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Karnati Kumar Sai Charan – Dual Degree ECE

Karnati Kumar Sai Charan received his MS-Dual Degree in Electronics and Communication Engineering by Research (ECE). His  research was supervised by Dr. Aftab M Hussain.

 

Here’s a summary of Sai Charan’s thesis,   Design of micro-heaters inspired by space-filling fractal curves as explained by him: 

Micro-heaters are of major importance in various applications such as thermotherapy, drug delivery, gas sensing and other MEMS applications Further, recent studies have shown the use of micro-heaters for targeted destruction of malign cancer cells. One key area of application for micro-heaters is gas sensing, where temperature uniformity is required to have high sensitivity and low power.

Illustration of a flexible metallic heat-pad based on a fractal metal coil design that can be used for thermotherapy

Textile electronics are increasingly becoming an important field of research. One of the key features of smart textiles is the ability to control core body temperature in different weather conditions. Particularly, the idea of battling cold weather conditions using self-heated textile is intriguing. It can be done in various types of textiles like in jackets for military personnel who fight in the cold climate and in hand gloves for skiers [9] etc. Another important aspect is that the heating element needs to be stretchable since it is used in textiles. The key requirements of using a micro-heater are low power consumption, low areal footprint, low cost, and fast response. This work presents the idea of using a space filling fractal curve as the heating element in micro heaters. Since the heating element of a micro-heater are based on metal coils, that will be the costliest component of a micro-heater. However, if we try to increase the spacing in between the metal coil that leads to hot-spots and thereby non-uniform distribution of temperature. Hence, a cost-effective heater should have excellent uniform temperature distribution, while having minimum metal consumption. Further, non-uniform temperature distribution will give rise to non-uniform temperature gradient between the environment and body. The geometry of the heater plays a crucial role in its average temperature (Tµ) and uniformity. This work talks about multiple types and orders of space filling fractal curves as the geometry for heaters, modelled and simulated all of them as heaters and showed that they are on par with the typical double-spiral heat-pad in terms of several criteria like average temperature and temperature uniformity while being cost-effective due to optimal distribution of metal. This work presents modelling of modified Hilbert, Moore and Peano fractal curves as micro-heaters.

Modified space filling fractal (a) Hilbert order-2 (b) Hilbert order -3 curves

Modified space filling fractal (a) Moore order-2 (b) Moore order-3 curves

Modified space filling fractal (a) Peano order-2 (b) Peano order-3 curves

Double spiral geometry modelled in COMSOL

In order to make a fair comparison among the heaters, a constant power of 1 W was supplied to all the heaters, also the heaters were confined to a fixed area of 30 mm x 30 mm. Finite Element Analysis (FEA) results showed that heating elements based on the geometries of Peano order 3 curve, Hilbert & Moore order 4 curves outperformed double-spiral heating element in terms of temperature uniformity with less metal consumption (cost effective), also all the geometries are modelled with same material, thickness and width. Heaters based on Peano order 3, Hilbert & Moore order 4 curves, showed a non-uniform temperature distribution () of 2.2%, 4.4% and 4.3% respectively whereas double spiral had a non-uniformity of 5.8%. However, the average temperature (Tµ) was lower by 10 K for Hilbert and Moore order 4 and 50 K for Peano order 3. Further, heaters one fractal order lower than these, i.e., Peano order 2, Hilbert & Moore order 3, have given the average temperature (Tµ) close to double spiral heater while consuming only half the metal that a double spiral takes, thus promising significant reduction in metal consumption. Peano order 2, Hilbert and Moore order 3, showed a a non-uniform temperature distribution of 7.24%, 11.7% and 11.6% respectively, which makes them slightly more non-uniform than the double-spiral heater. With many fractal patterns to choose from, space-filling fractal curves can provide very good performance while being cost effective as the heating elements in a micro heater.