Ultrasonic water-imperceptible touch detection sensor

Abstract

The present disclosure relates to an ultrasonic water-agnostic touch detection sensor. An ultrasonic touch sensing system that uses both compression waves and shear waves for touch and water detection is disclosed. When there is no touch or water, less shear wave energy and compression wave energy are absorbed, so neither the shear wave reflection nor the compression wave reflection has a significant amplitude reduction. When a finger touches the sensing plate, both shear wave energy and compression wave energy are absorbed, so both the shear wave reflection and the compression wave reflection have a significant amplitude reduction. When water touches the sensing plate, compression energy is absorbed and little or no shear wave energy is absorbed, so although the compression wave reflection has a significant amplitude reduction, the shear wave reflection does not have a significant amplitude reduction. From these amplitudes, it can be determined whether there is no touch on the sensing plate, whether there is a touch on the sensing plate, or whether there is water on the sensing plate.

Description

[0001] Cross - Reference to Related Applications

[0002] This patent application is a partial continuation application of U.S. Patent Application No. 16 / 917,779, filed Jun. 30, 2020, the entire content of which is incorporated herein by reference for all purposes. Technical Field

[0003] The present disclosure generally relates to touch sensing, and more particularly, to an ultrasonic water agnostic touch detection system capable of detecting touches and water on a detection surface. Background Art

[0004] Many types of input mechanisms are currently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, and the like. Touch-sensitive surfaces, and in particular touchscreens, have become extremely popular due to their simplicity and flexibility in operation and their ever-declining price. A touchscreen may include a touch sensor panel and a display device such as a liquid crystal display (LCD), the touch sensor panel may be a transparent panel having a touch-sensitive surface, and the display device may be partially or fully positioned behind the panel such that the touch-sensitive surface may cover at least a portion of the visible area of the display device. A touchscreen may allow a user to perform various functions by touching the touch sensor panel at a location typically indicated by a user interface (UI) displayed by the display device using a finger, a stylus, or other object. Generally speaking, a touchscreen may identify a touch and the location of the touch on the touch sensor panel, and the computing system may then interpret the touch based on the display content that appears when the touch occurs, and may then perform one or more actions based on the touch.

[0005] As touch-sensitive surfaces are incorporated into more and more devices, the types of physical and surrounding environments in which they are expected to operate are also increasing. For example, touch sensing capabilities are desired in devices where water or other liquids may be present, and there is increasing interest in incorporating touch sensing into thicker sensing surfaces and metallic sensing surfaces. However, capacitive touch sensing systems may experience degraded performance due to the possible indistinguishable contact of electrically floating objects (e.g., water droplets) with the touch-sensitive surface from an actual touch. In addition, capacitive touch sensing systems may have difficulty detecting touches on metallic touch surfaces and on thick touch surfaces. On the other hand, force sensing can detect an actual touch and ignore water or other liquids, but may not work well on thick or metallic surfaces because these types of surfaces may be hard enough to resist the bending or compression required for accurate force sensing. Summary of the Invention

[0006] The present disclosure relates to an ultrasonic touch sensing system that uses both compression waves and shear waves to improve touch and water (or other liquid) detection. For example, an ultrasonic shear transducer can transmit shear waves through a sensing plate (e.g., cover glass) and can also generate parasitic compression waves. When touch or water (or other liquid) is present on the sensing plate, the shear waves and compression waves react differently. When a finger touches the sensing plate, both shear wave energy and compression wave energy are absorbed, and the amplitudes of the reflections of both the shear wave and the compression wave are significantly reduced. In contrast, when water (or other liquid) touches the sensing plate, the compression energy is absorbed, and the amplitude of the reflection of the compression wave can be significantly reduced, while little or no energy from the shear wave is absorbed, so the reflection of the shear wave can be received without a significant reduction in its amplitude. Additionally, one or more of the ultrasonic stimulation center frequency, stimulation spectrum, material type, and material thickness can be selected such that the reflections of the shear wave and the compression wave can be received at different time periods. The amplitudes of the reflections from the shear wave and the compression wave can be measured within those different time periods. From these amplitudes, it can be determined whether there is no touch on the sensing plate, whether there is a touch on the sensing plate, or whether there is water (or other liquid) on the sensing plate. When multiple ultrasonic shear transducers are employed, such as in an array, the position of the touch or water can also be determined.

[0007] The present disclosure also relates to an ultrasonic touch sensing system that can utilize multiple ultrasonic transducers to each generate both shear and compression non-propagating (i.e., standing or resonant) waves at different resonant frequencies at a sensing plate (e.g., front crystal). When a touch object (e.g., finger) is present on the sensing plate, or when water (or other liquid) is present on the sensing plate, the shear standing wave and the compression standing wave can respond differently within the sensing plate. When an object (such as a finger) touches the sensing plate, both shear wave energy and compression wave energy can be absorbed, and the amplitudes of the energies of both the shear wave and the compression wave within the sensing plate are significantly reduced. When water (or other liquid) touches the sensing plate, the compression wave energy can also be absorbed, and the amplitude of the energy of the compression wave within the sensing plate is also significantly reduced. However, when water (or other liquid) is present, little or no shear wave energy can be absorbed, so the amplitude of the energy of the shear wave within the sensing plate is not significantly reduced. The amplitudes of the resonant shear wave and the resonant compression wave can be measured at each transducer. From these amplitudes, it can be determined whether there is no object or liquid at the position of the transducer on the sensing plate, whether there is an object at the position of the transducer on the sensing plate, or whether there is a liquid at the position of the transducer on the sensing plate. When multiple ultrasonic transducers are employed, such as in an array, the position of the object or liquid can also be determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figures 1A to 1EAn electronic device according to an example of the present disclosure that may include ultrasonic touch and water detection is shown.

[0009] Figure 2 A block diagram of an electronic device according to an example of the present disclosure that includes an ultrasonic touch and water sensing system is shown.

[0010] Figure 3A A symbolic shear wave transducer implementation that generates shear waves according to an example of the present disclosure is shown.

[0011] Figure 3B A symbolic shear wave transducer implementation that generates compression waves according to an example of the present disclosure is shown.

[0012] Figure 4A A symbolic shear wave transducer implementation in the absence of a touch object according to an example of the present disclosure is shown.

[0013] Figure 4B A symbolic shear wave transducer reflected wave timing diagram corresponding to Figure 4A the shear wave transducer implementation according to an example of the present disclosure is shown.

[0014] Figure 5A A symbolic shear wave transducer implementation in the presence of a touch object according to an example of the present disclosure is shown.

[0015] Figure 5B A symbolic shear wave transducer reflected wave timing diagram corresponding to Figure 5A the shear wave transducer implementation according to an example of the present disclosure is shown.

[0016] Figure 6A A symbolic shear wave transducer implementation in the presence of water according to an example of the present disclosure is shown.

[0017] Figure 6B A symbolic shear wave transducer reflected wave timing diagram corresponding to Figure 6A the shear wave transducer implementation according to an example of the present disclosure is shown.

[0018] Figure 7A A symbolic shear wave transducer reflected wave timing diagram according to an example of the present disclosure, where shear wave reflection and compression wave reflection are separated in the time domain, is shown.

[0019] Figure 7B Another symbolic shear wave transducer reflected wave timing diagram according to an example of the present disclosure, where shear wave reflection and compression wave reflection are separated in the time domain, is shown.

[0020] Figure 8AShows yet another exemplary shear wave transducer reflected wave timing diagram according to the present disclosure, where shear wave reflections and compression wave reflections are separated in the time domain.

[0021] Figure 8B Shows yet another exemplary shear wave transducer reflected wave timing diagram according to the present disclosure, where shear wave reflections and compression wave reflections are separated in the time domain.

[0022] Figure 9 Shows a symbolic plan view of a touch-sensitive surface including an ultrasonic shear wave transducer array according to an example of the present disclosure.

[0023] Figure 10 Shows a flowchart for water-agnostic touch detection for ultrasound according to an example of the present disclosure.

[0024] Figures 11A to 11C Shows the main layers of an ultrasonic transducer array according to an example of the present disclosure.

[0025] Figure 11D Shows according to an example of the present disclosure Figures 11A to 11C a plan view of the laminated structure of the layer of

[0026] Figure 12A Shows according to an example of the present disclosure Figure 11D a cross-sectional view of two ultrasonic transducers in the array of

[0027] Figure 12B Shows an exemplary shear level dispersion curve for selecting non-propagating shear waves according to an example of the present disclosure.

[0028] Figure 12C Shows an exemplary Lamb / compression dispersion curve for selecting non-propagating compression waves according to an example of the present disclosure.

[0029] Figure 13A Shows the concept of non-propagating shear wave and compression wave imaging according to an example of the present disclosure.

[0030] Figure 13B Shows a symbolic plan view of non-propagating shear wave and compression wave imaging according to an example of the present disclosure.

[0031] Figure 14A Shows a cross-sectional view of shear wave generation and detection using an independent transducer according to an example of the present disclosure.

[0032] Figure 14B Shows a cross-sectional view of compression wave generation and detection using an independent transducer according to an example of the present disclosure.

[0033] Figure 15AShows a signal received at an ultrasonic receiver according to an example of the present disclosure, the ultrasonic receiver being configured to detect resonant shear wave energy after the ultrasonic transmitter has stopped generating resonant shear waves.

[0034] Figure 15B Shows a signal received at an ultrasonic receiver according to an example of the present disclosure during Figure 15A the reception window of

[0035] Figure 15C Shows a signal received at an ultrasonic receiver according to an example of the present disclosure, the ultrasonic receiver being configured to detect resonant shear wave energy while the ultrasonic transmitter is generating resonant shear waves.

[0036] Figure 16A Shows a cross-sectional view of shear wave generation and detection using the same transducer according to an example of the present disclosure.

[0037] Figure 16B Shows a cross-sectional view of compression wave generation and detection using the same transducer according to an example of the present disclosure.

[0038] Figure 17A Shows a signal received at an ultrasonic transducer according to an example of the present disclosure, the ultrasonic transducer being configured to perform both shear wave or compression wave generation and detection.

[0039] Figure 17B Shows a signal received at an ultrasonic receiver according to an example of the present disclosure during Figure 17A the reception window 1776 of

[0040] Figure 18 Shows a flowchart of performing water-agnostic touch using non-propagating (resonant) shear waves and non-propagating (resonant) compression waves according to an example of the present disclosure. Detailed Description

[0041] In the following description of various examples, reference will be made to the accompanying drawings which form a part of the following description and in which specific examples that can be implemented are shown by way of illustration. It should be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples.

[0042] Examples of the present disclosure relate to an ultrasonic touch sensing system that uses both compressional waves and shear waves to improve touch and water (or other liquid) detection. For example, an ultrasonic shear transducer can transmit a shear wave through a sensing plate (e.g., cover glass) and can also generate parasitic compressional waves. When touch or water (or other liquid) is present on the sensing plate, the shear wave and the compressional wave react differently. When a finger contacts the sensing plate, both the shear wave energy and the compressional wave energy are absorbed, and the amplitudes of the reflections of both the shear wave and the compressional wave are significantly reduced. In contrast, when water (or other liquid) contacts the sensing plate, the compressional energy is absorbed, and the amplitude of the reflection of the compressional wave can be significantly reduced, while little or no energy from the shear wave is absorbed, so that the reflection of the shear wave can be received with its amplitude not being significantly reduced. Additionally, one or more of the ultrasonic stimulation center frequency, stimulation spectrum, material type, and material thickness can be selected such that the reflections of the shear wave and the compressional wave can be received at different time periods. The amplitudes of the reflections from the shear wave and the compressional wave can be measured during those different time periods. From these amplitudes, it can be determined whether there is no touch on the sensing plate, whether there is touch on the sensing plate, or whether there is water (or other liquid) on the sensing plate. When multiple ultrasonic shear transducers are employed, such as in an array, the position of the touch or water can also be determined. Note that although the term "water" may be mainly used herein for brevity, it should be understood that the examples of the present disclosure are not limited to detecting water but include detecting liquids other than water.

