Last Updated on November 4, 2021 by You Ling
Piezoelectric sonar technology & underwater detection system
The main applications:
- Underwater imaging
- Sonars for the underwater detection system
1. What’s Sonar?
Sonar, it can be called “Sound Navigation And Ranging, “Sound Navigation And Ranging” is an electronic device that uses the propagation characteristics of sound waves underwater, through electro-acoustic conversion and information processing, to complete underwater detection and communication tasks.
Observation and measurement in the water, only sound waves have unique conditions. This is because the range of action of other detection methods is very short, and the penetration ability of light in water is very limited. Even in the clearest sea, people can only see objects within a dozen meters to tens of meters; electromagnetic waves are also in the water. The attenuation is too fast, and the shorter the wavelength, the greater the loss. Even if high-power low-frequency electromagnetic waves are used, they can only propagate tens of meters. However, the attenuation of sound waves propagating in water is much smaller. When a bomb of several kilograms is exploded in the deep-sea soundtrack, signals can be received from 20,000 kilometers away, and low-frequency sound waves can penetrate several kilometers of the seafloor. And get the information in the stratum. For measurement and observation in water, no more effective means than sound waves has been found so far.
Sonar is not a human patent, many animals have their own “sonar”. Bats use their throats to emit ultrasonic pulses 10-20 times per second and use their ears to receive their echoes. With this “active sonar” it can detect very small insects and metal wire obstacles with a thickness of 0,1 mm. Insects such as nocturnal moths have “passive sonar”, which can clearly hear the ultrasound of bats 40m away, so they can often avoid attacks. However, some bats can use high-frequency ultrasound or low-frequency ultrasound beyond the insect’s listening range, so that the hit rate of catching insects is still very high.
In the past, the underwater acoustic emission transducer of sonar was mainly made of piezoelectric ceramic material (PZT). The underwater acoustic transducer made of this material has a high frequency (above 20kHz), and at the same time has a small emission power, a large volume, and is very heavy. In addition, with the development of naval stealth technology, modern naval vessels can absorb sound waves with frequencies above 3.0kHz and play a role of stealth. All industrialized countries are vigorously developing low-frequency (frequency tens to 2000 Hz), high-power (sound source level of about 220dB) sonar or underwater acoustic countermeasures launching underwater acoustic transducers, and have been used to equip the navy.
2. Piezoelectric ceramic for Underwater Imaging Application
Piezoceramics are used in transducers for underwater imaging systems. Their purpose is to measure and describe targets in the water and on the bottom. They are used also for the identification of the features on the bottom of oceans, lakes, rivers, etc. Underwater imaging uses sonars directed towards the bottom and other imaging principles. They provide accurate 2D or 3D images with detailed information of the surveyed area.
2.1 How it works ?
Sonar-based systems all rely on sonar transducers to generate a sound wave or pulses of sound. Sonar systems can be divided into three categories depending on the complexity of the sonar. The complexity of the sonar decides how much information you can extract from the sonar. Underwater imaging is the most complex type of sonar, where the returning echoes of the sound waves are displayed in detailed 2D or 3D mapping.
2.2 Which piezo material can be used for underwater imaging?
Devices for underwater imaging are usually fitted with piezo components made of soft piezoelectric materials (PZT-5A, PZT-5H). They have various shapes and sizes depending on the application. Noliac can deliver single elements of piezoelectric blocks in sizes up to 100×100 mm, which could be consequently diced to a matrix of elements with uniform properties.
3. Piezoelectric ceramic for Fishfinders Applications
Fishfinders are usually constructed with piezo components of various shapes and sizes depending on the application. Materials for simple sonars could be the hard type of piezoceramics (PZT-4, PZT-8, ). They provide high power density and high sensitivity. However, for smart sonars working with high resolution, respectively with aperture synthesis, it would be better to use soft piezoelectric materials (PZT-5A, PZT-5H). The soft material has low mechanical Q and provides higher resolution. The multilayer piezo ceramic could be used effectively as a separate transmitter of waves. It reduces the necessity of high voltage driving. Compared to normal monolayer piezoceramic elements, the driving voltage could be reduced by increasing the number of layers in the multilayer element case.
4. Sonars for the underwater detection system
Sonar (sound navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name “sonar”: passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of “targets” in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used for robot navigation, and SODAR (an upward-looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.
The first recorded use of the technique was by Leonardo da Vinci in 1490 who used a tube inserted into the water to detect vessels by ear. It was developed during World War I to counter the growing threat of submarine warfare, with an operational passive sonar system in use by 1918. Modern active sonar systems use an acoustic transducer to generate a sound wave which is reflected from target objects
4.1 What piezo material we can recommend to you?
Transducers for underwater communication devices are usually fitted with piezo components of various shapes manufactured of soft piezoelectric materials (PZT-5A, PZT-5H). However, for high power applications, electrically hard materials (PZT-45, PZT-44, PZT-47) should also be considered. Sizes depend on the application.