Kiran Kumar Amireddy

Bio: Kiran Kumar Amireddy is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Metamaterial & Lens (optics). The author has an hindex of 4, co-authored 7 publications receiving 84 citations.

Holey-structured metamaterial lens for subwavelength resolution in ultrasonic characterization of metallic components

Abstract: This paper presents the implementation of holey structured metamaterial lens for ultrasonic characterization of subwavelength subsurface defects in metallic components. Experimental results are presented, demonstrating ultrasound-based resolution of side drilled through-holes spaced (λ/5) in an aluminum block. Numerical simulation is then used to investigate the parameters that can help improve the resolution performance of the metamaterial lens, particularly, the addition of end-conditions. This work has important implications for higher resolution ultrasonic imaging in the context of practical non-destructive imaging and non-invasive material diagnostics.

Deep subwavelength ultrasonic imaging using optimized holey structured metamaterials

Abstract: This paper reports the experimental demonstration of deep subwavelength ultrasonic imaging of defects in metallic samples with a feature size of λ/25 using holey-structured metamaterial lenses. Optimal dimensions of the metamaterial’s geometric parameters are determined using numerical simulation and the physics of wave propagation through holey lenses. The paper also shows how the extraordinary transmission capacity of holey structured metamaterials comes about by the coupling of higher frequencies in the incident ultrasonic wave field to resonant modes of the lens.

Porous metamaterials for deep sub-wavelength ultrasonic imaging

Abstract: This paper reports the application of a porous medium as an aperiodic metamaterial lens for ultrasonic imaging in the context of nondestructive evaluation and non-invasive diagnostics. Experimental results are presented, demonstrating a deep sub-wavelength imaging down to 1/36th of the operating wavelength, which is the highest resolution demonstrated worldwide using bulk ultrasound. The improvement in the resolution is shown to be linked to aperiodicity overcoming the Wood anomaly, which sets limits on wave transmission by holey structured lenses.

Characterization of Deep Sub-wavelength Sized Horizontal Cracks Using Holey-Structured Metamaterials

Abstract: Image resolution in classical wave applications is limited by the diffraction limit which corresponds to half the operating wavelength (λ). To achieve higher resolution, ways of overcoming the natural diffraction limits are of interest. In this paper, an experimental demonstration of deep sub-wavelength resolution in the ultrasonic regime using a metamaterial lens is presented. Metamaterial lenses effectively transfer the evanescent waves to the imaging plane, which carry the details of the sub-wavelength features. The successful transmission of the decaying evanescent waves which contain much larger wave vectors than the propagating waves enables to overcome the diffraction limit set by the operating wavelength. We report an imaging technique using optimized holey-structured metamaterial lens to characterize a horizontal crack of size λ/25 in a layered aluminium sample.

Subwavelength imaging of cracks in metallic materials

Abstract: In this paper we demonstrate the application of a holey-structured metamaterial lens for sub-wavelength imaging of defects in a metallic sample, in the ultrasonic regime. This type of lens, operating on the Fabry-Perot resonance principle, has earlier been demonstrated for super-resolution in the acoustic regime, and by the authors for nominal sub-wavelength resolution in the ultrasonic regime. Here we experimentally demonstrate a subwavelength imaging of an artificially created crack of size λ/15 in the aluminium sample: to our knowledge this is the highest resolution achieved in the ultrasonic regime. The subwavelength image obtained with the ultrasonic system incorporated with the holey-structured metamaterial is shown to compare favourably with corresponding results obtained using X-ray Computed Tomography (CT).

Design, Fabrication, and Characterization of a Flexible Dual-Band Metamaterial Absorber

