EMF exposure of the skin at the mmw

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Brook Norris
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1 Session PW1 Workshop: EMF exposure from 5G equipment: the state of art of research and standardization EMF exposure of the skin at the mmw (Marvin C. Ziskin, M.D. Temple University Medical School) Slide 1 Dr. C-K. Chou* TC95 Chairman International Committee on Electromagnetic Safety (ICES) Institute of Electrical and Electronics Engineers (IEEE) Piscataway, NJ, USA *Speaking as an individual and not for the IEEE

2 Outline Skin morphology RF penetration depths mmw therapy applications Thermal modeling in skin Temperature and pain thresholds DRL (epithelial power density) and ERL (incident power density) to limit temperature rise in skin Slide 2

3 mm 1-2 mm 1-6 mm Slide 3

4 Epidermis ( μm Thick) Layer Thickness Water (μm) (per cent) 1. Horny Clear Granular Prickle Cell Basal Cell Slide 4

5 Skin Thickness Region Epidermis (μm) Male Female Eyelid Postauricular Region Back Forehead Back of Arm Cheek Buttock Dorsum of Foot Dorsum of Hand Palm Sole Slide 5 AVERAGE

6 Effects of Age on Skin Skin of Infant Skin is completely formed at birth Stratum corneum is thinner and water content is higher Papillary dermis is thinner than in adults Production of sweat is reduced Slide 6

7 Effects of Age on Skin Skin of a Child After reaching one year of age, the skin of a child is essentially the same as that of an adult. Slide 7

Effects of Age on Skin Skin in Elderly Epidermis thins Blood vessels of the dermis become more fragile Sebum production decreases leading to increased

8 Effects of Age on Skin Skin in Elderly Epidermis thins Blood vessels of the dermis become more fragile Sebum production decreases leading to increased dryness and itching Fat layer thins leading to decreased ability to maintain body temperature Sweat production decreases making it harder to lose heat Slide 8

9 Skin Penetration 100 Penetration (cm) ,000 10, ,000 Freqeuency (MHz) Slide 9

10 94 GHz and 35 GHz penetrations in SKIN 94-GHz Penetration Depth Epidermis 150 µm Free nerve ending Dermis 35-GHz Penetration Depth Slide 10

11 Selected Frequency (GHz) Skin Depth (mm) Slide 11

12 Millimeter Wave Therapy Therapeutic wavelengths: 4.9, 5.6, and 7.1 mm (frequencies 61.22, and GHz) Exposure of patient s skin: acupuncture points, forehead, occiput sternum; big joints, surgical wounds min session; one session per day; sessions per course Slide 12

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14 mmw therapy Millimeter wave irradiation used in therapy, if sufficiently intense, can activate thermo-receptors and free nerve endings in the outer layers of the skin. Typical therapeutic exposures = W/m 2 No sensation for exposures < 350 W/m 2 No pain for exposures < 1000 W/m 2 Slide 14

15 Millimeter Wave Irradiation Heating is a major mechanism for bioefffects Most of energy is absorbed within a few tenths of a millimeter Wavelengths in tissue are comparable with biological structures Irradiation is frequently in the near field Slide 15

16 Skin Thermal modeling 3-Layer Model 4-Layer Model Slide 16 Where 1 = Stratum Corneum 2 = Epidermis + Dermis

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20 Reflection from boundary between two tissues n n r( f) = i i i n + n i + 1 i+ 1 Slide 20 Where r i = amplitude reflection coefficient = complex index of refraction of tissue i n i+1 = complex index of refraction of tissue i+1 n i

