Patent Description:
Biometric authentication can be an important feature for controlling access to devices, etc. Many existing products include some type of biometric authentication. Although some existing biometric authentication technologies provide satisfactory performance, improved methods and devices would be desirable.

In <CIT>, there is described an ultrasonic-based acoustic impedance calibration method. The method comprises the following steps. Step <NUM>: an ultrasonic sensor sends out an ultrasonic transmitting signal. Step <NUM>: the ultrasonic sensor receives an ultrasonic feedback signal. Step <NUM>: the ultrasonic transmitting signal and the ultrasonic feedback signal analyzed to obtain an ultrasonic transmission characteristic parameter. Step <NUM>: a pre-stored ultrasonic transmission characteristic parameter is obtained. Step <NUM>: the ultrasonic transmission characteristic parameter obtained in Step <NUM> is compared with that in Step <NUM> to determine whether the acoustic impedance of the ultrasonic transmission path is changed. If YES, calibration can be carried out in real time, and the sensing precision of the ultrasonic sensor is ensured.

In <CIT>, methods, systems, and devices for detection of a protective cover film on a capacitive touch screen are described. A device may include a capacitive touch screen having a surface and a sensor grid underneath the surface having a set of conductive columns and a set of conductive rows. The device may measure a mutual capacitance between a subset of conductive columns or a subset of conductive rows associated with a sensor grid, and compare the measured mutual capacitance between the subset of conductive columns or the subset of conductive rows to a baseline mutual capacitance associated with the set of conductive columns and the set of conductive rows. According to the comparison, the device may determine a presence of a protective layer in contact with the surface of the capacitive touch screen, and adjust an operating characteristic of the sensor grid.

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

Features of some embodiments are recited in dependent claims.

The following description is directed to certain implementations for the purposes of describing the innovative aspects of this disclosure. However, a person having ordinary skill in the art will readily recognize that the teachings herein may be applied in a multitude of different ways. The described implementations may be implemented in any device, apparatus, or system that includes a biometric system as disclosed herein. In addition, it is contemplated that the described implementations may be included in or associated with a variety of electronic devices such as, but not limited to: mobile telephones, multimedia Internet enabled cellular telephones, mobile television receivers, wireless devices, smartphones, smart cards, wearable devices such as bracelets, armbands, wristbands, rings, headbands, patches, etc., Bluetooth® devices, personal data assistants (PDAs), wireless electronic mail receivers, hand-held or portable computers, netbooks, notebooks, smartbooks, tablets, printers, copiers, scanners, facsimile devices, global positioning system (GPS) receivers/navigators, cameras, digital media players (such as MP3 players), camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, auto displays (including odometer and speedometer displays, etc.), cockpit controls and/or displays, camera view displays (such as the display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, microwaves, refrigerators, stereo systems, cassette recorders or players, DVD players, CD players, VCRs, radios, portable memory chips, washers, dryers, washer/dryers, parking meters, packaging (such as in electromechanical systems (EMS) applications including microelectromechanical systems (MEMS) applications, as well as non-EMS applications), aesthetic structures (such as display of images on a piece of jewelry or clothing) and a variety of EMS devices. The teachings herein also may be used in applications such as, but not limited to, electronic switching devices, radio frequency filters, sensors, accelerometers, gyroscopes, motion-sensing devices, magnetometers, inertial components for consumer electronics, parts of consumer electronics products, steering wheels or other automobile parts, varactors, liquid crystal devices, electrophoretic devices, drive schemes, manufacturing processes and electronic test equipment. Thus, the teachings are not intended to be limited to the implementations depicted solely in the Figures, but instead have wide applicability as will be readily apparent to one having ordinary skill in the art.

Many existing products, including but not limited to mobile phones, are configured for fingerprint-based authentication. Some such devices include an ultrasonic fingerprint sensor. It is common for mobile device users to apply or remove screen protective films, device covers, cases, etc. However, ultrasonic fingerprint sensor performance can be significantly affected by the presence of such layers, whether they are laminated film layers, case layers or cover layers. In some instances, a fingerprint sensor may accept a registration of a fingerprint underlying a cover or case, which can cause a false acceptance. Alternatively, or additionally, in some instances an ultrasonic fingerprint sensor may falsely interpret features (e.g., textures or patterns) of a case cover as being fingerprint features.

Some disclosed methods involve acquiring first ultrasonic signals via an ultrasonic sensor system at a first time. The first ultrasonic signals may include reference ultrasonic signals corresponding to reflections from a cover glass/air interface. In some instances, the first time may correspond to a factory calibration process. Some such methods involve acquiring second ultrasonic signals via the ultrasonic sensor system at a second time. The second time may correspond to an end user calibration process. Some such methods involve determining, based at least in part on a comparison of the first ultrasonic signals and the second ultrasonic signals, whether one or more layers reside on the cover glass at the second time. If it is determined that the one or more layers reside on the cover glass at the second time, some methods may involve determining one or more signal characteristics corresponding to properties of the one or more layers and determining, based at least in part on the one or more signal characteristics, whether the one or more layers are compatible with the ultrasonic sensor system. For example, some methods may involve determining whether the ultrasonic sensor system can be properly calibrated while the one or more layers are residing on the cover glass. Alternatively, or additionally, some methods may involve determining whether the one or more layers may present a security risk if they are used with the ultrasonic sensor system. If it is determined that the one or more layers are compatible with the ultrasonic sensor system, the method may involve calibrating the ultrasonic sensor system based, at least in part, on the one or more properties of the one or more layers. If it is determined that the one or more layers are not compatible with the ultrasonic sensor system, the method may involve prompting a user to remove the one or more layers.

Particular implementations of the subject matter described in this disclosure may be implemented to realize one or more of the following potential advantages. Detecting one or more protective film layers, cover layers, a protective case, etc., on an device that includes an ultrasonic sensor and calibrating an ultrasonic sensor accordingly can allow the ultrasonic sensor to function properly. In some instances, such detection and calibration may avoid false acceptances of underlying fingerprints and/or falsely interpreting ultrasonic features (e.g., textures or patterns) of a case cover as being fingerprint features in the phase of registration. According to some examples, the ultrasonic sensor system may include a piezoelectric layer, an electrode proximate a first side of the piezoelectric layer and an array of ultrasonic sensor pixels proximate a second side of the piezoelectric layer. The first ultrasonic signals and the second ultrasonic signals may, in some such examples, be received via the electrode. Such implementations are potentially advantageous for various reasons. One such potential advantage is that there may be a relatively higher signal-to-noise ratio if ultrasonic signals are received via the electrode instead of being received via the array of ultrasonic sensor pixels. Moreover, implementations in which ultrasonic signals can be received via the electrode instead of being received via the array of ultrasonic sensor pixels may be relatively faster, may use relatively less power and may be relatively less costly to operate.

