Development of an ultra-compact microwave resonator for electron-spin-resonance measurement

Authors

  • Yuya Ishikawa ⋅ JP Research Center for Development of Far-Infrared Region, University of Fukui

Abstract

In a typical inductively detected electron spin resonance (ESR) measurement system, the characteristics of the resonator are known to have a significant effect on sensitivity. The advantage of using a resonator is that it makes it possible to obtain a weak resonance signal by increasing the millimeter wave intensity irradiating the sample by a standing wave. In a typical X-band (~10 GHz) ESR system, a high Q-value (~2×104) is obtained by using a cavity resonator. It is known that the oscillating magnetic field generated in the resonator and the measurement sensitivity are approximately proportional to [V/(ω0Qu)]1/2 where Qu is the Q value at no load, V is the effective volume of the resonator, and ω0 is the resonant frequency.

Therefore, it is expected that high-sensitivity ESR measurement will be possible by providing the sample with an oscillating magnetic field component of high intensity. As a method to increase the oscillating magnetic field to the sample, it is possible to generate a localized oscillating magnetic field at the sample area by narrowing the volume V of the resonator. A loop-gap resonator (LGR) has been proposed by Twigg as a candidate for such an ultra-compact microwave resonator.

We have developed an ultra-small LGR for X-band ESR and investigated its resonance characteristics using calculations with COMSOL Multiphysics and an actual LGR fabricated by etching. An LGR with a notch of about 1 mm in width was fabricated on a disk of about 4 mm in diameter and placed on a stripline of about 1 mm in thickness, and its positional relationship with the stripline where the LGR has the largest resonance was investigated in the x-axis and z-axis directions. Simulations and measurements of the frequency response revealed that the vibration field generated at the center of the LGR is stronger at a distance of about 1.3 mm on the x-axis from directly above the stripline. From these resonance characteristics results, it is clear that the Q value is around 70. Based on the above results, ESR measurements of DPPH, a standard sample for ESR, were performed at room temperature. The center frequency was found to be 12.7 GHz, and changing its oscillation frequency by ±700 MHz resulted in a decrease in signal intensity. The details will be presented in this talk.

 

About the Speaker

Yuya Ishikawa, Research Center for Development of Far-Infrared Region, University of Fukui

Yuya Ishikawa is a senior assistant professor of the Research Center for Development of Far-Infrared Region, University of Fukui (FIR-UF). He obtained his Ph.D. in Advanced Interdisciplinary Science and Technology from the University of Fukui in 2018.
From 2018, he has been engaged in research and educational activities as an assistant professor at the Research Center for Development of Far-Infrared Region at the University of Fukui. He specializes in ultra-low temperature properties, low-dimensional magnetism and development of magnetic resonance systems. He received the Young Scientist Incentive Award from the Japan Society of Infrared Science and Technology in 2019, the Society of Electron Spin Science and Technology (SEST) of Japan in 2022, Young Scientist Award of Asia-Pacific EPR/ESR Symposium (China) in 2024, Best Presenter of Natural Science Category in the 2nd International Conference USN Kolaka (Indonesia) in 2024.

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Article ID

SPP-2025-INV-3D-02

Section

Invited Presentations

Published

2025-06-27

How to Cite

[1]
Y Ishikawa, Development of an ultra-compact microwave resonator for electron-spin-resonance measurement, Proceedings of the Samahang Pisika ng Pilipinas 43, SPP-2025-INV-3D-02 (2025). URL: https://proceedings.spp-online.org/article/view/SPP-2025-INV-3D-02.