TWI264384B - Interrogation method for passive sensor monitoring system - Google Patents

Abstract

A method of determining the frequency of a plurality of resonant devices (for example three SAW devices) comprises determining optimal interrogation frequencies for each of the devices, the optimal interrogation frequencies having maximum power spectral densities, accumulating a plurality of responses for each sensor, performing discreet Fourier transforms on the sampling results to estimate the three resonant frequencies, and averaging the results of the Fourier transforms to provide an indication of resonant frequencies. The averaging step may include the calculation of a standard deviation and the rejection of any results which fall more than a pre-determined multiple of the standard deviation from the average frequency result. The frequency is determined by the method may be employed to calculate the pressure and temperature of the sensor devices. The sensor devices may he located in a vehicle tyre.

Description

1264384 (1) 疚, invention description, ... (description of the invention should be clarified: the technical field, prior art, content, embodiment and schematic description of the invention) FIELD OF THE INVENTION The present invention relates to passive sensing using wireless communication The caller sensor system of the transponder 'for example' is used to measure the pressure and temperature of the vehicle tire. More specifically, a preferred embodiment of the present invention provides a passive sensor call signal operation that allows for high precision pressure and temperature measurements. Prior art

Many of the answers to the problem of a wireless call signal for passive pressure and temperature sensors have been known in the prior art. The sensors use a single bee delay line or a chirp resonator, preferably based on SAW technology, although other tastings are also possible (e.g., most sonic devices or dielectric resonators). I use the delay line (see F. Schmidt and G. Scholl's "Wireless SAW Identification and Integration, System". In "Surface Acoustic Wave Technology, Systems and Applications", the version is large.

V /y order, I w C

Ruppel and T.A. Fjeldly, Singapore, World Science, 211, page 2, page 87 or resonators [see W. Buff, S. Klett, Μ 1 1VI · K u s k ο » j

Ehrenpfordt and M.Goroll use SAW resonators to w, w - watt w / dish and

Pressure passive remote sensing, IEEE Journal, in ultrasonic, ferroelectric and frequency control, vol· 45, No. 5, 1998, 1388-1399 hundred, only J is based on the need to distinguish one passive sensor In response, and on the other hand, the signal is echoed with the environmental echo signal. The fact that the city uses the impulse response of the delay line and the fact that the resonators are longer than other spurious signals. The call signal of the passive s AW sensor based on the delay line is often performed via a very short (typical 〇1μ3) radio frequency pulse. As a result, the caller system needs to have a wider bandwidth such as 1 〇ΜΗζ or greater, which is not provided under the 'Unlicensed Industrial Scientific Medicine (ISM) band. The sensor based on the parameter 單埠 resonator is more suitable for the narrow band -6- 1264384 (7). Therefore, #^ Λ 1 should focus on the call signal of the passive sensor in the form of a resonator, which is based on s s , , c Α τ 疋 based on the S AW resonator. The main purpose of the call signal is to measure the natural oscillation of the resonator (resonance frequency, dip, year) excited by the long and narrow RF call signal pulse of the field, and to understand the allowable temperature and pressure calculation of the resonance frequency. In order to rule out the influence of the antennaitr of the first moon turtle: ten θ W, the vibration of the antenna frequency [see above W.Buff, ς by kiett ' M. Rusko, J. Ehrenpfordt and M. Goroll's book i method 4 J. The difference between the frequencies of the natural frequencies of similar resonators (possibly with different 妓椐 phase, α丄/, vibration frequency) connected to one antenna is measured. The right two resonators are at the same temperature. And with different pressure sensitivity, the pressure can be reduced from the difference between the page rate and the temperature. The active input response command signals that are naturally excited by the double harmonic RF pulses are synchronized in the two resonators [see GB 9 92 5 5 3 8.2]. When the call signal burst exceeds the response, it will exhibit a beat frequency such as an exponential decay difference beat signal equal to the measured frequency difference. The beat frequency can be accurately determined by size detection and cycle count. In the case of simultaneous measurement of pressure and temperature, at least three resonators are required to be connected to one antenna and two frequency differences are measured to calculate two unknowns, pressure and temperature [see W. Buff, Μ·Rusko, Μ· Gorol J. Ehrenpfordt and T. Vandahl, Pressure and Temperature SAW Sensors for Wireless Applications, 1997 IEEE Ultrasound Harmony, 1 997, 3 5 9-3 62 pages]. Measuring the beat frequency is less feasible in this case. The following call signal techniques are familiar to those skilled in the art. 1. The resonators are sequentially excited via radio frequency pulses. Intercepted through the antenna 1264384

