Source: http://www.google.com/patents/US7456726?dq=5,072,412
Timestamp: 2014-03-14 02:59:36
Document Index: 441183347

Matched Legal Cases: ['Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60']

Patent US7456726 - Method and apparatus for improving the efficiency and accuracy of RFID systems - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method and apparatus for transmitting a narrow signal beam are disclosed that allow the precise location of RFID tags to be determined and reduce tag collisions. Also disclosed are a method and apparatus for improving the efficiency of RFID systems....http://www.google.com/patents/US7456726?utm_source=gb-gplus-sharePatent US7456726 - Method and apparatus for improving the efficiency and accuracy of RFID systemsAdvanced Patent SearchPublication numberUS7456726 B2Publication typeGrantApplication numberUS 11/066,048Publication dateNov 25, 2008Filing dateFeb 25, 2005Priority dateMar 5, 2004Fee statusPaidAlso published asEP1743271A2, EP1743271A4, EP1743271B1, US20050212660, US20070252677, US20070252687, US20090066481, WO2005091889A2, WO2005091889A3Publication number066048, 11066048, US 7456726 B2, US 7456726B2, US-B2-7456726, US7456726 B2, US7456726B2InventorsThorkild Hansen, Michael L. OristaglioOriginal AssigneeSeknion, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (77), Non-Patent Citations (65), Referenced by (4), Classifications (18), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetMethod and apparatus for improving the efficiency and accuracy of RFID systemsUS 7456726 B2Abstract A method and apparatus for transmitting a narrow signal beam are disclosed that allow the precise location of RFID tags to be determined and reduce tag collisions. Also disclosed are a method and apparatus for improving the efficiency of RFID systems.
CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 60/550,355, filed Mar. 5, 2004, U.S. Provisional Application No. 60/550,411, filed Mar. 5, 2004, U.S. Provisional Application No. 60/561,433, filed Apr. 12, 2004, U.S. Provisional Application No. 60/603,531, filed Aug. 20, 2004, and U.S. Provisional Application No. 60/613,428, filed Sep. 27, 2004, each of which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION Radio Frequency Identification (�RFID�) is a generic term for technologies that use radio waves to automatically identify individual items. Objects can be identified using RFID by storing a serial number that identifies the object on a chip that is attached to an antenna. The chip and the antenna together are called an RFID tag. An RFID reader sends out electromagnetic waves that are received by the antenna on the RFID tag. Passive RFID tags draw power from this electromagnetic field to power the chip. Active tags use their own batteries to power the chip. The tag responds to the reader by transmitting a bit stream to the reader that contains information about the tag (serial number, etc.). The current state of RFID technology is described by [1] K. Finkenzeller in �RFID Handbook� (John Wiley & Sons, 2003).
The RFID reader's efficiency is related to its coverage or �accuracy,� which is measured by the percentage of tags within range that are read correctly. The accuracy of today's readers is not acceptable for many applications, which require 100 percent accuracy. For example, a study published in the article �Smart Tags for Your Supply Chain,� McKinsey Quarterly, 2003, Number 4, found that RFID-tagged pallets failed 3 percent of the time even when double-tagged, and only 78 percent of the individually tagged pallets were read accurately.
According to the article �RFID will present a stiff test,� published in Supply Chain Management Review, Jan. 15, 2004, the main cause of low reader accuracy is the inability of readers to transmit enough power to activate tags that are surrounded by other objects such as tags affixed to items stored in the middle of a pallet. The article reports that ad hoc repositioning of the RFID tags or increasing reader power can often fix this problem.
The problem of reader collisions is another barrier to the large-scale deployment of RFID. Reader collisions can occur when the interrogation zones of two or more readers overlap. In the article �Why UHF RFID Systems Won't Scale,� RFID Journal, July 2004, H. L. van Eeden states that �The main technical problem facing end-user companies is the possibility of large-scale reader interference that could render UHF RFID installations completely inoperable and severely limit the rollout of UHF RFID systems.�
The following five U.S. Provisional Applications describe RFID readers that transmit data signals that cause the tags to respond and scramble signals that do not cause the tags to respond: [2] �Method and apparatus for secure transmission of data using array,� U.S. Provisional Application No. 60/550,355, filed Mar. 5, 2004, [3] �Method and apparatus for preventing unauthorized transmitters from gaining access to a wireless network,� U.S. Provisional Application No. 60/550,411, filed Mar. 5, 2004, [4] �Method and apparatus for precise location of RFID tags,� U.S. Provisional Application No. 60/561,433, filed Apr. 12, 2004, [5] �Optically guided reader of RFID tags,� U.S. Provisional Application No. 60/603,531, filed Aug. 20, 2004, and [6] �Method and apparatus for improving the efficiency of RFID systems,� U.S. Provisional Applications No. 60/613,428, filed Sep. 27, 2004. These five provisional applications are incorporated herein by reference in their entirety.
