Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-04-24
2001-12-11
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572400, C340S572700, C340S572800, C343S873000, C343S91100R, C343S7000MS
Reexamination Certificate
active
06329915
ABSTRACT:
FIELD OF THE INVENTION
The field of the invention is the field of Radio Frequency (RF) transponders (RF Tags) which receive RF electromagnetic radiation from a base station and send information to the base station by modulating the load of an RF antenna.
RELATED PATENTS AND APPLICATIONS
Related U.S. Patents assigned to the assignee of the present invention include: U.S. Pat. Nos. 5,521,601; 5,528,222; 5,538,803; 5,550.547; 5,552,778; 5,554,974; 5,563,583; 5,565,847; 5,606,323; 5,635,693; 5,673,037; 5,680,106;5,682,143; 5,729,201; 5,729,697;5,736,929; 5,739,754; 5,767,789; 5,777,561; 5,786,626; 5,812,065; and 5,821,859. U.S. Patent applications assigned to the assignee of the present invention include: application No. 08/626,820, filed: Apr. 3, 1996, entitled “Method of Transporting RF Power to Energize Radio Frequency Transponders”, by Heinrich, Zai, et al.; application Ser. No. 08/694,606 filed Aug. 9, 1996 entitled RFID System with Write Broadcast Capability by Cesar et al. ; application Ser. No. 08/681,741 filed Jul. 29, 1996 entitled RFID Transponder with Electronic Circuitry Enabling and Disabling Capability, by Heinrich, Goldman et al.; and application Ser. No. 09/153,617 , filed Sep. 15, 1998, entitled RFID Interrogator Signal Processing System for Reading Moving Transponder, by Zai et al. The above identified U.S. Patents and U.S. Patent applications are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
RF Tags can be used in a multiplicity of ways for locating and identifying accompanying objects, items, animals, and people, whether these objects, items, animals, and people are stationary or mobile, and transmitting information about the state of the of the objects, items, animals, and people. It has been known since the early 60's in U.S. Pat. No. 3,098,971 by R. M. Richardson, that electronic components on a transponder could be powered by radio frequency (RF) power sent by a “base station” at a carrier frequency and received by an antenna on the tag. The signal picked up by the tag antenna induces an alternating current in the antenna which can be rectified by an RF diode and the rectified current can be used for a power supply for the electronic components. The tag antenna loading is changed by something that was to be measured, for example a microphone resistance in the cited patent. The oscillating current induced in the tag antenna from the incoming RF energy would thus be changed, and the change in the oscillating current led to a change in the RF power radiated from the tag antenna. This change in the radiated power from the tag antenna could be picked up by the base station antenna and thus the microphone would in effect broadcast power without itself having a self contained power supply. In the cited patent, the antenna current also oscillates at a harmonic of the carrier frequency because the diode current contains a doubled frequency component, and this frequency can be picked up and sorted out from the carrier frequency much more easily than if it were merely reflected. Since this type of tag carries no power supply of its own, it is called a “passive” tag to distinguish it from an active tag containing a battery. The battery supplies energy to run the active tag electronics, but not to broadcast the information from the tag antenna. An active tag also changes the loading on the tag antenna for the purpose of transmitting information to the base station.
The “rebroadcast” or “reflection” of the incoming RF energy at the carrier frequency is conventionally called “back scattering”, even though the tag broadcasts the energy in a pattern determined solely by the tag antenna and most of the energy may not be directed “back” to the transmitting antenna.
In the 70's, suggestions to use tags with logic and read/write memories were made. In this way, the tag could not only be used to measure some characteristic, for example the temperature of an animal in U.S. Pat. No. 4,075,632 to Baldwin et. al., but could also identify the animal. The antenna load was changed by use of a transistor. A transistor switch also changed the loading of the transponder in U.S. Pat. No. 4,786,907 by A. Koelle.
Prior art tags have used electronic logic and memory circuits and receiver circuits and modulator circuits for receiving information from the base station and for sending information from the tag to the base station.
The continuing march of semiconductor technology to smaller, faster, and less power hungry has allowed enormous increases of function and enormous drop of cost of such tags. Presently available research and development technology will also allow new function and different products in communications technology.
The physical size of radio frequency (RF) transponders is set by the size of the antenna used to pick up the RF signal from a base station when the antenna is “resonant” with the sent out signals. Resonant antennas are much more efficient than non resonant antennas in communicating between a base station and an RF tag.
An RF transponder placed on an RF conducting or absorbing object must in general be placed so that the antenna of the RF tag is separated from the conducting or absorbing material surface by from 1/10 to 1/4 wavelength of the RF energy. For example, at 2.45 Ghz, the wavelength of the RF waves is 12 cm in air. If the RF tag is separated from the surface by air, this means it must be 1.2 to 3 cm from the surface, and the usefulness of the transponder is limited.
A significant cost of an RF transponder is the connection of antennas to the semiconductor device which contains the non-volatile memory, logic, and RF circuitry necessary to communicate with a base station.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an RF tag which may be placed in close proximity to a surface of a conducting or absorbing material.
It is an object of the invention to provide an RF tag having minimum dimensions.
It is an object of the invention to provide an RF tag having minimum cost.
SUMMARY OF THE INVENTION
The RF transponder of the invention uses a high dielectric constant material in cooperation with the tag antenna to reduce the distance of the antenna from a surface which is conducting or absorbing of the RF radiation.
The RF transponder of the invention uses a high dielectric constant material in cooperation with the tag antenna to reduce the dimensions of the tag antenna.
In particular, the innovative RF transponder of the invention uses a high dielectric constant material in cooperation with the tag antenna to reduce the dimensions of the tag antenna so that the antenna is no larger than the semiconductor device containing the tag electronics. In this way, the entire tag may be produced on a normal semiconductor production line using lithographic techniques well known in the art for forming metal lines and features, and connecting such metal lines and features to the semiconductor material or underlying metal features. In this way, the separate step of producing an antenna and bonding the antenna to the chip when the chip has been sawn from the wafer is avoided.
The transponder package may be sealed, e.g. encapsulated within ceramics.
In an illustrative embodiment the new RF tag includes a patch antenna connected through a three-section impedance matching circuit to an input of an RF tag integrated circuit (IC). The patch antenna, matching circuit, and RF tag IC are all affixed to one side of a dielectric substrate so that the packaged tag can receive a conductive surface at the opposite side of the substrate. The RF tag package may be coupled to an external conductive surface, not through a via, but through a quarter wave transformer which operates as an RF short to the external conductive surface.
Any device which may change the transponder antenna loading to modulate the tag backscatter is anticipated by the inventors. These include, but are not limited to, devices to measure temperature, pressure, velocity, acceleration, orientation, direction of travel, position, sound, light, chemical constitution, and or th
Afzali-Ardakani Ali
Brady Michael J.
Duan Dah-Weih
Duncombe Peter R.
Field Christopher A.
Hodgson Rodney T.
Intermec IP Corp
Pham Toan
Wu Daniel J.
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