Performance of tourmaline hydrophones at low- and midfrequencies.

Abstract

Tourmaline hydrophones are well suited for measurement of underwater blasts and other impulsive type sounds having extremely fast rise times and high peak pressures. The physical characteristics of these small, lightweight sensors, however, make them an attractive choice for other applications. To determine their performance at low- and midfrequencies, substitution calibrations of two tourmaline sensors with a calibrated laboratory hydrophone were completed using a J-ll underwater sound transducer in a 100-gal tank. The calibration signals consisted of tone bursts containing 5–20 cycles at frequencies ranging from 250 to 10 000 Hz and having sound pressure levels from 110 to 180 dB re 1 μa. Results indicate that a tourmaline hydrophone coupled to an in-line charge amplifier and preamplifier to provide fixed voltage gains ranging from 100× to 10 000× has excellent performance over this range of frequencies. [Work supported by the National Oceanographic Partnership Program (NOPP) through ONR Award No. N000140710992.]