DESIGN STUDY OF INDUCTION
COIL FOR GENERATING
MAGNETIC FIELD FOR CANCER
HYPERTHERMIA RESEARCH
V. Nemkov, R. Ruffini, R. Goldstein, J. Jackowski – AMF Life
Systems, LLC, Michigan, USA
T. L. DeWeese, R. Ivkov - Department of Radiation Oncology and
Molecular Radiation Sciences, Johns Hopkins University School of
Medicine
Overview
• Coil Design for Low Volume In Vitro and
Small Animals Research
• Coil Design for Large Volume In Vitro
Research
• Magnetic Field Distributions for 2D and 3D
models
• Parameter Comparison for Different Coils
• Temperature Distribution in Magnetic Core
• Conclusions
Induction Coil for Low Volume In
Vitro and Small Animals Research
Distance Along Center Line (cm)
5
4
3
2
1
0
-1
-2
-3
-4
-5
0
200
400
600
Field Strength (Oe)
Coil features:
- Planar turns with gap variation
- Fluxtrol magnetic “caps” on the
coil ends
Magnetic field distribution
along the center line
Magnetic Field Mapping
Power supply 3 kW
Induction coil with Field
Probe on the stand
Large Volume Cell Culture Coil
• Goal: Design an inductor with even flux density
for heating of culture specimens
• The region of concern is a specimen holding
dish (24 or 96-well dish)
• Frequency must be 140-160 kHz
• Max flux density Bm=400 Gs
• Thermal influence of the
coil on the cell dish
must be minimal
Concept of New Induction Coil
Cooling
plate
Coil
tubes
Magnetic
controller
Coil “opening” dimensions:
A x B x H = 110 x 175 x 40 mm
Inductor with Magnetic Core
Challenges:
- 3D System
- Intensive heating of magnetic core due to
strong field, high frequency and long cycle time
Core temperature control:
1. Material selection with account for orientation
2. Intensive heat transfer to copper through a layer
of thermo-conductive epoxy compound
3. Use of additional cooling plate
4. Coil copper design with reduced 3D effects
Flux Density Map of Rectangular Coil
with Magnetic Core
Flux 2D program
Temperature Maps in 2D Approach
Tmax = 240 C
Tmax = 140 C
a – Core of Fluxtrol 50; b – Core of oriented Fluxtrol 75
Flux density 400 Gs
Induction Coil with Extended
Cross Legs
Cooling
plate
Extended
Cross Legs
Slot for thermal protection screen
Temperature Prediction for the
Core Made of Oriented Fluxtrol 75
a
b
Uniform coil winding
Winding with widened
cross-over leg
Electrical Parameters for Helmholtz
Coil and Rectangular Coils
Coil Type
Core
Helmholtz
None
Rectangular Fluxtrol
50
Rectangular Fluxtrol
50
Widened Fluxtrol
Cross-Leg
75
Program Bm
(Gs)
U
(V)
I
S
P
(kA) (MVA) (kW)
Flux 2D 400 1750
Flux 2D 400 650
8.4
3.8
14.7
2.5
74
24
Flux 3D 400
720
3.3
2.4
26
Flux 3D 400
660
3.5
2.3
25
Laboratory Tests
Power supply 25 kW
Frequency 150 kHz
Used power 18 kW
Coil head voltage
480 V
Magnetic field
density 280 Gs
Maximum core
temperature 1000C
Magnetic Flux Density Distribution
Plot of magnetic flux density through the center of the inductor
Induction Equipment at JHU
Inductor and capacitor battery
Power Supply 80 kW
15
Summary
• Induction coils for small volume tests require careful
manufacturing to provide uniform magnetic field in
test area; power supply may be small – 3 -12.5 kW
for field density 500 - 1000 Gs
• Design of induction system for large cell-well plates
is a challenging task
• Helmholtz coils require much higher reactive power
(6x), active power (3x), voltage and current than a
special coil with magnetic concentrator
• 2D simulation resulted in overvaluation of coil current
(24%) & undervaluation of voltage (10%) vs. 3D
Summary
• 3D effects lead to significant increase of the
magnetic core temperature especially in the corners
• Extension of cross leg copper significantly reduces
3D effects and diminishes local flux density and
core temperature
• Special attention must be paid to magnetic material
selection, orientation and application technique
• Fluxtrol 75 with optimal orientation and thermally
conductive glue provides the best results
• Results of the coil tests were in good agreement
with predicted values
Acknowledgement
This work was funded by a grant
from
the Prostate Cancer Foundation