Hidden ultrasonic sensing system suitable for advanced driver support

Abstract

To prevent an adverse effect from a surface covering a sensor even if the sensor is hidden behind a surface damaged little by a visible display or a haptic display.SOLUTION: As an example, an exemplary sensing method includes: transmitting an acoustic burst through a surface on an ultrasonic transducer; receiving an acoustic signal by using a micro electro-mechanical system (MEMS) microphone, in which the MEMS microphone represents the acoustic signal as an electric reception signal; and processing the electric reception signal in order to detect reflection of the acoustic burst.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] The present disclosure relates generally to ultrasonic proximity sensors for advanced driver assistance systems (ADAS), and more particularly to systems having such sensors concealed by an overlying surface. [Background technology]

[0002] Modern automobiles are equipped with an astonishing number and variety of sensors that enable an incredible variety of desirable features, including "kick-to-open," parking assist, automatic parking, door protection, occupant detection, intrusion monitoring, and blind spot monitoring, to name a few. Each of these exemplary features may be enabled, for example, with a suitably positioned ultrasonic sensor. Design aesthetics often require that such sensors be made as unobtrusive as possible, for example, by concealing the sensor behind an uncompromised surface with an opening, mesh, acoustic window, door, insert, or any other visible or tactile indication of a concealed sensor or concealed cavity. (An acoustic window is an area of ​​a surface that is substantially thinned or otherwise configured differently, for example, to have different dimensions or material properties, to better transmit an acoustic burst.) Examples of uncompromised surfaces may include the exterior skins (e.g., hood, trunk lid, doors, body panels, bumper shrouds) and interior surfaces (e.g., dashboard, headboard, inner door panels) of the automobile.

[0003] Although covert ultrasonic sensors have been shown to function adequately, their function may be adversely affected by overlying surfaces. One problem is the attenuation of the acoustic burst, which may reduce the maximum sensing range. Another problem is the long-term reverberation of the piezoelectric element caused by the mechanical coupling between the piezoelectric element and the overlying surface, which may prevent detection of nearby objects. One proposed solution to these problems uses impedance matching layers to reduce attenuation and uses additional layers or structures of damping material. However, the cost of the proposed solutions is expected to make them economically unfeasible for automotive applications. Summary of the Invention

[0004] Accordingly, disclosed herein are exemplary sensor controllers, sensors, sensing systems, and sensing methods that at least partially address the problems identified above. As an example, an exemplary sensing method includes transmitting an acoustic burst through a surface on an ultrasonic transducer, receiving the acoustic signal with a MEMS (microelectromechanical system) microphone, which represents the acoustic signal as an electrical receive signal, and processing the electrical receive signal to detect a reflection of the acoustic burst.

[0005] An exemplary sensor controller includes a transmitter configured to drive an ultrasonic transducer to transmit an acoustic burst, a receiver configured to receive an electrical receive signal representative of the acoustic signal from the MEMS microphone, and core logic configured to process the electrical receive signal to detect reflections of the acoustic burst.

[0006] An exemplary ADAS (Advanced Driver Assistance System) includes an ultrasonic transducer configured to transmit an acoustic burst through a surface on the ultrasonic transducer, a MEMS (Micro-Electro-Mechanical Systems) microphone configured to convert a received acoustic signal into an electrical receive signal, and a controller configured to detect a reflection of the acoustic burst based on the electrical receive signal.

