Search Results (6)

This study aims to explore the feasibility of producing submicrometer and nanometer cellulose fibers derived from rice husk treated with a novel method which selectively eliminate hemicellulose and lignin, while maintaining the integrity of the cellulosic and silica constituents. Three distinct processing methods are tested to extract the nanocellulose, namely hand milling, ball milling, and wet milling using a high-shear wet media mill from Masuko Sangyo Co., Ltd., Kawaguchi-city, Japan. A range of analytical methods, including Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA), are utilized to characterize the morphology, elemental composition, thermal stability, and chemical properties of the samples. The study revealed that among the tested methods, only wet milling successfully produced cellulose nanofibrils and silica nanoparticles, forming a biogenic organic–inorganic nanohybrid system. The nanofibers had lengths in the range of 120 nm and below, while the nanoparticles were in the tens of nanometers. The silica nanoparticles were found to adhere to the cellulose nanofibrils, forming a biogenic organic–inorganic nanohybrid system, with potential applications across diverse fields, including biomedical (drug delivery, biosensing, bone regeneration, and wound healing), cosmetic (skin and dental care), technical (insulating aerogels, flame retardants, and UV-absorbing pigments), and food applications (dietary supplements, thickeners). Full article

This paper comprehensively presents an approach for modeling form wound coils of a motor driven by an inverter, with focus on the electric stresses on the coil insulation. A 10 kV SiC testbed for medium voltage form wound coils was developed to support and validate the modeling techniques discussed. A finite element analysis (FEA) model of the motor coil is presented using COMSOL 6.1. The FEA model was used to determine parameters for an electrical model based on the multi-conductor transmission line theory. The linking of these models allows for a rapid analysis of the electrical stresses the insulation can be exposed to. An experimental method for model validation using the empirical transfer function estimation (ETFE) approach to find the impedance response of the testbed for comparison to the proposed electrical model is presented and employed. The paper also uses the model to analyze the impact of insulation delamination and voids and to demonstrate the implementation of a metric called insulation state of health monitoring for both healthy and damaged coils. Full article

To enable stating a final common sensor design of purely textile, measuring wound pads for the monitoring of surgically provided wounds with regard to tissue temperature, moisture release and stretching (as indicators for the most prominent wound healing disruptions bacterial inflammation, bleeding/seroma discharge, and haematoma/seroma formation), the aim of this investigation was to identify and quantify possible variables practically affecting the detection of water in a systematic study. The textile sensors comprise insulated electrical wires stitched onto a textile backing and parallel wires form a plane sensor structure whose electrical capacitance is increased by water (contained in blood or lymph) in the textiles. Only parallel sensor wires forming double meanders were examined because this structure enables all the parameters of interest to be measured. Surprisingly the results are complex, neither simple nor consistent. The change in electrical capacitance (measuring signal) upon the standardized addition of water was not additive, i.e., it was not found to be correlated to the moistened area of the sensor array, but inversely correlated to the diameter of the sensor wire, mildly pronounced in connection with smaller stitching spacing (stitching loops along the sensor wires). The measuring signal reached a maximum with medium sensor wire spacings and pronounced with a smaller stitching spacing. Without exception, the measuring signal was systematically higher in connection with smaller (compared with larger) stitching spacings. The results presented indicate that the optimization of the capacitive textile sensors cannot be calculated but must instead be carried out empirically. Full article

Power electronics switching devices currently represent the dominant technology for supplying low voltage (LV) electric motors. The fast switching processes exert a different class of stress on dielectric insulating materials than standard sinusoidal excitations. Such stresses result in an increase in the dynamic activity of the working electric field, which in turn lead to an increased likelihood of partial discharges (PD). The stator design of low voltage motor is often in form of random-wound windings, where the magnet wires (copper or aluminum round wires coated with thin layer of insulation) form a common system of coils with not precisely defined mutual position of particular turns, resulting in various turn-to-turn and coil-to-coil voltage distributions. Pulse Width Modulated (PWM) voltage waveforms from modern electronic inverters are characterized by very short rise times and presence of repetitively occurring overvoltages that can significantly stress the insulation of feeding cables and motors. These factors influence the inception and dynamics of PD and processes of space charge accumulation in electrical insulation. In this paper investigations performed on round magnet wire twisted-pair samples representing LV motor random-wound winding elements are presented. Special attention was afforded to the twist configurations, observed breakdown voltage and PD activity. To describe the field conditions for the formation of PD in the turn-to-turn insulation system, the results of numerical simulations of electric field distributions for winding wires with different diameters, modeled using the COMSOL program, were analyzed. PD created in the insulating systems of model twisted-pair systems were registered and analyzed using the phase resolved partial discharge analysis (PRPDA) method. Full article

Nanocellulose is cellulose in the form of nanostructures, i.e., features not exceeding 100 nm at least in one dimension. These nanostructures include nanofibrils, found in bacterial cellulose; nanofibers, present particularly in electrospun matrices; and nanowhiskers, nanocrystals, nanorods, and nanoballs. These structures can be further assembled into bigger two-dimensional (2D) and three-dimensional (3D) nano-, micro-, and macro-structures, such as nanoplatelets, membranes, films, microparticles, and porous macroscopic matrices. There are four main sources of nanocellulose: bacteria (Gluconacetobacter), plants (trees, shrubs, herbs), algae (Cladophora), and animals (Tunicata). Nanocellulose has emerged for a wide range of industrial, technology, and biomedical applications, namely for adsorption, ultrafiltration, packaging, conservation of historical artifacts, thermal insulation and fire retardation, energy extraction and storage, acoustics, sensorics, controlled drug delivery, and particularly for tissue engineering. Nanocellulose is promising for use in scaffolds for engineering of blood vessels, neural tissue, bone, cartilage, liver, adipose tissue, urethra and dura mater, for repairing connective tissue and congenital heart defects, and for constructing contact lenses and protective barriers. This review is focused on applications of nanocellulose in skin tissue engineering and wound healing as a scaffold for cell growth, for delivering cells into wounds, and as a material for advanced wound dressings coupled with drug delivery, transparency and sensorics. Potential cytotoxicity and immunogenicity of nanocellulose are also discussed. Full article

We present a rapid prototyping and a cost effective fabrication process on batch fabricated wafer-level micro inductive components with polymer magnetic composite (PMC) cores. The new PMC cores provide a possibility to bridge the gap between the non-magnetic and magnetic core inductive devices in terms of both the operating frequency and electrical performance. An optimized fabrication process of molding, casting, and demolding which uses teflon for the molding tool is presented. High permeability NiFeZn powder was mixed with Araldite epoxy to form high resistive PMC cores. Cylindrical PMC cores having a footprint of 0.79 mm ${}^2$ were fabricated with varying percentage of the magnetic powder on FR4 substrates. The core influence on the electrical performance of the inductive elements is discussed. Inductor chips having a solenoidal coil as well as transformer chips with primary and secondary coils wound around each other have been fabricated and evaluated. A core with 65% powder equipped with a solenoid made out of 25 µm thick insulated Au wire having 30 turns, yielded a constant inductance value of 2 µH up to the frequency of 50 MHz and a peak quality factor of 13. A 1:1 transformer with similar PMC core and solenoidal coils having 10 turns yielded a maximum efficiency of 84% and a coupling factor of 96%. In order to protect the solenoids and to increase the mechanical robustness and handling of the chips, a novel process was developed to encapsulate the components with an epoxy based magnetic composite. The effect on the electrical performance through the magnetic composite encapsulation is reported as well. Full article