<FIG> is a block diagram that shows example components of an apparatus according to some disclosed implementations. In this example, the apparatus <NUM> includes an ultrasonic sensor system <NUM> and a control system <NUM>. In some implementations, the apparatus <NUM> may include an interface system <NUM> and/or a cover glass <NUM>.

According to this example, the ultrasonic sensor system <NUM> is, or includes, an ultrasonic fingerprint sensor. In some examples, as suggested by the dashed lines within the ultrasonic sensor system <NUM>, the ultrasonic sensor system <NUM> may include an ultrasonic receiver <NUM> and a separate ultrasonic transmitter <NUM>. In some such examples, the ultrasonic transmitter <NUM> may include an ultrasonic plane-wave generator.

However, various examples of ultrasonic fingerprint sensors are disclosed herein, some of which may include a separate ultrasonic transmitter <NUM> and some of which may not. Although shown as separate elements in <FIG>, in some implementations the ultrasonic receiver <NUM> and the ultrasonic transmitter <NUM> may be combined in an ultrasonic transceiver system. For example, in some implementations, the ultrasonic sensor system <NUM> may include a piezoelectric receiver layer, such as a layer of polyvinylidene fluoride PVDF polymer or a layer of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymer. In some implementations, a separate piezoelectric layer may serve as the ultrasonic transmitter. In some implementations, a single piezoelectric layer may serve as both a transmitter and a receiver. In some implementations that include a piezoelectric layer, other piezoelectric materials may be used in the piezoelectric layer, such as aluminum nitride (AlN) or lead zirconate titanate (PZT). The ultrasonic sensor system <NUM> may, in some examples, include an array of ultrasonic transducer elements, such as an array of piezoelectric micromachined ultrasonic transducers (PMUTs), an array of capacitive micromachined ultrasonic transducers (CMUTs), etc. In some such examples, PMUT elements in a single-layer array of PMUTs or CMUT elements in a single-layer array of CMUTs may be used as ultrasonic transmitters as well as ultrasonic receivers.

Data received from the ultrasonic sensor system <NUM> may sometimes be referred to herein as "ultrasonic image data," "image data," etc., although the data will generally be received from the ultrasonic sensor system in the form of electrical signals. Accordingly, without additional processing such image data would not necessarily be perceivable by a human being as an image.

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

Some implementations of the apparatus <NUM> may include an interface system <NUM>. In some examples, the interface system <NUM> may include a wireless interface system. In some implementations, the interface system <NUM> may include a user interface system, one or more network interfaces, one or more interfaces between the control system <NUM> and a memory system, and/or one or more interfaces between the control system <NUM> and one or more external device interfaces (e.g., ports or applications processors).

The interface system <NUM> may be configured to provide communication (which may include wired or wireless communication, electrical communication, radio communication, etc.) between components of the apparatus <NUM>. In some such examples, the interface system <NUM> may be configured to provide communication between the control system <NUM> and the ultrasonic sensor system <NUM>. According to some such examples, the interface system <NUM> may couple at least a portion of the control system <NUM> to the ultrasonic sensor system <NUM>, e.g., via electrically conducting material (e.g., via conductive metal wires or traces. If the apparatus <NUM> includes an ultrasonic transmitter <NUM> that is separate from the ultrasonic receiver <NUM>, the interface system <NUM> may be configured to provide communication between at least a portion of the control system <NUM> and the ultrasonic transmitter <NUM>. According to some examples, the interface system <NUM> may be configured to provide communication between the apparatus <NUM> and other devices and/or human beings. In some such examples, the interface system <NUM> may include one or more user interfaces. The interface system <NUM> may, in some examples, 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 a serial peripheral interface (SPI)). In some implementations, the apparatus <NUM> may include a memory system. The interface system <NUM> may, in some examples, include at least one interface between the control system <NUM> and a memory system.

According to some examples, the apparatus <NUM> may include a cover glass <NUM>. The cover glass may or may not actually be made of glass, depending on the particular implementation. The cover glass <NUM> may be formed of any appropriate material, such as glass, a hard plastic, etc. If the cover glass <NUM> overlies a display, the cover glass <NUM> is preferably formed of transparent material.

In some implementations, the apparatus <NUM> may include a display <NUM>. For example, the apparatus <NUM> may include layers of a display, which layers may be referred to herein as a "display stack. " In some examples, the display <NUM> may be, or may include, a light-emitting diode (LED) display, such as an organic light-emitting diode (OLED) display.

The apparatus <NUM> may be used in a variety of different contexts, some examples of which are disclosed herein. For example, in some implementations a mobile device may include at least a portion of the apparatus <NUM>. In some implementations, a wearable device may include at least a portion of the apparatus <NUM>. The wearable device may, for example, be a bracelet, an armband, a wristband, a ring, a headband or a patch. In some implementations, the control system <NUM> may reside in more than one device. For example, a portion of the control system <NUM> may reside in a wearable device and another portion of the control system <NUM> may reside in another device, such as a mobile device (e.g., a smartphone). The interface system <NUM> also may, in some such examples, reside in more than one device.

<FIG> shows example components of an apparatus according to some disclosed implementations. As with other disclosed implementations, the types, number and arrangement of elements, as well as the dimensions of elements, are merely examples. According to this example, the apparatus <NUM> is configured to perform at least some of the methods disclosed herein. According to this implementation, the apparatus <NUM> has an ultrasonic sensor system <NUM> that includes a piezoelectric layer <NUM>, an electrode layer <NUM> on one side of the piezoelectric layer <NUM> and an array of sensor pixels <NUM> on a second and opposing side of the piezoelectric layer <NUM>. In this implementation, the piezoelectric layer <NUM> is an ultrasonic transceiver layer that includes one or more piezoelectric polymers.

According to this example, the electrode layer <NUM> resides between a passivation layer <NUM> and the piezoelectric layer <NUM>. In some examples, passivation layer <NUM> may include an adhesive, such as an epoxy film, a polymer layer (such as a polyethylene terephthalate (PET) layer), etc..