BRIEF SUMMARY OF THE INVENTION The present invention is directed to a method for interrogating RFID tags comprising transmitting a data beam that causes the tags to respond, transmitting one or more scramble beams that do not cause the tags to respond, and adjusting the data beam and the scramble beams such that the scramble beams overshadow the data beam in all but selected regions. A tag can respond to the data signal either by broadcasting or changing its stored information. A scramble beam can contain a separate intelligible data stream and can charge tags that are not being interrogated.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an 18-element linear array.
DETAILED DESCRIPTION OF THE INVENTION The present invention provides (a) designs for RFID readers, (b) a method for reducing the width of the interrogation region, (c) a method for providing a user defined interrogation zone for one or more readers, (d) a method for location of transceivers in 2D and 3D using more than one information-steering transmitter, (e) a method for precise tag location that works in the induction regime where the wavelength is much longer than the physical dimensions involved, (f) a new set of security measures for RFID systems, (g) a method for optically displaying the interrogation zone, (h) a method for overcoming multipath effects, (i) a method for optimal tag placement, and (j) a bistatic RFID reader. A common feature in items (a)-(f) is that two or more signals are transmitted simultaneously, including:
1. A data signal that causes the tags to respond. The data signal may instruct the tags to broadcast or modify stored information. The data signal may contain information about scan angles that the tags can retransmit back to the reader. Also, the data signal may employ any of the methods developed to solve the problem of tag collision that occurs when two or more tags transmit simultaneously [1, Chapter 7]. 2. One or more scramble signals that do not cause the tags to respond. The tags neither broadcast nor modify their stored information. A pure sine wave works as a scramble signal for UHF tags. The scramble signals can be used to charge the tags and to convey a separate intelligible information stream. The scramble signal can also be referred to as a guard signal. A reader is said to employ information steering when it transmits both data and scramble signals. The present invention makes extensive use of antenna arrays. The following references describe the theory and design of phased arrays: R. C. Hansen, �Phased Array Antennas,� John Wiley & Sons, 1998; R. J. Mailloux, �Phased Array Antenna Handbook,� Artech House, 1994; and, R. S. Elliot, �Antenna Theory and Design,� IEEE Press, 2003. With adaptive phased arrays, also known as smart antennas, the received signals and environmental parameters are fed to powerful processors that steer the beams to optimize performance. The technology for designing and constructing adaptive phased arrays with hundreds of elements that produce prescribed sum and difference patterns has reached a mature stage, as described in the following references: M. I. Skolnik, �Radar Handbook,� McGraw-Hill, 1990, 2nd edition; R. T. Compton, �Adaptive Antennas,� Prentice-Hall, 1998; and, G. V. Tsoulos, ed. �Adaptive Antennas for Wireless Communications,� IEEE Press, 2001.
Linear Arrays FIG. 1 is a graph of a linear array with 18 elements having element spacing of half of a wavelength. The data time signal is represented by a(t), which depends on the chosen modulation and coding techniques, and on the transfer functions of the antenna elements. The present invention works for any modulation and coding techniques and for any set of array elements.
Planar Arrays The present invention may also be used with planar arrays such as the 324-element array (18 elements by 18 elements) shown in FIG. 5. The element spacing is half a wavelength. FIG. 6 shows a typical set of sum excitation coefficients, and FIG. 7 shows the corresponding array sum pattern. The array pattern is almost independent of φ and has a main beam in the broadside direction. Standard methods, as previously noted, can be used to steer the beam in any desired direction.
