U-shaped Beam Research Articles

Design and fabrication of thermal actuators used for a micro-optical bench: application to a tunable Fabry-Perot filter

Recent studies of MEMS thermal micro-actuators have shown that simple devices can provide deflection on the order of 10 μm at low voltages. These thermo-mechanical devices operate by differential thermal expansion caused by ohmic heating in the U-shaped beam of the device. We report on a thermal actuator based on asymmetrical thermal expansion of two beams caused by ohmic heating. Because of the intervention of the different heat transfert mode (such as conduction, convection, and radiation), the motion simulation can be complex. This work demonstrates a good comprehension of the phenomena during a Joule heating process for micro-systems and the development of an analytical model and a finite element analysis. Comparisons between theory and experimental results validate the steady-state conditions. Therefore, this actuator has been successfully integrated in an optical bench and allows the displacement of a micro-lens supported by a movable silicon-frame. This optical bench has been tested to realize a tunable Fabry-Perot filter with a 0.8 μm laser diode and reflective mirror of 99%.

Prefabrication of large U-shaped beams and its application in Aljunied Bridge of PIE Expressway in Singapore

Prefabrication of large U-shaped beams and its application in Aljunied Bridge of PIE Expressway in Singapore

Determination of the modification of Young's modulus due to Joule heating of polysilicon microstructures using U-shaped beams

The modification of Young's modulus is determined before and after Joule heating generated by a current passing through polysilicon microstructures. U-shaped overhanging polysilicon beams are specially designed and fabricated to avoid both the heat transfer to substrate and the deformation by thermal expansion. Joule heating is performed by applying a current of 10–20 mA for 5–10 s, making beams heat up. The measured resonant frequencies shift up or down after Joule heating, attributed to the stress relaxation or the oxidation of beams. The modification of Young's modulus is negligible, implying that material properties after the reshaping are not changed much.

Silicon micro/nanomechanical device fabrication based on focused ion beam surface modification and KOH etching

Selective Ga+ ion implantation and milling by focused ion beam exposure and subsequent wet chemical etching is used to fabricate micro/nanomechanical elements in Si. Freestanding elements with a ≈ 30 nm membrane thickness are made by controlled selective underetching between unexposed and exposed areas. Ultrahigh-frequency cantilever beams have been made with resonances in the tens of MHz range. Using a U-shaped beam cross section, mechanical stiffness could be increased 100-fold, which in turn increased the beam resonance frequency to several hundreds of MHz. The direct-write patterning/milling technique was used to fabricate various arbitrary shapes with vertical sidewalls such as submicrometer-sized containers, cups, and other nanomechanical devices.

Elastic blade root connection in wind turbine using flexible elements from composites

The aim of an elastic blade root connection with a hub is to decrease loads in the blade root section during wind gusts. Two designs of connection were considered: for the load reduction on the blade in operating regime and for stopped blade unloading under storm wind. In the first case two versions of joint were discussed: the first one — with hinges and U-shaped composite beams, the second one — formed with straight beams oriented in different directions. Both joints have low torsional stiffness in wind direction and much higher stiffnesses around two other axes. Formulas for angular stiffnesses and the methods of obtaining the nonlinear behavior of the joint are presented. The objective of the flexible spar was to allow the blades to bend back out of the wind to reduce loads when the wind turbine was stationary in storm conditions. Calculations supported the feasibility of such a design. With a low torsional stiffness, spar (which can be rigidly connected to the blade) acts as a pitching beam for turbine control. A compound spar design consisting of pultruded bars clamped through specified distance was proposed. Torsional stiffnesses of different types of spars with equal specified bending rigidity were compared.