Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-09-08
2002-03-26
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572700, C340S568100, C340S010100, C340S010510
Reexamination Certificate
active
06362738
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to Radio Frequency Identification (RFID) technology, and more particularly relates to contactless programmable electrostatic RFID technology.
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation in part of a prior U.S. patent application Ser. No. 09/061,146, filed Apr. 16, 1998 by inventors Ted Geiszler et al, Attorney Docket No. IND00701P01, entitled “REMOTELY POWERED ELECTRONIC TAG WITH PLURAL ELECTROSTATIC ANTENNAS AND ASSOCIATED EXCITER/READER AND RELATED METHOD; RADIO FREQUENCY IDENTIFICATION TAG SYSTEM USING TAGS ARRANGED FOR COUPLING TO GROUND; RADIO FREQUENCY IDENTIFICATION TAG ARRANGED FOR MAGNETICALLY STORING TAG STATE INFORMATION; AND RADIO FREQUENCY IDENTIFICATION TAG WITH A PROGRAMMABLE CIRCUIT STATE” and assigned to Motorola, Inc. the disclosure of which prior application is hereby incorporated by reference, verbatim and with the same effect as though it were fully and completely set forth herein.
BACKGROUND OF THE INVENTION
Radio Frequency Identification (RFID) technology allows identification data to be transferred remotely which provides a significant advantage in identifying persons, articles, parcels, and others. In general, to access identification data stored in a RFID transponder (a.k.a. a tag) remotely, a RFID reader/encoder generates an energy field to activate the RFID transponder and subsequently to retrieve data stored in the transponder unit from a distance. The data retrieved is then processed by a host computer system to identify the person or article that is associated with the transponder. While a transponder that derives its power from the energy field is known as a passive transponder, a transponder that has its own power source is known as an active transponder. RFID technology has found a wide range of applications including tracking, access control, theft prevention, security, etc.
For some applications, RFID technology is more preferable than magnetic strip technology, which also finds applications in a few of the areas above. The reason is systems employing RFID technology can store a lot more information than magnetic strip technology. Magnetic strip technology as commonly deployed has very limited memory capability. Moreover, magnetic strip technology requires relatively high maintenance (e.g., heads cleaning). Furthermore, magnetic strip technology is prone to moisture damages, dust damages, magnetic field damages, etc.
RFID technology should be distinguished from Radio ID technology which uses ordinary radio waves, or more precisely far field electromagnetic (EM) waves which are also known as radiation waves. Far field means the distance between the transceiver and transponder is great compared to the wavelength of the EM carrier signal used. An example of Radio ID technology is the Identify Friend or Foe (IFF) systems used with military aircraft. Far field EM waves have a field strength that varies inversely with the distance involved.
In contrast, conventional RFID technology is based upon inductive coupling utilizing magnetic field waves. Conventional RFID technology operates in the near field where the operating distance is far less than one wavelength of the EM field. Unlike far field radio waves, the magnetic field strength is approximately proportional to the inverse cube of the distance from the source. In inductance-based RFID technology, an electromagnetic field is generated for use both as a power source for the transponder and for transferring data and clock information between the reader/encoder and transponder. Magnetic fields are generated by causing RF alternating current to flow in coils that typically have multiple turns. However, it is often difficult to integrate the coils in an integrated circuit. Generally, these coils are required to be wire wound or etched metal. This requirement adversely impacts the costs, manufacturability, and packaging flexibility of inductance-based RFID technology. Due to the prohibitive costs and high degree of manufacturing difficulty, electromagnetic RFID technology is not practical in high volume/low cost disposable applications. The bulky packaging, which is typical for electromagnetic RFID technology, further limits its application to those where thickness is not of primary importance.
In general, an Electronic Article Surveillance. (EAS) system is designed to prevent article thefts and is widely used in retail stores as well as libraries. An EAS system is typically implemented using magnetic strip technology wherein a magnetic strip is inserted into or attached to an article. Operationally, an EAS reader/detector constantly transmits a RF activation signal. When the magnetic strip receives the RF activation signal, it becomes activated and sends back the stored information. Accordingly, unless the magnetic strip has been removed from the article or deactivated by the attendant, it triggers the reader/detector to sound an alarm, which alerts the attendant of a potential theft. In designing an EAS system, operating range and responsiveness (i.e., read time) are the two primary considerations. Operating range is important to accommodate the vast differences in sizes of parcels, baggage, etc. Operating responsiveness is important because a person attempting to illegally remove an article from a secured area will not likely pause when passing through the sensing area of the surveillance system to allow the EAS system time to read the surveillance tag. While magnetic strip based EAS systems provide adequate read time and operating range, the stored authorization information can be erased if the magnetic strip is subject to external magnetic fields. Hence, magnetic strip based EAS systems are limited in their applications. Conventional RFID systems are too expensive, bulky, and limited in operating range to be used in EAS applications. Moreover, conventional RFID systems generally have a relatively low Quality (hereinafter ‘Q’) factor (e.g., in the 10's) and therefore low detection sensitivity. Accordingly, conventional RFID systems are currently not suitable for EAS applications. Furthermore, due to the amount of data information transfer involved, the read time of conventional RFID systems is also not suitable for EAS applications.
Thus, a need exists for a RFID apparatus, system, and method having the operating range, responsiveness, robustness, and sensitivity required for EAS applications that is also inexpensive, compact, and easy to implement.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides an apparatus, system, and method having the operating range, responsiveness, robustness, and sensitivity required for EAS applications that is also inexpensive, compact, and easy to implement.
The present invention meets the above needs with an enhanced range combined Radio-Frequency Identification (RFID)/Electronic Article Surveillance (EAS) reader functioning as a base station. The reader is capable of contactless bidirectional data transfer based on radio-frequency electrostatic fields rather than on electromagnetic fields for a substantial cost advantage. The reader generates an electrostatic field between two pads, called “electrodes”, for transmission of write/read signals to the transponder. The transponder receives the write/read signal and transmits back information via its two electrodes. This invention can be used for theft prevention as an additional benefit of an RFID system already installed for merchandising. The reader includes a detector circuit for detecting the presence of a signal carrier frequency transmitted by the transponder in response to a signal from the reader. The detector circuit comprises a piezoelectric resonator circuit which is coupled to a receiver electrode. The piezoelectric resonator circuit is employed for its high sensitivity characteristics due to its high quality factor ‘Q’ at resonance. The high sensitivity is used to detect EAS transponder signals thereby setting an alarm. In an alternate embodiment, the reader also includes the ability to write to or read elec
Hughes Terri S.
Motorola Inc.
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