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EP-4021275-B1 - ULTRASOUND TRANSDUCER DEVICES AND METHODS

EP4021275B1EP 4021275 B1EP4021275 B1EP 4021275B1EP-4021275-B1

Inventors

  • MOEHRING, MARK A.
  • KREINDLER, Daniel
  • GATES, GEORGE
  • CAMERON, Caitlin E.

Dates

Publication Date
20260506
Application Date
20200827

Claims (15)

  1. An ultrasound transducer comprising: a plurality of capacitive ultrasound transducer elements (100); and a base (102) having a largest dimension sized and shaped to be disposed with an external ear canal, wherein the plurality of capacitive ultrasound transducer elements (100) is mounted on the base (102); wherein the ultrasound transducer has an angular beam spread through a gaseous medium of greater than 15 degrees and an attenuation loss through the gaseous medium of greater than 10 dB measured at a distance 12.5 mm to 25 mm along a primary transmission axis of the ultrasound transducer.
  2. The ultrasound transducer of claim 1, wherein the largest dimension of the base (102) is less than 3 mm.
  3. The ultrasound transducer of claim 1, wherein the plurality of capacitive ultrasound transducer elements (100) at least one of: has a resonant frequency between 1.0 MHz and 3.0 MHz; has an average capacitance between 2.5 pF and 10.0 Pf; has an average cavity height of less than 1500 nm; or comprises at least 20 capacitive ultrasound transducer elements.
  4. The ultrasound transducer of claim 1, wherein each capacitive ultrasound transducer element (100) of the plurality of capacitive ultrasound transducer elements has a working surface with a diameter between 10 and 100 microns.
  5. The ultrasound transducer of claim 1, wherein the ultrasound transducer has an edge length of less than 1.5 mm.
  6. The ultrasound transducer of claim 1, wherein the ultrasound transducer is configured to be disposed within a speculum of an otoscope.
  7. The ultrasound transducer of claim 1, wherein one or more of the plurality of capacitive ultrasound transducer elements (100) has a plurality of openings in a working surface of one or more of the transducer elements (100), optionally wherein the plurality of openings at least one of: is arranged in a circle with a diameter of at least 10 microns; comprises at least three release holes per capacitive ultrasound transducer element; is circular or curved in shape; or comprises release slits with a slit-width of a least 0.4 microns and a spring length of a least 2 microns.
  8. The ultrasound transducer of claim 1, wherein the plurality of capacitive ultrasound transducer elements (100) is arranged on the base with a hexagonal closest packing structure, or wherein the plurality of capacitive ultrasound transducer elements (100) is arranged on the base within a circular area with a diameter equal to the edge length, or wherein the plurality of capacitive ultrasound transducer elements (100) is arranged on the base within a rectangular area with a longest side equal to the edge length.
  9. The ultrasound transducer of claim 1, wherein the ultrasound transducer has an 80% pull in voltage of less than 85 V.
  10. The ultrasound transducer of claim 1, wherein the ultrasound transducer has a signal to noise ratio greater than 15 dB measured at a distance 12.5 mm to 25 mm along a primary transmission axis of the transducer.
  11. The ultrasound transducer of claim 1, wherein the ultrasound transducer has a fractional bandwidth that exceeds 10%.
  12. The ultrasound transducer of claim 1, wherein the ultrasound transducer has a projected intensity of about 10 Pa or more measured at a distance 12.5 mm to 25 mm along a primary transmission axis of the transducer.
  13. The ultrasound transducer of claim 1, wherein the ultrasound transducer has a frequency bandwidth of plus or minus 25% of center frequency at full width at half maximum.
  14. A system comprising: the ultrasound transducer of any of claims 1 to 13 and a speculum, wherein the ultrasound transducer is disposed with the speculum and wherein the speculum is configured to be removably coupled an otoscope.
  15. A method of measuring a fluid, the method comprising: providing the ultrasound transducer of any of claims 1 to 14; applying a pneumatic challenge to a surface of the fluid; and observing with the ultrasound transducer a perturbation in a waveform reflected from the surface in response to the pneumatic challenge.

