WO2002040331A1

WO2002040331A1 - Method of and device for acquiring data of dynamic physical processes via a radio link

Info

Publication number: WO2002040331A1
Application number: PCT/EP2001/013359
Authority: WO
Inventors: Leonhard Reindl
Original assignee: Transense Technologies Plc
Priority date: 2000-11-17
Filing date: 2001-11-19
Publication date: 2002-05-23
Also published as: CN1486256A; CN1280141C; DE10057059C2; AU2002221866A1; US7026977B2; JP2004514123A; EP1343670A1; US20030214419A1; DE10057059A1

Abstract

For acquiring data of dynamic physical processes via a radio link, a transponder antenna (17) is excited by an electromagnetic exciting wave at the resonance frequency of the transponder antenna (17), and a back-scattered electromagnetic sensor wave which is modulated by a sensor (16) having an electrical impedance dependent of the data to be acquired is received an analysed. The sensor (16) is directly connected to the transponder antenna (17) so that the sensor changes the eletrical impedance of the transponder antenna (17) with every variation of the data to be acquired. The electromagnetic wave which is back- scattered by the transponder antenna (17) is received as the sensor wave at the same time as the transponder antenna (17) is excited by the exciting wave.

Description

Method of and device for acquiring data of dynamic physical processes via a radio link

The invention relates to a method according to the preamble of claim 1 and to a device according to the preamble of claim 14. The transmitter antenna and the receiver antenna of the device can be one and the same component.

Generally, the invention deals with wireless reading out a sensor to acquire data of a dynamic physical process which may also be referred to as measurement values. Especially, the invention deals with such methods and devices in which neither the sensor including the time-varying electrical impedance nor the transponder antenna assigned to the sensor have an own power supply (e.g. in form of a line to an electrical energy supply net or in form of batteries) to produce the sensor wave which encodes the data to be acquired.

Such a passive radio sensor facility can advantageously be used in various technical environments, especially on rotating or moving parts. An especially interesting area of application of the invention, however, is the measurement of the strain of a tyre element of a tyre of a vehicle during its contact with the roadway while the vehicle is moving. From a measured strain curve the coefficient of friction between the tyre and the roadway can be estimated. This concerns monitoring the adhesion of the tyre to the roadway in order to avoid a breaking out of the vehicle when driving along curves, decelerating or accelerating. In particular, monitoring the coefficient of friction is of interest considering the risk of water or ice formation on the roadway in order to output a warning to the driver of the vehicle or to directly control the steering element or to intervene in the drive or the brakes of the vehicle.

A method and a device according to the preambles of the claims 1 and 14 which also relate to the special problems of the measurement of the strain of a tyre element during the contact with the roadway while the corresponding vehicle is moving are described in DE 198 07 004 A1. To separate the sensor wave from the exciting wave, a time domain division between the exciting wave and the sensor wave is used. The remote transponder unit, also referred to as a radio sensor, comprises a sensor, a transponder antenna, and an energy storing means which stores energy out of the exciting wave until the exciting wave and all environmental echoes are faded away. Then the sensor wave is generated by using the stored energy. The sensor wave encodes the information of the measurement values to be monitored. For energy storing a well known surface acoustic wave device is used which gives back one or several time delayed echoes of the signal which is applied to it. Using these delayed signals, the time domain division between the exciting wave and the sensor wave is implemented. One of the time delayed signals is controlled by a sensor impedance which is sensitive to the measurement value. The instantaneous reflection coefficient of the transponder antenna is not changed by the sensor but the amplitude and phase of one or more of the delayed re-emitted signals is changed. To assure the time domain division the exciting wave must be a pulsed one with a time length less than the storage time, or a so called FMCW- signal (frequency modulated continuous wave) which changes its frequency as a function of time so that the sensor wave differs in frequency from the actual exciting wave. A continuous wave (CW) signal containing one single frequency could not be used because this would destroy the time domain division. To uphold the time domain division between the exciting wave and the sensor wave a very fast sampling has to be performed in the receiver unit, which may be much faster than the sampling necessary to resolve the dynamics of the measurement values.

It is the problem of the invention to provide a more simple method and device in which the energy storing means can be omitted and also a continuous wave (CW) exciting wave having one single frequency can be used.

This problem is solved by the method as defined in claim 1 and by the device as defined in claim 14. Preferred embodiments of the method and the device are provided by the subclaims 2 to 13 and 15 to 18.

