Workshop on Final Results of Dosimetry Projects. Exposure Setups for Laboratory Animals and Volunteer Studies using Body-Mounted Antennas

Transcription

1 Workshop on Final Results of Dosimetry Projects Exposure Setups for Laboratory Animals and Volunteer Studies using Body-Mounted Antennas A. Bahr (1), C. Adami (1), H. Dorn (2), L. Rüttiger (3), A. Rennings (1) (1) IMST, Kamp-Lintfort, Germany, (2) Charité Universitätsmedizin Berlin, Germany (3) Universitätsklinikum Tübingen, Germany This work was funded by the Federal Office for Radiation Protection (BfS) within the German mobile telecommunication research (DMF) program 1

2 Outline Two Body-Mounted Antenna Systems for localized Exposure Volunteer Studies [B6] Exposure Setups for Study on Laboratory Animals [B5] Motivation and Objectives Antenna design Used signals for exposure Dosimetric evaluation Block diagram of the computer controlled exposure setup Conclusion 2

3 Objectives for Volunteer Study DMF study Investigation of volunteers exposed to electromagnetic fields of mobile phones Analysis of possible effects on brain activity in sleep and waking Wake outcome variables Spontaneous EEG Evoked and event related potentials Cognitive functions Sleep outcome variables Classical sleep parameters Quantitative parameters derived from the raw data 3 Contact: heidi.danker-hopfe@charite.de

4 State of the Art Antenna Solutions Exposure setups simulating mobile phone usage Commercially available mobile phone [Lee, 2003] Patch antennas in a wooden mount [Huber, 2000] Quasi-far-Field [Borbély, 1999] Body worn antenna [Schmid, 2004] 4

5 Antenna Specs and Intended Use Position Specifications: Localized mobile phone like exposure GSM and WCDMA coverage Exposure times of 8 hours during day and night Dual band antenna surrounding the pinna 5

6 Antenna Details PCB with a PIFA type radiator 40 mm 110 mm 1 mm Weight: 14 g Total thickness: 4 mm Free space reflection coefficient: PCB covered by foam and a washable textile cover s11 [db] 0,0-5,0-10,0-15,0-20,0-25,0 6-30, f [MHz]

7 Exposure Signal Characteristics GSM: 900 MHz Pulse modulated carrier s(t) T on = 553 µs T off = 4,062 ms WCDMA: Signal generation according to [Mbonjo, 2004] 1966 MHz QPSK signal with fast power control T on T off t 7

8 Measurement Method SAR measurement used for verification of FDTD model DASY4 system Tissue simulating liquids according to FCC requirements 8 Measurements in the flat section of SAM phantom

9 900 MHz Flat Phantom SAR Results Measurement Simulation No experimental artefacts due to antenna feeding cable 9 Widespread SAR distribution due to radiation of PCB

10 1966 MHz Flat Phantom SAR Results Measurement Simulation SAR maximum near the radiating element itself 10

11 Flat Phantom Localized SAR Values Measurement Simulation SAR [W/kg] SAR_1g SAR_10g SAR_1g SAR_10g 900 MHz 1966 MHz Simulated SAR > measured one (lossless antenna) 11 1 W antenna input power

12 Simulation Method with inhomogeneous Model Empire software Based on FDTD Heterogeneous Visible human head model (AFRL) Antenna is directly placed at the head model FDTD grid terminated by absorbing boundaries (PML) α y x 12

13 Visible Human Localized SAR Values SAR [W/kg] Original position Alpha+15 Increased head distance: +2 mm α y x 5 0 SAR_1g SAR_10g SAR_1g SAR_10g 900 MHz 1966 MHz 1 W antenna input power % max. positioning dependency

14 Block Diagram of Complete Exposure Setup GSM WCDMA Computer controlled double blind protocol GSM, WCDMA and sham exposure (isolation >80 db) Permanent monitoring of power levels 14 Alarm generation and auto-switch-off in case of malfunctions

15 Objectives for Study on Laboratory Animals DMF Study: Possible influence of RF electromagnetic fields of mobile communication systems on the induction and course of phantom auditory experience (Tinnitus) Investigation of influences on the hearing system by using a behavioral animal model (rats) on Tinnitus Technical objectives: A localized, well defined SAR distribution inside the head/neck of the animal at 900 MHz For the behavioral experiments the rats needed to be unrestrained by the exposure system 15 Contact: marlies.knipper@uni-tuebingen.de

16 State of the Art for In Vivo Animal Studies Local exposure setup for a rat at 900 MHz developed during the French COMOBIO research project [Leveque, 2004] Non-local exposition of 24 rats inside a radial waveguide [Bitz, 2003] 16

17 Our Body Mounted Antenna Solution Specifications: Local exposition of the rat s head or neck GSM 900 Rats need to be unrestrained 17 Loop-Antenna around the neck of the animal with a flexible feeding cable + rotary joints

18 Loop Antenna Details Metalized Kapton foil Meandered line to achieve self resonance at 900 MHz 6 mm Metallisierung Kapton-Folie s11 [db] f [MHz] Messung -15 Simulation mm 4 mm mm 4 mm Kunststoffträger mm 11 mm Reflection coefficient (with animal inside antenna) 18

19 Verification of FDTD Simulation Model Comparison of SAR values obtained for measurement and for FDTD simulation by using an homogeneous cylindrical phantom z SAR [W/kg/W] Messung Simulation z [mm] FDTD simulation without losses outside phantom 19 Acceptable SAR agreement

20 Inhomogeneous FDTD Model Inhomogeneous rat model (AFRL) Loop antenna is placed around the rat s neck FDTD computational domain is truncated by absorbing boundary conditions 20

21 SAR-Results Volume used for SAR averaging: (a) box incl. head/neck (b) volume around ears Averaged SAR values Auswertegebiet Mittlere SAR [W/kg] Lokal/Ganzkörper Kopfbereich (a) 16,18 7,0 Ohrbereich (b) 50,12 21,8 Ganzkörper 2,

22 Local SAR Distribution Longitudinal cut x z y y x z z Cross section trough ears 22

23 Block Diagram of the Exposure Setup 23 Simultaneous double-blind expose of two cage systems at GSM 900 SAR intensities range from 0 W/kg (sham exposure) up to 20 W/kg Rats can move in their cages due to rotary joints in the feeding waveguide

24 Conclusion 24 Development and characterization of bodymounted antennas for volunteer and animal in vivo studies Volunteers and animals were unrestrained by the exposure system Computer-controlled double-blind exposure Permanent power control and switch off in error case High wearing comfort due to low weight and ultra thin antenna used for exposure Very localized (concentrated) exposure and therefore high SAR efficiency