Getting to know your smartphone magnetometer
Summary
An introduction to using a smartphone to acquire measurements of the local magnetic field strength and direction. The students locate the location of the sensor in the smartphone, characterise its measurement axes, and assess its sensitivity and noise levels. They then take a measurement of the ambient field and compare it to the predicted reference field for their location, and then observe the effect of local magnetic sources in generating deviations from this field.
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Context
Audience
I intend to use this activity when next teaching geophysics (upper level undergraduate course). It is also appropriate for a virtual geophysics field camp.
Skills and concepts that students must have mastered
Students need a basic understanding of magnetic declination and inclination, and the general nature and shape of the Earth's magnetic field. An introductory powerpoint has been included with this activity that discusses these concepts.
How the activity is situated in the course
This can be used as a stand-alone exercise, or could potentially be used prior to an exercise or project that uses the smartphone to conduct a magnetic survey.
Activity Length
Max of 1-2 hours.Goals
Content/concepts goals for this activity
At the end of this activity students will be able to:
- collect magnetic data using their smartphones, with an understanding of the sensors operation and limitations;
- understand the nature of the Earth's magnetic field and how it varies with geographic location.
- understand the nature of magnetic anomalies as deviations from expected reference field.
- collect magnetic data using their smartphones, with an understanding of the sensors operation and limitations;
- understand the nature of the Earth's magnetic field and how it varies with geographic location.
- understand the nature of magnetic anomalies as deviations from expected reference field.
Higher order thinking skills goals for this activity
- basic data analysis
- 3D visualisation
- evaluation and comparison of data from different sources
- 3D visualisation
- evaluation and comparison of data from different sources
Other skills goals for this activity
- basic computer manipulation of collected data (max, min, average)
Description and Teaching Materials
Student Handout (Acrobat (PDF) 599kB May29 20)
Instructor Handout (Acrobat (PDF) 219kB May29 20)
Intro to Geomagnetic Field - Slides (PowerPoint 2007 (.pptx) 4.4MB May29 20)
Technology Needs
Students will need access to a smartphone with the Physics ToolBox Sensor Suite (a free app available on iOS and Android) installed. A computer and spreadsheet software is ideally needed to analyse the collected data, but this would be possible on a smartphone.Teaching Notes and Tips
I have yet to try this activity myself. I have validated the procedures on a single phone and OS (iPhone SE, iOS), so some troubleshooting with other phone models and OS's might be required.
I suspect the most difficulty will come when students assigning the (x,y,z measurements to specific physical sensor axes, and particularly the sign of the z axis).
I suspect the most difficulty will come when students assigning the (x,y,z measurements to specific physical sensor axes, and particularly the sign of the z axis).
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Assessment
Because I have yet to try this activity, I have not developed a good rubric, but the achievement goals are:
- locate sensor and assign sensor axes correctly
- take x,y,z measurement and correctly derive the field inclination.
- understand possible sources of deviation from reference field values.
- locate sensor and assign sensor axes correctly
- take x,y,z measurement and correctly derive the field inclination.
- understand possible sources of deviation from reference field values.