In the invention a sampling rate which is only necessary to resolve the dynamics of the measurement value is sufficient. On the other hand, the invention presented here is restricted to measurement tasks in which the measurement values have a sufficient high dynamic variation in time to produce a sufficient high frequency shift between the exciting wave and the sensor wave which are in the following also referred to as the read-out signal and the sensor signal.

In the present invention the time-varying electrical impedance of the sensor is connected directly to the transponder antenna, or even is an integrated part of the antenna itself. The physical process which is to be monitored by acquiring the data affects the sensor element, for instance due to a deflection, and thus changes the value of the electrical impedance. Thus, the reflection properties of the transponder antenna, like the radar cross section and the phasing of the reflected signal, change as well and with the same time characteristic as the physical process which is to be monitored.

The transponder antenna scatters back the electromagnetic read-out signal like a mirror scatters back incoming light, and like a mirror the transponder unit of the invention may be a passive one. Because of geometrical conditions, the amplitude of the sensor signal is far smaller than the amplitude of the read-out signal and also far smaller than many other environmental echoes. To distinguish the sensor signal from the read-out and all other interfering signals, the physical value to be measured must show a characteristic variation in time which produces a characteristic frequency shift of the sensor signal. In the invention presented here, the energy, which is necessary to perform this frequency shift from the frequency range of the read-out signal to the frequency range of the sensor signal is extracted directly from the physical process, which is to be monitored.

The electromagnetic read-out signal is received by the transponder antenna and partly re-emitted. This re-emitted signal is the sensor signal. The amplitude and phasing of this reflection process is determined by the reflection properties of the transponder antenna. The sensor signal is re-emitted immediately. Beside the electromagnetic resonance of the transponder antenna, which is determined by the loaded quality factor of the transponder antenna, no additional energy storing is involved in the process. The loaded quality factor of an antenna determines the swinging out of the electromagnetic signal which is emitted by this antenna after the antenna has been stimulated by a very short impulse. This storing of the read-out signal in the resonance of the antenna itself is by far shorter than the storing which is possible using a surface acoustic wave. Thus this storing is not sufficient to implement a time domain division between the read-out signal and the sensor signal. Therefore, the read-out signal and the sensor signal are received simultaneously in the receiver unit.

Because the present invention does not use any time domain division, no surface wave component nor any other component is necessary for the storing energy of the read-out signal. The present invention uses a frequency domain division between the read-out signal and the sensor signal which therefore can be received simultaneously. The term "simultaneously" neglects the run time of the read-out signal from the transmitter antenna to the transponder antenna, the very small storing time within the electrical resonant circuitry of the antenna, as well as the run time of the sensor signal from the transponder antenna to the receiver antenna. However, it is typical that these run and storing times are very short in comparison with the duration of the read-out signal. Actually, one can even use a permanent CW signal as the read-out signal, and in this case one also gets a permanent sensor signal.

Because the present invention uses a frequency domain division the sensor signal has to be spectrum analysed. This can be done using a Fourier analysis, or other high resolution spectral analysing concepts. With this spectrum analysis algorithms the received signal which is received by the receiver antenna can be decomposed into a first part accumulated at the read-out frequency which encloses the read-out signal and all static environmental echoes, and a second part with components whose frequency is shifted away from the read-out signal which encloses Doppler shifted components and other mixed or modulated spectral components, and then fed to an analysing part of the receiver. Strictly speaking the Doppler effect is doubled because it occurs in the point of the transponder antenna concerning the read-out signal and as well in the point of the transmitting and receiving unit concerning the sensor signal. However, the Doppler effect is not the part of the sensor signal which carries the information of interest here. The measuring signal is rather up-modulated to the Doppler signal, because the back-scattered signal form the transponder antenna will be Doppler shifted, without fail, if the transponder antenna is moving with regard to the transmitter and receiver antennas, and every modulation of the back scattering characteristics may lead to a further frequency shift of this signal.

It does not matter how the modulation of the sensor signal has been achieved, whether a frequency modulation, or a phase modulation, or an amplitude modulation has been applied, they all cause a frequency shift which separates the sensor signal from the read-out signal in the time domain.