The excitation coefficients for both the sum and difference patterns for the planar array may be obtained with semi-analytical methods to achieve prescribed side lobe levels and main beam widths. Alternatively, the coefficients may be obtained with nonlinear optimization techniques. The coefficients as shown in FIGS. 6 and 8 are obtained with the MATLAB� function FMINUNC, which minimizes a user-defined cost function. The cost function is designed to ensure that the side lobes are below a certain level for all φ.
Other Antennas User defined interrogation zones in accordance with the present invention may also be achieved with arrays that are neither linear nor planar. For example, the circular ring array shown in FIG. 10 is useful for providing 360� coverage. For ring arrays, the interrogation zones can be obtained with sum and difference patterns obtained from standard theory. Similar interrogation zones can be realized with reflector antennas as shown in FIG. 11 by applying the present invention to its feed, which is typically a smaller antenna located at the focal point. More generally, one may use the present invention for any antenna type to obtain sum and difference patterns that can be combined to achieve the desired interrogation zones.
For purposes of illustration, the examples herein are confined to sum and difference patterns because such patterns have been studied extensively in the radar literature. Interrogation zones in accordance with the present invention can be achieved, however, with any combination of array patterns in which one of the patterns (the �difference pattern�) has a null in the direction of the tags of interest and is larger in magnitude than the other pattern (the �sum pattern�) in directions where other tags may be present.
A Four-Element Reader Consider a four-element tag reader operating at frequencies around 900 MHz. (RFID systems are allowed to operate at 915 MHz in the United States and at 869 MHz in Europe.) FIG. 12 shows a four-element array for a hand-held tag reader operating around 900 MHz, with element spacing=10 cm and total array length=30 cm. The tags to be interrogated are near the (θ,φ)=(90�, 90�) direction. As in [2], one feeds element #p with a signal of the form:
A Method for Reducing the Width of the Data Beam The width of the angular region of the data signal is reduced by dividing the data signal bits into two parts: the first part and the second part. The first part is transmitted while the scramble beam has its central null steered slightly to one side of the direction of the data beam. The second part of the data signal is transmitted while the scramble beam has its central null steered slightly to the other side of the direction of the data beam. The division of the data signal must be such that a tag responds only if it receives both the first and second part of the data signal.
A Constant-Level Scramble Beam A reader can be designed such that its radiated power is omni-directional while its data signal stays highly directional. Consider the 8-element array in FIG. 16 that consists of z-directed dipoles and operates at 2.4 GHz, with element spacing=6.25 cm and the total array length=50 cm. The tags to be interrogated are near the (θ, φ=(90�, 90�) direction.
Typical data and scramble beams for this array are shown in FIG. 17. All the zeros of the scramble beam, except the central one at φ=90�, are moved radially off the Shelkunoff unit circle to points on a circle in the complex plane of radius 1.06. (The theory related to the Shelkunoff unit circle is described in the book �Antenna Theory and Design� by R. S. Elliot, IEEE Press, 2003.) As a result, the scramble beam has only one null (the central one) and stays above the data beam everywhere else. Notice that the scramble beam �follows� the data beam closely, so that the power of the scramble beam is extremely low away from a 60� angular region centered on φ=90�. Hence, the reader provides little energy to charge or communicate with the tags that are located outside this 60� angular region.
Scanning Array Readers that Employ Triangulation This section describes the method of the present invention for determining the precise location of tags. The method may be explained with reference to FIG. 19 where the tags are located inside a room with two array readers placed on the walls. The array readers transmit narrow signal beams surrounded by scramble beams as described above. The beams are scanned using standard beam steering.
Inductive RFID Systems Inductive RFID systems operate at frequencies below 50 MHz, where the wavelength is much longer than the physical dimensions involved, and the reader and tags are inductively coupled. Precise tag location and user-defined interrogation regions can be achieved with inductive RFID systems as described below.
The reader employs two small loops that lie in the x-y plane with their center points 10 cm apart. The spatial dependence of the magnetic fields emitted by such loops can be approximated well by the spatial dependence of the magnetic fields of z-directed static magnetic dipoles, as described in the reference �Plane-wave theory of time-domain fields� by T. B. Hansen and A. D. Yaghjian, IEEE Press, 1999.
