Hydrophones are, quite simply, underwater microphones for acoustic measurements. Wilcoxon Research hydrophones are built to withstand the rigors of continuous underwater exposure, in both sea water and fresh water environments. Each hydrophone uses piezoelectric crystals with a built-in electronic amplifier, to boost the low level signal of pressure waves underwater signals. The output is a dynamic AC signal superimposed upon the DC Bias Output Voltage (BOV). Typical applications are biological studies, ship studies, and monitoring underwater ordnance.