Determining Time-of-Flight Measurement Results and Distance Detection Systems with Reduced Dead Zones

Abstract

A distance detection system (150) includes an ultrasonic transducer (106) having at least one ultrasonic element (105) and a receiver (170) configured to receive a detection signal (172) from the ultrasonic transducer (106). The detection signal (172) includes a reverberation component representing the reverberation of the ultrasonic transducer (106) and a reflection component representing the reflected acoustic wave from an interface. The receiver is configured to receive a drive cancellation signal (174) that is inverted relative to the reverberation component of the detection signal. The receiver (170) is configured to determine a time-of-flight measurement result based on the detection signal (172), in which the reverberation component of the detection signal (172) is reduced by the drive cancellation signal (174).

Description

Technical Field

[0001] The subject matter herein generally relates to a distance detection system that uses a transducer to determine a distance between an interface and the transducer. Background Art

[0002] An increasing number of machines are being designed with sensors that detect the distance between an object and a detectable boundary. For example, vehicles use proximity sensors to determine whether there is an obstacle in the path of the vehicle and to warn the operator when an obstacle is identified. These proximity sensors can also be used to automatically control the vehicle, such as for avoiding collisions. One type of proximity sensor includes an ultrasonic transducer. The ultrasonic transducer generates sound waves in response to a specified drive signal. The sound waves can be intermittent pulses or continuous transmissions. The sound waves are reflected at a boundary where there is an impedance mismatch. For example, the sound waves can be reflected by a gas-liquid interface, a gas-solid interface, or a liquid-solid interface. The reflected sound waves are detected by the ultrasonic transducer. The duration for which the sound waves travel from and return to the ultrasonic transducer can be referred to as the "time of flight" (TOF). The TOF value is used to calculate the distance traveled by the sound waves and the distance between the ultrasonic transducer and the boundary.

[0003] The ultrasonic transducer can use one or more ultrasonic elements (such as piezoelectric elements) that are used to send sound waves (herein referred to as "pulse waves") and to detect the reflected sound waves (herein referred to as "reflected waves" or "echoes"). In some ultrasonic transducers, the same ultrasonic element can operate in different modes to send pulse waves and to detect (or receive) reflected waves. Although the above ultrasonic transducers can accurately estimate a certain distance range, detecting shorter distances can pose challenges. For example, when a pulse wave is reflected by an interface that is less than fifteen (15) millimeters away from the ultrasonic element, it may be difficult to calculate the distance.

[0004] More specifically, it is difficult to calculate the distance because the ultrasonic element responds to the drive signal and even after the drive signal stops. The drive signal is an electrical signal that excites the transducer. When responding to the drive signal, the vibration caused by the ultrasonic element generates sound waves. Even after the drive signal stops, the ultrasonic element continues to vibrate, thereby causing sound waves that are detected by the sensor. This phenomenon is referred to as "ringing" or "ring-down". Therefore, it may be possible to detect vibrations from the ultrasonic element itself before the reflected wave reaches the ultrasonic transducer. The signal caused by the vibration makes it difficult to determine whether any reflected wave has been received.

[0005] To solve this problem, ultrasonic transducers typically have a time window (referred to as a "dead zone") during which any detectable sound waves are not relied upon for distance calculations. For example, an ultrasonic transducer may only consider sound waves detected after 5.0 ms of the drive signal stopping. Reducing this window may require significant transducer / circuit design changes and significantly increase costs. Even if the ring-down time can be reduced, there is still a period during the drive signal when detectable sound waves are not considered. Therefore, it may not be possible to detect boundaries at a certain short distance from the ultrasonic element.

[0006] The problem to be solved by the present invention is to provide a distance detection system that can detect reflected sound waves when the ultrasonic element responds to a drive signal or during the ring-down of the ultrasonic element. Summary of the Invention

[0007] The above problem is solved by a distance detection system that includes a signal generator configured to provide a drive signal and an ultrasonic transducer having at least one ultrasonic element. The ultrasonic transducer is configured to send a pulse of sound waves in response to the drive signal. The pulse is directed towards an interface. The ultrasonic transducer is configured to detect the reflected sound waves. The distance detection system further includes a receiver configured to receive a detection signal from the ultrasonic transducer. The detection signal includes a reverberation component representing the reverberation of the ultrasonic transducer and a reflection component representing the reflected sound waves from the interface. The receiver is configured to receive a drive cancellation signal that is out of phase with respect to the reverberation component of the detection signal, and wherein the receiver is configured to determine a time-of-flight measurement result based on the detection signal in which the reverberation component of the detection signal is reduced by the drive cancellation signal. Brief Description of the Drawings

[0008] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0009] Figure 1 A distance detection system formed according to an embodiment is shown.

[0010] Figure 2 is a schematic diagram of a distance detection system formed according to an embodiment, which distance detection system can be similar or identical to Figure 1 the distance detection system.