Description

This application relates to ultrasound transducers. BACKGROUND Determination of an elasticity of a membrane or a viscosity of a fluid may be of interest to a variety of fields including medical diagnosis, medical imaging, manufacturing quality control, food product characterization, industrial process analysis, etc. In many of these applications, it may be beneficial to measure a reflected ultrasound signal using an air-coupled transducer which is small in size. However, small size may pose significant challenges for transducer performance. In an example, it may be beneficial to characterize a fluid adjacent a biological membrane. Physical access to the biological membrane may be limited. Additionally, coupling gels may not be feasible to use on certain biological membranes. In light of the above, improved systems, devices, and methods for small format air-coupled ultrasound devices are desired. The present application may be related to commonly owned U.S. Patent Publication 2018/0310917 and U.S. Patent Publication 2017/0014053. The following references may be of interest: U.S. Patent 7,545,075, U.S. Patent 8,531,919, U.S. Patent 9,925,561, U.S. Patent 9,925,561, U.S. Patent 7,545,075, U.S. Patent Publication 2014/0265720, U.S. Patent Publication 2010/0173437, U.S. Patent Publication 2014/0265720, and U.S. Patent Publication 2012/0068571. US 2017/014053 describes an ultrasound signal processor which uses an excitation generator to cause displacement of a tympanic membrane while a series of ultrasound pulses are applied to the tympanic membrane. Phase differences between a transmitted signal and received signal are e×amined to determine the movement of the tympanic membrane in response to the applied e×citation. An e×amination of the phase response of the tympanic membrane provides a determination as to whether the fluid type behind the tympanic membrane is one of: no fluid, serum fluid, or purulent fluid. The series of ultrasound pulses are applied to the tympanic membrane by a transducer which may be any of capacitive micromachined ultrasonic transducer (CMUT), or piezoelectric transducers, for example, formed with the piezoelectric material PZT. A paper by Hani H. Tawfik et al entitled "Reduced-gap CMUT implementation in PolyMUMPs for air-coupled and underwater applications" published in Sensors and Actuators A; Physical, volume 294, 1 August 2019, at pages 102 to 115 describes a capacitive micromachined ultrasonic transducer (CMUT) with a reduced-gap architecture implemented in the PolyMUMPs technology. The elements were operated at 70 V DC biasing and driven with a 5 V narrow pulse provided through a USB connection, making the CMUTs suitable for portable devices. Finite element simulations show that the proposed reduced-gap design provides a ~4× bias voltage supply. Acoustic measurements of the proposed CMUT in-air show a 3.33 MHz resonance frequency with a ranging distance up to 27 mm. The CMUT element was sealed using a Parylene-C coating under-vacuum for immersion-applications. In an underwater pulse-echo setup, the backplate-echo of a 3 mm thick aluminum plate was detected. Moreover, the Parylene-C coating served as a method for increasing the fractional bandwidth (BW) by more than 100% at the expense of shifting the CMUT resonance to a higher frequency up to 4.55 MHz US 2007/129632 describes a system and method for examining a patient for an ear disorder. Reflectance ultrasound is applied to a portion of the ear to determine the presence of ear effusion in a middle ear. If ear effusion is present, motion of the tympanic membrane is induced and ultrasound is further applied to the moving tympanic membrane. Echo signals resulting from the ultrasound applied to the moving tympanic membrane are analyzed to obtain information regarding the motion of the tympanic membrane and is used to characterize the ear effusion. SUMMARY Conventional ultrasound transducers may need to be used with a coupling fluid to match an impedance of a material to be characterized to an ultrasound transducer because the typical medium between the material and the transducer, such as air, may have an acoustic impendence with significant mis-match to a transducer and/or a material to be measured. Transducer devices which are air-coupled may therefore be desired for certain applications. In an example, it may be desirable to use air-couple ultrasound to characterize a fluid on the opposite side of a tympanic membrane of an ear, rather than filling an ear canal with ultrasound gel. Similarly, in this example, it may simultaneously be desirous to make a device small in order to decrease scattering of the ultrasound with air and loss of coherence. One more of sufficient intensity, spatial coherence, small divergence, and/or phase stability, which may be difficult to obtain for air-coupled transducer devices and systems, may be additionally affected by making a transducer device smaller. The present disclosure provides ultrasound trans