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在文献[1]中,我们曾经讨论了厚度模压电换能器在受到外电源的激励时直接产生的瞬变电压。曾指出这个电压同换能器接收超声信号时显示出的始脉冲宽度有直接联系,因而也和检测盲区的大小有直接联系。根据一维理论,这个应电压近似地是衰减的高频振荡,其频率接近于换能器所辐射声压的频率,叠加在一个指数曲线上,指数曲线系起源于外加瞬变电压对换能器钳定电容的充电。 本文给出了在阶跃电压的激励下具体计算应电压的步骤,并分析了几项结构参量对应电压的各自影响。理论采用了梅森(W.P.Mason)等效电路模型。这些参量是:(1)负载或背衬材料的声阻抗率,(2)压电片的机械Q值,(3)刚玉保护膜的厚度,(4)并联线圈的电感。 理论计算结果表明: (1)在轻负载或轻背衬时,高频振荡部分大而拖长;在重负载或重背衬时,则这部分小,并且较快地衰减。 (2)对于同一种压电陶瓷,当约Q<100,降低Q值会减小高频振荡部分的幅度,而当约Q>100,改变Q值并不显著地影响高频振荡。 (3)在轻负载的条件下,增加保护膜的厚度会加大高频振荡的幅度;在重负载的条件下,当负载的声阻抗率匹配或接近匹配压电陶瓷时,保护膜对应电压的影响不明显。 (4)从并联电感的初步探讨结果看,值得进一步研究加联电学元件的效应。 当压电材料为PT陶瓷时,关于改变负载或?
In [1], we have discussed the transient voltage generated directly by thickness-molded electrical transducers when excited by external power sources. It has been pointed out that this voltage is directly related to the initial pulse width displayed by the transducer when it receives an ultrasonic signal and is therefore directly related to the size of the detection blind spot. According to the one-dimensional theory, this voltage should be approximately a decaying high-frequency oscillation whose frequency is close to the frequency of the sound pressure radiated by the transducer and superimposed on an exponential curve originating from the applied transients Clamp capacitor charging. In this paper, we give a concrete step of calculating the voltage under the excitation of the step voltage, and analyze the respective influence of several structural parameters on the voltage. The theory uses the W.P. Mason equivalent circuit model. These parameters are: (1) the acoustic impedance of the load or backing material, (2) the mechanical Q of the piezoelectric sheet, (3) the thickness of the corundum protective film, and (4) the inductance of the parallel coil. Theoretical calculations show that: (1) At light loads or light backings, the high-frequency oscillations are large and prolonged; in the case of heavy loads or heavy backings, the part is small and fades more quickly. (2) For the same type of piezoelectric ceramic, reducing Q will reduce the amplitude of the high-frequency oscillation when Q <100, whereas changing Q approximately does not significantly affect the high-frequency oscillation when Q> 100. (3) Under the conditions of light load, increasing the thickness of the protective film will increase the amplitude of the high-frequency oscillation. Under the condition of heavy load, when the acoustic impedance of the load matches or closely matches the piezoelectric ceramic, the voltage of the protective film The effect is not obvious. (4) From the preliminary discussion of the parallel inductance, it is worth to further study the effect of adding electrical components. When the piezoelectric material is PT ceramic, about changing the load or?