[0011] Figure 3 is a flowchart showing a method formed according to an embodiment.

[0012] Figure 4 is a schematic diagram of a distance detection system formed according to an embodiment, which distance detection system has a first ultrasonic element and a second ultrasonic element operating with drive signals that are out of phase.

[0013] Figure 5is a graph showing a detection signal including a driving component and a reverberation component.

[0014] Figure 6 is a graph showing a detection signal after suppressing the driving component and the reverberation component according to an embodiment.

[0015] Figure 7 is a graph showing a detection signal having a suppressed driving component and a reflected component when the liquid level is at nine (9) millimeters (mm).

[0016] Figure 8 is a graph showing a detection signal having a suppressed driving component and a reflected component when the liquid level is at 2.5 mm.

[0017] Figure 9 is a graph showing the peak-to-peak voltage of a non-inverting driving signal, the non-inverting driving signal being reduced from an inverting driving signal, and the reflected component being in the frequency range of 2.4 - 3.6 MHz.

[0018] Figure 10 is a schematic diagram of a distance detection system formed according to an embodiment, the distance detection system having an ultrasonic element and a dummy ultrasonic element operating with an inverting driving signal.

[0019] Figure 11 is a schematic diagram of a distance detection system formed according to an embodiment, the distance detection system having a first ultrasonic element and a second ultrasonic element, the first ultrasonic element and the second ultrasonic element being displaced and operating with an inverting driving signal.

[0020] Figure 12 is a schematic diagram of a distance detection system formed according to an embodiment, the distance detection system having a first ultrasonic element and a second ultrasonic element, the first ultrasonic element and the second ultrasonic element having opposite polarities and operating with an inverting driving signal.

[0021] Figure 13 is a schematic diagram of a distance detection system formed according to an embodiment, the distance detection system having an ultrasonic element and an equivalent resonant circuit, the resonant circuit providing an inverting driving signal.

[0022] Figure 14A is can be used with Figure 13 the distance detection system of.

[0023] Figure 14B is also can be used with Figure 13 the distance detection system of.

[0024] Figure 15It is a schematic cross-sectional view of a piezoelectric ultrasonic element that can be used in one or more embodiments.

[0025] Figure 16 It is a schematic cross-sectional view of a capacitive micromachined ultrasonic transducer (CMUT) element that can be used in one or more embodiments.

[0026] Figure 17 It is a schematic cross-sectional view of a piezoelectric micromachined ultrasonic transducer (PMUT) element that can be used in one or more embodiments. Detailed Description

[0027] The embodiments described herein include a distance detection system, an ultrasonic sensor, and a method of operating the same. The ultrasonic sensor includes a transducer that directs acoustic waves to an interface (e.g., a liquid-air interface or an air-solid interface). The acoustic waves are reflected back to the transducer. The transducer detects the reflected acoustic waves and communicates an electrical signal to an electronic circuit for processing the electrical signal. The electronic circuit uses the electrical signal to determine useful information, such as a time-of-flight (TOF) measurement. The TOF measurement represents the time interval between when a pulse of acoustic waves is sent and when the reflected acoustic waves are detected. The TOF measurement can be used to determine a specified parameter, such as the distance between the ultrasonic transducer and the interface. The embodiments described herein can be used to determine the distance between one object and another object (e.g., a vehicle and an obstacle), or can be used to monitor a liquid level (e.g., the liquid level in a storage tank) and / or identify the type or quality of a liquid.

[0028] Figure 1 A distance detection system 100 formed according to an embodiment is shown. The distance detection system 100 includes a control module 102, an ultrasonic sensor 104, and a communication cable 110 that communicatively couples the ultrasonic sensor 104 and the control module 102. Thus, in the illustrated embodiment, the sensor 104 and the module 102 are wired to each other. However, in other embodiments, the sensor 104 and the module 102 can be communicatively coupled via a wireless standard (e.g., Bluetooth).

[0029] The sensor 104 includes an ultrasonic transducer 106 having at least one ultrasonic element 105. In certain embodiments, the ultrasonic element is a discrete crystal. Embodiments having multiple ultrasonic elements can be configured to form a specified array transducer. For example, the ultrasonic elements can be rectangular and positioned to form a specified array (e.g., a linear or one-dimensional array). The ultrasonic elements can be square and positioned to form a specified array (e.g., a two-dimensional array). The ultrasonic elements can be concentrically arranged rings to form an annular array. Optionally, embodiments can transmit and receive simultaneously. For example, one or more ultrasonic elements of the array can be used as transmitters while one or more ultrasonic elements of the array can be used as receivers.

[0030] As an alternative or addition to the above, single crystals (e.g., diced and filled, micromachined) can be fabricated to include discrete portions. These discrete portions can be used as discrete ultrasonic elements. Thus, single crystals can be fabricated to provide an array transducer. Examples can include one-dimensional arrays, two-dimensional arrays, and annular arrays. Optionally, embodiments can transmit and receive simultaneously. For example, one or more ultrasonic elements of the array can be used as transmitters while one or more ultrasonic elements of the array can be used as receivers.