[0043] Examples of the present disclosure also relate to an ultrasonic touch sensing system that can utilize multiple ultrasonic transducers to each generate both shear and compressional non-propagating (standing) waves at different resonant frequencies at a sensing plate (e.g., front crystal). When a touch object (e.g., finger) is present on the sensing plate, or when water (or other liquid) is present on the sensing plate, the shear standing wave and the compressional standing wave can respond differently within the sensing plate. When an object (such as a finger) contacts the sensing plate, both the shear wave energy and the compressional wave energy can be absorbed, and the amplitudes of the energies of both the shear wave and the compressional wave within the sensing plate are significantly reduced. When water (or other liquid) contacts the sensing plate, the compressional wave energy can also be absorbed, and the amplitude of the energy of the compressional wave within the sensing plate is also significantly reduced. However, when water (or other liquid) is present, little or no shear wave energy can be absorbed, so that the amplitude of the energy of the shear wave within the sensing plate is not significantly reduced. The amplitude of the resonant shear wave and the amplitude of the resonant compressional wave can be measured at each transducer. From these amplitudes, it can be determined whether there is no object or liquid at the position of the transducer on the sensing plate, whether there is an object at the position of the transducer on the sensing plate, or whether there is a liquid at the position of the transducer on the sensing plate. When multiple ultrasonic compressional wave transducers are employed, such as in an array, the position of the object or liquid can also be determined.

[0044] Figures 1A to 1E An electronic device that may include ultrasonic touch and water detection according to an example of the present disclosure is shown. Figure 1A A mobile phone 102 that may include ultrasonic touch and water detection according to an example of the present disclosure is shown. Figure 1B A digital media player 104 that may include ultrasonic touch and water detection according to an example of the present disclosure is shown. Figure 1C A personal computer 106 that may include ultrasonic touch and water detection according to an example of the present disclosure is shown. Figure 1D A tablet computing device 108 that may include ultrasonic touch and water detection according to an example of the present disclosure is shown. Figure 1E A wearable device 110 (such as a watch) that may include ultrasonic touch and water detection according to an example of the present disclosure is shown. It should be understood that Figures 1A to 1E The exemplary devices shown are provided by way of example, and other types of devices may include ultrasonic touch and water detection according to examples of the present disclosure.

[0045] Ultrasonic sensors may be incorporated into the above devices to add touch and water sensing capabilities to the touch sensing surface of the system. For example, in some examples, an ultrasonic touch sensing system may replace or enhance a touch screen (e.g., a capacitive touch screen, a resistive touch screen, etc.) to provide touch sensing capabilities in a wet environment or in situations where the device may get wet (e.g., exercise, swimming, rain, handwashing). In some examples, a non-touch-sensitive display screen may be enhanced with ultrasonic sensors to provide touch sensing capabilities. In such examples, a touch-sensitive display may be implemented without the stack-up structure required for a capacitive touch screen. In some examples, ultrasonic sensors may be used to provide touch sensing capabilities for non-display surfaces. For example, ultrasonic sensors may be used to provide touch sensing capabilities for a touchpad, buttons, a scroll wheel, a part or all of the housing, or any other surface of the device (e.g., on the front, back, or side).

[0046] Figure 2A block diagram of an electronic device including an ultrasonic touch and water sensing system according to an example of the present disclosure is shown. In some examples, a sensing plate 202 of device 200 (which may correspond to devices 102, 104, 106, 108, and 110 described above) may be coupled to one or more ultrasonic transducers 204. In some examples, ultrasonic transducer 204 may be a piezoelectric shear wave transducer that vibrates upon application of an electrical signal when acting as a transmitter and generates an electrical signal based on detected vibrations when acting as a receiver. In some examples, ultrasonic transducer 204 may be formed of a piezoelectric ceramic material (e.g., lead zirconate titanate (PZT) or potassium sodium niobate (KNN)) or a piezoelectric plastic material (e.g., polyvinylidene fluoride (PVDF)). In some examples, ultrasonic transducer 204 may be bonded to sensing plate 202 by an adhesive (e.g., a thin layer of rigid epoxy). In some examples, ultrasonic transducer 204 may be deposited on the surface of sensing plate 202 by processes such as deposition, photolithography, etc. In some examples, ultrasonic transducer 204 may be bonded to the surface of sensing plate 202 using a conductive or non-conductive bonding material. When electrical energy is applied to ultrasonic transducer 204, it may cause the transducer and any material in contact with the transducer to vibrate, and the vibrations of the molecules of the material may propagate through sensing plate 202 as ultrasonic waves in various modes.

[0047] In some examples, sensing plate 202 may be partially or completely disposed under or within a display 208 (e.g., an organic light emitting diode (OLED) display), where the dashed lines indicate its optional presence. In some examples, touch circuitry 212 may also be partially or completely disposed under or within display 208 to form a touch screen (e.g., a capacitive touch screen), and ultrasonic transducers 204 may be partially or completely disposed on (or coupled to) a portion of the touch screen. For example, the touch screen may include a glass or plastic panel (sensing plate), and the display area of the touch screen may be surrounded by a non-display area (e.g., a black border area around the perimeter of the display area of the touch screen). In some examples, ultrasonic transducers 204 may be partially or completely disposed in the black mask area of the touch screen panel (e.g., on the back surface of the panel behind the black mask) such that the transducers are not visible (or only partially visible) to the user. In other examples, ultrasonic transducers 204 may be partially or completely disposed under or behind a touchpad, or under one or more sides or the back of the housing.

[0048] Device 200 may further include an ultrasonic touch sensing circuit 206, which may include a circuit (e.g., a transmitting circuit) for driving an electrical signal to stimulate the vibration of ultrasonic transducer 204, and a circuit (e.g., a receiving circuit) for sensing the electrical signal output by the transducer when the transducer is stimulated by the received ultrasonic energy. In some examples, the timing operation of ultrasonic touch sensing circuit 206 may optionally be provided by an independent ultrasonic touch sensing controller 210, which may control the timing of the operation of the ultrasonic touch sensing circuit. In some examples, ultrasonic touch sensing controller 210 may be coupled between ultrasonic touch sensing circuit 206 and host processor 214. In some examples, the controller function may be integrated with ultrasonic touch sensing circuit 206 (e.g., on a single integrated circuit). The output data from ultrasonic touch sensing circuit 206 may be output to host processor 214 for further processing to determine touch or water contact with the device, as will be described in more detail below. In some examples, the processing for determining the touch object or water may be performed by ultrasonic touch sensing circuit 206, ultrasonic touch sensing controller 210, or an independent sub-processor (not shown) of device 200.

[0049] In addition to optional touch circuit 212, device 200 may further include an optional touch controller (not shown). In examples including a touch controller, the touch controller may be disposed between touch circuit 212 and host processor 214. Touch circuit 212 may be, for example, a capacitive or resistive touch sensing circuit, and may be used to detect contact and / or hovering of an object (e.g., a finger, a stylus) with and / or near a touch screen (particularly in the display area of the touch screen). Thus, device 200 may include multiple types of sensing circuits (e.g., touch circuit 212 and ultrasonic transducer 204) for detecting an object (and in some cases the position of the object) in different areas of the device and for different purposes, as will be described in more detail below.

[0050] The host processor 214 can receive ultrasonic output from the ultrasonic touch sensing circuit 206 or other touch output (e.g., capacitive) from the touch circuit 212, and perform actions based on the touch output. The host processor 214 can also be connected to the program storage device 216 and the display 208. The host processor 214 can communicate with the display 208, for example, to generate an image on the display, such as an image of the UI, and can use the touch sensing circuit 212 and / or the ultrasonic touch sensing circuit 206 (and in some examples their respective controllers) to detect a touch on or near the touch screen, such as a touch input to the displayed UI. The touch input can be used by a computer program stored in the program storage device 216 to perform actions, which can include but are not limited to: moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing an instruction, operating a peripheral device connected to the host device, answering a phone call, placing a phone call, terminating a phone call, changing the volume or audio settings, storing information related to phone communications (such as an address, frequently dialed numbers, incoming calls, missed calls), logging in to a computer or computer network, allowing an authorized individual to access a restricted area of a computer or computer network, loading a user profile associated with the arrangement of the user's preferred computer desktop, allowing access to web content, launching a specific program, encrypting or decrypting a message, and so on. The host processor 214 can also perform additional functions that may not be related to touch processing.

[0051] Note that one or more of the functions described herein can be performed by firmware stored in a memory and executed by the touch circuit 212 and / or the ultrasonic touch sensing circuit 206 (or their respective controllers) or stored in the program storage device 216 and executed by the host processor 214. The firmware can also be stored and / or conveyed within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device such as a computer-based system, a system including a processor, or other systems that can obtain instructions from and execute the instructions of the instruction execution system, apparatus, or device. In the context of this document, a "non-transitory computer-readable storage medium" can be any medium (excluding signals) that can contain or store a program for use by or in connection with an instruction execution system, apparatus, and device. Non-transitory computer-readable storage media can include but are not limited to electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, portable computer disks (magnetic), random access memory (RAM) (magnetic), read-only memory (ROM) (magnetic), erasable programmable read-only memory (EPROM) (magnetic), portable optical discs (such as CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW), or flash memory (such as compact flash cards, secure digital cards, USB memory devices, memory sticks, etc.).

[0052] The firmware may also be propagated within any transmission medium for use in or in conjunction with an instruction execution system, apparatus, or device, such as a computer-based system, a system including a processor, or other systems that can obtain instructions from and execute the instructions of the instruction execution system, apparatus, or device. In the context of this document, a "transmission medium" can be any medium that can transmit, propagate, or transport a program for use in or in conjunction with an instruction execution system, apparatus, or device. The transmission readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, or infrared wired or wireless propagation media.

[0053] It should be understood that device 200 is not limited to Figure 2 the components and configurations of, but may include other components or additional components in multiple configurations according to various examples. Additionally, the components of device 200 may be included within a single device, or may be distributed among multiple devices. Further, it should be understood that the connections between components are exemplary, and according to the embodiments, different unidirectional or bidirectional connections may be included between the components, regardless of Figure 2 the arrows shown in the configurations of.

[0054] As described above, examples of the present disclosure relate to an ultrasonic touch sensing system that uses both compression waves and shear waves to improve touch and water detection. Shear waves, also known as transverse waves, form displacements orthogonal to the direction of wave propagation. Shear waves (and their reflections) are advantageous for detecting an object on the surface of a sensing plate because their reflections are affected by the touch object, and (relatively) not affected by water. Thus, shear waves can be used to detect touch without detecting water. Additionally, shear waves can effectively detect touch on thick and metal sensing plates, and can detect light touches. Thus, shear waves can be used with a variety of different sensing plate configurations to make touch / no-touch determinations, providing the advantage of greater flexibility in terms of material type and thickness. However, shear waves cannot be used to positively detect the presence of water.

[0055] The ultrasonic transducer also generates ultrasonic energy in modes other than the shear mode, such as the compression mode. Compression waves form displacements in the same direction as the propagation of the wave. Different from shear wave reflection, compression wave reflection is affected by both the touched object and water. Since compression waves are affected by water, in certain cases, they can interact with water and cause attenuation of the reflected wave and introduction of ambiguity between the presence of touch and water, thus causing errors in the accuracy of touch sensing and loss of the ability to accurately sense water-agnostic touch. However, the examples of the present disclosure do not regard compression waves as noise or parasitic waves to be suppressed or removed, but regard the water detection property of compression waves as an advantage, and utilize compression wave reflection together with shear wave reflection to provide both touch and water detection, and in some examples, provide more accurate touch detection. For example, monitoring the decrease in the amplitude or energy of compression wave reflection can provide a more robust indication or measurement of the presence of touch. To make this determination, the returned ultrasonic energy in the reflected wave can be received by the transducer, and the ultrasonic energy can be converted into an electrical signal by the transducer to determine the amplitude or energy of the reflected wave.

[0056] To perform touch and water detection, examples of the present disclosure can determine whether the amplitude or energy of the reflected shear wave is lower than a first predetermined threshold and whether the amplitude or energy of the reflected compression wave is lower than a second predetermined threshold. If both conditions are met, it can be determined that there is a touch at the sensing panel. However, if the amplitude or energy of the reflected shear wave is higher than the first predetermined threshold and the amplitude or energy of the reflected compression wave is lower than the second predetermined threshold, it can be determined that there is water at the sensing panel. If the amplitude or energy of the reflected shear wave is higher than the first predetermined threshold and the amplitude or energy of the reflected compression wave is higher than the second predetermined threshold, it can be determined that there is no touch or water at the sensing panel.

