phase of the low frequency vibrations. Various examples are provided herein.

[0021] In some embodiments, the control system can be configured to cause the low-frequency vibration source to generate a first low-frequency vibration in the plane of the outer surface, to generate a first low-frequency vibration perpendicular to the plane of the outer surface, or to generate both a first low-frequency vibration in the plane of the outer surface and a first low-frequency vibration perpendicular to the plane of the outer surface. In some examples, the frequency and / or frequency range of the low-frequency vibration source can be tuned to produce maximum modulation of the fingerprint image feature in response to the low-frequency vibration. In some instances, the control system can be configured to perform high-pass filtering or band-pass filtering on the ultrasonic receiver signal. According to some examples, the control system can be configured to determine a contact quality metric corresponding to at least one of an image quality metric or a feature quality metric, and determine whether to actuate the low-frequency vibration source based at least in part on the contact quality metric.

[0022] Other innovative aspects of the subject matter described in this disclosure may be implemented via one or more methods. Some such methods may be or may include authentication methods. Some methods may involve controlling an ultrasonic transmitter to transmit a first ultrasonic wave, and controlling a low-frequency vibration source to generate the first low-frequency vibration. Such methods may involve synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave. Such methods may involve receiving an ultrasonic receiver signal from an ultrasonic receiver. The ultrasonic receiver signal may include a signal corresponding to a reflection of the first ultrasonic wave from a target object in contact with an outer surface of the device. Such methods may involve performing an authentication process based at least in part on the ultrasonic receiver signal.

[0023] According to some examples, synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave may include controlling the low-frequency vibration source for the generation of the first low-frequency vibration during a first time interval, and controlling the ultrasonic transmitter for the transmission of the first ultrasonic wave during a second time interval, the second time interval being after the first time interval.

[0024] However, in some embodiments, synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave may involve controlling the low-frequency vibration source for generation of the first low-frequency vibration during a first time interval, and controlling the ultrasonic transmitter for transmission of the first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval. Some such embodiments may involve detecting background noise in the ultrasonic receiver signal based at least in part on the first low-frequency vibration.

[0025] In some examples, controlling the low-frequency vibration source may involve causing at least one of localized low-frequency vibrations in only a portion of the device or global low-frequency vibrations in the entire device. In some embodiments, controlling the low-frequency vibration source and controlling the ultrasonic transmitter may involve controlling a single device, while in other embodiments, controlling the low-frequency vibration source and controlling the ultrasonic transmitter may involve controlling more than one device. In some embodiments, controlling the low-frequency vibration source may involve causing the low-frequency vibration source to generate a first low-frequency vibration in the plane of the outer surface and / or a first low-frequency vibration perpendicular to the plane of the outer surface. In some embodiments, controlling the low-frequency vibration source may involve causing the low-frequency vibration source to generate at least one of a single frequency or a plurality of frequencies. In some embodiments, controlling the low-frequency vibration source may involve causing the low-frequency vibration source to generate the low-frequency vibration intermittently or continuously.

[0026] Some methods may involve determining at least one characteristic quality metric. Some such methods may involve using the characteristic quality metric as a feedback signal for a low-frequency vibration source and controlling the low-frequency vibration source based at least in part on the feedback signal. Some such methods may involve determining whether the at least one characteristic quality metric is below a characteristic quality metric threshold, and if it is determined that the at least one characteristic quality metric is below the characteristic quality metric threshold, controlling the low-frequency vibration source to generate a second low-frequency vibration having an amplitude greater than an amplitude of the first low-frequency vibration.

[0027] As described above, some methods involve controlling a low-frequency vibration source for generation of a first low-frequency vibration during a first time interval, and controlling an ultrasonic transmitter for transmission of a first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval. Some such methods may involve controlling the ultrasonic transmitter for multiple instances of ultrasonic wave transmission during the first time interval.

[0028] Some such embodiments may involve capturing multiple sets of fingerprint image data via an ultrasonic receiver during a first time interval. In some instances, each set of fingerprint image data may correspond to reflections of ultrasonic waves transmitted from a target object during different instances of ultrasonic wave transmission. Some such methods may involve extracting background features from each set of fingerprint image data and distinguishing the background features from fingerprint features.

[0029] Some methods may involve performing a coherent feature detection method that involves synchronizing the times during which each set of fingerprint image data is captured by an ultrasonic receiver at a period and phase of a low-frequency vibration. Some such methods may involve multiplying each set of fingerprint image data by a corresponding weighting factor from a plurality of weighting factors to generate a weighted fingerprint image data value. In some examples, each weighting factor from the plurality of weighting factors may correspond to a phase of the low-frequency vibration.

[0030] Some such methods may involve summing weighted fingerprint image data values ​​to obtain a plurality of pixel-by-pixel correlations with low-frequency vibrations. Some such methods may involve determining an absolute value of each pixel-by-pixel correlation, comparing each absolute value to a threshold, and generating a binarization mask based on the comparison of each absolute value to the threshold. For example, the binarization mask may indicate edges of one or more of the fingerprint features.

[0031] Some methods may involve performing an incoherent feature detection method in which the time during which the fingerprint image is captured is independent of the period and phase of the low frequency vibrations.Various examples are disclosed herein.

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

[0033] For example, the software may include instructions for controlling one or more devices to perform one or more methods. According to some examples, the methods may correspond to the control system functionality disclosed herein. Some such methods may be or may include authentication methods. Some methods may involve controlling an ultrasonic transmitter to transmit a first ultrasonic wave, and controlling a low-frequency vibration source for generating the first low-frequency vibration. Such methods may involve synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave. Such methods may involve receiving an ultrasonic receiver signal from an ultrasonic receiver. The ultrasonic receiver signal may include a signal corresponding to a reflection of the first ultrasonic wave from a target object in contact with an outer surface of the device. Such methods may involve performing an authentication process based at least in part on the ultrasonic receiver signal.

[0034] According to some examples, synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave may include controlling the low-frequency vibration source for the first low-frequency vibration during a first time interval, and controlling the ultrasonic transmitter for the transmission of the first ultrasonic wave during a second time interval, the second time interval being after the first time interval.

[0035] However, in some embodiments, synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave may involve controlling the low-frequency vibration source for generation of the first low-frequency vibration during a first time interval, and controlling the ultrasonic transmitter for transmission of the first ultrasonic wave during a second time interval. Some such embodiments may involve detecting background noise in the ultrasonic receiver signal based at least in part on the first low-frequency vibration.

[0036] In some examples, controlling the low-frequency vibration source may involve causing at least one of localized low-frequency vibrations in only a portion of the device or global low-frequency vibrations in the entire device. In some embodiments, controlling the low-frequency vibration source and controlling the ultrasonic transmitter may involve controlling a single device, while in other embodiments, controlling the low-frequency vibration source and controlling the ultrasonic transmitter may involve controlling more than one device. In some embodiments, controlling the low-frequency vibration source may involve causing the low-frequency vibration source to generate a first low-frequency vibration in the plane of the outer surface and / or to generate a first low-frequency vibration perpendicular to the plane of the outer surface. In some embodiments, controlling the low-frequency vibration source may involve causing the low-frequency vibration source to generate at least one of a single frequency or a plurality of frequencies. In some embodiments, controlling the low-frequency vibration source may involve causing the low-frequency vibration source to generate the low-frequency vibration intermittently or continuously.

[0037] Some methods may involve determining at least one characteristic quality metric. Some such methods may involve using the characteristic quality metric as a feedback signal for a low-frequency vibration source and controlling the low-frequency vibration source based at least in part on the feedback signal. Some such methods may involve determining whether the at least one characteristic quality metric is below a characteristic quality metric threshold, and if it is determined that the at least one characteristic quality metric is below the characteristic quality metric threshold, controlling the low-frequency vibration source to generate a second low-frequency vibration having an amplitude greater than an amplitude of the first low-frequency vibration.

[0038] As described above, some methods involve controlling a low-frequency vibration source for generation of a first low-frequency vibration during a first time interval, and controlling an ultrasonic transmitter for transmission of a first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval. Some such methods may involve controlling the ultrasonic transmitter for multiple instances of ultrasonic wave transmission during the first time interval.

[0039] Some such embodiments may involve capturing, via an ultrasonic receiver, a plurality of sets of fingerprint image data during a first time interval. In some instances, each set of fingerprint image data may correspond to reflections of ultrasonic waves transmitted during different instances of ultrasonic transmission from a target object. Some such methods may involve extracting background features from each set of fingerprint image data and distinguishing the background features from fingerprint features.

[0040] Some methods may involve performing a coherent feature detection method that involves synchronizing the times during which each set of fingerprint image data is captured by an ultrasonic receiver at a period and phase of a low-frequency vibration. Some such methods may involve multiplying each set of fingerprint image data by a corresponding weighting factor from a plurality of weighting factors to generate a weighted fingerprint image data value. In some examples, each weighting factor from the plurality of weighting factors may correspond to a phase of the low-frequency vibration.

[0041] Some such methods may involve summing weighted fingerprint image data values ​​to obtain a plurality of pixel-by-pixel correlations with low-frequency vibrations. Some such methods may involve determining an absolute value of each pixel-by-pixel correlation, comparing each absolute value to a threshold, and generating a binarization mask based on the comparison of each absolute value to the threshold. For example, the binarization mask may indicate edges of one or more of the fingerprint features.

[0042] Some methods may involve performing an incoherent feature detection method in which the time during which the fingerprint image is captured is independent of the period and phase of the low frequency vibrations.Various examples are disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the following description. Additional features, aspects, and advantages will become apparent from the description, drawings, and claims. It should be noted that the relative dimensions of the following figures may not be drawn to scale. Identical reference numerals and names in different figures indicate identical elements.

[0044] Figure 1 is a block diagram illustrating example components of an apparatus according to some disclosed embodiments.

[0045] Figure 2 is a flowchart providing example blocks for some of the methods disclosed herein.

[0046] Figure 3 Example components of an apparatus according to some disclosed embodiments are shown.

[0047] Figure 4 An example is shown in which the generation of low-frequency vibrations and the transmission of ultrasonic waves are synchronized.

[0048] Figure 5 An example of a coherent detection method is shown.

[0049] Figure 6 An example of perturbation of fingerprint features within one period of the tactile perturbation signal is shown.

[0050] Figure 7An example of a method for detecting edges of fingerprint features is shown.

[0051] Figure 8 An example of rejecting background features using a binarization mask is shown.

[0052] Figure 9 Another example of rejecting background features using a binarization mask is shown.

[0053] Figure 10 An example of generating enhanced fingerprint image data is provided.

[0054] Figure 11A and Figure 11B Additional examples of perturbations of fingerprint features caused by low-frequency vibrations are provided.

[0055] Figure 12 An example is shown during which the time during which fingerprint image data is captured is independent of the period and phase of the tactile disturbance waveform.

[0056] Figure 13 Another example is shown in which the time during which fingerprint image data is captured is independent of the period and phase of the tactile disturbance waveform.

[0057] Figure 14 is a flow chart providing example blocks for some of the non-coherent detection methods disclosed herein.

[0058] Figure 15 Is provided in the implementation Figure 14 Block 1417 is a flow diagram of an example of a process that may be involved.

