| 摘要 |
<p>An apparatus for measuring electrical characteristics of a resonant circuit (14, 14') without physically contacting the resonant circuit (14, 14'). The EAS system includes a numerically controlled oscillator (416) for generating an alternating electric signal, the frequency of the alternating electric signal varying in accordance with a numerical frequency control signal; a transmitting antenna (16, 16a') connected to the numerically controlled oscillator (416) for establishing an electromagnetic field within a measurement zone; a receiving antenna (16, 16b') for sensing disturbances to the electromagnetic field within the measurement zone; a receiver (18, 18') for receiving signals from the receiving antenna (16, 16b') representative of disturbances to the electromagnetic field and for determining the Q and center frequency of the resonant circuit (14, 14'); and a clock (400) having a substantially fixed frequency connected to the numerically controlled oscillator (416). The frequency of the alternating electric signal is restricted to being an integer multiple of an integer sub-multiple of the clock frequency.</p> |
