N. M. Azizur Rahman

Spun yarn produced in the conventional spinning processes, even under the best conditions, has a certain minimum irregularity. Because: (i) t he number of fibers in the yarn cross-section is not constant, and (ii) i n contrast to synthetic staple fibers, natural fibers have variations in their fineness. So, ultimately, yarn thickness varies even when the number of fibers in the cross section remains the same.  Uster Evenness Tester is used to determine the index of irregularity of a yarn. Following the capacitive measuring principle, it measures the capacitance of the materials that pass through the capacitor electrodes of the tester.   Figure 1: Irregularity measuring principle of an evenness tester. Uster tester mainly determines the mass variation of fiber assembly using the capacitive measuring principle. This mass variation provides a mass diagram that is valuable for the detection of the following faults of a yarn. Random & seldom occurring events Long-term vari...

Piezoelectricity is a reversible phenomenon wherein certain materials generate an electric charge under mechanical stress and deform under an electric field. This article explores the core principles of piezoelectricity, commonly used materials, and characterization methods. Emphasis is placed on practical applications ranging from sensors and actuators to biomedical and nanotechnology fields. The discussion integrates both traditional piezoceramics like PZT and emerging nanostructures, underscoring their roles in modern engineering and science. Piezoelectric materials convert mechanical stress into electrical energy and vice versa. This unique property finds use in a wide range of technologies, including oscillators, actuators, and medical sensors. The phenomenon is inherent in certain crystals, ceramics, polymers, and biological materials. Fig. 1: Direct and converse piezoelectric effect Piezoelectric Materials Several materials exhibit strong piezoelectric behavior: Lead Zirconat...