Moving the sound transmission device along the sound transmission path (wire rope) point by point is a common measurement method for the acoustic field characterization in an anechoic chamber. In the actual testing process, due to the influence of the weight of the sound transmission device and the wire rope, the sound transmission path will change from an ideal straight line to a curve, resulting in the measurement error for acoustic characteristics. In this paper, the catenary theoretical model is established to describe the sagging wire rope. To consider the gravity of the sound device, the finite element method is used to simulate the sound transmission path. The experimental validation shows that our model can better express the deviation of the sound transmission path concerning gravity. It is of great significance to improve the accuracy and reliability of measuring the acoustic characteristics in an anechoic chamber.
Laser thermoelastic actuation is widely used in micro-actuation fields, such as MEMS and MOEMS. The advantage lies in non-contact, non-destructive, easy integration, and mobility. The low energy efficiency of the thermoelastic laser actuation limits its applications in manipulations of millimeters and submillimeters. In this study, we investigate the laser thermoelastic mechanism, and it is demonstrated to be an efficient non-contact way to achieve optical actuation. A millimeter-level nickel cantilever is successfully actuated with large amplitudes (several millimeters) at lower orders resonant frequencies by a nanosecond pulsed laser. The nonlinear modal interacted vibrations of the cantilever are also observed experimentally, the energy transfers from a high-frequency pulsed laser excitation to the low-frequency response of the cantilever. Moreover, we demonstrate that the first-order mode of the cantilever always dominates the nonlinear vibration at far high-frequency excitation, which would benefit the laser actuation control of the cantilever at a higher frequency. Furthermore, this work also presents a laser modulation method for a new widely spaced modal interaction. The results show that the appearance of the low-frequency mode has a slow modulation of the amplitude of the high-frequency mode. This study provides an effective non-contact approach for the optical excitation of the millimeter-level cantilever, empirically investigates the nonlinear features, and enriches applications in fields such as AFM sensing, precise processing and separation of bio-particles/cells, optical manipulation and operation of microrobots, and lab-on-a-chip devices.
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