[0057] Making these amplitude or energy threshold determinations can be complex or error-prone because shear wave reflection and compression wave reflection usually overlap in time. Therefore, examples of the present disclosure utilize the velocity difference between compression waves and shear waves (for example, for a specific material and thickness, compression waves are about 1.6 to 1.7 times faster than shear waves) to identify the time windows when shear wave reflection and compression wave reflection are separated. Within those windows, the amplitude or energy level of shear wave reflection or compression wave reflection can be measured more accurately with less interference from other waves.

[0058] Figure 3A A symbolic shear wave transducer implementation 300 that generates shear waves according to an example of the present disclosure is shown. In Figure 3AIn the example, the shear wave transducer 302 can be oriented along the x-axis (the polling axis) and formed together with the sensing plate 314 (e.g., bonded or otherwise coupled to the sensing plate). The shear wave transducer 302 can vibrate by repeatedly switching the polarity of the voltage on electrodes 304 and 306 to form a displacement 308 along the x-axis parallel to the surface of the sensing plate. If the polling direction and the electrode configuration are appropriately selected, a shear wave (symbolically shown at 310) can be formed along the z-axis (in the propagation direction 312). However, due to physical defects in the transducer 302 and electrodes 304 and 306, parasitic compression waves can also propagate in the z-direction.

[0059] Figure 3B A symbolic shear wave transducer implementation 300 for generating compression waves according to an example of the present disclosure is shown. In Figure 3B the example, the parasitic compression wave 316 can be formed due to small unintended displacements 318 of the shear wave transducer 304 in the z-direction and at the corners of the transducer. As can be seen from Figure 3A and Figure 3B the shear wave 310 and the parasitic compression wave 316 generated by the shear wave transducer 304 propagate in the z-direction, where objects such as fingers or water can be present on the surface of the sensing plate 314. However, as discussed in further detail below, the interactions of the shear wave 310 and the compression wave 316 with those objects produce different results.

[0060] Figure 4A A symbolic shear wave transducer implementation 400 in the absence of a touch object according to an example of the present disclosure is shown. In Figure 4A the example, the shear wave transducer 402 generates both a shear wave 404 and a compression wave 406 as discussed above, both of which propagate in the z-axis propagation direction 408. In the absence of an object touching the sensing plate 410, both the shear wave 404 and the compression wave 406 are reflected back to the shear wave transducer 402, as shown by the reflected waves 412 (symbolically showing two independent reflections) with a relatively small decrease in amplitude or energy.

[0061] Figure 4B A symbolic shear wave transducer reflected wave timing diagram 414 corresponding to the Figure 4A shear wave transducer implementation is shown. Note that Figure 4B all the waves, amplitudes, and timings shown are symbolic and not drawn to scale. In Figure 4BIn the example, the shear wave transducer can generate both a shear wave 404 and a compression wave 406 at time t0, and due to the greater velocity of the compression wave, the round trip of the first compression wave reflection 416 can be received back at the shear wave transducer at time t1. Next, due to the slower velocity of the shear wave 404, the round trip of the first shear wave reflection 418 can be received back at the shear wave transducer at time t2. Similarly, subsequent compression wave reflections can be received back at the shear wave transducer at times t3, t4, and t6, while subsequent shear wave reflections can be received back at the shear wave transducer at times t5 and t7. As Figure 4B shown in the example of, a time window 422 can be determined empirically or otherwise to capture the amplitude or energy of the first compression wave reflection 416, and a time window 424 can be determined empirically or otherwise to capture the amplitude or energy of the first shear wave reflection 418. Since there is no touch at the sensing plate 410, the amplitudes or energies of both the first shear wave reflection 418 and the first compression wave reflection 416 can be detected at the shear wave transducer to be respectively higher than a first threshold 426 and a second threshold 428, as Figure 4B shown in the inset 420 in. Therefore, no touch is detected.

[0062] Figure 5A FIG. shows a symbolic shear wave transducer implementation 500 in the presence of a touch object according to an example of the present disclosure. In Figure 5A the example, the shear wave transducer 502 generates both a shear wave 504 and a compression wave 506 as discussed above, both of which propagate in the z-axis propagation direction 508. In the presence of an object 530 on the touch sensing plate 510, both the shear wave 504 and the compression wave 506 are reflected back to the shear wave transducer 502, as shown by the reflected waves 512 (symbolically showing two independent reflections) with a relatively large drop in amplitude or energy.

[0063] Figure 5B FIG. shows a symbolic shear wave transducer reflection wave timing diagram 514 corresponding to the Figure 5A shear wave transducer implementation of. Note that Figure 5B all the waves, amplitudes, and timings shown are symbolic and not drawn to scale. In Figure 5BIn the example, the shear wave transducer can generate both a shear wave 504 and a compression wave 506 at time t0, and due to the greater velocity of the compression wave, the round-trip of the first compression wave reflection 516 can be received back at the shear wave transducer at time t1. Next, due to the slower velocity of the shear wave 504, the round-trip of the first shear wave reflection 518 can be received back at the shear wave transducer at time t2. Similarly, subsequent compression wave reflections can be received back at the shear wave transducer at times t3, t4, and t6, while subsequent shear wave reflections can be received back at the shear wave transducer at times t5 and t7. As Figure 5B shown in the example of, a time window 522 can be determined empirically or otherwise to capture the amplitude or energy of the first compression wave reflection 516, and a time window 524 can be determined empirically or otherwise to capture the amplitude or energy of the first shear wave reflection 518. Due to the presence of the touch object 530 at the sensing plate 510, the amplitudes or energies of both the first shear wave reflection 518 and the first compression wave reflection 516 can be detected at the shear wave transducer to be respectively lower than a first threshold 526 and a second threshold 528 (corresponding to Figure 4B the thresholds 426 and 428 in), as Figure 5B shown in the inset 520 in. Thus, a touch can be detected.

[0064] Figure 6A FIG. shows a symbolic shear wave transducer implementation 600 in the presence of water according to an example of the present disclosure. In Figure 6A the example, the shear wave transducer 602 generates both a shear wave 604 and a compression wave 606 as discussed above, both of which are in the z-axis propagation direction 608. In the presence of water 632 on the touch sensing plate 610, the shear wave 604 is reflected back to the shear wave transducer 602, as shown by the reflected wave 612 with a relatively small decrease in amplitude or energy (symbolically showing two independent reflections), while the compression wave 606 is reflected back to the shear wave transducer, as shown by the reflected wave 612 with a relatively large decrease in amplitude or energy.

[0065] Figure 6B FIG. shows a symbolic shear wave transducer reflected wave timing diagram 614 corresponding to the Figure 6A shear wave transducer implementation of. Note that Figure 6B all the waves, amplitudes, and timings shown are symbolic and not drawn to scale. In Figure 6BIn the example, the shear wave transducer can generate both a shear wave 604 and a compression wave 606 at time t0, and due to the greater velocity of the compression wave, the round trip of the first compression wave reflection 616 can be received back at the shear wave transducer at time t1. Next, due to the slower velocity of the shear wave 604, the round trip of the first shear wave reflection 618 can be received back at the shear wave transducer at time t2. Similarly, subsequent compression wave reflections can be received back at the shear wave transducer at times t3, t4, and t6, while subsequent shear wave reflections can be received back at the shear wave transducer at times t5 and t7. As Figure 6B shown in the example of, the time window 622 can be determined empirically or otherwise to capture the amplitude or energy of the first compression wave reflection 616, and the time window 624 can be determined empirically or otherwise to capture the amplitude or energy of the first shear wave reflection 618. Since water 632 is present at the sensing plate 610, separately speaking, it can be detected at the shear wave transducer 602 that the amplitude or energy of the first shear wave reflection 618 is higher than the first threshold 626, and it can be detected at the shear wave transducer 602 that the amplitude or energy of the first compression wave reflection 616 is lower than the second threshold 628 (the first threshold and the second threshold correspond to Figure 4B the thresholds 426 and 428 in), as Figure 6B shown in the illustration 620 in. Therefore, water can be detected.

[0066] Figure 4A , Figure 4B , Figure 5A , Figure 5B , Figure 6A and Figure 6BA time window for capturing a first compression wave reflection and a first shear wave reflection is shown, both of which are shown with a distinct time separation (i.e., non - overlapping). However, as can be seen from the third compression wave reflection at time t4 and the second shear wave reflection at time t5, compression wave reflections and shear wave reflections do not always have a distinct time separation, and in some cases, the reflections may undesirably overlap. A sensing laminate structure (if any) can also complicate the presence and timing of the reflections. For example, if there are various display layers between the shear wave transducer and the sensing plate surface, shear wave reflections, compression wave reflections, and / or mode conversions can occur at layer interfaces and other discontinuities, and multiple internal reflections can occur, which can make it difficult to find an appropriate time window. Examples of the present disclosure select one or more of the ultrasonic frequency and the shear plate material and thickness such that a specific compression wave reflection and a specific shear wave reflection can be identified with a sufficient time separation (e.g., no overlap, or minimizing the overlap between the wave tails of the shear wave and the compression wave such that the error caused by the overlap is below a specific threshold, thus ensuring sufficient touch detection performance), and due to this time separation, a time window can be identified to independently measure the reflections of both the shear wave and the compression wave. As used herein, "non - overlapping" means no time overlap or minimal time overlap such that the error caused by the overlap is below a specific threshold.

[0067] Each material used as a sensing plate has a specific shear wave and compression wave velocity at a specific thickness, and this velocity determines when the reflected waves return to the shear wave transducer. Additionally, the frequency and bandwidth of the shear wave and the compression wave determine the duration of the reflected waves. For example, a low - frequency wave within a given number of cycles will have a longer shear wave reflection and compression wave reflection pulse duration, which can increase the chance of reflection overlap. Conversely, a higher - frequency wave within the same number of cycles will have a shorter shear wave reflection and compression wave reflection pulse duration, which can reduce the chance of reflection overlap. Thus, consideration of material thickness and frequency can be an important consideration in maintaining the separation between shear wave reflections and compression wave reflections.

[0068] Figure 7A A symbolic shear wave transducer reflected wave timing diagram 700 according to an example of the present disclosure is shown, where the shear wave reflection and the compression wave reflection are separated in the time domain. Note that Figure 7A All of the waves, amplitudes, and timings shown are symbolic and not drawn to scale. In Figure 7A the example, the shear wave transducer can generate both a shear wave 704 and a compression wave 706 at time t0, and due to the greater velocity of the compression wave, the round - trip of the first compression wave reflection 716 can be received back at the shear wave transducer at time t1. Next, due to the slower velocity of the shear wave 704, the round - trip of the first shear wave reflection 718 can be received back at the shear wave transducer at time t2. InFigure 7A In the example of, the central frequency of the ultrasonic shear wave transducer is 5 MHz, and there are three cycles in each ultrasonic pulse, resulting in a pulse duration 720 of 0.6 μs for the shear wave reflection 718. In Figure 7A the example of, the shear plate is made of glass with a thickness of 15 mm, resulting in a compression wave speed of 5.4 mm / μs and a shear wave speed of 3.4 mm / μs. These speeds result in a round-trip time t1 of 5.5 μs for the compression wave reflection and a round-trip time t2 of 8.8 μs for the shear wave reflection, and ultimately result in a spacing 722 of 2.7 μs between the compression wave reflection and the shear wave reflection. At this spacing, a time window near the compression wave reflection time t1 = 5.5 μs and the shear wave reflection round-trip time t2 = 8.8 μs can be selected to measure these reflections with minimal interference from other reflections.

[0069] Figure 7B Another symbolic shear wave transducer reflected wave timing diagram 700 according to an example of the present disclosure is shown, where the shear wave reflection and the compression wave reflection are separated in the time domain. Note that Figure 7B all the waves, amplitudes, and timings shown are symbolic and not drawn to scale. Figure 7B Similar to Figure 7A , except that a lower central frequency is used. In Figure 7B the example of, the central frequency of the ultrasonic shear wave transducer is 1.5 MHz, resulting in a pulse duration 720 of 2 μs for the shear wave reflection 718. Therefore, Figure 7B the reflected wave pulse duration in Figure 7A is longer than that in Figure 7B , which generally increases the chance of reflection overlap. However, in Figure 7B the example of, there is still a spacing 722 of 1.3 μs between the compression wave reflection and the shear wave reflection. At this spacing, a smaller time window (such as compared to Figure 7A ) near the compression wave reflection time t1 = 5.5 μs and the shear wave reflection round-trip time t2 = 8.8 μs can be selected to measure these reflections with minimal interference from other reflections.

