High-Resolution Synthesized Magnetic Field Focusing for RF Barcode Applications

A prototype of a high-resolution synthesized magnetic field focusing (SMF) system for a possible application to radio frequency (RF) barcodes is proposed in this paper. It was recently found that coordinated control of array coil currents makes it possible to focus magnetic field, which is requisite for medical imaging, wireless power, and RF identification. Different from conventional phased array RF antennas, SMF is independent of frequency, which is quite promising for various applications. In this paper, an array of rectangular air coils is proposed, and various implementation issues, such as accurate control of coil currents and compact RF barcode design, are newly suggested. A prototype of an SMF system composed of a transmitter (Tx), an RF barcode, and a receiver (Rx) was implemented at below 1 MHz operating frequency. The Tx includes modularized control drivers, full-bridge switching converters, and 16 arrayed air coils, where the RF barcodes proposed in this paper include a self-resonating circuit at 20 mm × 20 mm and a tunable resonating circuit at 15 mm × 15 mm. In this way, a 5 mm resolution at a distance of 20 mm was achieved for the Tx arrayed air coils with spacing of 5 mm, which is about four times sharper magnetic field focusing compared to a nonfocusing conventional coil. Furthermore, the proposed SMF system allows the designed 5-bit RF barcode array to be fully distinguishable at a 15 mm distance.