US RE40353 E1
There is disclosed an automobile hang tag for use in parking control and the like with an integral radio transponder, together with interrogator apparatus associated therewith in a system for parking control or other purposes. The detection range for the RFID interrogator and transponder is at least about six meters (20 feet) to enable rapid control monitoring of parking facilities from a moving vehicle through the back window or front windshield of parked vehicles. Reliable and trouble-free monitoring of the hang tags in a customary rear view mirror location is facilitated by employing directional antennas in the RFID hang tags, increasing the antenna gain while suppressing false signals and noise and improving the range-to-power ratio for the system. The RFID hang tags may be battery powered but are preferably unpowered RFID transponders. Suitable directional antennas employed may include Yagi antennas, log periodic antennas, stacked dipole antennas, spiral or slot antennas or other monodirectional or bidirectional antennas, preferably those suitable for selected frequencies within the 1,000 megahertz to 10,000 megahertz range.
1. Vehicle monitoring apparatus using radio frequency identification technology comprising:
a transportable RFID interrogator having a transceiver with a transmitting antenna;
a plurality of individually encoded auto hang tags incorporating RFID transponders and suitable for affixing temporarily in a vehicle interior, each of said hang tags having at least one flat surface area with visible indicia thereon and configured to be affixed with the normal to said flat surface generally along a horizontal sight path through a window of said vehicle;
each said RFID transponder including a memory element having encoded readable data, a controller microcircuit connected to read from said memory element, a modulator configured to be operated by said controller microcircuit, a receiver with at least one directional antenna coupled to provide a received signal to said control microcircuit, and a coupling between said modulator and said at least one horizontally directional antenna for causing transmission therefrom to be modulated in response to data read from said memory element.
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7. Vehicle monitoring apparatus using radio frequency identification technology comprising:
a transportable RFID interrogator having a transceiver with a directional transmitting antenna;
a plurality of individually encoded auto hang tags incorporating RFID transponders and suitable for affixing in a vehicle near a rear view mirror, each of said hang tags having at least one flat surface area with visible indicia thereon and configured to be affixed with the normal to said flat surface generally parallel to the vehicle longitudinal axis;
each said RFID transponder including a micro-circuit memory having encoded readable data, a controller microcircuit connected to read from said memory, a modulator configured to be operated by said controller microcircuit, a receiver with a horizontally directional antenna coupled to provide a received signal to said control microcircuit, and a coupling between said modulator and said horizontally directional antenna for causing transmission therefrom to be modulated in response to data read from said memory element.
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14. In a vehicle monitoring apparatus using radio frequency identification technology an auto hang identification tag with radio transponder comprising:
a hang tag body having at least one flat surface area with visible indicia thereon and configured to reside at a rear view mirror be oriented with the normal to said flat surface generally parallel to the a vehicle longitudinal horizontal axis;
an RFID transponder embodied in said hang tag body including a microcircuit memory element having encoded readable data, a controller microcircuit connected to read from said memory, a modulator configured to be operated by said controller microcircuit, a receiver coupled to provide a received signal to said controller microcircuit, said receiver having a directional antenna with horizontal directionality favoring the a first direction of a normal relative to said flat surface and disfavoring directions 45 degrees or more horizontally from said normal first direction, and a coupling of said modulator to said at least one directional antenna for causing transmission therefrom to be modulated in response to data read from said memory.
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17. Apparatus as recited in claim 14 15 wherein said directional antenna comprises an active dipole element and at least one director element horizontally spaced from said active dipole element.
18. Apparatus as recited in claim 14 15 wherein said directional antenna comprises a plurality of active dipole elements.
19. Apparatus as recited in claim 14 15 wherein said directional antenna comprises an elongated conductive element having a convoluted shape in a plane perpendicular to the favored direction of directionality.
20. Apparatus as recited in
This invention relates to the field of radio frequency identification transponders (RFID tags), and particular applications thereof involving vehicle identification and parking control systems.
RFID tags receive RF electromagnetic radiation from an interrogating transmitter and return information recorded in the tag to a receiver and computer which is usually associated with the interrogator transmitter.
RFID tags can and have been used in many ways for locating or identifying tagged objects including animals, people, vehicles, or other objects either stationary or mobile. Usually the RFID tag returns distinctive information from the particular tag which may be variable or invariable in nature.
As shown in U.S. Pat. No. 3,098,971 to R. M. Richardson, it has long been proposed that the power necessary to transmit the return signal from the transponder be provided by the much stronger signal that is received by the transponder. This eliminates the necessity for a battery or other power source for the tag. Such an RFID tag is referred to as a passive tag, and it is the preferred form for use in the present invention. The present invention is not limited to such passive tags, however, and could be implemented with battery powered tags.
