RF Switch Integrated With CSRR Array for Subsurface Imaging of Composite Structures

In this work, a novel RF switchable sensor array based on complementary split ring resonator (CSRR) elements and PIN diodes is presented for subsurface imaging of composite structures. The proposed scheme utilizes a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> array of CSRR elements, which can be switched using 4 PIN diodes to facilitate a fast scanning of the test structure without any mechanical movement. The individual elements of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> CSRR array are carefully designed to resonate at four different frequencies to clearly distinguish their response simultaneously. The use of switches along with a 1–4 power divider at the input and a 4–1 power combiner at the output on a single board facilitates a simple two-port setup to conduct the measurement. The applicability of the proposed scheme is demonstrated by retrieving the image and shape of a few composite structures using the designed CSRR array.