Interrogation method for passive wireless sensor interrogation system

• US 8,296,087 B2
• Filed: 03/22/2010
• Issued: 10/23/2012
• Est. Priority Date: 03/25/2009
• Status: Active Grant

• Current Assignee: Transense Technologies Plc
• Original Assignee: Transense Technologies Plc
• Inventors: Kalinin, Victor Alexandrovich, Beckley, John Peter, Dixon, Bryn James
• Primary Examiner(s): Nghiem, Michael
• Assistant Examiner(s): Perez Bermudez, Yaritza H
• Application Number:
  US12/728,620
• Publication Number:
  US 20100250170A1
• Time in Patent Office: 946 Days
• Field of Search: 702/57, 702/75, 702/76, 702/77, 702/101, 702/104, 702/116, 702/129, 702/173, 702/179, 702/182, 702/183, 702/188, 702/199
• US Class Current: 702/76
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
• CPC Class Codes: B60C 23/0433 Radio signals
• CPC Class Codes: B60C 23/0449 Passive transducers, e.g. using surface acoustic waves, backscatter technology or pressure sensitive resonators near field passive transducers B60C23/0428

Abstract

A method of wirelessly interrogating a sensing device comprising a plurality of passive sensors, to determine a measurement parameter, comprises the steps of repeatedly interrogating the sensing device using a predetermined transmission signal and detecting the response; estimating the measurement parameter for each sensor by means of an analysis of the data accumulated as a result of the interrogation step, and determining the average of the parameters derived from the estimating step for each sensor, using a weighted average, in which the weightings depend on the amplitude of the sensor response. The measurement parameter may be a resonant frequency where the passive sensors are resonant devices, and the sensors may be SAW devices.

Claims

1. A method of wirelessly interrogating a sensing device comprising a plurality of passive sensors, to determine a measurement parameter, f, comprising the steps of:

(1) interrogating each passive sensor using a predetermined transmission signal, detecting the passive sensor response and analyzing the passive sensor response to find its amplitude and an estimate of the measurement parameter;

(2) repeating step (1) in order to obtain several estimates of the measurement parameter for each passive sensor; and

(3) determining the average of the measurement parameters for each passive sensor, using a weighted average, in which the weightings depend on the amplitude of the passive sensor response, wherein the averaged measurement parameter f_ave is given by

2. The method according to claim 1, wherein the weightings depend on the maximum power spectral density of the passive sensor response.

3. The method according to claim 1, wherein the weightings w_j are selected so as to minimize the standard deviation of f_ave for a given value of N.

4. The method according to claim 3, wherein the weightings w_j are selected according to the rule w_j=S/σ

_j², where S is a constant, and σ

_j is the standard deviation of the measured parameter.

5. The method according to claim 1, wherein the measured parameters are stored in an averaging buffer, and the weightings w_j are selected so as to minimize the time needed to fill the buffer while maintaining the standard deviation of the averaged measurement parameter.

6. The method according to claim 5, wherein the weightings are integer weightings where w_j≧

1, and each measured value f_j is written into the buffer w_jtimes.

7. The method according to claim 5, wherein the range of power spectral density values of the sensor responses is divided into K classes, and the weightings for measurement parameter values in each class are selected by minimizing the goal function

G=F₁(σ

_{f ave})+CF₂(<

N>

/N_a),

where F₁(x) and F₂(x) are monotonously increasing functions, C is a constant and the variance σ

²_{f ave} of the averaged measurement parameter is given by

8. The method according to claim 7, wherein the parameters governing the K classes are determined from test measurements performed for a given system of sensors.

9. The method according to claim 1, wherein the weightings are selected using a genetic optimization algorithm.

10. The method according to claim 1, wherein the determined measurement parameters are used to calculate pressure and temperature.

11. The method according to claim 1, wherein the passive sensors are SAW devices.

12. The method according claim 1, wherein the sensing device comprises a plurality of resonant devices, and the measurement parameter is the respective resonant frequency of each resonant device.

13. The method according to claim 12, wherein the resonant frequencies are estimated by means of spectral analysis of the data accumulated as a result of step (1).

14. The method according to claim 12, further comprising, prior to step (1), determining an optimal interrogation frequency for each resonant device, wherein in step (1) each resonant device is interrogated a plurality of times at its determined respective optimal interrogation frequency.

15. The method according to claim 12, wherein the spectral analysis in step (3) comprises performing discrete Fourier transforms, or is based on parametric signal modelling.

16. A method of wirelessly interrogating a sensing device comprising a plurality of passive sensors, to determine a measurement parameter, f, comprising the steps of:

(1) interrogating each passive sensor during an interrogation period using a predetermined transmission signal comprising an interrogation pulse followed by a device sampling period for receiving the response from the device and detecting the passive sensor response and analyzing the passive sensor response to find its amplitude and an estimate of the measurement parameter, and detecting interference by

detecting an interference signal during a detection period occurring at one of (i) the beginning of the interrogation period and (ii) both the beginning and end of the interrogation period, and

comparing the power spectral density of the interference signal with a predetermined threshold level,

wherein the duration of the detection periods corresponds to the length of the interrogation pulse plus the device sampling period, and comprises two discrete interference sampling periods during which respective interference signals are detected;

(2) repeating step (1) in order to obtain several estimates of the measurement parameter for each passive sensor by means of an analysis of the data accumulated as a result of step (1); and

(3) determining the average of the measurement parameters derived from step (2) for each passive sensor, using a weighted average, in which the weightings depend on the amplitude of the passive sensor response, wherein the averaged measurement parameter f_ave is given by

17. The method according to claim 16, wherein the interference sampling periods are equal in length, and are located respectively at the beginning and end of the detection period.

18. The method according to claim 16, wherein the length of the interference sampling periods does not exceed the length of the device sampling period.

19. The method according to claim 16, wherein the length of the interference sampling periods corresponds to a substantial portion of the length of the interrogation pulse.

20. The method according to claim 16, wherein the maximum power spectral densities of the interference signals detected in each interference sampling period are combined to determine a combined power spectral density value.

21. The method according to claim 20, wherein the combined power spectral density P is determined by:

P=(P₁^1/2+P₂^1/2)², where P₁ and P₂ are the respective maximum power spectral density values for the two interference sampling periods.

22. The method according to claim 20, wherein the combined power spectral density P is determined by:

P=P₁+P₂.

23. The method according to claim 20, wherein, if the combined power spectral density exceeds a predetermined threshold level, the interrogation period is delayed or a different device or sensor is selected for interrogation.

24. The method according to claim 16, wherein a second pair of interference sampling periods are located at the end of the repeated interrogation cycle of step (1), to detect interference emerging during the interrogation cycle.