Wireless Communication in Feedback-Assisted Active Sensors

A novel wireless high-resolution resonant-based microwave sensor is presented for chemical sensing applications. A combination of antenna with a planar microstrip resonator increases the flexibility, durability, and reliability while extending the application of the sensor to areas with limited access and harsh environments. The main core of this sensor is a passive planar resonator, which operates at 1.41 GHz and is reinforced by a regenerative active feedback circuitry. The regenerative active feedback loop compensates the power loss of the sensor and, as a result, provides an extremely high-quality factors. Four bow-tie slot antennas of the moderate gain of 5 dB, linearly polarized over the frequency span of 1.35-2 GHz is used to communicate in short range. The sensor model is implemented using the finite-element method and a complete set of simulation is presented. The simulation results are confirmed by the measurements for resonant profile variation in material sensing. The initial quality factor of the fabricated sensor, considering the antennas and resonator loss is Q ≈22000, which broadens the range of sensing platforms into classification of low concentrated (0.003125-0.1 g/mL) salt water as well as material detection of common chemicals such as IPA, acetone, ethanol, methanol, and water.