We present the design, fabrication and characterization of a novel bidirectional magnetic microactuator. The actuator has a planar structure and is easily fabricated using processes based on laser micromachining and soft lithography, allowing it to be readily integrated into microfluidic, microelectromechanical systems (MEMS) and lab-on-a-chip (LOC) designs. The new microactuator is a thin magnetic membrane with a central magnet feature. The membrane and magnet are both composed of a magnetic nanocomposite polymer (M-NCP) material that is fabricated by embedding magnetic powder in a polydimethysiloxane (PDMS) polymer matrix. The magnetic powder (MQP-12-5) has the chemical composition of (Nd 0.7 Ce 0.3 ) 10.5 Fe 83.9 B 5.6 , and contains grains that are 5-6 microns in size. The powder is uniformly dispersed at a weight percentage of 75 wt-% in the PDMS matrix, and micropatterned using soft lithography micromolding to realize magnetic microstructures, which sit on a thinner magnetic PDMS membrane of the same material. The molds are fabricated by laser-etching into Poly (methyl methacrylate) (PMMA) using a Universal Laser System's VersaLASER© laser ablation system. The PDMS-based M-NCP is then poured and spun over the mold patterns, producing a thin polymer membrane to which the polymer micromagnets are attached, forming a one-piece actuator. The M-NCP is initially un-magnetized, but is then magnetized by placing it in a 2.5T magnetic field to produce permanent bidirectional magnetization that is polarized in the specified direction. To characterize the bidirectional actuators, a uniform magnetic field is established via a Helmholtz coil pair, and is characterized by applying varying currents. The magnetic field (and thus the actuator deflection) is controlled by regulating the current in the Helmholtz pair. Using this apparatus, deflection versus field characteristics are obtained, with maximum deflections varying as a function of actuator dimensions and the applied magnetic field. Permanent rare earth magnets are used to produce supplemental fields for higher magnetic fields and higher deflections. Deflections of 100 micrometers and more are observed for 3 to 8 mm square membranes with central magnetic features ranging from 0.8 to 3.6 mm squares, in magnetic fields ranging from 52 to 6.2 mT. In addition, smaller membranes (1 mm and 2 mm with 0.4 mm and 0.6 mm central magnets, respectively) also deflect 20 and 50 microns, respectively, under 72 mT fields.
We present the large scale micro-pattering of an electrically conducting multiwalled carbon nanotube (MWCNT) polydimethylsiloxane (PDMS) nanocomposite polymer prepared by high frequency (42 kHz) ultrasonic agitation of MWCNTs in the PDMS polymer matrix. Large scale micropatterning of the MWCNT-PDMS nanocomposite is achieved via soft lithography employing a 12" x 24" poly-methyl methacrylate (PMMA, commercially known as Plexiglass) micromold. The process has a 20µm.minimum feature size. The PMMA micromold is fabricated by laser ablating 5-mm thick, 12 " x 24 " sheets using the Universal Laser System's VersaLASER© laser cutter system which employs a CO 2 laser. We have characterized and compared the resistivity of 1cm x 0.5cm x 0.5cm MWCNT-PDMS structures with varying weight percentage (wt-%) of MWCNT (1-10% wt%) in the PDMS matrix with a result that the percolation threshold is achieved at 2 wt-%. Furthermore, we have demonstrated the ability to fabricate large numbers of microelectrodes with a length of 3.0 cm, width of 500µm, and height of 400µm. The resistivity of these electrodes was found to be equal to 9.93Ωm with a deviation of approximately 10%, indicating uniformity across large areas of the substrate. We have also demonstrated a large scale 12" x 24 hybrid microfabrication process for combining micromolded MWCNT-PDMS nanocomposite microstructures with nonconductive PDMS polymer.
The growing number of applications requiring conformal electronic devices incorporated into unconventional and dynamic surfaces has led to an increase in the development of stretchable electronics. Together with novel materials and fabrication processes, innovative conductive patterns are being developed in order to meet the needs of modern applications. Here, we present the design, fabrication, and characterization of first-order curved Peano structures fabricated using a newly developed thick film copper metallization transfer process onto PDMS. In order to maximize the stretchability of these structures, we present a characterization and analysis of the relationship between relative resistance and tensile strain in fabricated devices while systematically varying the geometric parameters of various curve designs. The response of the structures to cyclic failure and recovery is also characterized. These results demonstrate that the newly developed transfer process can be used to fabricate stretchable Peano curves and provide insight into the geometric optimization of these curves in stretchable electronics applications. Stretchable electronics is an emerging technology enabling new devices that cannot be fabricated using traditionally rigid substrates. The particular advantages of stretchable devices over their rigid counterparts are the ability to conform to a curved surface (for example, the human body), the ability to be folded within a constrained volume, and the ability to otherwise be physically flexed or stretched without failing. Example applications are particularly prevalent in biomedicine and include wearable monitoring devices, 1,2 implantable neural or muscular stimulators, 3 implantable drug delivery systems, 4 fluid control systems, 4 flexible sensors and actuators, 5-7 and flexible integrated circuit technology. 8 In an effort to further the development of these devices, there are two primary areas of improvement; the first area is in fabrication process technologies, and the second is in investigating new geometries that enable more effective stretchable structures.With respect to fabrication technologies, there are several existing processes suitable for the development of stretchable electronics, including the direct metallization of polymers, nanocomposite polymer (NCP) fabrication, 9 fabrication using conductive polymers, 10 and inkjet printing of conductive inks.11 While many of these methods can produce impressive flexible features, the conductivity of non-metallic structures is generally poorer than deposited pure metals. Therefore, the metallization of polymers is commonly used due to high electrical performance and relatively low cost. In previous work, 12 we have shown a new process for low-cost, large-scale, thick-film metallization of PDMS; in this work, we demonstrate the application of this process to stretchable electronics.Using a given process, stretchable metal patterns on polymers can generally be achieved with pre-stressed, thin-film, metal conductors that form stretchable m...
We present the detailed characterization of a novel microfabrication process to produce thick-film copper microstructures that are embedded in polydimethylsiloxane (PDMS). This process has reduced fabrication complexity and cost compared to existing metal-on-PDMS techniques and enables rapid prototyping of designs using minimal microfabrication equipment. This technology differs from others in its use of a conductive copper paint seed layer and a unique infrared-assisted transfer process that results in copper microstructures embedded in PDMS. By embedding microstructures flush with the PDMS surface, rather than fabricating the microstructures on the substrate surface, we produce a metallization layer that adheres to PDMS without the need for surface modifications. In addition, the electrodeposition process results in a highly-conductive, thick-film, copper layer. Deposited patterns are shown to be 70-micrometers-thick with reliable feature sizes as small as 100 micrometers. The copper layer has a surface roughness of approximately 5 micrometers and a low film resistivity of approximately 2.5-3 micro--cm.
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