Presentation EMT

1. EMT PRESENTATION
A NOVEL WIRELESS 5-D ELECTROMAGNETIC
TRACKING SYSTEM BASED ON NINE-CHANNEL
SINUSOIDAL SIGNALS

2. GROUP MEMBERS:
M.SHERAZ(ELEN51F20R016)
USMAN ALI(ELEN51F20R020)

3. TABLE OF CONTENT
Preview
Abstract
1.Introduction
2.Methodology
A-Magnetic Dipole-Based Electromagnetic Tracking
B-Signal Amplitude Attraction
C-Tracking Algorithm
D-Initial Position and Orientation Determining

4. 3.Prototype And Experimental Evaluation
A-Prototype of the Proposed EMT’S
B-System Workflow
4.Calibration
A-Calibration Setup
B-Induction Coefficient Calibration
C-Pose Calibration of Transmitting Coils
5.Experimental Results

5. A-Stabilization Test
B-Accuracy Test
C-Tracking Speed Test
6.Conclusion’s And Future Work
7.References

6. PREVIEW
• Before starting our presentation topic we would like to first tell
you about what is EMT which is as follows:
• Electromagnetic Theory (EMT) is a subject in the electrical
engineering curriculum which covers static and dynamic electric
and magnetic fields and their interaction.
• Now we shall formally start our presentation by telling you the
abstract’s of it.

7. ABSTRACT
• Electromagnetic tracking systems (EMTSs) are widely employed
in medical instruments, virtual reality, game control, etc.
• An EMTS mainly consists of three parts: magnetic fields
generator connected with transmitting coils, control unit,
sensing and computing unit.
• In general, transmitting coils and induction coils of an EMTS
are of those type connected to the same control unit to
determine an induced electromotive force resulted from which
transmitting coil.

8. • In this study, a novel EMTS is presented, whose induction coils are
separated from the control unit; hence the wireless pose tracking can
be achieved.
• Now in order To improve the tracking speed and determine an
induced electromotive force resulted from which transmitting coil,
the transmitting coils are simultaneously excited by nine-channel
sinusoidal signals with different frequencies, instead of the switching
channels in chronological order.
• Thus, five degree-of-freedom (5-D) tracking of the miniature
induction coil is implemented.

9. • Experimental results show that the average position and
orientation errors are less than 2.3 mm and 0.2°.
• Respectively, which indicates that the proposed EMTS has
potential prospects for both medical and industrial
applications, especially for the magnetically controlled capsule
robot.
• Index Terms—Magnetic dipoles, algorithms, electromagnetic
induction, coils, tracking.

10. NOW FOR THE INTRODUCTION PART I WOULD
LIKE TO CALL UPON MY FELLOW GROUP MEMBER
TO GIVE YOU A BRIEF AND DETAILED INSIGHT OF
THIS PROJECT.

11. INTRODUCTION
• Electromagnetic(EM), optical, and radar technologies are the most
commonly employed tracking methods .
• For example, EMTS can alleviate the need for real-time radiological
imaging, replacing X-ray, or fluoroscopy with virtual imaging .
• EMTS provides high tracking accuracy in non-line-of-sight
environments, allowing device navigation in the positions where
optical and radar tracking does not work effectively .
• A variety of EMTSs and their applications were investigated.

12. PROPOSAL’S
• Yao et al: proposed a magnetic flux feedback control system in which
the motion commands are generated in real-time by the coordinated
geometry of the Hall probe and the magnetic object .
• Bert et al: introduced the concept of treatment verification via EMT
for interstitial brachytherapy .
• Ozgul et al: reported an electromagnetic navigation bronchoscopy for
the sampling of peripheral lung lesions.
• Raval et al: adopted an electromagnetic navigation tracking system to
detect miniature sensors integrated into the tip-tracked instruments.

13. • Although EMTSs have been employed broadly, the systematic designs
of commercial EMTSs are rarely reported.
• In general, an EMTS consists of three dominant parts: field generator
(FG), control unit, and EM sensors .
• To determine an induced electromotive force resulted from which
transmitting coil, both FG and EM sensors are connected to the same
control unit.
• I.E., the excitation signals and sensed signals are controlled by the
same microprocessor through cables.

