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16.1 Biological Effects of RF Energy and ARPANSA Exposure Standards

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ACMA Amateur Radio Advanced Recognition Certificate - Theory Exam

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1 Chapter 1: DC Theory, Circuit Laws & Passive Components

1.1 DC Circuit Analysis, Ohm's Law, and Kirchhoff's Laws 1.2 AC Fundamentals, Sine Waves, Peak, RMS, and Phase Relationships 1.3 Inductance, Capacitance, Reactance, and Time Constants

2 Chapter 2: Impedance, Resonance & Passive Filters

2.1 Complex Impedance, Phasors, and AC Circuit Analysis 2.2 Series and Parallel LC Resonance and Q Factor 2.3 Passive Filters, Cutoff Frequency, and Attenuator Pads

3 Chapter 3: Semiconductor Devices & Power Supplies

3.1 Semiconductor Diodes, Zener Regulators, and Rectifier Circuits 3.2 Bipolar Junction Transistors, FETs, and Operational Amplifiers 3.3 Thermionic Valves (Vacuum Tubes) and High-Power Linear Amplifiers 3.4 DC Power Supplies, Filter Networks, and Voltage Regulators

4 Chapter 4: Oscillators & Frequency Synthesis

4.1 RF Oscillators, LC Tank Topologies, and Frequency Stability 4.2 Phase-Locked Loops (PLLs) and Frequency Synthesisers 4.3 Direct Digital Synthesis (DDS), SDR Architectures, and Digital Filter Topologies

5 Chapter 5: RF Amplifiers & Linearity

5.1 Classes of Amplification, Conduction Angles, and Operating Efficiency 5.2 RF Power Amplifiers, Push-Pull Topologies, and Output Matching 5.3 Amplifier Stability, Neutralisation, and Intermodulation Distortion

6 Chapter 6: Modulation & Demodulation

6.1 Amplitude Modulation, Double Sideband, and Single Sideband (SSB) 6.2 Frequency Modulation, Phase Modulation, and FM Detectors 6.3 Digital Modulation Modes, Spectral Efficiency, and Weak-Signal Protocols

7 Chapter 7: Transmitters, Mixers & Receivers

7.1 RF Mixers, Frequency Translation, and Intermodulation 7.2 Transmitter Architectures, CW Keying, and Output Filtering 7.3 Superheterodyne Receiver Design, IF Selection, and Image Rejection 7.4 Receiver Performance Specifications, Dynamic Range, and Selectivity

8 Chapter 8: Transmission Lines & Waveguides

8.1 Transmission Line Characteristics, Impedance, and Velocity Factor 8.2 Standing Waves, Reflection Coefficient, SWR, and Return Loss 8.3 Resonant Line Sections, Quarter-Wave Transformers, and Stubs

9 Chapter 9: Impedance Matching & Baluns

9.1 Lumped-Element Matching Networks and Antenna Tuning Units 9.2 Baluns, Ununs, and Common-Mode Current Choking 9.3 Feedline Losses, High-SWR Stress, and Coaxial Installation Practice

10 Chapter 10: Practical Antennas & Arrays

10.1 Resonant Dipoles, Inverted-Vs, and Multiband Wire Antennas 10.2 Quarter-Wave Verticals, Ground Systems, and Radiation Efficiency 10.3 Parasitic Arrays, Yagi-Uda Antennas, and Quad Arrays 10.4 Antenna Gain, Aperture Antennas & Horns, ERP/EIRP, Radiation Patterns

11 Chapter 11: Radio Wave Propagation & Ionospheric Mechanics

11.1 Electromagnetic Wave Fundamentals, Polarisation, and Ground Waves 11.2 The Ionosphere, Solar Radiation, and Solar Cycles 11.3 Critical Frequency, Maximum Usable Frequency, and HF Propagation Paths

12 Chapter 12: VHF/UHF Propagation & Space Communications

12.1 Line-of-Sight, Tropospheric Ducting, and Diffraction 12.2 Sporadic-E, Auroral Scatter, and Trans-Equatorial Propagation 12.3 Amateur Satellites, Doppler Shift, and Earth-Moon-Earth (EME)

