![]() Piezos can be used at the resonance frequency for free-running, fixed-frequency applications such as ultrasonic vibrators. Operating well below the resonant frequency, the piezo can be modeled as a simple capacitor, C P. Impedance rolls off like a capacitance until resonance is reached. The electromechanical system of motion in a piezo is modeled by series LRC in parallel with the primary dielectric capacitor, C P (Figure 4). Improving displacement can be accomplished using multilayer (stacks) of piezos. Force (versus time) is the dominant factor in tactile feedback it determines a "good" user feel. applied voltage.įorce is proportional to applied voltage across the piezo (Figure 3). The displacement remains even if the electrodes are disconnected from the voltage source, except for the small leakage current found with any normal capacitor.įigure 3. ![]() Applied voltage does maintain a reasonably proportional relationship with the force generated by the piezo actuator (Figure 3C).Ĭharge on the piezo capacitance holds a good proportional relationship with the displacement over most of the piezo actuator's range of motion. Displacement of the piezo is proportional to the electric field, and the electric field is a function of the electrode voltages and the distance between the electrodes. When voltage is applied to the piezo, the capacitance also changes because the distance between the electrodes is changing (Figure 3A). ![]() But in the piezo, C is not constant since the spacing between electrodes changes with applied voltage. Based on its configuration and physical shape, the piezo will change shape as a (DC) voltage is applied across its terminals (Figure 2).Ĭoulomb's law states that Q = CV. Well below resonance, the piezo can be modeled as a simple capacitor.
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