[0007] Each of the foregoing examples may be used individually or in combination and may include one or more of the following features in suitable combinations: 1. The surface is free of openings or acoustic windows for transmitting the acoustic burst. 2. The surface includes an opening for passing the acoustic signal to the MEMS microphone. 3. The surface is a bumper cover or body panel of a vehicle. 4. The MEMS microphone is positioned to receive the acoustic signal as it passes around a side or edge of the surface. 5. The ultrasonic transducer and the MEMS microphone are part of a concealed assembly that further includes a controller configured to perform said processing. 6. The ultrasonic transducer is one of an array of ultrasonic transducers that cooperate to transmit the acoustic burst through the surface. 7. The acoustic burst is steerable by the array of ultrasonic transducers. 8. The ultrasonic transducer, the MEMS microphone, and the controller are each part of a concealed assembly that contacts the back side of the surface. 9. The ultrasonic transducer is further configured to convert the acoustic signal into a second electrical receive signal. 10. The controller operates on the second electrical receive signal and the electrical receive signal from the MEMS microphone to detect a reflection. 11. The core logic is configured to provide a controllable phase shift between the second electrical receive signal and the electrical receive signal from the MEMS microphone for controllable directional sensitivity. 12. The core logic is configured to determine at least one of a range, an azimuth angle, and an elevation angle to a reflector of the acoustic burst. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1 is a perspective view of an exemplary vehicle equipped with a hidden ultrasonic sensor. [Figure 1B] 1 is an overhead view of an exemplary vehicle equipped with a hidden ultrasonic sensor; [Diagram 2] FIG. 1 illustrates an isometric view of an exemplary ultrasonic sensor assembly. [Diagram 3] FIG. 2 is a block diagram of an example sensor controller. [Figure 4] FIG. 1 is a block diagram of an exemplary ADAS (Advanced Driver Assistance System). [Diagram 5] FIG. 1 is a flow diagram of an exemplary sensing method using a covert ultrasonic sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] It is to be understood that the drawings and the following description are not intended to limit the disclosure, but rather to provide a basis for those skilled in the art to appreciate all modifications, equivalents, and alternatives encompassed within the language of the claims.

[0010] As an exemplary use case, FIG. 1A shows a vehicle 102 equipped with a set of ultrasonic transducers 104 concealed by an overlying surface 105, in this case the cover of a vehicle bumper. The transducers are mounted (or otherwise abut) on a fender, quarter panel, hood, trunk lid, door, body panel, or other location under the vehicle's skin, although other placements are contemplated. An internal placement is also contemplated, for example, to monitor the vehicle cab from behind any of the panels and shrouds that form the interior lining of the cab. In addition to the ultrasonic transducers 104, the vehicle 102 includes one or more sensors 106, each having a MEMS (microelectromechanical system) microphone that can receive reflections of acoustic bursts emitted by the ultrasonic transducers 104. If part of a concealed sensor assembly, the MEMS microphone(s) may be positioned behind a small, e.g., 1-2 mm hole 107 or acoustic window that allows passage of an acoustic signal to the microphone. Such holes are much smaller and less obtrusive than the 2-4 cm openings or acoustic windows often used in conventional ultrasonic transducers.Alternatively, the MEMS microphone may be positioned under or behind the edge of a surface, for example, on the underside of a bumper, to receive acoustic signals passing under or around the edge.

[0011] In certain contemplated embodiments, the ultrasonic transducers 104 are part of a concealed sensor assembly that each includes a MEMS microphone, and similarly, the sensors 106 may each include an ultrasonic transducer concealed behind an overlying surface. In addition to detecting reflections of acoustic bursts emitted by the ultrasonic transducers 104, the sensors 106 may detect reflections of acoustic bursts from their integrated ultrasonic transducers and may also detect audible range acoustic signals, such as the sound of a siren from an emergency vehicle. If the ultrasonic transducers 104 are incorporated into a concealed sensor assembly with a MEMS microphone, the incorporated microphone may be configured to detect reflections of acoustic bursts from the ultrasonic transducers 104 and may be configured to detect audible range acoustic signals.

[0012] FIG. 1B is an overhead view of another exemplary vehicle 112 having an ADAS (Advanced Driver Assistance System) sensor configuration with a hidden ultrasonic transducer 104 and a MEMS microphone sensor 106 behind an overlying surface 105. Again, the MEMS microphone sensor 106 may include an ultrasonic transducer. The spaced arrangement of multiple sensors and ultrasonic transducers 104 may allow a transmitted acoustic burst to be controllably steered and directional information may be derived for detected reflections of the acoustic burst, improving the determination of distance information. The illustrated sensor configuration includes a MEMS microphone sensor 106 with an ultrasonic transducer integrated at each corner of the vehicle 112 and a pair of sensors 106 spaced apart on each side of the vehicle. An array of ultrasonic transducers 104 is provided at the front of the vehicle 112 and a second array of ultrasonic transducers 104 is provided at the rear of the vehicle. Other configurations are contemplated and may provide various tradeoffs between cost, coverage, detection range, power consumption, and measurement speed.