In an RFID tag of the passive type an interrogator signal picked up by the antenna of the tag induces an alternating current in an antenna circuit which may be rectified by an RF diode, and this rectified current can be used in a power supply for the electronic components of a microcircuit. A digital memory element of the microcircuit stores identification information and/or other data. A lower frequency signal generated in the microcircuit is caused to modulate the return signal transmitted from the RFID antenna thereby communicating information coded in the lower frequency signal modulation may be implemented either by altering the antenna loading or by other suitable form of modulation. Thus the RFID tag may be interrogated by a signal which both communicates with the RFID tag and supplies the power for its circuit so that the RFID tag can respond with an information carrying signal from its transmit antenna, all without requiring a battery or other power source for the RFID tag. In some systems information in signals received from the interrogator may be stored in a digital memory of the transponder as well.
Further refinements in RFID tag technology were made as shown in U.S. Pat. No. 4,075,632 to Baldwin et al. wherein tags were proposed with logic and read/write memories and transistors for modulating the return signal were also powered by the energy received by the transponder. Such refinements are also shown in U.S. Pat. No. 4,786,907 to Akoelle.
While improvements in semiconductor technology to provide microcircuits which are smaller and have lower power requirements have increased the capability of RFID tags and the systems which employ them, there are limitations which have still not been entirely overcome, particularly in the passive type of RFID tags. Use of such tags where the distance between the interrogator and the transponder is more than a few feet or about one meter presents difficulties. The amount of power transmitted by the interrogator is subject to regulations as well as practical limitations so that the effect of the well known square-of-the-distance power reduction factor militates against reliable use at longer ranges. There is an associated problem exacerbated by the low magnitude of the return signal power in that frequently more than one RFID tag is in the area being interrogated, presenting the likelihood that interference between return signals from different tags will adversely affect the reliability of a system.
The present invention relates to systems for parking control or other similar purposes utilizing automobile hang tags incorporating RDIF transponders with directional antennas facilitating remote interrogation of such transponders with increased range and reliability. When employed in a parking control application the detection range for the RFID interrogator and transponder will be at least about 6 meters (about 20 feet) and enables rapid control in monitoring of parking facilities from a moving vehicle employing a transmission path through the back window or the front windshield of parked vehicles. In a system according to the invention customary high gain directional antennas will be employed for the mobile interrogator unit, but the usual omni directional or low gain antennas or RDIF tags are replaced by directional high gain antennas for receiving the transmission from the interrogator and transmitting the reply signal to the interrogator. This is particularly useful in the vehicle parking control application, for in such systems the tags may conveniently be placed in the vehicle in a specified orientation, and the vehicles themselves will be arranged in prearranged parking stalls.
Thus according to the invention the combined directivity and associated gain for both the interrogator antenna and the transponder antenna are utilized to increase the range and sensitivity for response signals from hang tags in a predetermined preferred direction, while at the same time reducing the likelihood of interference from other hang tags in nearby vehicles. It is important that this system serves to increase the normal range-to-power ratio permitting use of lower power interrogator signals well within regulatory requirements. Suitable directional antennas employed may include Yagi antennas, log periodic antennas, stacked dipole antennas, spiral or slot antennas or other known monodirectional or bidirectional antenna forms. It is preferred that any radio frequencies employed be within the 1,000 megahertz to 10,000 megahertz range; a basic design approach for such antennas may include scaling of television or other communication antennas to smaller size and higher frequency.
Other known interference reduction techniques may be employed in the controllers software of the system, and, if desired, further interference reduction may be achieved by using radar techniques to maintain a range window corresponding to response signal return time. By this approach transponder return signals from more than a specified distance, 8 meters or 25 feet for example, may be suppressed to eliminate interference from such sources.
Certain specific designs of directional antennas are of interest and in particular those derived utilizing the antenna design techniques of the prior art listed below and incorporated by reference herein. Also listed below are vehicular RFID related patents.
