Wireless Power Transfer Using One-dimensional Free Access Mat

From the beginning we had used the electricity, wireless power transfer have been desired. There are several solutions for the wireless power transfer using the electromagnetic (EM) wave. For example, Felica utilizes the electromagnetically inductive coils [1]. And the evanescent wave through the surface of two-dimensional transmission sheet is studied [2]. In addition non-radiative mid-range energy transfer is one of the hottest issues [3]. There are some limitations for those solutions. The wireless power transfer using magnetic induction for very close range or very small power has small positioning tolerance of several mm. The wireless power transfer using omnidirectional or high directional antenna has large free space transmission loss and is not good at NLOS condition or for mobile objects. In addition two-dimensional transmission sheet needs special connectors to excite the sheet. There are some wireless networks for the confined area such as indoor sensor networks, personal area networks and body area networks. For these networks, EM power concentrated inside two-dimensional plane or a transmission line is useful and good for interference problem. We can put wireless devices anywhere on the two dimensional waveguide without a contact. The devices couple to the waveguide and power is supplied through the waveguide. We need a sheet-like waveguide which is efficient, safe and easy to use. We proposed a free access mat [4] with a simple structure of two layers of patch array. Those patches are tightly coupled to each other. The EM wave is concentrated into the free access mat and transmits in a small loss. The general antennas couple to it with a small loss. Good coupling provides efficient power transfer. One or two-dimensional array of the free access mat is available to a variety of uses of the wireless power transfer. It presents wireless energy transfer along the transmission line or through the planar waveguide. In addition, it is easy to use. We can just put the device on the free access mat and power is transferred by coupling. The free access mat is hard to be interfered. The wireless devices only on the free access mat can couple to it. The wireless devices outside of the free access mat barely couple to it. In addition the EM wave is strongly concentrated into the free access mat so that it has a small radiation electric field. In this paper we propose and demonstrate the wireless power transfer using onedimensional free access mat. Figure 1 shows the configuration of the free access mat and the image of wireless power transfer using the free access mat. The free access mat is connected to the power source and the power is wirelessly transferred to the devices on the free access mat. The wireless devices couple to the free access mat without contact points so that the safety and maintenance problems caused by contact points could be solved. In this paper we present the basic study of wireless power transfer using one-dimensional array of the free access mat. We design the free access mat which has a center frequency around 2.45 GHz. We present small transmission loss through the free access mat, good coupling between general antennas and the free access mat and power transfer efficiency.