Active material micro-actuator arrays fabricated with SU-8 resin

Abstract

Active materials such as piezoelectric ceramics and shape memory metal alloys commonly actuate active control and intelligent material systems. Commercially available piezoelectric materials exhibit small actuation stroke and shape memory metal alloys have limited bandwidth. The proposed micro-actuator array design and fabrication process increases the actuation stroke of piezoceramic material by a factor of 1.5 for a 2´2 array; two active material segments connected in parallel and two in series, and doubles the response time of a 1´4 shape memory alloy driven array; four active materials segments connected in series. A high aspect ratio fabrication method incorporating SU-8 resin and conventional lithography is the process that forms the array linkages. The SU-8 resin array structures are 300 lm tall. IntroductionActive materials such as piezoelectric (e.g. PZT) ceramics and shape memory alloy metals (SMA) are the core of many active control and intelligent material systems. These materials have limited performance parameters which restrict active control applications. Piezoelectric materials have a maximum actuation strain of 0.6% Cross (1998) reported. Shahin et al. (1994) found the actuation frequency limitation of a SMA wire 0.081 cm in diameter and 3 mm long to be 1/200 Hz for the case of free heat convention. PZT and SMA micro-actuator arrays mitigating stroke and frequency limitations are detailed in Figs. 1 and 2.The operation of the actuators is related to the geometry of the active material and the surrounding mechanical ampli®cation mechanism array. The strain of an array is greater than the strain of a monolithic piece of active material of length L if, nleR > L 1 or the total number of active material elements (n) within the array multiplied by the length (l) of the elements (assuming elements of equal length) multiplied by the ampli®cation ef®ciency term (e) and R the ampli®cation ratio value of the arrays (assuming consistent R values) is greater than the total length of the array and a monolithic active material element L. The ef®ciency of the ampli®-cation method is dependent on the ampli®cation method, material and design of the array. The mechanical advantage R is related to the mechanical ampli®cation system which re-balances the relationship between the force and actuation stroke of active materials and is a function of phi (/) as depicted in Fig. 3. The terms d in and d out indicate the stroke input from the active material and the levered stroke output of the ampli®cation mechanism. The term l applies to the length of the active material element. As active elements expand or contract within the ampli®ca-tion array they produce an ampli®ed stroke perpendicular to the direction of active material dimension change. Ampli®cation ratio relationships for several ampli®cation methods are summarized by Pertsh et al. (1998). The total force output of an array is dependent on the mechanical lever system and the number of array elements placed parallel to the output direction of the array. Increasi...

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