3D-Vectorfield Scanner for Magnetic Flux

1. Step: Proving our hypothesis:

Our first experiments started as we got a breakout board for an SMD magnetic sensor, commonly used in robotics to orient the robot according to earth’s magnetic field.

It measures the magnetic flux density in 3 dimensions and with 8 different ranges. We moved it by hand, one time without anything metallic nearby and one time with a used jig-saw blade (steel) about 20 cm away. Using an Arduino we send the three values for the flux density for every position we examined to the console and – yes, wrote them down by hand at first ;-)

As we converted these values to a chart by using the MATLAB program, we could see a huge difference! That was the point in which we realized that our idea could possibly work.

Of course we didn't want to continue measuring by hand so we built our own construction which is mostly composed of customized elements we designed using 123d design and printed with a 3d printer on our own.

We only used plastic because we didn’t want to have measuring deviations through metal and we used two stepper motors which should move the sensor through a kind of linkage, which is a parallel kinematic, meaning the motors can move the sensor without also being transported. Sadly this didn’t work well. We tried different threats but they slipped away, were so tight that the motors couldn’t move anymore or the single tracks moved shifted. We tried several designs, but could not get hold of proper belt drives like the ones being used in 3dprinters in time – we wanted to present our work at the youth science contest and had to develop another approach shorthanded…

And, yes, motors are made from metal and have a changing magnetic field around them during operation ;-)

We made sure that the motors (steppers) are far away enough not to influence the measurement itself – that’s why we tried to keep the motors outside the measurement area.

Since we wanted to do further experiments but couldn’t use our construction for it, because we could not solve the mechanical problem in time, we used another construction from fischertechnik from the 1980’s that has been laying around in our school ever since (unopened!) – a plotter.

We exchanged the steel tubes for carbon ones and changed the design a little bit as well. Instead of a pencil it now carries the sensor.

We used a motor shield from Adafruid, added an SD-Card-Shield we built ourselves from an Micro-SD-Card Adapter our self, an LCD-Display and Bluetooth to make the device controllable via a Smartphone-App. We programmed this app with "app inventor 2".

You can choose the sensor range and the scanning area from your smartphone – we developed some kind of protocol to transfer these informations back to the Arduino to do the measurement and record the data.

If you press the start button the sensor drives to a reference point.

From there it begins to measure bidirectional to save some time.

The data is saved to the SD-Card in a special format – it can be copied to the command window of mathworks and executed directly. You instantly have all the matrices you need to visualize or calculate the magnetic field. We did some short tests with a “normal” magnetic sensor and datalogger, that just records the overall magnetic field (no orientation) – and it seemed ok ;-)

We can now analyze the magnetic field by measurement of its flux density and visualize it in 3D. For the moment we only scan regions (a plane) and measure the three-dimensional vector (BX | BY | BZ) | of every single measuring point with assigned coordinates (Y X) automatically - and the result is a vector field.

So far we measured metallic different objects to watch whether you can recognize for example a current-carrying wire formed as a heart, a saw blade and a bullet casing (we found in Berlin after new years eve; it is an empty blanket, don’t worry).

Coming back to magnetic fields, we can determine the spatial orientation and intensity of the magnetic flux at any given point on a 2d plane (scanner area). As a result, we have a 5D-vector field of the examined magnets, which can be visualized with the aid of mathematics programs such as MATLAB and investigated further.

We didn't have any time yet but for further development we want to extend the scanning device so that the height of the scans can be changed as well by the principle of a delta 3D printer - then we would measure a 6D vector field…