Experiments with Piezo Ceramics (1)

What do capacitors, electret microphones and passive infrared sensors have to do with one another? It is often interesting to go back to first principles and carry out a few experiments on the underlying phenomena. Electronics and physics belong together: and here we look at the physics behind some electronic components.First, a simple experiment: take a ceramic capacitor and apply a high voltage. Now heat it briefly to 80 or 100 degrees Celsius, and let it cool slowly, keeping the voltage applied. The capacitor is now a completely new component with astonishing properties.The voltage used must be on the limit of what the capacitor can stand: this will, depending on the capacitor, typically be anywhere from around 50 to over 500 V. Great care is required when using high voltages. Figure 1 shows an isolated high-voltage supply, which allows a voltage in the desired range to be generated. Here a kind of adjustable transformer has been constructed from two transformers. A model railway transformer (without its rectifier) can also be used. A resistor limits the current to a safe value. The contacts must still nevertheless not be touched: and the voltage across the charged capacitor is not safe and can lead to painful skin burns.