Large Dynamic Range in Acoustic Detection Realized by a Dual-Diaphragm Based Sensing System With IQ-PGC Phase Demodulation

Abstract

A dual-diaphragm based acoustic sensing system has been proposed to increase the dynamic range by using a thin diaphragm (70 nm) of gold diaphragm to decrease minimum detectable acoustic pressure and a thick one (300 nm) to increase maximum detectable acoustic pressure. Signals from the two diaphragms are synchronously demodulated using frequency division multiplexing (FDM) combined with an in-phase/quadrature (IQ) and a phase generated carrier (PGC) phase demodulation. Signal crosstalk from the two diaphragms is avoided by adding a carrier modulation frequency shift to one of them. The underwater sensing performance of the system is tested under the acoustic signals ranging from 100 to 1500 Hz. Experimental results demonstrate that the average dynamic range reaches 98.4 dB in 300 ~ 1500 Hz, which is obviously improved comparing to the sensor barely using a 70 nm diaphragm (81.2 dB) or a 300 nm one (74.2 dB). In addition, the sensor performs high and flat sensitivity under low acoustic pressure (less than 110 Pa) with an average phase sensitivity of −164.2±2.6 dB re 1 rad/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Pa. Due to the characteristic of large dynamic range and compact size, the proposed sensing system is believed to have potential application prospects in acoustic detection area.