A microwave Surface Resonator Array (SRA) structure is described for use in Electron Paramagnetic Resonance (EPR) spectroscopy. The SRA has a series of anti-parallel transmission line modes that provides a region of sensitivity equal to the cross-sectional area times its depth sensitivity, which is approximately half the distance between the transmission line centers. It is shown that the quarter-wave twin-lead transmission line can be a useful element for design of microwave resonators at frequencies as high as 10 GHz. The SRA geometry is presented as a novel resonator for use in surface spectroscopy where the region of interest is either surrounded by lossy material, or the spectroscopist wishes to minimize signal from surrounding materials. One such application is in vivo spectroscopy of human finger-nails at X-band (9.5 GHz) to measure ionizing radiation dosages. In order to reduce losses associated with tissues beneath the nail that yield no EPR signal, the SRA structure is designed to limit depth sensitivity to the thickness of the fingernail. Another application, due to the resonator geometry and limited depth penetration, is surface spectroscopy in coating or material science. To test this application, a spectrum of 1.44 μM of Mg2+ doped polystyrene 1.1 mm thick on an aluminum surface is obtained. Modeling, design, and simulations were performed using Wolfram Mathematica (Champaign, IL; v. 9.0) and Ansys High Frequency Structure Simulator (HFSS; Canonsburg, PA; v. 15.0). A micro-strip coupling circuit is designed to suppress unwanted modes and provide a balanced impedance transformation to a 50 Ω coaxial input. Agreement between simulated and experimental results is shown.
the equivalent T-shaped line. Here, the equivalent T-shaped line works like a bandstop filter at the second harmonic frequency. Therefore, the proposed BPF has better characteristic with the second harmonic rejection than the earlier one. These BPFs show insertion losses of 1.2 and 0.75 dB and return losses of 17.8 and 18.2 dB at the central frequency of 10 GHz and bandwidth of 18%, respectively. The characteristic of the second harmonic rejection for the compact BPF with T-shaped line is 21.5 dB at 17.3 GHz. The new BPFs can be fabricated with microelectro mechanical systems, nanoelectro mechanical systems, and hybrid microwave integrated circuits or the MMIC technique due to its entirely planar structure. ACKNOWLEDGMENTS
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