Using calculations from first principles and harmonic transition state theory, we investigated the permeability of a single graphene sheet to protons and hydrogen atoms. Our results show that while protons can readily pass through a graphene sheet with a low tunneling barrier, for hydrogen atoms the barriers are substantially higher. At the same time, the presence of defects in the membrane can significantly reduce the penetration barrier in a region that extends beyond the defect site itself.

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Ultrasound has been recently proposed as an alternative modality for efficient wireless power transmission (WPT) to biomedical implants with millimeter (mm) dimensions. This paper presents the theory and design methodology of ultrasonic WPT links that involve mm-sized receivers (Rx). For given load (R) and powering distance (d), the optimal geometries of transmitter (Tx) and Rx ultrasonic transducers, including their diameter and thickness, as well as the optimal operation frequency (f) are found through a recursive design procedure to maximize the power transmission efficiency (PTE). First, a range of realistic fs is found based on the Rx thickness constrain. For a chosen f within the range, the diameter and thickness of the Rx transducer are then swept together to maximize PTE. Then, the diameter and thickness of the Tx transducer are optimized to maximize PTE. Finally, this procedure is repeated for different fs to find the optimal f and its corresponding transducer geometries that maximize PTE. A design example of ultrasonic link has been presented and optimized for WPT to a 1 mm implant, including a disk-shaped piezoelectric transducer on a silicon die. In simulations, a PTE of 2.11% at f of 1.8 MHz was achieved for R of 2.5 [Formula: see text] at [Formula: see text]. In order to validate our simulations, an ultrasonic link was optimized for a 1 mm piezoelectric transducer mounted on a printed circuit board (PCB), which led to simulated and measured PTEs of 0.65% and 0.66% at f of 1.1 MHz for R of 2.5 [Formula: see text] at [Formula: see text], respectively.

Energy harvesting from extremely low frequency magnetic fields using magneto‐mechano‐electric (MME) harvesters enables wireless power transfer for operating Internet of Things (IoT) devices. The MME harvesters are designed to resonate at a fixed frequency by absorbing AC magnetic fields through a composite cantilever comprising of piezoelectric and magnetostrictive materials, and a permanent magnetic tip mass. However, this harvester architecture limits power generation because volume of the magnetic end mass is closely coupled with the resonance frequency of the device structure. Here, a method is demonstrated for maintaining the resonance frequency of the MME harvesters under all operating conditions (e.g., 60 Hz, standard frequency of electricity in many countries) while simultaneously enhancing the output power generation. By distributing the magnetic mass over the beam, the output power of the harvester is significantly enhanced at a constant resonance frequency. The MME harvester with distributed forcing shows 280% improvement in the power generation compared with a traditional architecture. The generated power is shown to be sufficient to power eight different onboard sensors with wireless data transmission integrated on a drone. These results demonstrate the promise of MME energy harvesters for powering wireless communication and IoT sensors.

A novel bow‐tie slot antenna fed by CPW is investigated. It is designed to work on a thick substrate (h=62 mil) with a high dielectric constant (εr=10.1). Two metal stubs are introduced at the center of the bow‐tie slot antenna to control the impedance matching and the cross‐polarization level. As a result, no balun network is required. A parametric study based on a numerical spectral domain is performed. A bandwidth of more than 40% is achieved, and the experimental results are presented. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 206–211, 2000.

Integrating tunable characteristics and multiple functions into a single metasurface has become a new scientific and technological undertaking that needs to deal with huge challenges, especially in the terahertz frequency region. The multifunctional design combining the broadband absorption and broadband polarization conversion using a single switchable metasurface is proposed in this paper. The switchable performance can be realized by treating the insulation to metal phase transition properties of vanadium dioxide (VO2). At high temperature (74 °C), the proposed metasurface can be used as a broadband absorber which consists of a VO2 square ring, polyimide (PI) spacer, and VO2 film. Simulated results show that the terahertz wave absorption can reach above 90% with the bandwidth ratio of 75% in the frequency range of 0.74 THz-1.62 THz. This absorber is insensitive to polarization resulted from the symmetry structure and also shows a good performance at large incident angles. Once the temperature is lower than the cooling phase transition temperature (about 62 °C) and VO2 is in insulation state, the metasurface can be transformed into a broadband linear-to-circular polarization converter. Numerical simulation depicts that the ellipticity reaches to -1 and the axis ratio is lower than 3 dB from 1.47 THz to 2.27 THz. The designed switchable metasurface provides the potential to be used in the fields of advanced research and intelligent applications in the terahertz frequency region.

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