Application of Spread-Spectrum Ultrasonic Evaluation to Concrete Structures

Concept Validation and Detectability Limitations for Direct-Sequence Spread-Spectrum Ultrasonic Evaluation System

“…at the baseline and after introduction of each incremental flaw. All-bit shift register code with 5 MHz carrier and 2.5 MHz code chipping rate was used [2,5,8].…”

“…Two independent prototype instruments have been designed with different approaches, a hardware and a software implementation. The instruments record the aggregate acoustic state of the test object and the associated measurement system in the form of "ultrasonic correlation signature" [1,2]. These correlation signatures are compared with the signatures obtained at a later point in time (or from an identical object) to detect if the test object has undergone any change in its geometry, composition and homogeneity etc.…”

“…Various tradeoffs associated with implementation of the DSSSUE technique are addressed. Figure 1 shows the basic signal processing model of the DSSSUE system [2]. The governing equation for the output cross-correlation, RJt) , can be written as [3],…”