WO2024041179A1 - 一种换能器以及成像系统 - Google Patents

一种换能器以及成像系统 Download PDF

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Publication number
WO2024041179A1
WO2024041179A1 PCT/CN2023/103232 CN2023103232W WO2024041179A1 WO 2024041179 A1 WO2024041179 A1 WO 2024041179A1 CN 2023103232 W CN2023103232 W CN 2023103232W WO 2024041179 A1 WO2024041179 A1 WO 2024041179A1
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WIPO (PCT)
Prior art keywords
electrode
transducer
unit
upper electrode
subunit
Prior art date
Application number
PCT/CN2023/103232
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English (en)
French (fr)
Inventor
陈旭颖
于媛媛
徐景辉
谢金
屈梦娇
Original Assignee
华为技术有限公司
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Publication of WO2024041179A1 publication Critical patent/WO2024041179A1/zh

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00

Definitions

  • the present application relates to the field of ultrasonic imaging, and in particular, to a transducer and an imaging system.
  • Transducers are used in various scenarios that require energy conversion.
  • ultrasonic transducers can convert mechanical signals, that is, acoustic signals and electrical signals.
  • PMUT micromachined piezoelectric ultrasonic transducer
  • PMUT realizes the mutual conversion of acoustic signals and electrical signals based on the forward and reverse voltage effect.
  • alternating signals are applied between the upper and lower electrodes, and the piezoelectric material drives the diaphragm to vibrate under the inverse piezoelectric effect to generate sound waves; when receiving sound waves, the diaphragm vibrates under the driving of external sound waves, and the piezoelectric material passes through the piezoelectric effect.
  • the effect generates an electric charge and reads an electrical signal through the upper and lower electrodes, which can be used to image, for example, a target reflecting sound waves.
  • the imaging resolution of PMUT is related to the bandwidth of PMUT.
  • This application provides a transducer and an imaging system.
  • An array formed by coupling transducer units of different sizes can realize transmission and reception of the fundamental frequency band and the harmonic band in the same transducer unit, thereby increasing the transmission and reception of the fundamental frequency. receiving bandwidth and can meet the needs of harmonic imaging.
  • this application provides a transducer, including: a plurality of transducing units and a substrate, the plurality of transducing units are arranged in an array on the substrate;
  • each transducer unit includes an upper electrode and a lower electrode.
  • an excitation electrical signal is applied to the upper electrode and lower electrode to cause the diaphragm to vibrate to generate sound waves.
  • the transducer unit deforms. To generate charges between the upper electrode and the lower electrode, and receive electrical signals through the upper electrode and the lower electrode output, and the received electrical signals are used to generate an output image;
  • the plurality of transducing units can be divided into at least one reference sub-unit and at least one compensation sub-unit, the aspect ratio of the reference sub-unit is not less than the aspect ratio of the compensation sub-unit, and the aspect ratio of the reference sub-unit is not less than the aspect ratio of the first sub-unit.
  • a threshold so that the reference subunit is used to generate resonance in the fundamental frequency band and the harmonic band, and the compensation subunit generates resonance in the fundamental frequency band.
  • the first threshold is calculated based on the fundamental frequency band and the harmonic band.
  • the size of the transducer unit is calculated based on the transducer unit.
  • the resonance frequency of the unit is calculated; and, usually, the dimensions of the compensation subunit and the reference subunit are not exactly the same as the side length or aspect ratio of the reference subunit, so that the resonance peak of the compensation subunit in the fundamental frequency band and the reference subunit are between
  • the resonant peaks in the fundamental frequency band are different, so that the resonance peaks of the compensation subunit and the reference subunit in the fundamental frequency band are coupled, increasing the resonance bandwidth of the transducer in the fundamental frequency band.
  • the harmonic section is N multiples of the fundamental frequency, where N is a positive integer greater than 1.
  • the harmonic section can be the second multiple, triple the fundamental frequency, etc., that is, the harmonic section can include third-order resonance, The frequency point corresponding to the resonance peak such as fifth-order resonance.
  • the aforementioned aspect ratio of the reference subunit and the compensation subunit is the aspect ratio of the cross section of the reference subunit and the compensation subunit in the direction perpendicular to the substrate, or in other words, the aspect ratio of the cross section toward the substrate.
  • the cross-section can be understood as having at least two mutually perpendicular axes of symmetry, and the aspect ratio is the ratio between the two mutually perpendicular axes of symmetry.
  • transducer units of different sizes arranged in an array are provided on the surface of the substrate.
  • the transducer units of different sizes can receive received waves in different frequency bands, and realize the various functions of different sub-units in the fundamental frequency band.
  • the staggered coupling of resonant peaks achieves the complementary effect of peaks and troughs, thereby obtaining the effect of a large bandwidth of the fundamental frequency through multi-resonant peak coupling; and the high-order modes of each transducer unit are designed to be around twice the central frequency of the fundamental frequency, thereby achieving harmonic It has the function of wave reception, thereby realizing harmonic imaging and improving imaging resolution.
  • the first threshold can be calculated based on the condition that the reference subunit needs to resonate in the fundamental frequency band and the harmonic band as That is, the aspect ratio of the base subunit is usually not less than
  • the harmonic reception function can be ensured, so that the third-order mode of the reference sub-unit is at least twice the frequency of the first-order mode, achieving reception of the fundamental frequency band and the harmonic band.
  • the compensation subunit also resonates in the harmonic band.
  • the size of the compensation subunit can be adjusted so that the compensation While the ionizer unit resonates at the fundamental frequency to broaden the bandwidth of the fundamental frequency band, it can also achieve harmonic band reception and harmonic imaging.
  • At least one reference subunit and at least one compensation subunit are arranged centrally symmetrically on the substrate, thereby achieving a symmetrical vibration mode, which enables reception of the fundamental frequency band and each harmonic band, thereby achieving Increase in receive bandwidth.
  • the upper electrode includes a plurality of segmented electrodes.
  • the center electrode may include a The geometric center point of the upper electrode is the closest to at least one electrode. Therefore, the upper electrode of the transducer unit can be divided into multiple segmented electrodes.
  • different segmented electrodes can be excited to achieve different transmitting modes and receiving frequency bands, which can be achieved during both transmitting and receiving. Achieve large-bandwidth transmission and reception.
  • the received electrical signal is obtained through the center electrode, that is, the modal stress amplitude of each order is the largest and the sign is consistent.
  • the area is used as a receiving electrode, which can take into account the reception of multiple modes.
  • the receiving sensitivity of only using the center electrode is higher than that of the corresponding electrode designed based on the stress distribution of each mode. Receive sensitivity.
  • the plurality of segmented electrodes can be divided into at least one inner electrode and at least one outer electrode, and the at least one outer electrode surrounds the at least one inner electrode; when the acoustic wave is emitted, at least one outer electrode and at least one
  • the inner electrode uses reverse-phase excitation; when receiving sound waves, differential reception can be used for at least one outer electrode and at least one inner electrode, thereby achieving reverse-phase excitation and differential reception through the inner electrode and the outer electrode, which can further increase the receiving capacitance and improve the resistance. Parasitic interference capability.
  • a plurality of segmented electrodes are arranged symmetrically. Therefore, through symmetrically arranged block electrodes, when using the center electrode to receive signals, using the center electrode to receive can take into account the receiving sensitivity of the first, third, and fifth order modes.
  • multiple segmented electrodes of each transducer unit are arranged asymmetrically, so that an asymmetrical electrode design is used to excite the asymmetric vibration mode of the diaphragm and suppress even-order modes (i.e., troughs). ), reduce the sensitivity difference between odd-order modes (such as 1st, 3rd order, etc.), thus increasing the bandwidth.
  • the distance between adjacent transducer units does not exceed 1.5 times the wavelength of the fundamental frequency, thereby ensuring that grating lobes do not appear in the sound field radiated by the transducer array.
  • the transducer unit includes a micromachined piezoelectric ultrasonic transducer PMUT unit, and a piezoelectric sensing layer is also disposed between the upper electrode and the lower electrode in each PMUT unit.
  • the transducer unit includes a micromechanical capacitive ultrasonic transducer CMUT unit, an insulating layer is included between the upper electrode and the lower electrode, and a cavity is provided in the insulating layer.
  • the shape of the surfaces of the multiple transducing units may include at least one of an ellipse or a polygon (such as a rectangle or a square) with at least two central axes of symmetry, and the length and width of the reference sub-unit The ratio is greater than 1.
  • the shape of at least one reference subunit surface is at least one of a rectangular ellipse or a polygon with at least two central symmetry axes, and the shape of at least one compensation subunit surface is a circle or a regular polygon.
  • the width of the array is less than 1.5 times the operating wavelength of the transducer.
  • this application provides a transducer, including: a substrate and a plurality of transducing units arranged on the substrate; each transducing unit includes an upper electrode and a lower electrode, and emits During the sound wave, the excitation electrical signal is applied to the upper electrode and the lower electrode to cause the diaphragm to vibrate to generate sound waves.
  • the transducer unit When the sound wave is received, when the sound wave is transmitted to the transducer unit, the transducer unit deforms, so that the upper electrode and the lower electrode Charges are generated in between, and electrical signals are received through the upper electrode and lower electrode output, and the received electrical signals are used to generate output images; wherein, the aspect ratio of each transducing unit is greater than 1, and the upper electrode of each transducing unit includes multiple A plurality of segmented electrodes are arranged asymmetrically along a central axis parallel to the short side of the substrate.
  • an asymmetric electrode design is used to excite the asymmetric vibration mode of the diaphragm, stimulate the generation of even-order asymmetric modes, and reduce the sensitivity between odd-order modes (such as 1st, 3rd order, etc.) difference, thereby increasing the sending and receiving bandwidth.
  • the number of block electrodes in the upper electrode is related to the required highest order mode.
  • the number of electrodes can be (n+1)/2 blocks, which requires the highest order mode. It is an n-order mode, so the number of segmented electrodes can be adjusted according to the actual application scenario, so as to meet the needs of the actual scenario and have strong generalization.
  • the first threshold can be calculated based on the condition that the transducer unit needs to resonate in the fundamental frequency band and the harmonic band.
  • the aspect ratio of the base subunit is usually not less than
  • the harmonic reception function can be ensured, so that the third-order mode of the reference sub-unit is at least twice the frequency of the first-order mode, achieving reception of the fundamental frequency band and the harmonic band.
  • the first threshold can be calculated based on the frequency of the fundamental band as That is, the aspect ratio of the base subunit is usually not less than
  • the harmonic reception function can be ensured, so that the third-order mode of the reference sub-unit is at least twice the frequency of the first-order mode, achieving reception of the fundamental frequency band and the harmonic band.
  • the receiving sensitivity is higher than the receiving sensitivity corresponding to the electrode design based on the modal stress distribution of each order.
  • the shape of the surfaces of the multiple transducing units may include at least one of an ellipse or a polygon (such as a rectangle or a square) with at least two central axes of symmetry, which increases the transducing capacity provided by this application. Preparability of energy devices.
  • the distance between adjacent transducer units does not exceed 1.5 times the wavelength of the fundamental frequency, thereby ensuring that grating lobes do not appear in the sound field radiated by the transducer array.
  • the width of the array is less than 1.5 times the operating wavelength of the transducer.
  • the transducer unit includes a micromachined piezoelectric ultrasonic transducer PMUT unit, and a piezoelectric sensing layer is also provided between the upper electrode and the lower electrode in each PMUT unit.
  • the piezoelectric sensing layer is used for Collect charge signals generated based on mechanical signals.
  • the transducer unit includes a micromechanical capacitive ultrasonic transducer CMUT unit, an insulating layer is included between the upper electrode and the lower electrode, and a cavity is provided in the insulating layer.
  • this application provides an imaging system, including: a probe and a processor;
  • the probe is provided with a transducer as mentioned in any optional embodiment of the first aspect or the second aspect;
  • the probe is used to emit ultrasonic waves to the target area and receive the ultrasonic echo returned from the target area to obtain ultrasonic echo data;
  • the processor is used to generate an ultrasound image based on the ultrasound echo data.
  • the imaging system may further include: a display for displaying ultrasound images.
  • multiple transducers are provided in the probe, and the multiple transducers are arranged in an array.
  • the multiple transducers form multiple channels, for example, each column in the array forms a channel.
