# US 9,437,183 B2 · Metamaterial based acoustic lenses for structural health monitoring

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- Number: US 9,437,183 B2
- Document ID: US9437183B2
- Status: Granted
- Kind: B2
- Application number: 14/577,556
- Filed: 2014-12-19
- Published: 2015-08-13
- Granted: 2016-09-06
- Earliest claimed: 2013-12-19
- Assignees: University of Notre Dame du Lac
- Applicants: University of Notre Dame du Lac
- Inventors: Fabio Semperlotti; Hongfei Zhu
- Web page: https://patentgrep.com/patent/US9437183B2

## CPC

- G10K 11/30: using refraction, e.g. acoustic lenses
- G01N 29/04: Analysing solids (using acoustic emission techniques G01N29/14)
- 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)}
- G01N 2291/0231: Composite or layered materials
- G01N 2291/02491: Materials with nonlinear acoustic properties
- G01N 2291/0258: Structural degradation, e.g. fatigue of composites, ageing of oils
- G01N 2291/042: Wave modes
- G01N 2291/106: one or more transducer arrays
- G10K 11/343: {using frequency variation or different frequencies}
- 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
- 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)

## Abstract

An embedded acoustic metamaterial lenses allows for ultrasonic beam-forming and high resolution identification of acoustic sources for structural health monitoring. The lenses design provides an alternative to conventional phased-array technology enabling the formation of steerable and collimated (or focused) ultrasonic beams by exploiting a single transducer. The ultrasonic beam can be steered by simply tuning the frequency of the excitation. Also, the embedded lens can be designed to achieve sub-wavelength resolution to clustered acoustic sources which is a typical scenario encountered in incipient structural damage.

## Claims

### Claim 1

A metamaterial based acoustic lens for structural health monitoring comprising:
a transducer;
a thin plate; and
a metamaterial lens embedded within the thin plate, wherein the plate is positionable such that the metamaterial lens at least partially overlays the transducer;
wherein selected sectors of the metamaterial lens at prescribed azimuthal location include line defects to create localized modes at selected frequencies inside the bandgap.

### Claim 2 (depends on 1)

A metamaterial based acoustic lens as recited in claim 1, wherein the thin plate is an aluminum plate.

### Claim 3 (depends on 1)

A metamaterial based acoustic lens as recited in claim 1, wherein the line defects are located at ninety degrees.

### Claim 4 (depends on 3)

A metamaterial based acoustic lens as recited in claim 3, wherein at least one of the line defects is created by altering the stiffness properties of the inclusions in a 20° -wide sector centered at the geometric center of the metamaterial lens.