| JP2004325160 | ON-VEHICLE RADAR |
| JP3726472 | WINDSHIELD ANTENNA UNIT FOR AUTOMOBILE |
| JP09321519 | GLASS ANTENNA FOR VEHICLE |
SJÖGREN, Staffan (Jutevägen 5C, Sollentuna, S-192 77, SE)
| Claims 1. A Radio Frequency IDentification (RFID) system comprising an RF reader, a directional RFID patch antenna and at least one Doppler sensor, characterized in that said RF reader is adapted to operate said RFID patch antenna at below 1 GHz and to operate said at least one Doppler sensor(s) at a different and higher frequency. 2. The RFID system according to claim 1, wherein said at least one Doppler sensor(s) is/are directional Doppler sensor(s). 3. The RFID system according to claim 1 or 2, wherein said RF reader is adapted to operate said at least one Doppler sensor(s) at 2.4 GHz or higher 4. The RFID system according to any of claims 1-3, wherein said RF reader is adapted to operate said at least one Doppler sensor(s) at 9 GHz or higher. 5. The RFID system according to any preceding claims, wherein the RFID patch antenna comprises a ground plane (32) upon which an RFID antenna patch (33) and one or many Doppler sensor patches of said Doppler sensor are arranged. 6. The RFID system according to claim 5, wherein the RFID antenna patch (33) is designed for linear polarization (34) and that the Doppler sensors (31) are placed at the ground plane (32) along the non-radiating side of said patch where essentially no radiating field (35) exists. 7. The RFID system according to any preceding claim, wherein the Doppler sensors are operated in a pulsed mode with low duty cycle. 8. The RFID system according to any preceding claim, wherein said at least one Doppler sensor make use of patch antennae (41, 42) on a dielectric substrate. 9. The RFID system according to claim 8, wherein the patch antennae of the Doppler sensor(s) are each designed with an array of at least two antenna patches for increased directivity. 10. The RFID system according to any preceding claim, wherein the system further comprises an antenna housing enclosing said RFID patch antenna and said at least one Doppler sensor(s), and that said antenna housing has a flat structure having a rectangular shape with a maximum size of 40 x 40 cm and a height of less than 6 cm. 11. The RFID system according to any preceding claim, wherein said RFID reader is adapted to be switched from an idling state with low power consumption to an active state in dependence of an activation signal from said at least one Doppler sensor. 12. The RFID system according to claim 11, wherein said RFID reader is adapted to be switched back to said idling state when a predetermined time period has lapsed. 13. The RFID system according to any preceding claim, wherein the RFID reader further comprises a communication unit adapted for wireless communication, and that said communication unit is adapted to be switched from an idling state with low power consumption to an active state in dependence of an activation signal from said at least one Doppler sensor. 14. The RFID system according to any preceding claim, wherein the system is powered by solar cells (11) or a wind turbine generator and a battery (13), and that the system communicates its data with a central system via a radio method such as WLAN or GPRS. 15. The RFID system according to any preceding claim, wherein said RFID antenna comprises one Doppler sensor, and that the lobe generated by that Doppler sensor is larger than the lobe generated by the RFID antenna patch. 16. The RFID system according to any of claims 1-14, wherein said RFID reader is adapted to operate with a directional RFID patch antenna at below 1 GHz, where said patch antenna is integrated with at least two directional Doppler sensors (31) and where said Doppler sensors operate at 9 GHz or higher, such that said RFID system is adapted to be used for railways. 17. The RFID system according to claim 16, wherein the RFID antenna, is adapted to be mounted such that the it is directed essentially orthogonal (16) to a railway track and that each of the Doppler sensors are directed essentially away from orthogonal in each (14, 15) of the two track directions. 18. The RFID system according to any of claims 16 or 17, wherein the Doppler sensor that points in the direction of an arriving train makes the RFID reader to switch from idling state with low power consumption to active state with operating transmitter for identification of tags on the passing train. 19. The RFID system according to any of claims 16-18, wherein a detection signal (25) from the Doppler sensor that points in the train's departure direction is compared with the detection signal (24) from the Doppler sensor that points in the train's arrival direction to keep the RFID reader active for as long a time as is needed for safe identification of tags on the train and to thereafter switch the reader to idling state. 20. The RFID system according to any of claims 16-18, wherein said RFID reader is adapted to be switched back to said idling state when a predetermined time period has lapsed. 21. The RFID system according to any of claims 16-20, wherein the system, in addition to the identification, also is adapted to determine the direction of passage by means of logic. 