In this example the thin-film transistor (TFT) layer <NUM> includes a TFT substrate and circuitry for the array of sensor pixels <NUM>. The TFT layer <NUM> may be a type of metal-oxide-semiconductor field-effect transistor (MOSFET) made by depositing thin films of an active semiconductor layer as well as a dielectric layer and metallic contacts over a TFT substrate. In some examples, the TFT substrate may be a non-conductive material such as glass.

In this example, the apparatus <NUM> includes a display <NUM>, which is an OLED display in this instance. Here, the display <NUM> is attached to the TFT layer <NUM> via an adhesive layer <NUM>.

According to this implementation, the TFT layer <NUM>, the array of sensor pixels <NUM> and the electrode are electrically coupled to at least a portion of the control system <NUM> and one side of the ultrasonic transceiver layer <NUM> via a portion of the interface system <NUM>, which includes electrically conducting material and a flexible printed circuit (FPC) in this instance.

In this example, the apparatus <NUM> is configured to perform at least some of the methods disclosed herein. In this example, the control system <NUM> is configured to control the ultrasonic sensor system <NUM> to transmit one or more ultrasonic waves <NUM>. According to this example, the ultrasonic wave(s) <NUM> are transmitted through the TFT layer <NUM>, the display <NUM> and the cover glass <NUM>. According to this example, reflections <NUM> of the ultrasonic wave(s) <NUM> are caused by acoustic impedance contrast at (or near) the interface <NUM> between the outer surface of the cover glass <NUM> and whatever is in contact with the outer surface, which may be air, one or more protective layers (e.g., of a protective film, cover or case), ridges and valleys of a fingerprint, etc. (As used herein, the term "finger" may refer to any digit, including a thumb. Accordingly, a thumbprint will be considered a type of "fingerprint.

<FIG> is a flow diagram that provides examples of operations according to the independent claims. The blocks of <FIG> may, for example, be performed by the apparatus <NUM> of <FIG> or <FIG>, or by a similar apparatus.

In this example, block <NUM> involves acquiring first ultrasonic signals via an ultrasonic sensor system at a first time. For example, block <NUM> may involve the control system <NUM> of <FIG> or <FIG> controlling the ultrasonic sensor system <NUM> to acquire first ultrasonic signals at a first time. In some examples, the "first time" may correspond to a factory calibration process. In some such examples, the "first time" may correspond to the first time that the ultrasonic sensor system and/or a device that includes the ultrasonic sensor system, is booted up for the first time.

According to this example, the first ultrasonic signals include reference ultrasonic signals corresponding to reflections from a cover glass/air interface and/or a cover glass/target interface. In some such implementations, the reference ultrasonic signals corresponding to reflections from a cover glass/air interface are obtained because at the first time there is no protective film, protective cover, etc. on the cover glass of the ultrasonic sensor system, or on the cover glass of a device that includes the ultrasonic sensor system. Alternatively, or additionally, the reference ultrasonic signals may correspond to reflections from a cover glass/target interface. The cover glass/target interface may correspond to a target, such as an alignment target, that is in contact with the cover glass during the first time. Such reference ultrasonic signals may, for example, be obtained when the "first time" corresponds to a factory calibration process. In alternative implementations (e.g., wherein the apparatus is shipped to end users with a protective film on the cover glass), the reference ultrasonic signals may correspond to reflections from another interface, such as a protective film/air interface.

In some implementations, for example as shown in <FIG>, the ultrasonic sensor system may include a piezoelectric layer, an electrode proximate a first side of the piezoelectric layer and an array of the ultrasonic sensor system includes a piezoelectric layer, an electrode proximate a first side of the piezoelectric layer and an array of ultrasonic sensor pixels proximate a second side of the piezoelectric layer. According to some such implementations, the first ultrasonic signals may be received via the electrode instead of, or in addition to, being received via one or more of the ultrasonic sensor pixels. Such implementations are potentially advantageous, at least in part because there may be a relatively higher signal-to-noise ratio if ultrasonic signals are received via the electrode instead of being received via the array of ultrasonic sensor pixels and the corresponding TFT circuitry. Moreover, implementations in which ultrasonic signals can be received via the electrode instead of being received via the array of ultrasonic sensor pixels may be relatively faster, may use relatively less power and may be relatively less costly to operate. However, in alternative implementations, the first ultrasonic signals may be received via one or more of the ultrasonic sensor pixels.

According to this example, block <NUM> involves acquiring second ultrasonic signals via the ultrasonic sensor system at a second time. For example, block <NUM> may involve the control system <NUM> of <FIG> or <FIG> controlling the ultrasonic sensor system <NUM> to acquire second ultrasonic signals at the second time. In some instances, the "second time" may correspond to an end user calibration process. For example, the second time may correspond to the first time that an end user turns on a device that includes the ultrasonic sensor system.

Some implementations may involve controlling a display to present one or more graphical user interfaces corresponding to a factory calibration process and/or a fingerprint registration process. Some examples are disclosed herein and described below. Some such implementations may involve controlling a display to present a graphical user interface prompting a user to ensure that there is no layer residing on the cover glass prior to acquiring the first ultrasonic signals. Alternatively, or additionally, some implementations may involve controlling a display to present a graphical user interface indicating an ultrasonic sensor system area and prompting a user to ensure that there is no finger or other object in the ultrasonic sensor system area prior to acquiring the second ultrasonic signals.

According to some examples, blocks <NUM> and <NUM> may involve acquiring the first ultrasonic signals and the second ultrasonic signals by controlling the ultrasonic sensor system to transmit ultrasonic waves that include a range of frequencies, e.g., a range of <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, etc. Some implementations of the ultrasonic sensor system may be configured to transmit "broadband" ultrasonic waves that include the entire range of frequencies, or may be configured to sweep a range of ultrasonic waves at a series of peak frequencies that spans the entire range of frequencies. Other implementations of the ultrasonic sensor system may need to transmit multiple instances of ultrasonic waves (e.g., multiple bursts) in order to include the entire range of frequencies. Whether a single broadband transmission, a sweep that includes a range of frequencies or a series of individual instances of transmission, the ultrasonic wave transmission process corresponding to blocks <NUM> and <NUM> may be thought of as occurring at the "first time" or the "second time.

