Experimental evaluation of multifrequency ultrasonic range finder in air with a reduced number of frequencies

The multifrequency acoustic range finder in air was proposed and investigated experimentally using a frequency aperture of 42 kHz around 210 kHz The ranee accuracy was 1/30 times the wavelength, namely 50 mu m. However, the number of elements in a frequency array was as large as 64 and the frequency aperture width was only 10% of the center frequency, which is typical of the acoustic transducer in air. In this study, the number of elements in a frequency an ay is reduced to 16 within the passband of the transducer. The range accuracy is improved by aperture extrapolation applying an autoregressive (AR) model to a series of complex amplitudes measured at frequency elements, overcoming these limitations. After aperture extrapolation, the frequency array has 32 elements and an aperture width of 20% of the center frequency. The experimentally obtained accuracy of the spacing between two targets is 1/17 to 1/33 times the central wavelength.