Effect of excitation point on surface phonon fields in phononic crystals in real- and k-space

Abstract

We investigate surface phonon propagation in a triangular-lattice phononic crystal of microscopic holes in a gold-coated polymer by time-resolved two-dimensional imaging and by finite-element simulations at sub-gigahertz frequencies. The simulations allow the effects of exciting different points in the crystal lattice to be studied in real space, and also in k-space by spatiotemporal Fourier analysis. The acoustic field in a sub-surface plane below the reach of the holes is also revealed in real- and k-spaces. In addition, we demonstrate pitfalls in the analysis of k-space data when searching for the presence of band gaps. Applications include surface-acoustic wave filter quality control.

Extraordinary transmission of gigahertz surface acoustic waves

“…The temporal variation of the excitation is a step-like function (a quarter period of a sinusoid) with a 1 ns rise time. This acoustic source produces a spectrum of surface acoustic waves up to ~2 GHz as in experiments with sub-picosecond optical pulse excitation 21 22 23 24 . This acoustic source is applied to the left-hand block, as shown in Fig.…”

“…For both types of structure we choose microscopic sizes in order to give acoustic resonances in the gigahertz range, as such frequencies correspond to those used in surface acoustic wave filters and devices. Furthermore, direct surface acoustic wave imaging techniques exist for this frequency range 21 22 23 24 , and so our work is therefore experimentally realizable.…”

Refraction, beam splitting and dispersion of GHz surface acoustic waves by a phononic crystal

“…All-optical time-resolved two-dimensional (2D) imaging techniques for surface acoustic waves up to GHz frequencies have been the subject of much attention over the last two decades [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] . These techniques make use of light pulses with picosecond temporal durations to generate the acoustic waves and to image the acoustic wavefield as a function of time and 2D spatial position.…”

Time-domain imaging of gigahertz surface waves on an acoustic metamaterial

“…Although time-domain imaging of acoustic waves in metamaterials has been carried out in a variety of studies [15][16][17][18][19], to date the frequency range has been restricted to below 1 MHz. Building on progress in imaging surface acoustic waves (SAWs) in phononic crystals [20][21][22][23][24], in this paper we present results for time-domain imaging of gigahertz-frequency SAWs on a regular array of silica microspheres adhered to a substrate-an acoustic metamaterial exhibiting contact resonances [25][26][27][28]-using ultrashort optical point-source excitation inside and outside the metamaterial region. By means of Fourier transforms we derive the acoustic dispersion relation and probe the transmission properties at different frequencies, and interpret the results with an analytical model of the microsphere resonant interactions between themselves and with the substrate.…”