Contactless and absolute linear displacement detection based upon 3D printed magnets combined with passive radio-frequency identification

Abstract

Within this work a passive and wireless magnetic sensor, to monitor linear displacements is proposed. We exploit recent advances in 3D printing and fabricate a polymer bonded magnet with a spatially linear magnetic field component corresponding to the length of the magnet. Regulating the magnetic compound fraction during printing allows specific shaping of the magnetic field distribution. A giant magnetoresistance magnetic field sensor is combined with a radio-frequency identification tag in order to passively monitor the exerted magnetic field of the printed magnet. Due to the tailored magnetic field, a displacement of the magnet with respect to the sensor can be detected within the sub-mm regime. The sensor design provides good flexibility by controlling the 3D printing process according to application needs. Absolute displacement detection using low cost components and providing passive operation, long term stability and longevity renders the proposed sensor system ideal for structural health monitoring applications.

Comparison of Sensitivity and Low-Frequency Noise Contributions in Giant-Magnetoresistive and Tunneling-Magnetoresistive Spin-Valve Sensors with a Vortex-State Free Layer

“…The detectivity comparison is shown in Figure 6. It is calculated using equation (8) with the obtained parameters from the fitted noise data in Figures 3 and 4. The plotted areas indicate the detectivity obtained from the measured array configuration of 10 serially connected devices, considering all applicable supply voltages as described in section III.…”

“…Magnetoresistive spin valve sensors operated in a magnetic vortex configuration show negligible hysteresis while saturating at high magnetic field [6]. These properties make them very attractive for linear current sensors or position sensors with the need for a high dynamic range and accuracy, since the latter is limited by hysteresis [7,8]. Other examples are wheel speed or angle sensing applications [9,10] where this principle could facilitate the mechanical adjustment as well as enabling more freedom setting the working point.…”

Additive-Manufactured Anisotropic Magnets for Harsh Environments

“…Research up to now has been focused on mixing magnetic powder with polyamide (PA6, PA11 and PA12), because it is easy to fabricate elastic filaments at low temperatures that can be easily handled by conventional 3D printers. These polymers were also used in one of the first successful prints by Huber et al [2] After that there where many printings using the MEX technique and PA in different forms with Sr-ferrite [3,4] , Nd-Fe-B [5][6][7][8][9], Mn-Al-C [10,11] and a mixture of Nd-Fe-B and Sm-Fe-N [12] and Nd-Fe-B with Sr-ferrite [13]. Until now, PPS and magnetic particles were only used in specialized printers, like Big Area Additive Manufacturing (BAAM) printers [14], but no results have been presented when using a conventional 3D printer, probably because the printing is difficult on low-budget printers due to the high printing temperature required and the poor printing results.…”

The Magnetic Properties of a NdFeB Permanent Magnets Prepared by Selective Laser Sintering

“…The pump case, pump impeller, and magnetic clutch based on permanent magnets were prepared by additive manufacturing. In [3,4], the possibility of creating linear encoders by 3D printing of units made from magnetic materials with spatially varied magnetic properties was shown. Actuators [5], rotors for synchronous electrical engines [6], elements of neutron optics [7], and other articles are prepared by additive manufacturing.…”