We propose a novel design of a near-field transmitting focused metasurface, which transforms a linearly polarized planar incident wave into a near-field focused beam with multiple foci and multiple nulls in this paper. A generalized method of obtaining the metasurface field distribution on its aperture for specified near-field foci and nulls is firstly introduced. Then, a three-layer metasurface particle structure with close to full range reconfigurable amplitude and phase transmitting response for realizing the required field distribution is studied. By adjusting the arc length and the rotating angle of the middle-layer metasurface particle structure, a transmitting response with arbitrary amplitude and phase is achieved. Finally, a focused metasurface with two near-field foci and two near-field nulls is designed based on the proposed theory and metasurface particle structure. The designed metasurface is full-wave simulated, fabricated, and measured in the experiment. The experimental results agree well with the full-wave simulating results, showing that both the foci and nulls are well presented at the specified positions and the measured power of the near-field nulls is more than 26 dB below the power of the foci.

A hybrid higher order discontinuous Galerkin time-domain (DGTD) method and finite-element time-domain (FETD) method with parallel technique is proposed for electromagnetic (EM)–circuital–thermal co-simulation in this article. For electromagnetic simulation, DGTD method with higher order hierarchical vector basis functions is used to solve Maxwell equation. Circuit simulation is carried out by modified nodal analysis method. For thermal simulation, FETD method with higher order interpolation scalar basis functions is adopted to solve heat conduction equation. To implement electromagnetic–circuital–thermal co-simulation, the electromagnetic and circuital equations are strongly coupled through voltages, currents, and electric fields at the lumped ports first. Then the electromagnetic and thermal equations are weakly coupled with electromagnetic loss and temperature-dependent medium parameters. Finally, large-scale parallel technique is used to accelerate the process of multiphysics simulation. Numerical results are given to validate the correctness and capability of the proposed electromagnetic–circuital–thermal co-simulation method.

In this paper, a loop-bowtie strap feed antenna with $\lambda /4$ meandered dipoles and modified T-matching networks is proposed. T-matching networks are employed to guide current, enhancing gain of the antenna. Aiming to improve robustness of the antenna used both on metallic objects and in air, two steps are implemented, respectively. Noticeably, the method is universal to design antimetal tag which also has a good performance in air. Four movable connection stubs and H-slots together raise degrees of freedom to tune global RFID frequency band. Besides, a simple equivalent circuit is presented, giving a convenient design rule and reasonable analysis of the design. Finally, reflection coefficients are measured using two methods, one is using the calibration kit made by us and the other is using port extension. Reading distances in different cases are also measured, showing the maximum distances are 1.8 and 2.7 m on metallic objects and in air, respectively. Measured and simulated results are with a good agreement, verifying the rationality of the design.

We discuss a noninvasive technique to detect glucose changes with enhanced sensitivity based on parity-time (PT) symmetry. We detect glucose level changes within the skin by measuring the frequency shift in the electromagnetic resonance induced within a PT-symmetric system that sandwiches the tissue sample under analysis. Even though the sample itself is lossy, and therefore, resonances would be damped, the introduction of balanced gain and loss enables an efficient sensing mechanism that bypasses the conventional limitations of passive sensing schemes. Our results indicate that the resonance shift can be made fairly linear with respect to the glucose concentration variations, and the expected accuracy is large. We also investigate a realistic system to implement the noninvasive PT-symmetric glucose sensor using loop antennas and negative impedance converters, exploring its sensitivity with respect to design errors and disorder.

In this article, pseudorandom noise (PN) sequence time-modulated reflective metasurfaces are proposed to provide a low-cost, low-complexity, simple solution for target recognition. By covering the target to be recognized with a time-modulated metasurface modulated by a PN time sequence, the metasurface scatters the interrogating harmonic wave into a binary PN-modulated wave. As a result, the radar detector with the foreknowledge of the modulating PN sequence may recognize the target by applying the properties of strong autocorrelation and weak cross correlation of PN sequences and performing cross correlation between the modulating PN sequence and the picked-up signal after downshifting its frequency without actually decoding and reading the scattered information. A 1-bit reconfigurable metasurface unit cell operating at 2.4 GHz is proposed and full-wave simulated to achieve out-of-phase reflective responses by controlling the ON and OFF states of the p-i-n diode for PN time modulation. The target recognition is demonstrated by experiment in two different scenarios where only one metasurface and multiple metasurfaces are present for recognition. The experimental results show that by providing an appropriate threshold in the cross-correlation detecting results, the proposed method can recognize the targets well in both scenarios.

Sensors are key components in structural health monitoring. Although significant improvements have been made on monitoring technologies by using many advanced smart sensors, the need of cables and power supplies still causes much inconvenience in the practical implementation of these technologies. In this paper, we propose a novel rectangular patch antenna to monitor the structural health in a wireless and passive manner so that the drawback of traditional monitoring methods can be fully overcome. The antenna is used as a sensor and its resonant frequency will change linearly in terms of its size changes in both horizontal and vertical directions. The antenna will transmit an electromagnetic wave with the resonant frequency information to a reader by a long distance and activate the chip in the reader. According to the received information about the resonant frequency, the change of the targeted structure’s strain can be measured in real time and its health state can then be evaluated. Simulations and experiments show that the designed antenna is an excellent strain sensor and can be applied to the health detection for many types of structure.