14. • Therefore, its application scenarios are limited.
• For example, it cannot be employed to track a capsule robot
inside the human body .
• Researchers have tried to achieve wireless electromagnetic
tracking, i.e., the FG and EM sensors do not connect to a single
control unit.
• Shah et al: introduced a wireless EMTS named Calypso medical
four-dimensional (4D) positioning system .

15. • In general, two or three beacon transponders (Φ1.85 mm ×L8.5 mm)
embedded in a bioglass shell, are implanted close to the target.
• The transponders are tracked by an EM array consisting of radiofrequency
(RF) transmitting coils and induction coils.
• RF transmitting coils are loaded EM signals with selected frequencies to
excite each transponder sequentially according to its specific resonant
frequency.
• Then transponders re-transmit the decaying signals to the EM array.
• The accuracy is below 1 mm, and the tracking volume covers an area of 140
mm ×140 mm ×190 mm.

16. • The update rate of the Calypso system is 10 Hz, also leading to
approximately 3.3 Hz per transponder.
• Balter et al: reported a similar beacon positioning system .
• The array contains four source coils and thirty-two receiving coils.
• The source coils generate an oscillating field, which induces a
resonance in the transponder.
• When the oscillating field is switched off, the transponder signal
during relaxation is adopted to establish its pose.

17. • The position accuracy is about 1 mm at the tracking volume of 140
mm ×140 mm ×270 mm, and the position update rate is about 3 Hz.
• Besides, the control unit and EM sensor of Polhemus Liberty Latus are
wirelessly connected with large tracking area and high tracking
speed.
• However, its EM sensor (88.9 mm ×42.2 mm ×24.6 mm) is too big to
be embedded in the small objectives.
• To alleviate such limitations, we develop a novel EMT system that the
tiny induction coil and the control unit are wirelessly connected.

18. • Following fig. shows the system diagram of the proposed wireless EMTS.
• The induction coil can be attached to the tracked object.
• The object pose with respect to the coordinate system can be acquired
through the computing unit.
• As the induction coil is a single axis, the orientation around its rotation axis
cannot be obtained.
• Thus, the only 5-D pose of the induction coil can be acquired.
• The nine transmitting coils are excited by nine-channel sinusoidal waves,
which are with different frequencies.

20. • A typical application scenario for this wireless EMTS is the tracking of a
capsule robot during the human gastrointestinal examination.
• Following fig. shows the schema of a capsule endoscope, whose pose can be
tracked via the proposed wireless EMTS.
• The circuits are powered by a button battery.
• First, the induced electromotive force generated by the induction coil is
magnified by a signal receiving circuit.
• Secondly, the magnified signal is sampled by a sampling module and
processed by the computing unit; then the 5-D pose is acquired.

22. • On the contrary, the induced signal of the Calypso 4D tracking
system is transferred via the beacon transponders; hence the
tracking volume is restricted.
• The mobile markers of the Polhemus wireless EMTS are too
large in most application scenarios.
• Finally, we systematically evaluated the system, and it can
provide real-time tracking with high precision.

23. NOW FOR THE METHODOLOGY PART I WOULD
LIKE TO CALL UPON MY FELLOW GROUP MEMBER
TO EXPLAIN IT’S METHODS

24. METHODOLOGY
• a system of methods used in a particular area of study or
activity.
• A-Magnetic Dipole-Based Electromagnetic Tracking:
• As following Fig. shows, a small electromagnetic coil loaded
with a sine wave signal can be regarded as a magnetic dipole.