22. The RFID system according to any of claims 16-21, wherein the system is adapted to determine if the passing train is running on the desirable track or on an adjacent, parallel track, by means of sensing the strength of the Doppler signals from the sensors. 23. The RFID system according to any of claims 16-22, wherein the system is adapted to determine if the passing train is running on the desirable track or on an adjacent, parallel track, by means of sensing the strength of FFT analysis of the Doppler signals from the sensors. 24. Radio Frequency IDentification (RFID) system for railways, characterized by that an RFID reader operates with a directional RFID patch antenna at below 1 GHz, where said patch antenna is integrated with at least two directional Doppler sensors (31) and where said Doppler sensors operate at 9 GHz or higher. 25. RFID system according to claim 24, characterized by that the, RFID antenna is directed essentially orthogonal (16) to the track and that each of the Doppler sensors are directed essentially away from orthogonal in each (14, 15) of the two track directions. 26. RFID system according to any of claims 24 and 25, characterized by that the RFID antenna patch (33) is designed for linear polarization (34) and that the Doppler sensors (31) are placed at the ground plane along the non-radiating side of said patch where essentially no radiating field (35) exists. 27. RFID system according to any of the previous claims 24-26, characterized by that the Doppler sensors are operated in a pulsed mode with low duty cycle. 28. RFID system according to any of the previous claims 24-27, characterized by that the Doppler sensor that points in the direction of an arriving train makes the RFID reader to switch from idling state with low power consumption to active state with operating transmitter for identification of tags on the passing train. 29. RFID system according to any of the previous claims 24-28, characterized by that detection signal (25) from the Doppler sensor that points in the train's departure direction is compared with the detection signal (24) from the Doppler sensor that points in the train's arrival direction to keep the RFID reader active for as long a time as is needed for safe identification of tags on the train and to thereafter switch the reader to idling state. 30. RFID system according to any of the previous claims 24-29, characterized by that the Doppler sensors make use of patch antennae (41, 42) on a dielectric substrate. 31. RFID system according to any of the previous claims 24-30, characterized by that the patch antennae of the Doppler sensors are each designed with an array of at least two antenna patches for increased directivity. 32. RFID system according to any the previous claims 24-31 , characterized by that the system, in addition to the identification, also determines the direction of passage by means of logic. 33. RFID system according to any of previous claims 24-32, characterized by that the system determines if the passing train is running on the desirable track or on an adjacent, parallel track, by means of sensing the strength of the Doppler signals from the sensors. 34. RFID system according to any of the previous claims 24-33, characterized by that the system determines if the passing train is running on the desirable track or on an adjacent, parallel track, by means of sensing the strength of FFT analysis of the Doppler signals from the sensors. 35. RFID system according to any of previous claims 24-34, characterized by that the system is powered by solar cells (11) or a wind turbine generator and a battery (13), and that the system communicates its data with a central system via a radio method such as GPRS. |
RFID system
Field of the invention
The present invention relates to a system according to the preamble of the independent claims. In particular it relates to an RFID system for railways, and for other vehicles, e.g. trucks, busses, cars and also bicycles. It may also be used to detect and identify human beings and animals. Background of the invention
Automatic identification of trains by means of Radio Frequency IDentification (RFID), with RFID readers along the track and RFID tags on the vehicles, makes it possible to instantly know which wagons that are passing at a certain location and a certain time. A reader can be integrated with its antenna, or use one or more separate antennae.
RFID is an established technology for keeping track of freight wagons, passenger wagons, locomotives and other rolling stock in order to shorten transportation times and minimize capital tie-up in transported material. Through analysis of the identification data, RFID can also be used to monitor the mileage of the rolling stock and determine an optimal schedule for preventive maintenance, such as lubrication of bearings, turning of wheels and adjustment of brakes.
The above has created a large market for RFID in railways, however with several problems. Some of the problems are in particular relevant when using RFID systems in railways, but some are also relevant in other areas.
