抄録
New noncontact velocity measuring systems are proposed. The theory and the experimental results are described. These systems are composed of LASER, the spatial filters, and the photo-detectors. The spatial filters are combined to pass a single spatial frequency μ0 from the random pattern of measuring object transparency distribution. When the object moves at the velocity v, the output spectrum of the photo-detector is the narrow band random signal and its center frequency is μ0v. By measuring the center frequency, the object velocity is known.
In this paper, the random pattern of the object is assumed to be the two dimensional gaussian random process and the general relation between the power spectrum of the photo-detectors' output and the transparency distributions of the spatial filters is analyzed. After this relation, it is discussed how to make spatial filters to pass a single spatial frequency.
The theory of this paper can describe the characteristics of the system, called the “LASER doppler velocimeter”, systematically. As the results of this theory, the system performance is greatly improved by using a special photo-detector array instead of a single photo-detector. The signal to noise ratio and the range of velocity measurement are also improved.
The experimental results concerning the center frequency and the spectral width are in accordance with the theory. The standard deviation of the velocity measurement was 0.5%.
These systems are good at low velocity and extremely local velocity measurement.