25. • According to Biot-Savart Law, the magnetic flux intensity at
point (x, y, z) generated by the transmitting coil is Β, whose
three orthogonal components are as follows:
• where (m, n, p) T is the normalized direction vector of the
electromagnetic coil; (a, b, c) T is the centric position of the
transmitting coil;

26. • L=√(𝑥 − 𝑎)2 + (𝑦 − 𝑏)2 + (𝑧 − 𝑐)2 is the distance from the
centric position of the transmitting coil to the point (x, y, z).
• Assuming (x, y, z) is the centric position of an induction coil
and (vx , vy , vz) T is the normalized direction vector of the
induction coil.
• As the magnetic flux intensity B is not parallel to the vector (vx
, vy , vz) T , the vector projection of Β on (vx , vy , vz) T is
defined as:

27. • According to Faraday’s Law of electromagnetic induction, the
induced electromotive force generated by the induction coil is
expressed as:
• where N is the number of loops of the induction coil; S is the
surface of the induction coil; is the magnetic flux through the
induction coil.
• By using a tiny induction coil, the magnitude of magnetic flux
intensity on the induction coil surface would be considered
identical.
• Thus, it can be modified as:
• Assuming the transmitting coil emits a sinusoidal signal with

28. • The induced electromotive force generated by the induction coil
is a cosine signal with the same frequency as the emitting
sinusoidal signal.
• Assuming ET is equal to -ωNS , the amplitude of induced
electromotive force is described as:
• Because there are six unknown variables (x, y, z, vx , vy , vz) for
an induction coil, at least six equations are needed to calculate
six parameters.
• In the experiment, nine electromagnetic coils simultaneously
emit sinusoidal signals with frequencies differing from one
another; hence nine equations are set up.
• Because (vx , vy , vz) T is just a unit vector, vx^2 +vy^2 + vz^2
=1 can be added as a constraint.

30. B-SIGNAL AMPLITUDE EXTRACTION
(FREQUENCY DIVISION EXCITATION)
• The transmitting coils emit nine sinusoidal waves with different
frequencies simultaneously.
• Hence, the induction coil generates the electromotive force that
comprises nine sinusoidal wave components, where each component
is generated by a corresponding transmitted sinusoidal wave.
• The electromotive force is sampled at a frequency of 170 kHz in this
study, and then the sampled data is sent to the amplitude extracting
module.
• This module adopts the FFT (Fast Fourier Transform) algorithm to
extract the amplitude of each sinusoidal wave component and
determine an induced electromotive force resulted from which
transmitting coil. Hence, error is obtained.

31. C-TRACKING ALGORITHM
• Is a nonlinear least-squares optimization problem. Powell, downhill
simplex, Direct, Multilevel Coordinate Search (MCS), Levenberg-
Marquardt (LM) algorithm, and heuristic optimization method can be
adopted to solve the optimization problem.
• Powell and downhill simplex are sensitive to the initial guess
solution.
• The speeds of DIRECT and MCS are lower than that of LM.
• The time of heuristic optimization methods is much longer than the
algorithms mentioned above. LM is an appropriate algorithm because
it can provide high accuracy, satisfactory tolerance for the initial
guess solution, and faster speed.

32. D-INITIAL POSITION AND ORIENTATION
DETERMINING
• LM algorithm requires an initial guess solution within the
vicinity of the true solution for the initial iteration.
• This initial guess solution cannot be determined by the
gradient algorithm, whereas the heuristic optimization method
is an exceptional choice.
• In contrast with the genetic algorithm and ant colony
optimization algorithm, the PSO algorithm acquires a faster
rate as it does not need operations such as heredity and
mutation.
• Therefore, the PSO algorithm is utilized to find the initial

34. • where c1 and c2 are acceleration constants, adjusting the
weight of single-particle extremum’s contribution and global
extremums’ contributions.
• The experience values for both c1 and c2 are set to 2, which
means equal contribution.
• Inertia weight w, whose value is set to a random number
between 0.5 and 1, indicates the effect of the particle’s
previous speed on the current speed. r1 and r2 are random
numbers in the interval [0, 1].
• The fitness value for the PSO algorithm is also the E defined by
(8).
• The solution of the PSO algorithm is utilized as the initial guess

35. NOW FOR PROTOTYPE AND EXPERIMENTAL
EVALUATION I WOULD LIKE TO CALL UPON MY
GROUP MEMBER FOR EXPLANATION.

36. PROTOTYPE AND EXPERIMENTAL
EVALUATION
• A-Prototype of the Proposed EMTS:
• The prototype implementation of the proposed EMTS is shown
below:

