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 kHz
Max flux density Bm=400 Gs
Thermal influence of the
coil on the cell dish
must be minimal 5

6. 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 A

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 7

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
Cooling plate
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
650
3.8
2.5 24
Flux 3D
720
3.3
2.4 26
Widened Cross-Leg
Fluxtrol 75
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 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 – kW for field density 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 16

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 17

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