Human Body and Implant Material

Interaction with Radio-Frequency and

Microwave Radiation Dr. K. Padmanabhan

ProfessorMechanical Engineering SVCE, Sri Perumbudur

There were impregnations, there were powers, there was

energy below, there was impulse above

-Rig Veda, Existence, 10.129.5

RadiationNatural Man Made

Ionizing Non- ionizing

Radio Frequency

Microwaves X Rays U V

Freq. domain of RF : 1 Hz to 300 GHz

MicrowavesDesignation Frequency range

L band 1 to 2 GHz

S band 2 to 4 GHz

C band 4 to 8 GHz

X band 8 to 12 GHz

Ku band 12 to 18 GHz

K band 18 to 26.5 GHz

Ka band 26.5 to 40 GHz

Q band 30 to 50 GHz

U band 40 to 60 GHz

V band 50 to 75 GHz

E band 60 to 90 GHz

W band 75 to 110 GHz

F band 90 to 140 GHz

D band 110 to 170 GHz (Hot)

Non-Ionizing RadiationDoes not have sufficient quantum energy to ionize an atom.i.e. They cannot eject electrons from an atom or molecule to produce a positively charged core or ion.

RF and Microwave RangeThe radiation contributes to random molecular motion which can be described as thermal energy.Chemical and physiological effects occur as a result of thermal energy absorption.An indirect effect !

Criteria for AbsorptionThere must be quantum energy level pairs which match the photon energy of the radiation.Must have high dielectric constant i.e. high relative permittivity.

For Low AbsorptionLow dielectric constant and low relative permittivity means low loss,higher transmission,low capacitance and low absorption. This is better for health.

………. But

Values of Material Parameters (real part of relative permittivity έr, Effective conductivity σeff and density ρ ) at 900 MHz.

Material έr σeff (S/m) ρ kg/m3

Tissue-equivalent liquid (TEL) 42.50 0.850 1000

Muscle 55.95 0.969 1050

Bone 16.62 0.242 1645

Fat 05.00 0.025 1100

Skin 41.40 0.867 1090

Nylon 6 cast 3.20 – 12.0 - 1120 – 1170

Values of Material Parameters (real part of relative permittivity έr, Effective conductivity σeff and density ρ ) at 900 MHz.

 

Material έr σeff (S/m) ρ kg/m3

Nylon 66 Extruded 3.20 – 5.00 - 1130 – 1350

Nylon 666 Un reinforced 2.90 – 10.0 - 1030 – 1710

Polycarbonate (unfilled) 3.17 - ~1200

Polycarbonate (30% glass) 3.35 - ~1430

Esters 3.30 – 4.40 - ~1050 – 1390

UHMWPE 2.30 - 945

Acrylic resin (cast) 2.70 - 1180 – 1190

Poly methyl methacrylate (PMMA) 3.20 – 3.70 - 1190

Plastic human-The MythAn all fibre reinforced plastic, reinforced plastic or plastic human would have been healthier against microwave exposure !Also Hydroxy Apatite (HAP) which is a bone substitute is lower loss compared to bone!

ResonanceResonance occurs when exposed radiation ( microwaves) has wavelengths comparable to the dimensions of trunk ,waist and limbs. This happens at RF frequencies of ~ 300 MHz which is never used in communication,normally.

ResonanceAn adult head,babies,macaques and mature fetuses resonate at ~ 1 GHz.

Many cell phones operate at 850/900 MHz !

Skin EffectAt 3 GHz and above one experiences skin effect where the transmission is restricted to the surface of the body.Analogy from electricity power transmission !

Thermal EffectsQuantification of thermal effects! Specific Absorption Rate (SAR) measures rate at which electromagnetic energy is absorbed by exposed object in Watts per Kilogram (W/Kg).Safety exposure limits !

Thermal Effects30 minute exposure with an SAR of 1 W/Kg caused an averaged human body to heat by 1ºC.In cell phone usage up to 2 W/Kg is encountered !

More Thermal EffectsAt 2.65 GHz, for an SAR of 4 W/Kg retinal and corneal damages are observed in monkeys. SAR of 15W/Kg for half an hour produced severe malformations !Pulsed fields appear to be more detrimental that continuous fields as they are normally generated with more field strength!Pulsed radiation not used in mobile communication !

