High-Precise Microwave Active Antenna Sensor (MAAS) formulated for sensing liquid properties

In this study, a microwave active antenna sensor (MAAS) was designed and manufactured from PCB boards operating at a frequency of approximately 3 GHz to sense the characteristics of mineral oils (high voltage transformer oils) and chemical liquids such as methanol, chloroform, and ethanol. The proposed sensor has been designed using the automation software system named ADS (advanced design system). The antenna was linked with a radio amplifier; therefore, the antenna is called active antenna. As a result, the reflection coefficient changed from − 39.98 dB to − 66.26 dB, and also the quality factor changed from 350 to 27,000. The measuring and simulation results were quite identical in both active and passive antenna cases. An M-shaped channel with a capacity of 150 μL was built on a microscope glass slide, where the glass slide was placed in contact with the above face of the designed antenna (near field). That a slit channel was placed on the areas in which the electric field is concentrated. Then, the sensor was tested by injecting the channel with new and damaged transformer oil. Despite the small sample size, the amount of resonant frequency change was 2.23 MHz and 1.48 MHz for the active and passive antennas, respectively. A mathematical model was built to calculate the breakdown voltage of high voltage transformer oil, and the error value in the breakdown voltage value did not exceed ± 0.1606%. The other application of the antenna is to sense chemical liquids and to calculate the electrical permittivity of those samples by finding a mathematical model based on the resonant properties of the antenna. The measured permittivity of the liquids have been compared with the theoretical values, which gives a good qualitative agreement for our results.