3. Conclusions

A microplasma actuator is a device with no moving parts that has advantages over conventional actuators. It can be energized at voltages of about 1 kV, and thus requires a smaller size power supply and less electrical insulation compared with macro-plasma actuators. Moreover, due to the use of pulse voltage to energize the actuator, the energy consumption is low.

The use of a microplasma actuator for flow control showed the capability of the actuator to induce flow and also to change the direction of the flow. By using devices with field-effect transistor (FET) switches to energize the actuator, the flow direction was changed from diagonal leftward to diagonal rightward when the duty ratio of applied voltage was changed. This could be useful if the actuator were to be attached to small drones. The characteristics of the flow were investigated both experimentally and using numerical simulations. A numerical simulation code was developed based on the Suzen-Huang model, which calculates the body force from the potential of the external electric field and the potential of the charge density of the plasma, and implements the body force in Navier-Stokes equations. The experimental results confirmed the validity of the developed code.

#### Acknowledgements

The authors would like to thank Professor Hitoki Yoneda from the University of Electro-Communications, Tokyo, Professor Damon Chandler, Mr. Yoshinori Mizuno, Mr. Akihiko Ito and Mr. Daisuke Nonaka from Shizuoka University, Hamamatsu, for the fruitful discussions.

## Author details

Kazuo Shimizu\* and Marius Blajan \*Address all correspondence to: shimizu@cjr.shizuoka.ac.jp Shizuoka University, Hamamatsu, Japan

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The maximum values of the flow of 0.82 m/s were calculated near the HV1 electrodes. For the diagonal flow, the value was 0.43 m/s. The value obtained by PTV method was 0.42 m/s for the diagonal flow. In the case of experimental results, due to the microplasma light emission near the active electrodes, the flow could not be measured properly; thus, the simulation gave us valuable insight into the microplasma actuator phenomena. The leftward diagonal flow obtained at D = 20% has a smaller angle with the horizontal axis compared with the rightward

Figure 17. Flow for duty ratio D = 70%: After 50 ms, the leftward diagonal flow is changing gradually to rightward

diagonal flow at D = 70%.

diagonal flow.

18 Actuators


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22 Actuators

**Chapter 2**

Provisional chapter

**An SU-8 Microgripper Based on the Cascaded V-Shaped**

DOI: 10.5772/intechopen.75544

This chapter presents the design, fabrication, numerical simulations and experimental investigations of a polymeric microgripper designed using the cascaded V-shaped electrothermal actuators. The microgripper has a total length around 1 mm and a total thickness of only 20 μm. The microgripper was simulated using electro-thermo-mechanical finite element method (FEM) in order to check the performance of the gripper. As structural material of the microgripper, the SU-8 biocompatible polymer was used during the fabrication process. A fabrication process was implemented to realize the microgripper using a symmetrically sandwich structure. The metallic micro-heaters were encapsulated in the polymeric actuation structure of the microgrippers to reduce the undesirable out-of-plane displacement of the gripper tips and the mechanical stress, to improve the thermal efficiency, and for obtaining the electrical isolation of the structure. Experimental testing has been performed to determine the openings and the temperatures of the microgripper tips as function of electrical current. A displacement of the tips of more than 50 μm can be obtained at an electrical current of around 26–28 mA. A comparison between the simula-

An SU-8 Microgripper Based on the Cascaded V-Shaped

**Electrothermal Actuators: Design, Fabrication,**

Electrothermal Actuators: Design, Fabrication,

**Simulation and Experimental Investigations**

Simulation and Experimental Investigations

Additional information is available at the end of the chapter

tion results and the measurements were also presented.

Keywords: actuator, electro-thermal, microgripper, SU-8, simulation, polymer

Microgrippers used as end-effectors are essential tools for holding and manipulating fragile objects. A variety of applications for the microgripper structures was reported. These tools are suitable for handling, positioning, pick and place and biological micro-manipulations such as

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75544

Rodica-Cristina Voicu

Rodica-Cristina Voicu

Abstract

1. Introduction

#### **An SU-8 Microgripper Based on the Cascaded V-Shaped Electrothermal Actuators: Design, Fabrication, Simulation and Experimental Investigations** An SU-8 Microgripper Based on the Cascaded V-Shaped Electrothermal Actuators: Design, Fabrication, Simulation and Experimental Investigations

DOI: 10.5772/intechopen.75544

Rodica-Cristina Voicu Rodica-Cristina Voicu

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75544

#### Abstract

This chapter presents the design, fabrication, numerical simulations and experimental investigations of a polymeric microgripper designed using the cascaded V-shaped electrothermal actuators. The microgripper has a total length around 1 mm and a total thickness of only 20 μm. The microgripper was simulated using electro-thermo-mechanical finite element method (FEM) in order to check the performance of the gripper. As structural material of the microgripper, the SU-8 biocompatible polymer was used during the fabrication process. A fabrication process was implemented to realize the microgripper using a symmetrically sandwich structure. The metallic micro-heaters were encapsulated in the polymeric actuation structure of the microgrippers to reduce the undesirable out-of-plane displacement of the gripper tips and the mechanical stress, to improve the thermal efficiency, and for obtaining the electrical isolation of the structure. Experimental testing has been performed to determine the openings and the temperatures of the microgripper tips as function of electrical current. A displacement of the tips of more than 50 μm can be obtained at an electrical current of around 26–28 mA. A comparison between the simulation results and the measurements were also presented.