A comparison

Muscular people heat more than thin people as muscle absorbs more microwaves!

AttenuationAttenuation as a measure of absorption!Most of the power from a mobile phone is absorbed with in a few centimetres of the head!Skin Depth= depth at which field strength reduces to 1/exponential of its value.

DosimetryDosimetry-effect of radiation distribution studies.Attenuation is less in patients with plastic ,RP,FRP implants.It is preferable not to use ceramics and CMCs as implant materials!

AnechoicsAnechoic Phenomena and building absorption.Ghost Signals Correction.Building Warm Up.

AbsorptionPower absorbed by the body is ultimately decided by the field strength expressed in volts/metre.Electric field Sq.root of power.RF power amplifiers up to 2 KW in the frequency range of 10KHz to 8GHz generate field strength of 200V/m.

StandardsWHO/ European Union recommend up to 41.2V/m. More would increase occurrence of Leukemia.

StandardsNRPB: National Radiological Protection Board of UK have listed influence on

cancer,impairment of reproduction,neurobehavioural effects,cardiovascular effects,tumor,cognition neurotransmitter effects,sleep pattern ,pregnancy, hypersensitivity and mood states.

Near field and far field effects

General public and occupational exposure !Head ache,parasthesiae ,diarrhea, malaise and lassitude.Occupational Skin burns.

The Fatigue Analogy

Field Strength/RadiationPowerLevel

No. of cycles to failure (N)

FatigueStrength/EnduranceLimit

Fatigue of exposure to pulsed vs continuous fields ?

Standards and Regulations

Occupational and general public covering pulsed and continuous radiation and acceptable levels!ANSI/IEEE C.95 Series.National Council on Radiation Protection and Measurements (NCRP,1986).

Standards and Regulations

The American Conference on Governmental Industrial Hygienists (ACGIH,1993).The National Radiological Protection Board (NRPB,1993).The International Radiation Protection Association (IRPA,1993).

Standards and Regulations

US Department of Labour, Occupational Safety and Health Administration (OSHA).Federal Communication Commission (FCC).The Environmental Protection Agency ( EPA,USA).

Standards and Regulations

The International Commission on Non-Ionizing Radiation Protection (ICNIRP).The National Institute for Occupational Safety and Health (NIOSH, USA).The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).Health Protection Agency Standards (HPA, Britain).

Standards and Regulations

Threshold SAR of 4 W/kg averaged over the whole body above which adverse health effects occur.Most of the above standards have determined a maximum field strength not exceeding 10 V/m.However, WHO/ICNIRP recommends up to 41.2 V/m.

Types of CommunicationThe standards and regulations hold good to TDMA,FDMA,CDMA, GPRS ( General Packet Radio service) and GSM ( Global System for Mobile Communication ) in the 800 MHz to 2 GHz operating range.Some of the new cordless phones operate at 2.45 GHz.

Standards and Regulations

There are two sets of limits for occupational and general public exposures.The occupational environment has an acceptable power limit of up to five times the non-occupational environment for frequencies up to 3 GHz.

Stark RealitiesMultiple effects not understood properly.Like living near a transmission mast/mobile tower,being pregnant,operating microwave ovens, using RF amplifiers ,cordless and cell phones extensively !

Indian Scenario Vertical and Horizontal growth of cities.When more people use mobile phones,power can be reduced but only up to a certain population density. There is an optimum. This rule doesn’t work for large public gatherings where absorption by individuals ruins reception.

Vertical and Horizontal

Demography Demographic problems are different in India due to the optimum curve of power vs population density being different.Studies have to be conducted on optimum power usage and the influence of multiple effects,interference and jamming

DemographyFurther as building densities are heavier and we have not built anechoic buildings, EMI ( Electromagnetic interference) studies gain prominence.Japanese model for the EMI shielded buildings and anechoic buildings.Remember! Anything absorbs/reflects.

National Policy Demographic problems, exposure levels and safety limits have to be addressed by the Ministry of Communications and IT and Ministry of Health and Family welfareA national policy has to be evolved before someone slowly gets skinned alive!

The Rig Veda Again There were impregnations, there

were powers, there was energy below, there was impulse above

-Rig Veda, Existence, 10.129.5

Thank You