13 Chapter 13: Test Equipment & RF Measurements

13.1 Decibels, Power Ratios, and Cascaded Stage Calculations 13.2 RF Power Meters, Directional Couplers, and Dummy Loads 13.3 Multirange Meters, Waveform Diagnostics, Oscilloscopes, and Frequency Counters

14 Chapter 14: Advanced RF Analysis & Diagnostics

14.1 Spectrum Analyser Architecture, Operation, and Spectral Purity 14.2 Antenna Analysers, Vector Network Analysers, and Smith Charts 14.3 Calibrated Signal Generators, Grid Dip Meters, and Component Testing

15 Chapter 15: Electromagnetic Compatibility & Interference

15.1 Sources of Interference, Coupling Mechanisms, and Audio Rectification 15.2 Receiver Susceptibility, Desensitisation, and Front-End Intermodulation 15.3 Practical RFI Suppression, Filter Design, and Bonding Techniques

16 Chapter 16: Electrical, RF & Station Safety

16.1 Biological Effects of RF Energy and ARPANSA Exposure Standards 16.2 Safe Separation Distances, Power Density, and Duty Cycles 16.3 Station Electrical Safety, Battery Hazards, and Safe Headphone Use 16.4 Mast and Tower Construction, Power Line Clearance, and Lightning Protection

16.1 Biological Effects of RF Energy and ARPANSA Exposure Standards

Key Takeaways Explain This Topic AI

RF photons from 100 kHz to 300 GHz have energies far below ionization energies. Excessive RF exposure can heat tissue; the lower RF range also requires protection against electrostimulation. Non-ionizing does not mean harmless at high power.

Specific Absorption Rate (SAR), in W/kg, is absorbed RF power per unit tissue mass. Whole-body limits are 0.4 W/kg occupational and 0.08 W/kg public, averaged over 30 minutes: reduction factors 10 and 50 respectively below the 4 W/kg whole-body operational threshold used in deriving the limits.

The human body functions as an electric dipole antenna exhibiting resonance in the 30 to 300 MHz 30\text{ to }300\text{ MHz} 30 to 300 MHz (VHF) spectrum, where an adult height ( 1.5 − 2.0 m 1.5 - 2.0\text{ m} 1.5 − 2.0 m ) corresponds to approximately 0.4 λ 0.4\lambda 0.4 λ in free space or 0.25 λ 0.25\lambda 0.25 λ when standing on a ground plane, causing maximum whole-body RF energy absorption.

Excessive local RF heating can damage tissue, including the eye. The lens lacks blood vessels and relies on heat transfer to surrounding tissues. Injury depends on absorbed energy, exposure time and cooling; a transmitter type alone does not establish the risk.

ARPANSA RPS S-1 (Rev.1, 2021) distinguishes 30-minute whole-body exposure from 6-minute local exposure for both occupational and public categories. Whole-body public power-density reference levels are one-fifth of occupational values; the amateur class licence requires public reference levels at publicly accessible places.

Last updated: November 2026

16.1 Biological Effects of RF Energy and ARPANSA Exposure Standards

Advanced stations may use up to 400 W 400\text{ W} 400 W PEP for specified SSB emissions on relevant bands. Other emissions generally have a 120 W 120\text{ W} 120 W mean-power limit there; lower-frequency bands and other conditions have separate limits in the class licence. When combined with high-gain directional antennas, effective isotropic radiated power (EIRP) can easily reach several kilowatts. Ensuring human safety requires an exact, evidence-based understanding of how electromagnetic fields interact with biological tissue, the physiological mechanisms of heat dissipation, and the legal compliance framework established by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).

Biological Interaction of Non-Ionizing Electromagnetic Radiation

Electromagnetic radiation spans a continuous spectrum from direct current ( 0 Hz 0\text{ Hz} 0 Hz ) through radio waves, infrared, visible light, ultraviolet, X-rays, and gamma radiation. Crucially, the electromagnetic spectrum is bifurcated into two fundamentally distinct physical domains: ionizing and non-ionizing radiation. Photon Energy and RF Safety

  • RF:100kHz ───────────────────────────────300GHz
  • E=hf:4.14×10⁻¹⁰eV ─────────────────────1.24×10⁻³eV
  • │
  • Insufficient for ionization
  • │
  • High RF exposure can still heat tissue
  • Lower RF frequencies can also stimulate nerves

Ionizing ultraviolet,X-rays and gamma rays have much higher

photon energies; the boundary depends on the material.