  • the multiple channels are used to collect echo signals, thereby achieving high-resolution ultrasonic imaging and harmonic imaging.
  • Figure 1 is a schematic structural diagram of an imaging system provided by this application.
  • Figure 2 is a schematic structural diagram of a probe provided by this application.
  • FIG. 3 is a schematic structural diagram of a PMUT provided by this application.
  • Figure 4 is a schematic structural diagram of a transducer provided by this application.
  • FIG. 5 is a schematic structural diagram of another PMUT unit provided by this application.
  • FIG. 6 is a schematic structural diagram of a CMUT unit provided by this application.
  • FIG. 7 is a schematic structural diagram of another transducer provided by this application.
  • FIG. 8 is a schematic structural diagram of another transducer provided by this application.
  • Figure 9 is a schematic diagram of the receiving effect of a transducer provided by this application.
  • FIG. 10 is a schematic diagram of the receiving effect of another transducer provided by this application.
  • FIG 11 is a schematic structural diagram of another transducer provided by this application.
  • Figure 12 is a schematic diagram of the receiving effect of another transducer provided by this application.
  • FIG. 13 is a schematic diagram of the receiving effect of another transducer provided by this application.
  • FIG 14 is a schematic structural diagram of another transducer provided by this application.
  • FIG. 15 is a schematic diagram of the receiving effect of another transducer provided by this application.
  • Figure 16 is a schematic diagram of the receiving effect of another transducer provided by this application.
  • FIG 17 is a schematic structural diagram of another transducer provided by this application.
  • Figure 18 is a schematic structural diagram of another transducer provided by this application.
  • the transducer provided by this application can be used in various mechanical signal and electrical signal conversion scenarios, such as wearable devices, ultrasonic imaging scenarios, ultrasonic ranging or communication scenarios, etc. specifically.
  • wearable devices in response to the large bandwidth and harmonic imaging requirements in the field of ultrasonic imaging, it can be used for tissue imaging of users and can also be used for flaw detection of industrial devices.
  • the transducer provided by the present application can be disposed in a flexible substrate for real-time imaging of the user's tissue.
  • the imaging system may include a probe, a processor, and a display device.
  • the probe may send ultrasound waves to the target tissue and receive echo signals returned from the target tissue.
  • the processor may process the echo signals to generate ultrasound images.
  • the imaging probe emits sound waves to the human body, the imaging tissue reflects the sound waves and is received by the imaging probe.
  • the imaging probe processes the signal through internal circuits and algorithms, and then transmits the processed signal through cables or wirelessly (not shown in Figure 1 out) to the display device.
  • the built-in data processing APP of the display device can convert the received signal into a picture signal and display it in real time.
  • the transducer provided by this application can be installed in the probe.
  • the electrical signal is converted into an acoustic wave signal by the transducer provided by this application and radiated outward.
  • the electrical signal is converted into an acoustic wave signal by The transducer provided by this application converts acoustic wave signals into electrical signals.
  • the display device is an optional device that can be used to display ultrasound images to facilitate users to observe the specific conditions of the target tissue. Of course, in some scenarios, it is not necessary to display the ultrasound image on the display device.
  • the probe may include control circuits, analog front end (AFE) circuits or transducers, etc.
  • a selection switch can be set between the transducer and the AFE circuit to switch between sending signals and receiving signals.
  • a protective layer or acoustic lens structure can be provided on the front end of the probe.
  • the protective layer is usually made of polymer material and can prevent physical impact and chemical corrosion, thereby protecting the circuit structure inside the probe.
  • the acoustic lens can be used to focus sound waves.
  • the transducer is set at the front end of the probe. When a protective layer is set at the same time, the transducer is closely attached to the protective layer.
  • the transducer is used for transmitting and receiving ultrasound.
  • the transducer can be the transducer provided in the following embodiments of this application. energy device.
  • An AFE circuit is set up at the back end of the transducer, and the transmitting excitation channel and the echo receiving channel are selected by switching the switch.
  • the transmitting excitation channel includes a pulse transmitter, which is used to generate a certain frequency and replicated pulse excitation waveform.
  • the echo receiving circuit may include one of time gain compensation circuit (time gain compensation, TGC), low noise amplifier circuit (low noise amplifier, LNA), filter circuit or analog to digital converter circuit (analog to digital converter, ADC), etc. Or a variety of circuits for compensating, amplifying, filtering, and analog-to-digital conversion of the received echo signals.
  • the back end of the AFE circuit can be equipped with a control chip, as shown in Figure 2.
  • a control chip as shown in Figure 2.
  • the control chip as a programmable logic gate circuit (field programmable gate array, FPGA) as an example, it can be used for signal control and processing.
  • FPGA field programmable gate array
  • the transducer can convert electrical energy into acoustic wave signals and transmit them to the target object.
  • the PMUT device converts electrical energy into acoustic energy and transmits it to the imaging object through the inverse piezoelectric effect, and transmits the imaging object to the imaging object through the forward piezoelectric effect.
  • the echo sound energy is converted into electrical signals.
  • the main body of the PMUT unit structure includes a base layer (containing a cavity, the plane size of the cavity determines the diaphragm area), a bottom electrode, a piezoelectric layer and an upper electrode. Obviously, the transducer is crucial for the reception of acoustic signals.
  • the PMUT structure can be shown in Figure 3.
  • PMUT as an ultrasonic transceiver device, can be used for ultrasonic imaging.
  • the principle of ultrasonic imaging is to use the difference in acoustic impedance of different imaging tissues to produce acoustic reflections at the interface of each tissue. Imaging can be achieved by receiving reflected acoustic waves and performing signal processing.
  • the harmonic imaging function can also greatly improve the contrast and lateral resolution of ultrasound imaging.
  • harmonic imaging requires the transducer to have twice the fundamental frequency. reception function at the frequency.
  • some commonly used PMUT devices include multiple PMUT units.
  • the shape of the upper electrode can be rectangular or elliptical.
  • the rectangular (or elliptical) PMUT unit can excite multiple modes within the fundamental frequency bandwidth.
  • complementary compensation of wave peaks and valleys is achieved to achieve a large bandwidth, and an additional rectangular PMUT unit is introduced solely for harmonic band reception.
  • the additional introduction of the PMUT unit only for harmonic reception will reduce the sensitivity of the array, and the fundamental frequency transmitting unit and the harmonic receiving unit do not overlap in spatial position, which will affect the harmonic imaging performance.
  • the electrode block design is based on the stress distribution of the first, third and fifth order modes, and different PMUT modes are excited by using different excitation electrode configurations, thereby realizing multi-frequency PMUT.
  • the electrode block design is based on the stress distribution of the first, third and fifth order modes, and different PMUT modes are excited by using different excitation electrode configurations, thereby realizing multi-frequency PMUT.
  • only one mode can be excited under one electrode configuration, that is, different modes cannot be excited at the same time. Therefore, this solution can only achieve multi-frequency PMUT, but each mode cannot be coupled within the bandwidth and cannot achieve large-scale bandwidth.
  • the multi-mode coupled PMUT unit structure uses an asymmetric electrode design to excite the asymmetric vibration modes of the PMUT diaphragm, suppress the generation of even-order modes (troughs), and reduce odd-order modes (such as 1st and 3rd orders). ) to achieve modal coupling within the -3dB bandwidth range.
  • the bandwidth gain of this PMUT unit is limited. Only considering the modal coupling of the transmission performance to increase the transmission bandwidth, without considering the reception performance, the reception bandwidth will become smaller, resulting in the PMUT comprehensive bandwidth not increasing, so the imaging effect is not enhanced.
  • this application provides a transducer, which is an array formed by coupling transducer units of different sizes.
  • a transducer which is an array formed by coupling transducer units of different sizes.
  • large-bandwidth fundamental frequency band transceiver and harmonic band reception can be achieved, thereby increasing the fundamental frequency transceiver bandwidth. , improve the imaging resolution, and can meet the needs of harmonic imaging.
  • FIG 4 is a schematic structural diagram of a transducer provided by this application.
  • the transducer may include a plurality of transducing units 401 and a substrate 402, and the plurality of transducing units are arranged in an array on the substrate.
  • each transducer unit includes a diaphragm, which may include a structural layer, an upper electrode and a lower electrode.
  • a diaphragm When emitting sound waves, excitation electrical signals are applied to the upper and lower electrodes to cause the diaphragm to vibrate to generate sound waves.
  • the diaphragm When receiving sound waves, When sound waves are transmitted to the diaphragm, the diaphragm deforms to generate charges between the upper electrode and the lower electrode, and outputs and receives electrical signals through the upper and lower electrodes. The received electrical signals are used to generate output images.
  • the plurality of transducing units can be divided into at least one reference sub-unit and at least one compensation sub-unit based on size, that is, the at least one reference sub-unit and the at least one compensation sub-unit are arranged in an array on the substrate, and the reference sub-unit
  • the aspect ratio is not less than the aspect ratio of the compensation subunit, and the aspect ratio of the reference subunit is not less than the first threshold, so that the reference subunit can be used to generate resonance in both the fundamental frequency band and the harmonic band, and the compensation subunit can be used in the fundamental frequency band
  • the first threshold can be calculated based on the fundamental frequency band and harmonic band of the reference subunit that need to resonate.
  • the length and width of the reference subunit need to be met. Ratio, the size of each transducer unit can be calculated according to the frequency characteristics of the required resonance. Usually different sizes, such as different aspect ratios or different side lengths, can achieve the transmission and reception of acoustic signals in different frequency bands, thus Through the coupling of transducer units of different sizes, the reference subunit and the compensation subunit resonate at multiple frequency points in the fundamental frequency band, thereby achieving coupling of the transmitting and receiving frequency bands at multiple frequency points in the fundamental frequency band and broadening the bandwidth of the fundamental frequency band.
  • transducer units of different sizes arranged in an array are provided on the surface of the substrate.
  • the transducer units of different sizes can receive received waves in different frequency bands, and realize the various functions of different sub-units in the fundamental frequency band.
  • the staggered coupling of resonant peaks achieves the complementary effect of peaks and troughs, thereby obtaining the effect of a large fundamental frequency bandwidth through multi-resonant peak coupling; and the high-order modes of each transducer unit can be designed to be near twice the central frequency of the fundamental frequency, thereby achieving
  • the function of harmonic reception enables harmonic imaging and improves imaging resolution.
  • each transducer unit usually resonates with one of the frequency points in the fundamental frequency band, and the compensation subunit and the reference subunit usually resonate with each other.
  • Different frequency points within the fundamental frequency band generate resonance, thereby realizing staggered coupling of the resonance peaks of different sub-units in the fundamental frequency band to achieve the complementary effect of peaks and troughs, thereby increasing the fundamental frequency transceiver bandwidth.
  • the frequency of the output received electrical signal is related to the resonant frequency of the transducer unit.
  • the frequency of the received electrical signal includes the resonant frequency of the transducer unit or a frequency close to the resonant frequency.
  • the reference subunit and the compensation subunit resonate at different frequency points in the fundamental frequency band
  • different sizes can be set for the reference subunit and the compensation subunit, such as setting different aspect ratios and/or different side lengths, etc.
  • the resonance peaks of the reference subunit and the compensation subunit are at different frequency points, thereby achieving cross-coupling of the resonance peaks of different subunits to achieve the complementary effect of peaks and troughs.
  • the size of the transducer unit please refer to the calculation process in Scenario 1 mentioned below, which will not be described again here.
  • the first threshold can be calculated based on the frequency and harmonic frequency of the fundamental frequency band in which the reference subunit needs to resonate: That is, the aspect ratio of the base subunit is usually not less than
  • the harmonic reception function can be ensured, so that the third-order mode of the reference sub-unit is at least twice the frequency of the first-order mode, achieving reception of the fundamental frequency band and the harmonic band.
  • at least the third-order mode of the reference sub-unit needs to be located at twice the frequency of the first-order mode. It can be calculated that usually the aspect ratio of the reference sub-unit is ⁇
  • the compensation subunit can also resonate in the harmonic band.
  • the size of the compensation subunit can be adjusted so that while the compensation subunit resonates at the fundamental frequency to broaden the bandwidth of the fundamental frequency band, it can also achieve harmonic band reception and achieve harmonic imaging.
  • the compensation subunit can also resonate only in the harmonic band, thereby enhancing harmonic imaging.
  • the details can be adjusted according to the actual application scenario.
