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Wireless power transmission using mid-range magnetic resonance has become an important technology in body area sensor systems. Recent researches have used fine-tuned impedance matching for wireless power transmission at fixed distance. However, this method is significantly sensitive to the distance change between two devices since the impedances at both ends must be perfectly matched. Hence, it is a major challenge to achieve efficient wireless power transmission in mobile environment. We propose a new circuit architecture for wireless power transmission in the near field; the Resonator Isolation (RI) structure. Using the RI structure, the wireless power transmission becomes highly robust under mobile environment. In this paper, we present the circuit design of the RI structure and evaluate its performance with the actual systems we constructed. [ABSTRACT FROM PUBLISHER]

In wireless sensor networks, the lifetime of the sensors restricts the performance of the sensor network. In order to overcome this restriction, the sensors can be revived by frequently recharging the battery in each node. Recent technologies have simplified the energy charging process using wireless energy transmission. However, the efficiency of energy transmission reduces rapidly over long distance, consequently making it difficult to transmit energy to multiple nodes in a wide area. Energy can be delivered to each node by a wireless charging vehicle (WCV) which has high mobility and large energy capacity. Even with such WCV, a node battery is frequently depleted which makes the node stop operating until the battery is recharged by the WCV. If the frequency of energy charging is too low, the number of non-operating node will increase. If the frequency of energy charging is too high, each node will waste too much time in the energy charging process. In order to maximize the overall ratio of operating time of the sensor nodes, the WCV and sensor nodes require a proper scheme for the energy charging process. In this paper, we propose an energy charging scheme that can maximize the ratio of operating time of the sensor nodes, and thus improve the performance of the sensor network. [ABSTRACT FROM PUBLISHER]