Near-field measurement techniques and applications

Abstract

In Chapters 3 and 4 open-ended rectangular waveguides were used to inspect multi-layered dielectric composites and metals for surface cracks, respectively. Microwave non-destructive measurements are not exclusively conducted using open-ended rectangular waveguide probes. As mentioned in Chapter 1 other probes such as open-ended coaxial lines, monopole antennas, stripline resonators and many others may be employed depending on the application. However, no matter which probe is used, there is still a need for a complete measurement system complementing the probe used. Such a system requires a microwave frequency generator, some type of a detector and a means to separate the incident signal from that reflected by the specimen under test, or a mechanism to combine these two signals. Furthermore, unlike far-field approaches (i.e. radar systems) there is a wide range of parameters of interest that may need to be measured. These parameters include phase and magnitude of reflection coefficient, phase and magnitude of transmission coefficient, reflected and transmitted power, standing wave properties, quality factor and resonant frequency of a cavity, just to name a few. Consequently, there exists a wide variety of measurement systems that are capable of providing these sought for parameters.