# US 12,190,857 B2 · Metamaterial-based acoustic sensor beamforming

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- Number: US 12,190,857 B2
- Document ID: US12190857B2
- Status: Granted
- Kind: B2
- Application number: 17/743,878
- Filed: 2022-05-13
- Published: 2023-02-23
- Granted: 2025-01-07
- Earliest claimed: 2021-05-13
- Assignees: The Regents of the University of Michigan
- Applicants: The Regents of the University of Michigan
- Inventors: Bogdan Ioan Popa; Bogdan Epureanu; Hyung-Suk Kwon
- Web page: https://patentgrep.com/patent/US12190857B2

## CPC

- G10K 11/30: using refraction, e.g. acoustic lenses
- A61B 8/00: Diagnosis using ultrasonic, sonic or infrasonic waves
- B06B 1/067: {which is used as, or combined with, an impedance matching layer}
- G01N 29/221: {Arrangements for directing or focusing the acoustical waves (electronic orientation or focusing G01N29/262; sound directing or focusing G10K11/26; mechanical steering of sound transducers or their beams G10K11/35)}
- G01S 7/521: Constructional features
- G01S 15/42: Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S15/46)
- G01S 15/8909: {using a static transducer configuration}
- G10K 11/346: {using phase variation}
- B06B 1/0622: {on one surface}
- G01S 7/52079: {Constructional features (constructional features of transducers B06B; mounting transducers G10K11/00; constructional features of ultrasonic medical diagnostic devices A61B8/44)}
- G01S 15/931: of land vehicles
- H01Q 15/0086: {said selective devices having materials with a synthesized negative refractive index, e.g. metamaterials or left-handed materials}
- G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- B06B: METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, {e.g.} FOR PERFORMING MECHANICAL WORK IN GENERAL (for particular applications, see the relevant subclasses, e.g. B07B1/40, B23Q17/12, B24B31/06; measurement of mechanical vibrations G01H; in direction finding, locating, distance or velocity measuring G01S; {generating seismic energy G01V1/02}; control of mechanical vibrations in general G05D; sound-producing devices, e.g. bells, sirens, whistles G10K, {e.g. methods or devices for transmitting, conducting, or directing sound in general G10K11/00}; generation of electrical oscillations H03B; electromechanical resonators in general H03H; electromechanical transducers {for communication techniques, e.g. microphones, speakers} H04R)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- 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
- H01Q: ANTENNAS, i.e. RADIO AERIALS (radiators or antennas for microwave heating H05B6/72)

## Abstract

An acoustic lens to steer an acoustic beam includes a first structure, a second structure spaced from the first structure, an array of projections disposed between the first and second structures, each projection of the array of projections extending from the first structure toward the second structure to define a respective gap between the projection and the second structure, and an actuator configured to move the first structure, the second structure, or the array of projections for collective adjustment of the respective gaps of the array of projections. Each projection is configured to define one or more respective unit cells, each unit cell having a sub-wavelength size relative to the acoustic beam to establish an effective refractive index profile for the acoustic beam between the first and second structures. The actuator is configured such that the collective adjustment of the respective gaps varies across the array of projections to spatially modify the effective refractive index profile to steer the acoustic beam.

## Claims

### Claim 1

An acoustic lens to steer an acoustic beam propagating through the acoustic lens, the acoustic lens comprising:
a first structure;
a second structure spaced from the first structure;
an array of projections disposed between the first and second structures, each projection of the array of projections extending from the first structure toward the second structure to define a respective gap between the projection and the second structure; and
an actuator configured to move the first structure, the second structure, or the array of projections for collective adjustment of the respective gaps between the projections and the second structure;
wherein each projection of the array of projections is configured to define one or more respective unit cells, each unit cell having a sub-wavelength size relative to the acoustic beam to establish an effective refractive index profile for the acoustic beam propagating through the acoustic lens between the first and second structures, and
wherein the actuator is configured such that the collective adjustment of the respective gaps varies across the array of projections to spatially modify the effective refractive index profile for the acoustic beam to steer the acoustic beam.

### Claim 2 (depends on 1)

The acoustic lens of claim 1, wherein the actuator is configured to move the second structure.

### Claim 3 (depends on 1)

The acoustic lens of claim 1, wherein one of the first and second structures is flexible.

