Ray characteristics of ultrasonic waves are formed in a straight line when they encounter two substances with different acoustic impedance ratios.At the interface, reflection and refraction transmission occurs. The reflection and refraction of ultrasonic waves follow the laws of geometric optics. The greater difference in the acoustic impedance ratio between the two interface media has the stronger reflection, and the smaller the acoustic energy is penetrating into the second medium. In the two parallel reflective interfaces of the layer, the sound waves can be reflected back and forth multiple times until the energy is reduced to zero. When the sound beam of transducer for flowmeter is projected onto the concave or convex surface or the irregular interface, it also causes focusing and scattering like light. When the wavelength of the ultrasonic wave is compared with the size of the obstacle, diffraction phenomenon occurs and when the ultrasonic wavelength is much smaller than the size of the obstacle, the diffraction phenomenon is negligible.
Absorption characteristics of ultrasonic waves in addition to the energy attenuation introduced by the the wavefront, are mainly the energy absorption attenuation of the propagation medium. For the simple harmonic plane wave, if the medium absorption problem is considered, the particle displacement motion of the simple harmonic wave is propagating in the positive direction of ultrasonic fuel level transducer is described. About doppler effect,When there is relative motion between the sound source and the target, the sound wave is reflected from the target will appear frequency shift phenomenon. This phenomenon is called Doppler effect. 4f is the frequency shift value, V is the relative motion speed between the target and the sound source, and Y is the angle between the incident direction of the ultrasonic wave and the target moving direction, and is also the wavelength. When the direction of propagation of the sound wave coincides with the direction of motion of the object,which is a negative value; otherwise a positive value. This is the basic principle of doppler speed measurement.
The main performance index of the ultrasoni transducers in addition to determining its resonant frequency characteristics, it is more important to understand its electrical-to-sound conversion characteristics and acoustic radiation characteristics. The main performance indicators of the transducer are as follows aspects: (1) The working frequency f is mostly selected near the mechanical resonance frequency of the transducer. Therefore, the operating frequency of the transducer generally refers to the mechanical resonance frequency of the transducer. The electromechanical cohesion coefficient K electromechanical coupling coefficient K is an important parameter indicating the coupling between the mechanical energy and the electric energy of the piezoelectric transducer.
Because the mechanical energy of the piezoelectric vibrator is related to the shape and vibration mode of the vibrator, the vibration mode is different and the electromechanical cohesion coefficient is also different. In general, additional subscripts are used to indicate different modes of vibration, such as Kp, which represents the electromechanical cohesion factor of the radial vibration mode of a thin wafer. Obviously, K is a dimensionless physical quantity. The electromechanical quality factor Qm, Qm is the physical quantity that refers to the electrical quality factor Qe to the mechanical vibration system. Qm also has three definitions,mounted outside ultrasonic transducer is represented at the resonant frequency. The frequency value on the left and right half power points is called the bandwidth of the transducer.
Because the mechanical quality factor m reflects the degree of mechanical energy loss of the piezoelectric vibrator during the resonance process, the mechanical quality factor of the transducer is closely related to its electromechanical coincidence coefficient. In addition, it is also closely related to the electromechanical properties of the transducer structure, materials as well as the radiation impedance of the medium. the same transducer is easily 30 in the liquid medium and 20 in the air. It can be seen that the frequency band of the ultrasonic transducer in the air medium is relatively narrow.
The impedance characteristics of the transducer are based on the equivalent electromechanical six-terminal diagram of the transducer, each with a certain characteristic impedance. Therefore, the transducer is required to match the impedance of the final stage of the transmitting circuit (or the primary of the receiving circuit). In addition, depending on the ray characteristics of the ultrasound, the transducer is also required to match the radiated acoustic load (or receiving acoustic load). How to realize electromechanical impedance matching and acoustic impedance matching technology is one of the key problems that must be solved in the development of ultrasonic transducers. The directional characteristic of the transducer is suitable for both the transmitting and receiving ultrasonic transducers. When the size is greater than or equal to the wavelength of the acoustic wave of the medium, the acoustic energy emitted/received is concentrated in certain directions, and the acoustic energy is concentrated. (or sound pressure) is a function of azimuth. Usually, the curve of sound pressure with azimuth is called a directional pattern.
Frequency characteristics of the ultrasonic flowmeter transducer is one of the main parameters of the transducer. It refers to the characteristics of impedance, sound pressure and sensitivity as a function of frequency. In practical applications, it is generally desirable for the ultrasonic transmitter to obtain a flat impedance characteristic in a certain frequency band to adapt to changes in the load, to avoid impedance mismatch, which is resulting in circuit heating, reduced energy conversion efficiency, and even damage to the device. The wideband of ultrasonic receiver is capable of receiving a narrow pulse signal or a wobble signal with a short afterglow time, and thus has an extremely high displacement resolution in the direction of the acoustic axis. The power and energy conversion efficiency of the transducer are also technical indicators that must be considered in the development of ultrasonic transducers. Among them, the efficiency of the transducer depends on the shape of the vibration,it is the material of the transducer, the structure of the mechanical vibration system and the washing of the operating frequency.
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