[0059] Figure 16 Example components of an apparatus according to one embodiment are shown.

[0060] Figure 17 Example components of an apparatus according to an alternative embodiment are shown.

[0061] Figure 18A is a flowchart providing example blocks for some of the methods disclosed herein.

[0062] Figure 18B is a graph of disturbance versus tactile frequency according to an example.

[0063] Figure 19 is a flowchart providing example blocks of another disclosed method.

[0064] Figure 20 Representatively depicted are aspects of a 4x4 pixel array of sensor pixels for an ultrasound sensor system.

[0065] Figure 21A and Figure 21BAn example arrangement of ultrasound transmitters and receivers in an ultrasound sensor system is shown, wherein other arrangements are also possible.

[0066] Figure 21C An example of an ultrasound transceiver array in an ultrasound sensor system is shown. DETAILED DESCRIPTION

[0067] For the purpose of describing the innovative aspects of the present disclosure, the following description is directed to certain embodiments. However, one of ordinary skill in the art will readily recognize that the teachings herein may be applied in a variety of different ways. The described embodiments may be implemented in any device, apparatus, or system including the biometric system disclosed herein. Furthermore, it is contemplated that the described embodiments may be included in or associated with a variety of electronic devices such as, but not limited to: mobile phones, multimedia internet enabled cellular phones, mobile television receivers, wireless devices, smart phones, smart cards, wearable devices (such as bracelets, armbands, wristbands, rings, headbands, patches, etc.), Bluetooth devices, personal data assistants (PDAs), wireless email receivers, handheld or portable computers, netbooks, notebooks, smart books, tablet computers, printers, copiers, scanners, fax machines, global positioning system (GPS) receivers / navigators, cameras, digital media players (such as MP3 players), portable cameras, game consoles, watches, clocks, calculators, television monitors, flat panel displays, electronic Reading devices (e.g., e-readers), mobile health devices, computer monitors, automotive displays (including odometer and speedometer displays, etc.), cockpit controls and / or displays, camera vision displays (such as the display of a rearview camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, microwave ovens, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable memory chips, washing machines, dryers, washer / dryers, automated teller machines (ATMs), parking meters, packaging (such as in electromechanical systems (EMS) applications, including microelectromechanical systems (MEMS) applications, as well as non-EMS applications), aesthetic structures (such as the display of an image on a piece of jewelry or clothing), and various EMS devices. The teachings herein may also be used in a variety of applications such as, but not limited to, electronic switching devices, radio frequency filters, sensors, accelerometers, gyroscopes, motion sensing devices, magnetometers, inertial components of consumer electronics, parts of consumer electronics, automotive doors, steering wheels or other automotive parts, varactor diodes, liquid crystal devices, electrophoretic devices, drive schemes, manufacturing processes, and electronic test equipment. Therefore, the present teachings are not intended to be limited to only the embodiments depicted in the accompanying drawings, but rather have broad applicability, which will be apparent to one of ordinary skill in the art.

[0068] Poor coupling of the finger to the pressure plate of the ultrasonic fingerprint sensor is a common problem. (As used herein, the term "finger" may refer to any finger, including the thumb.) Poor coupling may occur when the finger is dry and / or low finger pressure is applied. In some embodiments, the device may include an ultrasonic sensor system, a low-frequency vibration source, and a control system. According to some examples, the ultrasonic sensor system may include an ultrasonic receiver and an ultrasonic transmitter, the ultrasonic receiver and ultrasonic transmitter being configured to transmit ultrasonic waves in the range of 1 MHz to 30 MHz. However, other embodiments may be configured to transmit ultrasonic waves in other frequency ranges, such as frequencies below 1 MHz and / or frequencies above 30 MHz. In some embodiments, the low-frequency vibration source may be configured to generate low-frequency vibrations in the range of 5 Hz to 2000 Hz. However, other embodiments may be configured to generate low-frequency vibrations in other frequency ranges, such as frequencies below 5 Hz and / or frequencies above 2000 Hz. In some embodiments, the control system may be configured to synchronize the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave.

[0069] Particular embodiments of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages. Low-frequency vibrations can improve coupling in various ways. For example, low-frequency vibrations may cause a user to press harder on the pressure plate, may cause pores to exude more sweat and / or oil, may spread out oil and / or sweat to better couple the finger to the pressure plate, etc. In some instances, the low-frequency vibrations may "hammer down" the fingerprint ridges. Some embodiments utilize a low-frequency vibration source (such as a tactile device or speaker, such as those found in existing cell phones) to improve the coupling between the finger and the fingerprint sensing system pressure plate.

[0070] Figure 1 is a block diagram illustrating example components of an apparatus according to some disclosed embodiments. In this example, apparatus 101 includes an ultrasonic sensor system 102, a control system 106, and a low-frequency vibration source 110. Some embodiments of apparatus 101 may include an interface system 104.

[0071] In some embodiments, the low-frequency vibration source 110 can be configured to generate low-frequency vibrations in the range of 5 Hz to 2000 Hz. In some examples, the low-frequency vibration source 110 can be or include a piezoelectric actuator, an eccentric rotating mass, and / or a linear resonant actuator. In some embodiments, the low-frequency vibration source 110 can be or include a haptic device or speaker, such as those found in existing mobile phones. In some embodiments, the speaker can be the entire display panel or the housing of the mobile phone.

[0072] In some examples, the low-frequency vibration source can be configured to induce localized low-frequency vibrations in only a portion of the device. For example, the vibrations can be induced by a buzzer integrated into the fingerprint sensor while being physically isolated from the phone housing. In other embodiments, the low-frequency vibration source can be configured to induce global low-frequency vibrations throughout the entire device or substantially the entire device. For example, the vibrations can be induced by a buzzer physically integrated into the phone housing.

[0073] In some examples, the control system can be configured to control the low frequency vibration source to produce a single frequency. In other examples, the control system can be configured to control the low frequency vibration source to produce multiple frequencies, such as to produce a frequency modulated waveform. In one such example, the frequency modulated waveform can be a "linear frequency modulation", which is a signal whose frequency increases (upper linear frequency modulation) or decreases (lower linear frequency modulation) over time. In some such examples, the highest frequency of the linear frequency modulation can be in the kHz range. In some instances, the control system can be configured to control the low frequency vibration source to produce the low frequency vibration continuously, for example, during a time interval. In other examples, the control system can be configured to control the low frequency vibration source to produce the low frequency vibration intermittently, for example, during a time interval. For example, the time interval can be as described below with reference to Figure 4 The time interval 404 is described.

[0074] Although the ultrasonic sensor system 102 and the low frequency vibration source 110 Figure 1 Although shown as separate blocks in FIG, according to some examples, the ultrasonic sensor system 102 can be configured to function as a low-frequency vibration source. In some such examples, a single device can include the low-frequency vibration source 110 and the ultrasonic transmitter 105.

[0075] In some examples, as shown by dashed lines within the ultrasonic sensor system 102, the ultrasonic sensor system 102 can include an ultrasonic receiver 103 and a separate ultrasonic transmitter 105. In some such examples, the ultrasonic transmitter 105 can include an ultrasonic plane wave generator, such as those described below.

[0076] However, various examples of ultrasonic sensor systems 102 are disclosed herein, some of which may include a separate ultrasonic transmitter 105 and some of which may not include a separate ultrasonic transmitter 105. Figure 1Although shown as separate elements, in some embodiments, the ultrasonic receiver 103 and the ultrasonic transmitter 105 can be combined in an ultrasonic transceiver system. For example, in some embodiments, the ultrasonic sensor system 102 can include a piezoelectric receiver layer, such as a polyvinylidene fluoride (PVDF) polymer layer or a polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymer layer. In some embodiments, a single piezoelectric layer can function as both an ultrasonic transmitter. In some embodiments, a single piezoelectric layer can function as both a transmitter and a receiver. In some embodiments including a piezoelectric layer, other piezoelectric materials, such as aluminum nitride (AlN) or lead zirconate titanate (PZT), can be used in the piezoelectric layer. In some examples, the ultrasonic sensor system 102 can include an array of ultrasonic transducer elements, such as a piezoelectric micro-mechanical ultrasonic transducer (PMUT) array, a capacitive micro-mechanical ultrasonic transducer (CMUT) array, and the like. In some such examples, the PMUT elements in a single-layer PMUT array or the CMUT elements in a single-layer CMUT array can function as both ultrasonic transmitters and ultrasonic receivers.

[0077] In some examples, ultrasonic sensor system 102 and low-frequency vibration source 110 can be mechanically coupled. In some examples, ultrasonic sensor system 102 and low-frequency vibration source 110 can be indirectly coupled. For example, ultrasonic sensor system 102 and low-frequency vibration source 110 can each be coupled to a portion of device 101. In some such examples, ultrasonic sensor system 102 and low-frequency vibration source 110 can each be coupled to a portion of a control system. However, in some examples, ultrasonic sensor system 102 and low-frequency vibration source 110 can be directly coupled to each other.

[0078] The control system 106 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 a combination thereof. The control system 106 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. Thus, although the memory system is not in Figure 1Although not shown in FIG. 1 , the apparatus 101 may include a memory system including one or more memory devices. The control system 106 may be configured to receive and process data from the ultrasonic sensor system 102, such as data from the ultrasonic receiver 103. If the apparatus 101 includes a separate ultrasonic transmitter 105, the control system 106 may be configured to control the ultrasonic transmitter 105, for example, as disclosed elsewhere herein. In some embodiments, the functionality of the control system 106 may be divided between one or more controllers or processors, such as between a dedicated sensor controller and an application processor of a mobile device. Some examples are described below.

[0079] Some embodiments of the apparatus 101 may include an interface system 104. In some examples, the interface system may include a wireless interface system. In some embodiments, the interface system may include a user interface system, one or more network interfaces, one or more interfaces between the control system 106 and a memory system, and / or one or more interfaces between the control system 106 and one or more external device interfaces (e.g., a port or an application processor).

[0080] The interface system 104 can be configured to provide communication between components of the device 101 (which can include wired or wireless communication, such as electrical communication, radio communication, etc.). In some such examples, the interface system 104 can be configured to provide communication between the control system 106 and the ultrasonic sensor system 102, as well as between the control system 106 and the low-frequency vibration source 110. According to some such examples, the interface system 104 can couple at least a portion of the control system 106 to the ultrasonic sensor system 102 and the low-frequency vibration source 110, for example, via conductive material (e.g., via conductive metal lines or traces, such as printed circuit board (PCB) traces). For example, the PCB can be rigid or semi-rigid, or a flexible printed circuit. If the device 101 includes an ultrasonic transmitter 105 separate from the ultrasonic receiver 103, the interface system 104 can be configured to provide communication between at least a portion of the control system 106 and the ultrasonic transmitter 105. According to some examples, the interface system 104 can be configured to provide communication between the device 101 and other devices and / or humans. In some such examples, the interface system 104 can include one or more user interfaces. In some examples, interface system 104 can include one or more network interfaces and / or one or more external device interfaces (such as one or more Universal Serial Bus (USB) interfaces or Serial Peripheral Interface (SPI) interfaces). In some embodiments, apparatus 101 can include a memory system. In some examples, interface system 104 can include at least one interface between control system 106 and the memory system.