  • the aforementioned at least one reference sub-unit and at least one compensation sub-unit can be centrally symmetrically arranged on the substrate, thereby achieving a symmetrical radiation sound field, and can radiate acoustic signals perpendicularly or nearly perpendicularly to the substrate, so as to achieve alignment with the substrate. Transmission and reception of frequency bands and individual harmonic bands.
  • the upper electrode includes a plurality of segmented electrodes.
  • the center electrode can be understood as being connected to the center electrode of the upper electrode.
  • the center point is the closest to one or more electrodes. Therefore, the upper electrode of the transducer unit can be divided into multiple segmented electrodes.
  • different segmented electrodes can be excited to achieve different transmitting modes and receiving frequency bands, which can be achieved during both transmitting and receiving. Achieve large-bandwidth transmission and reception, thereby achieving large-bandwidth imaging.
  • the plurality of splitting electrodes can be excited.
  • the center electrode that is, the area with the largest modal stress amplitude and consistent sign at each order is used as the receiving electrode.
  • the receiving sensitivity using only the center electrode is higher than the receiving sensitivity corresponding to the electrode design based on the stress distribution of each order mode.
  • the plurality of electrodes can be divided into at least one inner electrode and at least one outer electrode.
  • the at least one outer electrode surrounds the inner electrode.
  • reverse excitation can be used for the inner electrode and the outer electrode.
  • differential reception is performed through the center electrode, that is, the received signals of the inner electrode and the outer electrode have opposite phases.
  • the center electrode can include an inner electrode and an outer electrode arranged on the central axis, thereby achieving differential reception through the inner electrode and the outer electrode.
  • the receiving capacitance can be further increased to improve the ability to resist parasitic interference.
  • the individual segmented electrodes in the transducer unit are arranged symmetrically, and are usually symmetrical along a central axis parallel to the wide edge. Therefore, through symmetrically arranged block electrodes, when using the center electrode to receive signals, using the center electrode to receive can take into account the receiving sensitivity of the first, third, and fifth order modes.
  • the multiple segmented electrodes in the transducer unit can also be arranged asymmetrically, so that an asymmetrical electrode design can be used to excite the asymmetric vibration mode of the diaphragm and even-order asymmetric modes.
  • the generation of reduces the sensitivity difference between odd-order modes (such as 1st, 3rd order, etc.), thereby increasing the bandwidth.
  • this application also provides a transducer.
  • the difference between this transducer and the transducer shown in Figure 4 is that the upper electrode of the transducer can include multiple segmented electrodes.
  • the segmented electrodes are asymmetrically arranged on the substrate along a central axis parallel to the short sides of the substrate.
  • this application also provides a transducer, including: a substrate and a plurality of transducing units arranged on the substrate; each transducing unit includes an upper electrode and a lower electrode. , when emitting sound waves, the excitation electrical signal is applied to the upper electrode and lower electrode, The diaphragm vibrates to generate sound waves. When the sound waves are received, when the sound waves are transmitted to the transducer unit, the transducer unit deforms to generate charges between the upper electrode and the lower electrode, and receives electrical signals through the output of the upper electrode and the lower electrode.
  • the frequency of the received electrical signal is related to the frequency of resonance of each transducer unit, and the received electrical signal is used to generate an output image; where the aspect ratio of each transducer unit is greater than 1, and the upper electrode of each transducer unit It includes a plurality of segmented electrodes arranged asymmetrically along a central axis parallel to the short side of the substrate.
  • the number of block electrodes in the upper electrode is related to the required highest order mode.
  • the number of electrodes can be (n+1)/2 blocks, which requires the highest order mode. It is an n-order mode, so the number of segmented electrodes can be adjusted according to the actual application scenario, so as to meet the needs of the actual scenario and have strong generalization.
  • each transducer unit can be referred to the relevant introduction of the aforementioned reference subunit, and the similarities will not be introduced here.
  • multiple block electrodes in the transducer unit can be arranged in an asymmetrical arrangement.
  • the sizes of each block electrode are different, so as to achieve reception mainly in the fundamental frequency band. , or it can also take into account the reception of low-order modes, so that the reception of waves in various frequency bands can be achieved through block electrodes of different sizes, and the bandwidth can be broadened.
  • the distance between adjacent transducer units does not exceed 1.5 times the fundamental frequency wavelength to ensure that no grating lobes appear in the radiation sound field of the array.
  • the aforementioned transducing unit may include a PMUT unit.
  • the diaphragm in each PMUT unit may include an upper electrode, a lower electrode and a piezoelectric sensing layer.
  • the piezoelectric sensing layer is disposed between the upper electrode and the lower electrode.
  • the upper electrode and the piezoelectric sensing layer may be used to collect sound waves based on signal generated by the charge signal.
  • the structure of the PMUT unit can be as shown in Figure 5.
  • the diaphragm of the PMUT unit can include an upper electrode 501, a piezoelectric sensing layer 502, a lower electrode 503 and a structural layer 504.
  • the PMUT unit can also include a substrate 505. A cavity is provided in the substrate 505 , and the piezoelectric sensing layer 502 is provided between the upper electrode 501 and the lower electrode 503 .
  • an alternating signal can be applied between the upper electrode and the lower electrode.
  • the piezoelectric sensing layer drives the entire diaphragm to vibrate under the reverse piezoelectric effect to generate sound waves, and transmits the sound waves outward.
  • the sound waves arrive When the target tissue is used, the target tissue reflects the ultrasonic wave, thereby reflecting it back to the PMUT unit.
  • the PMUT unit When the PMUT unit is in the receiving mode, when the echo reflected by the target tissue is transmitted to the diaphragm, the diaphragm vibrates driven by the echo, and the piezoelectric induction layer generates charges through the piezoelectric ratio and transmits them to the upper and lower electrodes.
  • the received electrical signals can be read through the electrodes and lower electrodes.
  • the transducer unit provided by this application can adopt a PMUT structure to realize conversion of mechanical signals and electrical signals, and to realize the sending and receiving of mechanical signals.
  • the aforementioned transducer unit may include a micromachined capacitive ultrasonic transducer (Capacitive micromachined ultrasonic transducer, CMUT) unit.
  • CMUT capacitive micromachined ultrasonic transducer
  • An insulating layer is provided between the upper electrode and the lower electrode, and a cavity is provided in the insulating layer.
  • the structure of the CMUT unit may be as shown in FIG. 6 .
  • the CMUT unit may include a diaphragm.
  • the diaphragm may include an upper electrode 601 , an insulating layer 602 , a lower electrode 603 and a structural layer 604 .
  • the CMUT unit may also include a substrate 605 , a cavity is provided in the insulating layer 602, and the insulating layer 602 is provided between the upper electrode 601 and the lower electrode 603.
  • CMUT unit When the CMUT unit is in the transmitting mode, a voltage can be applied between the upper electrode and the lower electrode, and the diaphragm will bend and deform under the action of electrostatic force, thereby applying an alternating voltage of the required frequency to the upper electrode and the lower electrode.
  • the diaphragm is excited to reciprocate, converting electrical energy into mechanical energy, and radiating energy outwards, thereby generating ultrasonic waves.
  • CMUT unit When the CMUT unit is in the receiving mode, a DC bias voltage is applied between the upper electrode and the lower electrode, and the diaphragm reaches a static equilibrium under the action of electrostatic force and diaphragm restoring force.
  • the echo reflected by the target tissue is transmitted to
  • the diaphragm moves, the diaphragm will be excited to vibrate, and the cavity spacing between the upper electrode and the lower electrode will change, causing a change in the capacitance between the upper and lower electrodes, thereby outputting and receiving electrical signals.
  • the transducer unit provided by the present application can adopt a CMUT structure, thereby realizing the conversion of mechanical signals and electrical signals, and realizing the transmission and reception of acoustic wave signals.
  • the shape of the surface of the transducing unit may specifically include at least one of a rectangle, an ellipse, or a polygon. It can be understood that the shape of the surface of the transducing unit may include at least one of an ellipse or a polygon with at least two vertical axes of symmetry.
  • the shape of the surface of the reference subunit is at least one of an ellipse or a polygon with at least two central symmetry axes
  • the shape of the surface of the compensation subunit can be a circle or a regular polygon, etc.
  • the compensation subunit It can be used to generate resonance in the fundamental frequency band, so that the reference sub-unit can resonate in both the fundamental frequency band and the harmonic band, thereby increasing the bandwidth of sending and receiving signals.
  • the width of the array is less than 1.5 times the operating wavelength of the transducer. This enables the array to receive signals in the fundamental frequency band and harmonic band.
  • This width can be understood as the base width of the transducer, which is usually the side length parallel to the shorter symmetry axis.
  • the width of the array composed of the upper electrode is usually as close as possible to the width of the base to improve The sensitivity of the array that the substrate can accommodate avoids wasting the area of the substrate.
  • the transducer can be called a PMUT transducer
  • the transducer can be called a PMUT transducer
  • the PMUT mentioned below can also be replaced by CMUT. Or other transducer units.
  • the transducer provided by this application may include PMUT units of multiple sizes, and the PMUT units of multiple sizes are coupled in an array arrangement on the substrate.
  • the PMUT unit can be divided into a reference sub-unit 701 and a compensation sub-unit 702, which are arranged in an array on a substrate 703.
  • the overall structure of the PMUT transducer may include four parts: a substrate, a bottom electrode (lower electrode), a piezoelectric layer, and an upper electrode.
  • the cross-sections along the x-axis and y-axis of the structure of each PMUT unit can be seen in Figure 8.
  • the upper electrode of each unit is divided into two parts: an inner electrode and an outer electrode, and both the inner electrode and the outer electrode are block electrodes.
  • the base material can usually be silicon, or it can be materials such as glass or organic polymers.
  • the base is usually etched to create a cavity structure, which facilitates the structural vibration of the upper part of the cavity; the lower electrode and the upper electrode are used to provide excitation for the piezoelectric layer. Signal or collect charge signal generated by stress in the piezoelectric layer.
  • the lower electrode and upper electrode materials can be various conductive materials, including metal materials Al, Au, Ag, Pt, Cu, Mo, Ti, etc., or some conductive polymers Materials, etc.; Piezoelectric layer materials mainly include AlN and its alloy materials (Sc x Al 1-x N), ZnO and its alloy materials (V x Zn 1-x O), PZT and its alloy materials (PLZT, PNZT), KNN (K x Na 1-x NbO 3 ), PMN-PT, PVDF or PVDF-TRFE, etc. can be selected according to the actual application scenario.
  • PMUT units can be divided into reference sub-units and compensation sub-units according to their size.
  • the arrangement of the reference sub-unit and the supplementary sub-unit must satisfy a centrally symmetrical arrangement, and the intervals between the boundaries of the sub-units may be close to each other (such as according to The manufacturing process is set to the closest distance), and the upper limit is usually 1.5 times the fundamental frequency wavelength; the overall size of the array needs to be less than 1.5 times the wavelength in the x-axis or y-axis direction.
  • the PMUT unit coupling structures of different sizes can simultaneously achieve large fundamental frequency bandwidth and harmonic reception effects.
  • the resonant peaks of different sub-units are staggeredly coupled in the fundamental frequency band to achieve the complementary effect of peaks and troughs, thereby obtaining the effect of large bandwidth at the fundamental frequency through multi-resonant peak coupling; at the same time, each sub-unit
  • the high-order mode is designed to be near twice the frequency of the fundamental center frequency, thereby achieving the function of harmonic reception.
  • the geometric structure characteristics can be summarized from the characteristic frequency calculation formula of each mode of the rectangular PMUT unit.
  • f 0 is the characteristic frequency of the first-order mode
  • f m,1 is the characteristic frequency of the m-order mode along the long side
  • L is the length of the short side
  • k is the aspect ratio
  • T is the diaphragm. Bending stiffness
  • ⁇ is the surface density.
  • one type of sub-unit needs to have at least one resonance peak in the fundamental frequency band and/or harmonic band respectively, that is, the reference sub-unit, and the other type of sub-unit needs to have at least one resonance peak in the fundamental frequency band and/or harmonic band.
  • a resonant peak the compensation subunit. It can be seen from Formula 2 that the larger the aspect ratio k, the closer the characteristic frequency of the higher-order mode is to the characteristic frequency of the first-order mode.
  • the reference subunit is The aspect ratio of the subunit is not less than the aspect ratio of the compensation subunit.