A first problem with RFID systems for train identification is the difficulty to know in which direction a train is passing, unless two RFID readers are used. The time when a tag is identified in each of these two readers is then instantly recorded for conclusion about its passage direction. This method is however expensive because of extra readers and complex installation. A second problem, which essentially is general, is that RFID readers consume much more energy than desirable since they need to have their transmitters continuously activated while waiting for a train to arrive and be identified, or an item or person to emerge and be identified. Typically, an active reader consumes up to ten times as much power as a reader in idling state. To arrange a reader activation signal, the installer needs to connect the reader to at least one train detector remote from the reader in the expected direction of arrival. Such detector typically comprises an inductive or magnetic field sensor that is mounted to the track. A solution with inductive or magnetic train sensors is expensive since they have a price that is comparable with the reader, and since they can only be installed if the track is blocked for traffic during the installation.
A third problem is that power and data wiring for the RFID reader cannot easily be arranged. Wireless power and/or data would highly facilitate the use of RFID both for railway infrastructure organisations, train operators, as well as for e.g. road operators, since is would eliminate the need for expensive power- and/or data lines at remote locations, such as in a desert area. Wireless power and/or data would also make possible mobile RFID stations, to be temporary installed along the track, or road, e.g. at entrances/exits of companies, such as mines, that are served with transportation services. A fourth problem is that RFID systems that are set up to identify a train, a vehicle or a person, from the side, where the train vehicles have tags on both sides, by mistake identifies trains on an adjacent, parallel track, or a truck or car on an adjacent part of the road. A solution with a reader between the tracks, pointing upwards to read a tag under the train, is undesirable since any installation and maintenance requires that the track is closed. Another problem with said solution is that the RFID reader from time to time will be covered by wet snow that both is causing severe stress on the reader, attenuating the reader signals and makes the reader subject to damage from objects hanging down or being dropped from the train. A fifth problem with RFID for railways is that comparatively large RFID antenna structures are needed because of regulatory frequency requirements. While some RFID systems for railway operate in the public 2.45 GHz band (in many countries restricted to 2,400 - 2,483.5 MHz or a part thereof), a protected band for railway identification in Europe has been opened at 865 - 868 MHz, which is a prescribed band for RFID according to ISO 18000-6C and GSl . This requests an antenna size three times as large as a 2.45 GHz antenna, and the inventor has realized that it is therefore desirable to, if possible, add functionality to any unit with such an RFID antenna.
Frequencies near the frequencies used in Europe are used for railway identification also in e.g. Americas and Asia. Since directional RFID is needed, patch antennas with large ground planes are common. Such antennae typically employ a ground plane that is about 30 x 30 cm in size, leaving about 5 cm at each non-radiating side of the patch inside the antenna housing for other functions.
Thus, the object of the present invention is to achieve an improved RFID system which solves the above-discussed problems. Summary of the invention
The above-mentioned object is achieved by the present invention according to the independent claims.
Preferred embodiments are set forth in the dependent claims.
The present invention described herein is particularly useful in connection with railway applications and a number of exemplary embodiments in relation to these applications will be described in detail. However, the inventor has realized a number of different areas where the present invention is equally applicable. These areas are e.g. identification of road vehicles (busses, trucks, cars) for access or parking purposes; counting and/or registration of cycles and/or cyclists; registration of athletes, registration and counting of cattle, e.g. identification of cows for giving access to feeding or milking robots.
According to one embodiment, the invention comprises an RFID system with a directional patch antenna for frequencies within an allocated RFID band below 1 GHz, where said antenna is integrated with at least two directional Doppler sensors next to the antenna patch and where said Doppler sensors, for compact antenna dimensions and compliance with frequency regulations, preferably operate at 9 GHz or higher. In Europe, as well as in Asia and the Americas, frequency bands for Doppler sensors are allocated at 9 - 11 GHz.
Thanks to the much higher frequency of the Doppler radio than of the RFID system, the empty space on the ground plane of the RFID patch antenna can be used for the Doppler sensors and aiming the lobes at opposite directions to obtain high directional effect. In one embodiment of the invention, the RFID patch is designed for linear polarization with the Doppler sensors placed at the ground plane along the non-radiating side of said patch where essentially no radiating field exists. A linear polarized tag is by definition much more compact and low-cost than a circular polarized tag and therefore a preferred alternative for installation on railway vehicles, and further a linear polarized system is generally offering higher performance in terms of reading range than a circular polarized system.
