This paper presents a new type of an electromagnetic sensor for nondestructive testing of carbon-fiber-reinforced polymer composites. The sensor utilizes coupled planar spiral inductors operating typically in the range of 10-500 MHz. The method proposed here shows some similarity to the eddy current technique, but as will be shown, the principles of operation are different as the sensitivity to defects is mostly due to the magnetic field components tangential to the surface of a material. It is shown that the method is applicable to 3-D inspection of carbon-fiber-reinforced composites widely employed in the aerospace industry.Index Terms-Carbon-fiber-reinforced polymer (CFRP), composite material structures, coupled spiral inductors, eddy currents, nondestructive testing (NDT).

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A solid-state microwave generators system is considered as an alternative to the magnetron, in order to inject electromagnetic energy into the cavity of a microwave oven for domestic use. Over current devices, the use of solid state technology allows one to control the frequency and phase of the electromagnetic field generated. Considering a simplified cavity with 2 solid state sources, the influence of the electrical parameters on maximum efficiency obtainable in the process of microwave heating is investigated. By varying the frequency, different values of optimal phases and different values of maximum efficiency are detected. Moreover, the procedure is repeated with varying the position of one source port and the influence of geometry on the system performance is evaluated. Our results demonstrate that the ability to control the electrical quantities of a microwave heating process makes it possible to obtain better results in terms of energy efficiency over the current poorly controllable systems.

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This paper presents a customized measurement system for non-destructive testing of carbon-fiber-reinforced polymer composites. The measurement principle is based on changes in the magnitude of a transmission coefficient between two planar coupled spiral inductors caused by defects buried in the composite under test. The system consists of several measurement channels to speed up the scanning process performed with the array of sensors. Selected experimental results are shown.

We have developed an inexpensive computer controlled microwave oscillator system that enables quick and automatic measurements of the complex permittivity with a specific split post dielectric resonator (SPDR). It is based on a phase-locked loop Microwave Voltage Controlled Oscillator intended for the Q-factor and the resonance frequency measurements of SPDR. Multipoint resonance curve fitting procedure allows accurate Q-factor determination. The only external information that is necessary for the complex permittivity determination of a dielectric substrate or a ferroelectric film is the thickness of the sample under test. We compare the complex permittivity measurement results on few dielectric samples employing Vector Network Analyser and our measurements setup. We also present measurement results of the sheet resistance and resistivity of epitaxial GaN films deposited on sapphire substrates.

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