Design and Analysis for
Reconfigurable Encapsulated Microwave
Inclusive Dates: 02/05/02 - 06/05/02
Background - RFID (Radio Frequency Identification) systems are designed to manage assets of many types. Typically a small RFID tag is attached to the asset so that the asset is identified by the response of the tag to interrogation either by hand-held interrogators or fixed-site interrogators that are encountered in the course of asset movement. An example is the department store anti-theft tag. The Signal Exploitation and Geolocation Division, with long-standing history and experience in the RFID arena, has extended the RFID technology to detect, identify, and track assets at much longer ranges than commercially available systems. This function is performed in a variety of harsh environments. For this reason, tags for Institute systems must be tolerant of many hostile chemicals, abrasives, weather conditions and mechanical stresses.
Packaging of RFID tags performs several functions, including environmental protection and concealment. Of particular importance is that the packaging be compatible with the radio frequency (RF) performance of the tag. Tags can be de-tuned if packaged in a way that causes degradation in RF performance. This causes the range of tag detection to be reduced. An example of this type of environmental change is known by those who have experience with a "rabbit-ears" antenna that was once common with home television sets. When the antenna was touched and moved to different orientations the result was a change in the television picture, for better or worse. This same phenomena applies to the operation of RFID tags. Both are caused by changes in electromagnetic coupling. In the case of the RFID tag, it is dependent in part on the proximity of dielectric material to the RF components comprising the tag. A solution was needed that allows encapsulation of the RFID tag components and patch antennas without detrimental effects.
Approach - The team first selected several candidate materials for consideration. Next, a third-party software script was procured to aid in the design of the encapsulated RF patch antenna. An electromagnetic simulation tool was then used to fine-tune the design. The most promising candidate designs were then fabricated using a variety of dielectric materials and several different material thicknesses. These designs were then tested in an anechoic chamber to determine the signal levels and the polarization response of the encapsulated patch antennas.
Accomplishments - There were a number of positive outputs as a result of research performed under this quick-look project: 1) Improvement in the RFID tag packaging methodology by developing custom molds and exploring a variety of materials; 2) Development of an encapsulation technique resistant to mechanical, thermal and chemical stresses; 3) Generation and verification of a software script that predicted the initial design parameters of an encapsulated patch antenna, then iteratively fine-tuning the parameters with the modeling tool; 4) Successfully modeling and accurately predicting the RF effects of the antenna encapsulants, allowing for adjustment of the design parameters for a successful tag realization.