| 摘要 |
<p>PURPOSE:To enable accurate reception of data while eliminating the effect of a transmission coil on a reception coil, by providing a core inside the transmission coil and by providing a first reception coil element in the core and a second reception coil element wound in the direction reverse to that of the first reception coil element. CONSTITUTION:A cylindrical coil spool 31 having two grooves is fitted to the front of a case of a read-write head 30, and a transmission coil L1 is wound on the front side of the spool, while a second reception coil element L22 is wound at the back thereof. A cylindrical pot core 32 is provided in the spool and a first reception coil element L21 is wound on a coil bobbin 33. The reception coil element L21 is a coil for reception, while the reception coil element L22 is provided for canceling the effect of the transmission coil. The mutual inductance of the transmission coil L1 and the reception coil element L21 and the mutual inductance of the transmission coil L1 and the reception coil element L22 are made to be the same in amplitude with each other and opposite in a code to each other. When a data carrier 20 approaches, the resonance frequency of the data carrier changes and a reception signal is obtained in a coil L3. This attenuation signal is transmitted to a reception coil L2 and a signal of a waveform of which the period is long only in the initial part and the same with an attenuated oscillation thereafter is obtained for voltages obtained in the reception coils L21 and L22. This signal is amplified and subjected to wave-shaping and thus an output is obtained.</p> |