Abstract: This paper presents the theory, design, simulation, fabrication, and performance of a flexible dual-band MM absorber, which is resonant at microwave frequencies. The sandwich structure of the MM absorber is composed of the periodic array of the T-shaped metallic patches and a continuous metallic plane, which are separated by a middle flexible dielectric layer. The optimized geometric parameters were obtained by numerous simulations using the full wave finite integration technology of CST 2015. The simulated results indicate that the proposed MM absorber has two distinct absorption peaks at 16.77 and 30.92 GHz with the absorption ratio of 98.7% and 99.3%, respectively. The absorber has a thickness of 0.2403 mm, which is only 1/74 and 1/40 of the wavelength for the resonance frequency of 16.77 and 30.92 GHz. The influence of the material's properties and structural curvature on the absorption performance was investigated by numerous simulations. The proposed MM absorber is highly sensitive to the polarization of the incidence EM wave and has good absorption properties over a large range of the incidence angle for the incidence EM wave. The electric field and surface current distributions at two independent resonance frequencies were analyzed for providing insight into the EM wave absorption mechanism. Simulated results show that two different resonance modes are introduced into the single patterned metallic resonance structure to realize the dual-band performance. The laser ablation process was adopted to fabricate the sample of the proposed absorber. Measured results for the normally incident EM wave show an agreement with the simulated results. The fabricated MM absorber shows significant mechanical flexibility and can easily be conformed to the unusual surfaces such as cylindrical, pyramid, and spherical. Furthermore, this design concept can be extended to the other absorber structure and the other frequency bands, therefore, which can greatly enrich the applications in antenna, sensing, thermal image, and detection. For instance, in the design of projectile-borne conformal antenna array, a flexible ultrathin MM absorber can easily be loaded between the antenna and the projectile body to reduce the radiation interference, weaken the coupling loss, and reduce the RCS.

Broadband ultrasonic focusing in water with an ultra-compact metasurface lens

Abstract: Focusing of ultrasonic waves in water plays an important role in various scenarios ranging from biomedical imaging to nondestructive testing. Acoustic metasurfaces have been largely explored for acoustic focusing, but they are generally narrowband and mainly implemented for airborne sound because of their structural complexity. Nevertheless, our previous development of metasurfaces provides a great opportunity to solve the challenges. Here, we present numerically and experimentally the broadband focusing of ultrasonic waves in water with a metasurface lens consisting of an array of deep-subwavelength sized and spaced slots. The slot widths of the metasurface are optimized based on microscopic coupled-wave theory. Due to the non-resonant arrangement, the focusing effect is demonstrated over a broad band of frequencies. The metasurface lens with simplicity and an ultra-compact size provides a feasible means for the design of thin and lightweight ultrasonic devices and is suitable for practical applications in biomedical and industrial fields.

Additive manufacturing of cellular ceramic structures: from structure to structure-function integration

Abstract: Cellular ceramic structures (CCSs) have promising application perspectives in various fields. Recently, additive manufacturing (AM), usually known as three-dimensional printing (3D printing), has been increasingly adopted to produce CCSs. Usually, the structural properties of additively manufactured cellular ceramic structures (AM-CCSs), i.e., lightweight characteristics, load-bearing capacity, toughness, unconventional properties, are traditionally investigated. Interestingly, AM technologies have a significant advantage in achieving the structure–function integration for CCSs. Functional properties, e.g., electromagnetic property, acoustic property, thermal property, of CCSs can be achieved during the structural design synchronously. In this review, firstly, the AM technologies for CCSs are comparatively introduced. Then, structural AM-CCSs are summarized. After that, structure–function integrated AM-CCSs are further introduced in detail. Finally, challenges and opportunities towards structure–function integrated AM-CCSs are forecasted. This review is believed to give some guidance for the research and development of CCSs.

Mechanical Metamaterials on the Way from Laboratory Scale to Industrial Applications: Challenges for Characterization and Scalability

Abstract: Mechanical metamaterials promise a paradigm shift in materials design, as the classical processing-microstructure-property relationship is no longer exhaustively describing the material properties. The present review article provides an application-centered view on the research field and aims to highlight challenges and pitfalls for the introduction of mechanical metamaterials into technical applications. The main difference compared to classical materials is the addition of the mesoscopic scale into the materials design space. Geometrically designed unit cells, small enough that the metamaterial acts like a mechanical continuum, enabling the integration of a variety of properties and functionalities. This presents new challenges for the design of functional components, their manufacturing and characterization. This article provides an overview of the design space for metamaterials, with focus on critical factors for scaling of manufacturing in order to fulfill industrial standards. The role of experimental and simulation tools for characterization and scaling of metamaterial concepts are summarized and herewith limitations highlighted. Finally, the authors discuss key aspects in order to enable metamaterials for industrial applications and how the design approach has to change to include reliability and resilience.