1. An apparatus comprising: a structure having a plurality of components; a set of transmitters physically associated with the plurality of components, wherein the set of transmitters are configured to send signals into the plurality of components; a set of sensors physically associated with the plurality of components, wherein the set of transmitters are capable of detecting responses to the signals; and a structural health monitoring system in communication with the set of transmitters and the set of sensors, wherein the structural health monitoring system is configured to cause a transmitter in the set of transmitters to send a signal into a component within the plurality of components in which the signal has a frequency range that falls within a selected frequency range to form a transmitted signal; the structural health monitoring system further configured to receive an actual response to the transmitted signal from a sensor in the set of sensors; the structural health monitoring system further configured to generate a simulated response of the component to the transmitted signal using a functional model capable of modeling responses of the component to different frequency ranges falling within the selected frequency range; the structural health monitoring system further configured to create a transfer function using the response to a set of delay coefficients and a set of weight coefficient for the transfer function, wherein the transfer function simulates responses to input signals having frequency ranges encompassed by the selected frequency range; and the structural health monitoring system further configured to compare the simulated response to actual response to determine if a change has occurred in the material.