Ionizing versus Non-Ionizing Radiation

The physical property governing whether an electromagnetic wave can ionize matter is the quantum energy carried by individual photons, formulated by Max Planck: E = h f E = h f E = h f

where h ≈ 6.626 × 10 − 34 J ⋅ s h \approx 6.626 \times 10^{-34}\text{ J}\cdot\text{s} h ≈ 6.626 × 1 0 − 34 J ⋅ s is Planck's constant and f f f is frequency in Hertz. In electron-volts ( eV \text{eV} eV ), this is: E ( eV ) ≈ 4.1357 × 10 − 15 × f ( Hz ) E(\text{eV}) \approx 4.1357 \times 10^{-15} \times f(\text{Hz}) E ( eV ) ≈ 4.1357 × 1 0 − 15 × f ( Hz )

Ionizing Radiation: Frequencies exceeding approximately 3 × 10 15 Hz 3 \times 10^{15}\text{ Hz} 3 × 1 0 15 Hz (ultraviolet, X-rays, and gamma rays) carry photon energies greater than 10 to 25 eV 10\text{ to }25\text{ eV} 10 to 25 eV . This energy exceeds the binding energy holding orbital electrons to atomic nuclei. Consequently, ionizing photons physically strip electrons from biological molecules, breaking covalent chemical bonds, damaging chromosomes, and causing direct DNA lesions that can initiate oncogenesis.

Non-Ionizing Radiation: Radio frequencies (ranging from 100 kHz 100\text{ kHz} 100 kHz to 300 GHz 300\text{ GHz} 300 GHz ) possess photon energies between 4.14 × 10 − 10 eV 4.14 \times 10^{-10}\text{ eV} 4.14 × 1 0 − 10 eV and 1.24 × 10 − 3 eV 1.24 \times 10^{-3}\text{ eV} 1.24 × 1 0 − 3 eV ( 1.24 meV 1.24\text{ meV} 1.24 meV ). Even at the upper limit of the millimetre-wave spectrum ( 300 GHz 300\text{ GHz} 300 GHz ), the quantum photon energy is approximately four orders of magnitude lower than the weakest chemical covalent bond (which requires roughly 2 to 5 eV 2\text{ to }5\text{ eV} 2 to 5 eV to break) and far below the thermal kinetic energy of molecules at room temperature ( k T ≈ 26 meV k T \approx 26\text{ meV} k T ≈ 26 meV ). Therefore, RF fields cannot strip electrons, cannot alter atomic structure, and cannot cause direct mutagenic DNA strand breaks.

Note

The main hazard at amateur HF, VHF and microwave frequencies is excessive tissue heating . RPS S-1 also includes electrostimulation restrictions from 100 kHz to 10 MHz. When RF fields penetrate human tissue, alternating electric fields exert periodic forces on polar molecules (chiefly water, H 2 O \text{H}_2\text{O} H 2 ​ O ) and free electrolytes ( Na + , K + , Cl − \text{Na}^+, \text{K}^+, \text{Cl}^- Na + , K + , Cl − ). The rapid realignment and frictional rotation of polar water dipoles at millions of cycles per second converts electromagnetic energy directly into thermal kinetic energy (heat).

Specific Absorption Rate (SAR) and Thermodynamics

The fundamental dosimetric metric utilized internationally to quantify the absorption of RF energy inside biological tissue is the Specific Absorption Rate (SAR) . SAR represents the time rate at which radio frequency energy is absorbed per unit mass of biological tissue, expressed in Watts per kilogram ( W/kg \text{W/kg} W/kg ).

