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Abstract—The placement of a gastro-intestinal feeding tube is

a critical procedure for patients in intensive care, especially burn

victims. Using traditional non-guided methods, this placement

can take up to 15 hours, as X-ray confirmation is needed to make

sure that the tube has first cleared the lungs and then entered the

intestine via the pyloric valve. Syncro Medical Corporation has

developed and patented a magnetically-guided tube using a large,

2.5-kg hand-held permanent magnet which guides a small

permanent magnet on the tip of the feeding tube stylet. An

electronic reed switch is also used to determine the position of the

feeding tube. Using this new process, intestinal feeding tube

placement can be accomplished in 15 minutes. Syncro Medical

has been working with Youngstown State University to develop a

high-temperature superconducting (HTS) electromagnet for this

application, as this can be easily turned on and off during the

placement procedure. Results from HTS coil testing for Phase I

of this project are included in this paper.

Index Terms—feeding tube, HTS, electromagnet.

I. INTRODUCTION

technique for quickly placing post pyloric feeding tubes

inside patients have been under development by Syncro

Medical based on the initial concept of Dr. Sabry Gabriel [1].

The baseline magnet is a permanent magnet roughly 10 cm in

diameter and 4 cm thick, weighing ~2.5 kg including the

aluminum packaging.

In order to place the feeding tube inside the patient, a wire-

guided stylet is placed inside the feeding tube. A small

permanent magnet—2.5 mm OD, 0.5 mm ID, 10 mm long—is

attached to the tip of the stylet. The large external permanent

magnet is used to guide the internal stylet magnet. Once the

feeding tube is in the proper position inside the pylorus, the

stylet is removed, leaving only the feeding tube in place. A

photograph of this magnet is shown in Fig. 1.

Manuscript received 9 October 2012. This work was supported in part by

the U.S. Department of Defense.

J. P. Voccio was with American Superconductor Corp. for most of this

work and is now with the MIT Magnet Laboratory. Cambridge, MA

(jvoccio@mit.edu).

Frank Li and Jalal Jalali are with Youngstown State University,

Youngstown, OH 44505.

Craig Butrick is a student at Youngstown State University and is now with

Lincoln Electric Company, Cleveland, OH.

Michael Sammartino and Mike Kovach are students at Youngstown State

University.

Joe Winkler and Gary Wakeford were with Syncro Medical Corporation,

Youngstown Ohio 44505.

Fig. 1. Photograph of the baseline Syncro Medical PM magnet.

In order to understand the magnetic field profile of the

permanent magnet, an ANSYS finite element model was

developed. The magnetic flux plot for this magnet is

provided in Fig. 2. This magnet produces a magnetic field of

30 mT at a distance of 10 cm from the top surface of the

magnet. Therefore, the goal of the ensuing HTS electromagnet

is to achieve equal performance of the permanent magnet

while minimizing both size and weight. In the meantime, the

added benefits of turning on/off the high strength magnetic

field are essential for these feeding tube applications.

Fig. 2 Axisymmetric magnetic analysis model and flux plot for baseline

Syncro permanent magnet (PM). Peak flux density is 0.6 T near permanent

magnet and 30 mT 10 cm from magnet surface denoted by black dot. (The

PM is denoted by region 1, while area 2 denotes the cross-section for the HTS

electromagnet in ensuing analysis.)

High-Temperature Superconducting Coil For

Magnetically-Guided Feeding Tube Application

John Voccio, Frank Li, Jalal Jalali, Mike Kovach, Michael Sammartino, Craig Butrick,

Joe Winkler and Gary Wakeford

A

1 2

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II. DESIGN

Using the same model shown in Fig. 2, the finite element

analysis for the HTS electromagnet was performed. In this

case, region 1 was modeled as air and current density was

applied to region 2. The novel no-insulation approach to

superconducting magnet design [2] was used for this coil

design. With this approach, the magnet can be made lighter

due to the higher current density. This method allows for

greater packing factor of the HTS wire and also provides self-

protecting capability, as the turns short-out after the current

exceeds the critical current.