The exponential decay response of each resonator is used as the resonant frequency [see A. Pohl, G. Ostermayer and F. Seifert, Wireless Sensing Using Oscillator Power over Remote High QSAW Resonators, I e EE Journal In the Ultrasonic, Ferroelectric and Frequency Control, vol. 45, No. 5, 1998, 1161-11^ page] one of the gated polarization PLL is one of the input signals. This technique is more suitable for a single resonator and is difficult to bury and unreliable in the case of three resonators, especially when their frequencies are too close to each other. 2 • The resonators are sequentially excited via RF pulses. The exponential decay response of each resonator drawn through the antenna is downconverted to a lower intermediate frequency and then the period of natural oscillation is counted [see GB 9925538.2]. This method is also effective when the distance between a single resonator or resonant frequency is much greater than the resonator bandwidth. In any case, if it is less than ten times the bandwidth (as in the case of I S band), then more than one resonator will be excited by the RF pulse to cause the spurious frequency modulation of the sensor response and greatly reduce the accuracy of the measurement. 3 • All three resonators are energized at one time. The spectrum of the sensor response is analyzed at the receiver via discrete Fourier transform and all resonant frequencies are measured [see L. Reindl, G. Scholl, Τ·Ostertag, H. Scherr and F. Schmidt, Passive SAW Radio Transmitter Response The theory and application of sensors such as sensors, IE EE Journal, in Ultrasonic, Ferroelectrics and Frequency Control, vol. 45, No. 5, 1998, 128, page 1291]. This attempt allows for a large number of resonator call signals. In any case, it requires the use of a bandwidth RF pulse with the entire frequency range of the sensor actuation. Keep in mind that the peak power of the call signal pulse is limited to the ISM band (usually no larger than l〇mW). It is clear that the 1264384 (4) invention expands the spectrum of the pulse to reduce the effectiveness of the resonator excitation. It adversely affects the signal-to-noise ratio (SNR) and the accuracy of the measurements. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of calling signals to preserve the advantages of Fourier analysis and to provide both high performance of resonator excitation and high accuracy of measurement. According to one aspect of the invention, a method of calling a plurality of resonant devices to determine respective resonant frequencies of the devices comprises the steps of: (1) determining an optimal calling signal frequency for each resonant device; (2) Repeating the call signal of each resonance device at each of the optimal call communication frequencies as in the above step (1); and (3) performing discrete Fourier transform on the data accumulation as a result of the step (2); (4) determining the step ( 3) The average frequency. Embodiments Referring first to Figure 1, the present invention is particularly applicable to a temperature and pressure system for monitoring vehicle tires. In any event, it is understood that the invention is not limited by this application and can be applied to other environments that monitor temperature and pressure, or to environments where many other parameters are measured by a passive sensing system. A preferred embodiment of the present invention includes three surface acoustic wave devices SAW 1, SAW2 and SAW3 connected to a common antenna. Preferably, the SAW device is used to generate a signal indicating the sensed state. Please understand that the present invention is not limited. These devices and other passive sensors that can provide a suitable indication via the use of resonant frequencies. A particularly preferred application of the invention (vehicle tire pressure and temperature sensing), the SAW device, SAW1, SAW2, SAW3 and antenna 12 are mounted in a vehicle tire as a unit A. An excitation and monitoring unit B is located in the vehicle to provide an excitation signal to and receive sound from the vehicle mounting unit (5) 1264384. _ Therefore 1 2 communication. A call to the antenna 1 1 of the transmitter synthesizer 1C B. The interception thus accumulates the sensor response number through a front-end receiver synthesizer 3 ί 1 〇 the frequency difference is then the filter 4 and a | 8-bit or 10-bit sample rate, such as 1 (the internal memory coherent accumulation Fourier transform pressure and temperature. 1 and ADC6 and LNA2 increase h to ensure that the sensor as a synthesizer and the above system is also rejected. This will result in the removal of the early B including an antenna 11 for packaging The antenna pulse of the chirp is generated by a power amplifier 8. The pulse is transmitted by the RF switch 1 to the call signal unit, and the electromagnetic wave emitted by the sensor unit is sensed by the antenna 12 of the sensor unit. SAW resonators. The retransmission is transmitted via the sensor antenna and received by the antenna 。. The low noise amplifier 2 to the frequency converter and mixes the scoop signal. Hybrid receiver synthesizer 3 and transmitter synthesizer Equal to the intermediate frequency, such as 1 MHz. The IF signal passes through a clamp amplifier (which increases the dynamic range of the receiver) to the unary analog to digital converter 6 and has a sufficient ratio of 20 or 20 MHz. The sensing stored in the digital format on the dsp wafer 7 is responsive in that it is in the call signal procedure. The wafer then performs data for three SAW resonators to calculate three resonant frequencies, perform an averaging procedure and calculate the DSP wafer 7 and also control synthesizers 3 and 10, which in turn can cause and disable the power. Amplifier 8 ^ Isolation between receiver and transmitter. When one of the measured values is coherently accumulated, the same quartz oscillator 9 is used as a reference for the DSP chip. Can be performed using a dual conversion receiver to receive images. An alternative receiver architecture can be used in a direct frequency conversion. ‘A synthesizer and a second mixer and ADC to produce -10 - 1264384 萌萌 say _ continued (6) to create a fourth L channel. Referring now to Figure 2, a preferred method of the present invention will be described. The three resonators 5-8~1, 5-8~2, 58\¥3 have slightly different resonant frequencies and different temperature and pressure sensitivities. The manner in which the frequencies are selected is that the minimum distance between them is not less than the resonator bandwidth at any pressure and temperature. As a result, the entire active frequency band (e.g., the ISM band) is divided into three sub-bands that are occupied by three resonators.

