Loading coil

Abstract: This paper proposes a high-efficiency wireless power transfer system with an asymmetric four-coil resonator. It presents a theoretical analysis, an optimal design method, and experimental results. Multicoil systems which have more than three coils between the primary and secondary side provide the benefits of a good coupling coefficient, a long transfer distance, and a wide operating frequency range. The conventional four-coil system has a symmetric coil configuration. In the primary side, there are source and transmitter coils, and the secondary side contains receiver and load coils. On the other hand, in the proposed asymmetric four-coil system, the primary side consists of a source coil and two transmitter coils which are called intermediate coils, and in the secondary side, a load coil serves as a receiver coil. In the primary side, two intermediate coils boost the apparent coupling coefficient at around the operating frequency. Because of this double boosting effect, the system with an asymmetric four-coil resonator has a higher efficiency than that of the conventional symmetric four-coil system. A prototype of the proposed system with the asymmetric four-coil resonator is implemented and experimented on to verify the validity of the proposed system. The prototype operates at 90 kHz of switching frequency and has 200 mm of the power transmission distance between the primary side and the secondary side. An ac–dc overall system efficiency of 96.56% has been achieved at 3.3 kW of output power.

Abstract: This paper presents a magnetic resonance wireless power transfer (WPT) system that uses three coils, a planar receiver and operates at 6.78 MHz,. Effective power transfer is ensured by establishing an impedance matching condition for this WPT system. A metamaterial (MTM) array having dimensions of 20 cm Ⅹ 30 cm is also positioned near the load coil to concentrate the magnetic field and enhance the transfer efficiency. The result is a maximal improvement of 27% in the transfer efficiency at a transfer distance of 50 cm. The impact of a ground plane on the transfer efficiency is also examined. By utilizing the MTM array, making slits on the ground plane and increasing the gap between the ground plane and the load coil, it is possible to mitigate this impact. The highest transfer efficiency improvement is about 55% at a distance of 20 cm with the ground plane. A practical laptop model is fabricated to verify the impact of the load coil angle and position on the transfer efficiency. The result shows that the maximum transfer efficiency with the laptop model is 47.58% with the load coil angle of 90 degree.

Abstract: An electromagnetic tuning device for RF circuits and particularly loading coils for antennas is disclosed. The preferred devices have a coil which produces a generally torroidal shaped electromagnetic field that is intensified by either a core of ferromagnetic material or a second coil inside the other coil. An insulating material surrounds and hermetically seals the coil and field intensifying device that is inside said coil; and an electrically conductive tuning ring is positioned outside of the insulating material for producing a counter magnetic field which opposes and cuts down the field produced by the first mentioned coil. In one embodiment, the tuning ring is threaded and it threadably engages the insulating material so it can be adjustably positioned relative to the torroidal field. In another embodiment the tuning ring is connected in electrical series circuit with a variable resistor. In both embodiments the tuning ring is insulated from ground and the coil so that nonproductive current flow is prevented. In a further embodiment, an electrically conductive shield having magnetic field transmitting windows is positioned between the tuning ring and the coil to greatly reduce capacitive effects on the coil by the environment.

Abstract: PURPOSE: An antenna device for a radio communication terminal is provided to reduce a specific absorption rate of electromagnetic waves transmitted to a human body by improving a structure of antenna device. CONSTITUTION: An antenna device for a radio communication terminal is with by combining a helical antenna having length of λ/4 adapted for a standby state of signal and a communication state of signal with a monopole type whip antenna. A loading coil(102) is wound in the inside of a molding body formed with a non-conductive material. The loading coil(102) is wound with a spiral shape in order to transmit and receive effectively radio frequencies in the standby state of signal and the communication state of signal. The loading coil(102) is formed with a linear portion(102a) and a curve portion(102b) in order to reduce a specific absorption rate of electromagnetic waves transmitted to a human body.