Near-Field Microwave Power and Frequency Measurement With Magnon–Photon Coupled System

Near-field microwave detection plays a crucial role in various applications, including medical diagnosis, nondestructive testing, and electromagnetic compatibility (EMC) evaluations. This work presents a novel near-field microwave sensor that exploits the magnon-photon coupling properties of an yttrium iron garnet (YIG) sphere. The coupling between the microwave field and the ferromagnetic resonance (FMR) of the YIG sphere leads to the formation of hybridized modes. The frequency difference between these hybridized modes enables highly sensitive detection of both microwave power and frequency. Experimental results in the S-band range demonstrate an approximately linear relationship between the quartic root of the microwave power and the frequency difference, with a high sensitivity of 7.01 MHz/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt [{4}]{\text {mW}}$ </tex-math></inline-formula>, outperforming other frequency-based interpretation techniques. Moreover, the square root of the frequency difference exhibits an almost linear dependence on the microwave frequency, with sensitivities of −90.37 kHz/GHz and 100.2 kHz/GHz below and above the FMR frequency, respectively. The proposed sensing system leverages magnon-photon coupling to transduce microwave signals into the frequency domain, enabling broadband microwave detection potentially up to 40 GHz. This scheme offers a new approach to microwave metrology with promising applications in microwave imaging, EMC tests, and integrated circuit design.