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| Design Principle of Ultrasound Transducer |
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| Source：Suzhou Jiahui Ultrasonic Technology Co., Ltd Release time：2018-12-17 |
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Ultrasound mainly studies the generation, transmission, reception, information processing and related effects of ultrasound in different media.
I. Performance Indicators of Ultrasound Transducers
Ultrasound transducer is an energy converter. Its characteristic parameters include resonance frequency, frequency bandwidth, electromechanical coupling coefficient, electroacoustic efficiency, mechanical quality factor, impedance characteristic, frequency characteristic, directivity, emission and reception sensitivity.
(1) Performance indicators required by both transmitting and receiving transducers
1. Working frequency
The working frequency of the transmitting transducer is equal to its own resonant fundamental frequency. The working frequency of the active ultrasonic transducer in the receiving state is approximately equal to that of the transmitting state. The working frequency of the passive receiving transducer is a wider frequency band. At the same time, the resonant fundamental frequency of the transducer itself is required to be higher than the highest frequency band.
2. Electromechanical conversion coefficient n and electromechanical coupling coefficient K of transducer
The electromechanical conversion coefficient of ultrasonic transducer refers to the ratio of the mechanical quantity (or electrical quantity) after conversion to the electrical quantity (or mechanical quantity) before conversion.
For transmitting transducers, the electromechanical conversion coefficient n = force or vibration speed/voltage or current;
For receiving transducers: electromechanical conversion coefficient n = response potential or current/force or vibration speed;
The electromechanical coupling coefficient of transducer is a physical quantity describing the degree of energy coupling in the process of energy conversion.
For transmitting transducers: K2 = the alternating mechanical energy/the alternating electromagnetic energy stored in the electromagnetic system obtained by the mechanical vibration system due to the force effect;
For the receiving transducer, K2 = the alternating electromagnetic energy (AME) obtained by the electromagnetic system due to the electrical effect/the AME stored by the mechanical system due to the action of the acoustic field signal;
3. Impedance characteristics of transducers
The transducer should match the terminal circuit of the transmitter or the input circuit of the receiver in circuit design.
4. Quality Factor Q of Transducer
The Q value of the transducer is closely related to its working frequency bandwidth and energy transmission efficiency. Usually, the energy efficiency quality factor of the transducer is calculated by using the equivalent circuit diagram and the equivalent mechanical diagram of the transducer.
5. Directional characteristics
For the transmitting transducer, the sharpness of its directional characteristic curve determines the concentration of its acoustic energy. For the receiving transducer, the sharpness of its directional characteristic curve determines the scope of its exploration space direction angle.
6. Frequency characteristics of transducers
Frequency characteristics of transducers refer to the characteristics of some important parameters of transducers varying with working frequency.
(2) Specific performance indicators for transmitting transducers
1. Emission Acoustic Power
It is a physical quantity describing how much sound energy the transmitter radiates to the medium sound field per unit time.
2. Emission efficiency
Emission efficiency is usually described by three kinds of efficiency, namely, electromechanical efficiency, electroacoustic efficiency and electroacoustic efficiency.
Electromechanical efficiency refers to the efficiency of the transducer in converting electrical energy into mechanical energy.
Mechanical acoustic efficiency refers to the efficiency of the transducer in converting mechanical energy into acoustic energy.
Electroacoustic efficiency refers to the efficiency of the transducer in converting electrical energy into acoustic energy; it is equal to the product of electromechanical efficiency and acoustic efficiency.
(3) Specific performance indicators for receiving transducers
1. Sensitivity of Receiving Transducer
The so-called free-field voltage sensitivity of the receiving transducer refers to the ratio of the output voltage of the receiving transducer to the sound pressure of the free-field before the transducer is introduced into the sound field.
2. Equivalent Noise Pressure
A sinusoidal sound wave is incident on the receiver (if the receiver size is not much smaller than the acoustic wave, it should be projected on the vibration surface along the normal incident direction). When the effective value of the output voltage equals the RMS voltage of the receiver's self-noise over a Hertz bandwidth, the effective value of the incident sound pressure is called the effective noise pressure. The equivalent noise pressure of the receiver is numerically equal to the ratio of the RMS voltage of the self-noise to the sensitivity of the receiver over a Hertz bandwidth.
2. Research Method of Ultrasound Transducer
Three sets of basic equations are needed to study the energy conversion and transmission of transducers:
1. Mechanical Vibration Equation
2. Circuit State Equation
3. Electromechanical Conversion Relation
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