The RFID antenna is typically directed essentially orthogonal to the track or path where the identification objects are expected to pass, while the Doppler sensors are directed away from orthogonal in each of the two track directions. The Doppler sensor that points in the direction of an arriving train makes the RFID reader to switch from idling state with low power consumption, to active state with the operating transmitter for identification of tags on the passing train while it is passing through the reading zone. This way, the RFID reader stays in idle mode until an object classified as a valid one arrives and is to be identified by active reading of RFID tags on the vehicle(s). The Doppler radio works in pulsed mode to further save energy, but is pulsed often enough to stay alert for safe object detection.
The signals from the Doppler sensor that points in the train's departure direction is compared with the detection signal from the Doppler sensor that points in the train's arrival direction to determine the passage direction and to, regardless of if the passage takes place at high or low speed, keep the RFID reader active for as long a time as is needed for safe identification of all possible tags on the train and to thereafter switch the reader to idling state. The directional Doppler sensors can make use of patch antennae on a dielectric substrate for compact dimensions, and in a preferred embodiment the patch antennae of the Doppler sensors are each designed with an array of at least two antenna patches for increased directivity.
By means of sensing the strength of the Doppler signals from the sensors, the system can determine if the passing train is running on the desirable track or on an adjacent, parallel track. This determination is made by means of sensing the strength of the Doppler signals from the sensors and/or by FFT analysis.
In addition to determine the direction of passage by means of logic based on the sequence of signals from the Doppler sensors and identification of passing vehicles, the system can minimize reader's energy consumption and, thanks to the reduced power need, provide a power reserve for wireless communication with the reader.
The system can be powered by independent power sources such as solar cells or a wind turbine generator, and battery, and can communicate its data with a central system via a radio method such as GPRS or WLAN for installation and use at remote locations. EP0640235 published 1995-03-01 and EP2070001 published 2009-06-17 disclose inventions where Doppler sensing is combined with RFID.
While the fundaments of the present invention requires that different frequencies and separate circuitry are used for RFID and Doppler sensing, both EP0640235 and
EP2070001 make use of the same signal frequency and common circuitry for RFID and Doppler sensing.
In one embodiment of the present invention, the Doppler sensing zones need to be directed in different directions than the identification zone, and the Doppler sensing zones also preferably need to have a narrower beam width than that of the RFID zone to avoid non- desired identification of irrelevant objects such as people and animals. These
characteristics can only be achieved with significantly different frequencies for RFID and Doppler sensing, if not an antenna housing that is many times larger than that of the invention's shall be employed.
EP0640235 primarily relates to alarm and access applications, especially for use in automobiles and/or buildings, and where the Doppler sensing area generally is smaller than the identification area to make it possible to disarm the alarm function by means of a tag. This is different to the function of the here described invention where the Doppler sensing area generally is larger than or falls outside the identification area. Train identification is not mentioned in EP0640235.
EP2070001 primarily relates to managing inventory, electronic access control, security systems, automatic identification of cars on toll roads and electronic article surveillance. Doppler sensing is used to detect an object inside the interrogator zone, and to increase the output power of the RFID reader to obtain a safe identification. This is different to the function of the here described invention where the main part of the Doppler sensing area is located outside the identification area. In particular, train identification is not mentioned in EP2070001.
US2009303004 published 2009-12-10 describes an RFID system that includes
determining a motion parameter of the RFID tag based on detecting a Doppler frequency shift in a radio frequency signal received from the RFID tag. The present invention makes use of largely different frequencies for the RFID function and the Doppler sensing. Train identification is not mentioned in US2009303004.
One manufacturer of RFID readers for railways offers a reader that is designed for mounting between the rails and that can detect the direction of a train by means of a built- in Doppler radar. Also this reader makes use of the same frequency for Doppler sensing and RFID functions and operates at 2.45 GHz instead of below 1 GHz as is relevant to this invention. Said 2.45 GHz reader operates with battery-assisted tags only, while RFID readers according to this invention offer beam powering of the tags and therefore can operate with tags that do not have a battery. Although RFID for railways as well as RFID in combination with Doppler sensing technology is widely used since many years, no RFID system for railways has as far as known combined these two technologies in an optimal way for railway applications. In addition, the present invention is also applicable in other applications which have been mentioned above.
