MEMS' World - Actuation
MEMS often involves movable parts, making them microactuators. They can be vibrating, translating, rotating, etc., they all need a mechanical energy to move. This page tries to review briefly the commonly used technics to get a movement from an object, considering the tiny scales met in microactuators for MEMS actuators design, and the different constrains you have for a particular application. Here you will understand what we mean by electrostatic actuator, thermal actuator, etc. For every introduced technic, we will see principles and examples.
Problem: Get some energy!
To get a movement from an immobile object, you need some mechanical energy. There are a lot of ways to get it. It can come from electricity, chemical reaction, light, etc.
In a MEMS device, the only external energy you can easily bring is electricity. If you want another resource, you need it to be already present at microscale.
This can be a potential mechanical energy: a mechanical strain is applied to a part at the end of the fabrication process, but this is useful only temporary, then it is impossible to get some new energy except by straining the energy storing part again. This is used in the particular case of Shape Memory Alloy. We will see it later.
Optical energy can be used thanks to the optical pressure phenomena. In fact, optical energy is used to manipulate tiny objects. That's what we call Optical Tweezers. But they currently cannot be integrated, so the only available applications need quite heavy macroscopic equipment.
Thermodynamic energy, i mean air/liquid pressures, etc. could be another solution, but at the end, if you want an integrated system. These are very useful in microfluidics devices. But it concerns liquid or micro-objects manipulation, not MEMS's moving parts.
Chemical reaction would be another solution, and we should see in a few years only autonomous MEMS storing their own embedded fuel cells able to supply energy for a duration, before the need to load it again. But even in this case, the fuel cell would not be directly converted in mechanical energy, but in electricity. A tiny explosive motor could be fabricated, but at this scale, this solution is not relevant, or at least not yet.
The easiest way is currently by electricity coming from contacts placed around the device, both for controlling it and supply the needed energy.
So, if you want a movement, you need to integrate a transducer, able, by a way or another, to convert electrical energy in mechanical energy. The good news is that we know plenty of ways to convert electrical energy in other ones! These other ones are going to be widely used!! In the rest of this page, all actuation principles get their energy from electricity, conduction, from an external power supply.
I will probably not be exhaustive in these pages about the way of getting a movement. But these are the most widely used in the MEMS design.