Hydraulic controlled polyester-based micro adaptive mirror with adjustable focal length Ammar A. Alzaydi a , John T.W. Yeow b, * , Sangjune L. Lee c a Department of Mechatronics and Mechanical Engineering, University of Waterloo, ON, Canada N2L-3G1 b Department of System Design Engineering, University of Waterloo, ON, Canada N2L-3G1 c Department of Electrical Engineering, University of Waterloo, ON, Canada N2L-3G1 Received 30 November 2006; accepted 8 October 2007 Abstract Currently micro-electromechanical systems (MEMS) technology is creating micro-mirrors for applications such as scanning and adaptive optics. A 0.5 lm thin, reflective polyester sheet is used to create a 950 lm diameter flexible mirror that is capable of changing its concavity. A system that consists of electrical circuits and LabVIEW interfaces were used to control the mirror. This paper presents a micro-mirror that is fabricated from a 0.5 lm thin, reflective polyester sheet clamped with aluminum disks. An electromagnetic plunge actuator controls the pressure beneath the mirror to change the curvature of the mirror. The focal point of the micro-mirror ranges from approximately infinity to 3.5 mm. This range is much wider than the ranges that are typical of MEMS mirrors. The curvature of the micro-mirror can be altered at a maximum observable frequency of about 15 Hz. The micro-mirror center depth movement is at incre- ments of approximately 2 lm and the focal length increment of change is approximately 5 mm. The mirror is capable of dynamically focusing on objects at a distance of 6 cm to longer than 7 m away from the mirror. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Micro devices; Electro-mechanical systems; Hydraulic control; Polyester reflective film; Micro-mirror; Adaptive optics; Piezoelectric; Electro- magnetic actuation and image focusing 1. Introduction Unlike integrated circuits, MEMS devices consist of physical mechanical structures such as thin support mem- branes (for pressure sensors) or cantilevers (for accelerom- eters) that are created by methods of selective material removal and successive material addition [1,2]. One of the most popular MEMS applications is in the optical domain [10]. Optical MEMS devices such as micro-mirrors are used in applications such as barcode scanners [11], optical read- write heads [12], and scanned-beam imaging [13] or display systems [14]. Another application of micro-mirrors is in adaptive optics (AO) [15]. AO are optical systems, which adapt to compensate for optical effects introduced by the medium between the object and its image [16]. It provides means for compensating diffraction effects, leading to shar- per images [6]. Dynamic wave front aberration occurs in telescope systems due to turbulence in the earth’s atmo- sphere [7]. In order to restore the image, the light is reflected off of a deformable mirror, which cancels the dis- tortion of the wave front [4,5]. The miniaturization of mirrors has the potential for great impact on such applications as scanning and adaptive optics. The dynamic focus control of the micro-mirror can be used for applications such as in the optical imaging devices of endoscopes [17]. An array of mirrors could be used to improve images by wave front aberration correc- tion [18]. Micro-mirror with the capability to focus dynam- ically is likely to replace traditional MEMS micro-mirrors. 0957-4158/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mechatronics.2007.10.002 * Corresponding author. Tel.: +1 519 888 4567x32152; fax: +1 519 746 4791. E-mail address: jyeow@engmail.uwaterloo.ca (J.T.W. Yeow). URL: http://biomems.uwaterloo.ca (J.T.W. Yeow). Available online at www.sciencedirect.com Mechatronics 18 (2008) 61–70