[0081] Apparatus 101 can be used in a variety of different environments, some examples of which are disclosed herein. For example, in some embodiments, a mobile device can include at least a portion of apparatus 101. In some embodiments, a wearable device can include at least a portion of apparatus 101. For example, the wearable device can be a bracelet, a smartwatch, an armband, a wristband, a ring, a headband, or a patch. In some embodiments, control system 106 can be located in more than one device. For example, a portion of control system 106 can be located in a wearable device, and another portion of control system 106 can be located in another device, such as a mobile device (e.g., a smartphone). In some such examples, interface system 104 can also be located in more than one device.

[0082] Figure 2 is a flowchart providing example blocks of some of the methods disclosed herein. For example, Figure 2 The frame can be Figure 1 The method is performed by the device 101 or similar device. As with other methods disclosed herein, Figure 2 The method 200 outlined in the foregoing may include more or fewer blocks than indicated. Additionally, the blocks of the methods disclosed herein are not necessarily executed in the order indicated. In some examples, some blocks of the methods disclosed herein may be executed simultaneously.

[0083] In this example, block 203 involves controlling the ultrasonic sensor system, such as Figure 1 In some examples, block 205 may involve controlling the ultrasonic sensor system 102 to transmit an ultrasonic wave in the range of 1 MHz to 30 MHz. For example, the ultrasonic transmitter may be controlled to transmit the first ultrasonic wave.

[0084] According to this embodiment, block 205 involves controlling a low frequency vibration source to generate a first low frequency vibration. In some examples, block 205 may involve controlling an ultrasonic sensor system, such as Figure 1 The ultrasonic sensor system 102 may be configured to generate the first low-frequency vibration. Alternatively or additionally, block 205 may involve controlling a separate low-frequency vibration source to generate the first low-frequency vibration. In some examples, block 205 may involve causing the low-frequency vibration source to generate the first low-frequency vibration in a plane of an outer surface of the device that includes the low-frequency vibration source. Alternatively or additionally, block 205 may involve causing the low-frequency vibration source to generate the first low-frequency vibration perpendicular to the plane of the outer surface.

[0085] Some embodiments of method 200 may involve determining whether to activate a low-frequency vibration source. According to some such embodiments, the determination may be based at least in part on an estimate of the contact quality of a finger or other target object in contact with a device surface (e.g., a pressure plate, a cover glass of a display, etc.). According to some such examples, method 200 may involve determining a contact quality metric. The contact quality metric may correspond to one or more image quality metrics and / or feature quality metrics.

[0086] One example of an image quality metric is the ridge-valley signal-to-noise ratio (SNR). The ridge / valley SNR is unitless and, for example, can be defined as the ridge / valley delta divided by the average of the valley noise. Another example of an image quality metric is contrast. For example, contrast can be measured in units of grayscale, which can be defined as the dominant lp / mm (line pairs per millimeter) signal amplitude averaged over the entire image. Another example of an image quality metric is the unitless ridge / valley grayscale transition. The ridge / valley grayscale transition can be defined as the grayscale delta across the ridge / valley boundary divided by the valley noise.

[0087] Global ridge flow coherence is an example of a feature quality metric. Global ridge flow coherence can be defined as a quadratic polynomial fit of the vector field to the row and column coordinates. Directional coherence is another example of a feature quality metric. Directional coherence corresponds to smooth ridge flow variations. Directional coherence can be defined as 1 minus the average column directional increment. Another feature quality metric that may be used in some embodiments is the fingerprint curvature coefficient, which can be defined as the sum of the field polynomial coefficients divided by 2. In some examples, method 200 can involve determining to actuate the low frequency vibration source if the contact quality metric is equal to or below a contact quality metric threshold. The contact quality metric threshold may or may not be predetermined based on the particular embodiment.

[0088] According to this example, block 207 involves synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave. In some instances, block 207 may involve controlling the low-frequency vibration source to generate the first low-frequency vibration during a first time interval, and controlling the ultrasonic transmitter to transmit the first ultrasonic wave during a second time interval. The second time interval is subsequent to the first time interval. According to some examples, block 207 may involve controlling the low-frequency vibration source to generate the first low-frequency vibration during the first time interval, and controlling the ultrasonic transmitter to transmit the first ultrasonic wave during the second time interval, the second time interval at least partially coinciding with the first time interval. Some examples are described below.

[0089] In this example, block 209 involves receiving an ultrasonic receiver signal from an ultrasonic receiver. According to this example, the ultrasonic receiver signal includes a signal corresponding to a reflection of a first ultrasonic wave from a target object in contact with an outer surface of a transmitting ultrasonic receiver device, the device including an ultrasonic transmitter and an ultrasonic receiver. Some embodiments may involve processing the received ultrasonic receiver signal, for example, prior to the operation of block 211. According to some such examples, the control system may be configured to apply a high-pass filter (e.g., a first-order, second-order, or third-order high-pass filter) to the ultrasonic receiver signal. In one non-limiting example, the high-pass filter may pass frequencies greater than 10 kHz. In some such examples, the control system may be configured to apply a band-pass filter to the ultrasonic receiver signal. According to some such embodiments, the band-pass filter may pass frequencies in the range of 10 kHz to 20 kHz.

[0090] According to this example, block 211 involves performing an authentication process based at least in part on the ultrasonic receiver signal received in block 209. In some instances, block 211 may involve obtaining fingerprint image data corresponding to the signal. As used herein, the term "fingerprint image data" may generally refer to data obtained from an ultrasonic receiver or data based on a signal obtained from an ultrasonic receiver. In some instances, the fingerprint image data may correspond at least in part to a target object, such as a finger, which may include a fingerprint. The fingerprint image data may or may not be presented in a form recognizable to humans as an image. For example, the fingerprint image data may be or include a data structure in which numerical values ​​are arranged and / or stored. In some instances, the numerical values ​​may correspond to signals received from an ultrasonic sensor system, an optical sensor system, a capacitive sensor system, or the like. In some instances, the fingerprint image data may correspond to signals received from the sensor system during a time window. In some instances, the fingerprint image data may correspond to signals received from a specific area, such as a fingerprint contact area. In some instances, the fingerprint image data may be or include data that has been aggregated and / or processed in some manner after being acquired from the sensor system. Some examples of such processing are disclosed herein.

[0091] In some examples, block 211 may involve extracting features from the ultrasonic receiver signal. The authentication process may be based at least in part on the features. According to some examples, the features may be fingerprint features, such as the location, orientation, and / or type of fingerprint minutiae. In some such examples, the fingerprint image data may include an indication of one or more fingerprint features detected in at least a portion of the signal from the sensor system (such as the ultrasonic sensor system). The fingerprint features may include one or more fingerprint ridge features and one or more fingerprint valley features. For example, the fingerprint features may be comprised of fingerprint ridge features, such as Figure 1 The control system 106 is used to detect the control system.

[0092] Signals indicative of fingerprint ridge features can typically be obtained from sensor pixels of an ultrasonic sensor system that are responsive to ultrasonic waves that have reflected from the pressure plate / fingerprint ridge interface. Signals indicative of fingerprint valley features can typically be obtained from sensor pixels that are responsive to ultrasonic waves that have reflected from the pressure plate / fingerprint valley interface. Reflections from the pressure plate / fingerprint valley interface are typically reflections from the pressure plate / air interface, while reflections from the pressure plate / fingerprint ridge interface are typically reflections from the pressure plate / skin interface, corresponding to the area where the fingerprint ridge contacts the pressure plate.

[0093] According to some embodiments, method 200 may involve additional processes depending on the outcome of the authentication process of block 211. For example, if the authentication process ends successfully, the control system may allow access to the device and / or secure area. In some such instances, the control system may unlock the mobile device, laptop, door, car, or another device.

[0094] In some examples, the control system can be configured to determine at least one characteristic quality metric. According to some such examples, the control system can be configured to use the characteristic quality metric as a feedback signal for the low-frequency vibration source and control the low-frequency vibration source based at least in part on the feedback signal. In some instances, the control system can be configured to determine whether the at least one characteristic quality metric is below a characteristic quality metric threshold, and if it is determined that the at least one characteristic quality metric is below the characteristic quality metric threshold, control the low-frequency vibration source to generate a second low-frequency vibration having an amplitude greater than an amplitude of the first low-frequency vibration.

[0095] Figure 3 Example components of an apparatus according to some disclosed embodiments are shown. Figure 3 In the example shown, low-frequency vibration source 110 is a tactile device. According to this example, the fingerprint (FP) sensor system is an ultrasonic sensor system 102. In some examples, low-frequency vibration source 110 may include an eccentric rotating mass or a linear resonant actuator. In other examples, low-frequency vibration source 110 may include a piezoelectric actuator, such as a piezoelectric beam or a piezoelectric disk. According to some examples, ultrasonic sensor system 102 may include low-frequency vibration source 110.

[0096] In some examples, low-frequency vibration source 110 can be directly connected to ultrasonic sensor system 102, or to a control system configured to control ultrasonic sensor system 102. In some instances, low-frequency vibration source 110 can be connected to ultrasonic sensor system 102 (or to a control system configured to control ultrasonic sensor system 102) through a shared structure with ultrasonic sensor system 102, such as an organic light-emitting diode (OLED) panel. In some examples, the control system can be configured to cause the low-frequency vibration source to generate a first low-frequency vibration in the plane of outer surface 305, as indicated by arrow 301. Alternatively or additionally, the control system can be configured to cause the low-frequency vibration source to generate a first low-frequency vibration perpendicular to the plane of outer surface 305, as indicated by arrow 303.

[0097] Although the low frequency vibration source 110 is Figure 3 Although labeled as a "buzzer" in FIG, in some examples, at least some of the frequencies emitted by the low-frequency vibration source 110 may be below the range of human hearing. However, in other examples, the low-frequency vibration source 110 may be configured to generate vibrations within a frequency range (e.g., within the range of 400 Hz to 1000 Hz) that is known to be easily detected by human mechanoreceptors.

[0098] Figure 4 An example of synchronizing the generation of low-frequency vibrations with the transmission of ultrasonic waves is shown. In this example, FIG402a shows an example of controlling the low-frequency vibration source for the generation of low-frequency vibrations during time interval 404. FIG402a provides Figure 2 In some examples, the low frequency vibrations may be generated continuously during the time interval 404, while in other examples, the low frequency vibrations may be generated intermittently during the time interval 404.

[0099] In this example, diagram 402b provides Figure 2 402b illustrates an example of controlling the ultrasonic transmitter for transmission of ultrasonic waves during time interval 406a, where time interval 406 at least partially coincides with time interval 404. In some such examples, ultrasonic waves reflected from the target object may be received during a subsequent time interval that at least partially coincides with time interval 404. However, in other examples, ultrasonic waves reflected from the target object may be received during a time interval that does not overlap with time interval 404.

[0100] In this example, diagram 402c provides Figure 2According to this example, diagram 402c shows an example of controlling the ultrasound transmitter for transmission of ultrasound waves during a time interval 406b that does not coincide with the time interval 404, rather than after the time interval 404.

