Sai Aditya Raman Kuchibhatla

Bio: Sai Aditya Raman Kuchibhatla is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Metamaterial & Physics. The author has an hindex of 2, co-authored 9 publications receiving 20 citations. Previous affiliations of Sai Aditya Raman Kuchibhatla include Georgia Institute of Technology & National Institute of Technology, Karnataka.

A transformation elasticity based device for wavefront manipulation

Abstract: The authors propose a metamaterial plate made of gradient refractive index phononic crystals for manipulation of the wavefront of propagating elastic waves in solid media. A square unit cell with through holes is considered as the basis for the proposed metematerial. Guidance on the design of the hole pattern and the choice of materials is obtained with the aid of transformation elasticity principles. Manipulation of a plane wavefront into a cylindrical wavefront is first observed through Finite Element simulations at low frequency (100 kHz), and then practically demonstrated through experiments. Wave propagation with and without the holey region is compared and possible applications at higher frequencies are discussed.

Performance of magnetorheological elastomer based torsional vibration isolation system for dynamic loading conditions

Abstract: Vibration isolation is an effective method to mitigate unwanted disturbances arising from dynamic loading conditions. With smart materials as suitable substitutes, the conventional passive isolators have attained attributes of semi-active as well as the active control system. In the present study, the non-homogenous field-dependent isolation capabilities of the magnetorheological elastomer are explored under torsional vibrations. Torsional natural frequency was measured using the serial arrangement of accelerometers. Novel methods are introduced to evaluate the torsional stiffness variations of the isolator for a semi-definite and a motor-coupled rotor system. For the semi-definite system, the isolation effect was studied using the frequency response functions from the modal analysis. The speed-dependent variations for motor-coupled rotor system were assessed using the shift in frequency amplitudes from torque transducers. Finite element method magnetics was used to study the variations in the non-homogenous magnetic field across the elastomer. The response functions for the semi-definite rotor system reveal a shift in the frequency in the effect of the magnetic field. Speed-dependent variations in the frequency domain indicate an increment of 9% in the resonant frequency of the system.

A comparative study on the effectiveness of system parameters in monitoring pre-load loss in bolted joints

Abstract: This article presents the monitoring of bolt loosening in a single bolted lap joint between two steel beams. The bolt loosening is initially studied using system modal parameters for various boundary conditions. Natural frequency and modal damping ratio in lower modes were not found to be reliable. Transmissibility function was seen to have a more reliable trend to identify the state of the joint. An in-house setup was developed to produce loosening in the bolted joint. Testing configuration was optimized by structural analysis. Strain measurements were carried out using Fiber Bragg-grating sensors while sinusoidal load was applied on the test structure. The results have been used to discuss a viable approach to identify the health of, or recognize a loosening trend, in a bolted joint.

Semiconductor-based thermal wave crystals

Abstract: One-dimensional phononic crystals made of silicon (Si) and germanium (Ge), both of which are materials commonly used in semiconductor devices, are shown to be effective in inducing bandgaps in the dispersion of heat flow at the nanoscale. Numerical approaches are used to understand the dispersion and propagation of thermal waves in Si–Ge phononic crystals. The results show for the first time how nanostructuring could yield band gaps in the dispersion of thermal phonons in the GHz range. We arrive at conditions that can yield bandgaps as high as 40 GHz; this is a bandgap that exceeds the value reported thus far. Variations in the unit cell dimensions are studied to understand the corresponding evolution in the bandgap frequencies. The control of heat using such proposed media holds promise for better heat management solutions for modern electronic devices, nanoscale sensing as well as for novel applications including the development of thermal diodes and thermal cloaks.

