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EP-4504428-B1 - PIEZOELECTRIC MICRO-MACHINED ULTRASONIC TRANSDUCER

EP4504428B1EP 4504428 B1EP4504428 B1EP 4504428B1EP-4504428-B1

Inventors

  • DAHL, TOBIAS
  • TYHOLDT, FRODE

Dates

Publication Date
20260506
Application Date
20230331

Claims (15)

  1. A piezoelectric micro-machined ultrasonic transducer, PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702), arranged to interface with an amorphous medium such that in use ultrasonic signals to or from the PMUT pass through said amorphous medium, said amorphous medium (16) comprising a plurality of discrete reflectors (10; 110a, 110b; 111a, 111b; 210a, 210b) distributed therein, and characterised in that the discrete reflectors form a mesh or a porous membrane.
  2. The PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702) according to claim 1, arranged to interface with an acoustic resonance cavity (4; 104; 204; 304; 404; 504; 604; 704), the acoustic resonance cavity comprising the amorphous medium (16).
  3. The PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702), according to any preceding claim, wherein the discrete reflectors (10; 110a, 110b; 111a, 111b; 210a, 210b) are distributed in two-dimensions.
  4. The PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702) according to claim 2 or 3, wherein the discrete reflectors (10; 110a, 110b; 111a, 111b; 210a, 210b) have positions which are adjustable in use to adjust an acoustic property of the acoustic resonance cavity (4; 104; 204; 304; 404; 504; 604; 704).
  5. The PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702), according to any of claims 2 to 4, wherein a piezoelectric contraction element is arranged around the acoustic resonance cavity (4; 104; 204; 304; 404; 504; 604; 704).
  6. The PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702), according to any of claims 2 to 5, wherein a property of the acoustic resonance cavity (4; 104; 204; 304; 404; 504; 604; 704) is arranged to be adjusted as a frequency of a signal emitted by the PMUT changes during a chirp transmission.
  7. The PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702), according to any preceding claim, wherein the PMUT comprises a dedicated ultrasonic transmitter and at least one separate ultrasonic receiver on a single common semiconductor die.
  8. The PMUT (2; 102; 202; 302; 402a-402c; 502; 602; 702), according to any preceding claim, wherein the PMUT is mounted so as to be moveable by an actuator.
  9. A system for transmitting and receiving ultrasonic signals comprising: at least first and second PMUTs (2; 102; 202; 302; 402a-402c; 502; 602; 702), as claimed in any one of claims 1 to 8, a transmitter circuit arranged to drive said first PMUT as an ultrasonic transmitter and a receiver circuit arranged to detect signals from said second PMUT as an ultrasonic receiver.
  10. An arrangement comprising a plurality of PMUTs (2; 102; 202; 302; 402a-402c; 502; 602; 702), as claimed in any one of claims 1 to 8.
  11. The arrangement according to claim 10, wherein the PMUTs (2; 102; 202; 302; 402a-402c; 502; 602; 702) are spaced by λ/2, wherein λ is the wavelength of a central frequency over the range of frequencies at which the PMUTs transmit or receive.
  12. The arrangement according to claim 10 or 11, wherein the plurality of the PMUTs (2; 102; 202; 302; 402a-402c; 502; 602; 702) are arranged in an array and wherein the array is mounted so as to be moveable by an actuator.
  13. The arrangement according to any one of claims 10 to 12, wherein the plurality of the PMUTs (2; 102; 202; 302; 402a-402c; 502; 602; 702) are arranged in an array and wherein the array is not flat.
  14. The arrangement according to any one of claims 10 to 13, wherein the plurality of the PMUTs (2; 102; 202; 302; 402a-402c; 502; 602; 702) are arranged in an array and wherein different PMUTs in the array are of different sizes.
  15. A plurality of acoustic resonance cavities (4; 104; 204; 304; 404; 504; 604; 704), each acoustic resonance cavity comprising an array of PMUTs (2; 102; 202; 302; 402a-402c; 502; 602; 702 as claimed in any one of claims 1 to 8 arranged to interface with the acoustic resonance cavity.

