| 摘要 |
The disclosed device comprises electric conductors (1, 1'; 2, 2') arranged under the writing surface and associated to a writing implement provided with a permanent magnet of which the power supply is orientated in parallel to its longitudinal axis. Said conductors form elongated meandres-like windings covering the writing surface so that when the implement is displaced in parallel to said surface and tranversely to the meandres of the windings, a sinusoidal voltage is induced at the terminals of the windings provided the instrument is close enough to the writing surface. The pitch of the meandres of the windings is so selected as to induce a sinusoidal voltage having an amplitude higher than a given threshold for a predetermined interval between the writing implement and the writing surface. |
