Non-Hermitian Hamiltonians can have real eigen-values if they exhibit Parity and Time Symmetry (PT Symmetry). Parity is symmetry in space and time symmetry is reversal of the time arrow. Parity Time Symmetric systems exhibit completely real eigen states in unbroken PT region and complex eigen values in broken PT region. The broken and unbroken regions are connected by a transition point called exceptional point. There could be multiple exceptional points within a system, depending upon the degrees of freedom of the system. At exceptional points, the eigen values (complex in broken regime) and corresponding eigen vectors bifurcates as pitch-fork type orthogonal bifurcation to become two completely real and distinct eigen states. For a quantum mechanical system to be PT Symmetric, the complex potential energy should have positive imaginary part in left half of space and negative imaginary part in right half of the space. The negative imaginary part of potential energy can be achieved by supplying gain to the system.

My research is on studying classical coupled oscillators and possibility of using different types of soft materials to achieving the exceptional points. The gain in classical systems can be created by active feedback controlled driving whereas damping is an intrinsic property of various soft materials.

Materials which are stiff enough to support the structural weight and having the ability to damp vibrations are very important in many engineering applications. Vertically aligned carbon nanotubes or VACNT is a transversely isotropic foam like material which is stiffer than many packaging foam material and still more effective in damping vibrations due to its structural hierarchy and stiffness and density distributions. I work on synthesis of VACNT using chemical vapor deposition technique. The toluene vapors with Ferrocene as catalyst in an inert environment of Argon and Hydrogen deposits on a Silicon wafer substrate to form VACNT. The resultant 1-2 mm thick films of VACNT can be cut into small cylindrical pieces to study their quasistatic (stress relaxation) and dynamic (sinusoidal and ramp loading) mechanical properties.

I am also working in collaboration with beamline scientists of DND-CAT synchrotron research center, Argonne National Laboratory to characterize VACNT sample using X-ray diffraction analysis.

Nonlinear Acoustic Metamaterials

Locally resonant acoustic metamaterials exhibit low frequency ultra-wide band gaps which suppresses wave propagation through mechanical structures. Adding nonlinearity gives amplitude dependent tunability on the control of band gap width. I studied wave propagation in discrete periodic 1D and 2D chains using numerical techniques, analytical methods including modified Lindstedt Poincare method & harmonic balance method and experimental wave transmission measurement on 3D printed structures using laser doppler vibrometer.

Serpentine shaped microbolometer focal plane array

Microbolometers are uncooled infrared detectors as compared to their heavy and bulky cryogenically cooled counterparts. Microbolometer's electrical resistance changes as a response to incident thermal radiation (infrared radiations). The resistance change can be measured by supplying a constant current bias and then measuring the voltage. The whole focal plane array can be read by using multiplexer readout circuit. I worked on the thermoelectrical simulation of serpentine shaped microbolometer pixels and their 2D arrays using Ansys workbench. I also designed a multiplexer readout circuit for reading the output.