Homework # 4 EE517 Fall 2000 Due September 21, 2000

In Woodson & Melcher finish reading chapter 3 and start reading chapter 5 section 5.1.

In Woodson and Melcher do 3.1 and 3.2

Problem 1

A particular permanent magnetic material has a coercive force equal to 3.183 105 A/m and a remnant flux density equal to 1.6T. For comparison, the coercive force of SiFe (its saturation flux density is about 1.6 T) is approximately 34 A/m. The permanent magnet material is used as shown in Fig. 1. The magnet thickness th/2 is 0.25in and the air gap g/2 is 0.1in. The area of the core and magnets is 2cm2 and there are 100 turns.

Fig. 1

1. Plot the B-H loop of this material to scale. Remember that once the material saturates the magnetic flux density continues to increase as moH. You may assume the B-H loop is vertical at Hc.
2. Use Ampere's law to obtain an equation that gives the magnetic flux density or B field from the H field in the magnet. Plot this equation on top of your B-H loop form a) for a) when the current is zero.
3. What is the H and B fields in the magnet and the H field in the air gap when the current is zero
4. How much current is required to magnetize the magnet?
5. How much current is required to demagnetize a magnetized magnet?
6. What is the voltage at the open terminals of the winding if
in? What must w be equal to in order to get a 1V peak voltage?