The sensor is then responsive to a rectangular RF pulse having a spectral width equal to or less than the resonator bandwidth. This ensures that the resonator is effectively energized to the call communication frequency close to the resonant frequency of the resonator. In each sub-band, there are several discrete call signal frequencies selected with a distance equal to or less than the resonator bandwidth. The number of these discrete call signal frequencies is determined by the Q parameter of the SAW resonator. For example, if Q = 5,000, it is enough to have nine call communication frequencies within the 434MHz ISM band.

As a result, regardless of the temperature and pressure, there are always three call communication frequencies for the selected discrete frequency group to ensure optimal excitation of the three resonators. When the oscillation amplitude of the resonator approaches the maximum, it may be at the given excitation amplitude at the end of the call communication pulse, and the excitation is in the most ideal condition. The call signal program consisting of five main steps can be represented by the flow chart of Figure 2. 1. Determine the three best interrogation frequencies to maximize the power spectral density of the sensor response. In this step, the sensors are called one after the other at all discrete call communication frequencies. For example, it can down-convert the response via frequency to extract -11 - 1264384 and calculate the discrete Fourier transform. The three best frequencies are then selected to give the maximum peak of the spectral density at each subband. Alternatively, if a linear amplifier with automatic gain control is used for the receiver, the three can be selected to maximize the peak ratio of spectral density to the average of its side lobes. Alternatively, if the limited amplifier is used at the receiver, the three frequencies can be selected to maximize the length of the sensor response. At this step, we have been able to determine the three resonant frequencies by measuring the peak frequency of the spectral density. In any case, this gives us a rough estimate of the actual frequency of natural oscillations, because of the limited solution of Fourier analysis and the presentation of noise. 2. Coherent Accumulation of Sensor Response In this step, we repeat the call communication of the sensor N times for each optimal call communication frequency. The signal intercepted by the receiver is down-converted, sampled and co-ordinated to the three data arrays of the system memory. The purpose of this co-accumulation is to increase the SNR-coefficient. For example, coherent accumulation can be confirmed by using a common quartz stable oscillator in the receiver and transmitter synthesizer and as a pulse generator in the D S P wafer. In other words, the period of the call communication signal at the intermediate frequency and the distance between the call communication pulses are selected as an integer of the sampling period. Furthermore, the number of accumulated pulses N is chosen to be very small (N = 10....30) such that the time required for coherent accumulation (about 1....2 ms) is very small compared to the period of vehicle tire rotation (eg 1/40). As a result, a change in the position of the sensor antenna will not result in a large change in the phase of the sensor response at the time of accumulation. The viewpoint of minimizing the change in frequency between the three resonators caused by the change in antenna impedance is often important as the result of tire rotation -12 - 1264384 ι (8) |

