Reconstruction of wide-bandwidth scattering responses from narrow-bandwidth ultrasound echo in air

We present an experimental evaluation of high-resolution acoustic impulse responses of structured objects in air, obtained by a new signal processing technique. Typical acoustic transducers in air have a high Q of 20 and a narrow passband of 40 kHz around the resonance frequency of 200 kHz. First we simply deconvolved an echo signal from an object with the transfer function of the measuring system with the aid of a flat reflector. After an adequate extraction of the deconvolved spectrum in the passband, we extrapolated it to a wide-band spectrum from 0 Hz to 3 MHz by a factor of 75, applying a linear prediction using an autoregressive (AR) model and Levinson's recursive formula. Resolution of the reconstructed impulse responses of structured objects in air is equal to a sampling spacing Δx = 24 μm which corresponds to a sampling frequency of 7.14 MHz, and the range accuracy is within 5 Δx.