# Electromagnetic Damping

## What is Damping?

Damping plays an important role in regulating the movement of the material. It is an opposition to the motion of an object. The damping tends to reduce the velocity of a moving object. The object can have various forms of motion; rotational motion, linear motion, oscillatory motion, etc. The number of damping techniques is also used in rotating, moving, and oscillating systems. This involves fluid friction damping, air friction damping, traditional friction damping, and electromagnetic damping, to name a few.

Damping, in physics, inhibiting vibratory motion, such as mechanical oscillations, noise, and alternating electrical currents, by the dissipation of energy. If a child does not keep spinning a wheel, his motion dies because of damping. Shock absorbers in vehicles and carpet pads are examples of damping devices.

### Electromagnetic Damping Definition - An Introduction

Of all these methods, electromagnetic damping is one of the most interesting damping methods. This uses an electromagnetic current to control/regulate/slow the motion of the body without any direct physical contact with the moving object. To understand this fascinating damping technique, it is important to understand two concepts - Eddy Current and Electromagnetic Induction.

Electromagnetic Damping is associated with eddy currents.

### Electromagnetic Damping Examples

Let us brief you an example to understand the eddy currents -

Let there be a source of    B vector  B→   Now, if we shift a metallic plate towards and away from the source of B vector  B→  emf will be caused by the Law of Faraday in the conductive plate due to a change in magnetic flux

ϵ = − dΦ / dt
ϵ = −dΦdt

Now, what is Electromagnetic Damping - Thermal energy is produced in the plate due to the eddy current in the metal plates. This energy here comes at the cost of the kinetic energy of the moving plate, and therefore the metal plate slows down. This is the fundamental concept behind electromagnetic damping.

To reduce, we need to reduce the flow path of this current. We cut holes in the plate to popular the available routes. This helps to reduce the number of circular loops through which the current will flow. The loss of energy due to eddy current is therefore reduced and electromagnetic damping is therefore reduced.

### Electromagnetic Induction

The concept of electromagnetic induction was first studied by Michel Faraday in 1831. The electromagnetic induction is defined as "Changing magnetic field and inducing emf (electromotive force) into the conductor." The electromagnetic induction is achieved either by moving the conductor through a steady magnetic field or by placing the conductor in a variable magnetic field.

### Eddy Current

This induced emf to induce a current across the conductor. This induced current is called the Eddy current. Due to Eddy’s current, the electrons in the conductor follow a unique pattern, swirling around the conductor line, similar to swirling water in the whirlpool.

The eddy current in the conductor is swirling in such a way as to generate a magnetic field in the system. An external magnetic field is also experienced by the conductor. The magnetic field created by the eddy current is opposed to a change in the magnetic field felt by the conductor under Lenz's law. Thus, Eddy's current is flowing perpendicular to the magnetic field.

### The Theory Behind Electromagnetic Damping

A damping force is generated when these Eddy currents and magnetic fields interact with each other. It's called electromagnetic damping. Which, by nature, is a resistive force. This is contrary to the motion of the conductor/object. Thus, we may describe that "It is a damping technique where the electromagnetic current slows down the motion of an object without any actual touch".

### The Dependency of Electromagnetic Damping

As the distance between the magnet and the conductor decreases, the damping force increases. The electromagnetic damping force is proportional to the induced eddy current, the magnetic field strength, and the speed of the object. This means that the faster the object moves, the greater the damping and the slower the motion of the lower object will be damping, which will result in a smooth stopping of the object.

### Apparatus -

An aluminium block, a magnet, a magnet holder to hold the magnet.

## Procedure -

Hang the magnet out of the aid. Don't put the aluminium plate right now. Take the magnet to one side and release it. It's oscillating like a pendulum. Watch for around 10 oscillations. See if there is a large amplitude damping. Stop the magnet, please. Place the aluminium plate under the hanging magnet. The magnet should not touch the plate, and the partition should be small, say 1~mm. Now pull the magnet to one side and release it. Take a look at the oscillations. Can you watch for ten oscillations? The oscillations are damped very quickly.

## Discussion

As the magnet moves over the plate, the magnetic field changes in time over the parts of the plate. This changing magnetic field generates induced currents on the surface of the plate. These currents are opposed to the cause of the relative motion between the plate and the magnet. As a result, the magnet slows down very rapidly and almost stops at 2 or 3 oscillations.