In this example, block <NUM> involves determining, based at least in part on a comparison of the first ultrasonic signals and the second ultrasonic signals, whether one or more layers reside on the cover glass at the second time. According to this example, if it is determined that the one or more layers reside on the cover glass at the second time, block <NUM> also involves determining one or more signal characteristics corresponding to one or more properties of the one or more layers. In some instances, the properties may include layer thickness, material type and/or material patterning. According to some examples, additional ultrasonic signals may be obtained to determine the properties. The signal characteristics may include frequency, amplitude, phase and/or combinations thereof. In this example, block <NUM> involves determining, based at least in part on the one or more signal characteristics, whether the one or more layers are compatible with the ultrasonic sensor system. For example, determining whether the one or more layers are compatible with the ultrasonic sensor system may involve determining whether the ultrasonic sensor system can be properly calibrated while the one or more layers are residing on the cover glass. In some such examples, determining whether the one or more layers are compatible with the ultrasonic sensor system may involve determining whether a stored set of ultrasonic fingerprint sensor parameters corresponds with the one or more layers are residing on the cover glass. The stored set of ultrasonic fingerprint sensor parameters may, for example, reside in a data structure that includes compatible protective film, cover or case types and corresponding sets of ultrasonic fingerprint sensor parameters. Alternatively, or additionally, determining whether the one or more layers are compatible with the ultrasonic sensor system may involve determining whether the one or more layers may present a security risk if they are used with the ultrasonic sensor system.

In some instances, block <NUM> may involve determining that the one or more layers are compatible with the ultrasonic sensor system. According to some such implementations, the method <NUM> may involve calibrating the ultrasonic sensor system based, at least in part, on the one or more properties of the detected layer(s).

Calibrating the ultrasonic sensor system may involve determining at least one ultrasonic fingerprint sensor parameter modification and updating at least one setting of the ultrasonic fingerprint sensor based, at least in part, on the ultrasonic fingerprint sensor parameter modification. In some instances, the ultrasonic fingerprint sensor parameter modification(s) may include a gain value modification, a modification of a peak frequency of a transmitted ultrasonic wave, a range gate delay modification, a range gate window modification, a modification of an applied voltage and/or a modification of a voltage bias condition. Examples of these parameters are described below with reference to corresponding figures. According to some examples, determining the ultrasonic fingerprint sensor parameter modification(s) may involve obtaining one or more new ultrasonic fingerprint sensor parameters from a data structure. For example, determining the ultrasonic fingerprint sensor parameter modification(s) may involve obtaining a set of ultrasonic fingerprint sensor parameters from a portion of a data structure corresponding to a previously-evaluated type of protective film, protective cover, protective case, etc. The data structure may include protective film, cover or case types and corresponding sets of ultrasonic fingerprint sensor parameters. The data structure may, for example, have previously been saved to a memory of a device that includes the ultrasonic fingerprint sensor, e.g., during a factory calibration process.

Table <NUM> provides a simple example of a portion of one such data structure. In Table <NUM>, an example of a set of ultrasonic fingerprint sensor parameters corresponding to a particular protective layer type (type "2A") is shown. In this example, the set of ultrasonic fingerprint sensor parameters includes a voltage boost (VBOOST) of <NUM> Volts, a bias Voltage (DBIAS) of <NUM> Volts, an integration time of <NUM> microseconds, a range-gate delay (RGD) of <NUM> microseconds and a range gate window (RGW) of <NUM> microseconds. The meanings of the terms DBIAS, RGD and RGW, along with illustrative examples, are discussed below with reference to <FIG> and <FIG>. "Integration time" corresponds to the time period in which a pixel is enabled to sense for each tone burst. It is a good indicator of the system latency. The voltage boost VBOOST refers to the boost voltage applied to the transmitter. VBOOST can be adjusted, in some examples, via a sequencer.

In some instances, block <NUM> may involve determining that the one or more layers are not compatible with the ultrasonic sensor system. As noted above, in some instances an ultrasonic fingerprint sensor may falsely interpret ultrasonic features (e.g., textures or patterns) of a case cover as being fingerprint features, e.g., during a registration process. If such patterns have, in the past, led to such false positives, block <NUM> may involve determining that the one or more layers are not compatible with the ultrasonic sensor system. In some instances, block <NUM> may involve determining that the thickness and/or material type of one or more detected layers mean that the one or more layers are not compatible with the ultrasonic sensor system. In some implementations wherein block <NUM> involves determining that the one or more layers are not compatible with the ultrasonic sensor system, the method <NUM> may involve controlling a display to present a graphical user interface prompting a user to remove the one or more layers. Some implementations may involve further processes of determining whether the one or more layers have been removed (e.g., by acquiring more ultrasonic signals corresponding to the outer surface of the cover glass). Some such processes may involve a further calibration process, if necessary.

After the ultrasonic sensor system is calibrated (whether according to a factory calibration process or an end user calibration process), some implementations involve a subsequent fingerprint registration process. Some such implementations may involve controlling a display to present a graphical user interface indicating an ultrasonic sensor system area and prompting a user to touch the ultrasonic sensor system area during the fingerprint registration process. Additional examples of graphical user interfaces for a fingerprint registration process are described below. Some fingerprint registration processes involve controlling the ultrasonic sensor system to acquire third ultrasonic signals at a third time. The third ultrasonic signals may include registration ultrasonic signals corresponding to reflections from a digit in contact with the ultrasonic sensor system area.

In some examples, the control system <NUM> of <FIG> or <FIG> may be configured to receive, from the ultrasonic sensor system <NUM>, signals corresponding to reflections of ultrasonic waves from a surface of a portion of a target object, such as a finger, that is on an outer surface of the cover glass <NUM> or on the outer surface of one or more detected layers that reside on the cover glass <NUM>. In some examples, the control system <NUM> may be configured to obtain fingerprint data based on portions of the reflected ultrasonic waves that are received within a time interval corresponding with fingerprints. The time interval may, for example, be measured relative to a time at which ultrasonic waves corresponding to the third ultrasonic signals are transmitted. Obtaining the fingerprint data may, for example, involve extracting, via the control system <NUM>, fingerprint features from the first signals. According to some examples, the fingerprint features may include fingerprint minutiae, keypoints and/or sweat pores. In some examples, the fingerprint features may include ridge ending information, ridge bifurcation information, short ridge information, ridge flow information, island information, spur information, delta information, core information, etc..

In some examples, the control system <NUM> may be configured to perform a subsequent authentication process that is based, at least in part, on the fingerprint features. According to some examples, the control system <NUM> may be configured to compare the fingerprint features with subsequently-obtained features of target object, such as a finger.