If only this spectral part which is shifted further than the ordinary Doppler shift is evaluated, the time dependence of the physical process which is to be monitored and which affects the sensor and thus changes the value of the electrical impedance of the sensor can be reconstructed again by a transformation into the time domain. For many problems, however, it might be sufficient, to evaluate only the ratios between the fundamental and some higher harmonics of the sensor signal.

The new measurement arrangement is suitable for an on-line measurement of the strain of a tyre element of a vehicle during its contact with the roadway while the corresponding vehicle is moving. With the knowledge of the strain curve the coefficient of friction of this tyre with the roadway can be estimated.

In order to achieve this modulation of the back-scattered sensor signal, a dynamic change in time of the electrical properties of at least one component which is connected to the transponder antenna or which may be even incorporated into the transponder antenna as an integral part has to be performed by the physical process to be monitored. This can be achieved by deforming the shape of the antenna, thus tuning or modulating their resonant frequency, or by using a tuneable capacitance, inductance, or resistance to build up the sensor with which the transponder antenna is loaded. The sensor element can also have a more complicated structure with a circuit whose electrical characteristics is determined by one or more impedances which are changed by the process to be monitored. However this is not preferred. Details concerning alternatives in shape of the sensor using a changeable capacitance which is changed by the process to be monitored can be taken from DE 198 07 0004 A1.

In a favourite embodiment of the invention the transponder antenna itself also forms the sensor whose impedance is influenced by a mechanical bending or a strain. I.e., a specific type of antenna is used as transponder antenna which is sensitive to a strain or mechanical bending of the shape of the antenna. This strain may change the capacitive, inductive, resistive part, or any combination thereof of the resonant circuit which build up the electrical properties of the antenna, and may thus change its electrical properties, like the resonant frequency, the quality factor, the internal losses, the scattering cross-section and/or the phase of reflection. This favourite embodiment of the invention is adaptable to all physical processes which show a strain or bending which result in a strain or bending, or which can be transformed into a strain or a bending.

The preferred frequency range for the read-out signal is in the UHF and VHF region to reduce the size of the antennas, but the invention is also applicable in all other frequency ranges. In ranges of higher frequencies the Doppler shift may move towards the modulated spectral components, thus complicating the analysis.

A device according to the invention includes a sensor which has an electrical impedance and which is connected directly to the transponder antenna circuitry, the value of the electrical impedance being changeable so that it can be time dependency changed or modulated by the measurement values to be monitored. As a result, the back-scattering properties of the transponder antenna change according to the time dependency changes of the measurement values to be monitored. If the transponder antenna receives a read-out signal, which has been emitted by a transmitter antenna of a transmitter unit, the transponder antenna will be oscillating according to its quality factor and thereby re-emit a part of this read-out signal. If the electrical impedance of the sensor is changed or modulated by the measurement values to be monitored at the same time, the back-scattered signal part of the transponder antenna is changed with the same time characteristics as well. This modified back-scattered signal component is called the sensor signal or sensor wave. Together with the read-out signal and some environmental radar echoes, the sensor signal is received by the receiver antenna at the same time as the read-out signal is emitted, and analysed in an analysing part of the transmitting and receiving unit.

The radio transponder unit including the sensor and the transponder antenna shows a very simple structure. For example, both the sensor and the transponder antenna can together be made up of one conductive wire section which is bent to different shapes and which changes at least one of its electrical properties due to the bending. By using such conductive wire sections for monitoring the strain of a tyre element during its contact with the roadway while the corresponding vehicle is moving the friction coefficient of this tyre with the road can be estimated. Such a sensor tyre or "intelligent tyre" can easily and economically be produced in series production.

As already mentioned, some basic arrangements and some possible embodiments of the sensor element as such can be taken from DE 198 07 004 A1 , except for the fact that the invention works without any energy storage means.

The following calculations are added to further explain the invention. The calculation treats the on-line monitoring of the strain of a tyre element during the contact with the roadway while the corresponding vehicle is moving. With the knowledge of this strain curve the coefficient of friction of this tyre with the roadway can be estimated.

In the accompanying Figures:

Fig. 1 shows a measurement arrangement at a tyre of a wheel of a motor vehicle, and

Fig. 2 shows the strain of a tyre element of a free running wheel during its contact with the roadway while the corresponding vehicle is moving straight on. The following calculations assume the measurement configuration shown in Fig. 1 , in which a device 4 is provided for measuring the strain of a tyre element of a tyre 10 of a motor vehicle 8 during its contact with a roadway 15 while the vehicle 8 is moving.

