Ultrasonic probe is a sensor that generates ultrasound and receives its echo. Ultrasonic probes can convert electrical energy into sound energy, and sound energy into electrical energy.As the key component of the ultrasonic level gauge, the performance of the ultrasonic probe directly affects the intensity of the transmitted ultrasonic wave, the strength of the received echo signal, and the range of the level gauge. So it can be said that the quality of the ultrasonic probe directly determines whether the ultrasonic level gauge can work normally and stably.Ultrasound is generated by exciting an ultrasonic probe with high-frequency electric pulses, and the probe converts the reflected ultrasonic energy into a voltage signal. The piezoelectric ceramic in the piezoelectric probe has a piezoelectric effect, and the most common method to realize electro-acoustic energy is to use a piezoelectric probe.In order to enable users of the instrument to have a deeper understanding of the ultrasonic level gauge, this article discusses the structure and main performance indicators of the ultrasonic level gauge probe as follows.01 Piezoelectric probe structureThe structure of the piezoelectric probe: It is composed of piezoelectric ceramics, matching layer, damping block, protective film, shell and high-frequency cable.Damping block.It is made of some damping materials, adhered to the back of piezoelectric ceramics, mainly to absorb the ultrasonic waves on the back of piezoelectric ceramics to reduce noise.High frequency cable (high frequency cable)The ultrasonic probe needs to be connected to the ultrasonic drive circuit board through a high-frequency cable, which can shield the drive pulse and echo signal of the ultrasonic probe from various external interference noises.Protective film (protective film)Its function is to protect piezoelectric ceramics and electrodes from wear and damage. The protective film must have good wear resistance, high strength, small sound attenuation, good sound transmission performance and appropriate thickness.Piezoelectric ceramics (piezoelectric ceramics)Piezoelectric ceramic is the core component of the probe, and its performance is directly related to the quality of the probe. Its function is to transmit and receive ultrasonic waves. Both sides of the ceramic are coated with silver layers as electrodes to make the voltage supplied to the ceramic plate uniform. The electrode bonding wire on the ceramic board leads to the circuit, and the ground wire on the bottom is connected to the common point of the circuit to form a loop.A shell (housing)The probe housing is made of plastic and is mainly used to fix and protect the entire probe element.Matching layer (matching layer)The matching layer of the ultrasonic probe can match the acoustic impedance between the probe and the working load, which can effectively broaden the working frequency band of the probe, and further improve the ultrasonic resolution and work adaptability.02 main performance index of ultrasonic probeThe main performance indicators of the ultrasonic probe include: working frequency, sensitivity, quality factor, frequency response, electrical impedance, directional characteristics, etc. The performance indicators are now introduced as follows: 1. Working frequency f: The working frequency of the ultrasonic probe is determined by the resonance frequency of the piezoelectric ceramic, that is, the frequency at which the probe emits ultrasonic waves. When the ultrasonic probe works at this frequency, the output energy is the largest and the propagation distance is the farthest. 2. Quality factor Q: The quality factor Q of the ultrasonic probe is determined by the quality factors of the circuit part and the mechanical part. 3. Directional characteristics: The sharpness of the main lobe determines the range of the ultrasonic detection area, so the directional characteristics directly determine the working range and measuring range of the ultrasonic level gauge. The main lobe angle is the most important index of ultrasound directionality. The higher the ultrasonic frequency, the smaller the main lobe angle, the more concentrated the sound energy of the ultrasonic probe, and the narrower the sound velocity range. Figure: 4. Frequency response: The frequency response of the ultrasonic probe refers to the response ability of the ultrasonic probe to external signals and the frequency characteristics of the echo signal received by the probe. The frequency spectrum of the ultrasonic probe can be measured by a frequency analyzer to obtain parameters such as center frequency and bandwidth. 5. Sensitivity: Sensitivity refers to the ratio of the peak-to-peak value of the echo signal voltage output after the ultrasonic echo is converted by the probe to the peak-to-peak value of the driving pulse voltage applied to the probe. Sensitivity is a measure of the conversion efficiency between electric energy and sound energy of an ultrasonic probe. 6. Impedance characteristics: Due to the characteristics of the ultrasonic probe, the ultrasonic probe is required to match the impedance of the driving voltage to achieve the most ideal driving energy and echo receiving signal.
In fact, in practical applications, the requirements for the maximum test range, minimum test range (blind area), and launch angle (directional opening angle) of the probe are different, and comprehensive consideration is needed. After weighing the performance indicators, the probe structure should be selected. , Frequency, radiation surface, as far as possible to meet the actual needs.
Post time: 21-09-21