In some implementations, the control system <NUM> may be configured to extract sub-epidermal features from the third ultrasonic signals, or from other ultrasonic signals. In some such implementations, the sub-epidermal features may include sub-epidermal layer information corresponding to reflections received within a time interval corresponding with a sub-epidermal region. According to some implementations, a subsequent authentication process may involve comparing sub-epidermal features extracted from the third ultrasonic signals with subsequently-obtained sub-epidermal features.

The sub-epidermal features may, for example, include dermis layer information corresponding to reflections corresponding to the third ultrasonic signals, or to other ultrasonic signals. The dermis layer information may have been obtained within a time interval corresponding with a dermis layer. The subsequent authentication process may be based, at least in part, on the dermis layer information. Alternatively, or additionally, the sub-epidermal features may include information regarding other sub-epidermal layers, such as the papillary layer, the reticular layer, the subcutis, etc., and any blood vessels, lymph vessels, sweat glands, hair follicles, hair papilla, fat lobules, etc., that may be present within such tissue layers.

In some examples, the control system <NUM> may be configured for controlling access to the apparatus <NUM>, or to another device, based at least in part on the subsequent authentication process. For example, in some implementations a mobile device (such as a cell phone) may include the apparatus <NUM>. In some such examples, the control system <NUM> may be configured for controlling access to the mobile device based, at least in part, on the subsequent authentication process.

In some implementations an Internet of things (IoT) device may include the apparatus <NUM>. For example, in some such implementations a device intended for use in a home, such as a remote control device (such as a remote control device for a smart television), a stove, an oven, a refrigerator, a stove, a coffee maker, an alarm system, a door lock, a mail/parcel box lock, a thermostat, etc., may include the apparatus <NUM>. In some such examples, the control system may be configured for controlling access to the IoT device based, at least in part, on the subsequent authentication process.

In alternative implementations, an automobile (including but not limited to a partially or fully autonomous automobile), a partially or fully autonomous delivery vehicle, a drone, or another device typically used outside of the home may include the apparatus <NUM>. In some such examples, the control system may be configured for controlling access to the vehicle, the drone, etc., based at least in part on the subsequent authentication process.

In some examples, including but not limited to many IoT implementations, there may be a metal, plastic, ceramic or polymer layer between an outer surface of the apparatus <NUM>, or an outer surface of a device that includes the apparatus <NUM>. In such implementations, the acoustic waves transmitted towards, and reflected from, a finger or other target may need to pass through the metal, plastic, ceramic or polymer layer. Ultrasound and other acoustic waves can be successfully transmitted through e.g., a metal layer, whereas some other types of waves (e.g., light waves) cannot. Similarly, ultrasound and other acoustic waves can be successfully transmitted through an optically opaque plastic, ceramic or polymer layer, whereas some other types of waves, such as light waves, cannot. This feature is another potential advantage of some disclosed implementations, as compared to devices that rely upon optical or capacitive fingerprint sensors.

<FIG> show examples of screen protectors residing on cover glasses of devices that include fingerprint sensors. In these examples, the illustrated fingerprint sensors are instances of the ultrasonic sensor system <NUM> that is shown in <FIG>, the OLED display stacks are instances of the display <NUM> shown in <FIG> and the cover glasses are instances of the cover glass <NUM> shown in <FIG>.

The plastic film screen protector 400a of <FIG> and the tempered glass screen protector 400b of <FIG> are examples of the "one or more layers" residing on the cover glass <NUM> described above, e.g., with reference to block <NUM> of <FIG>. The plastic film screen protector 400a includes alternating layers of adhesive <NUM> and plastic <NUM>. The tempered glass screen protector 400b includes an adhesive layer <NUM>, a glass layer <NUM> and an anti-shatter film disposed between the adhesive layer <NUM> and the glass layer <NUM>.

<FIG> shows three superimposed graphs of ultrasonic signals received via an electrode. The electrode may, in some examples, be the electrode <NUM> of <FIG> or a similar electrode. In <FIG>, the dashed line <NUM> corresponds to ultrasonic signals received from a device having a plastic screen protector, such as the plastic film screen protector 400a of <FIG>, on its cover glass. In this example, the dashed line <NUM> corresponds to ultrasonic signals received from a device having a tempered glass screen protector, such as the tempered glass screen protector 400b of <FIG>, on its cover glass. In <FIG>, the solid line <NUM> corresponds to ultrasonic signals received from a device having no screen protector on its cover glass.

In <FIG>, the horizontal axis represents time in microseconds and the vertical axis represents signal amplitude. In this example, the graphs are scaled so that the received waveforms are clearly visible. As a consequence of this scaling, the transmit waveform was clipped because the amplitude of transmit waveform is very high compared to that of the received signals. In this example, the transmit signal includes five pulses at <NUM>, with a gradual ramp up and ramp down of amplitude. In other examples, a transmit waveform may include between <NUM> and <NUM> pulses at single frequency, a chirp waveform that contains many frequencies, or another type of broadband waveform. According to some such examples, the frequencies may be in a range between <NUM> and <NUM>.

Even in the time domain representation that is shown in <FIG>, the signals received from the device with no screen protector may be distinguished from the signals received from the device with a plastic screen protector and from the signals received from the device with a tempered glass screen protector. As shown in <FIG>, the received waveforms have distinctive signal characteristics, including but not limited to amplitude information, phase information, etc., corresponding to properties of the "one or more layers" of the screen protectors. These signal characteristics may be analyzed and characterized to detect a screen protector and to distinguish one type of screen protector from another.

<FIG> shows frequency domain representations of the graphs shown in <FIG>. In <FIG>, the dashed line <NUM>' corresponds to a fast Fourier transform (FFT) of the time-domain ultrasonic signals <NUM> shown in <FIG>, the dashed line <NUM>' corresponds to an FFT of the time-domain ultrasonic signals <NUM> shown in <FIG> and the solid line <NUM>' corresponds to an FFT of the time-domain ultrasonic signals <NUM> shown in <FIG>.

It may be observed that the frequency domain representations of these graphs are readily distinguishable from one another, particularly in the frequency range between <NUM> and <NUM>. For example, at approximately <NUM> the curve <NUM>' (corresponding to the device with no screen protector) reaches its highest magnitude, whereas the curve <NUM>' (corresponding to the device with a plastic screen protector) is at a much lower magnitude. At between <NUM> and <NUM>, the curve <NUM>' (corresponding to the device with a tempered glass screen protector) reaches its highest magnitude, whereas the curve <NUM>' reaches one of its lowest magnitudes. Accordingly, these signal characteristics may be analyzed and characterized to detect a screen protector and to distinguish one type of screen protector from another.