Mathematical Formulation of SAR

From Maxwell's equations and Poynting's theorem, the local power dissipated per unit volume inside a lossy dielectric material is P d = σ ∣ E int ∣ 2 P_d = \sigma |E_{\text{int}}|^2 P d ​ = σ ∣ E int ​ ∣ 2 , where σ \sigma σ is the electrical conductivity of the tissue in Siemens per metre ( S/m \text{S/m} S/m ) and E int E_{\text{int}} E int ​ is the root-mean-square (RMS) internal electric field strength in Volts per metre ( V/m \text{V/m} V/m ). Dividing by the tissue mass density ρ \rho ρ in kilograms per cubic metre ( kg/m 3 \text{kg/m}^3 kg/m 3 ) yields the fundamental SAR equation: SAR = σ ∣ E int ∣ 2 ρ \text{SAR} = \frac{\sigma |E_{\text{int}}|^2}{\rho} SAR = ρ σ ∣ E int ​ ∣ 2 ​

Thermodynamically, if thermal conduction, convection, and radiative cooling are neglected over an initial short exposure interval, the absorbed RF energy directly increases the temperature of the tissue: SAR = c t ( Δ T Δ t ) t → 0 \text{SAR} = c_t \left( \frac{\Delta T}{\Delta t} \right)_{t \to 0} SAR = c t ​ ( Δ t Δ T ​ ) t → 0 ​

where:

c t c_t c t ​ is the specific heat capacity of the biological tissue (typically 3500 to 3750 J / ( kg ⋅ ∘ C ) 3500\text{ to }3750\text{ J}/(\text{kg}\cdot^\circ\text{C}) 3500 to 3750 J / ( kg ⋅ ∘ C ) for high-water-content tissue such as muscle and brain tissue),

Δ T / Δ t \Delta T / \Delta t Δ T /Δ t is the initial rate of temperature rise in degrees Celsius per second ( ∘ C/s ^\circ\text{C/s} ∘ C/s ).

Extensive biomedical research indicates that an acute whole-body SAR of 4 W/kg 4\text{ W/kg} 4 W/kg sustained over 30 minutes 30\text{ minutes} 30 minutes elevates core human body temperature by approximately 1.0 ∘ C 1.0^\circ\text{C} 1. 0 ∘ C . In healthy adults, a 1.0 ∘ C 1.0^\circ\text{C} 1. 0 ∘ C rise represents the upper boundary of normal physiological thermoregulation; beyond this threshold, adverse behavioral, metabolic, and cardiovascular changes occur.

Human Body Resonant Frequency: The 30 to 300 MHz Phenomenon

The rate at which a human body absorbs RF energy from an external field is strongly frequency-dependent. The human body does not behave as a passive, uniform lump of matter; rather, it behaves as a complex, lossy conductive antenna. Approximate Human-Body Resonance Models

  • Electrically isolated Grounded
  • Dipole-like coupling Monopole-like coupling
  • Head Head
  • Voltage maximum Voltage maximum
  • O O
  • /|\ /|\
  • Current larger near middle Current larger near feet
  • / \ / \
  • Voltage maximum Lower voltage near ground
  • at feet ────────── Ground
  • Height ≈0.4λ in the Height ≈0.25λ in the
  • simplified worked model simplified worked model
  • The Whole-Body Dipole Antenna Model

An adult human standing in free space (isolated from ground) can be modeled electrodynamically as an upright, lossy, linear dipole antenna:

An adult of average height h = 1.75 m h = 1.75\text{ m} h = 1.75 m exhibits maximum whole-body resonance when its physical length equals approximately 0.4 λ 0.4\lambda 0.4 λ (slightly shorter than a theoretical half-wavelength λ / 2 \lambda/2 λ /2 due to the high dielectric constant of biological tissue, where ε r ≈ 50 − 70 \varepsilon_r \approx 50 - 70 ε r ​ ≈ 50 − 70 at VHF): h ≈ 0.4 λ ⟹ λ ≈ 1.75 m 0.4 = 4.375 m h \approx 0.4 \lambda \implies \lambda \approx \frac{1.75\text{ m}}{0.4} = 4.375\text{ m} h ≈ 0.4 λ ⟹ λ ≈ 0.4 1.75 m ​ = 4.375 m f 0 = c λ = 3.00 × 10 8 m/s 4.375 m ≈ 68.6 MHz f_0 = \frac{c}{\lambda} = \frac{3.00 \times 10^8\text{ m/s}}{4.375\text{ m}} \approx 68.6\text{ MHz} f 0 ​ = λ c ​ = 4.375 m 3.00 × 1 0 8 m/s ​ ≈ 68.6 MHz

