In this work, we combine the advantages of hard magnets, polydimethylsiloxane (PDMS) micro-molding and printed circuit board planar coils to propose an electromagnetically actuated bidirectional scanner with potential applications in bio-medical scanning. The proposed bidirectional scanner (4 mm × 4 mm × 250 μm) is fabricated by micromolding an isotropic Nd-Fe-B micropowder doped in a PDMS matrix at 80% weight percentage and magnetized using a standard dipole electromagnet. A reflective gold layer of 100 nm is evaporated onto the polymer composite structure. A maximum magnetic field of 20 mT is measured for the polymer magnetic mirror. Rectangular planar coils (trace width and spacing: 254 μm; 10 turns) are employed to actuate the bidirectional scanner electromagnetically by Lorentz force. Actuation in both static and dynamic excitation modes is tested. Power consumption at a maximum rotational angle (15 degrees -optical) is one watt at 40 Hz resonant frequency. Initial surface roughness of the mirror (165 nm) and radius of curvature (75 mm) has been addressed by depositing a thin layer of PDMS, resulting in 66.24 nm surface roughness and 321.37 mm overall radius of curvature after integration. Major advantages of the proposed bidirectional scanner include low fabrication cost, low input voltage and large actuator displacement compared to existing electrostatic scanners.Micromirror scanners have applications in portable digital displays with mirror arrays, automotive head-up displays, head worn displays, barcode scanning, raster scanning displays, optical spectrum analysis, optical switches to encounter the demand for routing the ever increasing internet traffic through fiber optic networks 1 and in the healthcare arena to develop scanning optical devices to cater to low cost, endoscopic, optical cross-sectioning systems for in vivo diagnostics. A variety of actuation mechanisms for scanners have been employed, including electrostatic actuation, 2 electromagnetism, 3 electrothermal, 4 magnetostriction, piezoelectricity, shape memory alloys, pneumatics and hydraulics.Though electrostatic actuated scanners are frequently adopted to drive micromirrors, drawbacks typically include the requirement of relatively high operational voltages for enough range of motion at static mode operation. Sub millimeter gaps and high voltages lead to device failure due to pull-in instability during operation and is a patient safety hazard. Further the overly compliant mechanical flexures results in the device being fragile. An alternative to electrostatic actuators are electrothermal bimorph actuators, which provide large static angular motion at lower driving voltages. 5,6 Drawbacks of the bimorph actuators to be implemented as scanners include extreme sensitivity to shock and vibration due to the design asymmetry and their high compliant characteristic at large displacements. A thermally driven scanner in resonance mode operation using the local heatinginduced thermal gradient effect mitigating vibration sensitivity has been shown....
Polymer composites based on permanent magnetic bonded powders exhibit immense potential for applications in microactuators and sensors with magnetic performances comparable to their fully dense counterparts. While fabrication and integration of magnetic devices based on bonded magnetic powders is challenging via conventional deposition and electrochemical growth techniques, hybrid fabrication offers a promising alternative. This paper presents the evolution of permanent magnetic materials into bonded magnetic powders, the magnetic performance figures of merit of permanent magnetic materials significant for the design and manufacture of polymer based sensors and actuators. A review of the hybrid fabrication techniques such as replica molding, squeegee coating, spin casting etc are reported. Critical factors affecting the fabrication of polymer magnetic composites such as filler particle size and effect of magnetic field during fabrication are discussed. Prior art based on polymer magnetic composites for the fabrication of hard magnetic films and hard magnetic actuators are presented.
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