Pyroelectric anemometers

A new class of pyroelectric anemometers is described based on a thin, narrow NiCr film heater and two symmetric electrodes simultaneously deposited on a thin z-cut LiTa03wafer. A NiCr ground plane is used on the other face. An ac voltage drives the heater to produce a thermal current at 2x the voltage frequency. This thermal current produced an ac current at each electrode. The differential signal is a measure of the average temperature difference of the two electrodes. In the absence of a fluid flow velocity, u(∞), the signal is zero. We find that the signal is proportional to u^1/2(∞) as expected and that it is proportional to the drive power squared. Flows as low as 1cm/ min in N2have been measured.