  • the first-order resonance peak of the compensation subunit should be located near the first-order resonance peak of the reference subunit.
  • the characteristics of the geometric dimensions of the PMUT unit surface provided in this application are: PMUT units of different sizes are divided into reference sub-units and compensation sub-units, and the aspect ratio of the reference sub-unit is greater than And the aspect ratio of the reference subunit ⁇ the aspect ratio of the compensation subunit, and the width of the compensation subunit is similar to the width of the reference subunit (within ⁇ 45%).
  • the arrangement of the reference subunit and the compensation subunit must meet the central symmetric distribution condition.
  • the spacing between different PMUT units needs to be as small as possible, and the specific range can be determined based on process errors.
  • the number of reference sub-units can be increased, that is, multiple reference sub-units can be set up, and the compensation sub-unit can also include multiple different lengths and widths. ratio or different width of PMUT cells.
  • the upper electrode of the PMUT unit provided by this application can be set as multiple segmented electrodes, and can be divided into inner electrodes and outer electrodes, so that the multi-modal PMUT unit has high receiving sensitivity in each mode.
  • the stress distribution simulation effects of different modes of the PMUT unit provided in this application can be seen in Figure 10.
  • this application divides the segmented electrodes into internal electrodes and external electrodes. Compared with receiving signals from the whole block, the internal and external segmented electrodes provided by this application can be expanded from only targeting a single mode to taking into account multiple modes, as shown in Figure 10.
  • the stress distribution of the rectangular PMUT in the first, third, and fifth order modes is quite different (only the first, third, and fifth order modes are used as examples here, and can also be replaced with other order modes). According to the The stress distribution designed electrode can usually only ensure the receiving sensitivity of its corresponding mode, while sacrificing the receiving sensitivity of other modes.
  • this application provides that the area with the largest modal stress amplitude and consistent sign at each order is used as the receiving electrode, that is, the central part (called the central electrode).
  • the central electrode Using the center electrode as the receiving electrode can take into account the receiving sensitivity of the first, third, and fifth order modes.
  • the receiving sensitivity of using only the center electrode is higher than that of each order mode.
  • the stress distribution corresponds to the receiving sensitivity of the electrode design.
  • the transceiver setting circuit for the internal and external electrodes can be shown in Figure 11.
  • the entire electrode needs to be excited, and when receiving, the center electrode is used to receive, and the transceiver switch is used as shown in Figure 11.
  • the inner and outer electrodes adopt reverse-phase excitation and differential reception.
  • the upper electrode can be divided into two parts, the inner electrode and the outer electrode, based on the tensile and compressive stress distribution of the first-order mode of PMUT.
  • Both the inner electrode and the outer electrode are independently set with a geometric center part as the receiving area, where the length of the center electrode of the inner electrode is 1/9-1/3 of the entire inner electrode.
  • the length of the center electrode can be determined according to the mode.
  • the center electrode of the fifth-order mode is 1/5;
  • the center electrode of the outer electrode is the same length as the center electrode of the inner electrode.
  • the PMUT unit provided in this application excites the entire electrode when transmitting, and its resonance peak frequency is consistent with the reception of the entire electrode. Therefore, using the center electrode to receive can avoid the transmitting resonance peak and the receiving resonance peak, so that the transmitting and receiving frequency bands can be achieved complement each other, thereby increasing the comprehensive bandwidth of sending and receiving.
  • the shape of the PMUT unit can include some shapes with an aspect ratio, that is, with a major axis and a minor axis, such as ellipses, polygons (rhombus to n-gon), and irregular geometries in which the major axis and minor axis are formed by arbitrary curves. .
  • This embodiment takes an ellipse as an example.
  • the comparison of the receiving bands of an elliptical PMUT unit and a rectangular PMUT unit can be shown in Figure 12.
  • the elliptical structure is similar to the rectangular structure and also has multi-modal characteristics.
  • the modes of each order can also be adjusted by adjusting the aspect ratio characteristics of the elliptical PMUT. Therefore, the elliptical structure can also achieve the same or similar effects in the rectangular PMUT through size adjustment.
  • the frequency difference of each order mode of the ellipse is larger than that of the rectangular structure (that is, under the same aspect ratio in Figure 10, the ellipse has only two modes in the frequency sweep range of 2-8MHz, And the rectangle has three modes), so the size feature points of the rectangular structure in the rectangular PMUT unit (such as the aspect ratio is greater than ) covers the structural characteristics of ellipses.
  • Other dimensional characteristic points about the rectangular PMUT structure are also applicable to the ellipse, including the spacing and number between units, the centrally symmetrical arrangement, the design of the internal and external electrodes of the blocks, etc., which will not be repeated here.
  • the reference subunit can adopt a PMUT with a certain aspect ratio shape
  • the compensation subunit can adopt a geometric structure without aspect ratio structural characteristics, such as a circle, a square or a regular polygon. wait.
  • the structure of the coupling of the circular compensation subunit and the rectangular reference subunit and its simulation effect can be seen in Figure 13.
  • the rectangular PMUT can be regarded as the reference subunit, and the circular PMUT can be regarded as the compensation subunit.
  • the valley compensation between the first and third-order modes of a rectangular PMUT through circular PMUT units of different sizes can also achieve the effect of a large bandwidth of the fundamental frequency.
  • the higher-order modes of the circular PMUT are far away from the fundamental frequency mode and cannot be adjusted,
  • the frequency ratio of the first two modes is 3.9.
  • the circular PMUT unit can only be used to receive fundamental band waves, but cannot receive harmonics. Therefore, in the embodiment of the present application, a large fundamental frequency bandwidth can be achieved through the reference subunit and the compensation subunit, and the harmonic reception function can be implemented only through the reference subunit.
  • the block design of the upper electrode is from the perspective of maximizing the receiving sensitivity of each order mode, and is mainly aimed at low-order modes, such as the first, third, and fifth orders.
  • This embodiment will further comprehensively receive From the perspective of sensitivity and bandwidth, the electrode block design is expanded.
  • the embodiment of the present application also provides another transducer.
  • the upper electrode of the PMUT unit in the transducer can be divided into multiple segmented electrodes.
  • the multiple segmented electrodes are arranged asymmetrically, and each PMUT
  • the number of segmented electrodes of the unit is related to the required receiving mode. For example, the higher the required mode, the greater the number of segmented electrodes required.
  • Figure 14 is a schematic structural diagram of another transducer provided by this application.
  • Figures 15 and 16 show the transmission sensitivity and reception sensitivity effects of PMUT units based on asymmetric arrangement.
  • the upper electrodes are arranged asymmetrically along the central axis parallel to the wide edge.
  • asymmetric block electrodes Through asymmetric block electrodes, a large bandwidth can be formed in a single-sized PMUT unit or an array thereof.
  • the ninth-order mode is taken as an example.
  • the block electrodes can be set according to the stress distribution of the ninth-order mode, which can increase the transceiver sensitivity of the ninth-order mode, thus solving the problem of excitation and excitation of the traditional monolithic electrode structure.
  • reception due to the low transmitting and receiving sensitivity of the ninth-order mode, it is unable to couple with the third, fifth, and seventh-order modes at -6dB.
  • the width of each electrode is the same or close to it, which is taken as the boundary between the internal and external stress of the first-order mode.
  • the length of each electrode will be 1/9 of the overall length of the inner electrode, which will increase the sensitivity of the ninth-order mode at the expense of other modes (three, 5, 7).
  • the overall area of the segmented electrode is selected to be basically the same as or close to the area of the entire electrode.
  • the gap between segmented electrodes is chosen to minimize the difference from the area of the entire electrode.
  • the size of the electrodes adjacent to the central electrode (b-2b) is larger than the size of the central electrode, and the size of the peripheral electrodes ( ⁇ b) is smaller than the size of the central electrode.
  • this embodiment proposes to arrange the segmented electrodes along the The wide parallel central axis is arranged asymmetrically. As shown in Figure 15, often The segmented electrodes used are symmetrically distributed along the central axes x and y, while the asymmetric electrodes in this embodiment are only symmetrically distributed along the x-axis and asymmetrically distributed along the y-axis.
  • the asymmetric electrode design can improve the sensitivity between the third and fifth orders and the fifth and seventh orders.
  • the asymmetric electrodes of this embodiment are implemented on the basis of the above-mentioned segmented electrodes. That is, the asymmetric arrangement can be achieved by exchanging the positions of the segmented electrodes 1 and 2 in Figure 16 .
  • the segmented asymmetric electrode of this embodiment is similar to the segmented electrode in the aforementioned scenario 1.
  • the entire electrode transmits and the center electrode receives.
  • three central electrodes can be selected for reception.
  • the three central electrodes are short-circuited through pad connection lines.
  • the width of the pad connection lines should be as small as possible to minimize The area of the pad connection line.
  • the electrode is divided into (n+1)/2 blocks according to the highest order (such as expressed as n order, n is usually an odd number) mode used; the size of the block electrodes does not vary. 1.
  • the area of the center electrode ⁇ the area of the electrode adjacent to the center electrode, the area of the center electrode is greater than the area of the edge electrode, and the overall area and coverage area of the segmented electrode need to be basically close to the entire electrode (based on the first-order modal stress distribution);
  • the block electrodes are asymmetrically distributed along the central axis parallel to the short side; when energizing, all block electrodes work at the same time, and when receiving, only the middle part of the electrodes works. It can reduce the receiving sensitivity difference between the odd-order and even-order modes of the multi-mode PMUT, facilitating the coupling of multiple modes within -6dB, thereby achieving a large bandwidth.
  • FIG. 17 are array expansion forms of Embodiment 1. Specifically, (a) in Figure 17 is the expansion along the y direction of Embodiment 1. Of course, the expansion direction can also be x direction, provided that the characteristic size in the expansion direction is less than 1.5 times the wavelength. The number of repeating units in the expansion direction can be set according to the limits on the overall size of the device in the actual application scenario. (b) and (c) in Figure 17 are the derivation and array expansion in the unit arrangement direction of Embodiment 1. In Embodiment 1, the arrangement is limited to center symmetry.
  • Figures (b) and (c) in Figure 17 (c) is another centrally symmetrical arrangement, that is, the orthogonal arrangement of the reference subunit and the compensation subunit is changed to a parallel arrangement.
  • the difference between (b) and (c) in Figure 17 is that ( In b), the compensation subunit and the reference subunit are centrally aligned, while in Figure 17(c), they are staggered.
  • (d) and (e) in Figure 17 are array expansion forms of the third and fourth embodiments respectively.
  • the arrangement of the units can also be in other centrally symmetrical forms, which will not be described again here.
  • (f) in Figure 17 shows the expanded form of the PMUT array in the aforementioned scenario 4.
  • the PMUT array can be composed of PMUT units of a single size to achieve a large bandwidth effect.
  • the arrangement of the array The cloth form is symmetrical along the geometric center, and can also be expanded to an axially symmetrical structure.
  • multiple transducers are provided in the probe. As shown in Figure 18, the multiple transducers are arranged in an array. The multiple transducers form multiple channels, and the multiple channels are used to transmit and collect echo signals, thereby increasing the imaging area.
  • the transducer provided by the embodiment of the present application can be applied to scenarios that require large-scale detection, and can achieve high-sensitivity and large-area detection. When applied to ultrasonic imaging scenarios, it can use the large bandwidth provided by the present application. transducer to produce higher resolution ultrasound images.