The tyre 10 is mounted to a wheel 9 of the motor vehicle 8 and rotates together with the wheel 9 in the direction of a turning arrow 14 about an axis of rotation 18. Thus, the motor vehicle 8 moves forward in a direction of an arrow 13 (x-axis).

The device 4 consists of a transmitting and receiving unit 7 which is fixed to the vehicle behind the wheel 9, of a frequency analysing unit 20 associated to the unit 7, and of a transponder unit 19 arranged within the tyre which is read out by means of radio signals. The transmitting and receiving unit 7 comprises a transmitter antenna 5 for emitting an electromagnetic exciting wave or read-out signal, and a receiver antenna 6 for receiving an electromagnetic sensor wave or sensor signal. The transmitter antenna 5 and the receiver antenna 6 can also be realised as one common antenna. The frequency analysing unit 20 controls the transmitter antenna 7 for emitting the read-out signal and analyses the signal received by the receiver antenna 6 for its frequency or frequency composition.

The sensor signal is back-scattered by the transponder antenna 17 of the transponder unit 19 as a response to the read-out signal and results in an output signal of the receiver antenna 7. The sensor signal is modulated as compared to the read-out signal by the time dependence of an sensor 16 which has an electrical impedance sensitive to the measurement value, and which is connected to the transponder antenna 17, and which thus changes the radar cross section (or radar reflectivity) of the transponder antenna 17 with the time dependence of the process to be measured. The sensor 16 can also be an integrated part of the transponder antenna 17.

The measurement value of interest here is the strain of a tyre element 12 of the tyre 10. Correspondingly, the sensor is arranged within the tyre 10 here. It may be assumed that the motor vehicle 8 shows a uniform linear movement in the direction of the arrow 13. Because the antennas 5 and 6 are placed behind the wheel 9, the tyre element 12 including the sensor element 16 is moving towards the antennas and generates a Doppler shift during passing through the contact area of the tyre 10 with the roadway 15.

If an arrangement of the antennas 5,6 in front of the wheel 9 would be chosen, the profile element 12 would move away from the antennas 5,6, thus changing the sing of the Doppler shift. Using an arrangement of the antennas 5, 6 vertical above the contact area, the Doppler shift would become zero. Nevertheless, the measurement method described here would work anyhow. In the following calculations only those movements in the direction of arrow 13 are considered; thus, the antennas may be regarded as being placed at the level of the roadway 15. If the altitude above the roadway 15 would be taken into account, this would not change anything concerning the basic considerations but the formulas would become more complicated.

The motor vehicle 8 may be moving with the velocity v_car

The tyre 10 may have the radius r

This results into an angular velocity ωwheei of the tyre 10 according to: v. car

^Vcar ~~ ^ω wheel ' ^{r → ω} wheel

Case 1 : Circular movement of the wheel without consideration of the flatness of the tyre in the contact area

The x-axis may be parallel to the direction of movement, and the y-axis may be that direction from the axis of rotation 18 to the contact area. If the motor vehicle is moving straight on in forward direction, the considered profile element 12 is moving in the x-y-plane. The antennas 5, 6, which are fixed to the motor vehicle 8 are assumed to be on the same level as the surface of the roadway 15. S, s_x, s_y are the location and the components of the location, and v, v_x, v_y are the velocity and the components of the velocity of the sensor element 16 in the x-y-plane or x-, y- direction with regard to the fixed antennas 5, 6. t is chosen in such a way that the profile element is in the centre of the contact area at t=0. So is the distance in x- direction between the antennas 5, 6 and the centre of the contact area, i.e. So is the distance in x-direction between the antennas 5, 6 and the axis of rotation 18 of the tyre 9. This results into:

s_n + r • sm aw eel t) s = r - cos(ω_wheei t)

S = ⁵ + ^Sy² = (⁵0 + ^{r • Si} (^ωw_hee_l t)f + (^{r ■} ∞s(ω_wheel )f = J + X + 2 ^• S_Q ^■ r ^• Sm(θ _wheel t)

The Doppler-shifted frequency fd of the reflected sensor signal can be calculated using the frequency of the read-out signal ft and the velocity of light c:

The maximum of the Doppler shift occurs in those two positions in which a straight line connecting the antennas 5, 6, which are fixed to the motor vehicle, and the transponder antenna 17 form a tangent to the wheel, i.e.:

Example: fo=1 GHz, Vcar=100km/h. This results into a maximum Doppler shift of fd- fo=92,5 Hz, Which can be measured easily by a CW-radar as can be seen from police speed measurements.

