Focusing of longitudinal ultrasonic waves in air with an aperiodic flat lens

Welter, John T.; Sathish, Shamachary; Christensen, Daniel E.; Brodrick, Philip G.; Heebl, Jason D.; Cherry, Matthew

doi:10.1121/1.3640841

Cited by 37 publications

(26 citation statements)

References 20 publications

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“…The phase through the electronic circuit is tunable as well, and it is an additional degree of freedom usable in some applications. For example, it can be used to implement unidirectional acoustic lenses by varying the phase delay through each cell in the same way reciprocal passive metamaterial lenses are designed [1][2][3][4][5][6] .…”

Section: Discussionmentioning

confidence: 99%

“…Thus, the extended range of material parameters provided by metamaterials has lead to the implementation of devices such as acoustic lenses [1][2][3][4][5][6] , or even exotic structures designed using coordinate transformation methods 7,8 . Recently, significant attention has been given to unidirectional devices that pass acoustic energy in only one direction [9][10][11][12][13][14][15] and therefore mimic the general behaviour of diodes in the microwave regime, and Faraday rotator media in the optical domain.…”

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confidence: 99%

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Non-reciprocal and highly nonlinear active acoustic metamaterials

2014

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Unidirectional devices that pass acoustic energy in only one direction have numerous applications and, consequently, have recently received significant attention. However, for most practical applications that require unidirectionality at audio and low frequencies, subwavelength implementations capable of the necessary time-reversal symmetry breaking remain elusive. Here we describe a design approach based on metamaterial techniques that provides highly subwavelength and strongly non-reciprocal devices. We demonstrate this approach by designing and experimentally characterizing a non-reciprocal active acoustic metamaterial unit cell composed of a single piezoelectric membrane augmented by a nonlinear electronic circuit, and sandwiched between Helmholtz cavities tuned to different frequencies. The design is thinner than a tenth of a wavelength, yet it has an isolation factor of 410 dB. The design method generates relatively broadband unidirectional devices and is a good candidate for numerous acoustic applications.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Non-reciprocal and highly nonlinear active acoustic metamaterials

2014

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“…By shaping the pump ultrasound field launched with a focused air-coupled transducer, and also with acoustic masks, focusing mirrors, [9][10][11] and Fresnel plates [11][12][13] ), the radiation pattern (i.e., spatial distribution of I) can be manipulated at the air/medium interface. In addition, ultrasound arrays can electronically scan the pump field across the interface.…”

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confidence: 99%

Air-coupled acoustic radiation force for non-contact generation of broadband mechanical waves in soft media

Ambroziński

Pelivanov

Song

et al. 2016

Applied Physics Letters

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A non-contact method for efficient, non-invasive excitation of mechanical waves in soft media is proposed, in which we focus an ultrasound (US) signal through air onto the surface of a medium under study. The US wave reflected from the air/medium interface provides radiation force to the medium surface that launches a transient mechanical wave in the transverse (lateral) direction. The type of mechanical wave is determined by boundary conditions. To prove this concept, a homemade 1 MHz piezo-ceramic transducer with a matching layer to air sends a chirped US signal centered at 1 MHz to a 1.6 mm thick gelatin phantom mimicking soft biological tissue. A phasesensitive (PhS)-optical coherence tomography system is used to track/image the mechanical wave. The reconstructed transient displacement of the mechanical wave in space and time demonstrates highly efficient generation, thus offering great promise for non-contact, non-invasive characterization of soft media, in general, and for elasticity measurements in delicate soft tissues and organs in bio-medicine, in particular. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4959827] Acoustic radiation force (ARF) is commonly used in ultrasound (US)-based elastography to remotely generate shear waves deep within tissue. 1-3 Detection of shear waves can be performed with a conventional ultrasound (US) imaging probe or with another imaging method, e.g., optical coherence tomography (OCT). The combination of ARF with high frame rate OCT can produce quantitative crosssectional maps of the shear modulus in soft tissues. 4 For many clinical applications, however, a totally non-contact system for generation/detection of mechanical waves is desirable and, in some cases (for instance, the eye), is necessary. OCT is an ideal approach for these applications if an efficient and robust non-contact generation technology can be developed.Generation of mechanical waves with an air puff was used in Ref. 5 to produce very narrow bandwidth displacements in the cornea, which may not be able to characterize corneal elasticity at the spatial resolution required for clinical decision making. Our group has recently demonstrated non-contact generation using absorption of pulsed UV laser light. 6 Although UV generation can provide the bandwidth required for high spatial resolution maps of corneal elasticity, it is not clear at this point whether the required UV energy levels will meet the safety requirement for routine clinical use.Here we propose a fully non-contact and non-invasive US technique to create efficient localized wideband mechanical waves in soft tissue. The method utilizes US launched with an air-coupled transducer (i.e., through air) to the air/ medium interface. The US wave reflected from this interface provides radiation force to the medium surface, which induces a transient displacement at that surface, ultimately generating a propagating shear/guided/interface/Lamb wave (wave type determined by boundary conditions). We will call this the mechanical wave to maintain ge...

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“…Inspired by the research on subwavelength, defined as less than the incident wavelength, focusing hypothesized by Veselago [1] and demonstrated by Pendry [2], several groups are exploring structures with subwavelength features to focus acoustic waves or to achieve acoustic cloaking. Three dimensional and two dimensional periodic [3][4][5][6][7][8][9][10][11][12][13] and aperiodic [14][15][16] Welter et al recently demonstrated subwavelength focusing of acoustic waves in air using a cylindrical aperiodic structure [19]. Focusing was examined in the frequency range of 80-90…”

Section: )mentioning

confidence: 99%