Elastic metasurfaces for splitting SV- and P-waves in elastic solids

Abstract: Although recent advances have made it possible to manipulate electromagnetic and acoustic wavefronts with sub-wavelength metasurface slabs, the design of elastodynamic counterparts remains challenging. We introduce a novel but simple design approach to control SV-waves in elastic solids. The proposed metasurface can be fabricated by cutting an array of aligned parallel cracks in a solid such that the materials between the cracks act as plate-like waveguides in the background medium. The plate array is capable of modulating the phase change of SV-wave while keeping the phase of P-wave unchanged. An analytical model for SV-wave incidence is established to calculate the transmission coefficient and the transmitted phase through the plate-like waveguide explicitly. A complete $2\pi$ range of phase delay is achieved by selecting different thicknesses for the plates. An elastic metasurface for splitting SV- and P-waves is designed and demonstrated using full wave finite element (FEM) simulations. Two metasurfaces for focusing plane and cylindrical SV-waves are also presented.

Fabricating and Assembling Acoustic Metamaterials and Phononic Crystals

Abstract: Acoustic metamaterials (AMM) and phononic crystals (PC) have the potential to unfold a new wave of disruptive technologies to radically transform human interactions, sensory communications, and beyond. Although essential, cultivating a deep understanding of the fundamental theory and design principles is insufficient alone, in the practical advancement of AMMs and PCs. Equally important is the physical realization of these artificial structures for tangible prototyping and experimental investigation; however, such aspects are seldom discussed in literature. Herein, the fabrication and assembly approaches for AMMs and PCs are critically examined, with a tight coupling of theoretical and experimental considerations. Crucial parameters like operating frequency, materials, and geometry for efficient structural implementation are addressed. Herein, fabrication methods for specific structure types are categorized under “single-step fabrication” including printing and machining and “multi-step fabrication” like microfabrication and molding. Various “assembly” techniques are proposed, such as for ordering colloidal assemblies or fastening components without adhesives. This framework uncovers innovative designs, e.g., origami-based structures with conductive coating, only accessible if fabrication and assembly aspects form an integral part of the initial design phase. By establishing a greater understanding and awareness of these methods, a host of undiscovered pathways, opportunities, and research gaps is revealed, supporting a fresh paradigm for innovation.

Non-reciprocal Wave Phenomena in Energy Self-reliant Gyric Metamaterials

Abstract: This work presents a mechanism by which non-reciprocal wave transmission is achieved in a class of gyric metamaterial lattices with embedded rotating elements. A modulation of the device's angular momentum is obtained via prescribed rotations of a set of locally housed spinning motors and are then used to induce space-periodic, time-periodic, as well as space-time-periodic variations which influence wave propagation in distinct ways. Owing to their dependence on gyroscopic effects, such systems are able to break reciprocal wave symmetry without stiffness perturbations rendering them consistently stable as well as energy self-reliant. Dispersion patterns, band gap emergence, as well as non-reciprocal wave transmission in the space-time-periodic gyric metamaterials are predicted both analytically from the gyroscopic system dynamics as well as numerically via time-transient simulations. In addition to breaking reciprocity, we show that the energy content of a frictionless gyric metamaterial is conserved over one temporal modulation cycle enabling it to exhibit a stable response irrespective of the pumping frequency.

Waveguide metamaterial rod as mechanical acoustic filter for enhancing nonlinear ultrasonic detection

Abstract: Nonlinear ultrasonic guided waves are among the most promising new tools for early stage damage detection owing to their high sensitivity and long-range propagation features. However, signatures from instrumentation, transducers, and couplant effects create false positives mixing with the material- or defect-induced nonlinearities, leading to inaccurate measurements. Here, we propose a novel technique using a waveguide metamaterial rod, which acts as a mechanical acoustic filter for suppression of higher harmonic components in the measured signal. The proposed waveguide metamaterial consists of an array of flat axisymmetric ridges arranged periodically on the surface of the rod. It is experimentally demonstrated that the higher harmonic components are filtered when the proposed metamaterial rod is placed at the transmission side, thus removing unwanted nonlinearities from the received signal in a pitch-catch configuration. Furthermore, the application of this method is demonstrated by detecting a discontinuity in the workpiece through its nonlinear response enhanced using the metamaterial. This technique is attractive for early stage material diagnosis in engineering, biomedicine, and health monitoring of critical engineering assets.