| 摘要 |
<p>A system for validating coins comprises a transmitter coil (2) for transmitting low-frequency electromagnetic radiation through a coin (1) to be validated and a receiver coil (3) for receiving radiation having passed through the coin. An inverting amplifier (4) is provided in a feedback path between the receiver coil (3) and the transmitter coil (2) thereby providing a 180 DEG phase shift. Thus, for the unique frequency which causes a 180 DEG phase shift within the coin, there is provided positive feedback, and a resonance condition occurs at that frequency. By measuring the frequency of this resonance and comparing it with a reference value, the coin can be validated.</p> |