<FIG> shows examples of acquisition time delays and acquisition time windows according to some implementations. Acquisition time delays may sometimes be referred to herein as range gate delays or RGDs. Acquisition time windows may sometimes be referred to herein as range gate windows or RGWs. These examples of RGDs and RGWs may, for example, be suitable for acquiring fingerprint data. However, <FIG> and the corresponding discussion also provide examples of ultrasonic fingerprint sensor parameters that may be applied in a calibration or re-calibration process such as those disclosed herein.

<FIG> provides an example of what may be referred to herein as "DBIAS sampling," in which the receiver bias voltage level changes when a signal is sampled. In this example, the receiver bias voltage level also changes when a signal is transmitted. In <FIG>, an acquisition time delay is labeled as "RGD," an acronym for "range-gate delay," and an acquisition time window is labeled as "RGW," an acronym for "range-gate window. " Graph 502a shows a transmitted signal <NUM> that is initiated at a time t<NUM>. The transmitted signal <NUM> may, for example, be a pulse of ultrasound.

Graph 502b shows examples of an acquisition time delay RGD and an acquisition time window RGW. The received waves 506a represent reflected ultrasonic waves that are received by an ultrasonic sensor array and sampled during the acquisition time window RGW, after the acquisition time delay RGD. In some examples, the acquisition time delay may be in the range of about <NUM> nanoseconds to about <NUM>,<NUM> nanoseconds or more. In some implementations, the acquisition time window may be in the range of <NUM> to <NUM> nanoseconds, or in the range of approximately <NUM> to <NUM> nanoseconds. In some examples, "approximately" or "about" may mean within +/- <NUM>%, whereas in other examples "approximately" or "about" may mean within +/- <NUM>%, +/- <NUM>% or +/- <NUM>%. However, in some implementations the first acquisition time window may be more than <NUM> nanoseconds.

According to some examples, a factory-calibrated acquisition time delay may correspond to an expected amount of time for an ultrasonic wave reflected from a surface of a cover glass to be received by at least a portion of the ultrasonic sensor system <NUM> (e.g., by an array of sensor pixels). Accordingly, the acquisition time delay and the acquisition time window may be selected to capture fingerprint features of a target object placed on a surface of the cover glass. For example, in some implementations with a cover glass about <NUM> microns thick, the acquisition time delay (RGD) may be set to about <NUM>,<NUM> nanoseconds and the acquisition time window (RGW) may be set to about <NUM> nanoseconds.

If it is determined in block <NUM> that one or more layers reside on the cover glass at the second time and that the one or more layers are compatible with the ultrasonic sensor system, one ultrasonic fingerprint sensor parameter modification may correspond to a detected thickness of the one or more layers and a previously-measured, or estimated, acoustic velocity of the one or more layers. For example, if the thickness and acoustic velocity of the one or more layers indicate that the expected amount of time for an ultrasonic wave reflected from an out surface of one or more layers to be received by the array of sensor pixels will increase by <NUM> nanoseconds, the RGD may be recalibrated to <NUM> nanoseconds. In some examples, the recalibration also may involve changing the peak frequency, bias voltage, applied voltage (e.g., for ultrasonic transmission) or other fingerprint sensor operating parameters in accordance with one or more layer properties. In some such implementations, the recalibration may involve retrieving a set of fingerprint sensor operating parameters that corresponds with a detected protective film, protective cover, etc., that corresponds with the one or more signal characteristics and/or properties determined in block <NUM>. The set of fingerprint sensor operating parameters may, for example, be retrieved from a data structure stored in a memory of a device that includes the ultrasonic sensor system.

<FIG> shows examples of an acquisition time delays and an acquisition time window according to some implementations of peak-to-peak sampling. Graph 650a shows a transmitted signal <NUM> that is initiated at a time t<NUM>. The transmitted signal <NUM> may, for example, be a pulse of ultrasound. In alternative examples, multiple pulses of ultrasound may be transmitted.

Graph 650b shows examples of an acquisition time delay RGD and an acquisition time window RGW. The received waves 670a represent reflected ultrasonic waves that are received by an ultrasonic sensor array and sampled during first acquisition time window RGW, after the acquisition time delay RGD. In some examples, the acquisition time delay may be in the range of about <NUM> nanoseconds to about <NUM>,<NUM> nanoseconds or more. In some implementations, the acquisition time window may be in the range of <NUM> to <NUM> nanoseconds, or in the range of approximately <NUM> to <NUM> nanoseconds. In some examples, "approximately" or "about" may mean within +/- <NUM>%, whereas in other examples "approximately" or "about" may mean within +/- <NUM>%, +/- <NUM>% or +/- <NUM>%. However, in some implementations the acquisition time window may be more than <NUM> nanoseconds.

<FIG> is a flow diagram that provides examples of operations according to some disclosed methods. The blocks of <FIG> may, for example, be performed by the apparatus <NUM> of <FIG>, <FIG>, <FIG>, or by a similar apparatus. As with other methods disclosed herein, the method outlined in <FIG> may include more or fewer blocks than indicated. Moreover, the blocks of methods disclosed herein are not necessarily performed in the order indicated. In some instances, one or more blocks may be performed concurrently.

In this example, block <NUM> involves a factory calibration process of a device that includes an ultrasonic sensor system. The factory calibration process may involve a number of ultrasonic fingerprint sensor parameters. According to some examples, the factory calibration process may involve "tuning" a particular frequency and RGD, as well as other ultrasonic fingerprint sensor parameters, with reference to a data structure such as a table.

In some implementations, every ultrasonic fingerprint sensor may be shipped from the factory with stored sets of predetermined ultrasonic fingerprint sensor parameter "offsets. " The offsets may be, or may include, groups of settings, such as RGD, frequency, some phase information, etc. For example, there may be a factory calibration involving a number of ultrasonic fingerprint sensor parameters, a group of ultrasonic fingerprint sensor parameter settings corresponding to "Offset <NUM>," a group of ultrasonic fingerprint sensor parameter settings corresponding to "Offset <NUM>," a group of ultrasonic fingerprint sensor parameter settings corresponding to "Offset <NUM>,"etc. In some examples, each offset may correspond to a different type of screen protector. According to some implementations, the factory calibration data and all of these offsets may be stored in a memory of the device that includes the ultrasonic sensor system (e.g., a memory of a cell phone that includes the ultrasonic sensor system). In some implementations, signal characteristics corresponding to each type of screen protector also may be stored. In some examples, block <NUM> may involve obtaining, via an electrode proximate a piezoelectric layer of the ultrasonic sensor system, first ultrasonic signals corresponding to reflections from a cover glass/air interface.

