Development of a new kind low frequency low-noise vector sensor

A new kind low frequency low-noise vector sensor (VS) with minimum size by relaxor-based ferroelectric crystals had been presented. The VS is composed with a built-in accelerometer and a JFET-based preamplifier, which has significant contribution to the self-noise performance. Measured equivalent noise pressure level (ENPL) of the prototype is about 52.8, 44.2 and 31.9dB/√Hz at frequencies 100, 200 and 500 Hz, respectively. It is significantly lower than the ambient noise of Knudsen Sea state zero at frequency band 60∼1000Hz. The obtained results exhibit a high level of consistency with the prediction by modelling the ENPL of VS. For decreasing the self-noise at low frequency, a cross-ring beam accelerometer using [011] cut relaxor-based ferroelectric crystal is proposed. Prototype has been fabricated and characterized. Measurements about performance of the prototype gives a sensitivity of -212.9dB@100Hz without amplification as well as a diploe directivity with null depth of -36.2dB, which is in good agreement with the finite element analysis. The designed prototype provides the possibility for practical applications of low frequency underwater sound detection.