RFID Security According to [1, Chapter 8], high-security RFID systems should have defense mechanisms against the following three types of attacks: (1) Unauthorized reading of a data carrier in order to duplicate and/or modify data. (2) The placing of a foreign data carrier within the interrogation zone of a reader with the intention of gaining access to a building or receiving services without payment. (3) Eavesdropping into radio communications and replaying the data in order to imitate a genuine data carrier (�replay and fraud�).
Method for Optically Displaying Interrogation Zones This section describes a method for optically displaying the interrogation zone of an RFID reader. The reader interrogates only tags located in the interrogation zone.
A Two Element Reader FIG. 24 shows a compact RFID reader design that employs a two-element antenna array, as described in [6]. The antenna elements can be of any type suitable for broadcasting at the RFID frequencies. The array elements can be tilted independently with respect to the array axis. FIG. 25 shows the schematic of RF control electronics for the two-element array. Each antenna element is driven by a linear combination of two RF signals: a data and a scramble signal. The beam patterns for each signal are determined by the weighting coefficients A1, A2, B1, and B2. Phase shifts (time delays) can be used to steer the beam patterns in a specific direction. To achieve a difference pattern for the scramble signal, one can set B1=−B2.
FIG. 26 shows the free-space field distributions in the x-y plane when the array elements are patch antennas with (1+cos(v)) patterns, where v is the angle between the element normal and the observation point in the x-y plane, displaying the strength of the data beam (Left) and the scramble beam (Right). (See R. J. Mailloux, �Phased Array Antenna Handbook,� Artech House, 1994, Chapter 4.) The elements are located at (x, y, z)=(2 m, 8.3 cm, 0) and (x, y, z)=(2 m, −8.3 cm, 0), with element normals pointing in the x direction. The antennas operate at 900 MHz with weighting coefficients A1=A2=B1=−B2=1. All time delays are zero so the beams point in the broadside direction.
A Three-Element Reader A standard commercially available reader can be augmented to achieve a narrow well-defined interrogation zone. The standard reader employs one antenna that broadcasts a single interrogation beam. From the discussion that follows, it is straightforward to augment standard readers that employ multiple antennas.
Using Multiple Sets of Excitation Coefficients to Overcome Multipath Effects In indoor environments, signals bounce off walls and other objects, so the field at a given observation point is the sum of signals that have traveled through different paths. In some areas the multipath field components can sum to produce a total field that is too weak to communicate with a tag. Further, one must consider areas of low field strength in the scramble signal, which cause the data signal to �leak� out into unintended regions.
Creating Well-Defined Interrogation Zones and Preventing Reader Collisions This section considers a network of readers and shows how to prevent interference and collisions between readers, as described in [6]. FIG. 38 shows two readers that are located in a room with a concrete wall, floor, and ceiling. The readers interrogate tags placed on items that move on two conveyer belts. Each reader uses the two-element array of patch antennas illustrated in FIGS. 24 and 25. The readers are in close proximity of each other and the concrete wall. Concrete is modeled by a homogeneous medium with a relative permittivity of 6 and a conductivity of 0.1 S/m. The field distributions are computed from geometrical optics with one bounce off each surface included. Polarization, reflection coefficients, and geometrical spreading are included in these calculations (this simulation and the other simulations are included simply for purposes of illustration; a different calculation of the field can be used in any given configuration to determine the fields to whatever order is needed). The power levels are adjusted so that when a reader operates in free space the data signal is just strong enough to set off tags 10 m away from the reader in the main-beam direction, as shown in FIG. 27.
More generally, one can set up a reader network with unknown parameters (array excitation coefficients, reader locations, and reader orientations) and optimize the parameters to create desired interrogation zones in a given environment. The optimization can be carried out by interactive methods that minimize a user-defined cost function (see, for example, P. Venkataraman, �Applied Optimization with MATLAB Programming,� Wiley, 2001). This approach is equivalent to an inverse source problem where the task is to determine the strength and location of sources that result in a desired field distribution.
One type of solution would determine the optimal source distribution (excitation coefficients) to maximize the signal from a tag placed on a particular object using the techniques described in the paper by David Isaacson entitled �Distinguishability of Conductivities by Electric Current Computed Tomography� (IEEE Trans. on Medical Imaging, Vol. MI-5, No. 2, 91-95, 1986).
