Angular Displacement Sensor Based on Double-Ring Resonator With a Novel Readout Circuit

This article presents an angular displacement sensor utilizing a double-ring resonator (DRR) and introduces an integrable and low-cost readout circuit to detect the transmission zero (TZ) position in the sensor’s frequency response. The proposed sensor comprises a DRR-based stator and an open-ended stub rotor. The interaction between the rotor and stator via ohmic contact causes a notable change in the effective electrical length of the stator, leading to a measurable shift in the position of the TZ. The theoretical analysis of the sensor is conducted using ABCD matrices, ensuring accurate modeling and characterization. A novel readout circuit is implemented by a frequency synthesizer and a power detector. The proposed circuit effectively detects notches or peaks in the frequency response of the device under test (DUT) by applying a precisely controlled sinusoidal signal and measuring the output power. This enables reliable detection over a wide frequency range of 35 MHz–4.4 GHz. The proposed readout circuit supports real-time measurements for resonant-based sensors in industrial applications, eliminating the need for expensive laboratory equipment. The experimental results show good agreement between the measurements from the readout circuit and those from a vector network analyzer (VNA), confirming the reliability and accuracy of the proposed method.