Mohammad A. Saed

A new radar architecture that features a compact size and only one RF active device was designed, fabricated, and tested for small motion detection and human range tracking. Unlike conventional board level radar systems, it contains a single antenna and does not use any low noise amplifier (LNA) or circulator in the RF front-end. The I/Q amplitude and phase imbalance present on the system were measured to be <1% and 5.17°, respectively. Besides the local oscillator (LO), there is no other active device consuming dc power. The fabricated radar system has dimensions of 36 mm × 72 mm (L×W) and a power consumption of 290 mW in continuous operation. Moreover, a 24-GHz single channel radar system was designed, fabricated, and tested using the proposed architecture. The dimensions of fabricated board are 24 mm × 27 mm (L×W) and total power consumption of 800 mW dissipated by the local oscillator. The range tracking capabilities of the implemented radar systems were demonstrated by successfully tracking the range of a human target walking back and forth on a hallway. Moreover, the high sensitivity of the proposed quadrature 2-port monostatic Doppler radar was demonstrated by effectively measuring a sinusoidal movement with an amplitude of 2.5 μm with a 5.8-GHz carrier.

This paper presents a new method for dielectric characterization as a function of temperature and frequency for nanomaterial-loaded polymers while they are heated with radio frequency (RF) energy. Specifically, the dielectric constant and electrical conductivity of polymers with conductive nanomaterials are measured in the RF frequency range (up to a few hundreds of MHz) while the material is undergoing a curing reaction using high-power RF energy source. The nanomaterials act as susceptors for RF energy to facilitate heating to desired temperatures for processing and curing polymers. Measurement techniques were developed to enable simultaneous in-situ RF heating and characterization of the polymer. Since some polymers used in this work are liquids at room temperature, such samples are placed in an alumina crucible located at the end of a microstrip-type applicator. Temperature is monitored using a FLIR thermal camera. Multiphysics simulations are used to help develop the appropriate applicator for RF heating and dielectric measurements. An appropriate calibration procedure along with a circuit model to enable extraction of the dielectric constant and electrical conductivity from the measured reflection coefficient is introduced.

Mitigation of multipactor in waveguides is of importance, and strategies have included the addition of external fields, materials engineering, or surface modifications. Here, geometry modifications of rectangular waveguide surfaces and the application of an axial magnetic field are investigated for suppressing multipactor growth. A Monte Carlo approach has been used to simulate electron dynamics. The empirical secondary electrons yield is modeled based on a modified Vaughan approach. The electric fields driving electron transport were derived from separate electromagnetic calculations to adequately include field perturbations due to the presence of surface patterns in the rectangular waveguide structure. Combinations of grooves and a DC magnetic field are shown to effectively mitigate multipactor growth at field strengths up to ∼10⁵ V/m. Finding optimal combinations for an arbitrary field and operating frequency requires further work.

The massive deployment of wireless sensors is a fundamental piece in the growing internet of things (IoT) industry. Therefore, it is imperative to use already existing hardware to realize new sensing functions with very few or no hardware added. As wireless power transfer (WPT) and near field communication (NFC) become standard features in smart phones, this paper investigates beverage freshness sensing based on the WPT/NFC technology compatible with smart phones. A circuit model for the beverage-coil interaction was developed and the performance of features from different nature (e.g., magnitude, amplitude, phase) for classification was analyzed and tested. Accuracies up to 96.7% were achieved using supervised machine learning for milk freshness classification, when 5 different types of milk were used and up to 100% when just 2% fat milk was used for classification. Additionally, the radio frequency bandwidth needed for classification was reduced to 10 MHz using singular value decomposition (SVD) and boxplot analysis without affecting the classification accuracy for two different methods of feature extraction.

This article presents a microwave imaging method based on the time‐reversed finite‐difference time‐domain method (FDTD‐TR) that enhances immunity to undesired interference and jamming signals. The method uses random noise as the source waveform that illuminates the imaging area. Signals scattered by objects in the imaging area are collected on a planar grid, followed by processing through a correlation operation, and then used in the FDTD‐TR algorithm to construct images on any desired plane in the computational domain. The method capability in suppressing interference noise is demonstrated through successful reconstruction of images for a test case consisting of a dielectric object behind a wall. The method is compared to conventional FDTD‐TR methods that fail the same image reconstruction test.

RF heating of carbon nanotubes enables local welding and increased strength between 3D-printed thermoplastic layers.

A circularly polarized microstrip patch antenna array with sequential rotation and reduced mutual coupling between its elements is proposed. A microstrip patch modified to suppress surface waves is used as the array element. The modifications include the addition of shorting pins and inclusion of a slot and edge truncations to produce a circularly polarized array element that does not excite surface waves. The designed element has higher gain and a more directional radiation pattern than a similar conventional microstrip patch antenna. In order to improve circular polarization bandwidth, sequential rotation techniques using the proposed microstrip antenna were investigated. Surface wave supersession of a 2 x 2 sequentially rotated array using the proposed design was achieved throughout the entire axial ratio bandwidth. One-layer directly fed array and two-layer aperture coupled array were investigated. The two-layer design achieved better impedance and axial ratio bandwidths than the single layer design. The design procedure, simulation results, and experimental measurements are presented.

A circular microstrip patch antenna design is proposed for applications that require suppression of surface waves and lateral waves. The proposed design is composed of a circular patch loaded with a single shorting pin on a grounded inhomogeneous dielectric substrate with a desired effective permittivity. The modal equation for the normalized resonance frequency of this design is solved numerically. Simulated and measured radiation patterns show that a good reduction of surface waves and lateral waves is achieved. A comparison between the present work and an alternative design in the literature is presented in this paper. The proposed design could find applications in large patch antenna arrays where mutual coupling needs to be eliminated and in high-precision global positioning system receivers where multipath interfering signals associated with low-angle reflection affect position accuracy.

A novel approach to microwave imaging in three dimensions based on time-reversed finite-difference time-domain method (FDTD-TR) is presented. The proposed computationally efficient technique allows the reconstruction of detailed images of scattering objects. Transmissions as well as reflection imaging modalities in the near-field and far-field were investigated. In this study, we implemented the FDTD-TR algorithm in three dimensions using time-reversed convolutional perfectly matching layers as boundaries to truncate the simulation domain. The method works for dielectric as well as conducting objects. The method’s capabilities in imaging multiple objects and behind-the-wall imaging are also presented.