Thermal Imaging Using Pyroelectric Detectors

Abstract

The pyroelectric detector is a new radiation detector that employs the temperature sensitivity of electrostatic polarization as the sensing principle. Electrically, the detector behaves as a capacitance on which a charge appears when thermally irradiated. This detector has a number of features that make its use attractive for thermal imaging. It does not require cooling, and no biasing voltage is needed. Being electrically capacitative, the noise decreases with frequency, and consequently it has a useful signal/noise ratio at frequencies far above that corresponding to its thermal time constant. Also, these characteristics suppress 1/f type amplifier noise and permit good performance at very low frequencies. A new thermal imaging device or thermograph has been developed to exploit these properties. This is a scanning radiometer that scans a 10 degrees x 10 degrees field in 30 sec with a 0.1 degrees x 0.1 degrees instantaneous element, thus giving 10,000 picture elements. It uses a 7.6-cm diam germanium objective lens and has a noise equivalent temperature of 0.1 degrees C. The thermal image is presented as either a black to white tonal picture or a color picture on Polaroid film. Examples of its use for nondestructive testing purposes are given.