[0101] Some disclosed embodiments may involve additional image processing for instances of transmitting and / or receiving ultrasound waves during time intervals that at least partially coincide with time intervals during which low-frequency vibrations are generated. Some such embodiments may involve detecting background noise in ultrasound receiver signals based at least in part on the low-frequency vibrations. For example, features modulated by the low-frequency vibrations may be actual fingerprint features, while features invariant to the low-frequency vibrations may be background features.

[0102] In some instances, such background features may arise from the mechanical construction of the fingerprint sensor and / or from the associated process of attaching the fingerprint sensor to other parts of the device (e.g., to a pressure plate, to a display device such as an OLED display). For example, the attachment process may involve lamination. These background features may vary with the temperature and aging of the sensor. The presence of such background features may reduce the quality of the fingerprint image, thereby reducing the accuracy of the authentication process. In some instances, the presence of background features may increase the false rejection rate and / or false acceptance rate of the authentication process. Eliminating at least some background features may improve the signal-to-noise ratio of the fingerprint image data. Therefore, although such background features may be static and non-random, background features may sometimes be referred to as "background noise" herein.

[0103] Figure 5 An example of a coherent detection method is shown. In this example, the time during which the ultrasonic receiver captures the fingerprint image (which may be referred to herein as the "acquisition time" or "sampling time") is synchronized with the period and phase of the low-frequency vibration. In this example and subsequent examples, the low-frequency vibration is referred to as a "tactile disturbance," a "tactile signal," or a "tactile disturbance signal." In some such examples, the low-frequency vibration is actually generated by a tactile device. However, in other examples, the low-frequency vibration described as a tactile disturbance, a tactile disturbance signal, etc. is not generated by a tactile device. The same principles discussed below apply to embodiments in which the low-frequency vibration is generated by another type of device.

[0104] exist Figure 5 In the example shown, the tactile disturbance signal is shown as a sinusoidal waveform for illustrative purposes. However, in alternative examples, the tactile disturbance signal can be a more complex signal, such as a modulated signal. According to this example, for each cycle of the tactile disturbance, a set of eight ultrasonic receiver signals is captured at phases of 0, 45, 90, 135, 180, 225, 270, and 315 degrees.

[0105] Figure 6 An example of the perturbation of a fingerprint feature over one cycle of a tactile perturbation signal is shown. To simplify the illustration, the fingerprint sensor is represented as a 16-pixel by 16-pixel square, and the fingerprint feature is represented as a square pattern. In this example, the unperturbed fingerprint feature occupies a 6-pixel by 6-pixel square. According to this example, the fingerprint feature is spatially modulated by the tactile perturbation signal. When the tactile signal is applied, the area occupied by the fingerprint feature increases to a size of 10 pixels by 10 pixels and decreases to a size of 2 pixels by 2 pixels. In this example, the spatial increase and decrease in size is correlated with the phase of the tactile signal.

[0106] Figure 7 An example of a method for detecting the edge of a fingerprint feature is shown in FIG. In this example, eight sets of fingerprint image data (numbered 0 to 7) are Figure 6 The tactile signals are collected at the same phase as the tactile signals shown. In this example, each sample of the fingerprint image data is multiplied by an appropriate weighting factor. In this embodiment, each pixel value in sample 0 of the fingerprint image data is multiplied by weighting factor W0, each pixel value in sample 1 of the fingerprint image data is multiplied by weighting factor W1, and so on. According to some examples, each weighting factor may correspond to the phase of the tactile signal. In some such examples, when the tactile signal is a sinusoidal signal, the weighting factor may be the sine or cosine of the phase index. According to this example, the weighting factor is the sine of the phase corresponding to the index.

[0107] In this embodiment, the weighted fingerprint image data values ​​are then summed to obtain a pixel-by-pixel correlation with the tactile signal. The absolute value of each pixel's correlation with the tactile signal is then compared to a threshold. The output of this comparison is a binarized mask that indicates the location of the edges of the actual fingerprint features in the raw fingerprint image data. The absolute value operation is performed because the correlation can be positive or negative depending on the mechanical configuration of the fingerprint sensor and platen, as well as the associated tactile signal.

[0108] Figure 7 The example shown indicates the summation of the various phases in one haptic waveform cycle. However, in some implementations, the summation can be performed over several haptic waveform cycles in order to increase the accuracy of the edge detection process.

[0109] Figure 8 An example of using a binary mask to reject background features is shown. In many instances, the fingerprint background features do not change when the tactile signal is applied. For example, Figure 8Fingerprint image data samples 0 through 7 in [ 0 ] include background features 803 and 805, which do not vary with the different phases of the tactile signal. Therefore, the pixel-by-pixel correlation between the background features calculated from the weighted sum of fingerprint image data samples 0 through 7 and the tactile signal is ideally zero, and in practice is very low. In some instances, the correlation can be at the noise level of the system. Therefore, in this example, when a binary threshold comparison is performed on the pixel-by-pixel correlation, the binary mask does not indicate any edges. Therefore, background features 803 and 805 are rejected.

[0110] exist Figure 8 In an example of a process, an ideal case with no noise is assumed. According to one such example, the pixel level is an 8-bit signed value, for example, an integer value between -128 and 127, inclusive. For example, a pixel value of -128 can represent white, while a pixel value of 127 can represent black. In this example, it is assumed that background features 803 and 805 have pixel values ​​of 64, while the remaining pixels have values ​​equal to 0, which represents an intermediate value of the grayscale range. According to this example, for the pixels within the background features, when performing a weighted sum operation, using weights W0 to W7, it can be seen that the output will be 64*0+64*0.707+64*1+64*0.707+64*0+64*(-0.707)+64*(-1)+64*(-0.707)=0. For the remaining pixels, when performing the weighted sum operation, using weights W0 to W7, we can see that the output will be 0*0+0*0.707+0*1+0*0.707+0*0+0*(-0.707)+0*(-1)+0*(-0.707) = 0. This clearly shows that the weighted sum rejects the background features because all pixels in the entire image are at 0, which is the middle of the grayscale range in this example.

[0111] exist Figure 8 In another example of the process, assume that the system has accumulated random noise, which takes the value of -1, 0, or 1 least significant bit (LSB). As in the previous example, the pixel level in this example is an 8-bit signed value. Because this noise is uncorrelated with the background features, all pixels (both background and non-background) will have similar weighted output values. Pixels within the background features and pixels not within the background features will both have the same noise level, which is at the system noise floor.

[0112] For example, the random noise for a particular pixel may be the sequence [-1, 0, 0, -1, 1, -1, -1]. Then, the weighted average of this noise sequence applied to a pixel may be -1*0+0*0.707+0*1+(-1)*0.707+1*0+(-1)*(-0.707)+(-1)*(-0.707)+(-1)*(-0.707)=1.414, which is rounded to 1 in 8-bit arithmetic. Further assume that the random noise for a second pixel is the sequence [0, 1, 0, -1, 1, 1, 0, -1]. Then, the weighted average of the noise sequence applied to the second pixel can be =0*0+1*0.707+0*1+(-1)*0.707+1*0+1*(-0.707)+0*(-0.707)+(-1)*(-0.707)=2.121, which is rounded to 2 in 8-bit operation.

[0113] Figure 9 Another example of rejecting background features using a binarization mask is shown. In this example, fingerprint image data samples 0 to 7 include background features 903 and 905, which do not vary with different phases of the tactile signal. According to this example, fingerprint image data samples 0 to 7 also include fingerprint feature 907, which does vary with different phases of the tactile signal. When both actual fingerprint features and background features are present in the fingerprint image data, as in this example, the pixel-by-pixel correlation calculated by the weighted sum of the individual fingerprint image data samples over the phases of the tactile signal identifies the actual fingerprint feature 907, but the background features 903 and 905 are rejected. Figure 9 As shown, the resulting binarization mask detects only the edges of the actual fingerprint feature 907 , but rejects the edges of the background features 903 and 905 .

[0114] Figure 10 An example of generating enhanced fingerprint image data is provided. According to this example, for example, as mentioned above with reference to Figures 7 to 9 As described, edges of original image features are identified in block 1005. Edges, including actual fingerprint image feature edges and background feature edges, can be detected using mathematical methods for identifying image areas or regions with sharp changes in image pixel values. For example, such mathematical methods may include a gradient operator that estimates the derivative of image pixel values. Regions with high gradients can be designated as image edges. These include actual fingerprint features 1010 and background feature edges 1015. This results in an "initial edge image" 1020.

[0115] The binary mask 1025 may be determined before, after, or simultaneously with the creation of the initial edge image 1020. For example, the binary mask 1025 may be as described above with reference to Figures 7 to 9According to this example, in process 1030, the initial edge image 1020 is multiplied pixel by pixel with a binarization mask 1025. The binarization mask 1025 is applied in process 1030 to detect the edges of actual fingerprint features and reject the edges of background features.

[0116] According to this example, in block 1035, the interior pixels of the actual fingerprint feature edges are filled, such as by a, to generate an enhanced fingerprint image 1040. For example, block 1035 may include applying a 4-connected border filling algorithm or an 8-connected border filling algorithm. Compared to the image quality of the individual fingerprint image samples (e.g., compared to the quality of fingerprint image samples 0 through 7 described above), the enhanced fingerprint image 1040 has a higher image quality. For example, the image quality can be quantified according to one or more image quality metrics, such as those disclosed elsewhere herein. Generating the enhanced fingerprint image 1040 can improve the performance of the fingerprint sensor, for example, it can reduce the false rejection rate and / or false acceptance rate of the fingerprint sensor.

[0117] Figure 6 、 Figure 7 、 Figure 9 and Figure 10 Examples are shown where the tactile signal causes an amplification or compression of the actual fingerprint features. Depending on the mechanical structure of the fingerprint sensor and the associated pressure plate, and depending on the displacement direction and / or rotation caused by the applied low-frequency vibrations, other spatial modulations of the fingerprint features may occur.

[0118] Figure 11A and Figure 11B Additional examples of perturbations of fingerprint features caused by low-frequency vibrations are provided. Figure 11A An example of lateral translation of a fingerprint feature caused by applied low-frequency vibrations is shown. Figure 11A The arrows shown show the direction in which the fingerprint features FP1 and FP2 move. Figure 11A In , BG1 and BG2 represent background features. The arrow also corresponds to an axis along which one or more components of the fingerprint sensor move in response to the applied low-frequency vibration. Figure 11B In the example shown, the applied low frequency vibrations result in rotation of at least a portion of the fingerprint sensor and a corresponding rotation of the fingerprint features.

[0119] refer to Figures 6 to 10 The described embodiments relate to examples where the capture of fingerprint image data by an ultrasonic sensor system is synchronized with a periodic tactile signal. Figure 12Examples are shown in which the time at which fingerprint image data is captured is independent of the period and phase of the tactile perturbation waveform. Such embodiments may be referred to herein as "incoherent detection" methods. According to some such embodiments, the tactile perturbation waveform may not have a constant frequency or phase. In some examples, the tactile perturbation waveform may be non-periodic.

[0120] Figure 13 Another example shows that the time at which fingerprint image data is captured is independent of the period and phase of the tactile perturbation waveform. In this example, perturbations of actual fingerprint features over eight fingerprint image capture times are shown. To simplify the illustration, fingerprint sensor 1305 is shown as a 16-pixel x 16-pixel square, and fingerprint features 1310 are simplified as a square pattern.