Keywords: actuator, electro-thermal, microgripper, SU-8, simulation, polymer

#### 1. Introduction

Microgrippers used as end-effectors are essential tools for holding and manipulating fragile objects. A variety of applications for the microgripper structures was reported. These tools are suitable for handling, positioning, pick and place and biological micro-manipulations such as

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

cells, blood vessels and tissues, for applications in micro-assembly of Microelectromechanical Systems (MEMS) and MOEMS components (lenses, fibers) and in micro-robotics.

2. Design

do not need an adhesion layer [23].

3. Finite element simulation

Figure 1. Schematic design of the SU-8 microgripper [22].

The SU-8 microgripper was designed in a previous work using the principle of the cascaded Vshaped electrothermal actuators [22]. The gripper was designed with two initial opening of 50 μm and 100 μm, respectively (Figure 1). When the gripper structure is electro-thermally actuated the arms and the jaws will close and will be able to handgrip a micro-object. The total length of the gripper arms used to grasp an object is of 920 μm. The arms were designed with a width of 20 μm [22]. A metallic micro-heater is implanted between two SU-8 layers. The heater lines have a width of 10 μm and were designed first, to be fabricated using Cr/Au/Cr materials and second, to be fabricated using only the gold. Usually, a chromium thin layer or other adhesion layers are used to improve the connection between the gold metal and the polymer. On the other hand, it was reported that the deposition of the SU-8 polymer over the gold metal

An SU-8 Microgripper Based on the Cascaded V-Shaped Electrothermal Actuators: Design, Fabrication, Simulation…

http://dx.doi.org/10.5772/intechopen.75544

27

The optimized design consists of symmetrically disposed of three material layers. A metallic layer for the heater is implanted between two SU-8 based structure layers having the same thickness, as described previously [18–22]. The thicknesses of the Cr/Au/Cr films were 10 nm/300 nm/10 nm. The thickness of the gold layer is 100–300 nm. For each SU-8 layer we obtained a thickness of 9 μm. The details of the fabrication process where using the Cr/Au/Cr films have been reported

The proposed microgripper in this work was designed symmetrically with encapsulated metallic micro-heaters in the structural material of the grippers, the SU-8 polymer, in order to reduce the undesirable out-of-plane displacement of the gripper, to obtain the electrical isolation of the heaters and to reduce the mechanical stress that can occur in the structure [22].

In order to check the performance of the microgripper, finite element simulations were performed. The microgripper with the initial opening of 50 μm was numerically investigated.

also previously in [21] and when using only gold in [24] but for other gripper designs.

Different actuators were investigated due to the significant role in the MEMS configuration. The actuation methods include mainly the electrostatic, electromagnetic, piezoelectric and electrothermal principles. Each actuation approaches have their proper disadvantages and benefits in agreement with the designed purpose. The actuators are usually integrated with MEMS for the necessary need of energy conversion, motion generation and force production [1–3]. The V-shaped actuators are widely used for grippers, micro-valves, micro-pumps and other devices. V-shaped electrothermal actuators have the advantages of generating a large force (up to several 100 mN), the simple structure design, a lower dive voltage and a large deformation. Que et al. [2] developed single and cascaded V-shaped electrothermal actuators and present the experimental results. Shen and Chen [3] present an analytical model for cascaded V-shaped actuators bringing a complete description of the mechanical performance. Usually, materials such as silicon, polysilicon or aluminum are used as the structural material of such actuators.

A variety of microgrippers have been studied using the SU-8 based electrothermal actuators designed on different configurations such as, U-shape or V-shape. This is proving the interest in the bio-micro-manipulation domain [1, 4–23]. SU-8 is a highly crosslinked epoxy-type photo-patternable polymer which has been used extensively as the preferred polymer material for fabrication of biocompatible structures. The SU-8 polymer has a relatively large coefficient of thermal expansion (CTE) of 52 ppm, good mechanical strength with a modulus of elasticity of around 4.02 GPa and good thermal stability with a glass transition temperature of 210C [15], which make it a good polymer material for fabrication of electrothermal actuators. The polymer V-shaped actuators are preferred for the better performance in aqueous medium [4].

Different processing technologies were investigated and realized in order to fabricate reliable microgripper with reduces out-of-plane displacement [17–22]. Usually two or three material layers are utilized to compose a sandwich structure.

In this chapter, we report a complete work regarding the design, numerical simulation results, fabrication process and the experimental investigations of an SU-8 polymeric microgripper. The design is based on the cascaded V-shaped electrothermal actuators. The SU-8 microgripper can be used for micro-robotics and bio-manipulation and assembly applications. The microgripper was numerically investigated using the coupled electro-thermo-mechanical simulations based on finite element method (FEM) and using the Coventorware 2014 software in order to confirm the performance of the microgripper. To fabricate the microgripper, a sandwich structure actuator with three layers was used. Two kings of fabrication processes were presented in order to improve the structure functionality. As structural material of the microgripper, the SU-8 biocompatible polymer was used during the fabrication process. The metallic micro-heaters were encapsulated in the polymeric actuation structures of the microgrippers to reduce the undesirable outof-plane displacement of the gripper tips, the mechanical stress and to improve the thermal efficiency and the electrical isolation of the structure. Experimental testing and characterizations have been performed to determine the openings and the temperatures of the microgripper tips as function of electrical current. A comparison between the simulation results and the measurements were also presented.
