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Scientists Design Highly Sensitive Force Sensor

Scientists at the Indian Institute of Science, Bangalore have proposed a new force sensor that can detect changes in forces as small as ten nano-Newtons. That’s one hundred millionth of a Newton, the unit of force! The proposed sensor uses a special crystal with specific resonation characteristics that can sense these tiny forces. Sensors that detect small forces are used in the fields of chemical sensing, bio sensing, temperature sensing, humidity sensing, pressure sensing, and stress sensing. An eight-member team from the Department of Electrical Communication Engineering and the Center for Nano Science and Engineering headed by Prof. T. Srinivas, is behind this innovation.

Photonic crystals have special optical properties because they have an insulator that can be polarized under an electric field. These crystals have a dielectric constant that alternates between high and low in a very specific arrangement. They can either let photons through their structure or not based on the energy of the photon. This results in “band gaps” where photons with a range wavelength are blocked, and “bands”, where photons of specific wavelengths allowed. This property gives rise to interesting optical phenomena, like variation of refractive index and low-loss wave guiding. The researchers have harnessed this in their innovation.

Though not the first of its kind, the proposed Photonic Crystal Resonator is a novel innovation. “It is better than the existing ones with greater sensitivity, Q factor, resolution and size of the sensor”, says Prof. Srinivas. Photonic sensors available today can detect forces in the range of 37nN, while this can detect forces as small as 10nN. 

The team was also successful in improving the “Q factor”, which often decreases drastically as applied force increases. The Q factor is a dimensionless parameter that indicates the energy losses within a resonant element.

When asked what one of the best achievements of their project was, T. Srinivas said that it was “ “The optimization of photonic crystal ring resonator to have high vertical quality factor and minimum radiation losses and hence can be used in applications where Q factor is crucial.”

What are the uses of such a sensitive device? “It can be used in accelerometer, since it is extremely sensitive to small forces, if the cantilever is appropriately functionalized, it can be used for various bio sensing applications,” says T. Srinivas. With the right additions and refinement, however, their proposal can be adapted to any field that requires sensing nanoscale forces. And in a world where nanotechnology will soon become the new norm, their work will be extremely significant when applied.

About the authors:

Prof. T Srinivas is an Associate Professor at the Department of Electrical Communication Engineering. Sreenivasulu T, V R Kolli, Anusree K, Yadunath TR and Badrinarayana T are research scholars at the same department.

Gopalkrishna Hegde and S Mohan are from the Center for Nano Science and Engineering. The corresponding author can be contacted on tsrinu@ece.iisc.ernet.in

About the paper:

This research work was presented at the IEEE SENSORS conference under the title “Photonic Crystal Based Force Sensor on Silicon Microcantilever”. The abstract can be found on http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=7370225&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D7370225