Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-03-13
2001-03-20
Wu, Daniel J. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572200, C340S572400, C340S870030, C340S870030, C342S042000, C342S114000
Reexamination Certificate
active
06204765
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.
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. 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.
Prior art tags have been used to measure the relative direction and motion between a tag and a base station. For example, U.S. Pat. No 4,728,955 uses multiple base station antennas to measure tag motion, and U.S. Pat. 5,510,795 uses a base station with a single antenna and a phase sensitive detection system to measure relative location and speed of the tag with respect to the base station. However, these systems are best used when the relative velocity is constant and the direction is known, as for a train moving on tracks or a package on a conveyer belt.
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.
RELATED PATENTS AND APPLICATIONS
Related U.S. Patents assigned to the assignee of the present invention include: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 Ser. No. 08/626,820, filed: Apr. 3, 1996 “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.
OBJECTS OF THE INVENTION
It is an object of the invention to produce an RF transponder comprising circuits which can be made at low cost. It is a further object of the invention to produce an RF transponder which can be used at high frequencies. It is a further object of the invention to produce an RF transponder with maximum range. It is a further object of the invention to produce an RF transponder with circuits which require very little current. It is a further object of the invention to produce an electronic chip for an RF transponder which can be produced simply with standard semiconductor manufacturing techniques. It is a further object of the invention to provide an RF transponder which may determine the relative direction of motion between the transponder and a base station. It is an object of the invention to produce a method of determining the relative velocity of motion between a base station and an RF transponder.
SUMMARY OF THE INVENTION
The present invention is a system, apparatus and method to use known characteristics of the RF field produced by a base station to determine the relative motion between the base station and an RF tag. A property of the RF field produced by the base station is determined at the position of the tag, and the rate of change of the property is used to determine whether the tag is approaching the base station or receding from the base station. If the RF field is asymmetric with respect to the base station, the direction of travel may be determined.
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Brady Michael J.
Martinez Rene D.
Moskowitz Paul A.
Hodgson Rodney T.
Inkrmec IP Corp.
Pham Toan
Wu Daniel J.
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