[0031] The control module 102 is configured to provide a drive signal to the sensor 104. For example, the control module 102 can include circuitry for generating an electrical drive signal that is communicated to the ultrasonic transducer 106. The drive signal causes the ultrasonic element 105 to oscillate and generate a pulse of sound waves. The drive signal can have various forms and a range of frequencies. For example, the drive signal can include a sine wave or a square pulse (e.g., unipolar, multi-level unipolar, bipolar). The drive signal can be inverted to produce a drive cancellation signal as described herein.

[0032] The sound waves are reflected by an interface (e.g., the boundary between a liquid and a gas), and a portion of the sound waves is reflected back to the ultrasonic element 105. The reflected sound waves cause the ultrasonic element 105 to oscillate, thereby generating an electrical signal that is communicated to the control module 102. When a drive signal is applied, the oscillation of the ultrasonic element 105 contributes to the electrical signal and is communicated to the control module 102. After the drive signal stops, the ultrasonic element 105 may continue to oscillate, and these oscillations also contribute to the electrical signal that is communicated to the control module 102.

[0033] Accordingly, the detection signal received by the control module 102 includes a drive component, a reverberation component, and a reflection component. The drive component is mainly caused by the oscillation of the ultrasonic element 105 when the ultrasonic element 105 is activated by the drive signal. The reverberation component is mainly caused by the oscillation of the ultrasonic element 105 after the drive signal stops activating the ultrasonic element 105.

[0034] As shown, the sensor 104 can include a fitting 108 and a sensor housing 116. The fitting 108 is configured to be coupled to a container or other device (not shown) for positioning the transducer 106. The sensor housing 116 is coupled to the transducer 106 and supports the transducer 106. The sensor housing 116 is elongated in the illustrated embodiment and can have any desired length based on the end application. The communication cable 110 can have connectors 118 at opposite ends, and the connectors 118 are configured to be mechanically and electrically coupled to mating connectors 119 of the control module 102.

[0035] The control module 102 includes an electronic circuit 112 for processing the detection signal to offset or suppress reverberation components and remove spurious reflected echoes. For some applications, the detection signal may be affected by the temperature of the medium (or media) through which the acoustic wave propagates. To this end, the control module 102 and / or the ultrasonic sensor 104 may include one or more temperature sensors for determining the temperature of the surrounding environment (such as liquid and / or air). When determining the TOF measurement result, the electronic circuit 112 may take the temperature into account.

[0036] In the illustrated embodiment, the electronic circuit 112 includes an analog front end (AFE) module 114 and a processor 113. The AFE module 114 is configured to drive the ultrasonic transducer 106 and convert the detection signal into digital signals representing the start (START) and end (STOP) of the TOF measurement result. The AFE module 114 or the processor 113 may process the detection signal to suppress reverberation components. The processor 113 may control the AFE module 114, measure the time difference between the start signal and the stop signal, and process the TOF measurement result into a liquid level value. The liquid level value may then be communicated to the user via the display 120 of the control module 102 or via another form of communication (such as a smartphone application).

[0037] In Figure 1 the electronic circuit 112 is shown as separate hardware components (AFE module 113 and processor 114). However, it should be understood that the electronic circuit 112 may be integrated into a single device or may have more than two electronic components. In addition, the functions and / or operations described herein performed by the AFE module 113 or the processor 114 may be shared and / or performed by other components or additional electronic components.

[0038] Although not shown in Figure 1 the electronic circuit 112 may include, among other things: a signal generator for generating a drive signal, an inverter circuit for inverting the drive signal, an adder circuit, and a receiver. In some embodiments, the electronic circuit 112 may include a switching circuit, a matching circuit, and a resonant circuit for changing the operating mode of the ultrasonic transducer 106.

[0039] Embodiments may reduce the time period (referred to as the "dead zone") during which any detectable acoustic wave is not relied upon for distance calculation. This time period effectively translates to a distance from the ultrasonic transducer at which reliable measurements cannot be made. As an example, embodiments may reduce the dead zone from 25 mm to 2.5 mm in a liquid level application. However, the size of the dead zone may affect the performance of various ultrasonic devices. Thus, embodiments may improve various ultrasonic devices and applications.

[0040] Conversely, embodiments can enable an ultrasonic transducer to be driven at a higher amplitude and / or a higher number of cycles, thereby generating a greater energy transfer. For certain applications, a greater energy transfer can improve the penetration depth. For example, embodiments can be applicable to military range sensors.

[0041] In addition to distance detection systems (e.g., liquid level monitoring systems), it is contemplated that embodiments can be utilized in density measurement systems that measure the optical density in a photosensitive material. Embodiments can enable the density measurement system to have a smaller footprint.

