Design and simulation of an optimized electrothermal microactuator with Z-shaped beams

ISSN 0188-6266 doi: 10.15174/au.2015.774 Design and simulation of an optimized electrothermal microactuator with Z-shaped beams Diseño y simulación de un microactuador electrotérmico optimizado con brazos en forma Z Margarita Tecpoyotl-Torres*, Ramón Cabello-Ruiz*, José Gerardo Vera-Dimas* ABSTRACT The displacement of the central shuttle of a Z-shape chevron actuator can be calculated using a developed approach from other authors. Who demonstrated that the actuators with this geometry offer a larger displacement compared with V-shape actuators. Z-shape offers a larger stiffness and output force for the case of only one arm. This paper is focused on the optimization of the Z-shaped beams of a chevron actuator of eight beams, which seeks to increase the previously described response. The structure is designed in parametric solid modeling 3D software Autodesk Inventor, and simulated by finite element method in Ansys 15.0. These simulations were implemented considering several modifications on the length of the Z-shaped beams in order to choose the most appropriate length. The electric potential applied in all cases was from 0.2 V up to 5 V. The Z-shape length of the arms for the case of the optimized Z-shape actuator increases the shuttle’s displacement in approximately 50% compared to V-shape actuator, and 38% compare to the original Z-shape. Analytical adjusted approach is extremely matched with the simulations results. Length of the Z-shape beam is the determinant factor of the displacement. The low stiffness of the optimized Z-shape actuator (89% lower than the original V-shape and 58% compared to Z-shape) can allow its use as load sensor. RESUMEN Recibido: 22 de abril de 2015 Aceptado: 29 de mayo de 2015 Keywords: MEMS; chevron; electrothermal; displacement. Palabras clave: MEMS; chevrón; electrotérmico; desplazamiento. Cómo citar: Tecpoyotl-Torres, M., Cabello-Ruiz, R. & VeraDimas, J. G. (2015). Design and simulation of an optimized electrothermal microactuator with Zshaped beams. Acta Universitaria, 25(3), 19-24. doi: 10.15174/au.2015.774 El desplazamiento de la flecha central de un actuador chevrón con brazos basados en una geometría de forma Z puede ser calculado utilizando una aproximación desarrollada por otros autores, quienes probaron que los actuadores con un solo brazo ofrecen un mayor desplazamiento comparado con los actuadores en forma V convencionales, y que a su vez también ofrecen mayor rango de rigidez y fuerza de salida. Este artículo está enfocado en optimizar un actuador de ocho brazos en forma Z, buscando incrementar la respuesta anteriormente mencionada. La estructura fue diseñada en un paquete de modelado paramétrico de sólidos en 3D, Autodesk Inventor y simulada por el método de elemento finito en Ansys 15.0. Se implementaron varias longitudes en el largo de la forma Z, con la finalidad de seleccionar la longitud que proporcione el mayor desplazamiento. El potencial eléctrico aplicado en todos los casos fue de 0.2 V hasta 5 V. En los resultados se muestra que utilizando la longitud de la forma Z de los brazos del actuador Z optimizado se obtiene un incremento en el desplazamiento de la flecha de aproximadamente 50% comparado con el obtenido en el actuador V, y de un 38% en el actuador Z original. Además, se puede notar que estos resultados, empleando la aproximación analítica, son extremadamente cercanos a los resultados obtenidos mediante la simulación. La longitud total de los brazos con forma Z es el factor determinante del desplazamiento de la flecha. La baja rigidez mostrada por el actuador Z optimizado (89% menor que el actuador V y 58% comparado con el chevrón Z original) hace que pueda utilizarse como sensor de carga. INTRODUCTION The Micro Electro Mechanical System (MEMS) consists of mechanical structures, microsensors, microactuators and microelectronic devices. Microactuators convert electrical input to mechanical output. Vertical actuators *Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos. Av. Universidad núm. 1001, Col. Chamilpa, Cuernavaca, Morelos, México, C.P. 62209. Tel.: (52) 777- 329 70 84, ext. 6224. Correos electrónicos: ; ; ; http://www.uaem.mx Vol. 25 No. 3 Mayo-Junio 2015 19 ISSN 0188-6266 are useful for many applications requiring out-of-plane displacements. Such applications include tunable parallel plate capacitors and other passive components, optical modulators, RF and optical switches, micromanipulators, devices inside of Scanning Electron Microscopes (SEM) (Cao, Chen, Filleter & Sun, 2015); (Varona, Tecpoyotl-Torres & Hamoui, 2009). It has been demonstrated that electrothermal actuators are compact, stable, and high-force devices under low actuation voltages (Chow & Lai, 2009). Actuation is based on the thermal expansion caused by Joule heating. Usually, the heating is achieved by passing current through the beams to cause resistive heating. V-shaped actuator or chevron is widely used due to its small footprint and high force (on the order of mN) (Zhu & Espinosa, 2005; Zhu, Moheimani & Yuce, 2012), but they cannot achieve large motion (typically up to a few μm) (Zhu & Espinosa, 2005). Two possible limitations exist for the V-shaped actuators. The first limitation comes from the slanted beams. Slanted beams pose challenges for fabricating small features with smooth sidewall surfaces, which deteriorate as the beams width gets close to the resolution of photolithography (typically ∼2 μm). Other limitation is due to the large stiffness of the Vshaped actuator (on the order of thousands of N m−1 and above). As a result, the V-shaped actuators cannot be used as load sensors and actuators simultaneously (Guan & Zhu, 2010). Thus, additional load sensors are required for applications such as nanomechanical testing (Zhu & Espinoza, 2005) and nanomanufacturing (Dong & Ferreira, 2008). Z-shape actuator unlike the previous, facilitates the fabrication due to not presents the slanted beams. Unique angles involves are present in Z-shape and they are right angles (Guan & Zhu, 2010). While the basic principle of operation is similar to the conventional actuator with V-shaped beams, the configuration of the Z-shaped beams means that the mechanism’s mechanical stiffness in the reverse direction is similar to that in the direction of actuation. Thus, two actuators can be effectively coupled back-toback to create a structure that possesses bidirectional motion (Rakotondrabe, Fowler & Moheimani, 2014). The objective of this paper is to present an electrothermal microactuator optimizing the length of the Z-shaped beams based on the geometry presented in (Guan & Zhu, 2010), which provides a larger displacement, compared to the V-shape actuator. An analysis of the beam shape was realized to find the length providing the larger displacements of the central shuttle. Simulations require the application of an electrical potential in the anchors of the actuator to thereby ob (...truncated)