[0121] In this example, the actual fingerprint feature is spatially modulated by the tactile signal: here, the tactile signal causes the fingerprint feature to increase or decrease in size. According to this embodiment, the undisturbed fingerprint feature is a 3-pixel by 3-pixel square. In this example, when the tactile signal is applied, the fingerprint feature increases to a 10-pixel by 10-pixel square and decreases to a 2-pixel by 2-pixel square. The degree of expansion and compression of the actual fingerprint feature is related to the amplitude and phase of the tactile signal. In this example, when the amplitude is equal to or close to zero, the fingerprint feature is a 6-pixel by 6-pixel square. According to this example, when the amplitude is equal to or close to +1, the fingerprint feature is an 8-pixel by 8-pixel square. In this example, when the amplitude is equal to or close to -1, the fingerprint feature is a 2-pixel by 2-pixel square.

[0122] Figure 14 is a flowchart providing example blocks of some of the non-coherent detection methods disclosed herein. For example, Figure 14 The frame can be Figure 1 As with other methods disclosed herein, Figure 14 The method outlined in the foregoing may include more or fewer blocks than indicated. Additionally, the blocks of the method disclosed herein are not necessarily executed in the order indicated. In some examples, some blocks of the method disclosed herein may be executed simultaneously.

[0123] In this example, block 1403 involves acquiring a baseline image (e.g., a set of what may be referred to herein as "fingerprint image data") at a time when low-frequency vibrations are not being applied. For example, the baseline image may be captured without tactile actuation. In some such examples, block 1403 may involve controlling an ultrasonic transmitter to transmit a first ultrasonic wave. Block 1403 may involve receiving a first ultrasonic receiver signal from an ultrasonic receiver. The first ultrasonic receiver signal may include a signal corresponding to a first reflection of an ultrasonic wave from a target object (such as a finger) in contact with an outer surface of the device.

[0124] Block 1403 or block 1405 may involve extracting features from the ultrasonic receiver signal. These features may include fingerprint features, such as the location, orientation, and / or type of fingerprint minutiae. However, in some instances, the features may include both actual fingerprint features and background features. In this example, block 1405 involves counting the number of features in the baseline image. In some examples, block 1405 may involve counting all detected features in the baseline image, while in other examples, block 1405 may involve counting some but not all features in the baseline image, e.g., every other feature, every third feature, every fourth feature, etc. The number of features counted may be referred to herein as M.

[0125] In this example, block 1407 involves detecting edges of at least some features in the baseline image. According to some implementations, block 1407 may involve detecting edges of each of the M features in the baseline image counted in block 1405. Block 1407 may involve determining edge coordinates corresponding to the detected feature edges and storing the edge coordinates, at least temporarily, in a data structure.

[0126] According to this example, block 1409 involves calculating the area of ​​each feature detected in block 1407. In some examples, such as here, block 1409 also involves determining the perimeter of each feature detected in block 1407. Block 1409 can involve determining feature area data and feature perimeter data and storing, at least temporarily, the feature area data and the feature perimeter data in a data structure.

[0127] In some embodiments, block 1409 may involve one or more iterative processes. In one such example, for k=1 to k=M, block 1409 may involve calculating the area and perimeter of each feature in the baseline image in increments of 1. This process may be represented as follows: for k=1:1:M, calculate the area [0, k] and perimeter [0, k] of each feature in the baseline image. In this example, the notation "k=1:1:M" indicates (starting point): (step size): (end point). In some alternative examples, only a subset of the total number of features may be included in the process, for example, every other feature (k=1:2:M), every third feature (k=1:3:M), every fourth feature (k=1:4:M), every fifth feature (k=1:5:M), etc.

[0128] In this embodiment, block 1411 involves controlling the low frequency vibration source to generate low frequency vibrations. Figure 14In the present invention, generating low-frequency vibrations is referred to as "haptic actuation", but as described elsewhere in this document, the term "haptic" does not limit the disclosed method to actuating haptic devices. Instead, any suitable type of device for generating low-frequency vibrations can be used.

[0129] In this example, block 1413 involves collecting L additional sets of fingerprint image data while the low-frequency vibration is applied, where L is an integer. The L sets of fingerprint image data may also be referred to as L images. In some examples, block 1413 may involve collecting at least two additional sets of fingerprint image data. In some examples, block 1413 may involve collecting 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more additional samples of fingerprint image data. In some such examples, block 1413 may involve controlling an ultrasonic transmitter to transmit L instances of ultrasonic waves. Block 1413 may involve receiving a set of L ultrasonic receiver signals from an ultrasonic receiver. The set of L ultrasonic receiver signals may include signals corresponding to a set of L reflections of the ultrasonic waves from a target object (such as a finger) in contact with an outer surface of the device. In this example, after the process of block 1413 is completed, the generation of the low-frequency vibration is stopped in block 1415.

[0130] In this example, block 1417 involves running an image post-processing loop on the set of L fingerprint image data collected in block 1413. According to this example, block 1417 also involves constructing at least one enhanced image.

[0131] Figure 15 Is provided in the implementation Figure 14 Block 1417 is a flow chart of an example of a process that may be involved. For example, Figure 15 The frame can be Figure 1 As with other methods disclosed herein, Figure 15 The method 1500 outlined in the foregoing may include more or fewer blocks than indicated. Additionally, the blocks of the methods disclosed herein are not necessarily executed in the order indicated. In some examples, some blocks of the methods disclosed herein may be executed simultaneously.

[0132] According to this example, method 1500 involves two nested loops, including an outer loop over M features in the baseline image, and an outer loop over Figure 14The inner loop is over the L sets of fingerprint image data or L images referenced in blocks 1413 and 1417 of FIG. In other words, the loop involves both the images and the features in each image. L images are captured while tactile actuation is applied (block 1411). According to this example, method 1500 involves obtaining statistics for each feature, which can then be evaluated to determine whether the feature is an actual fingerprint feature or a background feature.

[0133] exist Figure 15 In the example shown, L images are indexed as image(j), where j is between 1 and L, inclusive. According to this embodiment, each image(j) has k features, which are indexed as features(j, k). In this example, each feature(j, k) has an area(j, k) and a perimeter(j, k), and the vertical and horizontal spatial coordinates of the centroid of each feature(j, k) are located at the centroid(j, k).

[0134] In this example, block 1503 involves an iterative outer loop over each of the M features in the baseline image, with the iterative outer loop incrementing by 1 from k=1 to k=M. In this example, the iterative inner loop of block 1505 includes the processes of subblocks 1507 and 1509. According to this example, the process of subblock 1507 involves, for a particular one of the features k, calculating the centroid, area, and perimeter of all images from j=1 to j=L. This is represented in block 1507 as calculating the centroid (j, k), area (j, k), and perimeter (j, k) of feature (j, k) for each image (j). According to this example, the process of subblock 1509 involves, for a particular one of the features k, calculating the standard deviation of the centroid, area, and perimeter of all images from j=1 to j=L. This is represented in block 1507 as computing the standard centroid (k), standard area (k), and standard perimeter (k) for each of the L images.

[0135] In this example, block 1511 involves comparing the standard deviation of the centroid, the standard deviation of the area, and / or the standard deviation of the perimeter for a particular feature k to a corresponding centroid threshold, area threshold, and / or perimeter threshold, which are respectively Figure 15 In order to determine whether the threshold value is equal to or exceeds one or more of the threshold values, the threshold value is expressed as centroid_threshold, area_threshold and perimeter_threshold in order to determine whether the threshold value is equal to or exceeds one or more of the threshold values. As described elsewhere in this document, including but not limited to the above reference Figure 11A and Figure 11BAs discussed above, if one or more such thresholds are exceeded, it can be inferred that feature k is an actual fingerprint feature (block 1517). Therefore, in this example, the feature will be retained for the enhanced fingerprint image in block 1519. If one or more such thresholds are not exceeded, then in this example, it will be determined in block 1513 that the feature is a background feature. According to this example, in block 1515, the background feature will be omitted or deleted from the features included in the enhanced fingerprint image.

[0136] In some examples, block 1511 may involve comparing the standard deviation of the centroid, area, and perimeter of a particular feature k to corresponding centroid thresholds, area thresholds, and perimeter thresholds. According to some such examples, a feature is determined to be an actual fingerprint feature only if all three thresholds are equal to or exceed all three thresholds. In other embodiments, a feature is determined to be an actual fingerprint feature if only two of the three thresholds are equal to or exceed two of the three thresholds. In other embodiments, a feature is determined to be an actual fingerprint feature if only one of the three thresholds is equal to or exceeds one of the three thresholds.

[0137] In other examples, block 1511 may involve comparing the standard deviation of the centroid and the standard deviation of the perimeter of the particular feature k to corresponding centroid thresholds and perimeter thresholds. In some examples, block 1511 may involve comparing the standard deviation of the area and the standard deviation of the perimeter of the particular feature k to corresponding area thresholds and perimeter thresholds. In other examples, block 1511 may involve comparing only one of the standard deviation of the centroid, the standard deviation of the area, or the standard deviation of the perimeter of the particular feature k to only one of the corresponding centroid thresholds, the area thresholds, or the perimeter thresholds.

[0138] exist Figure 15 In the example shown, the process of iterating the outer loop continues until all M features have been evaluated. In some such examples, method 1500 ends after all M features have been evaluated.

[0139] Figure 16 1 shows example components of an apparatus according to one embodiment. In this example, the apparatus 101 includes a host application processor 1605, a fingerprint sensor 1607, and a tactile subsystem 1609. The host application processor 1605 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 a combination thereof.

[0140] The haptic subsystem 1609 includes some type of low frequency vibration source and is not necessarily a haptic device. According to this example, the haptic subsystem 1609 includes a haptic controller and a haptic actuator. Thus, the haptic subsystem 1609 may include the haptic controller and the haptic actuator described above. Figure 1 Both the low frequency vibration source 110 and a portion of the control system 106 are depicted.

[0141] In some examples, fingerprint sensor 1607 may include a fingerprint sensor similar to that described above. Figure 1 According to some embodiments, the fingerprint sensor 1607 may include the ultrasonic sensor system described above. Figure 1 A portion of the control system 106 is depicted.

[0142] According to some embodiments, the timing and activity of the tactile actuators of the fingerprint sensor 1607 and the tactile subsystem 1609 can be independently controlled by software commands issued by the host application processor 1605 through independent digital interfaces 1611 and 1613. For example, the digital interfaces 1611 and 1613 can be serial peripheral interfaces (SPI) or inter-integrated circuit (IC) interfaces. 2 C) Interface. In this embodiment, the timing and activity of the fingerprint sensor 1607 and the haptic subsystem 1609 can be independently controlled by the host application processor via the fingerprint sensor interrupt signal FP_INTR1 and the haptic interrupt signal HAP_INTR1. In this example, the fingerprint sensor 1607 and the haptic subsystem 1609 provide the fingerprint sensor interrupt signal FP_INTR2 and the haptic interrupt signal HAP_INTR2 to the host application processor 1605.

[0143] In this example, a digital interface 1615 is provided between the fingerprint sensor 1607 and the tactile actuator. Thus, one or more interrupt signals, such as INTR5 and INTR6, can be exchanged between the fingerprint sensor 1607 and the tactile actuator via the digital interface 1615. Such interrupt signals can allow the fingerprint sensor 1607 and the tactile actuator to synchronize the acquisition of fingerprint image data and the timing (frequency and phase) of tactile actuation through electronic hardware-level handshaking signals.

