Passive radio-frequency identification applications utilizing magnetoresistance

Abstract

Magnetoelastic resonance (MER) are capable of remotely interrogating many different physical quantities like stress, pressure, temperature, flow velocity, liquid viscosity, or even chemicals through special coatings. A combination of near field communication (NFC) smart labels and giant Magnetoresistance (GMR) magnetic field sensors allows to combine the advantages of MER sensors and NFC. MER sensoros are based upon amorphous metall glass (AMG) ribbons, which change their magnetic susceptibility based upon their internal stress. Within this thesis all steps from first prototype phases, allowing the detection of magnetic field changes within the mT regime, to a fully passive NFC based strain sensor are presented. Additionally, detection of linear displacements are also a possible application for the proposed system. Passive NFC tags only provide a small amount of energy supply to external periphery. Conventional Hall effect magnetic field sensors requeire too much energy for a combination with NFC and therefore GMRmagnetic field sensors are used. Additionally to their lower energy consumption, they offer a higher sensitivity and better temperature stability. Simulating magnetic fields with the finite element method (FEM) is used to optimize the sensor layout and performance. Using the proposed system is still possible with conventional RFID readers, rendering this system ideal for long therm application. For example structural health monitoring of bridge pillars, or asphalt road layers.