Measurement of Complex Permittivity for Rapid Detection of Liquid Concentration Using a Reusable Octagon-Shaped...

Area of Science:

• Microwave Engineering
• Sensor Technology
• Materials Science

Background:

• Substrate-integrated waveguides (SIWs) offer low cost and integration advantages in microwave systems.
• Accurate sensing of liquid properties is vital for environmental monitoring and process control.
• Existing methods may lack the sensitivity or integration capabilities required for real-time analysis.

Purpose of the Study:

• To design and validate a novel SIW-based resonator sensor.
• To investigate the sensor's response to variations in the complex permittivity of liquid solutions.
• To assess the sensor's potential for water quality monitoring and other applications.

Main Methods:

• An octagon-shaped SIW resonator was fabricated with dimensions of 79.2 mm × 59.8 mm.
• The sensor's resonant frequency and Q-factor were measured using ethanol-water and acetone-water mixtures.
• Electric field distribution was analyzed with liquid droplets at the sensor's center.

Main Results:

• The SIW resonator demonstrated a measurable shift in resonant frequency (minimum 15 MHz) and Q-factor with varying liquid concentrations.
• Sensor performance was validated in the S-band, operating at 2.45 GHz in air.
• A correlation between resonant frequency, temperature, and relative permittivity was established, with a measurement error of approximately 3.1%.

Conclusions:

• The developed SIW resonator sensor effectively detects complex permittivity variations in liquid solutions.
• The sensor shows promise for economical and convenient real-time monitoring in diverse testing environments.
• Results indicate good consistency between measured and actual relative permittivity values, validating the sensor's accuracy.