In the following, only the movement of the transponder unit along the x-axis will be considered to simplify the calculations. The above equations are thus simplified to: s_x = ₀ A- r - sm(ω_wheel t) ds„ v. = ^■ = r dt ^' ∞ heel ^• ∞ ∞ wheel 0 = ^ car ^' ∞s(<»»W 0 v v-

- </ ~^" - 0 1 + 2 -^- Λ - ι + 2 • cos(ω_w/ιee/ t)

^ J c

Case 2: Circular movement of the wheel with consideration of the flatness of the tyre 10 in the contact area

While passing through the contact area, the profile element 12 is no more moving circularly but linearly. Because the secant is shorter than the circular arc, a strain of the tyre 10 results with a bulge both in the running in area and in the running out area. If a circular movement is subtracted from the corresponding movement of the profile element, the movement shown in Fig 2 and denoted with x remains.

The curve denoted with x is now approximated with a sinus curve for further simplifying the calculations.

The maximum strain (approx. 0.45mm in Fig. 2) is denoted with Acontact. The length of the contact area (2a and 2b in Fig. 2) is denoted with Uontact . The total length of the sinus curve, which is an approximation of the actual strain of the profile element, is approximately given by 2* L_COntact.

The corresponding frequency f∞πtact and the angular frequency ωcontact of the movement through the contact areas can be derived from the fact that the motor vehicle 8 goes through the length 2* L_contact with its velocity v_car : v c„ar car J contact ' contact J a

2 ^ - -^ Tcontact

The movement s_xof the sensor 16 with regard to the fixed antennas 5, 6 in x- direction is given by: _{w e} N₀

Any time when the profile element 12 moves through the area ±L_∞ntact around the centre of the contact area, the specific movement due to the strain of the profile element 12, which is shown in figure 2 and denoted with x there, is added to the circular movement of the profile element 12. The sign is given by the fact, that the strain points away from the antennas 5, 6 in the first part of the contact area, which is the accelerating area, and then points towards the antennas 5, 6, in the second part of the contact area, which is the decelerating part. This means, that the ordinary movement of the tyre element is delayed in the running in area due to the bulge. At the time t=0 the tyre element 12 is again located at the distance so in the middle of the contact area. The velocity v_x is given by: _{; n e No}

Thus the Doppler is given by

1 I 2 ^{V ' 03v,,}'^{ed ' C0S}'-^α>"'--ee; ⁺ ^contact ^{' ω} contact ^{' C0S ω} contact ^' *) _0J. ^contact ^ 2 ^• π ^• T Lcontact

C V car fo _{l + 2} r - ω_whed - cos(ω_whed t) ^^ c

₁ , car _ΛΛrY,, Λ ■ -"-contact car „ „(,- -ft--_*. contact _<? ^■ + ,, ^> ' *£ ^* ' ^ . ^ contact

1 + 2 cos^ω^^ t)+ 2— ∞s >_con<_act ^■ t) ^for ≤ t - n - — < +^■ ^C contact ^{C V}car

= /o

V \

1 + 2 — — ■ cos(ω _wheel t) otherwise c

As a result, there are two portions of the Doppler shift, the amplitude of the strain of a tyre element being by the factor -τ*A_∞ntact / Lcontact smaller than the contribution of the turning of the wheel.

Example: Lcontact = 8cm (see Fig. 2) and A_COntact=0.45mm: Thus the Doppler shift is increased by approximately 1 ,8%, which is very hard to detect.

