TYPE 9718-A:bp0317
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Bruel&Kj&r hydrophones are individually calibrated waterborne-sound transducers which have a flat frequency response and are omnidirectional over a wide frequency range. Their construction is such that they are absolutely waterproof and have high corrosion resistance. All Bruel&Kj&r hydrophones are manufactured using lead-free nitrile butadiene rubber. There are four types of hydrophone: • Type 8103 is suitable for high-frequency laboratory and industrial use and particularly for the acoustic study of marine animals or for cavitation measurements • Type 8104 is a general purpose hydrophone, also ideal for calibration purposes • Type 8105 is a robust spherical hydrophone usable down to 1000 m ocean depth with excellent directional characteristics • Type 8106 has a built-in amplifier which gives a signal suitable for transmission over long cables. It is usable down to 1000 m ocean depth USES • Calibration reference standards • Ultrasonic measurements in liquids • Cavitation measurements • Laboratory and industrial measurements in liquids and gases • As underwater projectors (8103, 8104 and 8105) • Noise measurements in humid and polluted atmospheres FEATURES • Frequency ranges from 0.1 Hz to 180 kHz • Individually calibrated • Flat frequency response over wide range • Omnidirectional over wide frequency range • Working pressures up to 9.8 x 106Pa (100 atm. [1000 m]) • Shielded-element construction • Highly corrosion resistant SPECIAL FEATURES TYPE 8103 • Very small size (50 x 9.5 mm) • -3dB limit in air at 15 kHz • Double-shielded, low-noise integral cable SPECIAL FEATURES TYPE 8105 • Omnidirectional over full frequency range • No metallic parts exposed • -3dB limit in air at 7 kHz SPECIAL FEATURES TYPE 8106 • High sensitivity: -173dB re 1 V/^Pa • Built-in preamplifier with provision for insert-voltage calibration • Durable construction • Equivalent noise level well below sea-state zero

The Brüel & Kjær range of waterborne-sound transducers consists of the following: Fig. 1 Hydrophone Type 8103 A small-size, high-sensitivity transducer for making absolute sound measurements over the frequency range 0.1 Hz to 180 kHz with a receiving sensitivity of − 211 dB re 1 V/μPa. It has a high sensitivity relative to its size and good all-round characteristics, which make it generally applicable to laboratory, industrial and educational use. Type 8103’s highfrequency response is especially valuable when making acoustic investigations of marine animals and in the measurement of the...

Hydrophone Type 8105 A small, spherical transducer for making absolute sound measurements over the frequency range 0.1 Hz to 160 kHz with a receiving sensitivity of - 205 dB re 1V/p,Pa. It is rugged, being capable of withstanding pressures of up to 107Pa (100 atm.; 1000 m (3250 ft.) ocean depth). This hydrophone has excellent directional characteristics: at 100 kHz, it is omnidirectional over 360° in the x-y (radial) plane and 270° in the x-z (axial) plane. Type 8105 is illustrated in Fig. 3. Hydrophone Type 8106 A wide-range, general-purpose transducer for making absolute sound...

The four Brüel & Kjær hydrophones are piezoelectric transducers, that is, they use piezoelectric ceramics as sensing elements. The piezoelectric sensing element and its internal supporting structure are permanently bonded into sound-transparent, lead-free, nitrile butadiene rubber. The support bodies of Hydrophones Types 8103 and 8104 are made from a 70 – 30 CopperNickel alloy. Type 8106’s support body is made of Aluminium-Bronze alloy CuAl10Ni5Fe4 (ISO 428). Both alloys have extremely high corrosion resistance to virtually all hostile environments, and very good anti-fouling properties...

Fig. 6 Typical directivity patterns of Hydrophones Types 8103, 8104, 8105 and 8106

Hydrophone Calibration System Fig. 7 Hydrophone calibration system: Set-up for calibration in the 4 kHz to 100 kHz range using PULSE Multi-analyzer System Type 3560. Optional calibration up to 200 kHz is possible using Frequency Doubler WB-3475 Brüel & Kjær Hydrophone Calibration System Personal Computer Keyboard Emitted Tone Burst c = velocity of sound (in water) Hydrophone Calibration System 9718 Receiver Signal Current probe; Part of WB-3488 Measuring Gate Measured Received Signal Portion Water Tank Fig. 7 shows a PULSE-based system for calibration of the frequency response of...

systems terminating in Brüel & Kjær hydrophones. Type 4229 is battery powered and can be used both in the laboratory and in the field. The principle of operation of Type 4229 is the production of a sound pressure in the coupler cavity by four pistons which oscillate back and forth in phase. A frequency of 251.2 Hz is produced which is electronically maintained within ±0.1%. Fig. 8 shows sectional drawings of the calibrator. The calibrator couplers are shown fitted with their respective hydrophones. The typical sound pressure levels produced in the coupler volumes are 166, 162, 151.5 and 152...

Before measurements are taken, the high-impedance output signals from Hydrophones Types 8103, 8104 and 8105 should be routed through a signal-conditioning amplifier. Although the international standards call for calibration of the hydrophones’ voltage sensitivity (using a voltage amplifier), it is often more practical to use a charge amplifier, which will result in a charge sensitivity independent of the actual cable length. Although the entire Brüel & Kjær range of accelerometer preamplifiers is suitable, Conditioning Amplifier Type 2635, Measuring Amplifier Type 2525, or one of the NEXUS...

Hydrophones are particularly useful for measurements under extreme environmental conditions that could damage ordinary microphones or affect their performance, such as very high humidity and temperature, or polluted atmospheres. Hydrophones may also be used for measurement of extremely high sound pressure levels. Please note that Type 8103 is quite sensitive to acceleration (up to 115 dB/ms–2 when vibrated axially and up to 128 dB/ms–2 when vibrated perpendicular to the hydrophone axis. As always for hydrophones the dB reference pressure is 1 μPa. Typical receiving response in air for...