ADVISER:CHENG-HSIEN LIU ???

1
HOMOPOLAR MICROMOTOR WITH LIQUID METAL
ROTORTeimour Maleki and Babak ZiaieSchool of
Electrical and Computer Engineering, Purdue
University, West Lafayette, USA(Tel
1-765-494-0725 E-mail bziaie_at_purdue.edu)

• ADVISERCHENG-HSIEN LIU ???
• REPORTER???????
• ID9733530?9733593

TRANDUCERS EUROSENSORS07 The 14th
international Conference on Solid-State Sensor.
Actuator and Microsystems, Lyon. France. June
10-14,2007
2
Outline

• Abstract
• Introduction
• Algorithm
• fabrication
• 3-D computer aided simulation
• Conclusion
• Reference

3
Abstract
GA homopolar motor concept model
4
introduction

• First invented in 1821 by the famous ninetieth
  century English scientist Michael Faraday
  (1791-1867), he built a type of electric motor
  which nowadays is referred to as a homopolar
  motor.

Michael Faraday
5
introduction

• What is Homopolar ?
• -gt
• Requiring only the same electric polarity for
  its operation, substituting the word same with
  its Greek equivalent homos one arrives at the
  name homopolar.

6
introduction
Homopolar motor

• Current, magnetic field and magnetic force
  directions. Here the exerted torque causes the
  disc to rotate in an anti-clockwise direction.

7
introduction
general DC motor
8
introduction

• Homopolar DC motor compared with other DC motors
• The liquid rotor simplifies electrical connection
  to the rotating part and reduces friction and
  power loss.

Advantage Disadvantage
simple high current requirement which is typically mitigated by using superconducting wires
compact high current requirement which is typically mitigated by using superconducting wires
no force ripple high current requirement which is typically mitigated by using superconducting wires
do not require current or magnetic field controllers high current requirement which is typically mitigated by using superconducting wires
9
Introduction

• Homopolar Motor,made with drywall screw, alkaline
  cell, wire, and neodymium disk magnet. The screw
  and magnet contact the bottom of the battery cell
  and are held up by magnetic attraction.

homopolar electric motor

• The homopolar micromotor consists of a mercury
  droplet as the liquid rotor.

10
Algorithm
11
Algorithm

• Electric field(E) electric charge (q)
• Magnetic field(B)velocity of the particle (v)

12
Algorithm

• the force on a point charge due to
  electromagnetic fields Lorentz Force Equation
• Faradays law of induction
• is the magnetic flux through the loop.
• is the electromotive force(EMF) experienced.

13
Algorithm
motor
Moving charge
(Amperes low)
Magnetic field
current
generator
Changing the magnetic field
14
Algorithm
B
F
i
15
Algorithm
16
Fabrication
Mercury
A micromachined circular hole with the diameter
of 2mm.
Highly doped silicon wafer (0.001 O-cm)
200µm
A small hole was created in Silicon nitride layer
using RIE.
Neodymium super magnet
17
Fabrication
Fig. The optical image of the fabricated device
showing the magnet , two layers of high doped
silicon wafer ,a SU-8 cap and a Teflon rotor.
18

• 3-D COMPUTER AIDED SIMULATION

19
Find the generated electromagnetic force.
Amperes law
Taking divergence of (1)
COMSOL 3.3
20
3-D computer aided simulation
The magnetic field in the location of the motor
is mostly in z direction.
Fig. Simulation result for magnetic field
and current distribution in the micromotor
21
3-D computer aided simulation
Fig. The magnetic flux density z-component
magnitude on top of the magnet.
Fig. the current density distribution in the
rotor and top silicon part

• The magnet diameter should be as big as possible.
• The distance between the magnet surface and
  bottom of the mercury droplet should be kept at
  a minimum.
• Increasing the mass of the thickness of the top
  silicon does not change the electromagnetic
  force.

22
Result
Fig. Electromagnetic force vs. electric current.
Fig. Measured output RPM vs. current.
Because the measurement setup limitations.The
author mention that the micromotor can rotate
much faster than what is indicate in the
figure(300 round per minute (rpm))
The output of electrostatic MEMS micromotor which
is in the order of pN-m. The high-power MEMS
electric induction motors needs power more than
100V .
23
Conclusions

• Successfully simulated and fabricated a homopolar
  micromotor with a liquid rotor.
• The simulation result show that important
  parameters in designing the micromotor are the
  magnet diameter and the thickness of the bottom
  silicon which controls the distance between the
  surface and the bottom the magnet metal liquid.
• The other important parameter to increase both
  torque and rpm is the size of the hole in the top
  silicon which control the path length in the
  force equation.

24
reference

• A SIMPLE ROLLING HOMOPOLAR MOTOR(Seán M. Stewart)
• D.K. Cheng, Field and Wave Electromagnetics,
  Addison Wesley, 1992.
• The homopolar motor A true relativistic engine
• http//zh.wikipedia.org/wiki/Wiki

25
Thanks of your attention
26
About Silicon Nitride
Key Properties Key Properties
High strength over a wide temperature range High fracture toughness
High hardness Outstanding wear resistance, both impingement and frictional modes
Good thermal shock resistance Good chemical resistance
Typical Uses Typical Uses
Rotating bearing balls and rollers Cutting tools
Engine moving parts valves, turbocharger rotors Engine wear parts cam followers, tappet shims
Turbine blades, vanes, buckets Metal tube forming rolls and dies
Precision shafts and axles in high wear environments Weld positioners