[0042] Figure 2 is a schematic diagram of a distance detection system 150 formed according to an embodiment, which distance detection system 150 can be similar or identical to the distance detection system 100 ( Figure 1 )). For example, the distance detection system 150 includes an ultrasonic transducer 154 having an ultrasonic element 156. The distance detection system 150 also includes a signal generator 151 and a signal inversion circuit 152, which can also be referred to as a signal inverter. The signal generator 151 is configured to provide a drive signal for exciting the ultrasonic element 156. The ultrasonic element 156 generates pulses of acoustic waves 160 in response to the drive signal.

[0043] As Figure 2 shown, the drive signal 162 is sent through the signal inversion circuit 152. The signal inversion circuit 152 is configured to provide an inverted drive signal that can be used to effectively reduce or eliminate reverberation components. For example, the signal inversion circuit 152 can be configured to invert the drive signal such that the inverted drive signal is phase-shifted 180° relative to the non-inverted drive signal. In certain embodiments, the signal inversion circuit 152 can include a drive converter that effectively inverts the drive signal. The signal inversion circuit 152 is configured to provide the non-inverted drive signal 162 to the ultrasonic element 156 and provide the inverted drive signal 163 to the suppression module 164. In other embodiments, the signal inversion circuit 152 provides the non-inverted drive signal 162 to the suppression module 164 and provides the inverted drive signal 163 to the ultrasonic element 156. In certain embodiments, the signal inversion circuit 152 can include a center-tapped inductor. Such embodiments may be particularly suitable for lower frequencies (e.g., frequencies less than one megahertz).

[0044] As described above, the ultrasonic element 156 communicates the non-inverted detection signal 172 to the receiver 170. The detection signal 172 includes a drive component, a reverberation component, and a reflection component.

[0045] The suppression module 164 is an element configured to generate a drive cancellation signal 174 and communicate the drive cancellation signal to the receiver 170. As described herein, the term "suppression module" may include a resonant circuit, another active ultrasonic element, or a dummy ultrasonic element. For example, the suppression module 164 may be an ultrasonic element 181 driven by an inverted drive signal 163. The suppression module 164 may be an ultrasonic element 182 that is driven by an inverted drive signal 163 and has a polarity opposite to that of the ultrasonic element 156. The suppression module 164 may be an ultrasonic element 182 that is driven by a non-inverted drive signal 162 but has a polarity opposite to that of the ultrasonic element 156. The suppression module 164 may be an ultrasonic element 183 that is driven by a non-inverted drive signal 163 and has the same polarity as the ultrasonic element 156, but the ultrasonic element 183 is offset such that the ultrasonic element 156 and the ultrasonic element 183 are not planar. Accordingly, the pulses of the ultrasonic element 183 are out of phase with respect to the pulses 160 from the ultrasonic element 156. The suppression module 164 may be a dummy ultrasonic element 184 that is driven by a non-inverted drive signal 163 but has an absorber 186 that effectively blocks any pulses from the ultrasonic element 184. In some embodiments, the suppression module 164 may be a resonant circuit 184 configured to provide a drive cancellation signal. The resonant circuit 184 may respond to a drive signal or an inverted drive signal.

[0046] Optionally, one or more suppression modules may respond to the converted drive signal 163 and provide a drive cancellation signal 174 to the receiver 170.

[0047] The drive cancellation signal is used to offset or suppress the drive component and / or the reverberation component of the detection signal. When the drive component and / or the reverberation component are suppressed, the reflection component may be more easily identified. In a particular embodiment, the reflection component may be identified during ringdown or when the ultrasonic element responds to a drive signal.

[0048] In Figure 2 , the drive cancellation signal is referred to as an inverted detection signal. In other embodiments, the drive cancellation signal is a synthetic signal generated by a resonant circuit. Accordingly, the term "drive cancellation signal" includes an inverted detection signal and a synthetic signal generated by a resonant circuit.

[0049] The receiver 170 is configured to receive a detection signal 172 from the ultrasonic transducer 154 or more specifically from the ultrasonic element 156. The detection signal includes a reverberation component representing the reverberation of the ultrasonic element 156 and a reflection component representing the reflected sound wave from the interface. The receiver 170 is configured to receive a drive cancellation signal 174, which is in antiphase with respect to the reverberation component of the detection signal. The receiver 170 is configured to determine a TOF measurement result based on the detection signal 172, in which the reverberation component is offset by the drive cancellation signal 174.

