Micro Bubble Actuators (TET.6408)

Actuators are key components in microsystems: they are the machines that deliver mechanical work. To date we have basically two types of microactuators using electrostatic and thermal forces. Electrostatic actuators are weak but fast, while thermal actuators are strong but slow. In this project we intend to investigate an actuator which is potentially fast and strong. It employs the explosive-like generation of vapor bubbles in a liquid when a small electric resistor is heated quickly. Initial studies indicate the feasibility of the idea, but there is no demonstration that this principle can be used to actually use it for mechanical work, nor is the understanding of the associated phenomena on a level that allows the derivation of reliable models for the design of an actuator using explosive formation of bubbles. Naïve models suggest that it is possible to generate ten's of bar at a rate as large as ten's of kHz. In this project basic scientific issues and engineering issues will be addressed, both provide formidable challenges. Problems associated with microfabrication, experimental and theoretical studies, modeling and simulation, systems design all will be tackled in the project. The project will be carried out by two groups, one specialized in the physics of bubble generation, the other one specialized in microelectromechanical systems.

The need for faster and stronger microactuators is demonstrated by a statement often heard by engineers working in industry: Micromechanical systems are of no practical interest if the actuators are not capable to generate forces in the 1 Newton range (1 N = weight of 100 grams). Only then the actuators are strong enough to deliver the required acceleration of mechanical constructions (such as the optics in a DVD player). On the other hand it is stated that the use of microactuators for these types of systems would be very attractive and would facilitate further miniaturization of the systems. There are many other applications in which strong microactuators are needed, e.g. in pumps and flow controllers, microreactors, miniaturized chemical analysis systems, (ultra-) sound generators, microcoolers etc.
The project aims at a fundamental exploration of the properties, limits and drawbacks of the actuator. It will result in its basic understanding and an actuator in which a membrane is bent, delivering a pressure possibly up to 50 bar at a rate of up to 50 kHz. Such an actuator would outperform by far all existing microactuators - even if the performance would be substantially less - and would bring a new generation and new types of microsystems into reach.