[0013] The emitted burst propagates outward from the vehicle until it encounters and reflects off an object or some other form of acoustic impedance mismatch. The reflected burst returns to the vehicle as an "echo" of the emitted burst. The time between the emission of the burst and the receipt of the echo indicates the distance to the reflecting point. In many systems, only one sensor transmits at a time, although all of the sensors may be configured to measure the resulting echo. However, independent simultaneous transmissions may be supported through the use of orthogonal waveforms, transmission into non-overlapping detection zones, or transmission with signatures that allow screening of any echoes from different transmitters.

[0014] Each of the transducers 104 and sensors 106 are concealed behind the overlying surface 105, except for a small, unobtrusive hole 107 on each MEMS microphone. When positioned behind such a hole, on the side of the surface, or behind the edge of the surface, the MEMS microphones exhibit high sensitivity to audible and ultrasonic acoustic signals. The array of ultrasonic transducers may operate in concert to increase the effective acoustic burst amplitude and enhance the directivity of the emitted acoustic burst. It is noted that the concerted operation may be achieved by synchronous operation of the transducers, and the enhanced directivity may be achieved by a controllable phase shift between the emitted signals. Although it may be preferable for the transducers in each array to operate simultaneously, such simultaneous operation is not a requirement for proper processing.

[0015] FIG. 2 is an isometric view of an exemplary sensor assembly 106 having an ultrasonic transducer 202 that abuts, contacts, adheres, or otherwise mechanically couples to the underside of an overlying surface 105 (FIGS. 1A, 1B) to transmit an acoustic burst through the surface. The sensor assembly 106 includes a substrate 204, such as a PCB (printed circuit board) having control electronics for the sensor assembly. Mounted on the substrate 204 are a sensor controller 206 and a MEMS microphone 208. A hole 210 is provided in the assembly case to facilitate detection of acoustic signals by the MEMS microphone 210. The hole 210 may be aligned with an unobtrusive hole or acoustic window 107 in the overlying surface, or the assembly 106 may be configured to position the MEMS microphone 208 on the side of the overlying surface or behind an edge of the overlying surface where it may be unobtrusively sensitive to acoustic signals. In some contemplated sensor assemblies, the MEMS microphone 208 may be vertically displaced from the ultrasonic transducer 202 and work in concert with the transducer to enable direction of arrival (DoA) detection, from which the elevation angle of a reflector may be estimated. Alternatively, two vertically spaced MEMS microphones may be used for this purpose. Similarly, the MEMS microphone may be horizontally displaced from the ultrasonic transducer to enable estimation of the azimuth angle of a reflector. Two horizontally spaced MEMS microphones may alternatively be used for this purpose. Some contemplated sensor assemblies have multiple MEMS microphones that provide horizontal and vertical displacement relative to the transducer or relative to each other, enabling estimation of both elevation and azimuth angles.

[0016] FIG. 3 illustrates a block diagram of an exemplary sensor controller 206. It uses IO (input and output) pins that are multiplexed to a selected one of various IO protocol modules. 2Modules for the C, SPI (Serial Peripheral Interface) and DSI3 (Distributed System Interface 3rd Generation) communication bus protocols are shown as non-limiting examples only. Other contemplated protocols include those described in the LIN, CAN and SENT standards. The IO bus 302 couples the various IO protocol modules to the embedded microprocessor (μP). For example, an advanced microcontroller bus architecture (AMBA) bus, such as simplified advanced high-performance bus (AMB-Lite), may be used to couple the embedded microprocessor to various other functional blocks of the sensor controller 206. Such blocks may include, for example, a non-volatile firmware (FW) memory, a volatile working memory (MEM), a digital signal processor (DSP), a power-on reset (POR) module, a microphone signal receiver (RX M ) for ADC (Analog-to-Digital Converter), Transducer Signal Receiver (RX T ) for the second ADC, driving current for the transmitter (TX I ), and the driving voltage transmitter (TX V ) may be included. (The transmitters generate the drive signals for the ultrasonic transducers as controlled currents or controlled voltages, respectively.) A multiplexer may couple a selected one of the transmitters to an output pin to drive the transducer 202. FIG. 3 further shows an embedded oscillator (OSC) that generates one or more clock signals for various other blocks, optionally including a carrier frequency for the transmitter and receiver. The POR module may control distribution of the clock signals to enable sleep modes for unnecessary components and other power saving features.