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Abstract

一种换能器以及成像系统，通过不同尺寸的换能单元耦合而成的阵列，在同一个换能单元中可以实现基频段和谐波段的发射与接收，从而增加基频发射和接收带宽，并同时实现谐波成像。该换能器阵列包括：多个换能单元（401）在基底（402）上排列为阵列；每个换能单元的振膜包括结构层（504）、上电极（501）、压电层（502）和下电极（503）；该多个换能单元分为至少一个基准子单元（701）和至少一个补偿子单元（702），基准子单元（701）的长宽比不小于补偿子单元（702）的长宽比，基准子单元（701）用于在基频段和谐波段产生谐振，补偿子单元（702）在基频段或同时在基频段和谐波段产生谐振，且补偿子单元（702）在基频的谐振频率与基准子单元（701）在基频的谐振频率不同，从而扩宽基频收发带宽。

Description

一种换能器以及成像系统
本申请要求于2022年8月25日提交中国专利局、申请号为202211029594.X、申请名称为“一种换能器以及成像系统”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及超声成像领域，尤其涉及一种换能器以及成像系统。
背景技术
换能器在各种需要进行能量转换的场景中应用，如超声换能器可以实现机械信号，即声波信号和电信号的转换。以微机械压电超声波换能器(Piezoelectric micromachined ultrasonic transducer，PMUT)为例，PMUT是基于正逆电压效应实现声波信号和电信号的互相转换。在发射声波时，通过上下电极间施加交变信号，压电材料在逆压电效应下驱动振膜振动从而产生声波；接收声波时，振膜在外界声波驱动下振动，压电材料通过压电效应产生电荷并通过上下电极读取电信号，该电信号即可用于进行成像，如对反射声波的目标进行成像。
通常，PMUT的成像分辨率与PMUT的带宽相关，带宽越大，轴向分辨率也就越高。因此，如何提高换能器的成像分辨率，成为亟待解决的问题。
发明内容
本申请提供一种换能器以及成像系统，通过不同尺寸的换能单元耦合而成的阵列，在同一个换能单元中可以实现基频段和谐波段的发射与接收，从而增加基频的发射和接收带宽，并可以实现谐波成像的需求。
第一方面，本申请提供一种换能器，包括：多个换能单元和基底，多个换能单元在基底上排列为阵列；
具体地，每个换能单元包括上电极和下电极，当发射声波时，激励电信号施加在上电极和下电极上，以使振膜振动产生声波，接收声波时，换能单元产生形变，以使上电极和下电极之间产生电荷，并通过上电极和下电极输出接收电信号，接收电信号用于生成输出图像；
其中，该多个换能单元可以分为至少一个基准子单元和至少一个补偿子单元，基准子单元的长宽比不小于补偿子单元的长宽比，基准子单元的长宽比不小于第一阈值，以使基准子单元用于在基频段和谐波段产生谐振，补偿子单元在基频段产生谐振，该第一阈值为根据基频段和谐波段计算得到，换能单元的尺寸为根据该换能单元谐振的频率计算得到；并且，通常补偿子单元和基准子单元的尺寸与基准子单元的边长或者长宽比不完全相同，以使补偿子单元在基频段的谐振峰和基准子单元在基频段的谐振峰不相同，从而使补偿子单元和基准子单元在基频段内的谐振峰耦合，增加换能器在基频段的谐振带宽。并且，谐波段为基频的N倍频，该N为大于1的正整数，该谐波段可以是基频的二倍频、三倍频等，即谐波段可以包括三阶谐振、五阶谐振等谐振峰对应的频点。
需要说明的是，前述的基准子单元和补偿子单元的长宽比，为基准子单元和补偿子单元与基底垂直方向上的截面的长宽比，或者说朝向基底方向的截面的长宽比，该截面可以理解为至少具有两条互相垂直的对称轴，长宽比即该两条互相垂直的对称轴之间的比值。
因此，本申请实施方式中，在基底的表面设置了按照阵列排列的不同尺寸的换能单元，不同尺寸的换能单元可以对不同频段的接收波进行接收，在基频段实现不同子单元的各个谐振峰交错耦合达到波峰和波谷的互补效果，从而通过多谐振峰耦合获得基频大带宽的效果；且将各个换能单元的高阶模态设计为基频中心频率的二倍频附近，从而实现谐波接收的功能，进而实现谐波成像，提高成像分辨率。
在一种可能的实施方式中，可以根据基准子单元需在基频段和谐波段谐振的条件计算得到该第一阈值为即基准子单元的长宽比通常不小于可以保证谐波接收功能，使基准子单元的三阶模态至少位于一阶模态的二倍频处，实现对于基频段和谐波段的接收。
在一种可能的实施方式中，补偿子单元还在谐波段谐振。如可以调整补偿子单元的尺寸，从而使补 偿子单元在基频谐振从而拓宽基频段的带宽的同时，也能够实现谐波段接收，实现谐波成像。
在一种可能的实施方式中，至少一个基准子单元和至少一个补偿子单元在基底上呈中心对称排列，从而实现对称振动模态，可以实现对基频段和各个谐波段的接收，从而实现接收带宽的增大。
在一种可能的实施方式中，上电极包括多个分块电极，当上电极和下电极之间产生电荷时，通过多个分块电极的中心电极获取接收电信号，该中心电极可以包括与上电极的几何中心点距离最近的至少一个电极。因此，换能单元的上电极可以分为多个分块电极，在发射信号时，可以通过对不同的分块电极进行激励，实现不同的发射模态以及接收频段，在发射和接收时都能够实现大带宽发射和接收。
在一种可能的实施方式中，当发射声波时，对多个分块电极均进行激励；当接收信号时，通过中心电极获取接收电信号，即将各阶模态应力幅值最大且符号一致的区域作为接收电极，可以兼顾多种模态的接收，同时由于电极位置为每个模态的应力最大部分，故仅采用中心电极的接收灵敏度要高于依据各阶模态应力分布对应电极设计的接收灵敏度。
在一种可能的实施方式中，多个分块电极可以分为至少一个内电极和至少一个外电极，至少一个外电极包围至少一个内电极；当发射声波时，对至少一个外电极和至少一个内电极采用反相激励；当接收声波时，可以对至少一个外电极和至少一个内电极采用差分接收，从而通过内电极和外电极实现反相激励以及差分接收，可进一步增加接收电容，提高抗寄生干扰能力。
在一种可能的实施方式中，多个分块电极对称排列。因此，可以通过对称排列的分块电极，在采用中心电极接收信号时，使用中心电极来接收可以兼顾一、三、五阶等模态的接收灵敏度。
在一种可能的实施方式中，每个换能单元的多个分块电极呈非对称排列，从而采用非对称电极设计来激发振膜的非对称振动模态，抑制偶数阶模态(即波谷)的产生，减小奇数阶模态(比如1、3阶等)之间的灵敏度差异，从而增加带宽。
在一种可能的实施方式中，相邻的换能单元之间的距离不超过1.5倍基频波长，从而保证换能器阵列辐射声场中不出现栅瓣。
在一种可能的实施方式中，换能单元包括微机械压电超声波换能器PMUT单元，每个PMUT单元中上电极和下电极之间还设置了压电感应层。
在一种可能的实施方式中，换能单元包括微机械电容超声波换能器CMUT单元，上电极和下电极之间包括绝缘层，绝缘层中设置了空腔。
在一种可能的实施方式中，多个换能单元表面的形状可以包括椭圆或者具有至少两条中心对称轴的多边形(如矩形或者正方形等)中的至少一种，且基准子单元的长宽比大于1。
在一种可能的实施方式中，至少一个基准子单元表面的形状为矩形椭圆或者具有至少两条中心对称轴多边形中的至少一种，至少一个补偿子单元表面的形状为圆形或者正多边形。
在一种可能的实施方式中，阵列的宽度小于换能器的工作波长的1.5倍。
第二方面，本申请提供一种换能器，包括：基底和多个换能单元，所述多个换能单元排列在所述基底上；每个换能单元包括上电极和下电极，发射声波时，激励电信号施加在上电极和下电极上，以使振膜振动产生声波，当接收声波时，声波传输至换能单元时，换能单元产生形变，以使上电极和下电极之间产生电荷，并通过上电极和下电极输出接收电信号，接收电信号用于生成输出图像；其中，每个换能单元的的长宽比大于1，每个换能单元的上电极包括多个分块电极，该多个分块电极沿与基底的短边平行的中心轴呈非对称排列。
本申请实施方式中，采用非对称电极设计来激发振膜的非对称振动模态，激发偶数阶非对称模态的产生，减小奇数阶模态(比如1、3阶等)之间的灵敏度差异，从而增加收发带宽。
在一种可能的实施方式中，上电极中的分块电极的数量，与所需的最高阶模态相关，如电极的数量可以是(n+1)/2块，其所需的最高阶级为n阶模态，因此分块电极的数量可以根据实际应用场景调整，从而符合实际场景所需，泛化性强。
在一种可能的实施方式中，可以根据换能单元需在基频段和谐波段谐振的条件计算得到该第一阈值 为即基准子单元的长宽比通常不小于可以保证谐波接收功能，使基准子单元的三阶模态至少位于一阶模态的二倍频处，实现对于基频段和谐波段的接收。
在一种可能的实施方式中，可以根据基频段的频率计算得到该第一阈值为即基准子单元的长宽比通常不小于可以保证谐波接收功能，使基准子单元的三阶模态至少位于一阶模态的二倍频处，实现对于基频段和谐波段的接收。
在一种可能的实施方式中，当发射声波时，对多个分块电极均进行激励；当接收声波时，通过中心电极获取接收电信号，该中心电极为与上电极的中心点距离最近的至少一个电极，即将各阶模态应力幅值最大且符号一致的区域作为接收电极，可以兼顾多种模态的接收，同时由于电极位置为每个模态的应力最大部分，故仅采用中心电极的接收灵敏度要高于依据各阶模态应力分布对应电极设计的接收灵敏度。
在一种可能的实施方式中，多个换能单元表面的形状可以包括椭圆或者具有至少两条中心对称轴的多边形(如矩形或者正方形等)中的至少一种，增加了本申请提供的换能器的可制备性。
在一种可能的实施方式中，相邻的换能单元之间的距离不超过1.5倍基频波长，从而保证换能器阵列辐射声场中不出现栅瓣。
在一种可能的实施方式中，阵列的宽度小于换能器的工作波长的1.5倍。
在一种可能的实施方式中，换能单元包括微机械压电超声波换能器PMUT单元，每个PMUT单元中上电极和下电极之间还设置了压电感应层，压电感应层用于采集基于机械信号产生的电荷信号。
在一种可能的实施方式中，换能单元包括微机械电容超声波换能器CMUT单元，上电极和下电极之间包括绝缘层，绝缘层中设置了空腔。
第三方面，本申请提供一种成像系统，包括：探头以及处理器；
探头中设置如第一方面或第二方面任一可选实施方式提及的换能器；
探头用于向目标区域发射超声波，并接收目标区域返回的超声回波，以获得超声回波数据；
处理器用于根据超声回波数据生成超声图像。
可选地，该成像系统还可以包括：显示器，用于显示超声图像。
在一种可能的实施方式中，探头中设置了多个换能器，该多个换能器按照阵列排列。该多个换能器形成多个通道，如阵列中的每一列形成一个通道，该多个通道用于采集回波信号，从而实现高分辨率超声成像以及谐波成像。
附图说明
图1为本申请提供的一种成像系统的结构示意图；
图2为本申请提供的一种探头结构示意图；
图3为本申请提供的一种PMUT结构示意图；
图4为本申请提供的一种换能器的结构示意图；
图5为本申请提供的另一种PMUT单元的结构示意图；
图6为本申请提供的一种CMUT单元的结构示意图；
图7为本申请提供的另一种换能器的结构示意图；
图8为本申请提供的另一种换能器的结构示意图；
图9为本申请提供的一种换能器的接收效果示意图；
图10为本申请提供的另一种换能器的接收效果示意图；
图11为本申请提供的另一种换能器的结构示意图；
图12为本申请提供的另一种换能器的接收效果示意图；
图13为本申请提供的另一种换能器的接收效果示意图；
图14为本申请提供的另一种换能器的结构示意图；
图15为本申请提供的另一种换能器的接收效果示意图；
图16为本申请提供的另一种换能器的接收效果示意图；
图17为本申请提供的另一种换能器的结构示意图；
