2

When you apply a voltage to a insulator if the insulator is shaped appropriately its shape is changed.

When the piece of insulator returns to its initial state a voltage is generated by which is its polarity compared to the original voltage?

Voltage Spike
  • 75,799
  • 36
  • 80
  • 208
Se1fie
  • 97
  • 6
  • If C changes with shape, the. Q=CV is preserved if no leakage, but Current is generated from acceleration of motion (piezo effect). This is true for all ceramic except NPO – Tony Stewart EE75 Oct 08 '20 at 17:06
  • What about the direction of the current compared to the current which had changed the shape of the insulator. – Se1fie Oct 08 '20 at 17:17

1 Answers1

1

The voltage is related to the amount of mechanical strain/stress in the material and is a dynamic equation (has states changes over time): enter image description here Source: https://onscale.com/piezoelectricity/the-behavior-laws-of-piezoelectricity/

In short: to calculate the voltage generated, one needs to know

  1. the material and it's parameters
  2. the stress in the material (and how that is changing over time) which is derived from force and material properties.

When the piece of insulator returns to its initial state a voltage is generated by which is its polarity compared to the original voltage(step 1)?

Without getting too deep into the equations, the stress in the material starts to generate an electric field (the electrons have to be there in the first place). This then generates a voltage (and reduces the strain). If the strain is held steady then the voltage will be steady ( they build strain gauges with piezo electric materials). As the material relaxes, the voltage of the material falls (zero strain = zero voltage). So if the material is relaxing the voltage doesn't reverse, it falls toward zero. If you wanted to get a negative voltage, then you'd need to pull the piezo electric module instead of push it.

Voltage Spike
  • 75,799
  • 36
  • 80
  • 208
  • I'll add that some electronic cigarette lighters work by having a spring-loaded weight slam into a piezo crystal at high velocity. The relatively fast shockwave generates a high voltage, which emanates as a spark, igniting the fuel. – rdtsc Oct 08 '20 at 18:59
  • I've also seen a few equations where they have a constant for that specific module, so higher shock = higher voltage. Piezo transformers are really cool – Voltage Spike Oct 08 '20 at 19:17