[0017] The IO pins couple the sensor controllers 206 directly or indirectly (e.g., via a DSI3 bus master) to an ECU (electronic control unit). The ECU may communicate instructions to each of the sensor controllers to, for example, set values ​​for various configuration parameters of the sensors, initiate transmission of acoustic bursts, and collect signal data or other measurements. A microprocessor within each sensor controller operates according to firmware and stored configuration parameters to parse the instructions from the ECU and perform the appropriate actions, including transmitting acoustic bursts and receiving acoustic signals.

[0018] In various implementations, chirp modulated signals are used, for example, linear frequency modulated ("LFM") chirps. A chirp is a pulse that changes frequency during transmission. An up chirp is a signal pulse that increases in frequency during transmission, and a down chirp is a signal pulse that decreases in frequency during transmission. For clarity, the examples used herein consider a linear increase or decrease, but in various implementations, the increase or decrease is not linear. The echo of the chirp may be compressed in the correlator without introducing much or any correlation noise. Thus, echo peak detection is facilitated without reducing time resolution. Furthermore, LFM chirps tolerate Doppler frequency shifts without or with minimal increase in correlation noise. LFM chirps may be used as transmit pulses to measure distance and direction to obstacles or objects located within the sensing range of the sensor system.

[0019] Other implementations use AM (amplitude modulated) signals, e.g., pulses shaped with a fixed frequency carrier. AM signaling modes may allow for the use of shorter bursts (e.g., on the order of 200-300 microseconds), shortening transmission times and increasing sensitivity to nearby obstacles. Other implementations may employ pulses with modulated carriers, e.g., pulses modulated with Biphasic Phase Shift Keying (BPSK). For clarity, the term "burst" as used herein refers to an AM (fixed frequency), BPSK (modulated), or chirp (swept frequency) pulse, which may be one of a series of bursts generated by driving a piezoelectric or other ultrasonic transducer. A chirp modulated pulse may have a longer duration than a typical AM pulse, e.g., greater than 1 millisecond, such as in the range of 2-3 milliseconds. Note that burst length is used here to facilitate detection of nearby obstacles, while longer bursts are used to increase burst energy (and echo energy) for more distant obstacles. The burst length for detecting nearby obstacles may be half or perhaps a quarter of the burst length used for more distant obstacles. The sensor may be switched between modes for different detection distances.

[0020] It is believed to be particularly useful to systematically vary the characteristic frequency (e.g., start frequency, or equivalently, center or end frequency) of a series of chirp modulated pulses, although such frequency variations may also be applied to the carrier frequency of a series of AM pulses. The frequency variation may be expressed for each pulse as a frequency displacement from a nominal characteristic frequency (e.g., a nominal start frequency or a nominal carrier frequency).

[0021] To transmit an acoustic burst, the microprocessor commands the selected transmitter to drive the output pin of the ultrasonic transducer coupled to the piezoelectric element PZ. A transformer and / or a resonant tuning network may be provided for voltage amplification and control of the resonant frequency of the transducer. The transmitter may accept a carrier frequency signal, for example, from an oscillator having a nominal frequency of 50 kHz. The transmitter may use the carrier frequency signal to generate a series of AM (amplitude modulation) or chirp pulses, each pulse corresponding to an acoustic burst. An example of a chirp pulse may be a pulse (up-chirp) with a frequency swept upward from 7 kHz below the carrier frequency to 7 kHz above the carrier frequency. Alternatively, a down-chirp may be used, where the frequency is swept linearly downward instead of upward. In some contemplated implementations, the transmitter provides a custom pattern of frequency offsets to the acoustic burst to serve as a unique signature for that ultrasonic transducer.