37. • Magnetic fields generator: each power amplifier is connected to
a 32-bit high-performance microcontroller (STM32F103RCT6,
STMicroelectronics Inc., Switzerland) which generates a
sinusoidal signal with a specific frequency, i.e., 200 Hz, 400
Hz, 600 Hz, 800 Hz, 1000 Hz, 1200 Hz, 1400 Hz, 1600 Hz,
and 1800 Hz.
• Nine sinusoidal signals generated by microcontrollers
simultaneously are amplified via power amplifiers (TPA3116, TI
Inc., USA) and filtered via LC low-pass filters.
• Finally, the signals are loaded on the transmitting coils.
• Transmitting coils: nine identical four-layer transmitting coils
were designed and fabricated.
• The voltage applied to the transmitting coil is 24 V.

38. • The voltage applied to the transmitting coil is 24 V.
• The current amplitude of the transmitting coil array is limited to 3A
in this study as the excessive current will cause the transmitting coil
to heat up.
• In addition, the induced electromotive force can be amplified up to
8000 times, as the power supply of the analog-to-digital converter
(ADC) ranges from 0V to 10V.
• To ensure that the induction coil senses the transmitting signals in
the volume of 0.5 m3 and imitate the dipole accurately, the following
parameters are determined after five trials.
• The diameter of the copper wire is 0.8 mm, and the number of loops
of each layer is 60.
• The inner diameter of the coil is 50 mm; the outer diameter of the
transmitting coil is about 56 mm, and the height of each coil is 48
mm, thus the length-to-diameter ratio is about 0.83, which
approximates an optimized multilayer cylindrical coil, making the

39. • As shown in Fig. below:
• Induction coil: a mini-solenoid was designed and fabricated.
• Our goal is to fit the induction coil into a capsule endoscope or a
scalpel tip.
• Due to our present production process, the minimum inner diameter
of the solenoid can only be 0.6 mm.
• To make the diameter of the induction coil small, the copper wire
with a diameter of 0.035 mm is selected after five trials. The wire
number of the induction coil is defined according to the wire
diameter and length.

40. • the amplified signals mix noises with high frequencies, a
fourth-order low-pass filter (OPA2228, TI Inc., USA) was
designed to filter high-frequency noises.
• After that, the second-stage amplifier circuit (OPA2228, TI Inc.,
USA) was designed to amplify the signal to V-level as the mV-
level signal is too small to be sampled.
• The signal receiving circuit is shown below.

41. • Digital electromotive forces converted by an ADC card are
further processed in a computing unit or any other device that
can execute the tracking algorithm.
• The computing unit and receiving circuit module communicate
via the Universal Serial Bus (USB) 2.0 protocol.
• B-System Workflow:
• The system workflow is shown in following Fig. . Software and
hardware are initiated after the system starts, and then the
transmitting coils emit sinusoidal signals.
• The induction coil generates electromotive forces which are
magnified and filtered by a designed module, and then the
electromotive forces are sampled by a sampling module.

42. SYSTEM WORKFLOW CHART

43. NOW FOR CALIBRATION PART I WOULD LIKE TO
CALL UPON MY GROUP MEMBER FOR
EXPLANATION.

44. CALIBRATION
• A-Calibration setup:
• Calibration setup and experimental shelf: two printed circuit boards,
with the dimensions of 500 mm ×500 mm ×2 mm, is drilled with
small holes (Φ1 mm), and the positions of the holes on the two PCBs
are aligned, whose manufacturing precision is ±0.075 mm.
• One PCB is placed at the bottom, and its center point is the origin of
the reference coordinate system.
• The other PCB can move from 0 mm to 500 mm along the z-axis in
a 50 mm scale above the transmitting coil.
• However, moveable PCB cannot move along the x- and y-axes to
ensure the calibration and experimental accuracy.

