Electronic materials
(answer on a separate page, type answers)
1. Explain why the ionic contribution to the dielectric constant vanishes at frequencies greater than about 1GHz.
2. What is the relative permeability of a magnetic core material if the magnetizing field, H, saturates the core material?
3. For high frequency inductor core application in a low power converter what properties would an ideal magnetic core possess and why?
4. Write the Clausius-Mossotti equation for the ionic dielectric KI (potassium iodide) at low frequencies (dc) when the material appears under a microscope as in Fig. 1. Identify each parameter in the equation. What assumptions do you make if any?
5. Consider a planar spiral core microinductor. How would you reduce the size of the inductor without changing the inductance? What are two reasons why the electronics community does not pursue your suggestion?
6. Metallic steels, e.g., FeSi, FeNI, FeCo, meet most requirements for use as inductor materials but are not used above 10 kHz. Why is this?
7. Name three ways to increase inductance other than the use of magnetic core materials. What is an acceptable magnetic core material for 1 KHz applications? And, for 1 MHz applications, and why?
8. Explain the difference between hard and soft magnets. List at least one each of popular hard and soft magnets.
9. Explain the abrupt decrease in coercivity with grain size seen in the Herzer diagram.
10. One approach to increasing the energy product of hard magnets is to refine their morphology. What is the goal of refinement and why does it increase the energy product?
11. The operational frequency range of an inductor is determined in part upon its resistivity. Why?
12. For a magnetic insulator, what is commonly the larger of the two loss tangents (magnetic or electronic)? And why?
13. What are the three ways to increase the capacitance of a capacitor?
14. What are the principle paths to realizing supercapacitors (sometimes called ultracapacitors)?
15. A dielectric material that consists of lead zirconium titanate (PZT, a relaxor ferroelectric) as a 90% dense polycrystalline compact (10% by volume pores) experiences what kinds of dielectric polarization(s) at 60 Hz? And at optical frequencies?
16. Explain the ionic polarization mechanism as it pertains to a relaxor ferroelectric. What happens on the atomic level when excited by an ac voltage.
17. Intercalated carbon is often used as an electrode in a supercapacitor. Why?