Figure 3-1 plots the impedance response of an individual piezo ring before any gluing. There are two main resonant frequencies within the plotted frequency range. The first one at 59.4kHz is the radial mode of the piezo while the second one at 570kHz is the thickness mode. Mode 59.4kHz is mainly used for water cleaning; the high frequency mode at 570kHz, which has much lower impedance, is favorable for heating and therefore more suitable for de-icing.

Figure 3-1 Impedance Response of Piezo Only

The rated voltage of the piezo shall be defined by the peizo vendor. Our test shows that the piezo is possibly damaged when the Vp > 20V. When glued to a lens, the piezo can handle much higher voltage (~100V). Figure 3-2 shows the impedance response of a damaged piezo versus a healthy piezo for the radial mode. A damaged piezo shows a much higher impedance with additional noisy resonant peaks.

Figure 3-2 Damaged Piezo After Overdrive