Low-cost assembly of UHF RFID chips and flexible substrate antennas by magnetic coupling approach

This article deals with a novel low-cost technology for the assembly of flexible substrate antennas and UHF RFID Si chips. Such a technology exploits a magnetic coupling mechanism, thus avoiding the need for galvanic contacts between the Si chip and the antenna itself. The magnetic coupling is established by a planar transformer, whose primary and secondary windings are implemented on flexible substrate and Si chip respectively. As a result the Si chip can be assembled on the antenna with a mere placing and gluing process. First the idea has been validated by theory. Electromagnetic simulations of a square heterogeneous transformer (1.0 mm side) show a minimum loss of 0.6 dB at 900 MHz, under simultaneous matching conditions. Then a symmetrical PCB transformer (1.5 mm side) has been fabricated and tested. Measurements indicates a minimum loss of 0.3 dB at 900 MHz, thus confirming the validity of the proposed solution.