Development of Novel Microwave Sensors

There are three main features to address to realize highly efficient IoT while dealing with sensors. The sensors should be inexpensive, and highly integrable as well as provide real-time measurement capability to address where there is a need for fast-response feature requirements. So, the current research’s focus is to develop novel microwave sensors to address these requirements after all. Chapter 1 introduces the research aims as well as an introduction to IoT and the importance of sensors in relation to IoT. Then a general introduction is provided on microwave sensors, their various applications, fabrication technologies, and the applications that are in the field of interest of the current research. Chapter 2 gives an explanation of the general working principle of microwave sensors as well as the key components to realize such structures. In addition, some applications are introduced. In this chapter, the traditional techniques used to characterize the dielectric properties of various kinds of MUTs will be explained, such as the one based on the shift in the resonant frequency of perturbed cavities. Chapter 3 starts with a literature survey of methods based on electromagnetic readings at a single frequency. Then, a novel single-frequency measurement technique is proposed, and some example applications are shown, such as to read the content ratio of liquid mixtures or to characterize the complex permittivity of arbitrary MUTs. Finally, the chapter is closed explaining the advantages of the proposed retrieval methods over the others. Chapter 4 is the step-by-step explanation of how to exploit the single-frequency measurement of the transmission level of a two-port perturbed circular SIW cavity resonator in the presence of a liquid mixture to read the percentage as well as the calibration process. The liquids used for this study are isopropanol, acetone, and their corresponding mixtures at room temperature. At the end, a comparison between the results regarding the proposed and the traditional techniques is performed. The realization of the fabricated stand-alone microwave sensor system is the subject of Chapter 5, in which an oscillator is used as a signal source and a power detector is provided to measure the transmission amplitude at the desired frequency. At the beginning of the study, all the components were fabricated and studied separately and then assembled together using interconnections. Later, the overall system was united and fabricated on a single board. A calibration method is proposed and a comparison with the traditional method is provided. In Chapter 6, the same single-frequency measurement method is employed for the extrapolation of the complex permittivity of the MUTs. To characterize both the dielectric permittivity and the loss-tangent at a single frequency, at least two independent measured quantities are needed. To that aim, the amplitude and the phase of the S21 parameter have been selected. A novel calibration method defined as Error Vector Correction (EVC) is proposed which results in a significant reduction of the overall reading error. In Chapter 7 the same approach is followed as in Chapter 5, first the modular and then the integrated approach, employing a detector that is able to measure the magnitude and phase difference of two signals. Two lines are designed for the system to deliver the signal toward the detector, one of which is employed as a reference. Like all the other stand-alone systems, both systems presented in chapters 5 and 7 need extra components, namely supplies such as batteries and their corresponding supply regulator boards, data processors such as Arduino, etc. which are provided correspondingly. At the end of each chapter, a comparison between the proposed and the traditional methods is presented to compare the results and to signify the importance of the current study.