RFID Tag Antenna Using Electromagnetic Band Gap Substrate
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
RFID tags with dipole antennas often fail to function effectively when attached to conductive objects due to interference from the electromagnetic properties of these objects, which affect impedance, bandwidth, and radiation efficiency.
Innovation Solution
The use of an electromagnetic band gap substrate with a dipole antenna, which has a reflection phase different from 180° at the operating frequency, allowing the antenna to be positioned closer to conductive objects without destructive interference, and featuring a high impedance surface that insulates the tag and improves radiation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dipole antenna is used in an RFID tag, then the antenna can transmit and receive UHF signals, but the antenna does not work when attached to conductive objects due to destructive interference
Solution Approach 1:
The patent introduces an electromagnetic band gap (EBG) substrate as an intermediary layer between the dipole antenna and the conductive object. This EBG substrate modifies the reflection characteristics of the conductive surface, changing the reflection phase from 180° to a different value within the forbidden frequency band. This intermediary layer prevents destructive interference between the direct radiation from the antenna and the reflected radiation from the conductive object, thereby enabling the RFID tag to function reliably on conductive objects.
Solution Approach 2:
The patent changes the electromagnetic parameters of the substrate by using an electromagnetic band gap material with specific properties. The EBG substrate has a forbidden frequency band where surface waves cannot propagate, and within this band, the reflection phase is different from 180°. By operating the RFID tag within this forbidden frequency band, the patent achieves a reflection phase that prevents destructive interference, thus resolving the contradiction between antenna functionality and interference from conductive objects.
2Volume of moving object
If the antenna is placed closer to the substrate, then the tag design becomes more compact, but the radiation efficiency decreases due to destructive interference at 180° reflection phase
Solution Approach 1:
The patent changes the reflection phase parameter of the substrate from 180° to a different value by using electromagnetic band gap material. This parameter change allows the antenna to be placed closer to the substrate without suffering from destructive interference, as the reflected waves no longer cancel out the direct radiation. The EBG substrate creates a forbidden frequency band where the reflection phase is optimized for close proximity operation, enabling compact tag design while maintaining radiation efficiency.
3Adaptability or versatility
If the RFID tag is attached to conductive objects, then object tracking is enabled, but the electromagnetic properties of the objects strongly affect impedance, bandwidth and radiation efficiency
Solution Approach 1:
The patent uses the electromagnetic band gap substrate as a mediator that isolates the antenna from the adverse electromagnetic effects of conductive objects. The EBG substrate's unique property of having a different reflection phase (not 180°) within its forbidden frequency band allows it to prevent the strong interaction between the antenna and the conductive object. This intermediary layer stabilizes the impedance, maintains bandwidth, and preserves radiation efficiency, enabling reliable tracking of conductive objects despite their electromagnetic properties.
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
This configuration enables RFID tags to operate effectively on conductive objects by reducing interference, enhancing antenna performance, and allowing for slim tag designs with improved read ranges and impedance matching, even at close proximity to conductive surfaces.
Implementation Method 1
The electromagnetic band gap substrate has a reflection phase, which is different from 180° at the operation frequency of the antenna
Implementation Method 2
An electromagnetic band gap substrate is a substrate which exhibits a forbidden band gap at certain frequencies. At the forbidden frequencies, the surface wave can not transmit along the surface of electromagnetic band gap material and as a result the reflection phase from the surface of electromagnetic band gap material changes from 180° to −180° within the forbidden frequencies
Implementation Method 3
The electromagnetic band gap substrate may insulate the RFID tag from objects behind it and render the RFID tag less sensitive to such objects
Implementation Method 4
The reflection phase of the electromagnetic band gap substrate may thus improve the performance of antenna including antenna impedance and radiation efficiency
Data Source
AI summary
The present invention relates to an RFID Tag and Antenna for use with an RFID tag and a method of radio frequency identification (RFID). The RFID Tag comprises a RFID chip 5 for storing data, an antenna 6 and an electromagnetic band gap substrate 12. The RFID chip 5 and the antenna 6 are mounted above the electromagnetic band gap substrate 12. The electromagnetic band gap substrate has a reflection phase which is different from 180° at the operation frequency of the antenna. The electromagnetic band gap substrate enables the RFID to operate even if it is mounted on a conductive object, as the reflection phase is not 180° so it does not destructively interfere with the radiation from the antenna at the operating frequency. Preferably the reflection phase is between 340° and 115° or −95° and 145°. The preferred embodiment uses a band gap substrate having two mushroom-like conductive layers 3, 7 with a dielectric in between.