Miniature Integrated 2.4 GHz Rectennas Using Novel Tunnel Diodes.

This work presents the design, fabrication, and measured results of a fully integrated miniature rectenna using a novel tunnel diode known as the Asymmetrical Spacer Layer Tunnel (ASPAT). The term rectenna is an abbreviation for a rectifying antenna, a device with a rectifier and antenna coexisting as a single design. The ASPAT is the centrepiece of the rectifier used for its strong temperature independence, zero bias, and high dynamic range. The antenna is designed to be impedance matched with the rectifier, eliminating the need for a matching network and saving valuable real estate on the gallium arsenide (GaAs) substrate. The antenna is fully integrated with the rectifier on a single chip, thus enabling antenna miniaturisation due to the high dielectric constant of GaAs and spiral design. This miniaturisation enables the design to be fabricated economically on a GaAs substrate whilst being comparable in size to a 15-gauge needle, thus unlocking applications in medical implants. The design presented here has a total die size of 4 × 1.2 mm2, with a maximum measured output voltage of 0.97 V and a 20 dBm single-tone 2.35 GHz signal transmitted 5 cm away from the rectenna.

Wirelessly Powered Light and Temperature Sensors Facilitated by Electrically Small Omnidirectional and Huygens Dipole Antennas.

Wirelessly powered, very compact sensors are highly attractive for many emerging Internet-of-things (IoT) applications; they eliminate the need for on-board short-life and bulky batteries. In this study, two electrically small rectenna-based wirelessly powered light and temperature sensors were developed that operate at 915 MHz in the 902-928-MHz industrial, scientific, and medical (ISM) bands. First, a metamaterial-inspired near-field resonant parasitic (NFRP) Egyptian axe dipole (EAD) antenna was seamlessly integrated with a highly efficient sensor-augmented rectifier without any matching network. It was electrically small and very thin, and its omnidirectional property was ideal for capturing incident AC wireless power from any azimuthal direction and converting it into DC power. Both a photocell as the light sensor and a thermistor as the temperature sensor were demonstrated. The resistive properties of the photocell and thermistor changed the rectifier's output voltage level; an acoustic alarm was activated once a threshold value was attained. Second, an electrically small, low-profile NFRP Huygens antenna was similarly integrated with the same light- and temperature-sensor-augmented rectifiers. Their unidirectional nature was very suitable for surface-mounted wireless power transfer (WPT) applications (i.e., on-body and on-wall sensors). Measurements of the prototypes of both the light- and temperature-sensor-augmented omni- and unidirectional rectenna systems confirmed their predicted performance characteristics.

Multi-Junction Solar Cells and Nanoantennas.

Photovoltaic technology is currently at the heart of the energy transition in our pursuit to lean off fossil-fuel-based energy sources. Understanding the workings and trends of the technology is crucial, given the reality. With most conventional PV cells constrained by the Shockley-Queisser limit, new alternatives have been developed to surpass it. One of such variations are heterojunction cells, which, by combining different semiconductor materials, break free from the previous constraint, leveraging the advantages of both compounds. A subset of these cells are multi-junction cells, in their various configurations. These build upon the heterojunction concept, combining several junctions in a cell-a strategy that has placed them as the champions in terms of conversion efficiency. With the aim of modelling a multi-junction cell, several optic and optoelectronic models were developed using a Finite Element Tool. Following this, a study was conducted on the exciting and promising technology that are nanoantenna arrays, with the final goal of integrating both technologies. This research work aims to study the impact of the nanoantennas' inclusion in an absorbing layer. It is concluded that, using nanoantennas, it is possible to concentrate electromagnetic radiation near their interfaces. The field's profiles might be tuned using the nanoantennas' geometrical parameters, which may lead to an increase in the obtained current.

Optical rectification and thermal currents in optical tunneling gap antennas.

Electrically-contacted optical gap antennas are nanoscale interface devices enabling the transduction between photons and electrons. This new generation of device, usually constituted of metal elements (e.g. gold), captures visible to near infrared electromagnetic radiation and rectifies the incident energy in a direct-current (DC) electrical signal. However, light absorption by the metal may lead to additional thermal effects which need to be taken into account to understand the complete photo-response of the devices. The purpose of this communication is to discriminate the contribution of laser-induced thermo-electric effects in the photo-assisted electronic transport. We show case our analysis with the help of electromigrated devices.

Optical Nanoantennas for Photovoltaic Applications.

In the last decade, the development and progress of nanotechnology has enabled a better understanding of the light-matter interaction at the nanoscale. Its unique capability to fabricate new structures at atomic scale has already produced novel materials and devices with great potential applications in a wide range of fields. In this context, nanotechnology allows the development of models, such as nanometric optical antennas, with dimensions smaller than the wavelength of the incident electromagnetic wave. In this article, the behavior of optical aperture nanoantennas, a metal sheet with apertures of dimensions smaller than the wavelength, combined with photovoltaic solar panels is studied. This technique emerged as a potential renewable energy solution, by increasing the efficiency of solar cells, while reducing their manufacturing and electricity production costs. The objective of this article is to perform a performance analysis, using COMSOL Multiphysics software, with different materials and designs of nanoantennas and choosing the most suitable one for use on a solar photovoltaic panel.

Stretchable wideband dipole antennas and rectennas for RF energy harvesting.

The ultimate application of bio-integrated, stretchable electronics hinges on the indispensable modules of stretchable wireless data transmission and power supplies. While radiofrequency (RF) antennas and rectennas could enable wireless communication and RF energy harvesting in the far-field, their performance deteriorates because of the frequency detuning from mechanical deformations. Here, stretchable wideband antennas and rectennas are introduced to robustly operate and combine received RF power over their wideband upon mechanical deformations. Devices with stretchable wideband antennas and rectennas create application opportunities such as self-powered systems, remote monitoring of the environment, and clean energy. A comprehensive set of manufacturing schemes, device components, and theoretical design tools for the stretchable wideband antennas and rectennas is reported. A stretchable wideband rectenna integrated with various functional sensing modules and its demonstration with enhanced effective rectenna efficiency over the state-of-the-art by 10-100 times illustrates a system-level example of this technology.