A novel metamaterial rectifying surface (MRS) for electromagnetic energy capture and rectification with high harvesting efficiency is presented. It is fabricated on a three-layer printed circuit board, which comprises an array of periodic metamaterial particles in the shape of mirrored split rings, a metal ground, and integrated rectifiers employing Schottky diodes. Perfect impedance matching is engineered at two interfaces, i.e. one between free space and the surface, and the other between the metamaterial particles and the rectifiers, which are connected through optimally positioned vias. Therefore, the incident electromagnetic power is captured with almost no reflection by the metamaterial particles, then channeled maximally to the rectifiers, and finally converted to direct current efficiently. Moreover, the rectifiers are behind the metal ground, avoiding the disturbance of high power incident electromagnetic waves. Such a MRS working at 2.45 GHz is designed, manufactured and measured, achieving a harvesting efficiency up to 66.9% under an incident power density of 5 mW/cm², compared with a simulated efficiency of 72.9%. This high harvesting efficiency makes the proposed MRS an effective receiving device in practical microwave power transmission applications.

This letter presents a wideband metamaterial electromagnetic (EM) energy harvester with high capture efficiency and wide incident angle. It is an array of novel resonators comprising metallic mirrored split rings and hollow cylinders. The impedance of the harvester is engineered to match with free space, so that the incident EM energy is captured with minimum reflection, and then channeled maximally to the ports through optimally positioned vias. The hollow cylinder works equivalently as a shunt capacitance in series with an inductance to lower the resonator's quality factor, which significantly enhances the bandwidth. The power harvesting mechanism is analyzed using both the transmission line model and full-wave simulation. A metamaterial harvester of 10 × 10 unit cells is designed, manufactured, and measured, achieving a capture efficiency of up to 97.3% at 2.45 GHz. A wide relative bandwidth of 16% with efficiencies above 90% is observed from 2.3 to 2.7 GHz. Within a wide incident angle range (92° on E -plane and 44° on H -plane), the harvester manages to capture more than half of the incident energy.

For most microwave power transmission (MPT) applications, the microwave power is received within the near field of a large-scale transmitting antenna from a limited distance. This letter explores the design of a near-field focused transmitting antenna to concentrate the microwave power on the receiving antenna's aperture, and thereby to enhance the transmission efficiency of the MPT. A near-field planar array with a size of 1 m × 1 m working at 5.8 GHz is manufactured. To focus the microwave power at a distance of 10 m, its 8 × 8 radiation elements are fed with an equal amplitude but different phase using coaxial cables of different lengths. An MPT experiment is conducted. The measurement shows that, compared with a traditional equal-phase array, the near-field focused array obtains a much more concentrated microwave beam. The transmission efficiency is significantly increased from 32.98% to 41.85%.

Microwave selective/localized heating has been widely used in special areas, e.g., medical treatment and food processing, but the control of selective/localized heating in restricted space, e.g., microwave ovens, is difficult to accomplish. In this article, a Giuseppe Peano fractal phased-array antenna is designed, and the phase of each radiator is derived to achieve the arbitrary spatial division of the electromagnetic field in a cavity based on the superposition principle of waves. Then, a multiphysics model of microwave heating is established by coupling the electromagnetic field and heat transfer to simulate the directional control of microwave heating in a cavity. An experimental system is built, and the heating results are measured using an infrared thermal imager to verify the temperature distribution in different spatial regions. Finally, the feasibility of the model for different heating targets is discussed.

Impedance surfaces are artificially designed periodic structures that support surface waves. This paper presents a novel concept of a nonlinear impedance surface, whose impedance increases with the surface wave power. The proposed surface consists of a lattice of modified slotted mushroom-like cells loaded with varactor diodes and lumped circuits. The circuits are designed to sense the incoming surface wave power and feed back the signal to control the bias of the varactors, which eventually tunes the surface impedance. Such proposed power-dependent impedance surface has been demonstrated by a prototype consisting of 4 × 10 cells. It is observed from the experiments that as the power varies from 16 to 27 dBm, the surface exhibits a surface impedance range as much as j385 to j710 Ω. This characteristic enables the surface to be potentially useful in self-trapping surface-wave waveguide, power-dependent beam-steering antenna reflector, and other nonlinear applications.

A novel parameter extraction method for the Schottky diode’s large-signal equivalent-circuit model is proposed, and used to design high-efficiency microwave rectifying circuits. This method extracts the nonlinear SPICE parameters in the equivalent-circuit from measured I-V and C-V data, and the linear parasitic parameters from the broadband small-signal S-parameters. Moreover, it employs a de-embedding technology that adopts an equivalent circuit to remove the influence of the test fixture in the S-parameters measurement, thereby additional TRL calibration kits are not required. As a sample, large-signal equivalent-circuit parameters of the Schottky diode with model number MA4E1317 are extracted by the proposed method. Then it was used to design two Class-F microwave rectifying circuits working at 2.45 GHz and 5.8 GHz, respectively. Owing to the high accuracy of the extracted parameters by the proposed method, the simulation results such as the large-signal transient voltage waveforms across the diode agree well with the measured ones. Furthermore, two rectifying circuits exhibit very high rectifying efficiencies (e.g. 83.5% at 2.45 GHz and 82.1% at 5.8 GHz with 16.8 dBm input power).