Dr. Kshiteej J. Deshmukh
Department of Mechanical and Aerospace Engineering
University of Houston

Energy Conservation, Wave-Freezing and Other Phenomena in Space-Time Metamaterials

ABSTRACT: The spatio-temporal modulation of metamaterial microstructure has led to the discovery of novel and exciting properties like space-time mirrors, chromatic birefringence, space-time cloaking, and photonic-time-crystals (PTCs). Changing the microstructure properties of a space-time metamaterial while a wave is propagating through it, in general requires addition or removal of energy, which can be of exponential form depending on the type of modulation. This limits the realization and application of space-time metamaterials. In the first part of my talk, I will discuss how we resolve this issue by introducing a novel mechanism of conserving energy at temporal metasurfaces in a non-linear setting. The idea is first demonstrated by considering a wave-packet propagating in a discrete medium of 1-d chain of springs and masses. We then consider an interesting application of time-reversed imaging in 1-d and 2-d spring-mass systems with a wave packet traveling in the homogenized regime. Our numerical simulations show that, in 1-d, when the wave packet hits the time-interface two sets of waves are generated, one traveling forward in time and the other traveling backward. The time-reversed waves re-converge at the location of the source and we observe its regeneration. In 2-d, we use more complicated initial shapes and, even then, we observe regeneration of the original image or source. In the second part of my talk, I will discuss the interesting effects of introducing tailored non-local interactions at time-interfaces in phononic media. Most interestingly, our numerical simulations show the phenomenon of wave-freezing in 1-d and 2-d space-time materials, where a propagating wave can be halted on-demand without diffusing, at a location in space for as long as desired.

BIOGRAPHY: Kshiteej obtained his undergraduate degree in mechanical engineering, and has a masters degree from Indian Institute of Science, Bangalore in mechanical engineering. He got his PhD from Carnegie Mellon University in December 2021, where he was advised by Prof. Kaushik Dayal for his work on multiband homogenization for mechanical metamaterials. Following that, he was a Research Assistant Professor at the University of Utah in the Department of Mathematics where he worked with Prof. Graeme W. Milton on space-time media and finding bounds on effective properties. He will be starting a position as a postdoctoral fellow at University of Houston, where he will work with Prof. Pradeep Sharma.