| 摘要 |
PURPOSE:To prevent the space uniformity of a transmission high frequency magnetic field from being disturbed by connecting diodes which are connected reversely in parallel to a high frequency coil in parallel. CONSTITUTION:The diodes 5a and 5b which are connected reversely in parallel are connected to the high frequency coil 1 in parallel and the 1st - the 3rd varactor diodes 6a and 6b, 7a and 7b, and 8a and 8b which are connected reversely in series are used. A high frequency current induced at the coil 1 passes through the diodes 5a and 5b and returns to the coil 1. The impedance matching of the coil 1 is adjusted by varying a DC voltage applied to each varactor diode. Consequently, the impedance can be matched and adjusted at distance from the coil 1. Further, when a transmit pulse is applied, the capacity of each varactor diode is so set not as to satisfy impedance matching condition, and consequently an excessive voltage pulse is prevented from being applied to the input of a receiving preamplifier connected to the coil 1.
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