Search for: All records

The use of electromagnetic waves at microwave and millimeter-wave (mm-wave) frequencies in imaging has been growing rapidly in the last two decades with applications in security screening, biomedical imaging, nondestructive testing, and the inspection of goods and packages. The nonionizing nature of the radiation renders microwave and mm-wave imaging (MMI) safe for humans and, thus, attractive, especially for frequent imaging of living tissue and humans. At the same time, the radiation penetrates many materials, which are optically opaque: e.g., fog and foliage, soil and living tissue, brick and drywall, wood, fabrics, and plastics. Importantly, modern MMI systems offer compact and relatively low-cost hardware due to advancements in high-frequency microelectronics. 

The demand for biomedical devices that can collect high-fidelity data from patients in various environments, inside and outside medical clinics, and can provide high-precision diagnosis and long-term monitoring, is high in the healthcare industry. Among different sensing technologies, this study specifically focuses on providing a review of inductive sensing-based devices used in healthcare. Although the concept of inductive sensing has been used in other fields aside from healthcare, we believe that there is a high potential for a wide range of use of this sensing method across various biomedical devices due to the low cost, flexibility in the sensor design, mature fabrication technologies, and high sensitivity. This review first summarizes the mechanisms of inductive sensing-based devices and design considerations. Then, three main groups of applications that are used in healthcare and rely mainly on inductive sensing for their diagnosis and treatments are presented, including motion tracking and continuous monitoring systems, bio-signal detection systems, and imaging biological tissues. We conclude with a summary of the current status of inductive sensing devices used in healthcare, highlighting the promising capabilities and barriers to overcome. 

Nitrate (NO3) pollution in groundwater, caused by various factors both natural and synthetic, contributes to the decline of human health and well-being. Current techniques used for nitrate detection include spectroscopic, electrochemical, chromatography, and capillary electrophoresis. It is highly desired to develop a simple cost-effective alternative to these complex methods for nitrate detection. Therefore, a real-time poly (3,4-ethylenedioxythiophene) (PEDOT)-based sensor for nitrate ion detection via electrical property change is introduced in this study. Vapor phase polymerization (VPP) is used to create a polymer thin film. Variations in specific parameters during the process are tested and compared to develop new insights into PEDOT sensitivity towards nitrate ions. Through this study, the optimal fabrication parameters that produce a sensor with the highest sensitivity toward nitrate ions are determined. With the optimized parameters, the electrical resistance response of the sensor to 1000 ppm nitrate solution is 41.79%. Furthermore, the sensors can detect nitrate ranging from 1 ppm to 1000 ppm. The proposed sensor demonstrates excellent potential to detect the overabundance of nitrate ions in aqueous solutions in real time. 

Microwave imaging is a high-resolution, noninvasive, and noncontact method for detecting hidden defects, cracks, and objects with applications for testing nonmetallic components such as printed circuit boards, biomedical diagnosis, aerospace components inspection, etc. In this paper, an array of microwave sensors designed based on complementary split ring resonators (CSRR) are used to evaluate the hidden features in dielectric media with applications in nondestructive testing and biomedical diagnosis. In this array, each element resonates at a different frequency in the range of 1 GHz to 10 GHz. Even though the operating frequencies are not that high, the acquisition of evanescent waves in extreme proximity to the imaged object and processing them using near-field holographic imaging allows for obtaining high-resolution images. The performance of the proposed method is demonstrated through simulation and experimental results. 

There is a rapid trend in various industries to replace the metallic pipes by nonmetallic ones. This is due to the certain properties, such as high strength, lightweight, resilience to corrosion, and low cost of maintenance for nonmetallic pipes. Despite the abovementioned advantages, nonmetallic pipes are still affected by issues, such as erosion, defects, damages, cracks, holes, delamination, and changes in the thickness. These issues are typically caused due to the manufacturing process, type of carried fluid composition, and flow rate. If not examined well, these issues could lead to disastrous failures caused by leakages and bursting of the pipes. To prevent such major failures, it is extremely important to test the pipes periodically for an accurate estimation of their thickness profile. In this article, we propose a nondestructive testing (NDT) technique, based on near-field microwave holography, for identifying the fluid carried by a nonmetallic pipe and estimating the pipe's thickness profile. Identifying the carried fluid helps improve the thickness profile estimation. The performance of the proposed techniques will be demonstrated via simulations and experiments. 

In this paper, we investigate the application of using software-defined radio (SDR) and surface acoustic wave (SAW) device for wireless measurement of the response of in situ sensors. SDR uses software to realize different communication functions. After collecting the magnitude and phase of the response at discrete frequencies, we apply inverse Fourier transform to analyze the time domain responses which, in turn, allows for monitoring the changes of the response of the in situ sensor. We employ microwave signal flow graph concepts to improve the quality of the received signals. Comparing the normalized results obtained by SDR with those obtained from a commercial vector network analyzer (VNA), we demonstrate that the results are sufficiently close, and the SDR-based experiments can provide satisfactory measurement of the in-situ sensors. The objective is to eventually employ this wireless measurement system for soil nutrient sensing.