[0022] To receive the acoustic signal, the microprocessor commands one or both ADCs to digitize the electrical received signal from the MEMS microphone 206 and / or the piezoelectric element 202. The digitized signal may be provided directly to the DSP for real-time processing or may be buffered in memory for later processing by the DSP or ECU. To reduce IO bandwidth requirements, the DSP may implement data compression to reduce the number of bits required to represent the ZIF IQ data or to represent the magnitude of the baseband signal. To further reduce bandwidth requirements, the DSP may perform on-chip processing for peak detection and distance estimation. Various suitable processing techniques for detecting reflections of acoustic bursts are known in the art, including commonly owned U.S. Patent Application Publication No. 2024 / 0069192, entitled "Motion-compensated distance sensing with concurrent up-chirp down-chirp waveforms," ​​which is incorporated herein by reference.

[0023] The received electrical signal is typically in the millivolt or microvolt range, so the receiver RX M , R.X. T may include an amplifier for buffering and amplifying the signal from the receive terminal. An analog or digital mixer may be included to downconvert the received signal to baseband for further filtering and processing by the DSP. The mixer, in one implementation, is an in-phase / quadrature (I / Q) digital mixer that provides zero intermediate frequency (ZIF) IQ data as its output. (Although the term "ZIF" is used herein, the downconverted signal may actually be a low intermediate frequency or "near baseband" signal.

[0024] The DSP applies programmable methods to acquire the received signal, detect any echoes, and measure their parameters, such as time of flight (ToF), direction of arrival (DoA), duration, and peak amplitude. Such methods may use threshold comparison, minimum spacing, peak detection, zero crossing detection and counting, noise level measurement, and other customizable techniques tuned to improve reliability and accuracy. In particular, the peak detection process itself has variations, with some variations performing rising edge detection, falling edge detection, or peak maximum detection. Processing for nearby obstacle detection may be performed entirely in the controller 206, or may be shared with or delegated to an ECU or host processor, which receives certain data via the communication bus as described above.

[0025] FIG. 4 shows a set of interconnected ECUs (electronic control units) 401-403 organized in a hierarchical bus topology. Of course, other topologies, including serial, parallel, star, and ring topologies, are also suitable and contemplated for use in accordance with the principles disclosed herein. A first ECU 401 is coupled to an array(s) of ULS transducers 104 and MEMS microphone sensors 106, which may also include ULS transducers. To provide automated parking or driving assistance, a second ECU 402 may connect to a set of actuators, such as a turn signal actuator 406, a steering actuator 408, a brake actuator 410, and a throttle actuator 412. A third ECU 403 may couple to a user interactive interface 414 to accept user input and provide indications of various measurements and system status. Using the interfaces, sensors, and actuators, the ECUs 401-403 may provide automated parking, assisted parking, lane change assistance, obstacle and blind spot detection, and other desired functions.

[0026] 5 is a flow diagram of an exemplary sensing method using a MEMS microphone. Although MEMS microphones are not suitable for generating acoustic bursts, their small size, high sensitivity, and decoupling from the acoustic burst generator allow detection of the reflection of the acoustic burst from the covert ULS transducer despite attenuation and extended transducer reverberation potentially caused by overlying surfaces. The sensing method may be implemented by a sensor controller, by an ECU, or the steps of the method may be distributed among multiple components of the sensing system. The latter two implementations may be preferred when the operation of multiple transducers and sensor assemblies is coordinated.

[0027] If a single sensor assembly implements the method, block 502 may be skipped. Otherwise, the ECU coordinates the operation of the various sensors and transducers that cooperate in the obstacle detection / monitoring measurement. Such coordination may include setting measurement parameters (e.g., carrier frequency, burst duration, transmitter and receiver selection), timing synchronization, and trigger signals or measurement start commands.

