DESIGN STUDY OF INDUCTION COIL FOR GENERATING MAGNETIC FIELD FOR CANCER HYPERTHERMIA RESEARCH

1
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

2
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

3
Induction Coil for Low Volume In Vitro and Small
Animals Research
Coil features - Planar turns with gap variation
- Fluxtrol magnetic caps on the coil ends
Magnetic field distribution along the center line
4
Magnetic Field Mapping
Induction coil with Field Probe on the stand
Power supply 3 kW
5
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 Bm400 Gs
• Thermal influence of the
• coil on the cell dish
• must be minimal

6
Concept of New Induction Coil
7
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
• Material selection with account for orientation
• Intensive heat transfer to copper through a
  layer of thermo-conductive epoxy compound
• Use of additional cooling plate
• Coil copper design with reduced 3D effects

8
Flux Density Map of Rectangular Coil with
Magnetic Core
Flux 2D program
9
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
10
Induction Coil with Extended Cross Legs
Slot for thermal protection screen
11
Temperature Prediction for the Core Made of
Oriented Fluxtrol 75
Uniform coil winding
Winding with widened cross-over leg
12
Electrical Parameters for Helmholtz Coil and
Rectangular Coils
Coil Type Core Program Bm (Gs) U (V) I (kA) S (MVA) P (kW)
Helmholtz None Flux 2D 400 1750 8.4 14.7 74
Rectangular Fluxtrol 50 Flux 2D 400 650 3.8 2.5 24
Rectangular Fluxtrol 50 Flux 3D 400 720 3.3 2.4 26
Widened Cross-Leg Fluxtrol 75 Flux 3D 400 660 3.5 2.3 25
13
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
14
Magnetic Flux Density Distribution
Plot of magnetic flux density through the center
of the inductor
15
Induction Equipment at JHU
Inductor and capacitor battery
Power Supply 80 kW
15
16
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

17
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

18
Acknowledgement
This work was funded by a grant from the
Prostate Cancer Foundation