The role of Varactor, the Nonlinear Semiconductor, for Next Generation of Intelligent and Reconfigurable Radio Nodes

This paper highlights the significance of intelligent and reconfigurable radio nodes, incorporating the nonlinear and tunable semiconductor, varactors, in shaping the future of wireless communication. It presents their use in frequency generations at different bands, including IoT to mm-wave (MMW), in intelligent reflecting surfaces (IRS) for reflecting incident waves with beamforming, and enhanced performance of a machine learning (ML)-based system for number of tag/sensor detection and channel estimations. The focus is on the recent developed technique on a nonlinear ring resonator (NRR) capable of generating harmonic and subharmonic dual bands at 2.4 GHz and 4.8 GHz, extending its application to MMW frequencies at 60 GHz and 120 GHz. Additionally, the utilization of IRS using the proposed ring-based resonator is demonstrated, showcasing their capability in achieving 300-degree phase shifting. The paper also explores the integration and enhancement of the proposed dual band, tunable and reconfigurable circuit with ML-based tag collision recovery technique, enabling multi-tag and sensor detection. This leads to a remarkable 10 dB improvement in signal-to-noise ratio (SNR) and overall throughput of the system. The presented research contributes insights and advancements for the future intelligent communication and sensing technologies employing tunable and reconfigurable circuit and devices.