Pyroelectric anemometer

A fluid flow rate indicator comprising:

• a pyroelectric substrate;
• a longitudinal heater element located on the surface of said substrate;
• power supply means for applying a sine wave power input to said heater element;
• electrode means comprising two electrodes located on said substrate parallel to said longitudinal heater element, one of said electrodes located on each side of said heater element;
• differential amplifier means having two inputs one input connected to one of said electrodes and the other input connected to the other of said electrodes, said differential amplifier comprising means providing an output which is a function of the difference between charges present at said two electrodes;
• and
• lock-in-amplifier means having two inputs one of which is connected to the output of said differential amplifier and the other of which is connected to said power supply means, for providing an output indicative of the flow rate of a fluid flowing over said substrate in a direction perpendicular to the longitudinal orientation of said heater element.

A thermal conductivity indicator comprising:

• a pyroelectric substrate having at least one surface;
• means for applying a fluctuating heat input to said substrate, said input causing a fluctuating surface charge distribution in response to temperature fluctuations of said substrate;
• and
• electrode means on said surface for sensing a fluctuating surface charge on said surface, said charge fluctuations comprising said thermal conductivity indication.