In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The Helioseismic and Magnetic Imager (HMI) instrument and investigation as a part of the NASA Solar Dynamics Observatory (SDO) is designed to study convection-zone dynamics and the solar dynamo, the origin and evolution of sunspots, active regions, and complexes of activity, the sources and drivers of solar magnetic activity and disturbances, links between the internal processes and dynamics of the corona and heliosphere, and precursors of solar disturbances for space-weather forecasts. A brief overview of the instrument, investigation objectives, and standard data products is presented.

/pdf/the-helioseismic-and-magnetic-imager-hmi-investigation-for-2omq27f3k3.pdf

The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO)

https://cyberleninka.org/article/n/768408.pdf

Mechanical properties of graphene and graphene-based nanocomposites

Highly stretchable graphene-nanocellulose composite nanopaper is fabricated for strain-sensor applications. Three-dimensional macroporous nanopaper from crumpled graphene and nanocellulose is embedded in elastomer matrix to achieve stretchability up to 100%. The stretchable graphene nanopaper is demonstrated for efficient human-motion detection applications.

Highly Stretchable Piezoresistive Graphene–Nanocellulose Nanopaper for Strain Sensors

Sensing strain of soft materials in small scale has attracted increasing attention. In this work, graphene woven fabrics (GWFs) are explored for highly sensitive sensing. A flexible and wearable strain sensor is assembled by adhering the GWFs on polymer and medical tape composite film. The sensor exhibits the following features: ultra-light, relatively good sensitivity, high reversibility, superior physical robustness, easy fabrication, ease to follow human skin deformation, and so on. Some weak human motions are chosen to test the notable resistance change, including hand clenching, phonation, expression change, blink, breath, and pulse. Because of the distinctive features of high sensitivity and reversible extensibility, the GWFs based piezoresistive sensors have wide potential applications in fields of the displays, robotics, fatigue detection, body monitoring, and so forth.

Wearable and Highly Sensitive Graphene Strain Sensors for Human Motion Monitoring

The aim of this work is to illustrate the contribution of signal processing techniques in the field of Non-Destructive Evaluation. A component’s life evaluation is inevitably related to the presence of flaws in it. The detection and characterization of cracks prior to damage is a technologically and economically significant task and is of very importance when it comes to safety-relevant measures. The Laser Thermography is the most effective and advanced thermography method for Non-Destructive Evaluation. High capability for the detection of surface cracks and for the characterization of the geometry of artificial surface flaws in metallic samples of laser thermography is particularly encouraging. This is one of the non-contacting, fast and real time detection method. The presence of a vertical surface breaking crack will disturb the thermal footprint. The data processing method plays vital role in fast detection of the surface and sub-surface cracks. Currently in laser thermographic inspection lacks a com...

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=5141&context=qnde

Raw Data Based Image Processing Algorithm for Fast Detection of Surface Breaking Cracks Using In-Line Laser Thermography

We report on the physical properties of solar sequential chromospheric brightenings (SCBs) observed in conjunction with moderate-sized chromospheric flares with associated CMEs. To characterize these ephemeral events, we developed automated procedures to identify and track subsections (kernels) of solar flares and associated SCBs using high resolution H-alpha images. Following the algorithmic identification and a statistical analysis, we compare and find the following: SCBs are distinctly different from flare kernels in their temporal characteristics of intensity, Doppler structure, duration, and location properties. We demonstrate that flare ribbons are themselves made up of subsections exhibiting differing characteristics. Flare kernels are measured to have a mean propagation speed of 0.2 km/s and a maximum speed of 2.3 km/s over a mean distance of 5 x 10^3 km. Within the studied population of SCBs, different classes of characteristics are observed with coincident negative, positive, or both negative and positive Doppler shifts of a few km/s. The appearance of SCBs precede peak flare intensity by ~12 minutes and decay ~1 hour later. They are also found to propagate laterally away from flare center in clusters at 41 km/s or 89 km/s. Given SCBs distinctive nature compared to flares, we suggest a different physical mechanism relating to their origin than the associated flare. We present a heuristic model of the origin of SCBs.

