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Exposure setup for animal experiments using a parabolic

reflector

S. Schelkshorn J. Detlefsen

Lehrstuhl für Hochfrequenztechnik

Fachgebiet Hochfrequente Felder und Schaltungen

Technische Universität München

25th July 2006

Overview

• Overview

Introduction

Exposure Setup

Numerical

Dosimetry

Conclusion

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Introduction

Exposure Setup

Numerical Dosimetry

Conclusion

Motivation

• Overview

Introduction

• Motivation

• Project

Description

Exposure Setup

Numerical

Dosimetry

Conclusion

3 / 20

• Public concern about possible negative health effects

• Biological in-vivo experiments are indispensable to

create a strong body of evidence

• To verify the results, all experiments have to be carried

out under well defined and reproducible conditions

Project Description

• Overview

Introduction

• Motivation

• Project

Description

Exposure Setup

Numerical

Dosimetry

Conclusion

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• Investigation on cognitive faculties of

electromagnetically exposed Wistar rats

• Long-term, continuous exposition (20Months, 24 h/day)

with GSM and UMTS signals at 900MHz and 1966MHz,

respectively

Prerequisites

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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• Standard, controlled and reproducible exposure

conditions: e. g. linearly polarized plane wave

• Identical construction of the setup for three different

exposure groups: GSM (@900MHz), UMTS

(@1966MHz) and sham (no exposure)

• Shielding between the three groups and from external

fields

• Possibility to expose a large number (> 100) of

animals over a long period of time

• Appropriate conditions for the animal well-being: e. g.

air-conditioning, easy access to the cages

• Low-cost setup

Basic Principle

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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• Usage of a parabolic reflector to convert a spherical

wavefront to a plane wave

Focus Focus112 cm

320 cmz

y

Fig. 1: Parabolic reflector

• Mass-production reflector for the reception of satellite

TV, diameter: 320cm, focal distance: 112cm

• Exposure setup is placed in an electromagnetically

shielded chamber to decouple the three exposure

groups and to prevent influences from external fields

Basic Principle – First Simulations

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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• UTD assuming an ideal point source at the focus with

uniform illumination

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

0.1

0.2

0.3

0.4

0.5

ρ (m)

−z

(m)

0 0.5 1 1.50

2

4

6

8

10

ρ (m)

|E| (

V/m

)

Fig. 2: Phase fronts and absolute value (1966MHz)

• Main problems of the prime focus configuration when

using a real feed

◦ Feed spillover

◦ Uniform illumination

Basic Principle – Feed Defocussing

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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• Proposed solution: feed defocussing together with the

placement of the exposure zone away from the feed

Focus Focus

Fig. 3: Focused vs. defocused setup

• The exposure zone is placed where the feed’s spillover

effect can be neglected

• With the same feed beamwidth a greater illuminated

area is obtained

• The defocussing originates a smooth tapering of the

field at the focal plane, preventing ripples along the

wave trajectory caused by abrupt changes in the

illumination

Basic Principle – Feed Defocussing (2)

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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• The exposure zone is set to −250 cm < z < −200 cm

and 15 cm < ρ < 125 cm

• The feed is chosen to be an open waveguide

• The maximum and the standard deviations are

analyzed as a function of the defocussing distance dz

−70 −60 −50 −40 −30 −200

10

20

30

40

50

dz (cm)

Rel

ativ

e de

viat

ion

(%)

−70 −60 −50 −40 −30 −200

10

20

30

40

50

dz (cm)

Rel

ativ

e de

viat

ion

(%)

Fig. 4: GSM-band setup (Optimum dz = −59 cm)

Fig. 5: UMTS-band setup (Optimum dz = −56 cm)

Basic Principle – Comparison

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60

0.1

0.2

0.3

0.4

0.5

ρ (m)

−z

(m)

0 20 40 60 80 100 120 140 160200

210

220

230

240

250

x (cm)

−z

(cm

)

Fig. 6: Phase fronts for focused setup

Fig. 7: Phase fronts for defocused setup

Exposure Setup

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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Focus

Parabolic

reflector

Feed

Polysufone

Cage

Wood

Shelf

Absorber

material

64 cm

320 cm

34 cm

42.5 cm

57.1 cm

172 cm

112 cm

Fig. 8: Final exposure setup

Simulation Results (Method of Moments)

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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Fig. 9: E in the GSM / UMTS setup when the feed radiates 1W

• Plane wave condition achieved with a maximum phase

error of ±12◦ in a cage volume

• Electric field and power density standard deviation in a

cylindrical exposure volume (2.4m diameter and 0.5m

height, i. e. space for 40cages) of 7.6% and 15%

respectively

Real Setup

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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Fig. 10: Photos of the real setup

