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Ramasubramanian Kottumakulal Jaganatharaja (promotion date: 29 June 2011)

Cricket inspired flow-sensor arrays

Promotion date: 29. June 2011

Promotor: Prof. dr. ir. Gijs Krijnen

Located at the rear-end of crickets, a pair of sensory appendages exist, called cerci, consisting of numerous mechano-receptive filiform hairs. These are capable of detecting minute air fluctuations in their environment, down to 0.03 mm/s amplitude.

This work reports on the successful realization of artificial hair sensor arrays capable of sensing low-frequency air-flows. Each hair sensor consists of a SU-8 hair, mounted on a suspended silicon-rich nitride membrane with a pair of aluminum electrodes. The silicon substrate acts as a common bottom electrode, forming a pair of sensor capacitors. When there is an air flow, the hair deflects and induces a membrane tilt, causing a change in the sensor capacitors. Flow sensing is then performed employing a differential capacitive sensing technique. Characterization shows a clear directional sensitivity and a flow sensitivity limit up to 0.85 mm/s.

Further, this work looked at different ways to optimize the sensor design. Key focus was on improving the hair shape, sensor springs and viscous coupling between closely-packed hairs. Of these, the experimental and theoretical results on viscous coupling provide important guidelines towards optimal sensor array designs, while simultaneously shedding light on biophysical effects in closely-packed hair sensor arrays.

Which were the highlights of your thesis project?

Viscosity-mediated coupling effects between artificial hair sensors were investigated for the first time. Prior to this only simulations and measurements performed on real hairs of spiders were done. Making such experiments on the actual animals is very difficult, as the samples are very random and it is not always possible to make reliable and controllable measurements on them.

During my research a dedicated micro-fabricated chip was realized where the hairs were defined for their hair length and position. Viscous coupling measurements performed on these chips proved to be very reliable. Such experimental setups could be extended, to be very useful for bio-physicists to understand these effects.

Do you recall some memorable moments during the project?

My work was part of a EU project. I had a unique opportunity to meet talented scientists across Europe: from France, Germany, UK, Denmark and Belgium, twice every year. There were a lot of discussions and presentations on subjects varying from behavioral biology, computational modeling and biomimetic robotics. It gave me nice moments. I could meet new people across Europe and at the same time interact with my colleagues from the University of Twente.

How did you develop personally, as a scientist and researcher?

During my PhD, I had to model the hair sensor, use micro-fabrication techniques in the cleanroom and characterize the sensors. During this process, I learnt a lot of new skills. Further working with my supervisor, professor Gijs Krijnen, is in itself a huge learning experience. Especially, during the writing of my thesis, his accurate critical remarks were indeed lessons for a lifetime, to put it in simpler terms. Personally I owe him a lot for sharing his vast knowledge and his support throughout my research.

What are your future plans?

Right now, I am working at ASML in Eindhoven, as a design engineer for state-of-the-art lithography machines. The work is not entirely related to my PhD thesis, though.

Nevertheless, the work and the environment is very different than it was in the university. This is a different jungle and the rules of survival are way different. Work is always on the run here in the industry and I am enjoying that challenging pace. I plan to continue my career in the industry from now on.

How did you experience working at Mesa+?

I am lucky to have worked at the Mesa+ institute with its talented scientists, experts and personnel. I was able to use top-notch technical facilities during my research. It's nice to see Mesa+ keeps growing more and more, especially with the new state-of-the-art nanolab.