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A Self-Calibrated Resonant Sensor for Dielectric Characterization Based on Mode Splitting

A novel differential approach developed at the University of Messina reduces environmental effects in dielectric measurements

Dielectric characterization of materials plays a crucial role in several application domains, ranging from biomedical devices to industrial monitoring systems. However, conventional dielectric characterization techniques are often bulky, expensive, and require complex instrumentation.

Planar Resonators as an Alternative Solution

Researchers have introduced planar resonators as a promising alternative to conventional dielectric characterization techniques. Engineers can fabricate these devices using standard PCB manufacturing technologies, while their inherent compatibility with wireless systems enables contactless measurements. Despite these advantages, environmental factors such as temperature fluctuations and humidity variations often affect resonant sensors, reducing measurement accuracy.

A Self-Calibrated Resonant Sensor Based on Mode Splitting

To address this challenge, a research group from the University of Messina (Italy), led by Prof. Nicola Donato, member of Res4Net, developed a novel self-calibrated resonant sensor for dielectric characterization. The proposed device exploits the mode-splitting phenomenon to perform differential measurements and automatically compensate for environmental effects.

The research team designed the sensor around a planar ring resonator operating in the sub-GHz frequency range. A geometric asymmetry generates mode splitting, producing two orthogonal resonant modes. The first resonance (f₁) responds to changes in the relative permittivity (εr) of the material under test, while the second resonance (f₂) shows minimal dependence on the sample and acts as an internal reference.

Because environmental variations influence both resonant modes in a similar way, the frequency difference between them (Δf = f₂ − f₁) effectively suppresses common-mode disturbances while preserving sensitivity to changes in relative permittivity. This differential measurement strategy allows the sensor to maintain reliable performance even under varying environmental conditions.

Prototype Fabrication and Experimental Validation

The researchers fabricated the prototype using the Voltera NOVA inkjet printing prototyping system. They validated the device inside a controlled environmental chamber over a temperature range from 21 °C to 50 °C. The results showed that both f₁ and f₂ experienced similar linear frequency shifts with temperature. In contrast, the differential parameter Δf exhibited a significantly lower temperature dependence, with a slope approximately four times smaller than those of the individual resonances.

Results and Future Perspectives

These findings demonstrate the effectiveness of the proposed self-calibrated resonant sensor and highlight the potential of the mode-splitting approach for robust dielectric characterization in real-world environments.

The authors published the research in the IEEE Transactions on Instrumentation and Measurement.

For further details, readers can access the full paper at: https://ieeexplore.ieee.org/document/11052665