[0028] At block 504, the selected ULS transducer(s) each generate an acoustic burst that propagates through and beyond the overlying surface toward the region of interest. The acoustic burst reflects off any obstacles within range, and the reflections propagate back to the sensing array, which includes one or more selected MEMS microphones and, optionally, the transmitting ULS transducer or other selected ULS transducers. At block 506, the selected receiver captures an electrical receive signal from the sensing array. Blocks 502-506 may then be repeated with the same or different configurations of transmitters and receivers to collect additional receive signals.

[0029] Once the electrical receive signals are captured, the ECU and / or sensor controller may process them in block 508 and apply techniques described elsewhere for detecting echoes and determining corresponding obstacle distances. Such techniques typically include dynamic gain, filtering, correlation, magnitude determination, threshold comparison, and combining multiple measurements to improve signal-to-noise ratio and immunity to transient events. In block 510, the ECU and / or sensor controller determines whether an echo has been detected, for example, by determining whether the composite signal exceeds a threshold. If not, the process returns to block 508 to process the next receive signal. If so, in block 512, the ECU and / or sensor controller determines at least one of the distance (or equivalently, the travel time between the transmission and the echo). The ECU and / or sensor controller may further determine the direction to the reflector, for example, using the relative phase information to determine the direction of arrival, azimuth, and / or elevation. Other suitable direction detection techniques are available in the open literature. In block 514, the ECU and / or sensor controller may report the detected echo information to another ECU or a user to enable the obstacle to be avoided or otherwise considered as part of the ADAS system function.

[0030] 5 are treated as sequential for purposes of explanation, in reality the method may be performed by multiple system components operating simultaneously, and in some cases may be performed speculatively to allow for out-of-order operation.

[0031] The disclosed system may advantageously provide a cost-effective implementation of covert ultrasonic sensing since it does not require sophisticated damping materials for the ULS transducer. MEMS microphones may at least partially eliminate potential reverberation problems that would otherwise be faced when using ULS transducers as detectors. Furthermore, their small size and high sensitivity may allow for unobtrusive placement and reduce the number of sensors required for various ADAS system functions. MEMS microphones are also inexpensive and consume minimal power. Preliminary testing indicates that the disclosed covert transducer and sensor placement may provide over 5 meters in detection range without any visible impact on the aesthetics of the vehicle. While parking assistance, automatic parking, door protection, and kick-to-open are contemplated vehicle features that may be implemented using the disclosed sensors, other potential applications include occupant sensing and intrusion detection using covert sensors in vehicle cabs. Non-vehicle applications may include security monitoring (e.g., in display cases) and traffic monitoring (e.g., at building entrances).

[0032] Numerous modifications, equivalents, and alternatives will become apparent to those skilled in the art once the above disclosure is fully appreciated, and it is intended that the following claims be interpreted to include all such modifications, equivalents, and alternatives, as applicable.

Claims

1. A method of sensing comprising: transmitting an acoustic burst through a surface on an ultrasonic transducer; receiving an acoustic signal with a MEMS (microelectromechanical system) microphone, the MEMS microphone representing the acoustic signal as an electrical received signal; and processing the received electrical signal to detect a reflection of the acoustic burst.

2. 2. The method of claim 1, wherein the surface is a bumper cover or body panel of a vehicle that does not have an opening or acoustic window for transmitting the acoustic burst.

3. 3. The method of sensing of claim 1 or 2, wherein the surface includes an opening for passing the acoustic signal to the MEMS microphone, or the MEMS microphone is positioned to receive the acoustic signal as it passes around a side or edge of the surface.

4. 4. The method of sensing of claim 1, wherein the ultrasonic transducer is one of an array of ultrasonic transducers that cooperate to transmit the acoustic burst through the surface, and the acoustic burst is steerable by the array of ultrasonic transducers.

5. ADAS (Advanced Driver Assistance System), an ultrasonic transducer configured to transmit acoustic bursts through a surface on the ultrasonic transducer; a MEMS (microelectromechanical system) microphone configured to convert a received acoustic signal into an electrical received signal; and a controller configured to detect a reflection of the acoustic burst based on the electrical receive signal.

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