46. • B-Induction Coefficient Calibration:
• Electromotive force induced by the induction coil is linearly
correlated to the magnetic flux intensity at a given point.
• Therefore, the following equations are established:
• where kx , ky , and kz denote induction coefficients, which
incorporate parameters BT, ω, N, and S.
• The pose parameter (a, b, c, m, n, p) of each transmitting coil is
known in advance.
• In the tracking volume, M points can be predetermined,
wherein the pose parameters (x, y, z, vx , vy , vz) of the
induction coil are also predetermined.

47. • C-Pose Calibration of Transmitting Coils:
• All transmitting coils are fixed at a predetermined positions in
a specific direction with respect to the reference coordinate
system; however, the differences between the actual values and
predetermined values exist whether the transmitting coils are
fixed manually or mechanically.
• Thus it is necessary to calibrate the pose of the transmitting
coils to improve the positioning accuracy.
• The induction coil is placed at these points in known directions;
hence the induction coil parameters (x,y,z,Vx,Vy,Vz ) are

48. FOLLOWING EQUATIONS ARE ESTABLISHED:

49. NOW FOR EXPERIMENTAL RESULT PART I WOULD
LIKE TO CALL UPON MY GROUP MEMBER FOR
EXPLANATION.

50. EXPERIMENTAL RESULTS
• Three performance indicators, i.e., position accuracy, stabilization,
and speed, are tested for the proposed prototype.
• Experiments were carried out in a normal environment after the
calibrations of the induction coefficient, and the pose of each
transmitting coil.
• A-Stabilization Test:
• The sample variance is employed to indicate the intensity of the data
fluctuation.
• The larger the sample variance is, the higher the fluctuation of the
sample data is.
• The sample variance on the x-axis is defined as:

51. • where S 2 denotes the sample variance; xi is the i-th observed
x value; n is the number of the sampled data; x is the mean
value of observed n-point x values.
• Similarly, the sample variances in Table I are calculated
respectively as given.
• Table I shows, both position and orientation sample variances
are minimal, which indicates the fluctuation of data is within a
narrow range.
• The values of x, y, and z are shown in Fig.1; the values of vx ,
vy , and vz are shown in Fig.2 below, which indicates that the
fluctuation of data is insignificant.
• We make a comparison with NDI Aurora v3 EMTS.
• The induction coil was also placed at the point (-80 mm, -80
mm, 350 mm, 0, 0, 1).

52. SAMPLE VARIANCE TABLE

53. POSITION & ORIENTATION ERROR FIGURE’S

54. • B-Accuracy Test:
• Root mean square error (RMSE) is utilized to evaluate the
average accuracies of position and orientation.
• Here the smaller the RMSE is, the better the accuracy is.
• Therefore, the RMSE of position error on the x-axis is defined
as:
• Similarly, position errors YRMSE, ZRMSE, VxRMSE, VyRMSE, and
VzRMSE presented in Table II.

55. • Eight points were selected at the height of 200 mm, and seven
points were selected at each height of 250 mm, 300 mm, 350
mm, 400 mm, 450 mm, and 500 mm.
• These points are distributed on the 500 mm ×500 mm plane.
• Then the induction coil was placed at these points in a
predetermined direction, such as (0, 0, 1).
• To ensure that the induction coil is placed at the center of the
small hole in the same manner, the operator was trained 20
times before experiments.
• When testing one point, the predetermined position and
orientation coordinates of the induction coil were recorded
firstly, and then the position and orientation of the system
output were recorded.

56. TABLE 2
• Position errors Ex , Ey , and Ez of each point are shown in Fig.3,
and orientation errors Evx, Evy, and Evz of each point are
shown in Fig.4, where the angle is converted by 2sin-1(E/2)
with the unit of degree[30].
• The position error on the x-axis is defined as:

57. POSITION ERROR FIGURE

58. ORIENTATION ERROR FIGURE
• Position errors of points on the higher planes are slightly larger
than those on lower planes.
• The reason is that the signal-to-noise ratios at the points on
the higher planes are lower than those on the lower planes.