图18为本申请提供的另一种换能器的结构示意图。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本申请的说明书和权利要求书及上述附图中的术语“第一”、“第二”、“第三”、“第四”等(如果存在)是用于区别类似的对象，而不必用于描述特定的顺序或先后次序。应该理解这样使用的数据在适当情况下可以互换，以便这里描述的实施例能够以除了在这里图示或描述的内容以外的顺序实施。此外，术语“包括”和“具有”以及他们的任何变形，意图在于覆盖不排他的包含，例如，包含了一系列步骤或单元的过程、方法、系统、产品或设备不必限于清楚地列出的那些步骤或单元，而是可包括没有清楚地列出的或对于这些过程、方法、产品或设备固有的其它步骤或单元。
本申请提供的换能器可以应用于各种机械信号与电信号转换的场景，如穿戴设备、超声成像场景、超声测距或者通信场景等。具体地。例如，针对超声成像领域的大带宽和谐波成像需求，可以用于用户的组织成像，也可以应用于工业器件的检测探伤。又例如，可以在柔性基底中设置本申请提供的换能器，用于对用户的组织进行实时成像。
示例性地，本申请提供的成像系统可以如图1所示。该成像系统可以包括探头、处理器和显示设备，该探头可以向目标组织发送超声波，并接收从目标组织返回的回波信号，处理器可以对回波信号进行处理，生成超声图像。
可以理解为，成像探头向人体发射声波，成像组织反射声波并被成像探头接收，成像探头通过内部电路和算法对信号进行处理，然后将处理完的信号通过线缆或无线(图1中未示出)的方式传输到显示设备中，显示设备内置数据处理的APP，可将接收信号转换为图片信号并实时地显示出来。
具体地，该探头中可以设置本申请提供的换能器，在发送声波信号时，通过本申请提供的换能器将电信号转换为声波信号，并向外辐射，在接收声波信号时，通过本申请提供的换能器将声波信号转换为电信号。
该显示设备为可选设备，可以用于显示超声图像，从而便于用户观察目标组织的具体情况。当然，在一些场景中，也可以无需在显示设备中显示超声图像。
示例性地，以一种探头结构为例，如图2所示。探头中可以包括控制电路、模拟前端(analog front end,AFE)电路或换能器等。在换能器和AFE电路之间可以设置选择开关，用于在发送信号和接收信号之间切换。
可选地，可以在探头前端设置保护层或者声透镜结构等，保护层通常为聚合物材料，可以起到防物理冲击和化学腐蚀的作用，从而保护探头内部的电路结构。该声透镜可以用于会聚声波。
换能器设置在探头前端，当同时设置保护层时，换能器与保护层紧密贴合，该换能器用于超声的发射和接收，该换能器可以是本申请以下实施例提供的换能器。
在换能器的后端设置了AFE电路，通过切换开关来选择发射激励通道和回波接收通道，发射激励通道包括脉冲发射器，用于生成一定频率和复制的脉冲激励波形。回波接收电路可以包括时间增益补偿电路(time gain compensation，TGC)、低噪声放大电路(low noise amplifier,LNA)、滤波电路或者模数转换电路(analog to digital converter,ADC)等中的一种或者多种电路，用于对接收到的回波信号进行补偿、放大、过滤以及模数转换等操作。
AFE电路的后端可以设置控制芯片，如图2中所示，以该控制芯片为可编程逻辑门电路(field programmable gate array，FPGA)为例，可以用于进行信号控制和处理。
具体地，换能器可以将电能转换为声波信号发射到目标对象中，以PMUT为例，PMUT器件通过逆压电效应将电能转换为声能发射到成像对象，通过正压电效应将成像对象的回波声能转换为电信号。PMUT单元结构主体包括基底层(含有空腔，空腔平面尺寸决定振膜面积)、底电极、压电层和上电极。显然，换能器对于声波信号的接收至关重要。
以PMUT为例，PMUT结构可以如图3所示。
PMUT作为超声波收发器件可用于超声成像，超声成像的原理是利用不同成像组织的声阻抗差异而在各组织交界面产生声反射，通过接收反射声波并进行信号处理便可实现成像。为实现高分辨率超声成像，需从器件端优化PMUT的带宽：超声成像的纵向分辨率Rax＝C/2Δf，C为介质中的声速，通常受材料影响，Δf为带宽，显然，带宽大小直接影响分辨率的大小。此外，谐波成像功能也能极大地提升超声成像的对比度和横向分辨率。其工作原理是：通过接收发射声波在介质传播过程中由于非线性作用产生的谐波频段，通常主要为二倍频的声波进行成像，因此谐波成像需要换能器具备在基频的二倍频处的接收功能。
一些常用的PMUT通常实现的带宽不够，导致超声成像的效果也不佳。
例如，一些常用的PMUT器件，其中包括多个PMUT单元，上电极的形状可以是矩形或者椭圆形状，矩形(或椭圆)PMUT单元可以在基频带宽内激发出多个模态。通过调节不同矩形PMUT单元的谐振特征，实现波峰和波谷的互补补偿从而实现大带宽，且额外引入了矩形PMUT单元单独用于谐波段接收。然而，额外引入了PMUT单元仅用于谐波接收，将降低阵列的灵敏度，且基频发射单元与谐波接收单元在空间位置上不重叠，会影响谐波成像性能。
又例如，针对矩形PMUT的分块电极设计，电极分块设计依据一、三、五阶模态的应力分布，通过采用不同的激励电极配置激发出不同的PMUT模态，从而实现多频PMUT。然而，在一种电极配置下仅能激发出一种模态，即无法同时实现不同模态的激励，故该方案仅能实现多频PMUT，但各个模态无法在带宽内耦合，无法实现大带宽。且电极分块较多，引线及激励方式复杂。
还例如，多模态耦合PMUT单元结构采用非对称电极设计来激发PMUT振膜的非对称振动模态，抑制偶数阶模态(波谷)的产生，减小奇数阶模态(比如1、3阶)之间的灵敏度差异，实现-3dB带宽范围内的模态耦合。然而，该PMUT单元带宽增益有限。只考虑发射性能模态耦合，实现发射带宽增大，而没有考虑接收性能，接收带宽会变小，导致PMUT综合带宽并没有增大，因此对于成像效果并无增强。
因此，本申请提供一种换能器，通过不同尺寸的换能单元耦合而成的阵列，在同一个换能单元中可以实现大带宽的基频段收发和谐波段的接收，从而增加基频收发带宽，提高成像分辨率，且可以实现谐波成像的需求。
下面对本申请提供的换能器的结构进行介绍。
参阅图4，本申请提供的一种换能器的结构示意图。
该换能器可以包括多个换能单元401和基底402，该多个换能单元在基底上排列为阵列。
具体地，每个换能单元包括振膜，该振膜可以包括结构层、上电极和下电极，在发射声波时，激励电信号施加在上下电极上，以使振膜振动产生声波，当接收声波时，声波信号传输至振膜时，振膜产生形变，以使上电极和下电极之间产生电荷，并通过上电极和下电极输出接收电信号，该接收电信号用于生成输出图像。
其中，该多个换能单元可以基于尺寸划分为至少一个基准子单元和至少一个补偿子单元，即该至少一个基准子单元和该至少一个补偿子单元在基底上按照阵列排列，基准子单元的长宽比不小于补偿子单元的长宽比，基准子单元的长宽比不小于第一阈值，以使基准子单元可以用于在基频段和谐波段均产生谐振，补偿子单元可以在基频段产生谐振，该第一阈值可以根据基准子单元需进行谐振的基频段以及谐波段计算得到，即使基准子单元同时的基频段以及谐波段产生谐振时该基准子单元所需符合的长宽比，各个换能单元的尺寸可以根据需要谐振的频率特征计算得到，通常不同的尺寸，如不同的长宽比或者不同的边长等，可以实现对不同频段的声波信号的发送以及接收，从而通过不同尺寸的换能单元的耦合，使基准子单元和补偿子单元在基频段的多个频点谐振，从而实现基频段中多个频点的收发频段耦合，拓宽基频段的带宽。
因此，本申请实施方式中，在基底的表面设置了按照阵列排列的不同尺寸的换能单元，不同尺寸的换能单元可以对不同频段的接收波进行接收，在基频段实现不同子单元的各个谐振峰交错耦合达到波峰和波谷的互补效果，从而通过多谐振峰耦合获得基频大带宽的效果；且可以将各个换能单元的高阶模态设计为基频中心频率的二倍频附近，从而实现谐波接收的功能，进而实现谐波成像，提高成像分辨率。
需要说明的是，本申请中所提及的基频段中，为超声成像所需的频率，各个换能单元通常对基频段中的其中一个频点产生谐振，补偿子单元和基准子单元通常对基频段内的不同的频点产生谐振，从而在基频段实现不同子单元的各个谐振峰交错耦合达到波峰和波谷的互补效果，增加基频收发带宽。
且通常，输出的接收电信号的频率与换能单元的谐振频率相关。如接收电信号的频率包括换能单元的谐振频率或者与谐振频率临近的频率。
此外，为了使基准子单元和补偿子单元在基频段的不同频点谐振，可以为基准子单元和补偿子单元设置不同的尺寸，如设置不同的长宽比和/或不同的边长等，从而使基准子单元和补偿子单元的谐振峰为不同的频点，从而实现不同子单元的各个谐振峰交错耦合达到波峰和波谷的互补效果。如详细的换能单元的尺寸计算过程可以参阅以下所提及的场景一中的计算过程，此处不再赘述。
在一种可能的实施方式中，可以根据基准子单元需谐振的基频段的频率以及谐波频率计算得到该第一阈值为即基准子单元的长宽比通常不小于可以保证谐波接收功能，使基准子单元的三阶模态至少位于一阶模态的二倍频处，实现对于基频段和谐波段的接收。通常，为了保证换能单元对于谐波的接收，至少需要基准子单元的三阶模态位于一阶模态的二倍频处，可计算得到通常基准子单元的长宽比≥
在一种可能的实施方式中，补偿子单元还可以在谐波段谐振。如可以调整补偿子单元的尺寸，从而使补偿子单元在基频谐振从而拓宽基频段的带宽的同时，也能够实现谐波段接收，实现谐波成像。
当然，在一些场景中，补偿子单元也可以仅对谐波段产生谐振，从而增强谐波成像，具体可以根据实际应用场景进行调整。
可选地，前述的至少一个基准子单元和至少一个补偿子单元在基底上可以呈中心对称排列，从而实现对称的辐射声场，可以垂直或者接近垂直于基底向外辐射声波信号，可以实现对基频段和各个谐波段的发射以及接收。
可选地，上电极包括多个分块电极，当上电极和下电极之间产生电荷时，通过该多个分块电极的中心电极获取接收电信号，该中心电极可以理解为与上电极中的中心点距离最近的一个或者多个电极。因此，换能单元的上电极可以分为多个分块电极，在发射信号时，可以通过对不同的分块电极进行激励，实现不同的发射模态以及接收频段，在发射和接收时都能够实现大带宽发射和接收，进而实现大带宽成像。
具体地，在发射声波时，可以对该多个分快电极均进行激励，当接收声波时，可以通过中心电极来进行接收，即将各阶模态应力幅值最大且符号一致的区域作为接收电极，可以兼顾多种模态的接收，同时由于电极位置为每个模态的应力最大部分，故仅采用中心电极的接收灵敏度要高于依据各阶模态应力分布对应电极设计的接收灵敏度。
可选地，可以将多个电极分为至少一个内电极和至少一个外电极，该至少一个外电极包围内电极，当发射声波时，可以对内电极和外电极采用反向激励，当接收声波时，通过中心电极来进行差分接收，即内电极与外电极的接收信号的相位相反，中心电极可以包括设置于中轴线上的内电极和外电极，从而通过内电极和外电极实现差分接收，可进一步增加接收电容，提高抗寄生干扰能力。
在一种可能的场景中，换能单元中的各个分块电极对称排列，且通常沿与宽边平行的中心轴对称。因此，可以通过对称排列的分块电极，在采用中心电极接收信号时，使用中心电极来接收可以兼顾一、三、五阶等模态的接收灵敏度。
在另一种可能的场景中，换能单元中的多个分块电极也可以采用非对称排列，从而采用非对称电极设计来激发振膜的非对称振动模态，激发偶数阶非对称模态的产生，减小奇数阶模态(比如1、3阶等)之间的灵敏度差异，从而增加带宽。
或者说，本申请还提供一种换能器，该换能器与前述图4所示的换能器的区别在于，该换能器的上电极中可以包括多个分块电极，该多个分块电极在基底上沿与基底的短边平行的中心轴非对称排列。
