The Mind of an Engineer: Volume 2 pp 257-261 | Cite as

# R&D in Indian PSUs: My Experience

## Abstract

I was initiated into research at Applied Physics Laboratories, Andhra University to work in the area of thin films with specific task initially on the development of a thickness monitor for films formed using vacuum evaporation. In those days, universities did not introduce transistors in the curriculum. Only circuit design using vacuum tubes used to be taught and laboratories were equipped with the needed electronic components. The problem was to use reflectance of thin films as measure of thickness when aluminium is being deposited. Unfortunately, the light from the tungsten filament was much more than the reflected light of a source. In order to distinguish these two, one signal and another noise, the reflected beam needs to be made different in some way. One known solution was to use modulation for the source being beamed on the thin film on glass substrate by chopping it. Thus one is having a frequency component depending on the motor speed and number of holes on the circular disc connected to the axle of the motor through which light is sent to fall on the device under test. The job was to design a bandpass filter to select he needed frequency component and reject the huge noise (light from the filament). The whole process happens in few seconds to take the aluminium or other metal like tin, copper in a crucible kept in the heated filament.

## References

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