• Construction of the three identical electromagnetic

shielded chambers

• Measured electromagnetic shielding of the chambers

over 100dB

Measurement Results

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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Fig. 11: Measurement setup without and with animals

• Power density measured with aperture antennas

• Measurements without animals in the chamber and

with animals surrounding the measuring position

• Characterization of the mean power density incident at

each cage and its perturbation due to the surrounding

animals

Measurement Results (2)

• Overview

Introduction

Exposure Setup

• Prerequisites

• Basic Principle

• Exposure Setup

• Simulation Results

(Method of

Moments)

• Real Setup

• Measurement

Results

Numerical

Dosimetry

Conclusion

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0.49

0.92

0.94

0.75

0.85

0.89

0.51

0.96

1.18

0.92

0.70

1.00

1.20

0.97

1.07

1.07

0.61

1.09

0.79

1.18

1.21

1.24

1.03

0.93

1.18

1.31

0.95

1.46

1.25

1.01

0.92

1.14

1.35

0.98

1.53

1.04

1.11

0.64

1.13

0.84

1.27

1.29

0.89

1.14

0.91

0.73

0.99

1.47

1.05

0.47

0.94

0.97

0.87

0.81

1.05

0.55

0.49

0.49

0.65

0.62

0.75

0.70

0.50

0.49

1.16

1.57

1.38

1.15

0.98

0.27

1.00

1.47

1.25

1.10

1.03

1.63

0.57

1.85

1.21

0.99

1.51

0.80

1.83

0.94

1.88

1.30

1.03

1.34

0.74

1.68

0.93

1.01

1.56

1.27

1.01

0.88

1.48

0.47

0.36

1.23

1.48

1.35

1.13

1.06

0.30

0.46

0.51

0.58

0.58

0.62

0.66

0.46

Fig. 12: Normalized power density in the GSM / UMTS chamber

• Mean |E| for the best 40cage positions: |E| = 7.8 V/m for

the GSM setup and |E| = 8.2 V/m for the UMTS setup

(Pfeed = 1W)

• Standard deviation of the power density for the best

40cage positions: 14% for the GSM setup and 27% for

the UMTS setup

Rat Models

• Overview

Introduction

Exposure Setup

Numerical

Dosimetry

• Rat Models

• Rat Configurations

• SAR Simulation

Conclusion

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Fig. 13: Example rat model: Sprague-Dawley male rat 370g

• Voxel data sets are used to model the animals. The

animal is divided into cuboids of different biological

tissues

• The Specific Absorption Rate (SAR) is obtained by

using the Finite Integration Technique (FIT)

Rat Configurations

• Overview

Introduction

Exposure Setup

Numerical

Dosimetry

• Rat Models

• Rat Configurations

• SAR Simulation

Conclusion

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Fig. 14: Example multi rat scenario

• Different scenarios with male, female and baby rats

have been created. For each scenario, several

simulations with one incident plane wave coming from

different directions were carried out

SAR Simulation

• Overview

Introduction

Exposure Setup

Numerical

Dosimetry

• Rat Models

• Rat Configurations

• SAR Simulation

Conclusion

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• A statistical analysis of the Whole Body SAR (WB SAR)

is realized for six different multi-rat-scenarios

• To achieve a mean WB SAR of 0.4W/Kg a plane wave

with 102 V/m and 104 V/m for 900MHz and 1966MHz,

respectively, is required

• WB SAR standard deviation: 42% and 45% for

900MHz and 1966MHz respectively

• The WB SAR standard deviation of six single-animal

scenarios results in 50% and 26% for 900MHz and

1966MHz, respectively

SAR Simulation – Variations

• Overview

Introduction

Exposure Setup

Numerical

Dosimetry

• Rat Models

• Rat Configurations

• SAR Simulation

Conclusion

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Origin GSM Band UMTS Band

Cage position in the chamber 14% 27%

Animals in the neighborhood 7% 4%

Size and movement of the animals > 42% > 45%

in the cage

• The standard deviation of the WB SAR in the rats is

mainly due to the changes in size and attitude of the

rat and the effects of the cohabitant animals in the

same cage, i. e. by the long-term, in vivo characteristic

of the experiment.

Summary

• Overview

Introduction

Exposure Setup

Numerical

Dosimetry

Conclusion

• Summary

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• The exposure concept based on a defocussed

parabolic reflector results in a low-cost and energy

efficient exposure setup

• A high number of rats (40 cages) can be exposed

simultaneously

• High decoupling between the exposed groups

• Conditions for the animal well-being are assured

• SAR efficiency of 0.0024W·Kg−1/W

• The standard deviation of the WB SAR in the rats is

mainly due to the changes in size and attitude of the

rat and the effects of the cohabitant animals in the

same cage, i. e. by the long-term, in vivo characteristic

of the experiment