An energy-based design criterion for magnetic microactuators

Abstract

Magnetic actuators can be divided into two types: those in which motion changes the gap separation (type I) and those in which motion changes the gap overlap area but not the gap separation (type II). In conventional magnetic actuators of both types, it is assumed that most of the magnetic energy is stored in the gap due to the large reluctance of the gap compared with the negligibly small reluctance of the magnetic core. However, in magnetic microactuators, the fabrication limitations on the achievable cross-sectional area of the magnetic core as well as the finite core permeability increase the core reluctance to the point that this assumption may no longer be valid. In this case, the magnetic energy is distributed in both the gap and the magnetic core, in which the energy distribution is in proportion to the reluctance of the gap and the reluctance of the core respectively. Using an elementary structure of a magnetic actuator, it is shown that for type I microactuators, when the initial gap of the actuator is fixed (e.g., determining the stroke of the actuator), the generated magnetic force has maximum value when the gap overlap area is designed such that the reluctance of the gap is equal to the reluctance of the magnetic core (i.e., ). For type II actuators, the initial overlap area of the actuator is fixed (determining the stroke); therefore the generated magnetic force has a maximum value when the gap separation is designed such that the above equality holds. This paper details both analytical and finite element method (FEM) analysis confirmation for type I actuators. Extension to type II actuators is straightforward.

A universal electromagnetic microactuator using magnetic interconnection concepts

“…Also plotted on this graph is the theoretical curve of deflection versus current as generated by the previously mentioned simulations. Good agreement is seen in this range of operation; however, it is interesting to notice that the device does not behave like a classical variable reluctance actuator in which one would expect the deflection to increase as a function of the current squared (1,4,7,8,26). As mentioned in the previous section, careful analysis of the MagNet simulations shows that the beam begins to saturate at a very low current of around 20 mA.…”

“…Initially, a theoretical model of the device was created based on lumped parameter analysis methods for magnetic circuits (1,4,7,8,26); however, this model proved inadequate due to the significant fringing effects and nonlinearities associated with this device. Therefore, a finite-element model was developed using Infolytica's magnetic simulation package, MagNet 6.0.…”

“…This can, in some cases, eliminate the need for separate power supplies to drive control electronics and MEMS components. Power consumption in magnetic actuators is usually an important concern; however, if the air gap of the magnetic circuit is optimized [26], power consumption can be minimized. In this work, for example, our actuators are shown to be capable of achieving nearly 8 m of deflection at an input power of less than 20 mW.…”

Magnetic Microactuators

“…In these devices, schematically shown in figure 3.2, the actuator can generate both attractive and repulsive forces [3,[21][22][23][24][25][26][27]. Figure 3.2 A schematic of a planar magnetic microactuator using a spiral inductor to generate a magnetic field and actuate a small magnet situated directly above the inductor [3,10].…”

“…In type B structures, the magnetic slider moves into the air gap. Magnetic circuit theory can be used to find the force that can be generated by these actuators, as discussed next [12,21,22]. In this device, the overlap area between the deformable part and the magnet is fixed and only the distance varies (type A).…”