By processing of the Doppler shift alone no significant measurement signal describing the conditions of during passing the contact area can be extracted. Although the frequency ωLatsch is clearly higher than the turning frequency of the wheel ©w eel, the amplitude Acontact is also significant smaller as compared to the radius of the wheel r. Case 3: Circular movement of the wheel with consideration of the modulated back scattering process

According to the invention, the strain Λ_contact ^{■ s}iⁿ(^ω _{cont ct} " is now transformed into a modulation of the frequency of the back-scattered sensor signal. To this end, the electrical parameters of a frequency determining element of the sensor, e.g. a part of the transponder antenna 17, or any load of the transponder antenna 17, is altered at the angular frequency ©contact. This can be achieved by deforming the shape of the antenna due to the strain of a tyre element, thus tuning (or modulating) their resonant frequency, or, by using a strain gauge, like a tuneable capacitance, inductance, or resistance, to implement the sensor 16 as a load of the transponder antenna 17. Thus, the circuitry, which is provided by the transponder antenna 17 and the sensor 16 includes at least one element Z(t) the electrical impedance Z of which is changing due to the strain of the tyre element. The back-scattered sensor signal thus contains at least one component with the same time dependence as Z(t). The spectrum of this component corresponds to the spectral composition of Z(t) and thus to those of the strain of the tyre element.

If the electrical impedance of the load Z(t) is altered between open and short while the profile element passes the contact area, or if the resonance frequency of the antenna is altered by the fraction k/Q, Q giving the quality factor of the transponder antenna 17, the phase of the back scattered sensor signal is changed by ±180°, which corresponds to a shift of a "reflector mirror" by a distance of ±λ/2. Here, λ is the electromagnetic wave length of the sensor signal: λ=c//b. The sensor signal which is modulated in this way can be regarded as a signal which is Doppler-shifted by the frequency fLatsch, the amplitude Acontact of which, however, is λ/2π :

Hence, the shift of the sensor signal generated by the modulation of at least one electrical parameter of the back-scatter with the aid of the strain of the tyre profile element with regard to the Doppler shifted signal will be in the order of the ratio of 1 /Lcontact to 1/λ. Therefore, the coefficient λ/(2^»L_COntact) gives the relation between the sensor signal representing the strain of a tyre profile element and the Doppler- shifted back-scattered signal.

A typical example: Lcontact = 8cm (see Fig. 2). Using the international ISM bands (ISM = industrial, scientific, and medicine), the following results are achieved:

The absolute distance between the sensor signal characterising the strain of a tyre profile element and the Doppler-shifted back-scattered signal remains the same, but their ratio decreases with increasing frequency. If the electrical impedance Z(t) is changed by only a small amount due to the strain of a tyre profile element, the corresponding "reflector mirror" will be shifted by a smaller amount than λ/2. In this case the back-scattered signal can be decomposed into a first part with no change due to the strain at all, and a second part the phase of which changes by ±180°. The second component again has the same spectral composition like Z(t). Consequently, in this case not the spectral composition of the modulated back-scattered signal is changed but only the amplitude of the signal generated by a modulation of at least one electrical parameter of the back-scatter with the aid of the strain of a tyre profile element. If, for example, the back-scattered signal will be changed due to the variation of the electrical parameter Z(t) in amplitude or phase by only 1 %, then the modulated part of the whole signal will be 1/100, or -20dB of the full amount of the back-scattered signal. The modulation shift, however, is still

The total spectral composition of the back-scattered signal will again be fd, with: f v ^

J d ~ J O 1 + 2-*- c ±/_

_j Thus, the same formula as above results.

The aim of the present invention, however, is not only restricted to monitor the fundamental of the signal generated by a modulation of at least one electrical parameter of the back-scatter with the help of the strain of a tyre profile element, which is denoted with x in Fig. 2, but rather to also monitor higher harmonics of this signal. The ratios of the higher harmonics to the fundamental signal contains the desired information about the actual shape of the strain of a tyre profile element 12, which gives the information about the tyre on the road friction coefficient, and also information about local slipping processes of single profile elements 12 during the roadway contact. The frequency shift of this higher harmonics is yet higher than the frequency shift of the fundamental. Above calculations show that frequencies in the UHF and VHF region up to some 6 GHz are well suited for the described measurement method to monitor the strain of a tyre profile element.