U.S. Pat. No. 4,782,345 issued to Landt on Nov. 1, 1988; U.S. Pat. No. 4,786,907 issued to Koelle on Nov. 22, 1988; U.S. Pat. No. 4,816,839 issued to Landt on Mar. 28, 1989; U.S. Pat. No. 5,525,991 issued to Nagura et al. on Jun. 11, 1996; U.S. Pat. No. 5,661,473 issued to Paschal on Aug. 26, 1997; U.S. Pat. No. 5,771,021 issued to Veghte et al. on Jun. 23, 1998; U.S. Pat. No. 5,777,561 issued to Chieu et al. on Jul. 7, 1998; U.S. Pat. No. 5,912,632 issued to Dieska et al. on Jun. 15, 1999; U.S. Pat. No. 6,118,379 issued to Kodukula et al. on Sep. 12, 2000; U.S. Pat. No. 6,121,880 issued to Scott et al. on Sep. 19, 2000; U.S. Pat. No. 6,215,402 issued to Rao Kodukula et al. on Apr. 10, 2001; U.S. Pat. No. 6,236,315 issued to Helms et al. on May 22, 2001; U.S. Pat. No. 6,278,413 issued to Hugh et al. on Aug. 21, 2001; U.S. Pat. No. 6,307,524 issued to Britain on Oct. 23, 2001; U.S. Pat. No. 6,320,509 issued to Brady et al. on Nov. 20, 2001; and U.S. Pat. No. 6,353,443 issued to Ying on Mar. 5, 2002.
It is an object of the present invention to provide an automobile hang tag of convenient size and shape including the RFID transponder enabling the information recorded in the hang tag to be accessed by radio frequency identification (RFID) apparatus as well as visually or optically.
It is another object of the present invention to provide an RFID tag to be temporarily affixed in the interior of an automobile with a transponder circuit and directional antenna enabling it to be reliably interrogated from a distance of at least one car length (about 20 feet or 6 meters).
It is still another object of the present invention to provide a vehicle control system with RFID hang tags for mounting in the interior of vehicles for identification thereof and/or data related thereto, together with interrogator apparatus mounted in a vehicle enabling rapid identification among a plurality of vehicles such as those within a parking area to enable control and monitoring of parking facilities from a moving vehicle or for other purposes.
It is yet another object of the present invention to provide a vehicle identification system including automobile hang tags with individual RFID transponders and a vehicle mounted RFID interrogator such that the transmission and reception characteristics of the transponder and interrogator facilitate communication of coded information from the transponder through the rear window (or the front windshield) of vehicles while the interrogator is being transported along a line of parking stalls in a parking facility.
It is a further object of the present invention to provide RFID hang tags for such a parking control system which are not battery powered (i.e., passive tags) having the necessary range of operation through exploitation of antenna gain and directivity.
A still further object of the present invention is to provide RFID tags with antennas having bidirectional or monodirectional radiation patterns in the horizontal plane.
Other objects and advantages of the invention will be apparent from consideration of the following description in conjunction with the appended drawings described below.
Vehicles such as automobile 11 are parked front to front on either side of the barriers 5. The vehicles may be of any style and automobile 11 has a common configuration including a vehicle hood 31, front windshield 33, side windows 37 and 39, metal roof 41, back window 43, and rear portion 45. According to the invention a distinctive automobile hang tag 35 is situated near the rear view mirror of automobile 11; such hang tag has a long range, preferably directional propagation, RFID tag incorporated therein. Each of the other vehicles shown, automobiles 13, 15, 17, 19, 21, 23, 27 and 29 will be understood to be generally similar to automobile 11 for the purpose of explaining FIG. 1. It should be understood, however, that other styles of vehicles such as vans, small trucks and the like can be accommodated in the system with little or no adjustment.
According to this embodiment of the invention an interrogator 55 for communicating with the RFID transponder of hang tags 35 is preferably mounted in or on a security or control vehicle 50. Vehicle 50 has a front hood 51, front windshield 53, left side window 57, and right side window 59. The interrogator 55 may conveniently be mounted at a left side window 57 and/or right side window 59. The transmitter of the interrogator 55 preferably has a directivity pattern provided by its antenna which helps to eliminate interference from multiple response signals of adjacent automobiles such as 21 and 23 as shown in FIG. 1. The optimum directivity may be determined by consideration of the parameters shown in FIG. 1. These parameters are:
T-average center to center distance of rear view mirrors holding parking permit hang tag with RFID.
D—depth of field of RF interrogator.
V—variation in length of vehicles.
A—aperture (cone) of the signal from RF interrogator.
B—aperture (cone) of the signal from RFID transponder.
For clarity the B-aperture for the RFID transponder is shown relative to the transponder 35 of vehicle 27 as pattern 47. It will be understood however that all the RFID transponders 35 will have similar directivity as indicated by pattern 47 and its B-aperture.