Properties of Sequential Chromospheric Brightenings and Associated Flare Ribbons

Acoustic microscopy is extensively used for high-frequency imaging and material characterization. In a focused ultrasonic transducer, the presence of edge waves from the edge of the transducer is usually considered a disadvantage. For high-frequency imaging applications, the edge waves adversely affect the quality of the image. This paper discusses edge wave's influence on generating a surface wave in bulk metal samples using a limited aperture PVDF transducer. Acoustic microscopy-based defocusing experiments are conducted on aluminum, stainless steel, copper, and brass samples. A detailed wave-path analysis is done to understand the different wave components in a signal as obtained from defocusing experiments. The travel path of each wave component is analytically obtained and compared with the experimental results. The different wave modes observed in the experiments are identified by overlaying the analytical plots on the experimentally obtained B-scans. A good correlation is obtained between the experimental and analytical results. The surface wave velocity of the samples is calculated using the time-resolved method, and the percentage of error in the measurement is estimated. The challenges for using this method in measuring surface wave velocities in samples with bulk longitudinal velocities [Formula: see text] are also discussed.

The influence of edge waves in local surface skimming longitudinal wave generation using a focused PVDF transducer

: This Phase III research proposal was a continuation effort on the Phase I and II work. The overall program focuses on the development of new explorations towards the development of better understanding of non-linear ultrasonic methods for the quantitative materials state evaluation and characterization of damage in metallic alloys. Both theoretical and experimental works were carried out in order to understand the significance of the effects of microscopic damage in metals using the measurements of Non-Linear Effects of Ultrasound (NLU). The Phase III work effort extended the Finite Difference in Time Domain (FDTD) and the mass-spring lattice models (MSLM) to a 2D MSLM with NLU parameters while resolving some of the issues that were observed in Phase II. The experimental results were performed on copper alloys that have damage behavior that can be explained using literature data. The improved understanding of NLU is anticipated to lead to new measurement techniques that have applications in the area of vehicle health monitoring, nondestructive testing, and process monitoring of manufacturing processes.

Understanding of Materials State and its Degradation using Non-Linear Ultrasound (NLU) Approaches - Phase 3

A novel small footprint sensor patch (single-quadrant double-ring Single- Transmitter Multiple-Receiver (STMR) array) has been developed and demon- strated successfully for the simultaneous reconstruction of the elastic moduli, mate- rial symmetry, orientation of principal planes and defect imaging. The sensor array contains a single transmitter in the center of the array and two sets of receivers at two different radii on a single quadrant. A slowness based reconstruction algo- rithm is used to determine elastic moduli from measured fundamental Lamb wave mode velocities using the direct received signals at different angles in a quadrant. A method proposed by Cowin and Mehrabadi (1987) is used to determine material symmetry and orientation of principal planes. Imaging is carried out with a phased addition algorithm and the reconstructed elastic moduli using the signals from flaws and structural features. To show the applicability of the method, simulations were carried out to image defects with the single-quadrant double-ring STMR array con- figuration and are compared with the images obtained using simulation data of the full-ring STMR array configuration. The experimental validation has been carried out on a 3.15 mm thick quasi-isotropic graphite-epoxy composite plate.

Krishnan Balasubramaniam

Papers

Raw Data Based Image Processing Algorithm for Fast Detection of Surface Breaking Cracks Using In-Line Laser Thermography

Properties of Sequential Chromospheric Brightenings and Associated Flare Ribbons

The influence of edge waves in local surface skimming longitudinal wave generation using a focused PVDF transducer

Understanding of Materials State and its Degradation using Non-Linear Ultrasound (NLU) Approaches - Phase 3

A Novel Quadrant Array for Material Characterization and SHM of Orthotropic Plate-like Structures