Novel magnetic microdevices were developed for magnetic field generation and concentration and successfully characterized and tested for magnetic potential focusing which is very important for various MEMS applications such as magnetic particles manipulation. These microdevices have been fabricated using an innovative processing sequence which eliminates many problems associated with other fabrication techniques and provides a platform for adding other subsequent fabrication steps required to integrate the microcoils with other microcomponents. They consist of high aspect ratio planar coils made of electroplated copper embedded in the silicon substrate, with ferromagnetic pillars and backside plates made of a CoNiP ternary alloy. A large magnetic field gradient is generated and enhanced by two structural parameters: the small width and high aspect ratio of each single conductor and the ferromagnetic pillars positioned at high flux density locations. This arrangement creates very steep magnetic potential wells, in particular at the vicinity of the pillars. The manipulation of micromagnetic particles in a static and continuous flow conditions has been demonstrated.

This study demonstrates precise profile control of 3D lateral junction traps in silicon by exploiting a 2D mask layout and isotropic etching. The traps penetrate through silicon partitions and laterally link microfluidic channels. Since the trap constrictions cannot be registered directly by planar lithography, they are not trivial to define but critical for capturing cells in suspension. A special mask layout introduced here when combined with isotropic etching can form elliptic and circular constrictions. The mask layout offers three design parameters: two geometric angles and a separation distance between them. The design parameters have been systematically varied and a set of corresponding trap structures have been fabricated. Mapping of the constriction profiles to design parameters indicates that the constriction shape is mainly determined by the two design angles whereas the constriction size is controlled by the separation distance and total isotropic etching. It is shown that a circular constriction can be fabricated by setting the two angles such that their harmonic mean yields a critical value of about 45°. The constriction size may vary from several micrometers to tenths of micrometers depending on the separation distance and isotropically etched amount.

The dynamic analysis of a twin stator electrostatic wobble motor is presented incorporating finite element electric field predictions and rolling and sliding friction models. The problem of torque measurement in actual devices is then examined and a solution is described which allows the evaluation of torques smaller than 10(-7) Nm without affecting the wobble motion of the device. Theoretical and practical results for actual devices are compared. [308].

A novel design of an electrostatic wobble motor is presented, which incorporates multiple concentric rotor-stator surface pairs to increase the space-usage efficiency and a segmented bearing for the implementation of synchronous control. The device has been successfully fabricated using the Lithographie, Galvanoformung, Abformung (LIGA) technique. The finite-element method is used to predict the available output torque, and the potential for extracting the useful output from the device is assessed.

This work concerns the alleviation of friction in a novel design of multistator electrostatic wobble motor. The output torque and the kinematic accuracy of this device are limited by the sliding friction between the rotor and the top surface of the bearing. A solution for an axial bearing has been developed using an advanced LIGA technique to integrate polymethylmethacrylate (PMMA) cylinders into nickel micro structures. A new version of the micromotor has been fabricated, utilizing an axial electrostatic field to hold the rotor against an engineered sliding surface. The integrated bearing stabilizes the rotor and potentially permits operation in liquid environments by sealing the stator electrodes. [334].

Dynamic analysis of electromechanical microactuators requires a time domain solution of potentially complex coupled mechanical and electromagnetic problems. Finite element analysis (FEA) is a proven technique for the numerical solution of arbitrary problems, however the creation and evaluation of FEA descriptions can be expensive in computational resource and time requirements, particularly in three dimensional physical models. The solution of coupled problems increases the problem dimension and can place huge demands on computational resources. The dynamic analysis of a novel twin stator wobble motor is considered here with the aim of examining the accuracy of numerical electrostatic models and to demonstrate a procedure for the solution of coupled field problems in the time domain using existing FEA software. (3 pages)

Dynamic simulation of milimeter-scale micromotors using finite-element methods to model the electrical, mechanical, and fluidic force interactions requires that these representations be computationally efficient, yet sufficiently accurate to ensure convergence on a sound solution. This paper examines an analytic model, together with two-dimensional (2-D) and three-dimensional (3-D) finite-element electrostatic torque models, of a double-stator wobble motor, to assess the trade-off between accuracy and computational efficiency, with a view to incorporate the optimum model within a dynamic simulation of a motor of this type. [195]

The construction of a LIGA fabricated actuator is shown. Rotor positional information is provided by segmenting the bearing, where the momentary continuity between adjacent segments is detected as the rotor rolls around the perimeter of the bearing. To minimise the number of additional connections, the bearing segments are connected in two sets, with adjacent segments in different sets. Given a known starting position, the rotor motion can therefore be tracked. Using this method, the actuator can be excited with synchronous signals without introducing excessive complexity to the actuator or controller. The prototype devices are 300 microns tall with the rotor and stator fabricated separately and assembled manually. The stator outside diameter is 2600 microns and gear ratios of 228 and 114 and minimum rotor stator air gaps of 5 and 10 microns have been produced. A patterned sacrificial titanium layer was used to create undercuts to pass the connections from contact pads to the bearing segments and the inner stator