Krishnamurthy C. Venkata

Bio: Krishnamurthy C. Venkata is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Polarization (waves) & Terahertz radiation. The author has an hindex of 4, co-authored 6 publications receiving 33 citations.

Quad-Band Polarization-Insensitive Millimeter-Wave Frequency Selective Surface for Remote Sensing

Abstract: A novel millimeter-wave frequency selective surface (FSS) is presented for demultiplexing four atmospheric remote sensing bands with varying bandwidth (3–20 GHz) and frequency separation (50–195 GHz). The unit cell (670 μm × 670 μm) is a circular metal mesh loaded with a monopole integrated concentric ring on a 175-μm-thick quartz substrate designed to reject 50–60 GHz (B1), 87–91 GHz (B 2), and 148–151 GHz (B3), and transmit 175–195 GHz (B4) for transverse electric (TE) and transverse magnetic (TM) polarizations at oblique incidence (25°−35 °). Transmission response of the cascaded FSS measured using a continuous-wave terahertz source showed insertion loss of 15 dB and higher in the reflection windows (B1, B2, and B3) and less than 0.5 dB in the transmission window (B4) for TE and TM polarizations at 30° incident angle.

Thermomechanical response of metals: Maxwell vs. Kelvin–Voigt models

Abstract: Temperature changes are exhibited by a material when subjected to mechanical loads in the elastic as well as the plastic regimes. In this paper, we analyze the observed thermo-mechanical phenomenon from elastic cyclic loading tests (stress below yield point) conducted on stainless steel (SS304) using two well-known rheological models viz., Kelvin–Voigt model and Maxwell's models. The Kelvin–Voigt model is shown to be well-suited in characterizing the mechanical as well as the associated thermal response. In seeking a deeper basis for the success of the Kelvin–Voigt model, correlations are sought between the model's key parameter - viscosity and the material's microscopic property viz. the grain boundary sliding coefficient. A plausible description is offered for the ability of Kelvin–Voigt model to explain the thermo-mechanical response under elastic cyclic loading. The effect of grain size on thermomechanical response and the variation of grain boundary diffusion coefficient with applied load is demonstrated, theoretically. The new description is used to predict the thermo-mechanical behavior of various other polycrystalline materials such as aluminum. Based on the models developed, experiments are proposed for further research.

Step frequency continuous wave RADAR sensor for level measurement of molten solids

Abstract: Step frequency continuous wave (SFCW) RAdio Detection And Ranging (RADAR) sensor is proposed for non-contact measurement of the absolute level of molten solids in industrial furnaces. A con...

Multi-physics modeling to study the influence of tissue compression and cold stress on enhancing breast tumor detection using microwave radiometry.

Abstract: The influence of tissue compression and external thermal modulation on passive detection of breast tumors using medical microwave radiometry was investigated using multi-physics numerical modeling. A three-dimensional numerical model of the pendant breast with 10 and 6 mm diameter tumors at varying depths (15 mm, 30 mm) was analyzed at thermodynamic equilibrium using a circular waveguide as the receive antenna. The contrast in the brightness temperature, ΔTB , between the unhealthy and healthy breasts was found to be significantly more for breast compression alone, compared to thermal modulation of the tissue surface, irrespective of tissue composition, tumor size, and depth. The study also concludes that small deep-seated tumor with very low metabolic activity that is not detectable by a radiometer with 0.1 °C sensitivity could be detected under breast compression and short duration cold stress. Thus, detection of deep-seated breast tumors can be significantly improved under controlled tissue compression with an optional cold stress. Bioelectromagnetics. © 2019 Bioelectromagnetics Society.

Vibration of FG magneto-electro-viscoelastic porous nanobeams on visco-Pasternak foundation

Abstract: In this paper, the size-dependent vibrational behaviors of functionally graded (FG) magneto-electro-viscoelastic nanobeams in the presence of porosities and embedded in the viscoelastic medium are studied based on the nonlocal Timoshenko beam theory in conjunction with the Kelvin-Voigt viscoelastic model. The viscoelastic medium is modeled as a visco-Pasternak foundation with consideration of both shear modulus and medium damping coefficient. The FG material properties are supposed to vary along the thickness direction in a power-law exponent form, and two types of porosity distributions are considered. The present model is validated by comparison with several existing theories and a good agreement is achieved. Parametric studies are carried out to investigate the coupling influences of the nonlocal parameter, FG power-law index, porosity volume fraction, porosity distribution, boundary condition, structural damping coefficient and viscoelastic foundation parameters, as well as electric voltage and magnetic potential on the vibrational performance of FG magneto-electro-viscoelastic porous nanobeams. The results are helpful for the design and applications of nano-electro-mechanical systems (NEMS).

Deformation Experiments on Bowland and Posidonia Shale—Part II: Creep Behavior at In Situ pc–T Conditions

Abstract: To unravel their long-term creep properties at simulated reservoir conditions, we conducted constant stress deformation experiments at elevated confining pressures, pc = 50–115 MPa, and temperatures, T = 75–150 °C, on Posidonia (GER) and Bowland (UK) shale, which exhibit varying petrophysical and mechanical properties. Depending on applied pc–T conditions and sample composition, recorded creep curves exhibit either only a primary (decelerating) or additionally a secondary (quasi-steady state) and a tertiary (accelerating) creep phase during deformation. At high temperature and axial differential stress and low confining pressure, creep strain is enhanced and a transition from primary towards secondary and tertiary creep behavior is observable. Creep strain of Posidonia shale, which is rich in weak constituents (clay, mica, and organic content), is enhanced when compared to creep strain recorded during deformation of either carbonate- or quartz-rich Bowland shale. Electron microscopy observations revealed that creep strain is mainly accommodated by the deformation of weak minerals and local pore space reduction. In addition, microcrack growth occurred during secondary creep. An empirical correlation between creep strain and time based on a power law was used to describe the decelerating creep phase, also accounting for the influence of confining pressure, temperature, and axial differential stress. The results suggest that the primary creep strain can be correlated with mechanical properties determined from short-term constant strain rate experiments such as static Young’s modulus and triaxial compressive strength.