Transducer characteristics and calibration methods
A hydroacoustic transducer is a device that converts acoustic energy and electrical energy each other. The position in sonar is similar to the antenna in a radio, an acoustic system that emits and receives sound waves in seawater. A piezoelectric transducer ultrasound in which acoustic energy is converted into electrical energy is called a receiver or a hydrophone; a transducer that converts electrical energy into acoustic energy is called a transmitter. Some sonars use the same transducer to transmit and receive sound; others use separate emitters and hydrophones.
Hydrophone performance mainly refers to sensitivity and directionality. The receiving response of the hydrophone is the receiving sensitivity.
A hydrophone usually is an acoustic/electrical linear conversion device that has a scaling factor between the voltage it produces and the sound pressure of the sound field. This scale factor is called the response of the transducer. The receiving response ( receiving sensitivity) of the hydrophone is the terminal voltage of the hydrophone generated by the plane wave of the unit sound pressure (before the hydrophone is placed in the field). Conventionally, the receiving response is represented by an open circuit response in which the hydrophone is not connected to the load. Usually the receive response is recorded in decibels, the reference level is 1 dynes/cm2, and the sound pressure is 1V, and is written in dB. The transmitter's emission-current response indicates the axial distance in the beam pattern when the unit current is injected into the emitter. Sound pressure generated at 1 m. The emission response is usually expressed in decibels. The reference level is the sound pressure generated at the reference distance when is injecting the current of the emitter, and is written in dB. Conventionally, the reference distance refers to 1 m from the sound source; if the reference distance is 1 code, Plus 20log39.4/36, ie +0.87dB correction, transform the transmit response.It is the sound source level.
Hydrophones almost always use hydrophone arrays in their applications. Hydrophone arrays have a higher signal-to-noise ratio than individual hydrophone components because they can be used from isotropic or several identical noises. The signal of piezo tube stack is coming from the direction pointed by the array is extracted, that is, The directivity index is a receiving acoustic wave parameter used to measure the ability of a hydrophone array to extract signals from noise with its beam pattern. It is the number of decibels in which the signal-to-noise ratio at the output of the directional hydrophone is higher than the signal-to-noise ratio at the output of the non-directional hydrophone.
Calibration method In order to ensure the performance of the underwater acoustic equipment and the need for the transmission of the values, the hydrophone and transmitter must be calibrated. Calibrating a acoustic piezoelectric tubes is a function of the frequency and directivity of the transducer response. There are now a large number of methods for measuring transducer response. a summary of the calibration methods compiled by the Naval Ordnance Laboratory T.F. Johnston based on the literature. These methods have their own advantages and disadvantages for different transducer sizes and frequency ranges.
Transducing materials and acoustic materials PZT piezoelectric ceramics are developing towards industrialization. So far, lead zirconate titanate (PZT) piezoelectric ceramics have been used as water.The transducer material of the acoustic transducer still dominates. PZT piezoelectric ceramics developed by China Institute of Acoustics, commonly used models are PZT-4 (transceiver and dual-use), PZT-5 (receiving type) and PZT-8 (high-power emission type), and their performance can meet various underwater sounds. The needs of the transducer are compared to those of foreign countries. Transducing materials and acoustic materials Piezoelectric ceramics are developing towards industrialization.So far, lead zirconate titanate (PZT) piezoelectric ceramics still ranks first as the energy-transducing material for underwater acoustic transducers. PZT piezoelectric ceramics developed by China Institute of Acoustics, commonly used models are PZT-4 (transceiver and dual-use), PZT-5 (receiving type) and PZT-8 (high-power emission type), and their performance can meet various underwater sounds. They are needs of the transducer, its level and the foreign phase piezoelectric tube transducer d33 is measuring instrument developed in the piezoelectric ceramic measurement,which has been promoted more than 100 domestic,and edited the standard National Standard for Static Piezoelectric Strain Constant Measurement Method.Hydroacoustic materials mainly include sound absorption, anti-sound, sound and sound insulation materials, vibration damping materials and other research content. In this respect, the company has established the first underwater acoustic pulse tube test equipment, Fuyang's modulus and complex shear modulus test equipment, and is equipped with variable temperature and pressure device and microcomputer data processing system and high acoustic characteristics measurement system. In the field of sound absorbing materials, two kinds of water have been developed.They are acoustic sound absorbing material and three kinds of sound absorbing structure: flat cusp parallel channel type, square cusp and flat resonance type, which can meet the requirements of different frequency bands. The flat sound absorption tip has been widely used in the large and medium-sized muffler pools in China, and the sound pressure reflection coefficient is less than 10% in the frequency range of 8 to 100 kHz. In addition, T801 ~ T808 type sound-permeable rubber, cast type room temperature vulcanization, high-frequency sound absorption and sound-permeable materials, high sound absorption lining, sound absorption damping and putty type damping materials have been widely used in various engineering projects.Ultrasound simulation module series and ultrasonic simulation module series developed by ultrasonic human body tissue is the medical ultrasonic diagnostic instrument detection standard confirmed by the State Bureau of Technical Supervision and the State Administration of Medicine.
Hydroacoustic transducer and array
The most commonly underwater acoustic transducers are flat piston type, longitudinal vibrator horn type, round calibration type and curved type. China can design and manufacture various transducers that meet the needs of engineering, and the level is comparable to that of foreign countries.
(1) High-power transmitting transducer The high-density emission transducer (inlaid cylindrical transducer) of the ring is obtained, and the scientific and technological achievements of the Chinese Academy of Sciences are obtained. Among them, the "piezoelectric ring electrode" has obtained the utility model patent. The transducer is the first deep sea broadband in China. The high-power underwater acoustic emission transducer is used for sea-water exploration of the sea area. The technology has been successfully applied in acoustic systems such as underwater acoustic receivers, underwater positioning speedometers and analog targets. (2) bending transducer The vibration and sound radiation of the lantern-type flexural transducer were studied and analyzed by the finite element method, and the results have been widely applied to sonar equipment. Based on this, a concave bending transducer was also studied. Compared with the existing convex lantern-type bending transducers in the world, this transducer has higher sensitivity and volumetric speed, and is resistant to static pressure. In particular, this structure can achieve high broadband by using multimode vibration. The characteristics are highly praised by foreign water acoustic. (3) Research on piezoelectric composite hydrophone and rock transducer using PZT (3-3) sandwich composite piezoelectric material, the piezoelectric constant gh value is high and the figure of merit dh × gh is large and the vibration mode is better. Simple, and easy to match the characteristics of rock mass developed into broadband high sensitivity hydrophone and broadband narrow pulse rock ultrasonic transducer.
Process of Transducer:
The development of the piezoelectric sensor crystal involves a strong process and is often critical to achieving a new design. Combined with the research and development of underwater acoustic and ultrasonic transducers, a set of special technologies have been formed, such as polyurethane sulfur-free sound-permeable rubber casting and coupling process, composite pre-stressing technology, acoustic adhesive series and bonding technology has slow waveguide manufacturing processes, etc.,which have become extremely important technical means for the research work of transducers.