[0050] Figure 3 is a flowchart showing a method 200 formed according to an embodiment. The method 200 will be described with reference to the distance detection system 150( Figure 2 ). The method 200 may also be performed by one or more other embodiments, such as the distance detection system 400( Figure 10 ), the system 500( Figure 11 ), the system 600( Figure 12 ) and the system 700( Figure 13 ). The method 200 includes generating a drive signal 162 at 202, the drive signal 16 being configured to activate or excite the ultrasonic wave element 156 such that a pulse 160 of sound waves is emitted from the ultrasonic element 156 and directed towards the interface( Figure 2 not shown in). The drive signal 162 may be in the form of an electrical signal. The pulse of sound waves may include a series of sound waves (or sound wave cycles).

[0051] The pulse 160 of sound waves has a specified frequency. For example, the specified frequency may be between 500 Hz and 20 MHz. In a particular embodiment, the specified frequency is between 100 kHz and 10 MHz. The pulse 160 also has a number of cycles. For example, the pulse 160 may include three (3) cycles or more (e.g., 10 or more cycles). At 204, the drive signal 162 is inverted such that the inverted drive signal 163 is out of phase with the drive signal 162 by approximately 180°. The drive signal 162 is communicated to the ultrasonic element 156 at 205, and the inverted drive signal 163 is communicated to the suppression module 164 at 207.

[0052] At 206, the pulse 160 is transmitted from the ultrasonic element 156. The detection signal 172 is generated at the ultrasonic element 156 and communicated to the receiver 170. At 210, the detection signal is received by the receiver 170. The detection signal may include a drive component, a reverberation component, and a reflection component. For embodiments where the interface is outside the dead zone, the reflection component will be separated from the reverberation component and the drive component. However, if the interface is close enough to the ultrasonic element 156, the reflection coefficient may overlap with the reverberation component and possibly with the drive component.

[0053] In some embodiments, when the drive signal 162 is provided to the ultrasonic element 156, an inverted drive signal 163 is also provided to the suppression module 164. The inverted drive signal 163 activates the suppression module 164 at 212. At 214, the drive cancellation signal 174 is generated by the suppression module 164. The drive cancellation signal 174 is a function of the inverted drive signal 163. The drive cancellation signal 174 is received by the receiver 170 at 216.

[0054] The drive cancellation signal 174 is substantially out of phase with respect to the detection signal 172. In practice, due to possible non-ideal conditions and characteristics of the interface, the ultrasonic element(s), and the liquid with respect to gravity, the drive cancellation signal 174 cannot be completely out of phase. Thus, the drive cancellation signal 174 will be substantially out of phase with respect to the detection signal 172. At 218, the drive cancellation signal 174 can be used to reduce the drive component and the reverberation component.

[0055] At 220, the TOF measurement result can be determined. The TOF measurement result is the difference between a specified start point and a specified stop point. The start point is associated with the pulse emission from the ultrasonic transducer, and the stop point is associated with the echo detection by the ultrasonic transducer. The TOF measurement result can be used to determine a specified parameter. For example, the TOF measurement result can indicate fluid identity, concentration, or distance (e.g., liquid level). Using the TOF measurement result and the known speed of sound through the specified medium, the distance can be determined at 222. In some embodiments, the parameter is calculated using a programming algorithm. In other embodiments, a look-up table (LUT) can be used, for example, to identify the parameter, where the TOF measurement result is associated with the parameter value.

[0056] As indicated by the return arrow 224, the method 200 can be continuously repeated at a specified interval, etc. For example, the liquid level can be calculated multiple times every ten seconds.

[0057] Figure 4 and Figure 10-1 Different distance detection systems are illustrated in FIG. 4. In each case, embodiments can utilize the drive cancellation signal to reduce the size of the dead zone. Figure 4 is a schematic diagram of a distance detection system 300 formed according to an embodiment. The distance detection system 300 includes an ultrasonic transducer 301 having a first ultrasonic element 302 and a second ultrasonic element 304 that operate with different drive signals. The first ultrasonic element 302 and the second ultrasonic element 304 of the ultrasonic transducer The distance detection system 300 includes components similar or identical to those of the distance detection system 100 ( Figure 1 )). For example, the distance detection system 300 includes a signal generator 312 and a signal inverter 314. The distance detection system 300 also includes a switching circuit 316, a matching circuit 318, and a receiver 320.

[0058] As shown, a drive signal 324 is communicated to a signal inverter 314. After inverting the drive signal 324 to provide an inverted drive signal 326, the drive signal 324 and the inverted drive signal 326 are communicated to corresponding ultrasonic elements 302, 304.

[0059] Each of the ultrasonic elements 302, 304 has a surface covered by a material layer of the container 315. The ultrasonic probes 302, 304 emit pulses towards the interface 330. The acoustic waves of the pulses are reflected back to the ultrasonic elements 302, 304, which detect the reflected components. Obviously, the reflected components detected by the corresponding ultrasonic elements 302, 304 are substantially out of phase. The detection signal and the drive cancellation signal are then communicated to a matching circuit and then to a receiver 320.

