Magnetometer Alpha Build

After a lengthy process of gathering most of the materials and MacGyvering the rest, I’ve put together a proof-of-concept version of the magnetometer.

The materials used in this build are as follows:

  • One (1) 1.905 cm diameter, 0.1588 cm thick neodymium grade N48 axially magnetized magnet
  • One (1) 1.905 cm diameter glass mirror (craft supply)
  • A Helium-Neon (HeNe) laser (but any laser pointer would work for this alpha build)
  • A length of string
  • A plastic toothpick
  • Some office tape
  • A bit of silly putty I found
  • Some water

First, the magnet with the mirror, toothpick, and string taped on:

This first image presents a front view of the magnet-mirror system. The plastic toothpick hangs down from the magnet in order to extend into a pool of water and provide dampening for the pendulum motion. In this alpha build, the toothpick also acts as a sort of balance, straightening the magnet as it hangs from the string. The need to correctly balance the magnet so that it hangs vertically was not anticipated during the design phase. The degree to which the magnet-mirror needs to be balanced in future builds depends on which material ultimately replaces the string.

The second image presents a back view of the magnet-mirror system. The tape holding the string and the plastic toothpick in place can be more clearly seen. Both the string and the toothpick are taped in place slightly off center, a factor that contributes to the balancing problem. Approximately one meter of string is attached to the magnet, but one meter exceeds the minimum length required for this alpha build by a considerable amount.

The plastic toothpick is designed to extend into the water reservoir and provide dampening to the pendulum motion only, but it ends up helping balance the magnet-mirror vertically as well. But the toothpick alone is insufficient for this correction, so I added a glob a putty I found. In this third image, you can see the magnet-mirror suspended above the reservoir with the toothpick extending below the water’s surface. The laser beam’s reflected laser dot is visible near the center of the mirror.

Looking closely at the mirror reveals more details about how the laser interacts with it. When aimed at an opaque surface the laser produces a pattern that looks like a familiar laser pointer dot, but when the beam passes through the mirror the pattern is a little more interesting.

The reflected dot is viewed approximately 8 meters away:

In order to test that the basic idea of the magnetometer works in this alpha build – whether magnetically disturbing the hanging magnet corresponds to a measurable displacement in the reflected laser dot – I pick up a small metal nut and bring it close to the magnet. The result is quite encouraging:

After being disturbed, the corresponding laser dot oscillates for a short time and then returns to a stationary state. Dampening the pendulum oscillations using the plastic toothpick and water turns out to be a viable and welcome alternative to the suggested method of immersing the magnet-mirror in water. Since the magnet-mirror’s swinging motion can be dampened without submerging, it’s not necessary for the laser beam to travel through water in order to reach the mirror. Sending a laser through water could lead to all sorts of extra┬ávariables involving reflection, refraction, and dispersion of the beam.

Before moving forward I’ll need to acquire a long-term solution for a laser source and a string replacement, most likely a PASCO beryllium copper ribbon torsion band. Then I’ll start working on something of a beta build – one that lends itself to a more quantitative evaluation.

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