According to this example, block <NUM> involves normal fingerprint sensor operation. For example, block <NUM> may correspond to a time during which an end user has booted up the device that includes the ultrasonic sensor system and has started using the device. In some examples, block <NUM> may involve an initial process of obtaining the end user's fingerprint data, of using the fingerprint data to authenticate the end user and provide access to the device, etc. In this example, block <NUM> involves normal fingerprint sensor operation during a time before the end user has placed a protective cover, a screen protector, etc., on the device. In some examples, block <NUM> may involve obtaining, via an electrode proximate a piezoelectric layer of the ultrasonic sensor system, first ultrasonic signals corresponding to reflections from a cover glass/air interface.

In this example, block <NUM> involves periodically obtaining, via the electrode proximate the piezoelectric layer of the ultrasonic sensor system, second ultrasonic signals and comparing the second ultrasonic signals to the first ultrasonic signals. According to some examples, block <NUM> may involve determining whether a screen protector, a cover, etc., has been placed over a cover glass of the device, and if so what type of screen protector, cover, etc., has been placed over the cover glass. Block <NUM> may, in some examples, correspond to block <NUM> of <FIG>. In some examples, block <NUM> may involve determining whether a screen protector, cover, etc., that was previously placed over a cover glass of the device has been removed and/or replaced.

According to this implementation, block <NUM> involves determining whether a screen protector, cover, etc., that was detected and categorized in block <NUM> is compatible with the ultrasonic sensor system. According to some such implementations, block <NUM> may involve determining whether the device has a stored "offset," or set of ultrasonic fingerprint sensor parameters, corresponding with the screen protector, cover, etc., that was detected and categorized in block <NUM>. If not, in this example the process continues to block <NUM>, in which one or more prompts are provided to the end user to remove, replace or modify the screen protector, cover, etc. Some examples of user prompts are described below.

However, if it is determined in block <NUM> that the screen protector, cover, etc., that was detected and categorized in block <NUM> is compatible with the ultrasonic sensor system, the process continues to block <NUM>. In this example, block <NUM> involves an auto-calibration process (also referred to herein as a recalibration process), in which a stored set of ultrasonic fingerprint sensor parameters that corresponding with the detected screen protector, cover, etc., is applied to the ultrasonic fingerprint sensor.

According to this example, after block <NUM> the process continues to block <NUM>, in which one or more sets of fingerprint image data are obtained by the ultrasonic fingerprint sensor and the image quality of the obtained fingerprint image data is evaluated.

Block <NUM> involves determining whether the fingerprint image quality is acceptable, e.g., whether the fingerprint image quality is at or above a threshold level. If so, the changes to the ultrasonic fingerprint sensor parameters are confirmed in block <NUM>. If not, in this example the process reverts to block <NUM>. In some implementations, if it is determined in block <NUM> more than a threshold number of times that an auto-calibration process with the same set of ultrasonic fingerprint sensor parameters has failed more than a threshold number of times (e.g., <NUM> times, <NUM> times, <NUM> times, etc.), the process may continue to block <NUM>.

<FIG> shows an example of a graphical user interface (GUI) that may be presented in some implementations. In this example, the GUI <NUM> includes a message area <NUM> and indicates an ultrasonic sensor system area <NUM>. In this example, the message area <NUM> is presenting information and a prompt relating to acquiring the above-described "first ultrasonic signals" via the ultrasonic sensor system at a first time. The first time may correspond to an initial calibration process, such as a factory calibration process. In some instances, the first time may correspond to the first time that the ultrasonic sensor system, or a device that includes the ultrasonic sensor system, is booted up. Because the first ultrasonic signals are intended to include reference ultrasonic signals corresponding to reflections from a cover glass/air interface, the message area <NUM> includes a prompt to ensure that there is no film, finger or other object on the ultrasonic sensor system area <NUM>.

In some implementations, the message area <NUM> may be a virtual button with which a user may interact, e.g., by touching the message area <NUM>, in order to indicate that there is no film, finger or other object on the ultrasonic sensor system area <NUM>. In some such implementations, the device includes a touch screen, e.g., a touch screen overlying the display that is presenting the GUI <NUM>. A control system may be configured to interpret a touch in the message area <NUM> as a response to at least a portion of the text in the message area <NUM>, e.g., as an affirmation that there is no film, finger or other object on the ultrasonic sensor system area <NUM>.

<FIG> shows another example of a GUI that may be presented in some implementations. In this example, the GUI <NUM> includes a message area <NUM> and indicates an ultrasonic sensor system area <NUM>. In this example, the message area <NUM> is presenting information and a prompt relating to acquiring the above-described "second ultrasonic signals" via the ultrasonic sensor system at a second time. The second time may correspond to an end user calibration process. In some instances, the second time may correspond to the first time that the ultrasonic sensor system, or a device that includes the ultrasonic sensor system, is booted up after the user has applied a protective film, put on a protective cover, etc. In this example, the message area <NUM> is presenting information indicating that the apparatus has determined (e.g., by based on a comparison of the first ultrasonic signals and the second ultrasonic signals) that one or more layers reside on the cover glass and is about to perform a calibration process involving the one or more layers. In some examples, the calibration process may involve performing one or more additional scans in the ultrasonic sensor system area <NUM> in order to determine one or more signal characteristics corresponding to properties of the one or more layers, such as thickness, material type or material patterning. Accordingly, the message area <NUM> includes a prompt to ensure that there is no film, finger or other object on the ultrasonic sensor system area <NUM>. In some implementations, the message area <NUM> is a virtual button with which a user may interact, e.g., by touching the message area <NUM>, in order to indicate that there is no film, finger or other object on the ultrasonic sensor system area <NUM>.

