Solid-state frequency indicator

A new solid-state frequency indicator composed of a piezoelectric element and a liquid-crystal coating is fabricated, and first-order theoretical predictions are verified experimentally. The signal voltage is applied across the thickness of the piezoelectric element which is tapered in width along its length. As frequency is varied, the temperature rises locally near the region where the width is a half of a wavelength, because of vibration loss. This increase in temperature causes a color change of the liquid-crystal coating, and the position indicates the frequency of the applied signal. 7-8 s of rise and fall time are measured, and about 10 mW of electric power is sufficient for visual indication with a local temperature rise of several degrees centigrade. Many modificatios and applications should be possible.