[0060] It is generally believed that when two ultrasonic elements are driven in antiphase, the signals detected by the corresponding ultrasonic elements will cancel each other out. However, when the wavelength λ of the pulse is small and the separation between the two transducers is much greater than the wavelength λ, cancellation occurs only when the angular setting of the container is very precise. The distance between the two ultrasonic elements is small, and the critical angle is 0.55 degrees for 3 MHz. This condition is difficult to meet, and the received signals will not be cancelled. Slightly unstable liquid levels and non-ideal container settings can make it seem that there is no cancellation.

[0061] Figure 5 is a graph showing a detection signal (mV / μs) including a drive component 322 and a reverberation component 324. As shown, the drive component 322 starts at one microsecond and continues until five microseconds. After the drive signal stops, the ultrasonic element continues to oscillate, thereby generating a detectable signal that gradually decreases and forms the reverberation component 324. Figure 6 is a graph showing the detection signal according to an embodiment after suppressing the drive component 322 and the reverberation component 324. As shown, the drive component and the reverberation component have been significantly reduced.

[0062] Figure 7 and Figure 8 show the detection signals that may be obtained when the liquid is relatively high (9 mm, as Figure 7 shown) and when the liquid is relatively low (2.5 mm). Figure 7 and Figure 8 The number of cycles of the pulse in Figure 8 is 21 cycles, and the operating frequency is 3 MHz. As

[0063] Figure 9It is a graph showing the non-inverted drive signal, the non-inverted drive signal combined with the inverted drive signal, and the peak-to-peak voltage (mVpp) of the reflection component across the frequency range (2.4 - 3.6 MHz). For frequencies between 2.9 MHz and 3.4 MHz, the mVpp of the reflection component is greater than the non-inverted drive signal reduced by the inverted drive signal.

[0064] Figure 10 It is a schematic diagram of a distance detection system 400 formed according to an embodiment. The distance detection system 400 includes elements similar to or the same as those of the distance detection system 100 ( Figure 1 ). For example, the distance detection system 400 includes a signal generator 412 and a signal inverter 414. The distance detection system 400 also includes a switching circuit 426, a matching circuit 418, and a receiver 420.

[0065] The distance detection system 400 also includes a ultrasonic transducer 401 having a ultrasonic element 402 and a dummy ultrasonic element 404. To distinguish between the two, the ultrasonic element 402 ( Figure 4 ) may be referred to as the "active ultrasonic element", or the dummy ultrasonic element 404 may be referred to as the "dummy element". Different from the ultrasonic element 304, the dummy ultrasonic element 404 does not detect and communicate the reflection component. Instead, the dummy ultrasonic element 404 generates an electrical signal in response to the oscillation caused by the drive signal and subsequent reverberation.

[0066] In the illustrated embodiment, the ultrasonic element 402 and the dummy ultrasonic element 404 are driven by out-of-phase drive signals. The ultrasonic element 402 is configured to transmit pulses of sound waves and detect the reflection component from the pulses of sound waves. However, the dummy ultrasonic element 404 is arranged such that the pulses cannot be transmitted into the medium, and thus the reflection component cannot be detected by the dummy ultrasonic element 404. For example, the ultrasonic transducer 401 may include an absorber 415 that absorbs any sound waves generated by the dummy ultrasonic element 404. However, the dummy ultrasonic element 404 is driven by an inverted drive signal, causing the dummy ultrasonic element 404 to oscillate. The dummy ultrasonic element 404 generates an electrical signal in response to the oscillation of the dummy ultrasonic element 404.

[0067] Accordingly, only the ultrasonic element 402 emits a pulse towards the interface. The acoustic wave of the pulse reflects back to the ultrasonic element 402, and the ultrasonic element 402 detects the reflected component. The reflected component is not out of phase with any reflected component of the dummy ultrasonic element because the reflected component of the dummy ultrasonic element does not exist. However, the dummy ultrasonic element 404 provides an out-of-phase detection signal to the receiver 420, and the out-of-phase detection signal includes an out-of-phase drive component and an out-of-phase reverberation component. Accordingly, the dummy ultrasonic element 404 provides an out-of-phase detection signal for reducing the drive component and the reverberation component without reducing the reflected component of the detection signal from the ultrasonic element 402.

[0068] Figure 11 is a schematic diagram of a distance detection system 500 formed according to an embodiment. The distance detection system 500 has a first ultrasonic element 502 and a second ultrasonic element 504 that are displaced relative to each other such that one of the ultrasonic elements is disposed at a half wavelength in front of the other ultrasonic element. The first ultrasonic element 502 and the second ultrasonic element 504 are configured to be driven by a non-out-of-phase drive signal and an out-of-phase drive signal. The distance detection system 500 may have elements similar to or the same as the elements of the distance detection system 500.

