PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Development of Underwater Acoustic Transducers
Yang LIU1; Houlin FANG1; Liangyong ZHANG1; Fang ZHANG1; Deyu SUN
1

Northwest Institute of Nuclear Technology, China

ABSTRACT
Underwater acoustic transducer which undertakes the task of signal generation and reception is the coreequipment for sonar detection. For understanding the mechanism of underwater acoustic transducers, wehave reviewed recent typical transducers based on different working principles and different vibration modes,
including electrodynamic hydroacoustic transducer, explosive hydroacoustic transducer and flextensionaltransducers. Our research is of great importance for obtaining underwater acoustic transducer with higher
performance.
Keywords: Underwater acoustic transducer, Electrodynamic hydroacoustic transducer, Explosivehydroacoustic transducer, Flextensional transducer

1. INTRODUCTION
As the core component of sonar detection equipment, underwater acoustic transducer that
undertakes the signal generation and reception plays a decisive role in the realization of underwater
acoustic detection. Therefore, it is also vividly described as the "eyes and ears" in sonar system. In1914, the electric hydroacoustic transducer was designed and manufactured by Faison. The transducer
operates at a frequency range of 500Hz to 1 kHz and the emitting waves can detect icebergs up to two
kilometers away. In 1915, the submarine built by Canada was equipped with the hydroacoustic
transducer designed by Faison. Since then, underwater acoustic transducer has become importantunderwater acoustic equipment. In 1918, French physicist Langevin produced a new underw ater
acoustic transducer by the piezoelectric material quartz, which started the era of modern hydroacoustictransducers(1). After a hundred years of development, functional materials, new structure, newmechanism have been applied in hydroacoustic transducers to improve their performance, and these
new idea make the great effort for the development of modern sonar technology.
Hydroacoustic transducer can produce underwater acoustic signal from Hz to MHZ, and theirworking principle includes electrodynamic type, explosive type, magnetostriction, piezoelectricity
and so on, the vibration models include longitudinal vibration, lateral vibration, bending vibration andthe combination of several vibration models. What is more, the function materials applied inhydroacoustic transducers include Terfenol-D giant magnetostrictive materials, PZT piezoelectricmaterials, PMN-PT single crystal materials, PVDF piezoelectric polymer and so on. Therefore, somany typical transducers are manufactured, such as flexural transducer, cylindrical radiant transducer,
longitudinal transducer, cymbal transducer and Janus-Helmholtz transducer(2).
In this research, we have listed several typical hydroacoustic transducers, the investigation may
give an insight into designing the underwater acoustic transducer with high performance..

2. Hydroacoustic transducer
2.1 Electrodynamic hydroacoustic transducer
The representative electrodynamic low frequency transducers are the G -series and J-series
manufactured by U. S. underwater defense center, including G34, J9, J11, J15 and J15-3. As shown in
Figure 1, the electrodynamic low frequency transducer J9 has a working frequency range from 40 Hz
to 20 kHz, the vibrating diaphragm of radiant head is made of magnesium alloy and rubber suspension
system. Thus, its maximum underwater working depth can be 26m and the maximum sound source
level can reach 155dB(3).

1liuyang@nint.ac.cn

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Figure 1-Electrodynamic low frequency transducer J9Figure 2 shows the electrodynamic high-power low-frequency transducer UW600 with working
frequency range from 4 Hz to 1 kHz, working depth from 2 m to 200 m, and its maximum sound source
level can reach 188 dB. Figure 3 shows beam transducer produced by Alliant Techsystems. The central
frequency is 75Hz and its maximum sound source level can arrive at 197dB. In addition, there is aspecial pressure compensation device in the sound source, which induce the transducer to work in
700-1000m deep water(4).

Figure 2-Electrodynamic high-power low-frequency transducer UW600

Figure 3-Beam transducer produced by Alliant Techsystems
2.2 Explosive hydroacoustic transducer
The widely used explosive low-frequency hydroacoustic transducers are air gun and plasma soundsource. Air gun can emit the high-pressure compressed air into the water through the pulse mode.
Moreover, the high-speed gas induces the surrounding medium to generate low-frequency vibration,
which produces the low-frequency sound wave. Simple structure, small size, high emission power and
80% of the power concentrated in the low frequency band make the air gun be popular (5).
Nowadays, the popular air gun is the Par series air guns produced by American company Bo lt, asshown in figure 4. Its working frequency range is 100 Hz to 1.2 kHz, and it was widely used in theground acoustic inversion test by the U. S. military in 2003. The American company Hydroacoustics
has developed HLF low-frequency air gun with a working frequency range from 10 Hz to 300 Hz, and1944

its sound source level can be 190 dB to 215 dB. Moreover, HLF needs no pressure compensation
device while working in water depth above 300 meters. Since 1975, about 120 sets have been delivered
to the U.S. navy and other users(6).

(a) Par series air gun(b) Air gun array
Figure 4-Air guns and array
The acoustic emission mechanism of the plasma low-frequency sound source is the hydroelectriceffect, that is, the energy stored in the high-energy storage capacitors is discharged in water to form ahuge pulse current instantaneous. The electric energy is directly changed into the explosion energy,
which form a supersonic shock wave to propagate outward, and then attenuated into the sound pulse .
The sound source level can reach above 260 dB. Because of high electro-acoustic conversion
efficiency, a highly directional beam can be formed by acoustic lens focusing technology.
Representative plasma sound source is multi-electrode goe-spark series produced by Geo Marine
Survey Systems, as shown in figure 5. A single electrode of the sound source can release energy from
3J to 13J, and different number of electrodes can be combined to satisfy the requirement of high-power
emission(7).