The presentation of the existing interference is also detected at one of the three best call communication frequencies before the coherent accumulation. This can be achieved, for example, by comparing the maximum spectral density of the signal received in the no-call communication pulse with a suitable threshold level. If it exceeds the valve limit criteria, the system repeats the call communication after several delays. A simpler interference detection procedure can also be used in the coherent accumulation period. In this case, the interference can be detected by measuring the signal received prior to transmitting 1-2/zs of each call communication pulse. 3. Discrete Fourier transform and insertion

In this step, the results of the three data arrays obtained by coherent accumulation are used to calculate the three spectral densities using the discrete Fourier transform (DFT). Each spectrum contains a peak corresponding to the frequency response of a single resonator, although the excitation of the other resonators is due to other peaks. In any case, the main peak has both large amplitude and small peaks that are ignored. The main peak frequency corresponds to the relevant frequency of the natural oscillation. The solution Δf of the Fourier analysis is increased by zero filling to increase the analysis time, for example, from 10-20 /zs to 0. 1-0.2 ms at Δ f = 5-10 kHz. This accuracy is still insufficient for many applications. The increase in accuracy can be inserted near the peak frequency using a fourth order or higher order to accurately find the resonant frequency for each of the three resonators. As a result, this accuracy is no longer limited by the resolution of the Fourier analysis but is primarily affected by system noise. In addition to the random components of the noise measurement error, there are also finite lengths of the sensor response system components (bias). The bias value is determined by the initial phase angle of the sensor response pulse of the intermediate frequency and it can be invented from -13 - (9) 1264384. It is important to measure it because the initial coherence force is important. The change from one cycle to the other is determined by the unknown frequency and the frequency of the call, the frequency of the communication, and the frequency of the communication. The following methods are used to reduce and produce green. Observing the bias voltage and thus increasing the system a) coherent accumulation is repeated twice at each call and communication frequency but an additional 90 degree phase shift is accumulated in the ^ _ 接 L ^ 丄 brother two cycles into the call Communication pulse. Alternatively, the sample is delayed by ~.s ^ . ^ T^/Ufint) where fint is the nominal intermediate frequency (call communication frequency and the difference between the local WT j ^ ^ sines) during the second period of accumulation . DFT and insertion only ^ 仏 τ ~ order is also performed twice and the average of the two peak frequencies is found. This average frequency m Μ 七 ^ ^, becomes very close to the measured resonance radiance ' because the offsets and values of the two peak frequencies are deleted from each other. The ~ of this method has the opposite signal and is approximately equal to absolute b) The second method does not need to increase the measurement: the disadvantage is that the measurement time is doubled. The communication frequency is repeated once. The sampling ratio. Coincident accumulation is performed at the nominal intermediate frequency of each call Ts by the integer rate to be selected so that during sampling, TS = x / n where n = 1, 2 3. The division corresponds to the 9-degree phase shift . If it is equal to 〇.〇5w at τ = 0·25..., for example, if fint=1MHZ followed by TS optional sample start. Effectively, it means me. The first-DFT is executed from n. As a result, the insertion value of the phase of 90 degrees between the two sets of samples found by the operation of D F 有效 was effectively reduced. As an average of the peak frequencies and between the three resonant frequencies of the bias voltage of 35 0 kHz, the maximum value of the bias is 0.5 7 kHz. The minimum distance is reduced from 1.69 kHz to 4. The statistical processing of the resonance frequency data is performed in steps 1-3 (or 2 and 3 only if the analysis of the hills is early and the frequency is low and the frequency of step 1 is 14- 1264384, - _ (10) Hui Ping's performance rate is repeated as unnecessary. Data for continuous repetition and three resonance frequencies are stored in the three data arrays of the system memory. In the Μ period of the call communication (Μ can vary over a wide range such as 1 0 - 300), the average of one of the three resonant frequencies, 2, 3 and the standard deviation are calculated. As a result, the standard deviation of fi, 2, and 3 is further reduced by the Λ1 coefficient as compared with σ i, 2, and 3. Then all the frequencies in the relevant array & does not meet the following conditions 1,2,3

