Characterization of High-Frequency Dielectric Laminates Using a Scanning-Probe Based on EBG Structure

In this paper, an electromagnetic bandgap inspired scanning-probe sensor and its measurement platform is presented for the characterization of high-frequency dielectric laminates. In the proposed sensing technique, the material under test (MUT) is placed between the electromagnetic bandgap structure and a substrate comprising of 50-<inline-formula> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> microstrip lines. Transverse electric excitation is given from the microstrip line to the suspended electromagnetic bandgap structure via MUT, which allows the characterization of different types of damage and defect severities in the MUT. By tapping the material surface with the proposed sensor, a shift in the effective relative permittivity is calculated. The sensor structure consists of <inline-formula> <tex-math notation="LaTeX">$1 \times 3$ </tex-math></inline-formula> unit-cell elements. Each of the unit-cell structure has two asymmetrical H-shaped slots and a metal via. The sensor system is modeled and fabricated using Rogers isotropic thermoset microwave material of relative permittivity <inline-formula> <tex-math notation="LaTeX">$\varepsilon _{r} = 12.85$ </tex-math></inline-formula>, and loss tangent <inline-formula> <tex-math notation="LaTeX">$\tan \delta = 0.0018$ </tex-math></inline-formula>. The dispersion analysis of the electromagnetic bandgap structure shows frequency bandgap between 1.93 to 3.18 GHz, which defines the operating range of the sensor. The fit effective permittivity values obtained from simulation and measured results for nondefective samples are in close agreement with the literature. A deviation in the effective permittivity is obtained for the defective material which indicates the severity of the defect. The proposed method can be effectively utilized for fault monitoring and testing of larger dielectric laminates.