In order to explore a wide range of designs, a random

optimization was performed by changing the following

variables:

• Inside Diameter (cm): 5-15

• Outside Diameter (cm): 10-25

• Number of Pancakes: 1-4

• Expected Weight (kg): ~5 (inc. liquid nitrogen)

The results of this analysis are presented in Fig. 3 in terms

of the required coil operating current as a function of the coil

weight. Assuming a bare wire critical current of 100 A at

77 K, the coil critical current needed to be less than 70 A.

Furthermore, designs were screened to minimize both weight

and HTS wire usage. This filtering resulted in the selection

of the Best Designs shown in Table I.

Fig. 3 The operating current vs. weight graph indicates that the best design

weight for the bare (open square) and laminated tapes (solid square) is 0.8 and

1.2 kg, respectively. The bare HTS insert wire has no copper laminate.

III. COIL FABRICATION AND TESTING

Coil 1 was wound with copper-stablized, 2G conductor

from American Superconductor Corporation. This conductor

has a self-field critical current of ~80 Amp. A photograph of

this coil is shown in Fig. 4. This coil was fabricated using the

no-insulation winding method [2].

Table I COIL DESIGN PARAMETERS

Parameter Coil 1 Coil 2

Inside Diam. (mm) 50 100

Outside Diam. mm) 165 132

Wire Thickness (µm) 200 80

Insulation None None

Pancakes 2 2

Turns 450 412

Operating Current (A) 64 63

Field @ 100 mm (G) 250 160

Wire Length (m) 154 151

Weight (kg) 1.2 0.8

Fig. 4 Photograph of Coil 1.

The voltage-current data for this coil was taken manually

using an HP power supply and digital nanovoltmeter. Coil 1

exhibited a critical current of ~61 A, after which point the

turns started to short-out as designed, and the field decreased

and leveled off.

Coil 2 was smaller in outside diameter—132 mm, as

opposed to 165 mm for Coil 1. This coil was made with

thinner (80 µm), bare insert tape, which has no copper

stabilizer. A photograph of this coil is provided in Fig. 5.

The voltage-current curve for this coil is shown in Fig 6.

The critical current was only ~40 Amp, which is only ~60%

the design current of 63 Amp. This reduction in critical

current is due to the higher imposed magnetic field on the

inside diameter of this coil. Therefore, in order to meet the

63 Amp specification, the bare insert wire would need a self-

field critical current of ~120 Amp, instead of the ~80 Amp

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current tape used in this coil. This increased level of

performance is feasible with recent improvements in

conductor performance due to thicker YBCO layers—1.2 µm,

instead of only 0.8 µm for the standard tapes.

Fig. 5 Photograph of Coil 2.

Despite the decreased current and field capability, the no-

insulation behavior of this coil is depicted in the data of Fig. 6.

Above the 40 Amp critical current, the measured magnetic

field starts to level out, indicating that the turns are starting to

short out, thereby protecting the coil from burnout.

Fig. 6 Voltage-current curve for 2nd prototype coil, along with field (G)

measured at 10 cm distance.

IV. FORCE MEASUREMENT

While the initial design specification was to create a certain

magnetic field at a distance from the magnet, we came to

realize that creating the force on the stylet permanent magnet

is the real objective. Therefore, in order to establish a

baseline, the stylet magnet was suspended over the larger

permanent magnet via a string, and the attraction force was

measured using a simple spring scale. The results of this

testing showing the force as a function of distance from the

magnet surface is shown in Fig. 7. For a single stylet magnet,

the force at the 10 cm distance is only 20 mN, and the force

was doubled at this distance by adding a second stylet magnet.

As expected, these results show that the force is inversely

proportional to the square of the distance between the two

magnets. Adding a second permanent magnet to the stylet tip

increases the force, but the force is not doubled, as the second

magnet is further away and, therefore, has a lower force

contribution.

In addition, similar testing was performed with a 2T

superconducting magnet. Again, the stylet magnets were

suspended from a string, and the force was measured with a

simple spring scale. Since the superconducting magnet has an

open bore, the force was measured both outside (above the

magnet) and inside the magnet. These results are summarized

in Fig. 8.

