| 摘要 |
Apparatus for determining the resonant frequency of a passive sensor, for example a saw device, comprises: means (5,7, 3) for transmnitting signals of a plurality of frequencies to said passive sensor (2); means (3, 7) for receiving signals from said passive sensor simultaneously with said transmitting of signals; means (7) for comparing the received signals with the transmitted signals to identify a characteristic change in the relationship between the received signals and the transmitted signals which occurs when the sensor is being driven at its resonant frequency. Typically, as the frequency at which the passive sensor is driven passes through the resonant frequency of the sensor the phase and/or amplitude of the signal generated by the passive sensor win change. By identifying this change of phase and/or amplitude the point at which resonance occurs can be detected. The frequency of the transmitted signal at the moment when the comparison indicates that the sensor is being driven at its resonant frequency is the resonant frequency of the sensor. |
