The bistable snap-through behavior of a compressed beam is modeled and measured experimentally as its supporting surface is bent through positive and negative curvatures. When the supporting angle of the beam exceeds a critical angle, bistability is lost and only one stable state is supported. The critical angle is controlled only by the initial compressive stress in the beam, and we report a nondimensionalized calculation method for this angle. This large-deflection nonlinear model provides design rules for low-power sensors and actuators that can measure and control surface curvature from the micro- to macroscale.
In this paper, we explore microfabricated bistable actuators released as thin films from a silicon wafer. The actuators are based on a serpentine design where two cantilevers are coupled at the tips by a thin-film bar. These devices are parameterized by two lengths: cantilever length and the length of the coupling bar. These two dimensions are systematically varied to study the effect of design parameters on bistability. The three-dimensional devices have extremely large deflection (hundreds of microns rather than tens of microns for most planar microactuators of similar size) and are thermally actuated out of the plane of the wafer by applying a bias across either the left or right side of the serpentine. The bistability of these devices is evaluated using electron and optical microscopy. Potential applications include non-volatile mechanical memory, optical shutters, and reconfigurable antenna elements.
Advances in microelectromechanical systems (MEMS) continue to empower researchers with the ability to sense and actuate at the micro scale. Thermally driven MEMS components are often used for their rapid response and ability to apply relatively high forces. However, thermally driven MEMS often have high power consumption and require physical wiring to the device. This work demonstrates a basis for designing light-powered MEMS with a wavelength specific response. This is accomplished by patterning surface regions with a thin film containing gold nanoparticles that are tuned to have an absorption peak at a particular wavelength. The heating behavior of these patterned surfaces is selected by the wavelength of laser directed at the sample. This method also eliminates the need for wires to power a device. The results demonstrate that gold nanoparticle films are effective wavelength-selective absorbers. This “hybrid” of infrared absorbent gold nanoparticles and MEMS fabrication technology has potential applications in light-actuated switches and other mechanical structures that must bend at specific regions. Deposition methods and surface chemistry will be integrated with three-dimensional MEMS structures in the next phase of this work. The long-term goal of this project is a system of light-powered microactuators for exploring cellular responses to mechanical stimuli, increasing our fundamental understanding of tissue response to everyday mechanical stresses at the molecular level.
This letter outlines our work in generating and controlling microbubbles as protective “lids” for samples collected from the environment. The fabrication method uses “strain architecture” to construct three-dimensional cages with high surface area. These structures confine the bubbles and perform as electrodes for electrochemical sample collection and electrolysis-based gas bubble generation. The focus of this article is on the interaction between the microcages and generated bubbles, including the bubble generation mechanism, bubble growth rate, response to hydrostatic pressure, effect of interfacial-tension modifying coatings, and long-term stability.
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