可以理解为，本申请还提供的一种换能器，包括：基底和多个换能单元，所述多个换能单元排列在所述基底上；每个换能单元包括上电极和下电极，发射声波时，激励电信号施加在上电极和下电极上， 以使振膜振动产生声波，当接收声波时，声波传输至换能单元时，换能单元产生形变，以使上电极和下电极之间产生电荷，并通过上电极和下电极输出接收电信号，接收电信号的频率与每个换能单元产生谐振的频率相关，接收电信号用于生成输出图像；其中，每个换能单元的的长宽比大于1，每个换能单元的上电极包括多个分块电极，该多个分块电极沿与基底的短边平行的中心轴呈非对称排列。
在一种可能的实施方式中，上电极中的分块电极的数量，与所需的最高阶模态相关，如电极的数量可以是(n+1)/2块，其所需的最高阶级为n阶模态，因此分块电极的数量可以根据实际应用场景调整，从而符合实际场景所需，泛化性强。
在分块电极非对称排列的场景中，各个换能单元的尺寸结构可以参阅前述基准子单元的相关介绍，对于类似之处此处不再介绍。
例如，针对高频场景，通常此时无需接收谐波，可以设置换能单元中的多个分块电极呈非对称排列，如各个分块电极的尺寸不相同，从而实现主要对于基频段的接收，或者还可以兼顾低阶模态的接收，从而通过不同尺寸的分块电极实现对各个频段的波的接收，可以实现拓宽带宽。
通常，相邻的换能单元之间的距离不超过1.5倍基频波长，从而保证阵列的辐射声场不出现栅瓣。
在一种可能的场景中，前述的换能单元可以包括PMUT单元。每个PMUT单元中的振膜可以包括上电极、下电极和压电感应层，压电感应层设置在上电极和下电极之间，上电极和，该压电感应层可以用于采集基于声波信号产生的电荷信号。
例如，该PMUT单元的结构可以如图5所示，该PMUT单元的振膜、可以包括上电极501、压电感应层502、下电极503以及结构层504，该PMUT单元还可以包括基底505，基底505中设置空腔，压电感应层502设置在上电极501和下电极503之间。
当PMUT单元处于发射模式时，可以在上电极和下电极之间施加交变信号，压电感应层在逆压电效应下驱动振膜整体震动从而产生声波，并向外传输该声波，声波到达目标组织时，目标组织对超声波进行反射，从而反射回PMUT单元。
当PMUT单元处于接收模式时，经目标组织反射后的回波传输至振膜时，振膜在回波的驱动下震动，压电感应层通过压电小于产生电荷并传输至上下电极，通过上电极和下电极即可读取到接收电信号。
因此，本申请提供的换能单元可以采用PMUT结构，从而实现机械信号与电信号的转换，实现机械信号的发送以及接收。
在另一种可能的场景中，前述的换能单元可以包括微机械电容超声波换能器(Capacitive micromachined ultrasonic transducer，CMUT)单元。上电极和下电极之间设置有绝缘层，该绝缘层中设置了空腔。
例如，CMUT单元的结构可以如图6所示，该CMUT单元可以包括振膜，该振膜可以包括上电极601、绝缘层602、下电极603以及结构层604，该CMUT单元还可以包括基底605，绝缘层602中设置空腔，绝缘层602设置在上电极601和下电极603之间。
当CMUT单元处于发送模式时，可以在上电极和下电极之间加载电压，振膜将在静电力的作用下产生弯曲变形，从而通过在上电极和下电极施加所需频率的交变电压，激励振膜往复运动，实现将电能转换为机械能，并向外辐射能量，从而产生超声波。
当CMUT单元处于接收模式时，在上电极和下电极之间加载直流偏置电压，振膜在静电力和振膜回复力的作用下达到静态平衡，当经目标组织反射后的回波传输至振膜时，将激励振膜震动，上电极和下电极的空腔间距发生变化，引起上下电极之间的电容量的变化，从而输出接收电信号。
因此，本申请实施方式中，本申请提供的换能单元可以采用CMUT结构，从而实现机械信号与电信号的转换，实现声波信号的发送以及接收。
可选地，换能单元表面的形状即表面结构层或者基底层形成的形状，具体可以包括矩形、椭圆或者多边形中的至少一种。可以理解为，换能单元表面的形状可以包括椭圆或者具有至少两条垂直对称轴的多边形中的至少一种。
在一种可能的实施方式中，基准子单元表面的形状为椭圆或者具有至少两条中心对称轴多边形中的至少一种，补偿子单元表面的形状可以采用圆形或者正多边形等，补偿子单元可以用于对基频段产生谐振，从而使基准子单元可以对基频段和谐波段均实现谐振，提高收发信号的带宽。
在一种可能的实施方式中，阵列的宽度小于换能器的工作波长的1.5倍。从而使阵列实现对基频段和谐波段的信号接收。该宽度可以理解为换能器的基底宽度，通常是与较短的对称轴平行的边长，通常在制备上电极时，上电极组成的阵列的宽度通常与基底的宽度尽可能接近，以提高基底所能容纳的阵列的灵敏度，避免基底的面积浪费。
为便于理解，下面以PMUT为例(可以将换能器称为PMUT换能器)，对本申请提供的多种换能器的具体结构进行示例性说明，以下提及的PMUT也可以替换为CMUT或者其他的换能单元。
场景一、对称排列PMUT换能器
示例性地，本申请提供的另一种换能器的结构可以如图7所示。
首先，本申请提供的换能器中可以包括多种尺寸的PMUT单元，该多种尺寸的PMUT单元在基底上按照阵列排列耦合。如图7中所示，可以将PMUT单元分为基准子单元701和补偿子单元702，在基底703上排列为阵列。
具体地，本申请提供的PMUT换能器整体结构可以包括基底、底电极(下电极)、压电层和上电极四个部分。每个PMUT单元的结构的沿x轴和y轴的截面可以参阅图8，每个单元的上电极均分为内电极和外电极两部分，且内电极与外电极均为分块电极。
基底材料通常可以为硅，也可以为玻璃或有机聚合物等材料，基底通常被刻蚀产生空腔结构，从而便于空腔上部的结构振动；下电极和上电极用于为压电层提供激励信号或采集压电层由应力作用产生的电荷信号，下电极和上电极材料可以为各种导电材料，包括金属材料Al、Au、Ag、Pt、Cu、Mo、Ti等，或一些导电聚合物材料等；压电层材料主要包括AlN及其合金材料(ScxAl1-xN)、ZnO及其合金材料(VxZn1-xO)、PZT及其合金材料(PLZT、PNZT)、KNN(KxNa1-xNbO3)、PMN-PT、PVDF或PVDF-TRFE等，具体可以根据实际应用场景来选择。
按照尺寸大小可以将PMUT单元分为基准子单元和补偿子单元，基准子单元与补充子单元在排布上需满足中心对称排布，且子单元的边界之间的间隔进可能接近(如按照制造工艺设置为最近距离)，通常上限为1.5倍基频波长；阵列整体尺寸需满足在x轴或y轴方向小于1.5倍波长。
本申请提供的不同尺寸PMUT单元耦合结构，可以同时实现基频大带宽和谐波接收效果。例如，如图9中PMUT单元几何尺寸的仿真结果。显然，通过不同尺寸的PMUT单元耦合，在基频段实现不同子单元的各个谐振峰交错耦合达到波峰和波谷的互补效果，从而通过多谐振峰耦合获得基频大带宽的效果；同时将各个子单元的高阶模态设计为基频中心频率的二倍频附近，从而实现谐波接收的功能。
具体地，以矩形的PMUT单元为例，可从矩形PMUT单元各阶模态的特征频率计算公式归纳出几何结构特征。下列公式中，f0为一阶模态的特征频率，fm,1为沿长边方向的m阶模态的特征频率，L为短边长度，k为长宽比，T为振膜的弯曲刚度，σ为面密度。

从上述各个子单元的谐振耦合效果出发，需一类子单元在基频段和谐波段分别至少有一个谐振峰，即基准子单元，另一类子单元在基频段和/或谐波段分别至少有一个谐振峰，即补偿子单元。由公式2可知，长宽比k越大，高阶模态的特征频率越接近一阶模态的特征频率，为保证基准子单元较于补偿子单元在基频和谐波段具有更多的模态，基准子单元的长宽比不小于补偿子单元的长宽比。
通常，为保证谐波接收功能，至少需要基准子单元的三阶模态位于一阶模态的二倍频处，即f3,1＝2f0， 可得故基准子单元的长宽比
此外，为实现基准子单元和补偿子单元的有效耦合，补偿子单元的一阶谐振峰应位于基准子单元的一阶谐振峰附近，由公式1可得，在PMUT各层材料的种类和厚度确定的情况下(即T和σ为定值时)，矩形PMUT单元的一阶谐振频率主要取决于短边长度(即宽度)，设补偿子单元的一阶谐振频率位于基准子单元的一阶和三阶频率之间，并取k＝1，可得补偿子单元宽度的范围为基准子单元的宽度相近，如差距在±45％内。
因此，本申请提供的PMUT单元表面的几何尺寸的特征为：不同尺寸PMUT单元分为基准子单元和补偿子单元，基准子单元长宽比大于且基准子单元的长宽比≥补偿子单元的长宽比，补偿子单元的宽度与基准子单元的宽度相近(±45％内)。
此外，为了保证PMUT阵列辐射声场的z轴对称指向性，基准子单元与补偿子单元的排布需满足中心对称分布条件。此外，为提高阵列的整体面积利用率(即振膜面积/阵列整体面积)，不同PMUT单元间的间距需尽可能的小，具体范围可以根据工艺误差来确定。
并且，在满足阵列整体尺寸在x或y其中一个方向小于1.5倍波长的条件下，基准子单元的数量可以增加，即可以设置多个基准子单元，补偿子单元也可包括多个不同长宽比或不同宽度的PMUT单元。
其次，本申请提供的PMUT单元的上电极可以设置为多个分块电极，且可以分为内电极和外电极，从而兼顾多模态PMUT单元在各个模态下都具有较高的接收灵敏度。例如，本申请提供的PMUT单元的不同模态的应力分布仿真效果可以参阅图10。
具体地，在PMUT振膜振动过程中，振膜上存在拉(如称为正应力)、压(如称为负应力)应力两类区域。这两类区域产生的电荷极性相反，若某个电极同时覆盖拉、压应力区域，则压电材料产生的电荷会相互抵消，从而牺牲接收灵敏度。因此本申请将分块电极分为内电极和外电极，相对于整块接收信号，本申请提供的内外分块电极可以将仅针对单一模态拓展到兼顾多模态，如图10所示，矩形PMUT在一、三、五阶模态下的应力分布差异较大(此处仅以一、三、五阶模态为例，也可以替换为其他阶模态)，依照各阶模态的应力分布设计电极通常只能保证其对应模态的接收灵敏度，而牺牲其他模态的接收灵敏度。
而本申请提供的采取各阶模态应力幅值最大且符号一致的区域作为接收电极，即中心部分(称为中心电极)。采用中心电极作为接收电极可兼顾一、三、五阶模态的接收灵敏度，同时由于电极位置为每个模态的应力最大部分，故仅采用中心电极的接收灵敏度要高于依据各阶模态应力分布对应电极设计的接收灵敏度。
此外，各阶模态的应力分布可发现其外电极的中心部分的应力也保持一致，因此本申请额外引入外电极分布设计，通过内外电极差分接收，可进一步增加接收电容，提高抗寄生干扰能力。
如图10中所示，采用中心电极与整块电极接收时的谐振峰频率有差异，通常是由于中心电极与边缘电极受一、三、五阶模态应力影响不一致而造成的。
具体例如，针对内外电极的收发设置电路可以如图11所示，在发射模式下需要对整块电极激励，而在接收时，采用中心电极接收，通过如图11中所示的收发切换开关来实现发射与接收电极的切换，内外电极采用反相激励和差分接收。具体可以依据PMUT一阶模态的拉、压应力分布将上电极分为内电极、外电极两部分；内电极与外电极均独立设置几何中心部分作为接收区域，其中内电极中心电极的长度为内电极整体的1/9-1/3，通常中心电极的长度可以按照模态确定,比如五阶模态的中心电极为1/5；外电极的中心电极与内电极的中心电极等长。本申请提供的PMUT单元在发射时是整块电极激励，其谐振峰频率与整块电极接收一致，因此采用中心电极接收可以使得发射谐振峰与接收谐振峰避开，这样可以实现发射与接收频带的互补，从而增大收发综合带宽。
场景二、椭圆形换能器
其中，PMUT单元的形状可以包括一些具有长宽比的形状，即具有长轴和短轴，如椭圆、多边形(菱形到n边形)、以及长轴、短轴通过任意曲线构成的不规则几何体。