The here described invention discloses a solution with an RFID system, in particular for railways, in combination with Doppler sensing technology where all of the mentioned problems have found an elegant solution.
Short description of the appended drawings
The invention will now to be described more in detail where
Figure 1 is a schematic block diagram illustrating the present invention.
Figure 2 shows an RFID antenna with one Doppler sensor.
Figure 3 schematically illustrates the lobes of an RFID antenna with one Doppler sensor. Figure 4 shows schematically an RFID system for railway identification.
Figure 5 shows a sequence of signals for logical conclusions about a passing train.
Figure 6 shows an RFID antenna with two Doppler sensors.
Figure 7 shows a Doppler sensor with an antenna array.
Detailed description of preferred embodiments of the invention
Referring to figure 1 the present invention relates to a Radio Frequency IDentification (RFID) system comprising an RF reader, a directional RFID patch antenna and at least one Doppler sensor. The RFID reader is adapted to operate the RFID patch antenna at below 1 GHz and to operate said at least one Doppler sensor(s) at a different and higher frequency. Preferably the frequency is 2.4 GHz or higher, and most preferred the frequency is 9 GHz or higher. Preferably the at least one Doppler sensor(s) is/are directional Doppler sensor(s). In embodiments where two or more Doppler sensors are used, it is not a requirement that all Doppler sensors work at the same frequency as long as the frequency requirement set out above is fulfilled, i.e. all frequencies must be 2.4 GHz or higher, and most preferred the frequencies are 9 GHz or higher..
The RFID reader is powered by a power source, that preferably comprises one or many of a battery, solar cells and/or a wind turbine. It is naturally also possible to power the RFID reader via a wired connection to a main supply net.
The RFID antenna, i.e. comprising a typically passive patch antenna for the RFID signals and one or more active Doppler sensors, each with one or more patches and related electronic circuitry, is in turn powered by the RFID reader.
The RFID reader is connected to the RFID antenna e.g. via a coaxial cable for the RFID signals, and via an power- and communication cable for detection signals from the Doppler sensor(s) and to provide power to the Doppler sensor.
The RFID reader is also provided with a processing and control unit e.g. for applying relevant outputs to the RFID antenna, and for receiving sensor signals from the antenna.
The RFID patch antenna comprises a ground plane 32, see figures 2 and 6, upon which an RFID antenna patch 33 and one or many Doppler sensor patches of the Doppler sensor or sensors 31 are arranged. The RFID antenna patch 33 is designed for linear polarization 34 and that the at least one Doppler sensor(s) 31 is/are placed at the ground plane 32 along the non-radiating side of the patch where essentially no radiating field 35 exists.
In order to keep the energy consumption at a low level the Doppler sensor(s) are operated in a pulsed mode with low duty cycle.
Advantageously, the at least one Doppler sensor make use of patch antennae 41, 42, (see figure 7) on a dielectric substrate, and that the patch antennae of the Doppler sensor(s) are each designed with an array of at least two antenna patches for increased directivity. The RFID system is often used in rough environments where it is subjected to extreme whether conditions and where also limited spaces for mounting of the system are available. Therefore, the system advantageously further comprises an antenna housing enclosing the RFID patch antenna and the at least one Doppler sensor(s). The antenna housing preferably has a flat structure having a rectangular shape with a maximum size of 40 x 40 cm and a height of less than 6 cm. The housing is made from a robust material, e.g. a metal and plastic.
In order to achieve low power consumption requirements the RFID reader is adapted to be switched from an idling state with low power consumption to an active state in dependence of an activation signal from the at least one Doppler sensor.
