## Introduction

Magnetic bubbles are nothing new. They have been studied mainly from the point of view of using them in information technology devices (e.g. "bubble memory" device). However, the unique properties of magnetic bubbles may be used for other applications. I have applied their unique properties to the design of various magnet bubble motors.

## Magnetic Bubbles

Magnetic bubbles are (idealized) cylindrical regions in magnetic material in which the magnetization direction is reversed with respect to outside the cylindrical region. If a magnetic material were magnetized to have its magnetic north pole face on the "top" and its south pole face on the "bottom" of the material, then the faces of the cylindrical magnetic bubble region would have its south pole face on the top side and its north pole face on the bottom side of the magnetic material.

Notice that the magnetic bubble has a "bubble wall" through which the magnetization vector (indicated by an arrow) has to change its direction by 180 degrees.

Of particular interest, for my magnetic bubble motor, are "hard" magnetic bubbles. For hard magnetic bubbles, not only does the magnetization vector rotate by 180 degrees in the bubble wall, it also twists. Not only does the magnetization vector twist, it can twist in either a clockwise or a counter clockwise direction. Here are two magnetic bubbles. One has its magnetization vector twisting clockwise while the other bubble has its magnetization vector twisting counter clockwise.

The number of twists in the bubble wall is called the state number (S).

Hard magnetic bubbles move through the material at a non-zero "deflection" angle (-90 < angle < +90 degrees) with respect to the direction of an externally applied magnetic field gradient. (A magnetic field gradient is just the direction in which the magnetic field is getting stronger.)

The reason for this deflection away from the direction of the magnetic field gradient can be (loosely) explained as follows.

When a hard magnetic bubble is placed in a magnetic field gradient its wall structure changes. The twists (or "Bloch lines") bunch together on either the left or right hand side of the magnetic bubble (with respect to the magnetic field gradient direction.)

It is important to note that this rearrangement of the bubble's wall structure is a static property. That is, it does not depend on the bubble moving through the material.

Since the magnet bubble's wall structure is no longer symmetrical with respect to the magnetic field gradient direction, the forces on the two halves (left, right sides) of the magnetic bubble as it moves through the material will not be balanced.

It is important to note that the force perpendicular to the direction of the magnetic field gradient (the "sideways" force) is a dynamic force. That is, it only occurs if the magnetic bubble is moving through the material.

Now lets see how we can use these hard magnetic bubbles to build a magnetic bubble motor.

The information provided here is subject to patent protection. USA patent pending, June, 1998

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