Optimum Tag Placement Numerous studies have demonstrated the difficulty of reading tags accurately, especially when other objects shield the tags from the interrogation signal (see, for example, �RFID will present a stiff test,� Supply Chain Management Review, Jan. 15, 2004). This section describes a systematic method for determining the optimal tag placement that will maximize the scattered field from the tags. The method involves the following steps:
(2) Numerically determine the total electric field for the scattering problem in which the field of the reader illuminates the model. For the soda bottles on the pallet, a finite-difference time-domain method would be suitable for determining the total electric field everywhere (A. Taflove and S. Hagness, �Computational Electrodynamics: The Finite-Difference Time-Domain Method,� Artech House, 2nd Ed., 2000). High-frequency methods (A. K. Bhattacharyya, �High-Frequency Electromagnetic Techniques,� John Wiley & Sons, 1995) and exact solutions (W. C. Chew, �Waves and Fields in Inhomogeneous Media,� IEEE Press, 1995) are also useful for solving the scattering problems.
Bistatic RFID Reader Configuration A bistatic reader configuration is shown in FIG. 49 where the transmitter and receiver are not collocated. FIG. 49 shows a bistatic RFID reader consisting of a transmitter and a receiver that interrogates a collection of tags that are placed on items in a box. The difference field in FIG. 47 attains its maximum values at locations that are approximately 90� away from the transmitting antenna of the reader. Hence, if the receiving antenna of the reader were placed 90� away from the transmitting antenna, the reader would more effectively interrogate the tag in this configuration where the tag is on the side of the cylinder. Moreover, by separating the transmitter from the receiver, the direct coupling is significantly reduced and the read range is no longer limited by the condition that the tag signal may be no more than 100 dB below the level of the transmitters carrier signal. (See page 145 of reference [1] cited above for a discussion of the 100 dB condition.)
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(abstract).17(No author), "Harris Corporation Awarded $ 13.6 Million Contract by Raytheon for U.S. Navy's DD-X-Phased Array Antenna Program," Newswire, pp. 5391, May 20, 2003. (abstract).18(No author), "Hughes Network Systems Europe Signs Value-added Reseller Agreement With Excelerate Technology Limited; Excelerate Will Market Satellite-Based VPN Service to UK & European Enterprises," Newswire, Sep. 16, 2003. (abstract).19(No author), "Infineon Enhances Leadership Position in Optical Communications, Adds XFP Modules to Expand 'Single-Source' 10 Gbps Portfolio," Newswire, p. 5454, Mar. 10, 2003. (abstract).20(No author), "Japan's T-Engine Forum and MontaVista Software Create Enhanced Ubiquitous Computing Platform," Newswire, pp. 5634, Mar. 18, 2003. (abstract).21(No author), "L-3 Communications Acquires Aeromet, Inc.," Newswire, pp. 5204, Jun. 12, 2003. 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(abstract).Referenced byCiting PatentFiling datePublication dateApplicantTitleUS8421631 *Mar 31, 2008Apr 16, 2013Rf Controls, LlcRadio frequency signal acquisition and source location systemUS20070096909 *Jun 5, 2006May 3, 2007Matthew LallyInteractive networking deviceUS20100225480 *Mar 31, 2008Sep 9, 2010Rf Controls, LlcRadio frequency signal acquisition and source location systemUS20120098644 *Oct 21, 2011Apr 26, 2012Electronics And Telecommunications Research InstituteMethod and apparatus for visualizing recognition area of rfid* Cited by examinerClassifications U.S. Classification340/10.2, 340/10.34, 340/10.3, 340/572.1International ClassificationG06K7/10, H04Q5/22, H04K3/00, G06K7/00Cooperative ClassificationH04K2203/32, H04K3/43, H04K3/825, G06K7/10079, H04K2203/20, G06K7/0008European ClassificationH04K3/82B, H04K3/43, G06K7/10A1E, G06K7/00ELegal EventsDateCodeEventDescriptionMay 13, 2012FPAYFee paymentYear of fee payment: 4Jun 13, 2005ASAssignmentOwner name: SEKNION, INC., CONNECTICUTFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HANSEN, THORKILD;ORISTAGLIO, MICHAEL L.;REEL/FRAME:016326/0424Effective date: 20050427RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google