To achieve that, the sensor lobe(s) of the Doppler sensor(s) must have a coverage in relation to the coverage of the lobes of the RFID antenna, such that an object first is detected by the Doppler sensor(s). This is illustrated in both figure 3, where the Doppler sensor lobe 8 is wider and larger than the RFID antenna lobe 9, and in figures 4 and 5, where the Doppler sensor lobes 14, 15 have specific directions. The RFID reader may be adapted to be switched back to said idling state when a predetermined time period has lapsed. The duration of this time period is naturally dependent of the use of the system and may be set to any time ranging from a couple of seconds to many minutes, or even hours. The RFID reader often comprises a communication unit adapted for wireless
communication, e.g. via WLAN or GPRS. The communication unit preferably is adapted to be switched from an idling state with low power consumption to an active state in dependence of an activation signal from the at least one Doppler sensor. Also the communication unit may be switched back to the idle state after a predetermined time period, or be kept switching between idle and active state at regular intervals to conserve energy while still regularly open itself for communication of data with external devices. According to one embodiment, which is illustrated by figures 2 and 3, the RFID antenna comprises one Doppler sensor. As indicated above such a system may be used in many different areas. Preferably, the lobe 8 generated by that Doppler sensor is larger than the lobe generated by the RFID antenna patch. By larger is meant that in at least some direction the lobe from the Doppler sensor has a larger range than the lobe 9 of the RFID antenna patch.
Figures 4-7 specifically relate to embodiments of the present invention when used in railway applications. However, many aspects of these embodiments may also be applicable in other areas, e.g. in relation to road vehicles, identification of persons, e.g. athletes.
Figure 4 shows a railroad track 17 and a pole 12 where solar cells 11 and a battery 13 powers the RFID reader with antenna and Doppler sensors on the pole. To save energy, the Doppler sensors are preferably operated in a pulsed mode with low duty cycle. The left sensor lobe 14 is aimed toward the left side of the pole and the right sensor lobe 15 is aimed toward the right side of the pole. Each lobe is dedicated to first detect arriving trains from left or right respectively. Once a train arrival is detected by means of algorithms in or with the related Doppler sensor, the RFID reader is activated so that tags on the train vehicles can be read in RFID lobe 16.
Figure 5 shows tracks A and B that are in parallel and adjacent to each other. The tracks are dedicated to moving trains in right direction 21 and left direction 26.
The Doppler detection signals 24 and 25, when the train passes through zones 22 and 23, emerge in the order of the train's moving direction. Points 27, 28, 29 and 30 correspond to the edges of the detection zones. Depending on the Doppler signal strength and/or frequency components, the moving direction can be determined by logic and/or FFT. This way, the system saves energy, registers train's movement direction and reads vehicle tags on the correct track only, which is a major advantage of the present invention. Figure 6 shows a directional RFID patch antenna for frequencies below 1 GHz, where the patch 33 is placed in front of a larger ground plane 32. Two Doppler sensors 31 are mounted at the ground plane beside the patch where essentially no radiating field exists. Since the Doppler sensors operate with patch antennae above 9 GHz, their antennae are proportionally smaller than the RFID antenna. When air is used between ground plane and patch in the RFID antenna, and a dielectric material with dielectric constant higher than air is used between ground plane and patch in the Doppler sensor patch antenna, this difference is even more pronounced and makes possible an array of two or more patch antennae in the Doppler sensor for optimal directionality.
With high directionality in the Doppler sensor, it is possible to direct the sensor slightly upwards so that only trains are detected and not animals or persons moving on the ground. This way it is secured that only trains and not persons or animals will start an RFID identification attempt.
Figure 7 shows a Doppler sensor with an array 41 of two patch antennae for transmission and another array 42 of two patch antennae for receiving. Since the arrays comprise patches above one another, the vertical lobe width is narrowed down so that only a relatively high railway vehicle is detected and a relatively low object such as a person or animal is not detected.
In order to fully understand the present invention a short discussion is made in the following regarding relevant issues when designing patch antennas. The size of the antenna is inversely proportional to the frequency, and also inversely proportional to the square root of the dielectric constant in the space between the patch and the ground plane. A UHF patch antenna (1 GHz) provided with air as dielectric material will therefore be quite large, whereas a microwave patch (10 GHz) will be much smaller. The patch will have a size of approximately one half wavelength when the dielectric material is air, which is about 15 cm, and approximately 1 cm when the dielectric material is a microwave substrate having an epsilon value of 3-10. The ground plane must be about 40 % larger than the patch to achieve an acceptable directional effect of the antenna, which results in a free space outside the patch, which in the specific case discussed above is about 6 cm, where one or many Doppler sensor(s) may be arranged.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations readily apparent to those skilled in the art may be made without departing from the spirit and the scope of the present invention as defined by the following claims.