Grounded Condition: If the individual stands barefoot or in thin shoes upon moist conductive ground, the body behaves as a quarter-wave ( λ / 4 \lambda/4 λ /4 ) grounded vertical monopole. The resonant frequency decreases in this simplified model: h ≈ 0.25 λ ⟹ λ ≈ 7.0 m ⟹ f 0 ≈ 40 to 45 MHz h \approx 0.25 \lambda \implies \lambda \approx 7.0\text{ m} \implies f_0 \approx 40\text{ to }45\text{ MHz} h ≈ 0.25 λ ⟹ λ ≈ 7.0 m ⟹ f 0 ​ ≈ 40 to 45 MHz

Children and Smaller Statures: Because children possess smaller physical heights ( h ≈ 0.8 to 1.2 m h \approx 0.8\text{ to }1.2\text{ m} h ≈ 0.8 to 1.2 m ), their resonant frequencies shift upward into the 100 to 150 MHz 100\text{ to }150\text{ MHz} 100 to 150 MHz range (encompassing the 2-metre amateur allocation and FM broadcast band).

Important

Whole-body coupling can be especially efficient around body resonance in the VHF region. Resonance depends on body dimensions, posture, grounding and polarization; it does not occur at every frequency in a broad band. Current RPS S-1 whole-body reference levels have a low, flat region above 30 MHz through 400 MHz.

Local Heating and Sensitive Tissues

RF energy absorbed in tissue becomes heat. The resulting temperature rise depends on absorption, duration, conduction and blood flow. Whole-body heat stress and localized burns are distinct hazards; compliance requires the applicable whole-body and local limits.

1. The Eyes

The ocular lens and cornea are avascular. Their heat is transferred to surrounding tissues rather than removed by blood circulating through the lens or cornea themselves. Sufficiently intense and prolonged exposure can damage the eye. RF-induced cataracts have been demonstrated under severe experimental exposures, but a single incident power density or lens temperature is not a universal human injury threshold. Keep eyes and other body parts away from energized antennas and high-field regions.

2. Other Tissues

Excessive heating can damage skin and deeper tissues. The testes are temperature-sensitive, but they are not avascular; ordinary use of a handheld radio is not evidence of sterility. Likewise, blood-brain-barrier alteration is not an established RF health effect in the ICNIRP assessment underlying this standard. Use the exposure limits and an appropriate station assessment rather than inferring injury from a device label or an unsupported biological mechanism.

The Australian RF Exposure Regulatory Framework

ARPANSA RPS S-1 (Rev.1, 2021) , Standard for Limiting Exposure to Radiofrequency Fields –100 kHz to 300 GHz , provides the Australian RF exposure limits. It replaced RPS3 and follows ICNIRP2020. The Radiocommunications (Amateur Stations) Class Licence 2023 , Schedule 1, applies these limits to amateur stations. ARPANSA Exposure Framework

  • BASIC RESTRICTIONS REFERENCE LEVELS
  • Internal induced E-field External E-field and H-field
  • Whole-body/local SAR Incident power density
  • Local absorbed power density Other specified exposure quantities
  • │ │
  • └──── dosimetry/modelled coupling ──┘
  • 1. Basic Restrictions and Reference Levels

Basic restrictions limit the quantities directly associated with established adverse effects. Whole-body average SAR applies from 100 kHz to 300 GHz. Local SAR applies up to 6 GHz; above 6 GHz, local absorbed power density limits surface heating. Induced internal electric-field restrictions also protect against electrostimulation from 100 kHz to 10 MHz.

Whole-body SAR limits are 0.4 W/kg occupational and 0.08 W/kg general public , averaged over 30 minutes. Up to 6 GHz, local head/torso SAR limits are 10 W/kg occupational and 2 W/kg public , averaged over a 10 g cubic mass and 6 minutes. Limb limits are 20 W/kg and 4 W/kg respectively. These are different spatial averages: a local SAR value is not a whole-body average.

