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

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.

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.

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 one-dimensional, dual frequency, active retrodirective array is proposed for wireless power transfer applications. Microstrip circular patch antennas with four shorting pins are used as array elements to suppress surface waves. The proposed design eliminates undesired coupling between array elements due to surface waves present in conventional microstrip antenna arrays in order to improve array performance. The antenna array uses circularly polarized microstrip elements with higher gain than conventional microstrip antennas. The proposed retrodirective array operates at 2.4 GHz for the interrogating signal and 5.8 GHz for the retransmitted signal, using up-converting mixers. The beam scanning inherent in retrodirective arrays ensures a constant power level available to the charging devices, regardless of their location within an angular sector over which retrodirectivity is achieved. A two-element experimental prototype provided uniform power density within a 60 • angular sector. The Design procedure, simulation results and experimental measurements are presented.