59. • C-Tracking Speed Test:
• The execution time of tracking each point was written into the file to
obtain the speed of the tracking induction coil.
• Fig. below shows the execution time of the 500-point tracking.
• The average time to position one point is about 0.096 s, and the
time to position each point ranges from 0.08 s to 0.105 s, which
denotes the maximum update rate of tracking is about 10 Hz.
• This update rate is closely related to system design.
• The data sampling frequency of the ADC card is set to 170 kHz, and
the positioning of one point needs16384 sampling data.
• It takes 0.096 s to sample 16384 data, and the tracking algorithm
spends about 0.01 s for computing one point, which is far less than
the data sampling time.

60. • Therefore, the increase of the sampling rate will effectively improve
the tracking rate. Which is shown below:
• In addition, the maximum moving speed of the induction coil is
evaluated.
• The moving speed ranges from 10 mm/s to 140 mm/s in the interval
of 10 mm/s.
• The results of the LM(Levenberg–Marquardt) algorithm diverge when
the speed is 130 mm/s.

61. • Therefore, the maximum moving speed of the induction coil is
defined as 120 mm/s.
• The LM(Levenberg–Marquardt) algorithm tends to diverge when
the induction coil moves to fast, as the initial guess of the
LM(Levenberg–Marquardt) algorithm will be much far from its
actual position.
• Fig. below shows the trajectory of the induction coil when the
speed is less than the maximum value.

62. NOW FOR CONCLUSIONS AND FUTURE WORK
PART I CALL UPON MY GROUP MEMBER TO
CONCLUDE OUR TOPIC

63. CONCLUSIONS AND FUTURE WORK
• The concept and prototype implementation of a novel wireless
EMTS, which can determine the 5-D pose of the tiny induction
coil, is presented in this study.
• This EMTS has a remarkable feature that the connection
between the induction coil and the control unit is wireless,
which enhances its flexibility and electrical safety.
• The tiny induction coil can be possibly embedded inside a
capsule endoscope or the tip of a surgical instrument, and then
being tracked continuously.
• The current tracking volume of the proposed prototype is 0.5
m3 ; the RMSEs of position and orientation are less than 2.3

64. FUTURE WORK
• The future work will focus on the following aspects:
• 1) Improving the transmitting circuit to reduce thermal noises of the
emitting signal, as the overheating of the power amplifier leads to
the signal fluctuation.
• 2) Improving the receiving circuit to filter high-frequency noises
mixed in the induction process.
• 3) Improving the algorithms, such as back-propagation neural
network based on the LM algorithm to obtain more stable tracking
results.
• 4) Seeking a better calibration method to achieve more accurate
calibration parameters.
• 5) Representing the orientation of an induction coil with quaternion
to avoid the possibility of singularity by removing the term

65. REFERENCES
• [1] A.M. Franz, T. Haidegger, W. Birkfellner, K. Cleary, T.M. Peters,
and L. Maier-Hein, “Electromagnetic tracking in medicine–a review of
technology, validation, and applications,” IEEE Trans. Med. Imaging,
vol.33, no.8, pp.1702-1725, May 2014,
10.1109/TMI.2014.2321777.
• [2] A. Acemoglu, D. Pucci, L. S. Mattos, "Design and control of a
magnetic laser scanner for endoscopic microsurgeries," IEEE/ASME
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10.1109/TMECH.2019.2896248.
• [3] W. Jeon, A. Zemouche, R. Rajamani, “Tracking of vehicle motion
on highways and urban roads using a nonlinear observer,” IEEE/ASME

66. • [4] H. A. Jaeger et al., “Anser EMT: the first open-source
electromagnetic tracking platform for image-guided
interventions,” Int. J. Comput. Assist. Radiol. Surg., vol.12,
no.6, pp.1059-1067, Jun. 2017, 10.1007/s11548-017-1568-
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• [5] A. Schweinet al., “Electromagnetic tracking of flexible
robotic catheters enables ‘assisted navigation’ and brings
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10.1016/j.jvs.2017.01.072.

67. IN THE END, WE LIKE TO THANK YOU FOR
LISTENING TO OUR PRESENTATION .

68. THE END