Thermomechanical actuators

J. Puigcorbe, A. VUk, J. Cerda, A. Cirera, 1. Gracia, C. Cane, and J.R. Morante. Thermomechanical analysis of micro-drop coated gas sensors . Sensors and Actuators A97-98 (2002), 379-385. 

A thermomechanical valve is a device that regulates fluid flow (either gas flow, liquid flow, or slurry flow) by using an actuator which deforms under different temperatures to open, close, or partially obstruct various channels. 

Generally, the chemical and physical properties of most engineering materials vary with temperature. The (Mily difference hes in the degree to which the property changes with temperature. Among all the properties, the material shape change with temperature has mostly been used for the development of thermomechanical microvalves. The detailed mechanisms of thermomechanical microvalves will be discussed below. Briefly, the deformation of the material shape causes an actuation force, which can be used to induce mechanical actions through... 

Thermomechanical Valves, Fig. 6 A paraffin-actuated microvalve described in the text, (a) Schematic of the cross section of the microvalve (b) microscope... 

Thermomechanical Valves, Fig. 7 Schematic of a nonnally closed thennal bimorph-actuated valve... 

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... 

Thermomechanical Valves, Fig. 11 Bimetallically actuated gate microvalves... 

Thermomechanical Valves, Fig. 17 SMA pinch microvalve in (a) de-energized close state and (b) actuated open state... 

Thermomechanical Valves, Fig. 18 A gate microvalve actuated by an SMA wire at (a) open position and (b) closed position... 

TABLE 16.2 Comparison between Two Mechanical Properties of Different Actuating Materials Skeletal Muscles, Thermomechanical (Thermal Liquid Crystals and Thermal Shape Memory Alloys), Electrochemomechanical (Conducting Polymers and Carbon Nanotubes) and Electromechanical (Ionic Polymer Metal Composites, Field Driven Liquid Crystal Elastomers, Dielectric Elastomers)... 

The American company IC-Sensors offers a thermomechanically driven microvalve (with 2/2-way functionality) for gases (Fig. 6.113) [315]. The valve consists of an elastically suspended valve reed and a rigid valve base with a valve opening. The valve reed can be put into motion using the thermomechanical (bimetallic) effect. The temperature of the bimetallic structure of aluminium and silicon is used to control the actuator force. The normally closed valves are designed for a maximum pressure of 10... 200kPa. Gas flows of up to 0.11/min are achieved with a driving power of 300 mW. 

This section presents indicative implementations of actuator microconveyor platforms or actuators that could potentially be used for planar micromanipulation, separated into categories according to the classification made in the introduction thermomechanical, electrostatic, electromechanical and fluidic-mechanical. For each implementation, a brief description of the actuators, their operation principle as well as their reported performance characteristics is given unfortunately not all the information relevant within the scope of this chapter has been reported by the respective authors. At the end of the section, a comparison between the most promising actuators or platforms for planar micromanipulation is made in a concentrative table and the most suitable of them are determined based on the criteria proposed in the previous paragraph. 

Thermomechanical Valves, Figure 8 Schematic of a bimetallically actuated three-way valve... 

Various thermomechanical microvalves have been developed with the development of MEMS fabrication technology. Thermomechanical microvalves work by converting thermal energy into mechanical deformation. Compared with other microvalves, such as magnetic microvalves, electrostatic microvalves, and piezoelectric microvalves, thermally driven microvalves have their own advantages such as simplicity of fabrication, controllable deflection (by adjusting the input power), and a relatively large actuation force. 

Mraitazami R, Spillmann CM, Naciri J, Rama BR (2012) Enhanced thermomechanical properties of a nematic liquid crystal elastomer doped with gold nanoparticles. Sens Actuators A Phys 178 175-178... 

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