[0144] Some embodiments may not include a digital interface between the fingerprint sensor 1607 and the tactile actuator. If this interface is not present, the fingerprint sensor and tactile activity may be synchronized according to commands transmitted over interfaces 1611 and 1613.

[0145] Figure 171 shows example components of an apparatus according to an alternative embodiment. In this example, the apparatus 101 includes a host application processor 1705, a dual-use fingerprint sensor and haptic controller 1710, a fingerprint sensor 1715, and a haptic actuator 1720. The host application processor 1705 and the dual-use fingerprint sensor and haptic controller 1710 may include the above referenced Figure 1 1 . In this embodiment, the timing and activity of the fingerprint sensor 1715 can be controlled by the host application processor 1705 via the fingerprint sensor interrupt signal FP_INTR1. In this example, the fingerprint sensor 1715 provides the fingerprint sensor interrupt signal FP_INTR2 to the host application processor 1705. The host application processor 1705 and the dual-use fingerprint sensor and haptic controller 1710 can include one or more general-purpose single-chip or multi-chip processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs) or other programmable logic devices, discrete gate or transistor logic, discrete hardware components, or a combination thereof.

[0146] In some examples, fingerprint sensor 1715 may include a fingerprint sensor similar to that described above. Figure 1 As described elsewhere herein, the tactile actuator 1720 is a low frequency vibration source that is not necessarily a tactile device. For example, as described in reference Figure 1 As described with respect to the low-frequency vibration source 110 , the tactile actuator 1720 may be a piezoelectric device, a linear resonant actuator, an eccentric rotary mass actuator, or the like.

[0147] In this embodiment, the dual-purpose fingerprint sensor and tactile controller 1710 is configured to control the fingerprint sensor 1715 (including but not limited to any associated ultrasonic transducer) and the tactile actuator 1720 according to instructions from the host application processor 1705, such as through software commands issued on the digital interface 1716.

[0148] In this example, the interface between the dual-use fingerprint sensor and haptic controller 1710 and the fingerprint sensor 1715 (which in some instances may be constructed using TFT (thin film transistor) technology) may include one or more power (PWR) supply interfaces 1725, one or more receive (Rx) signal interfaces 1730, one or more digital (DIG) interfaces 1735 (e.g., for scanning fingerprint sensor pixels of the fingerprint sensor system 1715), and a ground (GND) line 1740. As an illustrative example, the number of power supply interfaces 1725 may be two (one each for analog signals and digital signals), the number of receive signal interfaces 1730 may be between 6 and 20, and the number of digital interfaces 1735 may be between 4 and 6.

[0149] According to this example, the interface between the dual-use fingerprint sensor and haptic controller 1710 and the haptic actuator 1720 may include one or more power supply interfaces 1745, one or more control signal interfaces 1750, one or more sensing interfaces 1755, and a ground line 1760. For example, the sensing interface may detect back electromotive force (emf), implement short-circuit protection, or track the resonant frequency of tactile disturbances. In this embodiment, synchronization between the operation of the haptic actuator 1720 and the operation of the fingerprint sensor 1715 may be achieved through communication along an internal bus and other internal circuits and / or embedded firmware in the dual-use fingerprint sensor and haptic controller 1710.

[0150] Figure 18A is a flowchart providing example blocks of some of the methods disclosed herein. For example, Figure 18A The frame can be Figure 1 As with other methods disclosed herein, Figure 18A The method 1800 outlined in the foregoing may include more or fewer blocks than indicated. Additionally, the blocks of the methods disclosed herein are not necessarily executed in the order indicated. In some examples, some blocks of the methods disclosed herein may be executed simultaneously.

[0151] In this example, method 1800 involves tuning the tactile actuation frequency to produce maximum modulation of a fingerprint image feature in response to a tactile perturbation. In some instances, maximizing the perturbation of the fingerprint image feature can maximize the selectivity of actual fingerprint features over background features, thereby maximizing enhanced image quality after one or more disclosed tactile-based enhancement techniques are applied.

[0152] In this example, block 1803 involves an iterative process of measuring a perturbation of the fingerprint image feature at each of a plurality of frequencies p. In some examples, block 1803 may involve measuring a perturbation of the fingerprint image feature at a predetermined number of frequencies within a frequency range suitable for tactile actuation, such as vibrations in a range of 5 Hz to 400 Hz, vibrations in a range of 5 Hz to 800 Hz, vibrations in a range of 5 Hz to 1200 Hz, vibrations in a range of 5 Hz to 2000 Hz, and so on. In the case where the tactile frequencies have spectral content distributed across a frequency range, the tuned frequency may be an average frequency or a center frequency of the tactile actuation frequency range.

[0153] The predetermined number of frequencies may depend on various factors and may involve a trade-off between the desired level of accuracy and the amount of time required to implement method 1800. In some examples, the predetermined number of frequencies may be 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, etc.

[0154] According to this example, block 1805 involves selecting a frequency p that corresponds to a maximum perturbation of a fingerprint image feature. Figure 18B is a plot of perturbation versus tactile frequency according to an example. For example, Figure 18B The diagram shown can be based on Figure 18A The frequency and disturbance value determined in block 1803 of . Figure 18B In the example shown, the frequency corresponding to the local maximum perturbation value is selected as the optimal tactile actuation frequency. Figure 18A An example of box 1805 of .

[0155] Figure 19 is a flowchart providing an example block diagram of another disclosed method. For example, Figure 19 The frame can be Figure 1 As with other methods disclosed herein, Figure 19 The method 1900 outlined in the foregoing may include more or fewer blocks than indicated. Additionally, the blocks of the methods disclosed herein are not necessarily executed in the order indicated. In some examples, some blocks of the methods disclosed herein may be executed simultaneously.

[0156] In this example, method 1900 involves a process for refining the tactile-based image enhancement process disclosed herein. In some such embodiments, method 1900 involves using images with more complex sequences to fine-tune the algorithm's sensitivity to background features and the selectivity of background features to actual fingerprint image features. Depending on the particular embodiment, method 1900 may involve refining a deterministic algorithm or refining an adaptive algorithm based on machine learning.

[0157] According to this example, block 1903 is a background feature rejection process. According to some embodiments, block 1903 may be an iterative background feature rejection process. In some such examples, block 1903 may involve controlling the ultrasonic fingerprint sensor to capture an "air-only" image without a finger or other target object on the sensor or on the device on which the sensor is located. Thus, in such examples, block 1903 involves capturing only background image features. In some such examples, block 1903 may involve applying one or more of the disclosed background feature detection and rejection processes. In some examples, block 1903 may involve capturing only background image features using a sensor with exacerbated background aberrations, such as adhesive marks, incorrect mechanical lamination of one or more layers of the sensor, or incorrect mechanical lamination of the device on which the sensor is located.

[0158] According to some embodiments, block 1903 may involve adjusting the algorithm threshold and / or other detection parameters until all or substantially all background artifacts are detected and rejected. For example, in the case of an image with five background features, if an initial threshold of 1.0 results in the identification of three of the five background features, the threshold may be lowered to a value of, for example, 0.8, so that all five background features are properly identified. In some such embodiments, after the process of block 1903, the background image should be spatially uniform, or substantially uniform. In some such embodiments, a sufficiently or substantially uniform background image may have a variation between sensor pixels that is less than a certain threshold percentage (such as 0.5%, 1%, 1.5%, 2%, etc.).

[0159] In this example, box 1905 is a patterned target feature detection process. In some such examples, box 1905 may involve applying one or more of the disclosed methods to capture an image with a patterned target. In some such examples, the image with the patterned target can be captured using a sensor without background aberrations, so that the captured image is only the actual image. According to some embodiments, in box 1905, the algorithm threshold and / or other detection parameters can be adjusted until all actual image features of the patterned target are detected. In some such examples, box 1905 may involve comparing the enhanced image with a reference image of the patterned target. In one such example, both the patterned target and the reference image may include the same series of dashed lines with a known (e.g., 1 mm) spacing between the lines. After implementing box 1905, the captured ultrasound image should include the actual pattern of the target.

[0160] According to this example, block 1907 involves repeating block 1905 while using the aforementioned sensor with exacerbated background aberrations. In some embodiments, block 1907 may involve adjusting algorithm thresholds and / or other detection parameters until all fingerprint features of the predetermined set of fingerprint features are detected and all background features of the predetermined set of background features are rejected. According to some embodiments, block 1907 may involve adjusting algorithm thresholds and / or other detection parameters until the target pattern is detected, even if actual features of the target pattern overlap with background features. In some embodiments, block 1907 may involve an initial process using a sensor with exacerbated background aberrations, followed by a subsequent process using a sensor with less severe aberrations. In some such examples, the subsequent process may involve using a patterned target with relatively less pronounced target features. In some such embodiments, block 1907 may involve further refining the algorithm until even these less pronounced background features are rejected and faint actual image features are detected.

[0161] According to some embodiments, block 1909 may involve a process of capturing an ultrasound image from one or more actual human fingers. For example, block 1909 may involve imaging an actual fingerprint having sparse fingerprint features (such as an actual fingerprint having low spatial frequency content). According to some examples, block 1909 may involve a subsequent process involving imaging an actual fingerprint having fingerprint features that relatively overlap more with background features, imaging an actual fingerprint having a higher spatial image frequency than the fingerprint used in the early stages of block 1909, and the like. In some embodiments, block 1909 may involve adjusting algorithm thresholds and / or other detection parameters until all fingerprint features of a predetermined set of fingerprint features are detected and all background features of a predetermined set of background features are rejected. In some examples, after these goals are achieved, method 1900 ends.

[0162] Figure 20 Aspects of a 4×4 pixel array of sensor pixels for an ultrasound sensor system are representatively depicted. For example, each sensor pixel 2034 can be associated with a localized area of ​​piezoelectric sensor material (PSM), a pixel input electrode 2037, a peak detection diode (D1), and a readout transistor circuit (M3); many or all of these components can be formed on or in a substrate to form pixel circuitry 2036. In practice, the localized area of ​​piezoelectric sensor material in each sensor pixel 2034 can convert received ultrasonic energy into electrical charge. Peak detection diode D1 can register the maximum amount of charge detected by the localized area of ​​piezoelectric sensor material PSM. Each row of pixel array 2035 can then be scanned via a row selection mechanism, a gate driver, a shift register, or the like, and the readout transistor circuitry M3 in each column can be triggered to allow additional circuitry (e.g., a multiplexer and an analog-to-digital converter) to read the magnitude of the peak charge of each sensor pixel 2034. Pixel circuitry 2036 can include one or more TFTs to allow for gating, addressing, and resetting of sensor pixels 2034.

[0163] Each pixel circuit 2036 can provide information about a small portion of an object detected by the ultrasonic sensor system. Although for ease of illustration, Figure 20 The examples shown have relatively coarse resolution, but 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 based on the intended detection object. For example, the detection area can range from approximately 8 mm x 3 mm, 5 mm x 5 mm, or 9 mm x 4 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 used appropriately for target objects.

