We describe a time-resolved method for measuring nonlinear ultrasonic phenomena. Conventional approaches to the measurement of nonlinear phenomena utilize narrowband measurements of harmonic generation. These measurements are fundamentally narrowband and hence have poor time resolution. In contrast, our method utilizes a series of narrowband bursts that can be combined to form a composite time-resolved broadband impulse. Simultaneous time resolution and harmonic isolation are thereby obtained. The composite impulse can then be used to perform time-resolved measurements of weakly nonlinear phenomena. Such time-resolved measurements have the potential to dramatically improve the capability and performance of nondestructive testing systems that use acoustic nonlinearity to detect flaws.

We develop a mathematical theory by which these measurements can be explained, and describe an algorithm for performing the measurements. To evaluate the method and its utility, we present several demonstrative experiments. We also perform numerical simulations analogous to the experiments and apply theory in order to better understand the measurements and the underlying phenomena.