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This paper presents a wireless pressure sensor design based on magnetic fluid displacement over a planar coil and its corresponding inductance change. The design of the pressure sensor is presented followed by its fabrication and characterization. Experimental results show a good correlation with a nonlinear model relating the applied pressure to the change in coil self-resonant frequency. A prototype sensor (radius = 6 mm, thickness = 2 mm) based on the above principal using an oil-based ferrofluid (50 mu l, ferrite concentration 2%), a polyimide-embedded planar coil (L = 1 mu H), and a 25 mu m thick polyimide membrane shows a sensitivity of 3 KHz mmHg(-1) with a base-line resonant frequency of f(0) = 109 MHz.

An off-the-shelf, moisture-responsive, acetate-backed adhesive tape is investigated as a commercially available smart material for fabricating low-cost, multifunctional, humidity-responsive millimeter-scale structures. Laser ablation is used for cutting and thinning-down the tape to enhance its response. Water-submerged cantilevers show a radius of curvature of 3 mm or lower (for laser-thinned cantilevers). Additionally, their humidity response is a function of the angle between the longitudinal axis of the cantilever and polymer orientation. A cut angled at 80 degrees with respect to this orientation results in a tip rotation of up to 25 degrees, enabling the formation of bending cantilevers with twisting behavior. The tape cantilevers are further functionalized with magnetic nanoparticles and used to create four-finger grippers that close underwater within minutes and can sample 100 mu L of liquid. A cyclic humidity monitor is also fabricated using a tape strip that walks unidirectionally on a ratchet-shaped surface upon exposure to humidity variations. (C) 2013 Wiley Periodicals, Inc.

Paper is one of the oldest and most abundant materials known to man. Recently, there has been a considerable interest in creating paper devices by combining paper with other functional materials. In this letter, we demonstrate a simple fabrication technique to create water-resistant ferro-patterns on wax paper using CO2 laser ablation. A resolution of about 100 mu m is achieved which is mostly limited by the cellulose fiber size (similar to 50 mu m) in the wax paper and can be improved by using a smaller cellulose matrix. Laser ablation results in modification of surface morphology and chemistry, leading to a change in surface energy. We also present a 2D model for ferrofluid deposition relating the size of the pattern to the amount of ferroparticles deposited on the surface. Finally, a paper gripper is presented to demonstrate advantages of our technique, which allows microscale patterning and machining in a single step.

We report on the development of a batch fabricated biodegradable truncated-cone-shaped plug filter to overcome the postoperative hypotony in nonvalved glaucoma drainage devices. Plug filters are composed of biodegradable polymers that disappear once wound healing and bleb formation has progressed past the stage where hypotony from overfiltration may cause complications in the human eye. The biodegradable nature of device eliminates the risks associated with permanent valves that may become blocked or influence the aqueous fluid flow rate in the long term. The plug-filter geometry simplifies its integration with commercial shunts. Aqueous humor outflow regulation is achieved by controlling the diameter of a laser-drilled through-hole. The batch compatible fabrication involves a modified SU-8 molding to achieve truncated-cone-shaped pillars, polydimethylsiloxane micromolding, and hot embossing of biodegradable polymers. The developed plug filter is 500 mu m long with base and apex plane diameters of 500 and 300 mu m, respectively, and incorporates a laser-drilled through-hole with 44-mu m effective diameter in the center.

In this paper, we demonstrate the application of fluorocarbon evaporative cooling in thermoelectric energy scavenging. The fabrication and performance characterization of a prototype micro-device is presented. The device consists of a thermoelectric generator mounted on a silicon substrate and encapsulated in a poly(dimethylsiloxane) chamber with a flexible cover. By filling the chamber with a fluorocarbon liquid of low boiling point (34 degrees C), we were able to increase the body heat contact harvested energy by 226% compared to a device encapsulated in air. The availability of a variety of fluorocarbon liquids with different boiling points allows this harvesting amplification scheme to be used in a wide range of applications.

This paper presents a novel minimally invasive implantable pressure sensing transponder for continuous wireless monitoring of intraocular pressure (IOP). The transponder was designed to make the implantation and retrieval surgery simple while still measuring the true IOP through direct hydraulic contact with the intra-ocular space. Most parts of the sensor sit externally on the sclera and only a micro-needle penetrates inside the vitreous space through pars plana. In vitro tests showed a sensitivity of 15 kHz/mmHg with about 1 mmHg resolution. In vivo tests included one month implantation in rabbits, confirming the device biocompatibility and functionality.

In this Letter, we present a simple, low-temperature method for fabricating a wide-band (>80 kHz) thermo-acoustic sound generator on a porous polymeric substrate. We were able to achieve up to 80 dB of sound pressure level with an input power of 0.511 W. No significant surface temperature increase was observed in the device even at an input power level of 2.5 W. Wide-band ultrasonic performance, simplicity of structure, and scalability of the fabrication process make this device suitable for many ranging and imaging applications. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4737005]

In this paper, we report on the first laser-micromachined batch-fabricated single-layer elastomeric actuator with a corrugated surface profile. The structural material of the cantilever actuator is a single [polydimethylsiloxane (PDMS)] layer, and electrodes are soft lithographically patterned conductive carbon grease. The asymmetric corrugated surface provides a bending moment in a single PDMS layer without the need for a second inactive layer. An actuator which is 5 mm long, 1 mm wide, and 80 mu m thick can generate up to 2-mm out-of-plane displacement with zero applied force and 15 mu N at zero deflection while consuming 20 mu W of static power when actuated with 500 V.

In this note, we report on the development of a batch-fabricated laser-micromachined elastomeric cantilever actuator composed of a polydimethylsiloxane (PDMS) bilayer (active/inactive) and soft-lithographically patterned conductive carbon grease electrodes. The described unimorph structure has a low actuation voltage and large out-of-plane displacement. For a 4 mm long, 1 mm wide, and 80 mu m thick actuator, an out-of-plane displacement of 1.2 mm and a maximum force of 25 mu N were measured using 450 V actuation voltage.

We report a method for fabricating inexpensive microfluidic platforms on paper using laser treatment. Any paper with a hydrophobic surface coating (e. g., parchment paper, wax paper, palette paper) can be used for this purpose. We were able to selectively modify the surface structure and property (hydrophobic to hydrophilic) of several such papers using a CO(2) laser. We created patterns down to a minimum feature size of 62 +/- 1 mu m. The modified surface exhibited a highly porous structure which helped to trap/localize chemical and biological aqueous reagents for analysis. The treated surfaces were stable over time and were used to self-assemble arrays of aqueous droplets. Furthermore, we selectively deposited silica microparticles on patterned areas to allow lateral diffusion from one end of a channel to the other. Finally, we demonstrated the applicability of this platform to perform chemical reactions using luminol-based hemoglobin detection.

In this paper, we report on an inexpensive method of fabricating miniature magnetic actuators using ferrofluid-impregnated paper. Different types of papers (including soft tissue paper, cleanroom paper, Whatman-1 filter paper, printer paper, and newspaper) were loaded with oil-based ferrofluid, micromachined by a CO(2) laser and coated with a thin layer of parylene-C. The soaking capability of the different papers was investigated, with the soft tissue paper having the highest loading capacity, being able to absorb ferrofluid by as much as six times its original weight. Cantilever actuators fabricated from cleanroom and filter papers were able to generate the largest force (> 40-mg equivalent force), whereas the soft-tissue-paper cantilevers provided the greatest deflection (40 degrees tip angle).