Meta resonator based miniaturized planar microwave sensors for material permittivity characterization

Abstract

Material permittivity is essential in applications like material characterization, environmental monitoring, and quality control, as it determines the ability to store electrical energy and affects electromagnetic (EM) wave propagation. Low permittivity materials are essential in integrated circuit design to reduce parasitic capacitance and propagation delay, thus ensuring electronic system performance. Measuring material permittivity precisely is challenging due to the limited sensitivity of measurement equipment, complex calibration processes, environmental factors, frequency dependence issues with material interfaces, sample size and uniformity. These challenges impact material characterization, device design, and performance. Techniques like the resonance method, resonant cavity method, free space method, and microstrip line method are being developed to measure permittivity, with the resonance based method being popular for its compact size, low cost, easy fabrication, and high sensitivity. Metamaterial technology is promising for enhancing the sensitivity of resonance-based sensors in the microwave frequency range. This research focuses on designing two microwave sensors for permittivity measurement with enhanced sensitivity and a compact size of 25 mm × 20 mm × 0.79 mm. The first sensor, a labyrinth-shaped circular split ring resonator (LC-SRR), is designed to operate at 2.57 GHz. This sensor achieves a high sensitivity of 10.50% for permittivity variation. The LC-SRR sensor was calibrated for a relative permittivity range of 2.2 to 4.3. The second sensor is a dual-notch maze-shaped complementary split ring resonator (MCSRR) that operates at 2.88 GHz and at 4.05 GHz. The MCSRR sensor shows sensitivities of 10.48% for the first notch and 17.36% for the second notch and calibrated for a relative permittivity range of 2.2 to 11.2, respectively. Both sensors are validated by fabricating and measuring prototypes. An inverse regression model is utilized to predict the permittivity of the material under test (MUT) directly from the sensor's resonant frequency. The contribution of this thesis is to design a split ring resonator (SRR) and a complementary split ring resonator (CSRR) that adopt a unique and compact structure, featuring high electromagnetic (EM) field intensity. This design contributes to a more precise sensing mechanism in the microwave frequency range.