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Dennis van den Broek (promotion date: 31 October 2008)

Explosive micro-bubble actuator

Promotion date: 31 October 2008

Thesis advisor: Prof. Dr. Miko C. Elwenspoek

A new type of micro-actuator is built, using explosive bubble generation to achieve a fast and powerful deflection of a membrane. Specific properties and achievements, such as stroke, force and operating frequency are studied.

What was the main challenge when you started this project?

I studied at Delft University of Technology, and came into contact with the MESA+ institute in Twente. I visited several groups, looking for a thesis-project. From the beginning I liked this subject.

First of all, it was formulated in a very open way. The question was to construct and show this new actuator principle, and formulate the physical advantages it could bring.

Secondly the project involved micro- and nano-features. The heating element I used is 10-50 x 200 micrometer, the membranes are about one millimetre big, but their thickness is only one micron but it must be able to deflect, in a short time, until about eight micron.

Why is such a new actuator necessary?

In micro-systems a lot of principles are used, all having their advantages and disadvantages. For example: electrostatic actuators are not that powerful and thermal actuators are a little slow in some circumstances. Piezo-elements are often made of toxic materials and are more difficult to incorporate in the standard fabrication processes. The micro-bubble actuator could have a nice combination of properties, suitable for specific applications, for example to pump certain liquids.

What were your findings?

First of all, it appeared possible to construct these actuators using proven Mems fabrication techniques. In building the actuator, I also constructed a platform to investigate the bubble dynamics. The process of the bubble formation, growth and collapse still raises a lot of questions. An advantage is the transparency of the membrane, which facilitates further investigations.

An important moment was when I saw the actuator functioning well. This was a short period before an important conference. We did some measurements, which showed it was really working. We took some risk by sending our contribution immediately towards the conference.

Can we find this actuator in applications in the future, you think?

That depends. I could show the actuator is fast, and it performs well as it handles the deflections quite well. I hope the project will have a second stage soon.

The challenge is to select an application where existing actuators don’t perform well enough. The actuator should be build in, in an integrated chip. A nice feature of the membranes is that the smaller they become the better they perform, relatively.

What future plans do you have?

I am looking for a job in industry. Research I like, but preferably not in an academic setting. The application side I find very interesting.

What are important developments for MESA+ to remain successful in the future?

There are certain trends that MESA+ responds to very well, for example the growing importance of nano/bio combinations.

MESA+ further has a healthy combination of freedom in investigating new principles and fundamental research on the one hand, and looking for applications on the other.

The existence of small company spin-offs, surrounding the university, guarantees that the development of new technologies are taken further on the line, towards real commercial applications. This is a big advantage, I think, in comparison with other institutes.