Abstract
Self-noise is an important specification of hydrophone with preamplifier. This paper presents the modelling, measurement and optimization of the self-noise of hydrophone with preamplifier. Through analyzing various noise sources of hydrophone and its preamplifier, an effective self-noise model of hydrophone with preamplifier was established, and the self-noise was mainly affected by the hydrophone quality factor, preamplifier noise and thermal noise of preamplifier input resistance. In order to measure the self-noise of hydrophone with preamplifier, a measurement system was constructed and used for measuring the self-noise of a RHSA30 hydrophone which manufactured by Hangzhou Applied Acoustics Research Institute (HAARI) and has a typical sensitivity of -173 dB. After optimization of the self-noise of RHSA30 hydrophone, the measured equivalent noise pressure spectral density level was close to 30 dB at the frequency of 1000 Hz. The measurement results proved that the preamplifier current noise which mainly coming from the Operational Amplifier played a leading role at low frequencies of hydrophone with preamplifier. And some basic principles for self-noise optimization of hydrophone with preamplifier were given at the end.
Highlights
Hydrophones are electroacoustic transducers that produce electrical signals in response to water borne pressure signals [1], they were widely used in SONAR equipments and marine acoustic instruments for detecting underwater targets or measuring underwater sound signals
Reference hydrophones did not equip with integral preamplifiers, and they were calibrated by absolute calibration methods
In order to increase Signal to Noise Ratio (SNR) of the measurement system, most of the measuring hydrophones were equipped with integral preamplifiers
Summary
Hydrophones are electroacoustic transducers that produce electrical signals in response to water borne pressure signals [1], they were widely used in SONAR equipments and marine acoustic instruments for detecting underwater targets or measuring underwater sound signals. Measuring hydrophones were often calibrated by comparison methods, and used for measuring the sound pressure in water directly. The hydrophones used in underwater acoustics were piezoelectric type, and the preamplifiers used in measuring hydrophones were voltage preamplifiers. The performance of underwater acoustical measurement systems were largely determined by the characteristic of measuring hydrophones with preamplifier, and self-noise is one of the important specifications for them, especially for the systems which measuring noises in water. It directly affects the equivalent noise pressure spectral density level and dynamic range of the underwater acoustical measurement system. On the basis of these, the parameters of hydrophone with preamplifier such as capacitance and sensitivity of hydrophone, input resistor, preamplifier current noise and preamplifier voltage noise were investigated, and several basic principles for optimization of the self-noise of hydrophone with preamplifier were given at the end
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