As shown in
According to the invention a similar employment of directivity in the transponder antenna enhances this effect and the reliability of the system as shown by the pattern 47 and the B aperture thereof. In the case of the hang tag transponders 35 the directivity pattern 47 increases the sensitivity for transmissions from interrogator 55 when aligned with vehicle 27 and at the same time renders the transponder 35 of vehicle 27 relatively insensitive when the interrogator vehicle 50 is in a position to interrogate some other vehicle such as a vehicle 29. Usually the pattern for transmitting a response from RDIF transponders 35 will have similar directivity and, to some degree, this may also reduce likelihood of interfering signals being received at the interrogator 55. While there will be unwanted reflected radiation in this environment, it too will tend to be suppressed by the directivity considerations discussed above.
The diagrams of
Transponder antennas, such as directional antenna 140, preferably have horizontal polarization (as provided by horizontally disposed dipoles, for example). Other radiation polarization such as vertical polarization or circular polarization may be employed for the transponder antennas (and the interrogator antennas) as circumstances may indicate. Except for
The radiation pattern for RFID transponders 35 is indicated in
In referring to bidirectional and monodirectional antennas it will be understood that there is some directivity associated with even the most omni-directional antennas. In referring to bidirectional or monodirectional antennas in this discussion it will be understood that these terms are meant to describe antennas with significantly greater directivity than an ordinary simple dipole antenna without intended directional characteristics.
As shown in
The transponder function is implemented by a tag receiver section 36A which feeds signals to a tag clock section 40A (in this embodiment) and to a tag logic section 42A. The tag clock section 40A also feeds a signal 102A to the tag logic section 42A which transmits information signals to and from a tag memory section 44A. The operation of such RFID transponders is described in detail in the references listed in the background section above.
Signals received from antenna 140 are processed in a detector 142 and communicated to a control unit 138. Control unit 138 has micro circuitry programmed to carry out the control operations for the transponder in accordance with known computer digital logic technique and standards. The primary function of control unit 138 is to recognize an interrogation signal received through directional antenna 140 and to access a data memory 146 for data to respond to the interrogation signal. Data memory 146 is connected to control unit 138 to provide this capability. In more sophisticated RFID implementations the control unit 138 may have the capability of receiving data signals beyond the simple interrogation command and to store such data by writing it into the data memory 146. In this more sophisticated implementation the data stored in data memory 146 would be accessible for transmission in a response to a subsequent interrogation. These additional functions are optional, however, and the basic implementation of the RFID transponder requires a read-only memory for the identification function of the RFID microcircuit.
An optional battery 148 is shown in
It is well known that the RFID circuits as shown in
The modulation frequency for microcircuit 118 encoding control information and data is subject to much variation as known in the art and may be selected from the range of 1 kilohertz to 1 megahertz. Amplitude modulation or other forms such as frequency or pulse modulation may be employed. The operation of the directional antenna 140 which is a primary feature of the invention favors higher operation frequencies and the concomitant shorter wavelengths, but otherwise no particular characteristics for known RFID transponder circuitry are required by the invention.
The interrogator circuit 218 shown in
Interrogator circuit 218 includes a control circuit 238 preferably implemented with digital micro circuitry and programmed to control operations of transmitter 242 and receiver 244 and to communicate with memory 246 and computer 247, all of which are preferably implemented with integrated circuit technology in one or more circuits. Memory 246 is preferably a read/write memory and computer 247 includes a central processor unit and usual associated displays for locally communicating information to the operator.
In most instances the computer 247 will have a link to a base computer which will serve to collect, compile and store information and data received from one or more interrogators over a period of time. Interrogator circuit 218 is provided with a power supply 248 preferably including a storage battery rechargeable from a vehicle direct current system or from fixed alternating current receptacles.
The interrogator circuit 218 and the antenna 240 may be of well known conventional form provided only that the antenna 240 is capable of providing the directivity needed to carry out preferred forms of the invention. Since there are no severe limitations on the size or shape of the antenna 240, which will typically be mounted in or on a vehicle 50, desired antenna directivity can be achieved by common known techniques in the antenna art without difficulty.
More detail of an exemplary preferred form of auto hang tag with RFID transponder 35 is shown in FIG. 5. Hang tag 35 may be of a shape commonly used for such hang tags without RFID capability and may include an engagement opening 101 for affixing the tag in the vehicle in the rear view mirror with the tag oriented with the normal to its plane surface approximately horizontal and directed longitudinally fore and aft of the vehicle. This will normally provide a line of sight from one side of a tag through the vehicle front windshield and a line of sight from the opposite face of the tag through the vehicle rear window. If this situation does not prevail with a particular vehicle, accommodation can be made to locate the tag to provide a line of sight through a vehicle window so that microwave frequency radiation to and from the tag is not blocked or reflected. Usually heating wires in rear windows will not present a problem, but such can be overcome by using a different window.