[0070] Figure 7A and Figure 7B The examples of illustrate the following general concept: The selection of the ultrasonic stimulation frequency and the number of cycles in each ultrasonic pulse can be used to increase or decrease the reflected wave duration, so that the time spacing between the reflected shear wave reflection and the reflected compression wave reflection is shorter or longer.

[0071] Figure 8A Another symbolic shear wave transducer reflected wave timing diagram 800 according to an example of the present disclosure is shown, where the shear wave reflection and the compression wave reflection are separated in the time domain. Note thatFigure 8A All of the waves, amplitudes, and timings shown are symbolic and not drawn to scale. In Figure 8A the example of Figure 8A , the shear wave transducer can generate both a shear wave 804 and a compression wave 806 at time t0, and since the compression wave has a greater velocity, the first round trip of the compression wave reflection 816 can be received back at the shear wave transducer at time t1. Next, since the shear wave 804 has a slower velocity, the first round trip of the shear wave reflection 818 can be received back at the shear wave transducer at time t2. In Figure 8A the example of

[0072] Figure 8B Figure 800 shows another symbolic shear wave transducer reflected wave timing diagram according to an example of the present disclosure, where the shear wave reflection and the compression wave reflection are separated in the time domain. Note that Figure 8B all of the waves, amplitudes, and timings shown are symbolic and not drawn to scale. Figure 8B Similar to Figure 8A , except that a thinner glass plate is used, which requires the use of a higher center frequency to maintain a sufficient reflection spacing. In Figure 8B the example of Figure 8B , the shear plate is made of glass with a thickness of 1.5 mm, and the center frequency of the ultrasonic shear wave transducer is 15 MHz. The combination of the thinner sensing plate and the higher center frequency results in a compression wave reflection round trip time t1 of only 0.55 μs and a shear wave reflection round trip time t2 of only 0.88 μs, which generally reduces the reflection spacing time. However, the higher center frequency also results in a pulse duration 820 of only 0.2 μs for the shear wave reflection 818. Thus, Figure 8A the reflected wave pulse duration in Figure 8BIn the example of, there is still a spacing 822 of 0.13 μs between the compressive wave reflection and the shear wave reflection. At this spacing, a smaller time window (e.g., compared to Figure 8A can be selected around the compressive wave reflection time t1 = 0.55 μs and the shear wave reflection round-trip time t2 = 0.88 μs to measure these reflections, with the least interference from other reflections.

[0073] Figure 8A and Figure 8B The examples of and illustrate the following general concept: the thinner the sensing plate is used, the shorter the resulting reflection time, and the smaller the interval between the shear wave reflection and the compressive wave reflection. The examples of the present disclosure can compensate by increasing the center frequency of the ultrasonic shear wave transducer to shorten the reflection pulse width and maintain the time spacing between the shear wave and the compressive wave. More generally, a given sensing plate material can result in a characteristic ultrasonic compressive wave velocity and a characteristic ultrasonic shear wave velocity. The thickness of the material can be selected to determine the round-trip reflection distance and also the timing of the shear wave reflection and the compressive wave reflection (since their velocities are known). Therefore, the material and the thickness of the material can be selected such that the first reflection from the ultrasonic shear wave received at a specific transducer does not overlap in time with the first reflection from the ultrasonic compressive wave received at the specific transducer.

[0074] Therefore, Figure 7A , Figure 7B , Figure 8A and Figure 8B The examples of and show that by carefully selecting the sensing plate thickness and the ultrasonic shear wave transducer frequency, a duration between the compressive wave reflection and the shear wave reflection can be obtained such that a time window can be determined within which the amplitudes or energies of the shear wave reflection and the compressive wave reflection can be determined without significant interference from other reflections. Then, these amplitudes or energy levels can be used to determine whether there is a touch and whether there is water.

[0075] The previous examples discussed above all utilize the first shear wave reflection and the second shear wave reflection to determine the reflection amplitude or energy level and the presence of touch or water. In some examples, the first reflection can be advantageous because at this time no other reflections or ringing occur (e.g., pseudo-waves from the transducer rather than interacting with other objects or interfaces and reflecting back to the transducer). Utilizing reflections other than the first reflection can also produce attenuated signals because under two or more round-trip reflections, the wave interacts with multiple surfaces, interfaces, and other defects due to diffraction.

[0076] However, in some examples, it may be beneficial to use a second reflection or a third reflection (or other subsequent reflections). These reflections can be more sensitive to a touch object or water because they will interact with the top surface of the sensing plate multiple times, causing the object or water to absorb additional waves (depending on the type of wave). Additionally, using downstream reflections can be beneficial for thin laminate structures because in such configurations, the first reflection can arrive very quickly when the transducer electronics may still be ringing from the emission, making those first reflections difficult to distinguish. However, as noted above, it may be difficult to find a time period during which these downstream reflections can be measured without other reflections interfering.

[0077] In examples of the present disclosure, the sensing plate can be formed of glass, sapphire crystal, plastic, metal, and other materials. The key criterion for the material can be how much ultrasonic attenuation it will cause.

[0078] Although the examples of the present disclosure presented above only show a single ultrasonic shear wave transducer, in other examples of the present disclosure, an ultrasonic shear wave transducer array can be employed to not only determine the presence of touch or water, but also determine the location of the touch or water above a larger surface.

[0079] Figure 9 A symbolic plan view of a touch-sensitive surface 900 including an array of ultrasonic shear wave transducers 902 according to an example of the present disclosure is shown. In Figure 9 the example, the ultrasonic shear wave transducers 902 are located below the sensing plate 904. The ultrasonic shear wave transducers 902 located below a touch object 906 can use the shear wave reflections and compression wave reflections described above to detect the presence of the object. Additionally, the known locations of those ultrasonic shear wave transducers 902 that detect the presence of the object 906 can also be used to calculate the location of the object (e.g., the centroid) and estimate the touch boundary of the object. Similarly, the ultrasonic shear wave transducers 902 located below a water droplet 908 can use the shear wave reflections and compression wave reflections described above to detect the presence of the water droplet. Additionally, the known locations of those ultrasonic shear wave transducers 902 that detect the presence of the droplet 908 can also be used to calculate the location of the droplet (e.g., the centroid) and estimate the boundary of the droplet.

[0080] Figure 10 A flowchart 1000 for ultrasonic water-agnostic touch detection according to an example of the present disclosure is shown. In Figure 10 the example, at 1002, shear waves and compression waves are generated by an ultrasonic shear wave transducer and propagated through the sensing plate. At 1004, independent time windows for receiving shear wave reflections and compression wave reflections are identified. At 1006, shear wave reflections and compression wave reflections are received at the ultrasonic shear wave transducer. At 1008, the presence or absence of touch and the presence of water (if any) can be determined based on the amplitudes or levels of the received shear wave reflections and compression wave reflections.

[0081] The foregoing example utilizes an ultrasonic shear transducer to propagate shear waves and parasitic compression waves having a specific excitation center frequency and spectrum through a sensing plate of a specific material type and thickness in order to separate the reflections of those waves. By measuring the amplitudes of the reflected shear waves and the reflected parasitic compression waves, it can be determined whether an object or liquid is present on the sensing plate. However, in other examples of the present disclosure described below, multiple ultrasonic transducers can be utilized to generate both shear non-propagating (standing) waves and compression non-propagating (standing) waves each at a different resonant frequency within the sensing plate. By measuring the amplitudes (i.e., their energy levels) of the shear wave and the compression wave when the shear wave and the compression wave resonate within the sensing plate, it can be determined whether an object or liquid is present on the sensing plate. Figure 2 The functional blocks can be used to implement examples of the present disclosure described below.

[0082] Figures 11A to 11C Shows a main layer of an ultrasonic transducer array according to an example of the present disclosure. Figure 11A Shows a first conductive material layer 1132 for exciting a piezoelectric material according to an example of the present disclosure. In Figure 11A the example, the first conductive material layer 1132 can be formed on the back surface of the sensing plate and patterned as row electrodes. In cases where transparency is required, such as when an ultrasonic sensor is used above a display to form a touch screen, for example, the first conductive material layer 1132 can be a transparent conductive material such as indium tin oxide (ITO). Figure 11B Shows a piezoelectric material layer 1134 for generating ultrasonic compression waves and ultrasonic shear waves according to an example of the present disclosure. In Figure 11B the example, the piezoelectric material layer 1134 can be formed on the first conductive material layer 1132. In cases where at least partial transparency is required, for example, the piezoelectric material layer 1134 can be at least partially transparent piezoelectric material such as aluminum nitride or zinc oxide. Figure 11C Shows a second conductive material layer 1136 for exciting a piezoelectric material according to an example of the present disclosure. In Figure 11C the example, the second conductive material layer 1136 can be formed on the piezoelectric material layer 1134 and patterned as column electrodes. In cases where transparency is required, for example, the second conductive material layer 1136 can be indium tin oxide (ITO).

[0083] Figure 11D Shows according to an example of the present disclosure Figures 11A to 11C a plan view of a stacked structure of the layers of Figure 11DIn an example, the first conductive material layer 1132 may be formed on the back surface of the sensing plate 1138, the edges of which may optionally be coated with a black mask and terminate at a flange. A piezoelectric layer (not shown) may be formed on the first conductive material layer 1132, and a second conductive material layer 1136 may be formed on the piezoelectric layer. It should be understood that the stacked structure may include adhesive layers and refractive index matching layers not shown. The first conductive material layer 1132 and the second conductive material layer 1136 may be electrically connected to a wiring trace 1140, which may be formed of a low-resistance, highly conductive material such as copper when routed in the black mask region. The wiring trace 1140 may be routed to a flexible circuit 1142. These wiring traces 1140 may be used to apply an AC excitation signal to a specific row of the first conductive material layer 1132 and a specific column of the second conductive material layer 1136, such that the piezoelectric material 1134 located at the intersection of that row and that column functions as an ultrasonic transmitter and generates a shear wave or a compression wave at that intersection. Additionally, the wiring traces 1140 may be used to detect the voltage on that row and that column when the piezoelectric material 1134 located at the intersection of a specific row of the first conductive material layer 1132 and a specific column of the second conductive material layer 1136 functions as an ultrasonic receiver. In other words, at each intersection of a row and a column, an ultrasonic transducer may be activated as a transmitter or a receiver, thereby forming a two-dimensional array of ultrasonic transducers.

[0084] Although Figure 11D the stacked structure shows the first conductive material layer 1132 and the second conductive material layer 1136 in a row / column arrangement, it should be understood that the terms "row" and "column" may be used interchangeably herein and are intended to describe a generally orthogonal arrangement. Additionally, transducer arrangements other than row / column are also contemplated herein, such as polar coordinate transducer arrangements and pixelated transducer arrangements, where each transducer may be individually excited. Further, in some examples, the ultrasonic transducers may be selectively and dynamically reconfigured into a capacitive touch sensing arrangement, where the first conductive material layer 1132 and the second conductive material layer 1136 function as mutual capacitance drive and sense electrodes, or as self-capacitance electrodes if separated by a suitable dielectric material that is also ultrasonically transparent. Selectively providing capacitive touch sensing enables the additional capability of proximity (hover) sensing.

[0085] Figure 12A A cross-sectional view of two ultrasonic transducers in an Figure 11D array according to an example of the present disclosure is shown. In Figure 12AIn the example, a piezoelectric material 1234 (e.g., aluminum nitride, zinc oxide, etc.) having a polling direction 1240 can be sandwiched between a row electrode in a first conductive material layer 1232 and two column electrodes in a second conductive material layer 1236. The row electrode can be formed on a sensing plate 1238 (e.g., front crystal glass or other materials serving as good resonators). As will be further explained in detail below, in order to generate a resonant shear wave within a sensing plate 1238 having a specific thickness, the row electrode and the two column electrodes can receive an AC excitation voltage at a frequency that can generate a lateral (shear) displacement in the piezoelectric material 1234 sufficient to generate a shear wave at the shear wave resonant frequency of the sensing plate 1238. Although compressive displacement can also be generated simultaneously (mainly due to the Poisson effect), since the shear wave excitation frequency is far from the compressive wave resonant frequency (e.g., 0.5 GHz) of the sensing plate 1238, a minimum compressive wave can be generated. In order to generate a resonant compressive wave within a sensing plate 1238 having a specific thickness, the row electrode and each column electrode can receive an AC excitation voltage at a frequency that can generate a compressive displacement in the piezoelectric material 1234 sufficient to generate a compressive wave at the compressive resonant frequency of the sensing plate 1238.