[0069] As Figure 11 shown, the first ultrasonic element 502 and the second ultrasonic element 504 are offset relative to each other. Accordingly, any reflected components detected at the first ultrasonic element 502 and the second ultrasonic element 504 are not canceled out. More specifically, the ultrasonic element 504 is disposed at a half wavelength in front of the ultrasonic element 502 such that the reflected component is not canceled out at the front axis. However, the drive component and the reverberation component of the out-of-phase drive signal are out of phase with the drive component and the reverberation component of the non-out-of-phase drive signal. Accordingly, the drive component and the reverberation component of the out-of-phase drive signal are used to reduce the drive component and the reverberation component of the non-out-of-phase drive signal. However, the reflected components are not out of phase.

[0070] Figure 12FIG. 0 is a schematic diagram of a distance detection system 600 formed according to an embodiment, having a first ultrasonic element 602 and a second ultrasonic element 604, the first ultrasonic element 602 and the second ultrasonic element 604 having opposite polarities (as indicated by "+ / -" and "- / +"). The first ultrasonic element 602 and the second ultrasonic element 604 are driven by a non-inverted drive signal and an inverted drive signal, respectively. The distance detection system 600 includes an ultrasonic transducer 601 having the first ultrasonic element 602 and the second ultrasonic element 604. Because the first ultrasonic element 602 and the second ultrasonic element 604 have opposite polarities, the out-of-phase drive signals cause the first ultrasonic element 602 and the second ultrasonic element 604 to move in phase. However, the detection signals provided by the first ultrasonic element 602 and the second ultrasonic element 604 with respect to the drive and reverberation components are out of phase and can be used to reduce the drive and reverberation components.

[0071] Figure 13 FIG. 4 is a schematic diagram of a distance detection system 700 formed according to an embodiment. The distance detection system 700 includes an ultrasonic transducer 701 having an ultrasonic element 702 and an equivalent resonant circuit 704. The distance detection system 700 may further include elements similar to or the same as those of the distance detection system 100 ( Figure 1 ). For example, the distance detection system 700 includes a signal generator 712 and a signal inverter 714. The distance detection system 700 further includes a switching circuit 716, a matching circuit 718, and a receiver 720.

[0072] As shown, a drive signal 724 is communicated to the signal inverter 714. After generating an inverted drive signal 726, the drive signal 724 and the inverted drive signal 726 are respectively communicated to the ultrasonic element 702 and the equivalent resonant circuit 704. Similar to the above embodiment, the ultrasonic element 702 is configured to provide a detection signal including a drive component, a reverberation component, and a reflection component. The equivalent resonant circuit 704 is configured to receive the inverted drive signal 726 and generate an inverted detection signal, which is used to reduce the drive and reverberation components.

[0073] Figure 14A and 14B FIGS. 15 and 16 are circuit diagrams of equivalent resonant circuits 742 and 744 that can be used with the distance detection system 700 ( Figure 13 ), respectively. The resonant circuit 742 is a pure piezoelectric resonator equivalent circuit, where air is at the front and back of the ultrasonic element. At a low frequency f << f0, the measured capacitance C ≈ Cs + Cp, and at a high frequency f >> f0, the measured capacitance C ≈ Cs. At the resonance f0, the measured resistance R ≈ Rs. When the materials at the front and back are plastic / water and absorbent, other resistances can be added.

[0074] Figure 15-17 illustrates an element which, alone, can form an ultrasonic element as described herein, or can form a part of an ultrasonic element as described herein. More specifically, Figure 15 is a schematic cross-sectional view of a piezoelectric ultrasonic element 760 that can be used by one or more embodiments. The element 760 includes a piezoelectric material 762 sandwiched between highly conductive electrode layers 764, 766, which can include, for example, gold or platinum. The electrode layer 766 is supported by a backing layer 768. The electrode layers 764, 766 are electrically coupled to conductors 770, 772, respectively.

[0075] Figure 16 is a schematic cross-sectional view of a capacitive micromachined ultrasonic transducer (CMUT) element 774 that can be used by one or more embodiments. As shown, the CMUT element 774 includes a metallized suspended diaphragm 776 (e.g., silicon nitride (Si x N y )) disposed over a cavity 778. The CMUT element 774 also includes a rigid substrate 780. When a DC voltage is applied between two electrodes 782, 784, the diaphragm 776 is deflected, attracted towards the substrate by an electrostatic force. A mechanical restoring force caused by the stiffness of the diaphragm 776 resists the attractive force. As a result, ultrasonic waves can be generated from the vibration of the diaphragm 776 in the case of an AC voltage input.

[0076] Figure 17 is a schematic cross-sectional view of a piezoelectric micromachined ultrasonic transducer (PMUT) element 784 that can be used by one or more embodiments. The PMUT element 784 includes a membrane 786 sandwiched between electrode layers 788, 790. The deflection of the diaphragm 786 in the PMUT element 784 is caused by a lateral strain generated from the piezoelectric effect of the diaphragm 786. The diaphragm 786 includes at least one piezoelectric layer 792 and a passive elastic layer 794. In operation, the resonant frequency of the PMUT does not directly depend on the thickness of the piezoelectric layer 792. Instead, the flexural mode resonance frequency is closely related to the shape, size, boundary conditions, intrinsic stress, and mechanical stiffness of the diaphragm.

