Scalable, high-performance magnetoelastic tags using frame-suspended hexagonal resonators

This paper presents the analysis, design and experimental evaluation of miniaturized magnetoelastic tags using frame-suspended hexagonal resonators. Magnetoelastic tags—also known as acousto-magnetic or magnetomechanical tags—are used in wireless detection systems—for example, electronic article surveillance and location mapping systems—that electromagnetically query the resonant response of the tags. In order to obtain a strong resonant response for miniaturized tags, a frame-suspended configuration is utilized to diminish the interaction between the vibrating portion of the tag and the substrate. The signal strength can be boosted by utilizing signal superposition with arrayed or clustered magnetoelastic tags. The hexagonal tags with a diameter of 1.3 mm are batch fabricated by photochemical machining from 27 μm thick MetglasTM 2826 MB, which is an amorphous NiFeMoB alloy. A preferred dc magnetic field bias for these tags is experimentally determined to be ≈31.5 Oe. A single frame-suspended magnetoelastic tag shows quality factors of 100–200. This design provides ≈75X improvement in signal amplitude compared to the non-suspended disc tag with similar size and resonant frequency. Across ten individual frame-suspended tags, the average resonant frequency is 2.13 MHz with a standard deviation of 0.44%, illustrating that this fabrication method provides repeatability. Linear signal superposition of the response has been experimentally measured for sets of frame-suspended tags that include as many as 500 units.