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The pyrochlore-type rare-earth oxides attract considerable attentions due to their outstanding properties and extensive applications. In this work, contour maps of mechanical/thermal properties as a function of A and B cation radii across a wide variety of A 2 B 2 O 7 (A = La-Lu and Y; B = Ti, Sn, Hf, Zr, Pr and Ce) pyrochlore oxides are studied using the first-principles calculations. The mechanical/thermal properties vary dramatically with increasing of the B cation sizes but do not show a strong systematic dependence on the A cation sizes. Furthermore, the machine learning algorithm is performed for the large family of pyrochlores and the parameters playing key role on mechanical/thermal properties are clarified. Besides, the expressions of focused mechanical and thermal properties are constructed. These results are expected to guide the future material design through composition tailoring. K E Y W O R D Sfirst-principles calculations, mechanical properties, pyrochlore, thermal conductivity

Abstract-With the increase of low power devices, the design of a compact and efficient rectenna is essential for supplying energy to the devices. This paper presents a compact rectenna for high efficient WiFi energy harvesting. A novel fractal geometry is introduced in the design of antenna for miniaturization, and the ability to harvest WiFi energy is enhanced due to its characteristics of self-similarity and space filling. Besides, a single stub matching network is designed to achieve high conversion efficiency with a relatively low input power ranging from −20 dBm to 0 dBm. Simulation and experiments have been carried out. The results show that the proposed antenna features a good characteristic of reflection coefficient and realized gain at WiFi band. The highest RF to DC conversion efficiency of the rectenna is up to 52% at 2.45 GHz with the input power of 0 dBm. This study demonstrates that the proposed rectenna can be applied to a range of low power electronic applications.

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A novel efficient rectenna is proposed in this paper for radio frequency (RF) energy harvest from ambience at 2.45 GHz ISM band. A compact fractal antenna is designed based on a Lévy C curve. The performance of antenna with the ground plane of the conventional geometry, the rectangular‐slot geometry and the newly designed geometry is investigated and compared. Besides, a typical rectifier with a 73‐degree radial stub matching network is presented. Simulation and experiment are performed to validate the performance of the presented rectenna. The results indicate that the antenna is characterized with a good matching characteristic with a stable omnidirectional radiation pattern. The rectifier has a relatively high efficiency of 30% under the low input power of −10 dBm. The measured maximum RF to DC conversion efficiency of the rectenna is 70% with the output voltage of 2.2 V at 0 dBm when the input power ranging from −20 dBm to 0 dBm.

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In wireless power transfer, the transfer efficiency decreases with the increase of the transfer distance. To improve the power transfer performance, the operating characteristics of a conformal coplanar four-coil magnetic resonant coupling wireless power transfer system are investigated and analyzed under four different resonant states. Based on the complete equivalent circuit model, the transmission coefficient and the input impendence are calculated. The performance of the systems operated under four resonant states is studied and compared. Also, the origin of the difference is specifically analyzed. The simulation results indicate that the wireless power transfer system operated under State 1, the state where the compensated serial capacitance makes the coils work at the frequency of the maximum Q-factor, shows the most excellent transfer characteristic among the four resonant states. The transmission coefficient can be well maintained above 0.8 within the transfer distance of 30 cm. Experiment has been carried out for validation, and the result indicates that more power can be delivered to the load for the system operated under State 1. K E Y W O R D S operating characteristics, resonant state, transmission coefficient, wireless power transfer 1 | INTRODUCTION Wireless power transfer has received a great deal of attention as it provides a possibility to deliver energy without power lines. A variety of wireless power transfer techniques have been developed, which are based either on near-field or farfield electromagnetic coupling. 1,2 Previous studies have demonstrated that higher power transfer efficiency can be obtained via the near-field techniques than the far-field approaches. In the near-field techniques, compared with the traditional inductively coupled scheme, magnetic resonant coupling wireless power transfer (MRC-WPT) has been a hot research area due to its longer transfer distance. 3 Thus, it is applied in various applications such as implanted biomedical devices, portable electronics, and electric vehicle charging system. 4-6 Generally, most MRC-WPT systems are featured with two coils. It has been revealed in other studies 7-9 that the transfer performance of the two-coil system deteriorates with the increase of the transfer distance due to the weakened magnetic coupling. To extend the transfer distance, MRC-WPT systems with repeaters positioned between transmitting and receiving coils have been investigated. 10-15 Nevertheless, the transmission efficiency