11. Ultrasonics, Material Properties
From some low frequency scattering investigations in radar, it is suggested that interrogating the target with "ramp" function has distinct advantages. This "ramp" function is a ramp in amplitude, not frequency. The returning echo is predicted to exhibit directly in the time domain, information of the cross-sectional area of a target as the ramp passes the target. From this information, one can infer size, volume, and orientation of the target. The theory for this interpretation is based on the physical optics approximation. This approximation is commonly used in acoustic and elastic wave scattering when the boundary conditions are approximate. The concepts can be "verified" by exact scattering theories for back-scatter from hard spheres (acoustic) and spherical voids (elastic). Our calculation for these two cases do show that their returning could show cross-sectional information. A proposed system to launch and receive ramp pulses will be discussed. The generation mechanism uses the demodulation properties of absorbtive, nonlinear media on a large amplitude pulse train. The detectior mechanism utilizes fiber optics.
Cook, Bill D., "Interrogation of Voids in SOlids Utilizing Ramp Function Ultrasonic Pulses" (1980). Proceedings of the DARPA/AFML Review of Progress in Quantitative NDE, July 1978–September 1979. 69.