Research ArticleAPPLIED PHYSICS

Coupling and confinement of current in thermoacoustic phased arrays

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Science Advances  01 Jul 2020:
Vol. 6, no. 27, eabb2752
DOI: 10.1126/sciadv.abb2752
  • Fig. 1 Sound generation from a thermoacoustic phased array.

    (A) Schematic of a two-element array. (B) Sound measured from a graphene-based seven-element array with incremental phase difference: Δξ = ±π/6 resulting in P and N, respectively. The normalized sound pressure, |δp|, (f = 16 kHz) is shown as a function of angle, φ, across the array at a fixed distance, r, from its center (r = 0.16 m). (C) Dipolar (left) and quadrupolar (right) sound measured from a graphene-based 2 × 2–element array. The sound field is shown above the schematic. In (B) and (C), radial length depicts the magnitude of δp, and the fill color depicts its phase, ψ. (D) Source phases were incremented in a clockwise manner (1, 2, 4, 3) = (0, π/2, π, 3π/2). The resulting sound magnitude (simulated) is shown above the schematic. Orthographic projections (right) of the resulting experimental |δp| (bottom) and ψ(r) (stack) are shown in tilted perspective.

  • Fig. 2 Transforming sound into joule heat.

    Radiated heat and joule heat were measured from a graphene-based 2 × 2–element array (fig. S1A) driven as a quadrupolar source. a.u., arbitrary units. (A) Thermal reconstruction of the array from the Fourier component at the second harmonic of the drive frequency (1 Hz). (B) Acoustic reconstruction from far-field sound measurements at 300 kHz. In both reconstructions, the magnitude (top) and phase (bottom) are shown using the same color and spatial scales.

  • Fig. 3 Types of thermoacoustic array.

    (A) Measured beam profile of the dipolar sound from two elements of a graphene-based 16-element array (top) and reconstructed thermal phase of the array surface (bottom) shown in tilted perspective. Insets show acoustic reconstructions of individual elements (fig. S1A). (B) Integrated |δp| measured from a two-element dipole as a function of element separation (circles). The result from an analytical model of two point sources is also shown (line). (C) A 6-mm square indium tin oxide film run as a dipole: sources (1, 2) and grounds (G). Top: The measured thermal phase (left), orthographic projection of the far-field sound phase (middle), and acoustic magnitude reconstruction (right). Bottom: Stream plots of the current (from numerical modeling) as it moves between the electrodes. (D) Measured beam steering by a seven-element gold junction array, to compare directly with Fig. 1B. Bottom: Thermal phase (left) and acoustic magnitude (right) reconstructions of a two-element junction dipole.

  • Fig. 4 Phantom sound sources.

    (A) Measured beam profile and thermal phase reconstruction of a dipole formed by two elements of a 16-element array that share a common ground trace. Left: A zoomed region (right) showing the vortex formed at the element-trace junction and its suppression by the addition of a DC current. (B) Integrated sound pressure (blue) and joule power (green) as a function of the phase difference between two sources in a zinc-based three-branch array (inset): experiment (circles) and theory (line) for the coupled case and theory (dashed line) for the uncoupled. (C) Total absolute joule power from a three-branch array measured as a function of voltage ratio and phase difference; experimental (circles) and theoretical (line) path of minimum power. Insets: simulated orthographic projections of the sound phase at ϕ = π/3 and different voltage ratios. (D) Measured thermal magnitude (top) and phase (bottom) reconstructions of the three-branch array in the case f2 = 4f1.

Supplementary Materials

  • Supplementary Materials

    Coupling and confinement of current in thermoacoustic phased arrays

    David M. Tatnell, Mark S. Heath, Steven P. Hepplestone, Alastair P. Hibbins, Samuel M. Hornett, Simon A. R. Horsley, David W. Horsell

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