A spiral wave front beacon for underwater navigation: Basic concept and modeling

Chen

et al. 2018

Adv Funct Materials

Acoustic metasurfaces that can manipulate and control sound waves at 2D subwavelength scales open new avenues to unusual applications, such as asymmetric transmission, super-resolution imaging, and particle manipulation. However, the long-standing goals of pushing frontier metamaterials research into real practice are still severely constrained by cumbersome configuration, large acoustic loss, and rigid structure of the existing metamaterials. An ultrathin metasurface (10-300 µm in thickness, up to ≈λ/650, λ the wavelength) that is capable of imparting sound wave with a nontrivial phase shift with high transmittance (>80%) in the range of 5-30 kHz is fabricated here. The metasurface is comprised of a porous network of soft polymer fiber/rigid beads that are physically equivalent to crosslinked spring-mass resonators. Moreover, the traditional paper-cutting art to carve the ultrathin metasurface into hollow-out patterns is incorporated, resulting in a variety of remarkable functions, including acoustic vortex, focusing, and super-resolution. The hollow-out patterning approach innovates the traditional one-step metadevice fabrication process into two separated steps: 1) fabrication of ultrathin metasurfaces; 2) hollow-out patterning of metasurfaces. The strategy opens an avenue to mass production of acoustic metadevices, shedding light on the applications of the metamaterials in acoustic cloaking, acoustic positioning, and particle manipulation.

Section: Resultsmentioning

confidence: 99%

Hollow‐Out Patterning Ultrathin Acoustic Metasurfaces for Multifunctionalities Using Soft fiber/Rigid Bead Networks

Chen

et al. 2018

Adv Funct Materials

The Journal of the Acoustical Society of America

“…Transducers producing first order spiral fields have been recently developed for use in underwater bearing estimation. [7][8][9] This idea is extended to the general case and it is shown that for a given position in space, each spiral wave front appears to come from a different source position. Hence, for free-field reproduction within a circular array of higher order sources each Nth order speaker is similar in performance to an array of 2N þ 1 point sources, a) Author to whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

Comparison of sound reproduction using higher order loudspeakers and equivalent line arrays in free-field conditions

Poletti

Betlehem

Abhayapala

2014

Higher order sound sources of Nth order can radiate sound with 2N + 1 orthogonal radiation patterns, which can be represented as phase modes or, equivalently, amplitude modes. This paper shows that each phase mode response produces a spiral wave front with a different spiral rate, and therefore a different direction of arrival of sound. Hence, for a given receiver position a higher order source is equivalent to a linear array of 2N + 1 monopole sources. This interpretation suggests performance similar to a circular array of higher order sources can be produced by an array of sources, each of which consists of a line array having monopoles at the apparent source locations of the corresponding phase modes. Simulations of higher order arrays and arrays of equivalent line sources are presented. It is shown that the interior fields produced by the two arrays are essentially the same, but that the exterior fields differ because the higher order sources produces different equivalent source locations for field positions outside the array. This work provides an explanation of the fact that an array of L Nth order sources can reproduce sound fields whose accuracy approaches the performance of (2N + 1)L monopoles.

The Journal of the Acoustical Society of America

“…[1][2][3] The spiral source transmits a pulse whose phase is a function of the azimuthal angle relative to the source while the reference source transmits a pulse whose phase is constant with angle. By comparing the phases of the two pulses, the vehicle can determine the direction to the beacon.…”

Section: Introductionmentioning

confidence: 99%

“…These sources use two different methods to produce the spiral wave front. 2 The first, the "physical-spiral" transducer, uses a single, active element formed around a spiral backing. The second design, the "phased-spiral" array, uses an array of elements each driven with the appropriate phase to produce the spiral wave front.…”

Section: Introductionmentioning

confidence: 99%

“…Each of these sources was modeled in the free field to examine how well it produced a spiral wave front. 2 Recent experiments have emphasized that the performance of the spiral beacon is affected not only by the design of the source, but also by the environment in which it operates. 5 As range from the beacon increases, it becomes necessary to understand how the ocean waveguide affects the phase information carried by the pulses.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Acoustic propagation from a spiral wave front source in an ocean environment

Hefner

Dzikowicz

2012

Self Cite

A spiral wave front source generates a pressure field that has a phase that depends linearly on the azimuthal angle at which it is measured. This differs from a point source that has a phase that is constant with direction. The spiral wave front source has been developed for use in navigation; however, very little work has been done to model this source in an ocean environment. To this end, the spiral wave front analogue of the acoustic point source is developed and is shown to be related to the point source through a simple transformation. This makes it possible to transform the point source solution in a particular ocean environment into the solution for a spiral source in the same environment. Applications of this transformation are presented for a spiral source near the ocean surface and seafloor as well as for the more general case of propagation in a horizontally stratified waveguide.