Figure 5-Multi-electrode plasma sound source goe-spark series
In addition, the laser sound source is also be studied by many researchers. The mechanism of lasersound source includes thermal expansion, electrostriction, explosion, surface gasification and opticalbreakdown. The sound source level induced by laser sound source can reach more than 220dB, and thefrequency band can cover several Hertz to several hundred kilohertz. Therefore, it has great
development potential in underwater target positioning, communication and detection.
2.3 Flextensional transducers
Flextensional transducers can be divided into many types, and the most widely used type is IV
flextensional transducer. The flexural vibration of the longitudinal oscillator can let the elliptical shellemit low-frequency high-power sound, which induce IV flextensional transducer be the low-frequency
active sonar. As shown in figure 6, 18 sets of high-power IV flextensional transducers form the verticaltransmitting active sonar, named SURTASS-LFA. Its working frequency band range from 100 Hz to500 Hz and the sound source level can reach 220-235 dB. The single transducer is driven by two
S11-48 power amplifiers with an output voltage of 1600 V, which produces a maximum sound source
level of 215 dB(8).

1945Figure 6-Towed low-frequency active sonar (SURTASS-LFA)
Figure 7 shows the ITT's 6969-3500 flextensional transducer with glass-fiber elliptical shell. Its
resonant frequency is 3.2 kHz, available bandwidth can be 2.8 kHz to 10 kHz (nearly two octaves), themaximum sound source level is 200dB and the maximum depth is 230m(9).

Figure 7-6969-3500 flextensional transducer with glass-fiber elliptical shell
As shown in figure 8, Moosad from India designed a new IV flextensional transducer withresonance frequency of 3 kHz in 2010. The parabolic reflector is equipped in front of the ellipticalshell, which leads to 1.7 dB to 8 dB higher in the range of 2.5 kHz to 4 kHz along the sound axis. Thus,
the new structure has realized the directional emission(10).

Figure 8-Flextensional transducer with parabolic reflector
In 2009, Richard from Canada designed a new concave cylindrical flextensional transducer. As
shown in Figure 9, setting several transducers in a finite volume can maximize the volume
displacement and realize high-power characteristics. The vertex clusters of six concave cylindricalflextensional transducers are connected to form a "three-dimensional six-pointed star" type transducer,

1946which possesses compact structure, low frequency, high power, wide frequency band and so on. Firstly,
when the fundamental resonance frequency is 1.15 kHz, its fully directional transmission voltage
response is 127 dB. Secondly, the transmission voltage response is greater than 120dB in the frequency
range from 800 Hz to 10 kHz(11). Lastly, when the frequency is higher than 4.75 kHz, the directivity
fluctuation is obvious (about 6dB).

Figure 9-"three-dimensional six-pointed star" transducer

3. Conclusions
In summary, our research lists the latest hydroacoustic transducers in the following three parts:
Electrodynamic hydroacoustic transducer, explosive hydro- acoustic transducer and flextensionaltransducers. We present their working principle and performance in detail and we hope that ourinvestigation should be the great effort for designing high-performance underwater acoustic
transducer.

REFERENCES
1.

Song H C., Cho S., Kang T. Long-range acoustic communication in deep water using a towedarray[J]. J. Acoust. Soc. Am, 2011, 129(3):71-75.
2. Frederic Mosca, Guillaume Matte. Low-frequency acoustic source for long-range underwatercommunication [J]. J. Acoust. Soc. Am,2013, 133(1): 61-67.
3. Gordon D. Tyler. The emergence of low-frequency active acoustics as a critical antisubmarine
warfare technology[J]. Johns Hopkins APL Technical Digest, 1992,13(1): 145-159.
4. JanF. Lindberg. Material challenges for transducer designers in the 21 st century [C]. Bangalore:SPIE, 2002: 485-498.
5. Rolt K D. History of the flextensional electroacoustics transducer[J]. J. Acoust. Soc. Am. 1990,87(3): 1340-1347.
6. Xiping Mo, Houqing Zhu . Thirty years progress of underwater sound projectors in China [C].
Beijing: AIP(OA2012), 2012: 94-104.
7. Harold C. Robinson, James M. Powers, Mark B. Moffett. Development of broadband, highpower single crystal transducers. Proceedings of the 2006 SPIE International Symposium onSmart Structures and Materials.
8. Kenji Saijyoua, Tomonao Okuyama. Design optimization of wide-band Tonpilz piezoelectrictransducer with a bending piezoelectric disk on the radiation surface[J]. J. Acoust. Soc. Am.,
2010,127(5): 2836-2846.
9. S. C. Butler. High frequency multi-resonant broadband transducer development at NUWC, UDT
2002: 588-594.
10. Ralph S. Woollett. Basic problems caused by depth and size constraints in low-frequency
underwater transducers[J].J. Acoust. Soc. Am, 1980, 68(4): 1031-1037.
11. Butler, A.L, Butler, J.L. A deep-submergence, very low-frequency, broadband, MultiportTransducer[C]. OCEANS’02 MTS, IEEE, 2002: 2350-2353.

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