The problem of maximization of the power received by an array of compact antennas connected to a number of loads (such as rectifiers) through an optimal matching network is investigated, analytically, numerically and by means of a prototype. The matching network is optimized to match the antennas and load impedances. A decrease in conversion efficiency may be caused by the parasitic capacitance of the rectifier diode. To overcome this issue, we propose an improved detector topology. In this topology, a series inductor L is included in the conventional half bridge detector in order to compensate the effect of the rectifier parasitic capacitance. This LC resonance technique, significantly increases the available DC output power. Measured maximum values of the rectifier's RF-to-DC conversion efficiency of 30% and 50% have been obtained for input power levels ranging from -10 dBm and -2 dBm, at frequencies of approximately 1.84 GHz. The output DC voltage of the rectifier with two input signals of 0 dBm was measured to be 3.10 V at 1.84 GHz.

In this paper, we present a new inspired metamaterial rectenna which is designed in the microstrip line structure at 5.8 GHz for the wireless transmission of microwave power. The proposed rectenna achieves RF-to-DC conversion efficiency of 52% and a DC voltage of 0.8 V when the received RF power is 1 mW at 5.8 GHz. The feasibility of this concept is presented through full-wave simulations. These simulations results will be updated at the conference with measurement results.

Conventional beamforming methods for reconfigurable reflector antennas assume full control over the amplitude and phase of the reflected field. Here, we develop a novel beamforming methodology for reflecting Programmable Metasurfaces (PMS) with capacitive memory. Although utilizing such fully reactive PMS simplifies antenna design and reduces energy consumption, the PMS reflection magnitude is unity and thus a global optimization of the reflection phases over the PMS unit cells is required in each beamforming scenario. We propose an implementation of such an optimization method rooted in the traditional Fourier transform-based beamforming and evaluate its performance. Additionally, we show that a pair of trained feed-forward neural networks (FFNN) with one input, one hidden, and one output layer can replace time-consuming global optimizations in the case of a PMS comprising $3\times 10$ unit cells. We train the FFNNs on a dataset obtained for typical single- and dual-beam beamforming scenarios. After training, the FFNNs perform requested beamforming tasks within a fraction of second and with about the same accuracy as the original optimization algorithm. The proposed methodology may find applications in future mobile telecommunication systems that require real-time beamforming on low-end hardware. The same beamforming methodology can be also employed in short-range wireless power transfer systems.

Conjugate impedance matched metamaterials are shown to be effective traps for electromagnetic waves. Objects made of such materials are able to receive radiation even when it is not directly incident on their surface. Here, we develop methods of physical modeling of such objects and investigate interactions of conjugate impedance matched superabsorbers with passing electromagnetic radiation. We study realizations of such metamaterials with meshes of loaded transmission lines and develop a theory of electromagnetic wave propagation and absorption in such media. Peculiar wave propagation, wave trapping and absorption effects in metamaterial black holes and wormholes are demonstrated. Possible modifications under the goal of optimizing absorption while minimizing complexity of the involved metamaterials are discussed. Conjugate-impedance matched superabsorbers may find applications as efficient harvesters of electromagnetic radiation, and as novel antennas and sensors.

In this paper, we investigate a metamaterial- inspired small rectenna (rectifying antenna) system for microwave energy harvesting and wireless power transfer at 5.8 GHz. We also study the received-power maximization technique using an array of antennas connected to a single load by an optimal RF power combiner. This investigation is done both in simulation and experiment. The power combiner is embedded between the metamaterial- inspired antennas and the load (including rectifier) for maximizing the power, harvested by the input antennas and to deliver it to the load in the most optimal way. Moreover, we design and test proof-of-concept prototypes of the main components of the investigated energy harvesting systems. The similarity between the simulation and the experimental results also confirms our method of investigation.