LIST OF REFERENCE NUMERALS ;

1 running in area

2 contact area

2a contact area, accelerating

2b contact area, braking

3 running out area

4 device

5 transmitter antenna

6 receiver antenna

7 transmitting and receiving unit

8 motor vehicle

9 wheel

10 tyre

11 profile

12 tyre element, which may be a profile element

13 arrow

14 turning arrow

15 roadway

16 sensor

17 transponder antenna

18 axis of rotation

19 transponder unit

20 frequency analysing unit

Claims

C L A I M S:

1. A method of acquiring data of dynamic physical processes via a radio link comprising the steps of : providing a sensor having an electrical impedance dependent of the data to be acquired; exciting a transponder antenna by an electromagnetic exciting wave at the resonance frequency of the transponder antenna; and receiving and analysing a back-scattered electromagnetic sensor wave which is modulated by the sensor; characterized by the steps of: connecting the sensor (16) directly to the transponder antenna (17) so that the sensor changes the electrical impedance of the transponder antenna (17) with every variation of the data to be acquired; and receiving the electromagnetic wave which is back-scattered by the transponder antenna (17) as the sensor wave at the same time as the transponder antenna (17) is excited by the exciting wave.

2. The method of claim 1 , characterized in that the value of the electrical impedance of the transponder antenna is time dependently changed or modulated by the data to be acquired so that the changed or modulated impedance changes the back-scattering properties of the transponder antenna (17) which modulates the back- scattered sensor wave with the same time characteristics as shown by the data to be acquired.

3. The method of claim 1 or 2, characterized in that the sensor is provided as a passive sensor.

4. The method of any of the claims 1 to 3, characterized in that the sensor wave is analysed with regard to the ratio of amplitudes of at least two frequency components.

5. The method of any of the claims 1 to 4, characterized in that the sensor wave is analysed with regard to a frequency modulation.

6. The method of any of the claims 1 to 5, characterized in that the sensor wave is analysed with regard to an amplitude modulation.

7. The method of any of the claims 1 to 6, characterized in that a radio sensor unit (19) including the sensor (16) and the transponder antenna (17) is provided on an object rotating about an axis (18) of rotation, whereas a transmitting and receiving unit (7) provided for transmitting the exciting wave and for receiving the back-scattered sensor wave is fixed and not rotating with the object.

8. The method of claim 7, characterized in that the data to be acquired is the strain of a tyre element of a tyre (10) of a vehicle during its contact with a roadway (15) while the vehicle is moving.

9. The method of any of the claims 1 to 8, characterized in that the sensor (16) has an electrical capacitance, inductance, and/or resistance, whose electrical value is time dependently changed or modulated by the data to be acquired.

10. The method of any of the claims 1 to 9, characterized in that the sensor (16) is connected as a load and to the base of the transponder antenna (17).

11. The method of any of the claims 1 to 10, characterized in that the sensor (16) is integrated into a resonant circuitry of the transponder antenna (17).

12. The method of claim 11 , characterized in that the transponder antenna (17) itself is provided as the sensor element (16) in that it changes its back-scattering properties due to a mechanical bending.

13. The method of any of the claims 1 to 12, characterized in that the exciting frequency is emitted within a frequency range of 100 MHz to 6 GHz

14. A device for acquiring data of dynamic physical processes via a radio link, especially for carrying out the method according to any of the claims 1 to 13, the device comprising: a transmitter antenna for emitting an electromagnetic exciting wave; a transponder antenna for receiving the exciting wave; a sensor having an electrical impedance dependent of the data to be acquired; a receiver antenna for receiving a back-scattered electromagnetic sensor wave modulated by the sensor; and an analysis unit for analysing the received sensor wave; characterized in that the sensor (16) is directly connected to the transponder antenna (17) so that the sensor changes the electrical impedance of the transponder antenna (17) with every variation of the data to be acquired; and the receiver antenna (7) receives the electromagnetic wave which is back-scattered by the transponder antenna (17) as the sensor wave at the same time as the transmitter antenna (5 ) emits the exciting wave.

15. The device of claim 14, characterized in that the value of the electrical impedance of the sensor is time dependently changed or modulated by the data to be acquired so that the changed or modulated impedance changes the reflection properties of the transponder antenna (17), which modulates the back-scattered sensor wave with the same time characteristics as shown by the data to be acquired.

15. The device of claim 14 or 15, characterized in that the sensor (16) is a passive sensor.

16. The device of any of the claims 14 to 16, characterized in that the sensor (16) is provided in the profile area (11 ) of a tyre (10).

17. The device of any of the claims 14 to 16, characterized in that the sensor (16) is provided in a tyre element in a running zone of a tyre (10).

18. The device of any of the claims 14 to 17, characterized in that the sensor (16) and the transponder antenna (17) are both formed as one section of a conductive wire which is bent to different shapes.