[0086] For a given stack structure of materials and thicknesses generally as Figure 12A shown, the shear wave resonant frequency and different compressive wave resonant frequencies of the sensing plate 1238 can be determined to generate non-propagating resonant waves within the sensing plate. It may be desirable for the non-propagating waves to confine the energy of the waves within a specific region of the sensing plate 1238 and maintain a high signal-to-noise ratio (SNR). If the frequencies are chosen such that the shear wave and the compressive wave can propagate horizontally along the sensing plate 1238, the propagating waves can be reflected back from the ends of the plate to the transducer and cause an undesired baseline level shift. To avoid this, in some examples, the shear wave resonant frequency can be empirically determined by selecting a specific frequency that generates a shear horizontal (SH) wave mode with a near-zero group velocity (i.e., a non-propagating shear wave). Similarly, the compressive wave resonant frequency can be empirically determined by selecting a specific frequency of a symmetric (S) or asymmetric (A) mode of a specific order (e.g., the first-order Lamb wave) that generates a near-zero group velocity (i.e., a non-propagating compressive wave).

[0087] In the previous examples of the propagating shear wave and the propagating compressive wave discussed above Figure 8B it should be noted that a thinner sensing plate requires a higher transducer center frequency to maintain a sufficient reflection spacing. This example using non-propagating shear waves and non-propagating compressive waves can also benefit from a thinner sensing plate, but higher frequencies become more problematic in Figures 11A to 11D the example where high-resistance ITO can be used to form an ultrasonic transducer to provide the desired transparency. The higher resistance of the ITO can filter out high-frequency content. Therefore, it may be desirable to select frequencies that are low and also generate shear waves or compressive waves with a near-zero group velocity (i.e., that are non-propagating).

[0088] Generally speaking, for a given sensing plate material and thickness, the frequency of shear resonance in the sensing plate can be determined (e.g., empirically) to provide a non-propagating standing wave in the sensing plate suitable for shear imaging. Similarly, for a given sensing plate material and thickness, the frequency of compression resonance can be determined (e.g., empirically) to provide a non-propagating standing wave with the maximum amplitude in the transducer region for compression imaging. In addition, if the mechanical properties of all the layers in the laminate structure are known, theoretical calculations can be used to identify non-propagating shear waves and non-propagating compression waves. When the mechanical properties are known, the shear horizontal wave dispersion curve and the Lamb guided wave dispersion curve can be calculated, and a mode with a frequency having a near-zero group velocity can be selected.

[0089] Figure 12B An exemplary shear horizontal dispersion curve for selecting non-propagating shear waves according to an example of the present disclosure is shown. In Figure 12B the example, the shear horizontal dispersion curves of the first non-propagating shear horizontal wave SH1 to the fifth non-propagating shear horizontal wave SH5 at various frequencies for a given material thickness (x-axis) are plotted. For the curves SH1 to SH5, it can be seen that the group velocity (y-axis) is close to zero in the frequency ranges f SH1 to f SH5 respectively. In one example, in view of the high resistance of ITO discussed above, the first mode SH1 and the shear resonance frequency within the frequency range f SH1 can be selected to generate a near-zero group velocity.

[0090] Figure 12C An exemplary Lamb / compression dispersion curve for selecting non-propagating compression waves according to an example of the present disclosure is shown. In Figure 12C the example, the Lamb / compression dispersion curves of the symmetric zero-order mode S 0 and the symmetric first-order mode S 1 as well as the asymmetric zero-order mode A 0 and the asymmetric first-order mode A 1 at various frequencies for a given material thickness (x-axis) are plotted. For the curves A 1 and S 1 , it can be seen that the group velocity (y-axis) is close to zero in the frequency ranges f A1 and f S1 respectively. In one example, in view of the high resistance of ITO discussed above, the asymmetric first-order mode A 1 and the compression resonance frequency within the frequency range f A1 can be selected to generate a near-zero group velocity.

[0091] In some examples, the sensing plate 1238 may be formed of a front crystal (e.g., glass) material having a thickness d1 = 500 microns, the first conductive material layer 1232 may have a thickness d2 = 0.2 microns, the piezoelectric material 1234 may have a thickness d3 = 2 microns, and the second conductive material layer 1236 may have a thickness d4 = 0.2 microns. At these dimensions, a shear wave resonance frequency of about 3 MHz (e.g., 3.28 MHz) and a compression wave resonance frequency of about 5 MHz (e.g., 5.2 MHz) may be selected. Compared to the relatively wideband frequencies of the propagating shear waves and propagating compression waves generated in the previous examples, these shear wave resonance frequencies and compression wave resonance frequencies may be much narrower (e.g., a fractional bandwidth of about 1% to 5%). The transducer pair may be driven with a 3.28 MHz excitation signal to generate resonant shear waves within the sensing plate 1238, and the amplitude of the resonant shear waves may be captured for determining whether an object or a liquid (or neither) is present on the sensing plate. At different times, each transducer may be driven with a 5.2 MHz excitation signal to generate resonant compression waves within the sensing plate 1238, and the amplitude of the resonant compression waves may be captured for determining (along with the amplitude of the resonant shear waves) whether an object or a liquid (or neither) is present on the sensing plate.

[0092] Figure 13A Concepts of non-propagating shear wave and compression wave imaging in accordance with examples of the present disclosure are shown. In Figure 13AIn the example, the first conductive material layer, the piezoelectric material layer, and the second conductive material layer are collectively shown as transducer layer 1342, which is attached to the back side of sensing plate 1338. Graph 1344 represents the amplitude (energy level) of the shear wave resonating within sensing plate 1338, as detected by a transducer configured as a receiver (to be discussed in more detail below). Graph 1346 represents the amplitude (energy level) of the compressional wave resonating within sensing plate 1338, as detected by a transducer configured as a receiver (to be discussed in more detail below). When no object 1348 (e.g., finger) or liquid 1350 (e.g., water) is in contact with sensing plate 1338, as shown at position x0, the amplitudes of both the shear wave and the compressional wave can be maintained at (relatively) high voltage levels 1354-S and 1354-C, respectively, which are higher than the shear wave threshold voltage level 1352-S and the compressional wave threshold voltage level 1352-C, respectively. When object 1348 contacts sensing plate 1338, as shown at position x1, the object can absorb some of the energy of the resonating shear wave and the resonating compressional wave, and thus, the amplitudes of both the shear wave and the compressional wave can drop to (relatively) low voltage levels 1356-S and 1356-C, respectively, which are lower than the shear wave threshold voltage level 1352-S and the compressional wave threshold voltage level 1352-C, respectively. When liquid 1350 contacts sensing plate 1338, as shown at position x2, the liquid can absorb some of the energy of the resonating compressional wave, and thus the amplitude of the compressional wave can drop to a (relatively) low voltage level 1358-C, which is lower than the compressional wave threshold voltage level 1352-C. However, liquid 1350 may not absorb much of the energy of the resonating shear wave, and thus the amplitude of the shear wave may only decrease slightly to 1358-S, remaining above the shear wave threshold voltage level 1352-S. In some examples, the shear wave amplitude itself can be used to determine whether no object 1348 or liquid 1350 is present, whether an object is present, or whether a liquid is present. However, in other examples, by comparing the amplitudes of both the shear wave and the compressional wave with the threshold voltage levels 1352-S and 1352-C at the same transducer location, it can be more reliably determined whether no object 1348 or liquid 1350 is present, whether an object is present, or whether a liquid is present. Although Figure 13A only one shear wave threshold 1352-S and one compressional wave threshold 1352-C are shown, in other examples, multiple shear wave thresholds and / or multiple compressional wave thresholds can be employed to ensure that the energy levels are high or low enough to be reliably identified.

[0093] To compare the shear image shown in graph 1344 and the compression image shown in graph 1346 at each ultrasonic transducer position in the two-dimensional array of ultrasonic transducers along the surface of the sensing plate 1338, two images can be captured. The shear image can be captured by obtaining shear wave amplitude information at each transducer in the two-dimensional array, and the compression image can be captured by obtaining compression wave amplitude information at each transducer in the two-dimensional array. In some examples, a complete shear wave image can be captured first, followed by a complete compression wave image, or vice versa. However, if a specific frame rate (e.g., 60 Hz) is desired, it may not be practical to capture the shear image and the compression image independently. In other examples, to take advantage of the efficiency in transducer addressing, configuration, and excitation, at one transducer, the shear image and the compression image can be obtained at two different shear resonance frequencies and compression resonance frequencies before moving to the next transducer, or along a single row (or column) of transducers, the shear image and the compression image can be obtained before moving to the next row (or column).

[0094] Figure 13B A symbolic plan view of non-propagating shear wave and compression wave imaging according to an example of the present disclosure is shown. In Figure 13B each of the four examples provided, the object and the liquid are touching the sensing plate. In the upper left example, the shear wave is resonating within the sensing plate, and the region of the sensing plate without the object or liquid can produce a shear wave amplitude of 1354-S. At the location of the touching object, a shear wave amplitude of 1356-S can be produced, and at the location of the liquid, a shear wave amplitude of 1358-S can be produced. In the lower left example, the compression wave is resonating within the sensing plate, and the region of the sensing plate without the object or liquid can produce a compression wave amplitude of 1354-C. At the location of the touching object, a compression wave amplitude of 1356-C can be produced, and at the location of the liquid, a compression wave amplitude of 1358-C can be produced. If both the region of the touching object in the shear image (where a shear wave amplitude of 1356-S is produced) and the region of the touching object in the compression image (where a compression wave amplitude of 1356-C is produced) are larger than the area expected to be occupied by a finger or a thumb, then in some examples, a palm touch can be detected. In the upper right example, the shear wave is resonating within the sensing plate, and the entire sensing plate is immersed in the liquid. The region of the sensing plate without the object can produce a shear wave amplitude of 1358-S. At the location of the touching object, a shear wave amplitude of 1356-S can be produced. In the lower right example, the compression wave is resonating within the sensing plate, and the entire sensing plate is immersed in the liquid. The region of the sensing plate without the object can produce a compression wave amplitude of 1358-C. At the location of the touching object, a compression wave amplitude of 1356-C can be produced.

[0095] In some examples, regions of the sensing plate that are free of objects or liquid can be used to determine whether the sensing plate is immersed in liquid. For example, if it is determined that a predetermined region of the sensing plate (larger than the region expected to be occupied by a touch finger or droplet) has a shear wave amplitude of 1354-S and a compression wave amplitude of 1354-C, it can be further determined that the sensing plate is in air. On the other hand, if a predetermined region of the sensing plate is determined to have a shear wave amplitude of 1358-S and a compression wave amplitude of 1358-C, it can be further determined that the sensing plate is immersed in liquid. Although Figure 13B is not shown, if it is determined that a predetermined region of the sensing plate has a shear wave amplitude of 1356-S and a compression wave amplitude of 1356-C, it can be further determined that a large object (e.g., a palm, a cheek, etc.) is touching the sensing plate. For example, these further determinations can be used in various algorithms to trigger further functions and operations.

