A Speckle Pattern Velocimeter Using a Periodical Differential Detector

Abstract

A new method for non-contact velocimeter is proposed. A one-dimensional photodiode array, whose diodes are connected differentially, is used instead of a parallel slit array, in order to remove the low frequency noise. Then, the output signal of the differential detector is restricted to a narrow band signal, whose center frequency is proportional to the velocity of a rough surface. Since the output can be directly fed to a frequency counter, the restriction of the measurement range due to the cut-off frequency of the high pass filter is lifted. The characteristics of the proposed velocimeter are studied with the aid of spectrum analysis and some experimental results are shown.