JNTU B.Tech III ELECTRICAL ENGINEERING MATERIALS Previous Question Paper (September - 2021 - R16)

Dielectric loss represents the energy dissipated as heat when a dielectric material is subjected to an alternating electric field. The primary factors affecting this loss are:

• Frequency: Dielectric loss is directly related to the frequency of the applied field. As frequency increases, the dipoles within the material struggle to reorient rapidly, leading to increased internal friction and higher energy dissipation.
• Temperature: An increase in temperature generally increases dielectric loss. Higher thermal energy enhances the mobility of charge carriers and ions, increasing conduction losses, and can also affect the relaxation time of dipoles.
• Voltage Stress: Higher electric field strengths can lead to non-linear increases in loss, particularly if the material approaches its dielectric breakdown strength or if partial discharges occur within voids.
• Material Purity and Moisture: Impurities and absorbed moisture act as charge carriers. Moisture significantly increases the dielectric loss tangent due to its high polarizability and ionic conductivity.
• Molecular Structure: Materials with high dipole moments exhibit greater orientation polarization losses. The chemical structure determines the ease with which dipoles can rotate within the molecular lattice.

Piezoelectric materials generate an electric charge in response to mechanical stress. Common materials include:

• Quartz (Natural Crystal): Known for high mechanical strength and excellent temperature stability. It is widely used in frequency control and precision oscillators but has a relatively low piezoelectric coefficient.
• Barium Titanate (BaTiO3): A ceramic material with a high piezoelectric constant, making it very sensitive. It is cost-effective but exhibits significant temperature dependence and aging effects.
• Lead Zirconate Titanate (PZT): The most widely used industrial piezoelectric ceramic. It offers a superior combination of high electromechanical coupling and sensitivity. It can be tailored for specific applications by doping, though it contains toxic lead.
• Polyvinylidene Fluoride (PVDF): A piezoelectric polymer. Unlike ceramics, it is flexible, lightweight, and has low acoustic impedance, making it ideal for sensors and medical transducers, though it has a lower operating temperature range.