[0164] Figure 21A An example of an exploded view of an ultrasonic sensor system is shown. In this example, the ultrasonic sensor system 2100a includes an ultrasonic transmitter 20 and an ultrasonic receiver 30 below a pressure plate 40. According to some embodiments, the ultrasonic receiver 30 may be Figure 1 An example of an ultrasound receiver 103 is shown in FIG. 1 and described above. In some embodiments, the ultrasound transmitter 20 may be Figure 1 An example of an ultrasonic transmitter 105 is shown and described above. The ultrasonic transmitter 20 may include a substantially planar piezoelectric transmitter layer 22 and may be configured to function as a plane wave generator. Depending on the applied signal, ultrasonic waves may be generated by applying a voltage to the piezoelectric layer to expand or compress the layer, thereby generating a plane wave. In this example, the control system 106 may be configured to induce a voltage, which may be applied to the planar piezoelectric transmitter layer 22 via the first and second transmitter electrodes 24, 26. In this manner, ultrasonic waves may be generated by varying the thickness of the layer via the piezoelectric effect. The generated ultrasonic waves may travel through the platen 40 toward a finger (or other object to be detected). A portion of the wave not absorbed or transmitted by the object to be detected may be reflected, returning through the platen 40 and being received by the ultrasonic receiver 30. The first and second transmitter electrodes 24, 26 may be metallized electrodes, e.g., metal layers coating opposing sides of the piezoelectric transmitter layer 22.

[0165] The ultrasound receiver 30 can include an array of sensor pixel circuits 32 and a piezoelectric receiver layer 36 disposed on a substrate 34 (which can also be referred to as a backplate). In some embodiments, each sensor pixel circuit 32 can include one or more TFTs or silicon-based components, electrical interconnect traces, and in some embodiments, one or more additional circuit elements, such as diodes, capacitors, etc. Each sensor pixel circuit 32 can be configured to convert surface charge generated by the piezoelectric receiver layer 36 near the pixel circuit into an electrical signal. Each sensor pixel circuit 32 can include a pixel input electrode 38 that electrically couples the piezoelectric receiver layer 36 to the sensor pixel circuit 32.

[0166] In the illustrated embodiment, a receiver bias electrode 39 is disposed on a side of the piezoelectric receiver layer 36 proximal to the platen 40. The receiver bias electrode 39 can be a metallized electrode and can be grounded or biased to control which signals are passed to the array of sensor pixel circuits 32. Ultrasonic energy reflected from the exposed (top) surface of the platen 40 can be converted into surface charge by the piezoelectric receiver layer 36. The generated surface charge can be coupled to the pixel input electrode 38 and the underlying sensor pixel circuit 32. The charge signal can be amplified or buffered by the sensor pixel circuit 32 and provided to the control system 106.

[0167] The control system 106 can be electrically connected (directly or indirectly) to the first transmitter electrode 24 and the second transmitter electrode 26, as well as to the receiver bias electrode 39 and the sensor pixel circuit 32 on the substrate 34. In some embodiments, the control system 106 can operate substantially as described above. For example, the control system 106 can be configured to process the amplified signal received from the sensor pixel circuit 32.

[0168] The control system 106 may be configured to control the ultrasonic transmitter 20 and / or the ultrasonic receiver 30 to obtain ultrasonic data, which may include fingerprint data. According to some embodiments, the control system 106 may be configured to provide functionality such as described herein.

[0169] Regardless of whether the ultrasonic sensor system 2100a includes a separate ultrasonic transmitter 20, in some embodiments, the control system 106 can be configured to obtain attribute information from the ultrasonic data. In some examples, the control system 106 can be configured to control access to one or more devices based at least in part on the attribute information. The ultrasonic sensor system 2100a (or an associated device) can include a memory system comprising one or more memory devices. In some embodiments, the control system 106 can include at least a portion of the memory system. The control system 106 can be configured to obtain attribute information from the ultrasonic data and store the attribute information in the memory system. In some embodiments, the control system 106 can be configured to capture a fingerprint image, obtain attribute information from the fingerprint image, and store the attribute information obtained from the fingerprint image (hereinafter referred to as fingerprint image information) in the memory system. According to some examples, the control system 106 can be configured to capture a fingerprint image, obtain attribute information from the fingerprint image, and store the attribute information obtained from the fingerprint image, even while the ultrasonic transmitter 20 is in an "off" state.

[0170] In some embodiments, the control system 106 can be configured to operate the ultrasonic sensor system 2100a in an ultrasonic imaging mode or a force sensing mode. In some embodiments, the control system can be configured to maintain the ultrasonic transmitter 20 in an "off" state when operating the ultrasonic sensor system in the force sensing mode. The ultrasonic receiver 30 can be configured to function as a force sensor when the ultrasonic sensor system 2100a is operating in the force sensing mode. In some embodiments, the control system 106 can be configured to control other devices, such as a display system, a communication system, etc. In some embodiments, the control system 106 can be configured to operate the ultrasonic sensor system 2100a in a capacitive imaging mode.

[0171] The pressure plate 40 can be any suitable material capable of acoustically coupling to the receiver, examples including plastic, ceramic, sapphire, metal, and glass. In some embodiments, the pressure plate 40 can be a cover plate, such as cover glass or lens glass for a display. In particular when using the ultrasonic transmitter 20, fingerprint detection and imaging can be performed with a relatively thick pressure plate (e.g., 3 mm or thicker) if desired. However, for embodiments in which the ultrasonic receiver 30 is configured to image fingerprints in a force detection mode or a capacitive detection mode, a thinner and relatively more compliant pressure plate 40 may be required. According to some such embodiments, the pressure plate 40 can include one or more polymers, such as one or more types of parylene, and can be substantially thinner. In some such embodiments, the pressure plate 40 can be tens of microns thick or even less than 10 microns thick.

[0172] Examples of piezoelectric materials that can be used to form the piezoelectric receiver layer 36 include piezoelectric polymers having suitable acoustic properties (e.g., an acoustic impedance between approximately 2.5 megaraisleil and 5 megaraisleil). Specific examples of piezoelectric materials that can be used include ferroelectric polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymers. Examples of PVDF copolymers include 60:40 (mol %) PVDF-TrFE, 70:30 PVDF-TrFE, 80:20 PVDF-TrFE, and 90:10 PVDR-TrFE. Other examples of piezoelectric materials that can be used include polyvinylidene chloride (PVDC) homopolymers and copolymers, polytetrafluoroethylene (PTFE) homopolymers and copolymers, and diisopropylammonium bromide (DIPAB).

[0173] The thickness of each of the piezoelectric transmitter layer 22 and the piezoelectric receiver layer 36 can be selected to be suitable for generating and receiving ultrasonic waves. In one example, the PVDF planar piezoelectric transmitter layer 22 is approximately 28 μm thick, and the PVDF-TrFE receiver layer 36 is approximately 12 μm thick. Example frequencies of ultrasonic waves can be in the range of 5 MHz to 30 MHz, with wavelengths on the order of millimeters or less.

[0174] Figure 21B An exploded view of an alternative example of an ultrasound sensor system is shown. In this example, the piezoelectric receiver layer 36 has been formed into discrete components 37. Figure 21BIn the illustrated embodiment, each of the discrete components 37 corresponds to a single pixel input electrode 38 and a single sensor pixel circuit 32. However, in alternative embodiments of the ultrasound sensor system 2100b, there need not be a one-to-one correspondence between each of the discrete components 37, a single pixel input electrode 38, and a single sensor pixel circuit 32. For example, in some embodiments, there may be multiple pixel input electrodes 38 and sensor pixel circuits 32 for a single discrete component 37.

[0175] Figure 21A and Figure 21B An example arrangement of an ultrasonic transmitter and receiver in an ultrasonic sensor system is shown, although other arrangements are possible. For example, in some embodiments, the ultrasonic transmitter 20 may be above the ultrasonic receiver 30 and therefore closer to the object to be detected. In some embodiments, the ultrasonic transmitter may be included in an ultrasonic sensor array (e.g., a single layer of transmitters and receivers). In some embodiments, the ultrasonic sensor system may include an acoustic delay layer. For example, the acoustic delay layer may be incorporated into the ultrasonic sensor system between the ultrasonic transmitter 20 and the ultrasonic receiver 30. The acoustic delay layer may be used to adjust the timing of ultrasonic pulses while also electrically insulating the ultrasonic receiver 30 from the ultrasonic transmitter 20. The acoustic delay layer may have a substantially uniform thickness, with the material used for the delay layer and / or the thickness of the delay layer selected to provide a desired delay in the time it takes for reflected ultrasonic energy to reach the ultrasonic receiver 30. Thus, energy pulses carrying information about an object (due to having been reflected from the object) can be allowed to reach the ultrasonic receiver 30 during a time range when energy reflected from other parts of the ultrasonic sensor system is less likely to reach the ultrasonic receiver 30. In some embodiments, the substrate 34 and / or the platen 40 may function as the acoustic delay layer.

[0176] Figure 21C An exploded view of an example of an ultrasonic sensor system is shown. In this example, the ultrasonic sensor system 2100c includes an ultrasonic transceiver array 50 below the pressure plate 40. According to some embodiments, as Figure 1As shown and described above, the ultrasonic transceiver array 50 can function as both an ultrasonic receiver 103 and an ultrasonic transmitter 105. The ultrasonic transceiver array 50 can include a substantially planar piezoelectric transceiver layer 56 configured to function as a plane wave generator. Ultrasonic waves can be generated by applying a voltage across the transceiver layer 56. The control system 106 can be configured to generate a transceiver excitation voltage, which can be applied to the piezoelectric transceiver layer 56 via one or more underlying pixel input electrodes 38 or one or more upper transceiver bias electrodes 59. The generated ultrasonic waves can travel through the platen 40 toward a finger or other object to be detected. A portion of the wave that is not absorbed or transmitted by the object can be reflected, thereby returning through the platen 40 and being received by the ultrasonic transceiver array 50.

[0177] The ultrasound transceiver array 50 can include an array of sensor pixel circuits 32 disposed on a substrate 34. In some embodiments, each sensor pixel circuit 32 can include one or more TFTs or silicon-based components, electrical interconnect traces, and in some embodiments, one or more additional circuit elements, such as diodes, capacitors, etc. Each sensor pixel circuit 32 can include a pixel input electrode 38 that electrically couples a piezoelectric transceiver layer 56 to the sensor pixel circuit 32.

[0178] In the illustrated embodiment, a transceiver bias electrode 59 is disposed on a side of the piezoelectric transceiver layer 56 proximal to the platen 40. The transceiver bias electrode 59 can be a metallized electrode and can be grounded or biased to control which signals can be generated and which reflected signals can be passed to the array of sensor pixel circuits 32. Ultrasonic energy reflected from the exposed (top) surface of the platen 40 can be converted into surface charge by the piezoelectric transceiver layer 56. The generated surface charge can be coupled to the pixel input electrode 38 and the underlying sensor pixel circuit 32. The charge signal can be amplified or buffered by the sensor pixel circuit 32 and provided to the control system 106.

[0179] The control system 106 can be electrically connected (directly or indirectly) to the transceiver bias electrodes 59 and the sensor pixel circuitry 32 on the sensor substrate 34. In some embodiments, the control system 106 can operate substantially as described above. For example, the control system 106 can be configured to process the amplified signal received from the sensor pixel circuitry 32.

