Sonar systems with piezoelectric transducers

Piezoelectric transducer, as a part of the sonar system, is a crucial component. The sonar system can only function properly when the components of the sonar are in good condition. The transducer is responsible for transmitting and receiving signals. To improve efficiency, transducers are typically arranged in an array. Let’s now learn about what sonar is, what a piezoelectric transducer is, and its applications through the following article.

1、What is Sonar?

Sonar, short for “Sound Navigation And Ranging,” is a technology that utilizes the propagation and reflection characteristics of sound waves in water for navigation and distance measurement. It also refers to the electronic devices used for detecting (presence, location, properties, motion direction, etc.) and communicating with underwater targets using this technology. Sonar is the most widely applied and important device in underwater acoustics, available in two types: active and passive.

Sonar systems have various applications in civilian fields, including depth sounders, multibeam echosounders, seabed profiling instruments, and Doppler navigational sonars. In the military, they are used for ship-based active and passive sonars, towed variable-depth sonars, towed array sonars, helicopter-dipped sonars, positioning, tracking, buoy sonars, and more. Piezoelectric sonar has played a significant role in both World Wars and civilian applications.

2、What is a Piezoelectric Transducer?

A piezoelectric transducer is a device made using the positive and inverse piezoelectric effects of piezoelectric materials. As the name suggests, a transducer is a device that can convert energy from one form to another.

Piezoelectric transducers utilize the piezoelectric effect of certain single-crystal materials and the electrostrictive effect of certain polycrystalline materials to convert electrical energy into acoustic energy and vice versa. Due to their high electro-acoustic efficiency, large power capacity, and the ability to be designed for specific applications based on their structure and shape, piezoelectric transducers find widespread use in the field of power ultrasonics.

3、What is the Langevin Transducer?

The Langevin transducer, initially used in fish finders, is made by bonding a 60mm diameter and 5mm thick piezoelectric ceramic disc with two steel pillars that are 14mm thick. It weighs approximately 700 grams and has a resonant frequency of 50kHz. When used as a transmitting and receiving transducer, its actual structure is shown in Figure 2. The transducer is encapsulated with rubber, and the sound waves radiate into the water through an approximately 1cm thick acoustically transparent rubber (the loss caused by the rubber is only 1dB, which can be neglected). The transducer portion outside the radiating surface is enclosed in sponge rubber, allowing the sound waves to radiate in only one direction.

4、Working Principle of the Langevin Transducer

Under high-power vibrating conditions, the Langevin transducer is prone to piezoceramic cracking. Figure 3 illustrates the structure of a composite rod transducer. By applying preload with a screw, the piezoelectric ceramic disc is not only bonded tightly between the front and back cover plates but also subjected to additional compressive stress, improving the resistance to ceramic damage and debonding under high-power operation. The front cover plate of the composite rod transducer is made of tapered light metal, which provides better impedance matching with the water medium and increases the radiating surface area. The back cover plate is made of tapered heavy metal, minimizing rear-end sound radiation and forming a good natural single-sided radiating vibrator.

5、What is echo sounders?

Echo sounding is based on the principle that ultrasonic waves will propagate in a straight line at a uniform speed in a homogeneous medium and will be reflected at the interface of different media, select the ultrasonic wave with the best penetration ability to water and a frequency around 1500 Hz, and emit sound vertically to the bottom of the water. The signal is recorded, and the time interval from the sound wave emission to the return of the signal from the bottom of the water is recorded, and the water depth is determined by the simulation method or direct calculation.

Echo sounders can also be used to detect and locate underwater objects, such as rocks, wrecks, and fish. They are commonly used by ships, submarines, and other underwater vehicles, as well as by scientists studying the ocean floor and marine life.

There are various types of echo sounders, including single-beam and multi-beam echo sounders, which emit sound pulses in different patterns and are used for different purposes.

6、How echo sounders works?

The working principle of the echo sounders is to use the transducer to emit sound waves in the water. When the sound waves encounter obstacles and reflect back to the transducer, according to the round-trip time of the sound waves and the speed of the sound waves in the measured waters, it can be obtained. The distance between the obstacle and the transducer.

Overall, echo sounders work by emitting a sound wave into the water and measuring the time it takes for the wave to bounce back, allowing the depth of the water to be calculated.

As a crucial component of sonar systems, piezoelectric transducers are responsible for sending and receiving signals to ensure the normal functioning of sonar systems. These transducers are often arranged in arrays to improve efficiency. Sonar technology utilizes the propagation and reflection characteristics of sound waves in water for navigation and distance measurement. Piezoelectric transducers are devices that can convert electrical energy into acoustic energy, and vice versa, using the piezoelectric effect. The Langerhans-type transducer, which consists of a piezoelectric ceramic plate and two steel columns, was one of the earliest transducers used for fish detection and has a resonant frequency of 50 kHz. The working principle of the Langerhans-type transducer involves the phenomenon of piezoelectric ceramic plate vibration under high power. The composite rod-shaped transducer is designed to withstand greater tension and improve damage and delamination in high-power operating states. The front cover of the composite rod-shaped transducer is made of light metal with a tapered shape to match the impedance of the water medium, while the rear cover is made of heavy metal with a tapered shape to minimize rear radiation and form a better natural single-sided radiation vibrator.

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