The article presents the results of designing, manufacturing, and studying the resonant properties of a square silicon membrane for use in a fiber-optic acoustic receiver. The dependences of resonant frequency on edge length (6-9 mm) and thickness of the membrane (30-50 μm) are obtained. The geometrical parameters of the membrane satisfying the values of resonant frequency (2-60 kHz), pressure (0.1-14 Pa), and deviation (10 nm) are determined: edge length is 8 mm and thickness is 40-50 μm (9.2-42.3 kHz). A series of square silicon membranes was fabricated by anisotropic wet etching. The amplitude-frequency characteristics of the membranes were experimentally measured using an adaptive holographic interferometer. For a square membrane of 8×8×0.044 m3, the experimentally measured resonant frequency was 10.1 kHz, which is consistent with the results of numerical simulation.
We present laser microweight biosensor based on the adaptive holographic interferometer. The sensing element of the sensor is gold coated silicon microcantilever with dimensions of 210×40×5 μm3. Biomolecules of the interest being attached to the cantilever increase its mass which in its turn leads to decreasing the cantilever resonance frequency. The frequency shift of the detected signal is directly proportional to the total mass of adsorbed molecules. Cantilever oscillations are detected by the adaptive holographic interferometer based on two-wave mixing in a photorefractive CdTe crystal. For measuring the concentration of biological molecules dissolved in water the cantilever was installed in a cuvette which contains the solution. In the experiment, adsorbed molecules of BSA (Bovine Serum Albumin) with total mass of 3.1 ng were detected and weighted.
In this work, we present two-channel system for detecting acoustic waves which is based on adaptive holographic interferometer using multi-wave mixing in photorefractive crystal. Micromechanical silicon cantilevers with dimensions of 233×45×4 μm3 mounted on metal membrane are used as sensitive elements. For the first cantilever the detection threshold of acoustic pressure of the sensor on frequency of 6.9 kHz is 17 mPa. For the second cantilever the detection threshold of acoustic pressure of the sensor on frequency of 8 kHz is 49 mPa.
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