Thermal bimorph actuator

Thermal bimorph actuators consist of deformable microstructures that curl into and out of the substrate plane. 

Thermomechanical Valves, Figure 7 Schematic of a normally closed thermal bimorph-actuated valve... 

A thermal bimorph actuator is comprised of two materials with different coefficients of thermal expansion that are bonded together, as shown in Figure 5.12. As the materials heat up they expand at different rates, causing the actuator to deflect toward the side that expands the least. 

When silicon is in contact with a metal, a low-temperature liquid eutectic can be formed, far below the melting temperature of either silicon or the metal. For example, the eutectic temperature for silicon and gold occurs around 370°C for 30% silicon. In contrast, the melting point for pure gold is 1064°C, and the melting point for pure silicon is 1410°C [5]. Aluminum and silicon can form a eutectic around 577°C at around 12% silicon. In designing thermal actuators, such as gold/silicon thermal bimorph actuators or suspended heaters with metal wires and contacts, the metal should not be used in the proximity of any silicon that is heated unless the temperature is kept below the eutectic point. 

Thermomechanical Valves, Fig. 10 A Si — Ni bimorph-actuated microvalve with thermal isolation comb regions, (a) Thermal isolation comb regions (b) photograph of the microvalve... 

Thermal actuation makes use of the thermal expansion of solids as they are heated, or the differences in the rates of thermal expansion between different materials as in a bimorph actuator. Relative to electrostatic... 

For a bimorph actuator comprised of two layers with different coefficients of thermal expansion, y and yj, the temperature change causes a strain mismatch between the layers, leading to curvature of the bimorph ... 

Electrothermal or Thermal Actuation Motion is generated by differential thermal expansion in materials such as sDicon or metals, while heat is typically injected into the actuator by means of Joule heat dissipation. Some actuator components expand more than others due to different cross-sections and therefore electrical resistance. Typical microactuator configurations include in-plane bimorph elements (Fig. 2a), out-of-plane bimorph plates, in-plane Chevron, or bent-beam elements (Fig. 2b) [3]. These types of actuators exhibit larger force capabiUties (in mN range), can achieve displacements of 100 pm or less but generally consume a lot of power (hundreds of mW), and have low bandwidth (Hz to KHz). Common methods of fabrication for electrothermal microactuators include surface micromachining... 

The developed bimorph beam model of IPMC was validated using the finite element method (FEM) and the used software was MSC/NASTRAN. As the software does not directly support the electromechanical coupling, the thermal analogy technique as described in [Lim et al. (2005) Taleghani and Campbell (1999)] was used. The simulated versus measured force-displacement relationship of an IPMC actuator is shown in Fig. 2.39. The relative errors for A = 0 between the calculated values and the measured data for 2V and 3V are 2.8% and 3.7%, respectively. The equivalent Young s moduli estimated from the equivalent beam model and the equivalent bimorph beam model are 1.01 GPa and 1.133-1.158 GPa, respectively, which are very close. However, the values from the equivalent beam model... 

Figure 5.12 Bimorph cantilever beam actuator. The top layer of the cantilever has a coefficient of thermal expansion y,op and the bottom layer has ybottom- One end of the beam, at x = 0, is thermally anchored to the substrate temperature, T. ...

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