| Abstract | The detection of a propagating wave usually requires the use of a physical sensor that measures a specific property - displacement, velocity, or pressure. Measurement devices such as hydrophones, microphones, accelerometers and seismometers are routinely used for the characterisation of sonic waves in various media. An interesting question arises, when establishing new measurement methods and standards for the calibration of such sensors, whether it is possible to use a wave, rather than a physical device, for sensing propagating disturbances. In our proposed scheme, we mix an infrasonic wave with a carrier acoustic wave at a fixed audible frequency and amplitude in air. The optical method based on photon correlation makes it possible to measure the carrier acoustic particle velocity at a point in space and thus reconstruct the carrier accoustic wave. Since the measured carrier signal is accoustically modulated by induced infrasonic signals, as well as disturbances such as ambient air flow, this alternative modulation scheme provides interesting and new detection capabilities for propagating infrasonic waves in air. Using a 2 kHz carrier, we experimentally demonstrate the feasibility of this technique for measuring infrasonic signals from 4 to 20 Hz, in relative agreement with a calibrated sound level meter. A systematic discrepency between the two techniques is still being investigated in order to achieve quantitative agreement between the two methods. |
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