Description

This invention relates to housings for ultrasonic transducers. Ultrasonic transducers are devices that generate and receive sound waves with frequencies higher than those audible to humans. They can be used in many applications from simple ranging applications, where the distances to objects can be estimated by measuring the time between transmitting an ultrasound signal and receiving a reflected echo signal, to complex medical imaging applications. US10118054B2 describes an implantable device having a sensor configured to detect an amount of an analyte, a pH, a temperature, strain, or a pressure, and an ultrasonic transducer with a length of about 5 mm or less in the longest dimension, configured to receive current modulated based on the analyte amount, the pH, the temperature, or the pressure detected by the sensor, and emit an ultrasonic backscatter based on the received current. JP2001359287A describes a surface acoustic wave optical element comprising a piezoelectric film provided on a substrate. The piezoelectric film is configured to generate a surface acoustic wave so as to remove foreign material from the substrate, such as water droplets adhered to the substrate. US2017/0217794 describes a transducer and/or reflector that is a thin, non-planar structure arranged to separate particles or droplets from a host fluid. The thin, non-planar structure improves the operation of an acoustic standing wave generated by an acoustic transducer. The structure may operate as a pressure release boundary and may be constructed as plastic film. In many applications it is important to make transducers as small as possible - either because they are to be fitted into a small device or to allow large arrays to be used. One technology that has been developed for this purpose is that of piezoelectric micro-machined ultrasonic transducers (PMUTs) where a PMUT element may typically act as both a transmitter and receiver when coupled to the appropriate circuitry. Housings for ultrasonic transducers may be used to protect the PMUTs from external wear and tear. It is an object of the invention to provide improvements in certain aspects over currently available PMUTs. When viewed from a first non-claimed aspect, the present disclosure provides a piezoelectric micro-machined ultrasonic transducer (PMUT) arranged to interface with an acoustic resonance cavity, wherein the acoustic resonance cavity has at least one acoustic property which is adjustable in use depending on a signal being transmitted or received by the PMUT. The disclosure extends to a non-claimed method of imaging using the PMUT described above. Thus it will be seen by those skilled in the art that in accordance with the disclosure set out above, an acoustic property of the acoustic resonance cavity with which the PMUT interfaces is adjustable. Through adjustment of a property of the acoustic resonance cavity, an outgoing or incoming ultrasonic impulse or signal may be modified. The Applicant has recognised that this may be beneficial - e.g. to improve ultrasonic imaging - by improving the efficiency with which a PMUT produces an image. In a set of embodiments, the adjustable property is the acoustic resonance volume of the acoustic resonance cavity. For example, the acoustic resonance volume of the acoustic resonance cavity may be adjusted to match its resonant frequency to the outgoing frequency of a transmitted ultrasonic signal. This allows the cavity to be optimised even when the frequency used is not constant as will often be the case in a typical application. By matching the resonant frequency of the cavity to the outgoing frequency, the effective signal strength may be maximised for a given drive power. Similarly, matching the resonant frequency to that of an incoming signal may maximise the effective received signal strength of an ultrasonic receiver. The acoustic resonance volume may be adjusted in multiple ways, and in a set of embodiments, the acoustic resonance cavity comprises a deformable diaphragm, wherein a position and/or shape of the diaphragm is adjustable to adjust the acoustic resonance volume of the cavity. In some embodiments, the PMUT is provided on the deformable diaphragm such that the PMUT itself also moves with the diaphragm to adjust the volume within the acoustic resonance cavity. Alternatively, to adjust the properties of acoustic resonance cavity, in a set of embodiments the acoustic resonance cavity comprises an amorphous medium through which said ultrasonic signals pass in use, said amorphous medium comprising a plurality of discrete reflectors distributed therein. wherein the discrete reflectors have positions which are adjustable in use to adjust said acoustic property of the acoustic resonance cavity. The Applicant has recognised that having a plurality of discrete reflectors in an amorphous medium is novel and inventive in its own right, and thus according to the present invention, there is provided a piezoelectric micro-mach