21 R( f ) = { j ϕ 2 ( f ) j ( ϕ 2 ( f ) + ϕ 3 ( f )) j ϕ 3 ( f ) 1( ) 2( ) 3( ) 1( ) 2( ) 3( ) j ϕ2 ( f ) j ( ϕ 2 ( f ) + ϕ 3 ( f )) j ϕ 3 ( f ) r1 f r2 f e r1 f r3 f e r2 f r3 f e r f + r f e + r f e + r f r f r f e ( ) ( ) + ( ) ( ) + ( ) ( ) + j ( ϕ2( f ) + ϕ3( f ) + ϕ4( f )) j ( ϕ3( f ) + ϕ4( f )) r4( f ) e + r1( f ) r2( f ) r4( f ) e + j ( ϕ ( f ) + ϕ ( f ) + ϕ ( f )) j ( ϕ ( f ) + ϕ ( f )) r f r f e + r f r f e ( ) 4( ) 2( ) 4( ) j ϕ 4 j ϕ 2( f ) r3( f ) r4( f ) e ( r1( f ) + r2( f ) e ) j ϕ j ( ϕ ( f ) + ϕ ( f )) r f r f e r f r f r f r f e ( ) 4( ) + 1( ) 2 ( ) 3( ) 4( ) } 2 where ni ni ri ( f) = n + n i + 1 i+ 1 ϕ ( f ) = 2 ω( f ) n ( f ) m m h m c Slide 21

22 Parameters used in thermal modeling Parameter 3-layer model 4-layer model SC E - +D Fat* SC E - +D Fat* Muscle * ε ε 1.5± ± ± ± d, mm σ, S/m τ x 10 12, s Slide 22

23 Temperature distributions in multilayer tissue model with a fat thickness of 1, 2, or 4 mm before and after exposure to 42 GHz at 200 W/m 2 T, o C W/m mm 1 mm 2 mm 4 mm 0 W/m T, o C W/m mm mm mm Tissue depth, mm Tissue depth, mm Slide 23 Epidermis mm Dermis mm

24 Temperature measurements in the skin during mm-wave exposure with WG opening Lower forearm Index finger Generator G4-141 Slide 24 Frequency: GHz Output power: 52 mw

RESULTS WG 0 s 10 s 30 s 55 s 21 mm IR images show the forearm skin

The lighter band on the bottom of each thermogram corresponds to the

25 RESULTS WG 0 s 10 s 30 s 55 s 21 mm IR images show the forearm skin at 0, 10, 30, and 55 s following exposure with the WG (I o = 2080 W/m 2 ). The distance between the open end of WG and skin surface was 2.5 mm. The lighter band on the bottom of each thermogram corresponds to the warmer skin area located above a vein. Baseline skin temperature was 32.5 o C. Maximum temperature at 55 s was 35.7 o C. Slide 25

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30 Temperature distributions in homogeneous and multilayer tissue models before and after exposure to 42 GHz at 200 W/m 2 T, o C Multilayer model 200 W/m 2 Epidermis - 0.1mm Dermis -1.5 mm 0 W/m 2 Homogeneous model Fat mm Tissue depth, mm Slide 30

31 SURFACE TEMPERATURE THRESHOLDS FOR HUMAN OR PORCINE SKIN (Moritz and Henriques, p. 711, 1947) Slide 31

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33 Warmth Detection Threshold and Penetration Depth: Variation with Microwave Frequency Threshold (mw/cm 2 ) Skin Depth r 2 = Warmth Threshold r 2 = Microwaves IR Threshold Infrared ~ Depth of Energy Deposition (mm) Slide 33 Frequency (GHz)

34 Threshold vs. Heating Rate 46 Mean Temperature at Threshold (deg) n=10, mean + s.e.m. Slide Rate of Temperature Change (deg/sec)

35 Pain Thresholds and Safety Margins Normal Skin Temperature = 34 C Pain Threshold = C First Degree Burn = C Second Degree Burn = C Third Degree Burn = > 70 C Slide 35

36 RF Exposure Limits To limit steady state temperature rise < 3 o C in skin for the upper tier DRL is epithelial power density ERL is incident power density Averaging time 6 minutes Averaging area 4 cm 2 (for single pulses at GHz, 1 cm 2 ) Slide 36

37 Thank you Thank You Protect your skin Slide 37

EMF Energy Absorption Mechanisms in the mmw Frequency Range. Andreas Christ

EMF Energy Absorption Mechanisms in the mmw Frequency Range Andreas Christ Background The compliance of wireless devices up to the 4 th generation is tested against the basic restrictions by measuring