Gamma-Shielded Shorted Patch RFID Tag for Medical Use
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Solution Overview
Problem
RFID tags used in medical environments, particularly for implanted devices and surgical tools, face challenges due to radio frequency degradation from metal proximity and failure under gamma radiation sterilization, limiting read distances and practicality.
Innovation Solution
A small, passive wireless RFID transponder with a high dielectric substrate, shorted folded antenna structure, and a two-piece gamma-shielded enclosure using conductively bonded metallic materials to withstand gamma radiation and operate effectively near metals, enabling remote digital identification up to 15 feet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a small glass encapsulated RFID tag with onboard antenna is used, then the tag size is reduced, but the antenna suffers extreme radio frequency degradation and detuning due to metal proximity
Solution Approach 1:
A plastic encapsulant is introduced as an intermediary material between the RFID tag antenna and the metal object. This plastic encapsulant acts as a spacer that maintains a minimum distance (at least 0.6 mm) between the antenna and metal surface, preventing direct contact and reducing RF degradation while still allowing the tag to be mounted on or near metal objects.
Solution Approach 2:
The encapsulation structure is divided into multiple functional layers: a plastic encapsulant layer for spacing and protection, and a separate adhesive layer for mounting. This segmentation allows the spacing function to be independently optimized without affecting the mounting capability.
2Volume of moving object
If the RFID tag is placed in close proximity to metal for implantable devices, then the tag size can be reduced, but virtual contact must be maintained which makes communication with implanted devices impossible
Solution Approach 1:
The plastic encapsulant serves as a mediator that allows the tag to be positioned close to metal surfaces while maintaining the necessary RF isolation. This enables the tag to be small and mounted on implantable devices while still allowing reliable wireless communication without requiring virtual contact.
Solution Approach 2:
The minimum spacing distance is optimized to at least 0.6 mm, which is the critical parameter threshold that balances tag miniaturization with maintaining adequate RF performance and communication capability near metal surfaces.
3Ease of manufacture
If traditional RFID tags are used, then they can be manufactured with standard materials, but they suffer extreme degradation and failure when exposed to medical sterilization gamma dose rates
Solution Approach 1:
The tag encapsulation uses a composite structure combining plastic material (gamma-radiation resistant) with adhesive material (for mounting). The plastic encapsulant is specifically selected for its resistance to gamma radiation degradation, while the adhesive provides mounting capability. This composite approach allows the tag to withstand medical sterilization processes.
Solution Approach 2:
The adhesive layer is designed as a disposable component that remains on the tag after sterilization, eliminating the need to remove or replace the adhesive after gamma sterilization, simplifying the manufacturing and sterilization process.
4Object-affected harmful factors
If the ground plane is made thicker to improve gamma shielding, then the enclosure provides better gamma absorption, but the impedance matching may be affected
Solution Approach 1:
The ground plane thickness is optimized to at least 0.6 mm, which provides adequate gamma radiation shielding while maintaining proper impedance matching for RF operation. This thickness parameter balances the competing requirements of radiation protection and electrical performance.
Solution Approach 2:
The ground plane is made slightly thicker than the minimum required for gamma shielding, providing a margin of safety for radiation protection while the impedance matching is maintained through proper via placement and antenna design that compensates for the increased thickness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The RFID tag maintains functionality and read distances in metallic and non-metallic environments, withstands repeated gamma radiation sterilization, and minimizes size while ensuring high efficiency and reliability.
Implementation Method 1
The electrically insulating substrate material is comprised of a high dielectric and low loss tangent material that facilitates the drastic miniaturization and high efficiency operation of the device
Implementation Method 2
The unique design/construction of the RFID tag forms a heavily gamma shielded enclosure utilizing a two piece ground plane that is conductively bonded together to ensure complete enclosure of the RFID chip by a gamma absorbing metallic material
Implementation Method 3
The RFID tag of the present invention utilizes a shorted folded antenna structure that allows the antenna to resonate at 1⁄4 the wavelength of the frequency used for communicating with the RFID device
Implementation Method 4
The via is at a distance from the shorting wall whereby an impedance of the RFID circuit approximately matches an impedance of the antenna
Implementation Method 5
The incrementally lower impedance of the ground plane created by the overall thicker backplane, produces negligible performance difference as currents flow near the surface of the conductors at high operating frequencies ('skin effect')
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
An RFID tag includes a substrate made of a material with a high dielectric constant of greater than approximately 4 and having a first side and a second side. A patch antenna is mounted to the first side of the substrate. A metallic ground plane is mounted to the second side of the substrate, and includes a feed through hole. A metallic backplane is coupled with the ground plane, on a side of the ground plane opposite the substrate. The backplane and/or the ground plane includes a recess. An RFID circuit is positioned within the recess. A shorting wall includes a plurality of through holes extending through the substrate and interconnecting the antenna with the ground plane. The plurality of through holes are generally linearly arranged relative to each other along an edge of the ground plane. An electrically conductive via extends through the substrate and the feed through hole of the ground plane. The via has a diameter which is slightly less than the feed through hole. The via interconnects the antenna with the RFID circuit. The via is at a distance from the shorting wall whereby an impedance of the RFID circuit approximately matches an impedance of the antenna.