RFID articles such as labels, tags, etc are typically equipped with a microchip electrically, i.e., conductively, capacitively and/or inductively, connected to an antenna so that the chip may be read from and/or written to via radio frequency carrier energy provided and sensed, by an interrogator or reader. RFID articles often include an RFID inlay that carries the microchip and antenna on a convenient poly or paper base layer in a ‘wet’ format, i.e., coated on one side with a pressure sensitive adhesive for bonding the inlay to the article, or, in a ‘dry’ format with no adhesive. Inlays are provided by companies such as Alien Technologies of Morgan Hill, Calif., Avery Dennison of Clinton, S.C., and TAGSYS of Cambridge, Mass. To achieve manufacturing economies of scale, inlays are typically provided in a limited number of antenna formats for general use. In some cases, a customized antenna is desirable to achieve longer range or optimize performance where the size, shape or contents of an RFID article-equipped carton affect the rf performance of the inlay.
TAGSYS of Cambridge, Mass. offers an alternative to the conventional chip/antenna inlay combination with its AK™ of Active Kernel™ technology, “Kernel” refers to a relatively small (approximately ¾″ square) UHF (ultra high frequency) inlay consisting of a poly film carrying a microchip and a metallic loop antenna where the chip is conductively connected to the loop antenna. As the loop antenna is relatively small and simply shaped, the reading/writing range of the kernel inlay is relatively short, perhaps less than one foot, compared to a typical UHF inlay with a range of 3-10 feet. This “kernel” provides a “common denominator” or universal form factor inlay that may be used with a second antenna to increase reading/writing range and other performance characteristics. The kernel inlay is applied in relatively close proximity to the second antenna, but the kernel inlay typically does not touch or otherwise conductively connect to the second antenna. The kernel inlay inductively couples or resonates with the second antenna and this resonance increases reading/writing range of the combined kernel inlay and second antenna. The second antenna may be formed using a variety of known techniques, such as printing with a conductive ink, etching or grinding from a metallic layer, stamping a metallic foil, etc. and the second antenna may be carried on a variety of substrates such as paper or poly film. The structure and interaction of the kernel inlay and second antenna is disclosed in U.S. Pat. No. 6,172,608 of Cole, the disclosure of which is expressly incorporated herein in its entirety.