Claims

1. A distance detection system (150), comprising: A signal generator (151) configured to provide a drive signal (162); An ultrasonic transducer having at least one ultrasonic element (105), the ultrasonic transducer configured to send a pulse (160) of acoustic waves in response to the drive signal (162), the pulse being directed towards an interface (330), the ultrasonic transducer configured to detect reflected acoustic waves; and A receiver (170) configured to receive a detection signal (172) from the ultrasonic transducer, the detection signal including a reverberation component representing reverberation of the ultrasonic transducer and a reflection component representing reflected acoustic waves from the interface; Wherein the receiver is configured to receive a drive cancellation signal (174), the drive cancellation signal being out of phase with respect to the reverberation component of the detection signal, and wherein the receiver is configured to determine a time-of-flight measurement result based on the detection signal, in which the reverberation component of the detection signal is reduced by the drive cancellation signal, Wherein the ultrasonic transducer includes a first ultrasonic element, the pulse is a first pulse, and the detection signal is a first detection signal, and the distance detection system further includes: A second ultrasonic element for directing a second pulse of acoustic waves towards the interface in response to the drive signal, wherein the first ultrasonic element and the second ultrasonic element have opposite polarities; Wherein the receiver is configured to receive a second detection signal from the ultrasonic transducer, the second detection signal including the drive cancellation signal.

2. The distance detection system (150) according to claim 1, wherein the receiver (170) is configured to receive the detection signal when the pulse is sent towards the interface and determine the time-of-flight measurement result of the reflected component received when the pulse is sent.

3. The distance detection system (150) according to claim 1, further comprising a switching circuit (314) configured to switch between a transmission mode and a reception mode, the detection signal being received during the reception mode, and the reception mode occurring without a dead zone.

4. The distance detection system (150) according to claim 1, wherein the resonant frequency of the at least one ultrasonic element is between 100 kHz and 10 MHz, and the number of periods in the pulse includes at least 3 periods.

5. A distance detection system (150), comprising: A signal generator (151) configured to provide a drive signal (162); An ultrasonic transducer having at least one ultrasonic element (105), the ultrasonic transducer configured to send a pulse (160) of acoustic waves in response to the drive signal (162), the pulse being directed towards an interface (330), the ultrasonic transducer configured to detect reflected acoustic waves; and A receiver (170) configured to receive a detection signal (172) from the ultrasonic transducer, the detection signal including a reverberation component representing reverberation of the ultrasonic transducer and a reflection component representing reflected acoustic waves from the interface; Wherein the receiver is configured to receive a drive cancellation signal (174), the drive cancellation signal being out of phase with respect to the reverberation component of the detection signal, and wherein the receiver is configured to determine a time-of-flight measurement result based on the detection signal, in which the reverberation component of the detection signal is reduced by the drive cancellation signal, and Wherein the ultrasonic transducer includes a first ultrasonic element, the pulse is a first pulse, and the detection signal is a first detection signal, and the distance detection system further includes: A second ultrasonic element for directing a second pulse of acoustic waves towards the interface, wherein the signal generator (151) is configured to provide an out-of-phase drive signal to the second ultrasonic element, wherein the first ultrasonic element and the second ultrasonic element have opposite polarities; Receiving a second detection signal from the ultrasonic transducer, the second detection signal including the drive cancellation signal.

6. A distance detection method, comprising: A drive signal (162) is provided to an ultrasonic transducer (106) for transmitting a pulse (160) of acoustic waves to an interface (330); A detection signal (172) is received from the ultrasonic transducer, the detection signal including a reverberation component representing reverberation of the ultrasonic transducer and a reflection component representing reflected acoustic waves from the interface; A drive cancellation signal (174) is received, the drive cancellation signal being in antiphase with respect to the reverberation component of the detection signal; and A time-of-flight measurement result is determined based on the detection signal, in which the reverberation component is reduced by the drive cancellation signal, wherein the ultrasonic transducer includes a first ultrasonic element, the pulse is a first pulse, and the detection signal is a first detection signal, the method further comprising: Providing an antiphase drive signal to a second ultrasonic element for directing a second pulse of acoustic waves to the interface; Receiving a second detection signal from the ultrasonic transducer, the second detection signal including the drive cancellation signal.

7. The distance detection method according to claim 6, wherein receiving the detection signal includes receiving the reflected component when the pulse is sent towards the interface and determining a time-of-flight measurement result of the reflected component received when the pulse is sent.

8. The distance detection method according to claim 6, further comprising switching between a transmission mode and a reception mode, the detection signal being received during the reception mode, the reception mode occurring without a dead zone.

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