# Open Source Electromagnetic Trackers

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In the photo, each of the three receiver coils is ten millimeters long, and is a [Sonion] T 20 AG telecoil usually used in hearing aids.

## Key Personnel

## Goals of the Project

To teach the process of developing electromagnetic trackers for research, to foster an open community of researchers developing electromagnetic trackers, to develop open-source software and open-source hardware for working research electromagnetic trackers interfacing to Slicer through OpenIGTLink.

## Current Progress

6DOF Electromagnetic Tracker Construction HOWTO

5DOF Electromagnetic Tracker Notes

Pete's current efforts are towards developing low-cost coil-characterization methods which make sense electromagnetically, aiming for a published paper. Pete has yet to encounter a paper which covers this topic.

## References

- http://www.hackster.io/plume/plume http://rose.eu.org/2014/tag/plume a dead 6DOF EM tracker project.

- Project started at 2011 Summer Project Week

- Frederick H. Raab, Ernest B. Blood, Terry O. Steiner, Herbert R. Jones, "Magnetic Position and Orientation Tracking System", IEEE Transactions on Aerospace and Electronic systems, Vol. AES-15, No. 4, September 1979, pages 709-718. Iterative solution for 6DOF tracker. Includes sensitivity matrix of magnetic couplings partial derivatives with respect to position and orientation changes.

- Frederick H. Raab, "Quasi-Static Magnetic-Field Technique for Determining Position and Orientation", IEEE Transactions on Geoscience and Remote Sensing, Vol. GE-19, No. 4, October 1981, pages 235-243. Direct solution for 6DOF tracker.

- Tobias Schroeder, "An accurate magnetic field solution for medical electromagnetic tracking coils at close range", Journal of Applied Physics 117, 224504 (2015). Current-sheet model for cubical coils.

- C.A. Nafis, V. Jensen, L. Beauregard, P.T. Anderson, "Method for estimating dynamic EM tracking accuracy of Surgical Navigation tools", SPIE Medical Imaging Proceedings, 2006. Reports low-cost accuracy-measuring techniques and results for various trackers.

- C. L. Dolph, "A current distribution for broadside arrays which optimizes the relationship between beam width and sidelobe level," Proceedings of the IRE (now part of the IEEE), Vol. 35, pp. 335-348, June, 1946. The original Dolph-Chebyshev Fourier-transform window article. Dolph-Chebyshev window can give 140 dB rejection in the stopband.

- Albert H. Nuttall, "Some Windows with Very Good Sidelobe Behavior", IEEE Transactions on Acoustics, Speech, and Signal Processing 29 (1) 84-91, doi:10.1109/TASSP.1981.1163506, "U.S. Government work not subject to U.S. copyright", in particular Figure 10 window for -L/2 < t < L/2: w(t) = (1/L) (10/32 + 15/32 cos(2pi t/L) + 6/32 cos(4pi t/L) + 1/32 cos(6pi t/L)) has first sidelobe at -61 dB and 42 dB/octave sidelobe rolloff.

- Eugene Paperno, "Suppression of magnetic noise in the fundamental-mode orthogonal fluxgate", Elsevier, Sensors and Actuators A 116 (2004) 405-409. Picotesla noise in 20 mm long 1 mm diameter fluxgate magnetometer. To get low noise, the drive flux swings between saturation in one direction and zero flux. The usual noisy fluxgate drive flux swings between saturation in one direction and saturation in the other direction, to ease measurement down to DC.

- [| Nara etal, "Moore-Penrose generalized inverse of the gradient tensor in Euler's equation for locating a magnetic dipole"][| J. Appl. Phys. 115, 17E504 (2014)] on field-and-gradient single-coil 5DOF tracking closed-form algorithm.

- James M. Chappell, Samuel P. Drake, Cameron L. Seidel, Lachlan J. Gunn, Azhar Iqbal, Andrew Allison, Derek Abbott, "Geometric Algebra for Electrical and Electronic Engineers", Proceedings of the IEEE, Vol. 102, No. 9, September 2014, pages 1340 to 1363. Clifford algebra formulation of electromagnetics using vectors, bivectors, trivector.

- Anton Plotkin, Vladimir Kucher, Yoram Horen, and Eugene Paperno, "A New Calibration Procedure for Magnetic Tracking Systems", IEEE Transactions on Magnetics, Volume 44, Number 11, November 2008, Pages 4525 to 4528. In-system coil characterization using just receiver positions on the plane closest to the transmitter, which makes electromagnetic sense.