<FIG> shows another example of a GUI that may be presented in some implementations. In this example, a control system of the apparatus <NUM> has determined that one or more layers are residing on the cover glass and has determined that one or more layers are not compatible with the ultrasonic sensor system. Therefore, the control system is controlling the display to present the GUI <NUM>, including a message area <NUM> prompting a user to remove the one or more layers. According to some examples, the GUI <NUM> may be presented in block <NUM> of <FIG>.

<FIG> shows another example of a GUI that may be presented in some implementations. In some instances, the GUI <NUM> may be presented after the GUI <NUM> is presented. In this example, a control system of the apparatus <NUM> has determined that one or more layers that were previously residing on the cover glass have been removed. Therefore, the control system is controlling the display to present the GUI <NUM>, including a message area <NUM> prompting a user to ensure that there is no film, finger or other object on the ultrasonic sensor system area <NUM> so that the apparatus <NUM> can perform a calibration process. The calibration process may involve performing one or more additional scans in the ultrasonic sensor system area <NUM>. In some implementations, the message area <NUM> is a virtual button with which a user may interact, e.g., by touching the message area <NUM>, in order to indicate that there is no film, finger or other object on the ultrasonic sensor system area <NUM>.

<FIG> shows another example of a GUI that may be presented in some implementations. In this example, the GUI <NUM> is being presented in the context of an end-user fingerprint registration process. In some instances, the GUI <NUM> may be presented after an end-user calibration process. In this example, a control system of the apparatus <NUM> has determined that an object in contact with the ultrasonic sensor system area <NUM> is not a finger. Therefore, the control system is controlling the display to present the GUI <NUM>, including a message area <NUM> prompting a user to ensure that an actual finger is on the ultrasonic sensor system area <NUM> so that the apparatus <NUM> can perform a fingerprint registration process.

According to some examples, the apparatus may be configured to perform a liveness detection process or another type of spoof detection process. In some instances, spoofing may involve using a finger-like object that includes silicone rubber, polyvinyl acetate (white glue), gelatin, glycerin, etc., with a fingerprint pattern of a rightful user formed on an outside surface. In some cases, a hacker may form a fingerprint pattern of a rightful user on a sleeve or partial sleeve that can be slipped over or on the hacker's finger. In some implementations, the spoof detection process may be based, at least in part, on a sleeve detection process and/or on ultrasonic signals corresponding to sub-epidermal features. Some such liveness determinations may involve obtaining first sub-epidermal features from first ultrasonic image data at a first time and obtaining second sub-epidermal features from second ultrasonic image data at a second time. Some examples may involve making a liveness determination based on a change between the first sub-epidermal features and the second sub-epidermal features. This type of temporal change may, for example, correspond with the flow of blood within a finger.

<FIG> shows another example of a GUI that may be presented in some implementations. In this example, the GUI <NUM> is being presented in the context of a fingerprint authentication process. In some instances, the GUI <NUM> may be presented after an end-user fingerprint registration process. In this example, a control system of the apparatus <NUM> has determined that an object in contact with the ultrasonic sensor system area <NUM> is not a finger. Therefore, the control system is controlling the display to present the GUI <NUM>, including a message area <NUM> prompting a user to ensure that an actual finger is on the ultrasonic sensor system area <NUM> so that the apparatus <NUM> can perform the fingerprint authentication process.

<FIG> representationally depicts aspects of a <NUM> x <NUM> pixel array of sensor pixels for an ultrasonic sensor system. Each pixel <NUM> may be, for example, associated with a local region of piezoelectric sensor material (PSM), a peak detection diode (D1) and a readout transistor (M3); many or all of these elements may be formed on or in a substrate to form the pixel circuit <NUM>. In practice, the local region of piezoelectric sensor material of each pixel <NUM> may transduce received ultrasonic energy into electrical charges. The peak detection diode D1 may register the maximum amount of charge detected by the local region of piezoelectric sensor material PSM. Each row of the pixel array <NUM> may then be scanned, e.g., through a row select mechanism, a gate driver, or a shift register, and the readout transistor M3 for each column may be triggered to allow the magnitude of the peak charge for each pixel <NUM> to be read by additional circuitry, e.g., a multiplexer and an A/D converter. The pixel circuit <NUM> may include one or more TFTs to allow gating, addressing, and resetting of the pixel <NUM>.

Each pixel circuit <NUM> may provide information about a small portion of the object detected by the ultrasonic sensor system. While, for convenience of illustration, the example shown in <FIG> is of a relatively coarse resolution, ultrasonic sensors having a resolution on the order of <NUM> pixels per inch or higher may be configured with an appropriately scaled structure. The detection area of the ultrasonic sensor system may be selected depending on the intended object of detection. For example, the detection area may range from about <NUM> x <NUM> for a single finger to about <NUM> inches x <NUM> inches for four fingers. Smaller and larger areas, including square, rectangular and non-rectangular geometries, may be used as appropriate for the target object.

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

Implementations of the subject matter described in this specification also may be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on a computer storage media for execution by, or to control the operation of, data processing apparatus.

If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium, such as a non-transitory medium. Computer-readable media include both computer storage media and communication media including any medium that may be enabled to transfer a computer program from one place to another. Storage media may be any available media that may be accessed by a computer. By way of example, and not limitation, non-transitory media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Also, any connection may be properly termed a computer-readable medium.

Various modifications to the implementations described in this disclosure may be readily apparent to those having ordinary skill in the art. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the claims. The word "exemplary" is used exclusively herein, if at all, to mean "serving as an example, instance, or illustration.

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

Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

Claim 1:
An apparatus, comprising:
an ultrasonic sensor system (<NUM>);
a cover glass (<NUM>); and
a control system (<NUM>), at least part of which is coupled to the ultrasonic sensor system, the control system configured to:
acquire (<NUM>) first ultrasonic signals via the ultrasonic sensor system at a first time, the first ultrasonic signals including reference ultrasonic signals corresponding to reflections from at least one of a cover glass/air interface or a cover glass/target interface;
acquire (<NUM>) second ultrasonic signals via the ultrasonic sensor system at a second time;
determine (<NUM>), based at least in part on a comparison of the first ultrasonic signals and the second ultrasonic signals, whether one or more layers reside on the cover glass at the second time; and, if it is determined that the one or more layers reside on the cover glass at the second time:
i) determine one or more signal characteristics corresponding to one or more properties of the one or more layers, and
ii) determine, based at least in part on the one or more properties, whether the one or more layers are compatible with the ultrasonic sensor system by determining whether the ultrasonic sensor system can be properly calibrated while the one or more layers reside on the cover glass.