![]() Signal exciting a mechanical resonance in the piezo element. The resonances result from the electrical input The presence ofĮlectrical resonances and anti-resonances make the piezoelectric The impedance for a non-piezoelectric element (of the same shape andĭielectrical properties) is also shown in blue. For a (simple geometry) piezoelectricĮlement, the electrical impedance over a given frequency range will Impedance is defined as the voltage drop across an element divided by ![]() The difference stems from the coupling of electricalĮnergy input to mechanical motion output. Non-piezoelectric dielectric elements when driven at high-enoughįrequencies. It differs substantially from the impedance of The electrical impedance is a distinguishing characteristic for The following article covers some basics of impedance vs. If you can find the source of certain 'terms' used to describe piezoelectric crystal behaviour then we can try to interpret them for you. They are not including lower sub-harmonics which emit out the side of the crystal, and the driver amplifier is designed not to allow these out-of-band frequencies. This is equivalent to the "average resonant impedance". However the term "Fundamental Radial Resonance" refers to the center point between the peak resonant frequency and the peak anti-resonant frequency. I could not find the term "average resonant impedance", at least during the searches I did. For a given resonate frequency a small variation in frequency is allowed, with less output as you move further away from the center point of peak resonate output. It is a basic law of physics that the larger the crystal, the lower the resonate frequency. Damage would occur if the intensity of the signal was too strong, and/or the crystal gets too hot due to a lack of a heat sink or high ambient temperatures. The anti-resonant frequency consumes the most amount of current and produces the lowest output level possible. The resonant frequency consumes the least amount of current and produces the highest output level possible. This protects both the driver and the crystal from non-resonate frequencies and DC offset currents that can warp the crystal. Often the driver is custom made for a certain type of Piezoelectric crystal. Those for 1MHZ to 10MHZ ultra-sound are small rectangles epoxied to a resonant plate. These disc are about 1"/25mm in diameter. Those for audio and low frequency ultra-sound have a capacitance of about 150nF. Piezoelectric transducers have large capacitive values compared to other transducers. Piezoelectric transducers have several major issues from the driving circuits point of view:Ĭapacitance.
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