(where k can be 1 - 3) is excluded and the average frequency is recalculated again. The final program is then executed to eliminate the possible effects of interference and then accumulate in the coarse adjustment of the coherent frequency resulting in a sudden decrease in signal size. This standard deviation σ 1, 2, 3 can also be used as a measure of the validity of the information of the resonant frequency. 5. Calculation of pressure and temperature After the average of two different frequencies is calculated and then the pressure and temperature are found using the development as shown by R e f [ 4 ].

The proposed call communication method aims to achieve a resonance frequency measurement with an accuracy better than 5xl〇-6. In the case of a SAW resonator operating on a 434 MHz ISM band, it should give a pressure measurement better than 1 psi and the accuracy of the temperature measurement is better than 1 °C. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more apparent from the following description of the preferred embodiments of the present invention, but by way of example only, and in the accompanying drawings in which: Figure 1 illustrates a pressure and temperature monitoring system for use in a vehicle tire; Figure 2 illustrates the call signal logic operation suggested by the present invention. -15 - 1264384 Invention says _ Continued page (ίο 〈图代^表表说明〉

1 Radio frequency switch 2 Low hum amplifier 3 Receiver synthesizer 4 Filter 5 Limit amplifier 6 type of digital amplifier 7 DSP , crystal 8 power amplifier 9 Shiying crystal oscillator 10 Transmitter synthesizer 11 days line 12 common antenna

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Claims (1)

1264384 Pick and Read Patent Range 1. A method of making call communication with a plurality of resonant devices to determine the respective resonant frequencies of the devices, comprising the steps of: (1) determining an optimal call communication frequency for each resonant device (2) repeating the call communication for each resonance device a plurality of times according to the respective optimal call communication frequencies determined in the step (1); (3) performing discrete Fourier transform on the data accumulated as a result of the step (2); And (4) determining the average of the frequencies obtained from step (3). 2. The method of claim 1, wherein the step (4) comprises determining a standard deviation for each determined average frequency; rejecting any frequency that varies by more than a predetermined plurality of standard deviations from the average frequency; Calculate the average frequency after excluding the rejection data. 3. The method of claim 1 or 2, wherein the optimal call communication frequency is determined by a frequency at which a signal from the resonant devices has a maximum power spectral density. 4. The method of claim 3, wherein the maximum power spectral density is determined by down-converting, sampling the response at an intermediate frequency, and calculating a discrete Fourier transform. 5. The method of claim 3, wherein the maximum power spectral density is determined by a linear amplifier having automatic gain control, the optimum frequency being selected such that the peak of the spectral density is the average of its side lobes The quasi-rate ratio is the largest. 6. The method of claim 3, wherein the maximum power spectral density is determined using a limiting amplifier, and the frequencies are selected to give a sense of 1264384. The canister reads. Page i..... ....................................... The length of the detector response maximum. 7. The method of claim 1, wherein the best call communication frequencies are in respective sub-bands of an I S Μ band. 8. For the method of claim 1, wherein during the repetition of step 2 of item 1 of the scope of application, each received signal is down-converted, sampled and accumulated to provide a coherent accumulation of the optimal call communication frequency. 9. The method of claim 8, wherein the coherent accumulation is achieved using a common oscillator in the receiver and transmitter synthesizer and a clock generator in a DPS wafer. 10. The method of claim 1, wherein the number of repeated call communications in step 2 and the speed at which the call communications are performed is such that the entire call communication cycle is compared to any cyclicity of the sensor relative to the call communication device. The period of motion is relatively small. 11. The method of claim 1, wherein each coherent accumulation is repeated at each call communication frequency and an additional 90 degree phase shift is performed on those samples sampled at the second accumulation cycle time delay. The call communication pulse is imported during the accumulation period. 12. The method of claim 1, wherein the sampling rate is selected by a phase shift of a 90 degree period corresponding to an intermediate frequency divided by an integer. 13. The method of claim 1, wherein the determined frequency is used to calculate pressure and temperature. 14. The method of claim 1, wherein the resonant devices are SAW devices.