چكيده به لاتين
The use of sensors for measuring physical variables in our environment is both crucial and necessary. Sensor accuracy is defined by how closely the measured value aligns with the actual value of the measured variable. Any discrepancy between these values, particularly in sensitive situations, can lead to significant issues. While such differences, whether present from the outset or developing over time, are unavoidable, it is essential for a sensor to exhibit high accuracy from the beginning. Moreover, this accuracy must remain stable and resilient over time, even in the face of inevitable errors.
In this thesis, a high-sensitivity planar microwave sensor design is presented, capable of measuring the dielectric constant of a material with adjustable accuracy. The maximum accuracy can be tuned using a DC voltage over a range of material dielectric constants. This sensor operates based on a directional coupler in a frequency band above 1 GHz, where the Material Under Test (MUT) is placed on the coupling area between two microstrip transmission lines. Due to the disturbance in the coupling, power leaks to the isolated port of the coupler. The leaked power depends on the dielectric constant of the material under test, and the accuracy of the measurement varies across different dielectric constant ranges. By using a compensating element placed between the coupling lines, which is a varactor diode controlled by voltage, the maximum measurement accuracy can be adjusted to match the desired dielectric constant of the material. At the calibrated permittivity, even a small percentage of impurities can be detected. Within the measurement range of sensor, spanning permittivity values from 1 to 7, an average accuracy of 15.92 is achieved. To the best of the author's knowledge, this represents the highest average accuracy reported for planar microwave sensors to date. Full-wave simulations, along with the results from fabrication and practical measurements, have been presented to verify the performance of the sensor.
