Radio-frequency identification device with foam substrate
AssigneeUniversity of Kansas
InventorDaniel D. Deavours
Life of this patent
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Abstract
The present invention encompasses an antenna (12) for use with a radio-frequency identification transponder (10) that performs optimally in free space and near optimally when near a conductive surface. The radio-frequency identification transponder (10) broadly comprises an antenna (12); an integrated circuit (14); a matching circuit (16) interposed between the antenna (12) and integrated circuit (14); and a substrate (18). The antenna (12) is designed with a length so the antenna (12) as a microstrip resonates at a starting frequency and a matching circuit is constructed. The antenna (12) is placed near a conductive surface and the length of the antenna is adjusted until the antenna reactance is approximately the opposite of the integrated circuit reactance.
Claims21
A radio-frequency identification transponder comprising:
- an antenna;
- an integrated circuit;
- a matching circuit interposed between the antenna and the integrated circuit;
- and
- a substrate underlying the antenna, integrated circuit, and matching circuit,
- wherein
- the antenna behaves optimally as a dipole antenna when the transponder is operating in free space, and
- the antenna behaves near optimally as a microstrip antenna when the transponder is placed near a conductive surface.
An antenna for use with a radio-frequency identification transponder, wherein a maximum power transfer efficiency of the antenna is at least 95% when the transponder is operating in free space and at least 5% when the transponder is placed near a conductive surface.
A method for making an antenna for use with a radio-frequency identification transponder, the method comprising the steps of:
- (a) determining acceptance criteria based on the directivity, efficiency, and power transfer efficiency
- (b) using numerical simulation to estimate performance of an antenna in free space
- (c) evaluating antennas for acceptable results in free space based on acceptance criteria
- (d) simulating antennas identified in step (c) near a conductive surface
- (e) selecting antennas achieving acceptable results near a conductive surface based on the acceptance criteria
- (f) if no antennas achieve acceptable results near a conductive surface based on the acceptance criteria, relaxing one of the variables of the acceptance criteria and repeating steps (a) through (e) until an acceptable antenna is found.
A system for identification comprising a radio-frequency identification transponder, the radio-frequency identification transponder including:
- an antenna;
- an integrated circuit, and
- wherein the impedance of the antenna is substantially similar to the impedance of the integrated circuit when the transponder is in free space or placed near a conductive surface.
A radio-frequency identification transponder, comprising
- an integrated circuit;
- and
- an antenna, wherein the antenna is operable to present an impedance substantially similar to the conjugate impedance of the integrated circuit when the radio-frequency identification transponder is operating in free space or when placed near a conductive surface.
A radio-frequency identification transponder, comprising
- an integrated circuit;
- and an antenna, wherein the antenna is operable to present an impedance within approximately 50% of the conjugate impedance of the integrated circuit when the radio-frequency identification transponder is operating in free space or when placed near a conductive surface.
A radio-frequency identification transponder comprising:
- antenna;
- an integrated circuit;
- and a read range of at least approximately 20 feet when the transponder is placed near a conductive surface and at least approximately 20 feet when the transponder is in free space.
A method for making an antenna for use with a radio-frequency identification transponder operable near a conductive surface or in free space, the method comprising the steps of:
- (a) designing an antenna with a length so the antenna as a microstrip resonates at a first frequency;
- (b) constructing a matching circuit so the antenna operates efficiently in free space;
- (c) placing the antenna near a conductive surface and observing impedance
- (d) if the reactance is too small at a second frequency, adjusting the length of the antenna until the desired reactance is observed
- (e) modifying the matching circuit to provide an optimal impedance in free space
- (f) placing the antenna near a conductive surface and observing the reactance
- (g) adjusting the length of the antenna to achieve the desired reactance as a microstrip
- (h) repeating steps (a) through (g) until the desired free-space performance and the desired reactance as a microstrip is achieved.
Dependencies are inferred from the claim text.