本实施例以椭圆为例，椭圆形的PMUT单元和矩形PMUT单元的接收波段对比可以如图12所示。显然，椭圆结构与矩形结构类似，也具有多模态特征。进一步地，其各阶模态的也可以通过调整椭圆PMUT的长宽比特征进行调节，因此椭圆结构亦可通过尺寸调节实现矩形PMUT中相同或类似的效果。
此外，由于在相同长宽比下，椭圆各阶模态的频率差异要大于矩形结构(即图10中相同长宽比下，椭圆在2-8MHz的扫频范围内仅有两个模态，而矩形有三个模态)，因此矩形PMUT单元中针对矩形结构的尺寸特征点(如长宽比大于)涵盖了椭圆的结构特征。其他关于矩形PMUT结构的尺寸特征点亦适用于椭圆，包括单元间的间隔和数量、中心对称的排布方式，分块内外电极设计等，此处不再赘述。
场景三、圆形补偿子单元
在一种可选的实施方式中，基准子单元可以采用具有一定长宽比的形状的PMUT，补偿子单元则可以采用不具备长宽比结构特征的几何结构，如圆形、正方形或正多边形等。
以圆形补偿子单元为例，圆形补偿子单元与矩形基准子单元耦合的结构及其仿真效果可以参阅图13。可将矩形PMUT视为基准子单元，圆形PMUT视为补偿子单元。通过不同尺寸的圆形PMUT单元对矩形PMUT一、三阶模态间的波谷补偿可以同样实现基频大带宽的效果，但由于圆形PMUT的高阶模态离基频模态较远且不可调，如依据圆形PMUT不同模态谐振频率的计算公式，其前两阶模态的频率比值为3.9。圆形PMUT单元只可用于对基频段波进行接收，而无法对谐波进行接收。因此，本申请实施例中，可以通过基准子单元和补偿子单元来实现基频大带宽，仅通过基准子单元实现谐波接收功能。
场景四、上电极非对称排列
前述场景一种，上电极的分块设计是从最大化各阶模态的接收灵敏度角度出发的，且主要是针对低阶模态，如一、三、五阶，本实施例将进一步从综合接收灵敏度和带宽的角度出发，拓展电极分块设计。
其中，本申请实施例还提供另一种换能器，该换能器中的PMUT单元的上电极可以分为多个分块电极，该多个分块电极为不对称排列，且每个PMUT单元那种分块电极的数量与所需的接收，模态相关，如所需模态越高阶，所需的分块电极数量越多。
例如，参阅图14，本申请提供的另一种换能器的结构示意图，图15和图16为基于非对称排列的PMUT单元的发射灵敏度和接收灵敏度效果。
与前述场景一中提及的换能单元的区别在于，上电极沿与宽边平行的中心轴呈非对称排列。通过不对称分块电极，可在单一尺寸PMUT单元或其组成的阵列形成大带宽。
本实施例示例性地，以九阶模态为例，可以依据九阶模态的应力分布设置分块电极，可增大九阶模态的收发灵敏度，从而解决在传统整块电极结构激励和接收情况下，由于九阶模态的收发灵敏度偏低而无法与三、五、七阶模态在-6dB耦合的问题。
首先，分块电极的数目取决于所需优化的模态阶数n＝9，即分块电极数目等于(n+1)/2＝5块。针对每块电极的尺寸，在宽度方向上，与前述场景一种类似，每块电极的宽度一致或者接近，取为一阶模态内、外应力分界处。在长度方向上，若完全依照九阶模态的应力分布设计，则每块电极的长度为内电极整体长度的1/9，这将提升九阶模态灵敏度但牺牲其他阶模态(三、五、七)的灵敏度，因此为了在不牺牲其他阶模态的灵敏度情况下，分块电极的整体面积选为与整块电极面积基本一致或者接近。其中分块电极间的间隙取为最小化与整块电极面积的差异。对于每块电极的尺寸，基于仿真的优化结果，一般选取中心电极的尺寸b为九阶模态的最优尺寸a(内电极尺寸的1/n)附近(b＝a-1.8a)，与中心电极相邻的电极尺寸(b-2b)大于中心电极尺寸，外围电极尺寸(＜b)小于中心电极尺寸。
在分块电极的排布上，为提高接收灵敏度各阶谐振峰间波谷位置处的灵敏度，以实现各阶模态在-6dB范围内更好地耦合，本实施例提出将分块电极沿与宽平行的中心轴非对称排布。如图15所示，常 用的分块电极沿中心轴x、y均对称分布，而本实施例的非对称电极仅沿x轴对称分布，而沿y轴非对称分布，其实现效果可参考图15中右侧的接收灵敏度曲线图，非对称电极设计可将三五阶和五七阶间的灵敏度提升。在实现方式上，本实施例的非对称电极是在上述分块电极的基础上实现的，即将图16的分块电极1、2的位置对调即可实现非对称排布。
在工作模式上，本实施例的分块不对称电极与前述场景一中的分块电极类似，均为整块电极发射，中心电极接收。例如，可以本实施例选用中心3块电极接收，为方便引线，本实施例将中心3块电极通过pad连接线短接，其中pad连接线的宽度应取为尽量减小，以尽可能减小pad连接线的面积。
因此，在本申请实施方式中，电极分块根据所利用的最高阶(如表示为n阶，n通常为奇数)模态将电极分成(n+1)/2块；分块电极的大小不一，其中中心电极面积＜与中心电极相邻的电极面积，中心电极面积大于边缘电极面积，分块电极整体面积和覆盖区域需和整块电极(基于一阶模态应力分布)基本接近；分块电极沿与短边平行的中心轴不对称分布；激励时，所有分块电极同时工作，接收时，仅中间部分电极工作。可以实现对多模态PMUT奇数阶与偶数阶模态的接收灵敏度差值减小，便于多个模态在-6dB内耦合，从而实现大带宽。
场景五、大规模排列阵列
前对对本申请提供的PMUT换能器的各种结构进了介绍，在此基础上，还可以实现更大规模的阵列结构，如图17所示。图17中(a)、(b)、(c)为实施例一的阵列拓展形式，具体地，图17中(a)为实施例一沿y方向的拓展，当然，拓展方向也可以为x方向，前提是其拓展方向的特征尺寸小于1.5倍波长，拓展方向上重复单元的数目可根据实际应用场景对器件整体尺寸的限定而设置。图17中(b)和(c)为实施例一在单元排布方向上的衍生和阵列拓展，实施例一中对排布方式的限定为中心对称即可，图17中图(b)和(c)便是另一种中心对称的排布方式，即由基准子单元和补偿子单元的正交排布改成平行排布，图17中(b)和(c)的差别在于图(b)中补偿子单元与基准子单元为中心对齐排布而图17中(c)为交错排布。图17中(d)和(e)分别为实施例三和四的阵列拓展形式，当然，与前述场景一类似，其单元的排布也可为其他中心对称形式，在此不再赘述。图17中(f)为前述场景四中的PMUT阵列拓展形式，如前所述，采用分块不对称电极后，PMUT阵列可由单一尺寸的PMUT单元构成而实现大带宽效果，此外该阵列的排布形式为沿几何中心对称，也可以拓展为轴对称结构。
例如，本申请提供的成像系统中，在探头中设置了多个换能器，如图18所示，该多个换能器按照阵列排列。该多个换能器形成多个通道，该多个通道用于发射、采集回波信号，从而增大成像面积。
因此，本申请实施例提供的换能器，可以应用于需进行大规模探测的场景，可以实现搞灵敏度且较大面积的探测，当应用于超声成像场景时，可以通过本申请提供的大带宽换能器，生成分辨率更高的超声图像。
以上所述仅为本申请的可选实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。

Claims (19)

  1. 一种换能器，其特征在于，包括：基底和多个换能单元，所述多个换能单元在所述基底上排列为阵列；
    每个换能单元包括上电极和下电极，发射声波时，激励电信号施加在所述上电极和所述下电极上，以使振膜振动产生声波，当接收声波时，声波传输至所述换能单元时，所述换能单元产生形变，以使所述上电极和所述下电极之间产生电荷，并通过所述上电极和所述下电极输出接收电信号，所述接收电信号用于生成输出图像；
    其中，所述多个换能单元分为至少一个基准子单元和至少一个补偿子单元，基准子单元的长宽比不小于补偿子单元的长宽比，所述基准子单元的长宽比不小于第一阈值，以使所述基准子单元用于在基频段和谐波段产生谐振，所述补偿子单元在基频段产生谐振，所述第一阈值为根据所述基频段和所述谐波段得到，所述换能单元的尺寸为根据产生谐振的频率计算得到。
  2. 根据权利要求1所述的换能器，其特征在于，所述第一阈值为
  3. 根据权利要求1或2所述的换能器，其特征在于，所述补偿子单元还在谐波段谐振。
  4. 根据权利要求1-3中任一项所述的换能器，其特征在于，所述上电极包括多个分块电极，当所述上电极和所述下电极之间产生电荷时，通过所述多个分块电极中的中心电极获取所述接收电信号，所述中心电极包括与所述上电极的中心点距离最近的至少一个分块电极。
  5. 根据权利要求4所述的换能器，其特征在于，
    当发射声波时，对所述多个分块电极均进行激励；
    当接收声波时，通过所述中心电极获取所述接收电信号。
  6. 根据权利要求4或5所述的换能器，其特征在于，所述多个分块电极分为至少一个内电极和/或至少一个外电极，所述至少一个外电极包围所述至少一个内电极；
    当发射声波时，对所述至少一个外电极和所述至少一个内电极采用反相激励；
    当接收声波时，对所述至少一个外电极中的中心电极与所述至少一个内电极中的中心电极采用差分接收。
  7. 根据权利要求4-6中任一项所述的换能器，其特征在于，所述多个分块电极对称排列。
  8. 根据权利要求1-7中任一项所述的换能器，其特征在于，
    所述多个换能器在所述基底上呈中心对称排列。
  9. 根据权利要求1-8中任一项所述的换能器，其特征在于，相邻的换能单元之间的距离不超过1.5倍基频波长。
  10. 根据权利要求1-9中任一项所述的换能器，其特征在于，所述换能单元包括微机械压电超声波换能器PMUT单元，所述每个PMUT单元中所述上电极和所述下电极之间还设置了压电感应层。
  11. 根据权利要求1-9中任一项所述的换能器，其特征在于，所述换能单元包括微机械电容超声波换能器CMUT单元，所述上电极和所述下电极之间包括绝缘层，所述上电极和所述下电极间还设置了空腔结构。
  12. 根据权利要求1-11中任一项所述的换能器，其特征在于，所述多个换能单元的形状包括矩形、椭圆或者具有至少两条中心对称轴多边形中的至少一种，且所述基准子单元的长宽比大于1。
  13. 根据权利要求12所述的换能器，其特征在于，所述至少一个补偿子单元表面的形状包括长宽比等于1的圆形或者正多边形。
  14. 根据权利要求1-13中任一项所述的换能器，其特征在于，所述阵列的宽度小于所述换能器的工作波长的1.5倍。
  15. 一种换能器，其特征在于，包括：基底和多个换能单元，所述多个换能单元排列在所述基底上；
    每个换能单元包括上电极和下电极，发射声波时，激励电信号施加在所述上电极和所述下电极上，以使振膜振动产生声波，当接收声波时，声波传输至所述换能单元时，所述换能单元产生形变，以使所述上电极和所述下电极之间产生电荷，并通过所述上电极和所述下电极输出接收电信号，所述接收电信号用于生成输出图像；
    其中，每个换能单元的长宽比大于1，每个换能单元的上电极包括多个分块电极，所述多个分块电极呈非对称排列。
  16. 根据权利要求15所述的换能器，其特征在于，
    当发射声波时，对所述多个分块电极均进行激励；
    当接收声波时，通过设置于所述换能器的中心电极获取所述接收电信号，所述中心电极包括与所述上电极中心点距离最近的至少一个分块电极。
  17. 一种成像系统，其特征在于，包括：探头以及处理器；
    所述探头中设置至少一个如权利要求1-16中任一项所述的换能器；
    所述探头用于向目标区域发射超声波，并接收所述目标区域返回的超声回波，以获得超声回波数据；
    所述处理器用于根据所述超声回波数据生成超声图像。
  18. 根据权利要求17所述的成像系统，其特征在于，所述成像系统还包括：
    显示器，用于显示所述超声图像。
  19. 根据权利要求17或18所述的成像系统，其特征在于，所述探头中设置了多个换能器，所述多个换能器按照阵列排列。
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