[0096] Figure 14A A cross-sectional view showing shear wave generation and detection using an independent transducer according to an example of the present disclosure is shown. In Figure 14A the example, a piezoelectric material 1434 (e.g., aluminum nitride, zinc oxide, etc.) can be sandwiched between a row electrode in a first conductive material layer 1432 and a column electrode in a second conductive material layer 1436. The first conductive material layer 1432 can be formed on a sensing plate 1438 (e.g., front crystal glass or other material that is a good resonator). At time period t0 (upper cross-sectional view), a single row electrode in the first conductive material layer 1432 and two adjacent column electrodes 1460 and 1462 in the second conductive material layer 1436 can be configured as ultrasonic transmitters and driven with an AC excitation signal to generate resonant shear waves in the sensing plate 1438. In some examples, the AC excitation can be a narrowband signal, where the voltage ramps up from zero to a maximum amplitude voltage similar to a Gaussian-modulated sine pulse train with a narrowband. Driving two adjacent column electrodes 1460 and 1462 with the same signal can result in the generation of shear wave energy that reaches a maximum at the leftmost edge of column electrode 1460 and the rightmost edge of column electrode 1462, as indicated by the dashed line in the upper view of Figure 14A . Shear wave resonance can be mainly generated using the transverse piezoelectric coefficient d31 of the piezoelectric material 1434, which can cause the transducer to expand and compress laterally when an AC voltage is applied. This excitation mode can form a bipolar form of shear wave, where the maximum amplitude appears at the two ends of the transducer with opposite polarities. Using two adjacent column electrodes 1460 and 1462 can ensure that the shear wave energy at the outer edges is spaced far enough apart such that the shear wave energy exists in the regions 1470 and 1472 symbolically shown and is not canceled out. To maintain a sufficient distance, in some examples, the width of each column electrode 1460 and 1462 can be approximately 2.49 mm, resulting in a total edge spacing of approximately 5 mm.

[0097] Since the shear wave energy can reach a maximum at the leftmost edge of column electrode 1460 and the rightmost edge of column electrode 1462 and exists in regions 1470 and 1472, a single row electrode 1464 and column electrode 1466 on either side of column electrodes 1460 and 1462 can be configured as ultrasonic receivers to detect vibrations from the resonant shear waves in sensing plate 1438 (i.e., to detect the shear wave energy levels symbolically shown in regions 1470 and 1472) and generate a voltage representative of the resonant shear wave amplitude. As described above, the amplitude reduction caused by an object present on sensing plate 1438 can be detected by the ultrasonic receivers.

[0098] During time period t1 ( Figure 14A bottom cross-sectional view), the column electrodes can be reconfigured such that adjacent column electrodes 1462 and 1466 now act as ultrasonic transmitters, and column electrodes 1460 and 1474 act as ultrasonic receivers. During subsequent time periods (e.g., t2, t3, t4, etc.), the column electrodes can be sequentially reconfigured in a particular direction (e.g., the x-direction) until each transducer (i.e., ultrasonic "touch pixel") located at the intersection of each column electrode and the single row electrode has captured one or more shear wave amplitudes. Then, the Figure 14A shown sequential process can be repeated for different row electrodes (e.g., in the y-direction) until a complete two-dimensional shear wave image is captured. As can be clearly seen from the Figure 14A sequence, multiple ultrasonic touch pixels can capture shear wave amplitudes at different times (e.g., the pixel associated with column electrode 1466 can capture shear wave amplitudes at time periods t0 and t3). Thus, in some examples, when multiple shear wave amplitudes are captured at a particular touch pixel, these amplitudes can be averaged or otherwise processed to produce a single amplitude at that touch pixel.

[0099] Figure 14B A cross-sectional view showing compression wave generation and detection using independent transducers according to an example of the present disclosure is shown. During time period t0 (top cross-sectional view), a single row electrode in the first conductive material layer 1432 and a single column electrode 1460 in the second conductive material layer 1436 can be configured as ultrasonic transmitters and driven with an AC excitation signal to generate resonant compression waves in sensing plate 1438. In some examples, the AC excitation can be a narrowband signal where the voltage ramps up from zero to a maximum amplitude voltage similar to a Gaussian-modulated sine pulse train with a narrowband. Driving column electrode 1460 can result in the generation of compression wave energy that reaches a maximum at the center of column electrode 1460 (as indicated by the dashed line in the Figure 14B top view) and also exists in regions 1470 and 1472 shown symbolically.

[0100] Since the compressive wave energy can reach a maximum at the center of column electrode 1460 and exists in regions 1470 and 1472, a single row electrode 1464 and column electrode 1462 on either side of column electrode 1460 can be configured as ultrasonic receivers to detect vibrations from the resonant compressive waves in sensing plate 1438 (i.e., to detect the compressive wave energy levels symbolically shown in regions 1470 and 1472) and generate a voltage representative of the amplitude of the resonant compressive waves. As described above, the amplitude reduction caused by an object or liquid present on sensing plate 1438 can be detected by the ultrasonic receivers.

[0101] During time period t1 ( Figure 14B bottom cross-sectional view), the column electrodes can be reconfigured such that column electrode 1462 now acts as an ultrasonic transmitter and column electrodes 1460 and 1466 act as ultrasonic receivers. During subsequent time periods (e.g., t2, t3, t4, etc.), the column electrodes can be sequentially reconfigured in a particular direction (e.g., the x direction) until each transducer (i.e., ultrasonic “touch pixel”) located at the intersection of each column electrode and the single row electrode has captured one or more compressive wave amplitudes. Then, the Figure 14B sequence shown can be repeated for different row electrodes (e.g., in the y direction) until a complete two-dimensional compressive wave image has been captured. As can be clearly seen from the Figure 14B sequence, multiple ultrasonic touch pixels can capture shear wave amplitudes at different times (e.g., the pixel associated with column electrode 1462 can capture shear wave amplitudes during time periods t0 and t2). Thus, in some examples, when multiple compressive wave amplitudes are captured at a particular touch pixel, these amplitudes can be averaged or otherwise processed to produce a single amplitude at that touch pixel.

[0102] In some examples, the gap 1468 (referred to herein as a notch) between adjacent row electrodes and column electrodes in Figure 14A and Figure 14B can affect the timing when the ultrasonic receivers measure the energy of the resonant shear waves and resonant compressive waves. For example, in Figure 14AIn [the example], closely spaced electrodes with slits 1468 less than about 50 microns can result in crosstalk between column electrodes 1460 configured as part of an ultrasonic transmitter and column electrodes 1464 configured as part of an ultrasonic receiver. Similar crosstalk can exist between column electrodes 1462 configured as part of an ultrasonic transmitter and column electrodes 1466 configured as part of an ultrasonic receiver. Due to the possibility of crosstalk, in some examples, when the slit is less than about 50 microns, the ultrasonic receiver can be configured to detect resonant shear wave energy or resonant compression wave energy only after the ultrasonic transmitter has stopped generating resonant shear waves or resonant compression waves. In other examples, when the slit is greater than about 50 microns, the possibility of crosstalk can be reduced, and the ultrasonic receiver can be configured to detect resonant shear wave energy or resonant compression wave energy while the ultrasonic transmitter is generating shear waves or compression waves. Another advantage of row electrodes and column electrodes with slits less than 50 microns is that when used in touchscreen applications, these small gaps between the electrodes provide improved optical uniformity, while slits greater than 50 microns may form undesirable visual artifacts.

[0103] Figure 15A Shows a signal received at an ultrasonic receiver according to an example of the present disclosure, the ultrasonic receiver being configured to detect resonant shear wave energy after the ultrasonic transmitter has stopped generating resonant shear waves. In Figure 15A the example, the slit separating the transmitter and the receiver is about 10 microns, and due to the possibility of crosstalk, the transmitter is driven only with an AC excitation signal during the transmit window 1574. During the receive window 1576, even in the absence of a transmitter excitation signal, the resonant shear waves can continue to ring within the sensing plate. Since the signal decays slowly over a relatively long period of time, the receiver can detect the shear wave energy during the receive window 1576.

[0104] Figure 15B Shows an example according to the present disclosure of Figure 15A the signal received at the ultrasonic receiver during the receive window 1576. In Figure 15B the example, during the receive window, when no object is present, a larger resonant shear wave amplitude 1578 can be detected, and when an object is present, a smaller resonant shear wave amplitude 1580 can be detected. Although Figure 15B not shown in [the figure], when a liquid is present, a resonant shear wave amplitude slightly smaller than amplitude 1578 can also be detected. As described above, these amplitudes can be used to determine whether no object is present, whether an object is present, or whether a liquid is present.

[0105] Figure 15Cshows a signal received at an ultrasound receiver according to an example of the present disclosure, the ultrasound receiver being configured to detect resonant shear wave energy while an ultrasound transmitter is generating a resonant shear wave. In other words, the transmit window and the receive window may at least partially overlap in time. In Figure 15C 's example, the notch separating the transmitter and the receiver is about 50 microns, and due to the reduced likelihood of crosstalk, the transmitter can generate a resonant shear wave while the receiver detects the shear wave amplitude during the same transmit / receive window 1582. During the transmit / receive window 1582, a larger resonant shear wave amplitude 1578 can be detected when no object is present, and a smaller resonant shear wave amplitude 1580 can be detected when an object is present. Although Figure 15B is not shown, but when a liquid is present, a resonant shear wave amplitude slightly smaller than amplitude 1578 can also be detected. As described above, these amplitudes can be used to determine whether no object is present, whether an object is present, or whether a liquid is present.

[0106] Although Figures 15A to 15C has been described with respect to the generation and measurement of resonant shear waves, the same principles can be applied to the generation and measurement of resonant compression waves.

[0107] Figure 16A shows a cross-sectional view of shear wave generation and detection using the same transducer according to an example of the present disclosure. In Figure 16A 's example, a piezoelectric material 1634 (e.g., aluminum nitride, zinc oxide, etc.) can be sandwiched between row electrodes in a first conductive material layer 1632 and column electrodes in a second conductive material layer 1636. The first conductive material layer 1632 can be formed on a sensing plate 1638 (e.g., front crystal glass or other material that serves as a good resonator). At time period t0 (upper cross-sectional view), a single row electrode in the first conductive material layer 1632 and two adjacent column electrodes 1660 and 1662 in the second conductive material layer 1636 can be configured as an ultrasound transmitter and driven with an AC excitation signal to generate a resonant shear wave in the sensing plate 1638. In some examples, the AC excitation can be a narrowband signal, where the voltage ramps up from zero to a maximum amplitude voltage similar to a Gaussian-modulated sine pulse train with a narrowband. Driving two adjacent column electrodes 1660 and 1662 with the same signal can result in the generation of shear wave energy that reaches a maximum at the leftmost edge of column electrode 1660 and the rightmost edge of column electrode 1662, as indicated by the dashed line in Figure 16A . Using two adjacent column electrodes 1660 and 1662 can ensure that the shear wave energy at the outer edges is spaced far enough apart so that the shear wave energy is not canceled out. To maintain a sufficient distance, in some examples, the width of each column electrode 1660 and 1662 can be about 2.49 mm, resulting in a total edge spacing of about 5 mm.

[0108] Since the shear wave energy can reach a maximum at the leftmost edge of column electrode 1660 and the rightmost edge of column electrode 1662 after the generation of the resonant shear wave has stopped, column electrode 1660 can be reconfigured as an ultrasonic receiver to detect the vibrations from the resonant shear wave in the sensing plate 1638 and generate a voltage representative of the resonant shear wave amplitude (shear wave level). As described above, the amplitude reduction caused by an object present on the sensing plate 1638 can be detected by the ultrasonic receiver.

[0109] During time period t1 ( Figure 16A bottom cross-sectional view), the column electrodes can be reconfigured such that adjacent column electrodes 1662 and 1666 now act as ultrasonic transmitters, and after the generation of the resonant shear wave has stopped, column electrode 1662 can be reconfigured as an ultrasonic receiver. During subsequent time periods (e.g., t2, t3, t4, etc.), the column electrodes can be sequentially reconfigured in a particular direction (e.g., the x direction) until each transducer (i.e., ultrasonic "touch pixel") located at the intersection of each column electrode and a single row electrode has captured one or more shear wave amplitudes. Then, the Figure 16A shown sequential process can be repeated for different row electrodes (e.g., in the y direction) until a complete two-dimensional shear wave image is captured.

[0110] Figure 16B A cross-sectional view showing compression wave generation and detection using the same transducer according to an example of the present disclosure is shown. During time period t0 (top cross-sectional view), a single row electrode in the first conductive material layer 1632 and a single column electrode 1660 in the second conductive material layer 1636 can be configured as ultrasonic transmitters and driven with an AC excitation signal to generate a resonant compression wave in the sensing plate 1638. In some examples, the AC excitation can be a narrowband signal, where the voltage ramps up from zero to a maximum amplitude voltage similar to a Gaussian-modulated sine pulse train with a narrowband. Driving the column electrode 1660 can result in the generation of compression wave energy that reaches a maximum at the center of the column electrode 1660, as indicated by the dashed line in Figure 16B the figure.

