Resonant attenuation of surface acoustic waves by a disordered monolayer of microspheres

Abstract

Attenuation of surface acoustic waves (SAWs) by a disordered monolayer of polystyrene microspheres is investigated. Surface acoustic wave packets are generated by a pair of crossed laser pulses in a glass substrate coated with a thin aluminum film and detected via the diffraction of a probe laser beam. When a 170 μm-wide strip of micron-sized spheres is placed on the substrate between the excitation and detection spots, strong resonant attenuation of SAWs near 240 MHz is observed. The attenuation is caused by the interaction of SAWs with a contact resonance of the microspheres, as confirmed by acoustic dispersion measurements on the microsphere-coated area. Frequency-selective attenuation of SAWs by such a locally resonant metamaterial may lead to reconfigurable SAW devices and sensors, which can be easily manufactured via self-assembly techniques.

Vibrational dynamics of a two-dimensional microgranular crystal

“…[14]. The avoided crossing between the vertical resonance mode and the SAW, studied in previous works [7,9], is just outside the wavevector range of our measurements. In the absence of interparticle interactions, the contact resonance frequency, past the avoided crossing with the SAW, is expected to be independent of the wavevector [7].…”

“…The mode labeled V corresponding to the most prominent peak in the spectra, as shown in Fig. 2(e), was previously identified as the vertical contact resonance mode [7,9,10]. Figure 2(e) also shows small peaks to either side of the V-mode peak which we assigned to horizontal-rotational modes labeled HR and RH following Ref.…”

“…The initial efforts focused on the vertical contact resonance of microspheres, arising due to contact with the substrate, and its interaction with surface acoustic waves (SAWs). In these initial studies, the observed phenomena, such as an avoided crossing in the Rayleigh SAW dispersion [7] and the resonant attenuation of SAWs by microspheres [9], could be well accounted for by a simple model where microspheres did not interact with each other [7]. Refined measurements of the resonant attenuation of SAWs * avegaflick@gmail.com † maznev@mit.edu revealed horizontal-rotational modes enabled by interparticle interactions [10].…”

“…A new frontier was opened by laser-based experiments on 2D selfassembled monolayers of micron-sized particles on a solid substrate [7][8][9][10][11]. These experiments revealed the crucial role of adhesion, which is negligible for large particles but becomes an important factor in determining the contact stiffness at the microscale.…”

Nanocontact Tailoring via Microlensing Enables Giant Postfabrication Mesoscopic Tuning in a Self‐Assembled Ultrasonic Metamaterial

“…), is achieved through the use of optical‐microlensing to tailor nanocontact features. Our self‐assembled metamaterials mitigate the aforementioned manufacturing scalability challenges, and have been previously demonstrated in the context of, for instance, surface acoustic wave (SAW) filters to have massive attenuations of −0.25 dB µm −1 (similar to recent phononic crystal filters with −0.31 dB µm −1 attenuation). The introduction of such spatially localized, postassembly tuning opens the door for complex ultrasonic metamaterials devices such as gradient index lenses.…”