Building a Magnetometer

As explained in the first webinar video, one of the long-term goals of the Sprite project is to be able to deploy fleets of them throughout various parts of the solar system. These Sprites would sport a mix of sensors; a portion of them might analyze spectral data while others might have plates for capturing space dust. There’s a long way to go before Sprite fleets are traveling and collecting data outside of low Earth orbit, but Sprites with sensors other than the default temperature sensor could happen much sooner. The design team is considering incorporating a magnetometer, an accelerometer, or a gyroscope into some or all of the KickSat Sprites. While I wait to see whether any of these sensors make their way into my Sprite, I’ve decided to build a magnetometer of my own.

Firstly, I’d like to thank Alex Avtanski for his DIY Magnetometer design. The magnetometer I’m building will closely follow the design detailed on his site. Secondly, I should point out that this magnetometer works differently than any sensor that might show up on a Sprite. Alex’s design is macroscopic and more or less mechanical, while the likely magnetometer candidate for a KickSat Sprite is a much smaller, solid-state chip. Nonetheless, I feel like building this magnetometer will be a good exercise.

Alex Avtanski's Completed MagnetometerAlex Avtanski’s completed magnetometer (image by Alex Avtanski)

The essential design involves a laser pointer, a hanging magnet attached to a mirror, and a sensor for detecting the laser beam. The laser is directed at the mirror, which moves when the magnet is disturbed by a change in the surrounding magnetic field. This movement affects the reflected beam and is recorded by the sensor.

Alex Avtanski's Magnetometer GraphicThe essential design of the magnetometer (image by Alex Avtanski)

The sensitivity of the magnetometer can be adjusted by changing the distance the laser beam travels between the mirror and the sensor. A larger distance means that smaller mirror movements can be recorded, since small reflection angles still yield a measurable beam displacement.  However, using a larger travel distance for the beam means that noise is magnified as well. There are entire essays dedicated to defining noise, but suffice it to say that noise is any variation in the collected data that is not directly related to the phenomenon being studied. An example would be when a person walks near the apparatus, shaking the floor, the device, and the string supporting the magnet and mirror.

Before moving to the specifics of construction, one last design issue must be considered. In the magnetometer, changes in the magnetic field are indicated by the movement of a magnet on a string. But what happens after this magnet is disturbed? If it’s movement isn’t somehow restricted, the continued oscillations will result in false readings. In order to insure that the magnet and mirror quickly returns to equilibrium after being disturbed, Alex immersed it in a movement-dampening liquid (water). Before settling on water in my build, I’d like to explore other means of preventing oscillations – either considering an alternative fluid such as oil or a different mechanism all together.

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