Page 33 - Fall_DTF

Acoustic Leaky Wave
Antennas: Direction-Finding
via Dispersion
Christina]. Naify Acoustic leaky wave antennas use an analog aperture coupled to an active
Address: transducer to steer acoustic energy using spatial- to-spectral coupling.
Jet Propulsion Laboratory
California Institute of Technology introduction
4800 Oak Grove Drive Th d f b - - . . .
_ _ e soun o a laster in the classic Star Wars films is easily recognizable to
Pasadena. California 91109
many. It turns out that the wave phenomenon that produces that uni ue sound,
USA _ _ _ q
_ something known as dispersion, is central to the operation of a new type of
_ _ _ _ _ Email-' acoustic device known as a leaky wave antenna (LWA), which holds significant
i:hnstina._].naify@_]pl.nasa.goV . . . . . . . .

promise for use in acoustic navigation and unaging applications that require

Michael Hahuma low-power operation. LWAs are mechanical structures that lead to direction-

“ dependent radiation or reception of acoustic ener I

gy. n other words, when an

Address: acoustic LWA generates sound, it does not send out acoustic energy equally in all

D5P31'“‘“‘“‘ °f Medmfiical Engineering directions. Rather, the device has directionality and that directionality is dictated

d A 1' d R ch L b ' - - . .

mThel3n';Hsi::;Tex:S ;’t'aA“‘l’:: by its mechanical structure. Furthermore, the defining attribute of an acoustic
204 East Dean Keno“ SHE“ LV\lA is the ability to change its directionality by simply changing frequency.
Smp C2200 This frequency-dependent directionality is a result of the LWA dispersion that is

Ausqm Tum 73712 tailored by designing mechanical structures that make up the LWA. The design

USA of the dynamic behavior of these subwavelength mechanical structures is central

Email: to the creation of the LWA and the primary focus of recent works on the topic of

habgr]-n3n@u[gxa5_edu acoustic LWAs (Naify et al., 2013; Esfahlani et al., 2016).
Matthew D G fld So what is dispersion and how is it used to create an acoustic LWA? Furthermore,
‘ “ how can the LWA be engineered to create a compact low ' ' '

, -power acoustic-unaging

Address: or navigation device? This article provides a high-level overview of the physical

Us N3“! R5553YCh l;:3l>§Y*_17‘?g’ phenomena underlying the desirable attributes of acoustic LWAs. It further traces

o e - - . . . _
4555 Overlook Avenue SW theorigins of acoustic LVllAs to their analogues inelectromagnetic LWAs, describes
Washington, DC 20375 how ‘concepts in acoustic metamaterials are used in the creation of LWAs, and
USA provides examples and outlook on the future of this exciting technology.
E '1: . _ _ _ _
mmhewguud@nrl_nav;:il Acoustic EBEI1'IfDl'n'I_Ing and Direction I-'inding

To better understand the topic of acoustic LWAs, one must first understand the

Caleb F. Sieck motivation for the study of such a device: the need for compact, low-power systems

Add . for navigation using acoustics. Acoustic waves have long been used to locate objects

NRC Pofldodoml Rese::; in space and to navigate. A classic example of the use of sound for navigation is
Assodmeship Program echolocation-employed by bats and marine mammals in which the animal emits

Us Naval Resgamh Labommry an acoustic signal that then radiates out into the environment, primarily in front
code 7155 of the animal, until it encounters an object and some of the energy in the original

4555 Overlook Avenue SW signal is scattered back and received at the original location. If one knows the speed
W“5h“‘E‘°“v DC of sound in the medium carrying the wave (c), then the time elapsed between the
generation and reception of the acoustic signal (At) provides a.n estimate of the

- Email: distance (ii) between the animal and the object that scatters the signal; ii = cAt.
Caleb-5“‘3k-‘“'@“‘1-“3V}’-mil Although this is useful information, a single omnidirectional source-receiver pair

will only tell the distance between the two with no information about direction.
volume14,issue3 | Fall 2013 | Acouoizlcl Today | 31