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Joost van Honschoten (promotion date: 16 April 2004)

Modelling and Optimization of the Microflown

Promotion date: 16 April 2004

The Microflown is an acoustic sensor, a very small device measuring sound. This is of course something a microphone also does. In a microphone the pressure is measured. Sound is not also produced by pressure but also by a rapid movement of particles. The Microflown operates on the principle of measurement of the speed of sound. In a Microflown there are two very thin wires, much thinner than a hair – if air flows past it, one little wire will cool more rapidly than the other.

The temperature difference of the wires causes a resistance difference between the wires, which can be measured electronically. So in fact you measure the speed of the particles. This principle is used in the Microflown to measure sound.

What was your thesis about?

I had better first explain about the Microflown: The Microflown is an acoustic sensor, a very small device measuring 'particle velocity'. While normal microphones measure the acoustic pressure, the Microflown is based on the principle of measuring particle velocity; the movement of fluid particles due to a sound wave. In a Microflown there are two very thin wires, much thinner than a hair – if air flows past it, one little wire will cool more rapidly than the other. The temperature difference of the wires causes a resistance difference between the wires, which can be measured electronically. So in fact you measure the speed of the particles.

Why would you want to use a Microflown instead of a microphone?

A Microflown has certain advantages. It basically constists of two tiny wires and is therefore much cheaper. And a major advantage is that with a Microflown with three sets of wires you can also determine the direction of the sound. The sensor is also suitable for acoustic measurement in the so called 'very near field', and facilitates the measurement of structural vibrations.

I understand the Microflown is not your invention?

No, it already existed when I started my promotion research. Hans Elias de Bree invented it about 10 years ago here at this university and patented it. But it still needed a lot of modelling and some of the principles were not completely understood (as) yet. If you want to improve it, you need a more detailed understanding. We made a new model. On the basis of the model conclusions were made towards its optimum dimensions. The spin-off is a small business actually producing it now.

How big is it?

Well, of course it is bigger than these tiny sets of wires, because the device needs a packaging. But it is small, size of a short pen.

Was that the purpose of your research, the development of a small working device measuring sound?

I have a specific interest in modelling. I like the puzzle of it. The Microflown was a good subject. We understand the thing much better now and can meet specifications that trade and industry may want for certain purposes.

Did you experience any setbacks during your research?

Actually, I have been lucky. I established a contact with a Russian group, working with the micrflown for an acoustic company in Germany. I was extremely impressed by the expertise and inventiveness of Vitaly Svetovoy, who would certainly be a professor had he been in the Netherlands instead of Russia. We mailed and I he gave a tremendous impulse on the theoretical description. He has been here for a scientific visit for six months. He actually was a kind of mentor to me. He is now here for a second visit and is on the promotion committee.

What did you enjoy most?

The research itself, as I said I do like a puzzle. I also enjoyed the teaching part of it very much. I felt very much part of a team with the students.

What are you going to do next?

That is one thing I don’t like about being in research, the uncertainty. The possibility for a permanent position at a university is very limited. So in fact you go from postdoc to postdoc.

For personal reasons I would like to stay in Enschede, so I have been very active in the thinking up of new lines of research and writing up proposals for new research. I can’t afford to just sit and wait until something comes my way. But the writing up of such a proposal takes months – and I wrote three!- and after that you can only hope that the institutions are interested enough to provide the funds.

I managed to obtain a job for the next four years, which has to do with the Microflown again.