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This work focuses on the development of planar microwave resonators for use in electron spin resonance spectroscopic studies. Two half-wavelength microstrip resonators of different geometrical shapes, namely straight ribbon and omega, are fabricated on commercially available microwave laminates. Both resonators have a characteristic impedance of 50 Ω. We have performed electromagnetic field simulations for the resonators and have extracted design parameters that were used for fabrication. The effect of the geometry on the quasi-transverse electromagnetic (quasi-TEM) modes of the resonators is noted from simulation results. The fabrication is done using optical lithography in which laser printed photomasks are used. This prototyping technique allows us to fabricate resonators in a few hours with accuracy up to 6 mils. The resonators are characterized using a Vector Network Analyzer. The fabricated resonators are used in a home built low-temperature continuous wave electron spin resonance (CW-ESR) spectrometer which operates in S-band. It captures the absorption spectrum of the free radical DPPH, at both room temperature and 77 K. The measured g-factor using our resonators is consistent with the values reported in literature. Spin sensitivity of 1015 spins/gauss is achieved at 77 K. The designed resonators will be used in setting up a pulsed electron spin resonance spectrometer by suitably modifying the CW-ESR spectrometer.

In this work, we study the development of a coplanar waveguide (CPW) resonator and its use in an electron spin resonance (ESR) spectrometer. The CPW resonator is designed to operate in S-band (2-4 GHz), with a short circuit configuration leading to miniaturization. It is so constructed such that it has a characteristic impedance of 50 ohms. The resonator supports quasi-TEM mode of propagation owing to its uniplanar nature, demanding detailed electromagnetic simulation. The design parameters and the electromagnetic field distribution are obtained from the simulation. The resonator is fabricated using optical lithography with a rapid prototyping technique. The characteristic response of the resonator is measured by coupling it to a Vector Network Analyzer (VNA). The ESR absorption spectrum of free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) is captured by using this resonator in reflection geometry. The microwave magnetic field distribution at the sample position is investigated. The ascertained value of Lande g-factor is consistent with that reported in the literature. Spin sensitivity of the order of 1015 spins/gauss is achieved upon using this resonator at room temperature. The quality factor of this resonator is found to be low and this makes it suitable for use in a Pulsed ESR spectrometer.

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