Temperature Compensated Dielectric Constant Sensor Using Dual-Mode Triangular Structure

An aperture-coupled dual-mode triangular resonator (DMTR) sensor is presented for measuring sample under test (SUT) dielectric constant in real-time. Using this structure, it is possible to compensate for temperature variations without adding any components or circuits to the main resonator. With a specially designed slot in the middle, the proposed triangular resonator can provide two separate resonance frequencies: the lower frequency (
${F}{2}$
) is used for sensing, while the upper frequency (
${F}{1}$
) can be used for calibration purposes and temperature compensation. Changing the material in contact with the slot only affects
${F}{2}$
, while
${F}{1}$
remains the same. A sample structure is designed and fabricated to evaluate the performance of the proposed DMTR sensor. The measurement results indicate negligible changes at
${F}{1}$
equal to 2.425 GHz, providing an acceptable calibration frequency in the industrial, scientific and medical (ISM) band. In contrast, the sample-dependent band around 2.36 GHz shifts frequency by 1.6 MHz per unit dielectric constant for samples with permittivity ranging from 1.0 to 6.15. Loss tangents of up to 0.01 are also found to have no significant effect on frequency response. Temperature analysis reveals the sensor’s compensation capability. The frequency difference between
${F}{1}$
and
${F}{2}$
for any SUT remains constant over a wide temperature range from
$- 40\,\,^{\circ} \text{C}$
to
$140 ^{\circ} \text{C}$
. As a result, the frequency difference variations depend solely on the dielectric constant of the SUT at any given operating temperature.