As indicated in
As indicated in 158 the tag 35 will customarily include visual indicia that is found on auto hang tags without RFID capability. The showing of indicia 158 is exemplary only and indicia may occupy a larger area on the tag and be present on both the front and back surfaces thereof.
A particular form of directional antenna generally referred to as a stacked folded dipole antenna is illustrated in schematic form to be employed in the hang tag 35 of FIG. 5. By employing two or more vertically stacked horizontal dipoles, antenna 140 has increased directivity and increased gain as compared with a simple dipole antenna. A transmission line 152 of appropriate form connects folded dipole 151 to the transponder circuit 118 and an additional transmission line 153 also connects a second folded dipole 155 in parallel to the transponder circuit 118. Transmission line 153 may extend to additional folded dipoles not shown in FIG. 5.
By employing folded dipoles 151 and 155 the electrical length of each dipole is greater than its physical length and hence their optimum frequency may be lower than for an unfolded dipole; thus the antenna 140 of
It may be noted that the antenna 140 of stacked folded dipole configuration shown in
Antennas specifically for use in RFID tags implemented with printed circuit techniques have been developed and an adaptation of such antennas is utilized in the hang tag embodiment illustrated in FIG. 6. The antenna 160 incorporated in auto hang tag 6 illustrated in
Hang tag 6 may be of similar configuration to hang tag 35 and may be provided with an engagement opening 101. Hang tag 6 as well as the other hang tags illustrated herein may be modified to be dual purpose serving also as a magnetic data card by providing a magnetic strip 168 on an edge of the card located so as not to interfere with the operation of the RFID function of the hang tag.
Hang tag 6 has a transponder circuit 118 and may optionally be provided with a battery 148. Transponder circuit 118 is connected by a transmission line 152 to directional antenna 160; antenna 160 comprises a metallic strip 167 having a spiral or other convoluted shape; which fulfills the radiator function of the antenna. Optional matching elements may be provided for magnetic strip 167 such as matching bridge 165 connected between grounding post 161 and feed pin 163. Using known design considerations the directional antenna 160 and the metallic strip 167 will be configured to provide a desirable directivity pattern, center response frequency and bandwidth for the transponder function of hang tag 6.
Although automobile hang tags are conventionally in the form of a flat generally planar sheet material there is no fundamental or operational restriction to such a shape, and
A horizontal antenna configuration in
To utilize the directivity of auto hang tag 7 in an automobile one would situate the antenna portion extending in the opposite position of the desired directivity. That is, for reception and transmission through the automobile windshield one would locate the antenna portion 170 extending toward the rear of the vehicle, and, conversely, for rear window reception the antenna portion 170 would extend toward the windshield of the vehicle. In the example illustrated in
Another preferred embodiment illustrated in
Associated with the dipole 183 is a reflector 181 in the form of a metallic strip on the main vertical portion of hang tag 8. If desired, metallic strip 181 could alternatively be located on flap 182. Further metallic strips 184, 185 and 186 serve as directors thereby providing a Yagi antenna configuration with a directivity indicated by arrow 189 in dashed lines. This Yagi antenna for the RFID transponder for auto hang tag 8 may be configured for a particular frequency of operation using frequency scaling techniques for the very common Yagi antenna design used in numerous forms of radio frequency communication apparatus. As is well understood, a Yagi antenna as shown in
The amount of improvement in gain over a simple dipole antenna required for a particular implementation of the invention will depend upon operational requirements such as range and interference rejection. It should be noted that even a simple dipole antenna has some degree of directivity with radiation in a direction endwise discriminated against as compared with the broadside directions. Thus, when the antenna to be associated with the RFID transponder of a hang tag is described or defined as directive or directional it should be understood that the directional quality is not only the inherent directionality incidental to the use of a simple dipole antenna.
The use of the RFID system with auto hang tags according to the invention presently deemed to be of primary importance is vehicle control and monitoring in parking facilities. The invention is not limited to such uses however, and may find uses in highway toll collection or traffic control or other future uses beyond those specifically described herein.
While numerous variations and modifications for the invention have been described shown or suggested above, it should be understood that other modifications and alternative embodiments will be apparent to those skilled in the art and accordingly the scope of the invention is not to be deemed limited to those variations specifically described shown or suggested, but is rather to be determined by reference to the appended claims.