0 2.5 5 7.5 10

Distance (cm)

Fig. 7 Results of force measurement.

-15 -10 -5 0 5 10

Distance Above Magnet (cm)

Fig. 8 Force on stylet magnets in vicinity of superconducting magnet.

Interestingly, as the stylet magnets are lowered into the

open bore of the superconducting magnet, the force starts to

level off. This leveling off is due to the uniformity of the

background field; in other words, the field gradient is

decreasing. Therefore, these results indicate that the

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attractive force is a function of both the field and the field

gradient.

Furthermore, these results show that one stylet magnet with

the 2T field performs similarly to two stylet magnets at 1T

field. Also, two stylet magnets were tested at the 2T field,

showing twice the force magnitude of the one stylet magnet

test at the same 2T field. Both of these results make intuitive

senses.

In comparing the data from Fig. 7 and Fig. 8, it is

interesting to note that the large permanent magnet, which has

a 600 mT surface field, produces greater forces than the 1T

and 2T superconducting magnet tests, further demonstrating

the need for not only the field strength, but also field gradient.

V. PULSED FORCE MEASUREMENT

A third insulated coil was used for pulsed current testing, in

an effort to reduce the size and weight of the coil. This

double-pancake coil was only 10 cm in diameter and weighed

only 0.5 kg. Compared to the DC current source, the pulsed

current showed a ~30% increase of the dynamic force. In

order to measure dynamic response of the pulsed

electromagnet, the analog output of a Vernier DFS-BTA Force

Sensor was paired with an Agilent MSO6054A oscilloscope

capable of sampling at 500 MHz and recording 4 GSa/s. Peak

results were recorded and measured using the oscilloscope’s

built in functions for maximum precision. Fig. 9 shows the

force measurement (top trace) and current through the

electromagnet (bottom trace). Note that magnetic force is not

instantaneous; it builds over time and is peak right as the

electromagnet is turned off.

Fig. 9. Top curve-output from analog force sensor (500 mV/div); Bottom

signal-current pulse signal (20 Amp/div). Timescale is 2 msec/div.

This method allowed measurements to be taken independent

of frequency, voltage, and control technique. Results were

then precisely compared and validated to find the most

efficient combination.

Additionally, the pulsed electromagnet can have higher

current than that of the DC electromagnet, as long as the off

time is sufficient for the cooling. The high current leads to

higher force and could further reduce the weight of the

electromagnet.

VI. RECOMMENDATIONS FOR FUTURE WORK

As a result of this initial study, the following are

recommendations for further research:

• Investigate coils with higher field gradients,

particularly if they can be made with small outside

diameter.

• Develop cryogenic packaging, including a hand-held

insulated liquid nitrogen container.

VII. CONCLUSION

Light weight HTS electromagnets were demonstrated as a

possible replacement for the permanent magnet currently used

for the Syncro Medical feeding tube application. These coils

used the novel, no-insulation technique, which improves the

coil current density and also greatly enhances the coil stability,

as the turns simply short-out after the critical current is

reached. Future work will be performed on the packaging of

these coils to make a prototype handheld HTS electromagnetic

device for this application.

ACKNOWLEDGMENT

The authors would like to acknowledge the following

people for their help on this project: Linda Waple and Paul

Yankauskas of American Superconductor Corporation; Gary

Wakeford of Syncro Medical; and Nimesh Shrestha of

Youngstown State University.

REFERENCES

[1] S. A. Gabriel; B. McDaniel; D. W. Ashley; M. L. Dalton; T. C.

Gamblin. “Magnetically guided nasoenteral feeding tubes: a new

technique,” The American Surgeon 2001; 67(6):544-9.

[2] Seungyong Hahn, Dong Keun Park, Bascunan, J. Iwasa, Y. of the

Francis Bitter Magnet. Lab., Massachusetts Inst. of Technology,

Cambridge, MA, USA, “HTS Pancake Coils without Turn-to-Turn

Insulation,” IEEE Transactions on Applied Superconductivity, vol. 21,

June 2011, pp. 1592-1595.