### Claim 4 (depends on 1)

The acoustic lens of claim 1, wherein the actuator is configured to rotate one of the first and second structures about an axis parallel to a propagation direction of the acoustic beam so as to steer the acoustic beam.

### Claim 5 (depends on 1)

The acoustic lens of claim 1, wherein:
one of the first and second structures comprises an array of piezoelectric patches; and
the actuator comprises a plurality of voltage sources configured to apply a position-dependent voltage to the array of piezoelectric patches.

### Claim 6 (depends on 1)

The acoustic lens of claim 1, wherein the actuator comprises a plate that acts on one of the first and second structures.

### Claim 7 (depends on 1)

The acoustic lens of claim 1, wherein the collective adjustment of the respective gaps varies in a direction transverse to a propagation direction of the acoustic beam prior to steering.

### Claim 8 (depends on 1)

The acoustic lens of claim 1, wherein:
each projection of the array of projections has a respective length; and
the respective length of the projections varies along a propagation direction of the acoustic beam to provide impedance matching.

### Claim 9 (depends on 1)

The acoustic lens of claim 1, wherein:
the first and second structures define input and output apertures through which the acoustic beam enters and exits the slot acoustic lens, respectively;
the array of projections comprises input and output impedance matching sections at the input and output apertures, respectively; and
the projections have respective heights in the input and output impedance matching sections that progressively range up to, and down from, a primary height of the projections, respectively.

### Claim 10 (depends on 1)

The acoustic lens of claim 1, wherein the first and second structures comprise first and second plates, respectively.

### Claim 11 (depends on 1)

The acoustic lens of claim 1, wherein the array of projections are disposed in a periodic arrangement.

### Claim 12 (depends on 1)

The acoustic lens of claim 1, wherein the collective adjustment establishes that sizes of the respective gaps between the projections and the second structure vary across the array of projections.

### Claim 13 (depends on 1)

The acoustic lens of claim 1, wherein:
the first structure and second structure are spaced apart from one another to define a slot; and
the array of projections are disposed in the slot.

### Claim 14 (depends on 1)

The acoustic lens of claim 1, wherein the respective gaps are oriented orthogonally to a propagation direction of the acoustic beam.

### Claim 15

An acoustic device comprising:
a transducer configured to generate an input sound wave;
a waveguide coupled to the transducer to receive the input sound wave; and
a beam former comprising an input aperture coupled to the waveguide, an output aperture, and a gradient index lens disposed between the input and output apertures, the gradient index lens having a continuous refractive index profile;
wherein the gradient index lens comprises:
a first structure;
a second structure spaced from the first structure;
an array of projections disposed between the first and second structures, each projection of the array of projections extending from the first structure toward the second structure to define a respective gap between the projection and the second structure; and
an actuator configured to move the first structure, the second structure, or the array of projections for collective adjustment of the respective gaps between the projections and the second structure, and
wherein the actuator is configured such that the collective adjustment of the respective gaps varies across the array of projections to spatially modify an effective refractive index of the gradient index lens.

### Claim 16 (depends on 15)

The acoustic device of claim 15, wherein the transducer is a point source such that the input sound wave is cylindrical.

### Claim 17 (depends on 15)

The acoustic device of claim 15, wherein the waveguide comprises a parallel plate waveguide configured to direct the input sound wave to the input aperture of the acoustic lens.

### Claim 18 (depends on 15)

The acoustic device of claim 15, wherein the actuator is configured to rotate one of the first and second structures about an axis parallel to a propagation direction of the input sound wave.

### Claim 19 (depends on 15)

The acoustic device of claim 15, wherein the collective adjustment of the respective gaps varies in a direction transverse to a direction of propagation through the input aperture.

### Claim 20 (depends on 15)

The acoustic device of claim 15, wherein:
each projection of the array of projections has a respective length; and
the respective length of the projections varies along a propagation direction of the input sound wave to provide impedance matching.

### Claim 21 (depends on 15)

The acoustic device of claim 15, wherein:
the array of projections comprises input and output impedance matching sections at the input and output apertures, respectively; and
the projections have respective heights in the input and output impedance matching sections that progressively range up to, and down from, a primary height of the projections, respectively.

### Claim 22 (depends on 15)

The acoustic device of claim 15, wherein the first and second structures comprise first and second plates, respectively.

### Claim 23 (depends on 15)

The acoustic device of claim 15, wherein the array of projections are disposed in a periodic arrangement.