Apparatus and method for interrogating a passive sensor

• US 20020121988A1
• Filed: 02/25/2002
• Published: 09/05/2002
• Est. Priority Date: 09/02/1999
• Status: Active Grant

• Current Assignee: Transense Technologies Plc
• Original Assignee: Transense Technologies Plc
• Inventors: Lonsdale, Anthony, Lonsdale, Bryan
• Granted Patent: US 6,765,493 B2
• Time in Patent Office: Days
• US Class Current: 340/870.16
• CPC Class Codes: G01D 5/48 using wave or particle radiation means G01D5/26 takes precedence

Abstract

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.

Claims

1. Apparatus for determining the resonant frequency of a passive sensor, said apparatus comprising:

means for transmitting signals of a plurality of frequencies to said passive sensor;

means for receiving signals from said passive sensor simultaneously with said transmitting of signals;

means 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; and

means for determining the frequency of the transmitted signal at the moment when the comparison indicates that the sensor is being driven at its resonant frequency.

2. Apparatus according to claim 1 wherein the driving signal is a radio frequency signal which is frequency modulated with a sweeping range of frequencies which span the expected resonant frequency of the sensor.

3. Apparatus according to claim 1 wherein the driving signal is a radio frequency signal which comprises pulses having a sequential range of separate frequencies which spansthe expected resonant frequency of the sensor.

4. Apparatus according to any preceding claim wherein the signals are transmitted across a gap between the transmitter and the sensor as radio signals by means of an antenna associated with the driving/comparing system and an antenna associated with the sensor.

5. Apparatus according to any preceding claim wherein a single antenna is used in the driving/comparing system for both transmitting the driving signal to the sensor and receiving the resultant signal from the sensor.

6. Apparatus according to any preceding claim wherein the comparison of the transmitted and received signals is a phase comparison

7. Apparatus according to any preceding claim wherein the comparison of the transmitted and received signals is an amplitude comparison.

8. Apparatus according to any preceding claim wherein the comparison of the transmitted and received signals is effected using a homodyne receiver.

9. Apparatus according to any preceding claim wherein the sensor is a saw device.

10. A method for determining the resonant frequency of a passive sensor, said method comprising:

transmitting signals of a plurality of frequencies to said passive sensor;

receiving signals from said passive sensor simultaneously with said transmitting of signals;

comparing the received signals with the transmitted signals to identify a characteristic change in the relationship between the received signal and the transmitted signal which occurs when the sensor is being driven at its resonant frequency; and

determining the frequency of the transmitted signal at the moment when the comparison indicates that the sensor is being driven at its resonant frequency.