[0111] Since the compression wave energy can reach a maximum at the center of column electrode 1660 after the generation of the resonant compression wave has stopped, column electrode 1660 can be reconfigured as an ultrasonic receiver to detect the vibrations from the resonant compression wave in the sensing plate 1638 and generate a voltage representative of the resonant compression wave amplitude (compression wave level). As described above, the amplitude reduction caused by an object or liquid present on the sensing plate 1638 can be detected by the ultrasonic receiver.

[0112] During time period t1 ( Figure 16BIn the cross-sectional view below, the column electrodes can be reconfigured such that column electrode 1662 now acts as an ultrasonic transmitter, and after the generation of resonant compression waves has stopped, column electrode 1662 can be reconfigured to act as an ultrasonic receiver. During subsequent time periods (e.g., t2, t3, t4, etc.), the column electrodes can be sequentially reconfigured in a specific direction (e.g., the x direction) until each transducer (i.e., ultrasonic "touch pixel") located at the intersection of each column electrode and a single row electrode has captured one or more compression wave amplitudes. Then, the sequential process shown can be repeated for different row electrodes (e.g., in the y direction) until a complete two-dimensional compression wave image is captured. Figure 16B The sequential process shown until a complete two-dimensional compression wave image is captured.

[0113] Figure 17A Shows a signal received at an ultrasonic transducer according to an example of the present disclosure, the ultrasonic transducer being configured to perform both shear wave or compression wave generation and detection. In Figure 17A corresponding to Figures 16A to 16B In the example, the ultrasonic transducer is configured as a transmitter and is driven with an AC excitation signal only during the transmission window 1774. The transducer can then be reconfigured as a receiver, and during the reception window 1776, even in the absence of a transmitter excitation signal, the resonant waves can continue to ring within the sensing plate. Since the signal decays slowly over a relatively long period of time, the receiver can detect shear wave energy during the reception window 1776.

[0114] Figure 17B Shows an example according to the present disclosure during Figure 17A the reception window 1776 of the signal received at the ultrasonic receiver. In Figure 17B In the example, during the reception window, when there is no object, a larger resonant wave amplitude 1778 can be detected, and when there is an object, a smaller resonant wave amplitude 1780 can be detected. Although Figure 17B not shown in, but when there is a liquid, a resonant wave amplitude slightly smaller than amplitude 1778 can also be detected. As described above, these amplitudes can be used to determine whether there is no object, whether there is an object, or whether there is a liquid.

[0115] Figure 18 Shows a flowchart for performing water-agnostic touch using non-propagating (resonant) shear waves and non-propagating (resonant) compression waves according to an example of the present disclosure. In Figure 18In the example, a resonant shear wave is generated at 1882 and used to capture a shear image. At 1184, a resonant compression wave is also generated and used to capture a compression image. It should be understood that, according to various examples of the present disclosure, the order of 1882 and 1884 may be reversed or combined in the combined capture of a shear image and a compression image. At 1886, the captured shear image and compression image may then be used to determine touchless, touched objects, liquids, and optionally immersed regions.

[0116] Accordingly, in accordance with the foregoing, some examples of the present disclosure relate to a device that includes: a surface; a transducer array coupled to the surface, each transducer in the transducer array being configured to generate an ultrasonic shear wave and an ultrasonic compression wave and receive reflections of the ultrasonic shear wave and reflections of the ultrasonic compression wave during non-overlapping windows; and a processor coupled to the transducer array, the processor being configured for each transducer: determine that an object is in contact with the region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being less than a first threshold and the reflection from the ultrasonic compression wave being less than a second threshold; determine that a liquid is in contact with the region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being greater than the first threshold and the reflection from the ultrasonic compression wave being less than the second threshold; and determine that no object is in contact with the region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being greater than the first threshold and the reflection from the ultrasonic compression wave being greater than the second threshold. In addition to one or more of the examples disclosed above or alternatively, in some examples, each transducer in the transducer array is an ultrasonic shear wave transducer. In addition to one or more of the examples disclosed above or alternatively, in some examples, the x-direction is defined as parallel to the surface, and the z-direction is defined as perpendicular to the surface, and each ultrasonic shear wave transducer includes: a first electrode and a second electrode formed on the top and bottom of the ultrasonic shear wave transducer in the z-direction; wherein the polling direction of the shear wave transducer is aligned along the x-direction. In addition to one or more of the examples disclosed above or alternatively, in some examples, the reflection from the ultrasonic shear wave is the first reflection of the ultrasonic shear wave, and the reflection from the ultrasonic compression wave is the first reflection of the ultrasonic compression wave. In addition to one or more of the examples disclosed above or alternatively, in some examples, the reflection from the ultrasonic shear wave is a reflection after the first reflection of the ultrasonic shear wave, and the reflection from the ultrasonic compression wave is a reflection after the first reflection of the ultrasonic compression wave. In addition to one or more of the examples disclosed above or alternatively, in some examples, the surface has a characteristic ultrasonic compression wave velocity, a characteristic ultrasonic shear wave velocity, and a thickness, and the characteristic ultrasonic compression wave velocity, the characteristic ultrasonic shear wave velocity, and the thickness are selected such that the first reflection of the ultrasonic shear wave received at a particular transducer does not overlap in time with the first reflection of the ultrasonic compression wave received at the particular transducer.In some examples, in addition to or alternatively to one or more of the examples disclosed above, each transducer in a transducer array is configured to generate a plurality of pulses, each pulse comprising a first number of cycles at a first frequency; wherein the first number of cycles and the first frequency are selected such that a first reflection from an ultrasonic shear wave received at a particular transducer does not overlap in time with a first reflection from an ultrasonic compression wave received at the particular transducer.

[0117] Some examples of the present disclosure relate to methods for detecting objects and water on a surface, the method comprising: generating an ultrasonic shear wave and an ultrasonic compression wave from each transducer in a transducer array; receiving reflections of the ultrasonic shear wave and reflections of the ultrasonic compression wave during non-overlapping time windows; and for each transducer: determining that an object is in contact with a region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being less than a first threshold and the reflection from the ultrasonic compression wave being less than a second threshold; determining that a liquid is in contact with a region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being greater than the first threshold and the reflection from the ultrasonic compression wave being less than the second threshold; and determining that no object is in contact with a region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being greater than the first threshold and the reflection from the ultrasonic compression wave being greater than the second threshold. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises generating an ultrasonic shear wave and an ultrasonic compression wave from each transducer using an ultrasonic shear wave transducer. In addition to one or more of the examples disclosed above or alternatively, in some examples, the x-direction is defined as parallel to the surface, and the z-direction is defined as perpendicular to the surface, and the method further comprises orienting each ultrasonic shear wave transducer such that the polling direction of the ultrasonic shear wave transducer is aligned along the x-direction. In addition to one or more of the examples disclosed above or alternatively, in some examples, the reflection from the ultrasonic shear wave is the first reflection of the ultrasonic shear wave, and the reflection from the ultrasonic compression wave is the first reflection of the ultrasonic compression wave. In addition to one or more of the examples disclosed above or alternatively, in some examples, the reflection from the ultrasonic shear wave is a reflection after the first reflection of the ultrasonic shear wave, and the reflection from the ultrasonic compression wave is a reflection after the first reflection of the ultrasonic compression wave. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises selecting a material of the surface to have a characteristic ultrasonic compression wave velocity, a characteristic ultrasonic shear wave velocity, and a thickness such that the first reflection from the ultrasonic shear wave received at a particular transducer does not overlap in time with the first reflection from the ultrasonic compression wave received at the particular transducer. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises generating an ultrasonic shear wave and an ultrasonic compression wave from each transducer in the transducer array with a plurality of pulses, each pulse comprising a first number of cycles at a first frequency; wherein the first number of cycles and the first frequency are selected such that the first reflection from the ultrasonic shear wave received at a particular transducer does not overlap in time with the first reflection from the ultrasonic compression wave received at the particular transducer.

[0118] Some examples of the present disclosure relate to a device that includes: means for propagating an ultrasonic shear wave and an ultrasonic compression wave from each position in an array through a surface material; means for receiving reflections of the ultrasonic shear wave and reflections of the ultrasonic compression wave from each position in the array during non-overlapping time windows; and for each means for propagation: determining that an object is in contact with a region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being less than a first threshold and the reflection from the ultrasonic compression wave being less than a second threshold; determining that a liquid is in contact with a region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being greater than the first threshold and the reflection from the ultrasonic compression wave being less than the second threshold; and determining that no object is in contact with a region of the surface corresponding to the transducer based on the reflection from the ultrasonic shear wave being greater than the first threshold and the reflection from the ultrasonic compression wave being greater than the second threshold. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the means for generating an ultrasonic shear wave and an ultrasonic compression wave from each position in the array includes an ultrasonic shear wave transducer. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the x-direction is defined as parallel to the surface, and the z-direction is defined as perpendicular to the surface, and each ultrasonic shear wave transducer is oriented such that the polling direction of the ultrasonic shear wave transducer is aligned along the x-direction. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the reflection from the ultrasonic shear wave is a first reflection of the ultrasonic shear wave, and the reflection from the ultrasonic compression wave is a first reflection of the ultrasonic compression wave. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the reflection from the ultrasonic shear wave is a reflection after the first reflection of the ultrasonic shear wave, and the reflection from the ultrasonic compression wave is a reflection after the first reflection of the ultrasonic compression wave. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the surface material has a characteristic ultrasonic compression wave velocity, a characteristic ultrasonic shear wave velocity, and a thickness such that the first reflection of the ultrasonic shear wave received at a particular transducer does not overlap in time with the first reflection of the ultrasonic compression wave received at the particular transducer. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the means for propagation is configured to generate an ultrasonic shear wave and an ultrasonic compression wave from each transducer in the transducer array with a plurality of pulses, each pulse including a first number of cycles at a first frequency; wherein the first number of cycles and the first frequency are selected such that the first reflection of the ultrasonic shear wave received at a particular transducer does not overlap in time with the first reflection of the ultrasonic compression wave received at the particular transducer.

[0119] Some examples of the present disclosure relate to a device that includes: a sensing plate; a plurality of transducers coupled to a back side of the sensing plate, the plurality of transducers being configurable to generate ultrasonic waves within the sensing plate at a shear wave resonance frequency and at a compression wave resonance frequency at a plurality of transducer positions, and further being configurable to detect a shear wave level of a shear wave resonating within the sensing plate at the shear wave resonance frequency and a compression wave level of a compression wave resonating with the sensing plate at the compression wave resonance frequency at the plurality of transducer positions; and a processor coupled to the plurality of transducers and configured to, at each of the plurality of transducer positions: determine whether the shear wave level is less than a shear wave threshold and whether the compression wave level is less than a compression wave threshold; determine that an object is in contact with the sensing plate at the transducer position based on determining that the shear wave level is less than the shear wave threshold and the compression wave level is less than the compression wave threshold; and determine that a liquid is in contact with the sensing plate at the transducer position based on determining that the shear wave level is greater than the shear wave threshold and the compression wave level is less than the compression wave threshold. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to, at each of the plurality of transducer positions: determine that no object or liquid is in contact with the sensing plate at the transducer position based on determining that the shear wave level is greater than the shear wave threshold and the compression wave level is greater than the compression wave threshold. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to: determine that the sensing plate is in air based on determining that, for a first plurality of adjacent transducer positions representing a region greater than a first surface area, the shear wave level is greater than the shear wave threshold and the compression wave level is greater than the compression wave threshold. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to: determine that the sensing plate is immersed in a liquid based on determining that, for a first plurality of adjacent transducer positions representing a region greater than a first surface area, the compression wave level is less than the compression wave threshold and the shear wave level is less than the shear wave threshold. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to: determine that the sensing plate is touched by a palm based on determining that, for a first plurality of adjacent transducer positions representing a region greater than a first surface area, the compression wave level is less than the compression wave threshold and the shear wave level is less than the shear wave threshold. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the shear wave and the compression wave are non-propagating waves having a group velocity of approximately zero.In addition to or as an alternative to one or more of the examples disclosed above, in some examples, a plurality of transducers include: a first conductive material layer patterned into a plurality of rows and formed on the back surface of a sensing plate; a piezoelectric material layer disposed on the first conductive material layer; and a second conductive material layer patterned into a plurality of columns and disposed on the piezoelectric material layer, wherein transducers are formed at positions where the first conductive material layer intersects the second conductive material layer, and wherein the piezoelectric material layer is disposed between the first conductive material layer and the second conductive material layer. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to generate ultrasonic waves at a shear wave resonance frequency at adjacent second and third transducers during a first time period, and detect a shear wave level of the shear wave at the first and fourth transducers during the first time period, the second transducer being adjacent to the first transducer and the fourth transducer being adjacent to the third transducer, the first through fourth transducers being arranged continuously in a first direction. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to generate ultrasonic waves at a compression wave resonance frequency at the second transducer during a first time period, and detect a compression wave level of the compression wave at the first and third transducers during the first time period, the first transducer being adjacent to the second transducer and the second transducer being adjacent to the third transducer, the first through third transducers being arranged continuously in a first direction. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to generate ultrasonic waves at a shear wave resonance frequency at adjacent first and second transducers during a first time period, and detect a shear wave level of the shear wave at the first transducer during the first time period, the first and second transducers being arranged continuously in a first direction. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to generate ultrasonic waves at a compression wave resonance frequency at the first transducer during a first time period, and detect a compression wave level of the compression wave at the first transducer during the first time period. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the processor is further configured to generate an ultrasonic shear wave resonance frequency or an ultrasonic compression wave resonance frequency at the first transducer in a transmission window, and detect a shear wave level or a compression wave level at a second transducer adjacent to the first transducer in a reception window after the transmission window.In some examples, in addition to or as an alternative to one or more of the examples disclosed above, the processor is further configured to generate an ultrasonic shear wave resonance frequency or an ultrasonic compression wave resonance frequency at a first transducer within a transmit / receive window and to detect a shear wave level or a compression wave level at a second transducer adjacent to the first transducer within the transmit / receive window.

