On the microwave photonics based pulsed-time-of-flight techniques in the measurement of the thickness of dielectric sheets

This paper proposes a time domain measurement technique for characterizing the thickness of dielectric material based on pulse-domain microwave photonics and pulsed time-of-flight configuration. Short laser pulses from a semiconductor laser diode are converted to electrical pulses using a wideband photodetector. These pulses are fed to an antenna, providing a simple and accurate non-destructive measurement technique for material characterization. The thickness of the sample is calculated based on the propagation delay of a radio wave by measuring the transit time of a short electromagnetic pulse. The propagation delay is determined from the front edge of the energy envelope. Results show that the measured propagation delay is linearly dependent on the sample thickness. The technique achieves a measurement precision in the sub-mm range with a measurement time of 40ms.