[0180] The control system 106 may be configured to control the ultrasound transceiver array 50 to obtain ultrasound data, which may include fingerprint data. According to some embodiments, the control system 106 may be configured to provide functionality such as described herein, for example, such as described herein.

[0181] In other examples of ultrasound sensor systems having an array of ultrasound transceivers, the back side of the sensor substrate 34 can be attached directly or indirectly to the overlying platen 40. In operation, ultrasound waves generated by the piezoelectric transceiver layer 56 can pass through the sensor substrate 34 and platen 40, reflect from the surface of the platen 40, and return through the platen 40 and sensor substrate 34 before being detected by the sensor pixel circuitry 32 on or in the substrate sensor 34.

[0182] As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items, including single members. For example, "at least one of a, b, or c" is intended to encompass: a, b, c, ab, ac, bc, and abc.

[0183] The various illustrative logics, logic blocks, modules, circuits, and algorithmic processes described in conjunction with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or a combination of both. The interchangeability of hardware and software has been generally described in terms of functionality and illustrated in the various illustrative components, blocks, modules, circuits, and processes 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.

[0184] The hardware and data processing apparatus for implementing the various illustrative logics, logic blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented or performed using a general-purpose single-chip or multi-chip processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor 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, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, a combination of one or more microprocessors and a DSP core, or any other such configuration. In some embodiments, specific processes and methods may be performed by circuits specific to a given function.

[0185] In one or more aspects, the functions described may be implemented by hardware, digital electronic circuitry, computer software, firmware (including the structures disclosed in this specification and their structural equivalents), or any combination thereof. Implementations of the subject matter described in this specification may also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded in a computer storage medium, for execution by a data processing apparatus or to control the operation of the data processing apparatus.

[0186] If implemented by software, these functions can be stored as one or more instructions or codes in a computer-readable medium (such as a non-transitory medium) or transmitted via a computer-readable medium. The process of the method or algorithm disclosed herein can be implemented in a software module executable by a processor, which can be located in a computer-readable medium. Computer-readable media include computer storage media and communication media, and communication media include any medium capable of transferring a computer program from one place to another. The storage medium can be any available medium that can be accessed by a computer. As an example and not limitation, non-transitory media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage or other magnetic storage device, or any other medium that can be used to store the desired program code in the form of an instruction or data structure and can be accessed by a computer. In addition, any connection can be properly referred to as a computer-readable medium. Disks and optical disks as used herein include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), magnetic disks and Blu-ray discs, wherein magnetic disks usually reproduce data magnetically, while optical discs reproduce data optically with lasers. The above combination should also be included in the scope of computer-readable media. Additionally, the operations of a method or algorithm may be incorporated into a computer program product as one or any combination or set of codes and instructions in a machine-readable medium and a computer-readable medium.

[0187] Various modifications to the embodiments described in this disclosure will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the embodiments shown herein, but rather to be accorded the widest scope consistent with the claims, principles, and novel features disclosed herein. The word "exemplary" is used exclusively herein to mean "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0188] Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of individual embodiments may also be implemented in multiple embodiments individually or in any suitable subcombination. Furthermore, while features may be described above as functioning in certain combinations and even initially claimed as such, in some cases one or more features from a claimed combination may be deleted from that combination, and the claimed combination may be directed to subcombinations or variations of subcombinations.

[0189] Similarly, although operations are depicted in a particular order in the accompanying drawings, this should not be understood as requiring that the operations be performed in the particular order or sequence shown, or that all of the illustrated operations be performed to achieve the desired results. In some cases, multitasking and parallel processing can be advantageous. Furthermore, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated into a single software product or packaged into multiple software products. Additionally, other embodiments are also within the scope of the following claims. In some cases, the actions listed in the claims can be performed in a different order and still achieve the desired results.

[0190] It should be understood that unless the features in any particular described embodiment are explicitly identified as incompatible with each other, or the surrounding context suggests that they are mutually exclusive and not easily combined in a complementary and / or supporting sense, the overall concept and contemplation of the present disclosure contemplates that the specific features of these complementary embodiments can be selectively combined to provide one or more comprehensive but slightly different technical solutions. Therefore, it will be further understood that the above description is given only as an example, and detailed modifications may be made within the scope of the present disclosure.

Claims

1. A device comprising: an ultrasonic transmitter configured to transmit ultrasonic waves in a range of 1 MHz to 30 MHz; a low-frequency vibration source configured to generate low-frequency vibrations in a range of 5 Hz to 2000 Hz; wherein the ultrasonic transmitter and the low-frequency vibration source are mechanically coupled; an ultrasonic receiver; and The control system is configured to: controlling the ultrasonic transmitter to transmit a first ultrasonic wave; controlling the low-frequency vibration source to generate a first low-frequency vibration; Synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave, wherein synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave comprises: controlling the low frequency vibration source for generation of the first low frequency vibration during a first time interval; and controlling the ultrasonic transmitter to transmit the first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval; receiving an ultrasonic receiver signal from the ultrasonic receiver, the ultrasonic receiver signal including a signal corresponding to a reflection of the first ultrasonic wave from a target object in contact with an outer surface of the device; and An authentication process is performed based at least in part on the ultrasound receiver signal.

2. The device according to claim 1, wherein The low frequency vibration source includes one or more of a haptic device, a speaker, a piezoelectric actuator, an eccentric rotating mass, or a linear resonant actuator.

3. The device according to claim 1, wherein The low frequency vibration source is configured to at least one of induce local low frequency vibrations of only a portion of the device or induce global low frequency vibrations of the entire device.

4. The device according to claim 1, wherein The low frequency vibration source and the ultrasonic transmitter are included in a single device.

5. The device according to claim 1, wherein The control system is further configured to: determining a contact quality metric corresponding to at least one of an image quality metric or a feature quality metric; and A determination is made whether to actuate the low frequency vibration source based at least in part on the contact quality metric.

6. The device according to claim 1, wherein The control system is configured to control the low frequency vibration source to generate at least one of a single frequency or a plurality of frequencies.

7. The device according to claim 1, wherein The control system is configured to control the low-frequency vibration source to at least one of intermittently generate the low-frequency vibration or continuously generate the low-frequency vibration.

8. The device according to claim 1, wherein The control system is configured to extract features from the ultrasound receiver signal, and wherein the authentication process is based at least in part on the features.

9. The device according to claim 8, wherein The control system is configured to: determining at least one feature quality metric; using the characteristic quality metric as a feedback signal for the low frequency vibration source; and The low frequency vibration source is controlled based at least in part on the feedback signal.

10. The device according to claim 8, wherein The control system is configured to: determining at least one feature quality metric; determining whether the at least one feature quality metric is below a feature quality metric threshold; and if it is determined that the at least one feature quality metric is below the feature quality metric threshold, The low-frequency vibration source is then controlled to generate a second low-frequency vibration having an amplitude greater than an amplitude of the first low-frequency vibration.

11. The device according to claim 1, wherein The ultrasonic transceiver layer includes the ultrasonic transmitter and the ultrasonic receiver.

12. An authentication method, comprising: controlling the ultrasonic transmitter to transmit a first ultrasonic wave; controlling a low-frequency vibration source to generate a first low-frequency vibration; Synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave, wherein the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave is synchronized includes: controlling the low frequency vibration source for generation of the first low frequency vibration during a first time interval; and controlling the ultrasonic transmitter to transmit the first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval; receiving an ultrasonic receiver signal from an ultrasonic receiver, the ultrasonic receiver signal including a signal corresponding to a reflection of the first ultrasonic wave from a target object in contact with an outer surface of the device; and An authentication process is performed based at least in part on the ultrasound receiver signal. 13 . The method of claim 12 , further comprising detecting background noise in the ultrasound receiver signal based at least in part on the first low frequency vibration.

14. The method according to claim 12, wherein: Controlling the low frequency vibration source includes at least one of causing local low frequency vibrations of only a portion of the device or causing global low frequency vibrations of the entire device.

15. The method according to claim 12, wherein: Controlling the low frequency vibration source and controlling the ultrasonic transmitter includes controlling a single device.

16. The method according to claim 12, wherein: Controlling the low-frequency vibration source includes causing the low-frequency vibration source to generate the first low-frequency vibration in the plane of the outer surface or to generate the first low-frequency vibration perpendicular to the plane of the outer surface.

17. The method according to claim 12, wherein: Controlling the low-frequency vibration source includes causing the low-frequency vibration source to generate at least one of a single frequency or multiple frequencies.

18. The method according to claim 12, wherein: Controlling the low-frequency vibration source includes causing the low-frequency vibration source to at least one of intermittently generate low-frequency vibrations or continuously generate low-frequency vibrations.

19. The method of claim 12, further comprising extracting features from the ultrasound receiver signal, wherein The authentication process is based at least in part on the characteristics.

20. The method of claim 19, further comprising: determining at least one feature quality metric; using the characteristic quality metric as a feedback signal for the low frequency vibration source; as well as The low frequency vibration source is controlled based at least in part on the feedback signal.

21. The method of claim 19, further comprising: determining at least one feature quality metric; determining whether the at least one feature quality metric is below a feature quality metric threshold; and if it is determined that the at least one feature quality metric is below a feature quality metric threshold, The low-frequency vibration source is then controlled to generate a second low-frequency vibration having an amplitude greater than an amplitude of the first low-frequency vibration.

22. One or more non-transitory media having stored thereon software, the software comprising instructions for controlling one or more devices to perform an authentication method, the authentication method comprising: controlling the ultrasonic transmitter to transmit a first ultrasonic wave; controlling a low-frequency vibration source to generate a first low-frequency vibration; Synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave, wherein synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave comprises: controlling the low frequency vibration source for generation of the first low frequency vibration during a first time interval; and controlling the ultrasonic transmitter to transmit the first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval; receiving an ultrasonic receiver signal from an ultrasonic receiver, the ultrasonic receiver signal including a signal corresponding to a reflection of the first ultrasonic wave from a target object in contact with an outer surface of the device; and An authentication process is performed based at least in part on the ultrasound receiver signal.

23. An apparatus comprising: a transmitting component for transmitting ultrasonic waves in the range of 1 MHz to 30 MHz; Generating components for generating low-frequency vibrations in the range of 5 Hz to 2000 Hz; A receiving component, used for receiving ultrasonic waves; as well as Control components for: controlling the transmitting component to transmit a first ultrasonic wave; controlling the generating component to generate a first low-frequency vibration; Synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave, wherein synchronizing the generation of the first low-frequency vibration with the transmission of the first ultrasonic wave comprises: controlling the generating component for generation of the first low-frequency vibration during a first time interval; and controlling the transmitting component to transmit the first ultrasonic wave during a second time interval, the second time interval at least partially coinciding with the first time interval; receiving an ultrasonic receiver signal from the receiving part, the ultrasonic receiver signal including a signal corresponding to reflection of the first ultrasonic wave from a target object in contact with an outer surface of the device; and An authentication process is performed based at least in part on the ultrasound receiver signal.

24. A computer program product comprising computer readable instructions which, when executed by a processor, cause the processor to perform the method of any one of claims 12 to 21.

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