Microcoil Design and Analysis for Actuation of Microstructures and Devices

This technical brief presents an overview the design and analysis of planar microcoil designs for use in the actuation of magnetic microstructures and devices. The microcoil’s feature sizes are in the range of microns with current loads less than 1 Ampere. The primary manufacturing method that is considered in modeling and designs of the micro coils is standard MEMS processes; processing method’s limitations dictate design parameters that determine feature sizes and aspect ratios. Modeling consists of a variation in parameters of coil features, and an analytical computation of the theoretical electromagnetic field produced using Biot Savart’s Law. Superposition is used to model microcoil interactions with varying center-to-center distances. INTRODUCTION The field of manipulating and actuating microstructures and devices is continuously developing. Methods for manipulating micro-objects include: grasping with miniature end-effectors; piezo-electric vibrations; electromagnetic fields; etc. The method that this paper explores is the use of electromagnetic fields to produce the driving force of actuation for micro-objects and devices. Manipulating magnetic bodies through electromagnetic fields can be done by two main methods: large, external electromagnetic fields, or small, localized magnetic fields. For example, the use of four Helmholtz coils, external to the staging area, can be used to control the motion of a single magnetic structure. The advantage to this design is the manipulation of micro devices with a large macro-scaled apparatus. The disadvantage, however, is that it becomes difficult to control more than one structure or device as the EMF will influence all bodies within the staging area. The second method, which is explored in this paper, is to have a substrate of small planar microcoils (Figure 1) that can produce localized electromagnetic field to control the structures or devices. In conjunction with a vision system and associated controls, micromanipulation of structures and devices can be achieved simultaneously and independently. By way of analogy: the external electromagnetic fields method is similar to tilting a sphere on a single large platform, while the localized microcoils method is similar to a tilting small tiled divisions of a large platform. There has been some recent work on using a wire-bonder to create 3D micro-coils for similar applications [3]. This is a serial process while we are interested in developing a low-cost, parallel process, using standard fabrication processes that can scale to large substrates. Fig. 1. Square Planar Microcoils Realized on a Flexible Substrate using Conductive Ink. Coil Width: 300μm DESIGN The design of the micro-scaled electromagnet can either be a single current carrying loop, or meandering coil of multiple loops. The advantage of a single loop design is its simplicity, however in order to supply the loop with a sufficiently large current to generate a strong magnetic potential, the crosssectional area must be increased to compensate the current load. Microcoils created with multiple loops, with a similar cross-sectional area can generate a greater field potential due to superposition while maintaining a low current load. The initial design parameter of the inner coil diameter (20 μm) used for the coils are based off of previous work in [1], which successfully created microcoils using photolithography