[0120] Some examples of the present disclosure relate to a method for detecting an object or a liquid on a sensing plate, the method comprising: generating ultrasonic waves within the sensing plate at a shear wave resonance frequency and at a compression wave resonance frequency at a plurality of locations; detecting a shear wave level of shear waves resonating within the sensing plate at the shear wave resonance frequency and a compression wave level of compression waves resonating with the sensing plate at the compression wave resonance frequency at the plurality of locations; and at each of the plurality of locations: determining whether the shear wave level is less than a shear wave threshold and whether the compression wave level is less than a compression wave threshold; determining that an object is in contact with the sensing plate at the location based on determining that the shear wave level is less than the shear wave threshold and the compression wave level is less than the compression wave threshold; and determining that a liquid is in contact with the sensing plate at the location based on determining that the shear wave level is greater than the shear wave threshold and the compression wave level is less than the compression wave threshold. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises at each of the plurality of locations: determining that no object or liquid is in contact with the sensing plate at the location based on determining that the shear wave level is greater than the shear wave threshold and the compression wave level is greater than the compression wave threshold. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises: determining that the sensing plate is in air based on determining that for a first plurality of adjacent locations representing a region greater than a first surface area, the shear wave level is greater than the shear wave threshold and the compression wave level is greater than the compression wave threshold. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises: determining that the sensing plate is immersed in a liquid based on determining that for a first plurality of adjacent locations representing a region greater than a first surface area, the compression wave level is less than the compression wave threshold and the shear wave level is less than the shear wave threshold. In addition to one or more of the examples disclosed above or alternatively, in some examples, the shear wave and the compression wave are non-propagating waves having a group velocity of approximately zero. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises generating ultrasonic waves at the plurality of locations by applying an AC excitation signal across a piezoelectric material at each of the plurality of locations. In addition to one or more of the examples disclosed above or alternatively, in some examples, the method further comprises generating ultrasonic waves at a shear wave resonance frequency at adjacent second and third locations during a first time period, and detecting a shear wave level of the shear waves at a first location and a fourth location during the first time period, the second location being adjacent to the first location and the fourth location being adjacent to the third location, the first through fourth locations being arranged continuously in a first direction.In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the method further includes generating ultrasonic waves at a compressive wave resonance frequency at a second location during a first time period, and detecting a compressive wave level of the compressive wave at a first location and a third location during the first time period, the first location being adjacent to the second location and the second location being adjacent to the third location, the first through third locations being arranged continuously in a first direction. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the method further includes generating ultrasonic waves at a shear wave resonance frequency at adjacent first and second locations during a first time period, and detecting a shear wave level of the shear wave at the first location during the first time period, the first and second locations being arranged continuously in a first direction. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the method further includes generating ultrasonic waves at a compressive wave resonance frequency at a first location during a first time period, and detecting a compressive wave level of the compressive wave at the first location during the first time period. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the method further includes generating an ultrasonic shear wave resonance frequency or an ultrasonic compressive wave resonance frequency at a first location in a transmit window, and detecting a shear wave level or a compressive wave level at a second location adjacent to the first location in a receive window after the transmit window. In addition to or as an alternative to one or more of the examples disclosed above, in some examples, the method further includes generating an ultrasonic shear wave resonance frequency or an ultrasonic compressive wave resonance frequency at a first location in a transmit / receive window, and detecting a shear wave level or a compressive wave level at a second location adjacent to the first location in the transmit / receive window.

[0121] While the examples of the present disclosure have been described fully with reference to the accompanying drawings, it should be noted that various changes and modifications will become apparent to those skilled in the art. It should be understood that such changes and modifications are considered to be included within the scope of the examples of the present disclosure as defined by the appended claims.

Claims

1. An apparatus for detecting an object or a liquid on a sensing plate, comprising: the sensing plate; a plurality of transducers coupled to a back side of the sensing plate, the plurality of transducers being configurable to generate ultrasonic waves in the sensing plate at a shear wave resonance frequency and at a compressional wave resonance frequency at a plurality of transducer positions, and further being configurable to detect a shear wave level of a shear wave resonating in the sensing plate at the shear wave resonance frequency and a compressional wave level of a compressional wave resonating with the sensing plate at the compressional wave resonance frequency at the plurality of transducer positions; and a processor coupled to the plurality of transducers and configured to, at each of the plurality of transducer positions: determine whether the shear wave level is less than a shear wave threshold and whether the compressional wave level is less than a compressional wave threshold, determine, based on determining that the shear wave level is less than the shear wave threshold and the compressional wave level is less than the compressional wave threshold, that the object is in contact with the sensing plate at the transducer position, and determine, based on determining that the shear wave level is greater than the shear wave threshold and the compressional wave level is less than the compressional wave threshold, that the liquid is in contact with the sensing plate at the transducer position.

2. The apparatus according to claim 1, wherein the processor is further configured to, at each of the plurality of transducer positions: determine, based on determining that the shear wave level is greater than the shear wave threshold and the compressional wave level is greater than the compressional wave threshold, that no object or liquid is in contact with the sensing plate at the transducer position.

3. The apparatus according to claim 1, wherein the processor is further configured to: for a first plurality of adjacent transducer positions representing a region greater than a first surface area indicative of a finger touch or a droplet, determine, based on determining that the shear wave level is greater than the shear wave threshold and the compressional wave level is greater than the compressional wave threshold, that the sensing plate is in air.

4. The apparatus according to claim 1, wherein the processor is further configured to: for a first plurality of adjacent transducer positions representing a region greater than a first surface area indicative of a finger touch or a droplet, determine, based on determining that the compressional wave level is less than the compressional wave threshold and the shear wave level is greater than the shear wave threshold, that the sensing plate is immersed in a liquid.

5. The apparatus according to claim 1, wherein the processor is further configured to: for a first plurality of adjacent transducer positions representing a region greater than a first surface area indicative of a finger touch or a droplet, determine, based on determining that the compressional wave level is less than the compressional wave threshold and the shear wave level is less than the shear wave threshold, that the sensing plate is touched by a palm.

6. The apparatus according to claim 1, wherein the shear wave and the compressional wave are non-propagating waves having a group velocity of approximately zero.

7. The apparatus according to claim 1, the plurality of transducers comprising: a first conductive material layer patterned into a plurality of rows and formed on the back side of the sensing plate; A piezoelectric material layer disposed on the first conductive material layer; and A second conductive material layer patterned into a plurality of columns and disposed on the piezoelectric material layer; Wherein a transducer is formed at a position where the first conductive material layer intersects the second conductive material layer and the piezoelectric material layer is disposed between the first conductive material layer and the second conductive material layer.

8. The apparatus according to claim 1, wherein the processor is further configured to generate ultrasonic waves at the shear wave resonance frequency at adjacent second and third transducers during a first time period, and detect the shear wave level of the shear wave at the first and fourth transducers during the first time period, the second transducer being adjacent to the first transducer and the fourth transducer being adjacent to the third transducer, the first to fourth transducers being arranged continuously in a first direction.

9. The apparatus according to claim 1, wherein the processor is further configured to generate ultrasonic waves at the compression wave resonance frequency at the second transducer during a first time period, and detect the compression wave level of the compression wave at the first and third transducers during the first time period, the first transducer being adjacent to the second transducer and the second transducer being adjacent to the third transducer, the first to third transducers being arranged continuously in a first direction.

10. The apparatus according to claim 1, wherein the processor is further configured to generate ultrasonic waves at the shear wave resonance frequency at adjacent first and second transducers during a first time period, and detect the shear wave level of the shear wave at the first transducer during the first time period, the first transducer and the second transducer being arranged continuously in a first direction.

11. The apparatus according to claim 1, wherein the processor is further configured to generate ultrasonic waves at the compression wave resonance frequency at the first transducer during a first time period, and detect the compression wave level of the compression wave at the first transducer during the first time period.

12. The apparatus according to claim 1, wherein the processor is further configured to generate an ultrasonic shear wave resonance frequency or an ultrasonic compression wave resonance frequency at the first transducer in a transmission window, and detect the shear wave level or the compression wave level at a second transducer adjacent to the first transducer in a reception window after the transmission window.

13. The apparatus according to claim 1, wherein the processor is further configured to generate an ultrasonic shear wave resonance frequency or an ultrasonic compression wave resonance frequency at the first transducer in a transmit / receive window, and detect the shear wave level or the compression wave level at a second transducer adjacent to the first transducer in the transmit / receive window.

14. A method for detecting an object or a liquid on a sensing plate, comprising: Generating ultrasonic waves within the sensing plate at a shear wave resonance frequency and at a compression wave resonance frequency at a plurality of positions; Detecting a shear wave level of a shear wave resonating within the sensing plate at the shear wave resonance frequency and a compression wave level of a compression wave resonating with the sensing plate at the compression wave resonance frequency at the plurality of locations; and At each of the plurality of locations, Determining whether the shear wave level is less than a shear wave threshold and whether the compression wave level is less than a compression wave threshold, Determining that an object is in contact with the sensing plate at the location based on determining that the shear wave level is less than the shear wave threshold and the compression wave level is less than the compression wave threshold, and Determining that a liquid is in contact with the sensing plate at the location based on determining that the shear wave level is greater than the shear wave threshold and the compression wave level is less than the compression wave threshold.

15. The method according to claim 14, the method further comprising, at each of the plurality of locations: Determining that no object or liquid is in contact with the sensing plate at the location based on determining that the shear wave level is greater than the shear wave threshold and the compression wave level is greater than the compression wave threshold.

16. The method according to claim 14, the method further comprising: For a first plurality of adjacent locations representing a region greater than a first surface area indicative of a finger touch or a droplet, determining that the sensing plate is in air based on determining that the shear wave level is greater than the shear wave threshold and the compression wave level is greater than the compression wave threshold.

17. The method according to claim 14, the method further comprising: For a first plurality of adjacent locations representing a region greater than a first surface area indicative of a finger touch or a droplet, determining that the sensing plate is immersed in a liquid based on determining that the compression wave level is less than the compression wave threshold and the shear wave level is greater than the shear wave threshold.

18. The method according to claim 14, wherein the shear wave and the compression wave are non-propagating waves having a group velocity of approximately zero.

19. The method according to claim 14, the method further comprising: Generating the ultrasonic waves at the plurality of locations by applying an AC excitation signal across the piezoelectric material at each of the plurality of locations.

20. The method according to claim 14, the method further comprising: Generating ultrasonic waves at a shear wave resonance frequency at adjacent second and third locations during a first time period; and Detecting the shear wave level of the shear wave at a first location and a fourth location during the first time period, the second location being adjacent to the first location and the fourth location being adjacent to the third location, the first through fourth locations being arranged continuously in a first direction.

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