Reference levels use externally assessable quantities, including incident electric field ( E E E ), magnetic field ( H H H ) and power density ( S S S ). They provide a practical route to demonstrating compliance with the associated basic restrictions when the appropriate field-region, spatial and temporal conditions are met. Within the standard, exceeding a reference level calls for further assessment and does not alone establish that a basic restriction has been exceeded.

The amateur class licence imposes a separate operating condition: RF fields must not exceed general public reference levels at places accessible to a member of the general public . An operator cannot replace that condition with a claim that internal SAR remains below a basic restriction. Simultaneous transmissions must also meet the standard's multiple-frequency assessment requirements.

2. Exposure Categories and Averaging

Occupational exposure requires controlled conditions and suitable awareness, training and risk management. Appropriately trained amateur operators may be Aware Users; holding a certificate alone does not make neighbours or visitors occupationally exposed. Public limits protect people who cannot be expected to monitor or control their exposure. Pregnant occupationally exposed workers are subject to public limits.

For both categories , assess whole-body exposure over any 30-minute interval and local exposure over any 6-minute interval . Additional brief-exposure, instantaneous-field and limb-current conditions apply where relevant. Thus a low 30-minute average does not by itself establish compliance with every limit. Average squared field strengths, or power, rather than averaging RF field amplitude directly.

3. Whole-Body Reference Levels

The following values are from RPS S-1 Table 4 , for unperturbed rms fields averaged over 30 minutes and whole-body space. Here f M f_M f M ​ is frequency inMHz. “ES” means no whole-body E-field value is specified in that range: use the applicable instantaneous electrostimulation reference level in Table 7. “—” means that quantity is not applicable in this table.

  • Frequency Category E E E (V/m) H H H (A/m) S S S (W/m²)
  • 0.1–6.943 MHz Occupational ES 4.9 / f M 4.9/f_M 4.9/ f M ​ —
  • >6.943–30 MHz Occupational 660 / f M 0.7 660/f_M^{0.7} 660/ f M 0.7 ​ 4.9 / f M 4.9/f_M 4.9/ f M ​ —
  • >30–400 MHz Occupational 61 0.16 10

>400–2000 MHz Occupational 3 f M 3\sqrt{f_M} 3 f M ​ ​ 0.008 f M 0.008\sqrt{f_M} 0.008 f M ​ ​ f M / 40 f_M/40 f M ​ /40

  • >2–300 GHz Occupational — — 50
  • 0.1–6.27 MHz General public ES 2.2 / f M 2.2/f_M 2.2/ f M ​ —
  • >6.27–30 MHz General public 300 / f M 0.7 300/f_M^{0.7} 300/ f M 0.7 ​ 2.2 / f M 2.2/f_M 2.2/ f M ​ —
  • >30–400 MHz General public 27.7 0.073 2

>400–2000 MHz General public 1.375 f M 1.375\sqrt{f_M} 1.375 f M ​ ​ 0.0037 f M 0.0037\sqrt{f_M} 0.0037 f M ​ ​ f M / 200 f_M/200 f M ​ /200

>2–300 GHz General public — — 10

Whole-body power-density values for the public are one-fifth of occupational values. Corresponding field-strength ratios are approximately 1 / 5 1/\sqrt5 1/ 5 ​ , allowing for table rounding. The low, flat VHF reference levels reflect efficient whole-body coupling around body resonance; they extend to 400 MHz in the current table.

Table 4 is not the complete assessment. Local exposure uses Table 5 , with 6-minute averaging: for example, at 144 MHz its public reference levels are 62 V/m, 0.163 A/m or 10 W/m², subject to the table's field-region conditions. At frequencies up to 30 MHz the standard generally requires separate E and H assessment; the class licence permits a single E or H quantity for its specified 10–30 MHz far-field assessment. In the reactive near field, do not infer compliance from the plane-wave formula S = E 2 / 377 S=E^2/377 S = E 2 /377 . Apply the standard's relevant E/H or basic-restriction assessment method.

  • Step-by-Step Worked Calculations
  • Worked Example 1: Specific Absorption Rate and Tissue Heating

A section of human muscle tissue (conductivity σ = 0.85 S/m \sigma = 0.85\text{ S/m} σ = 0.85 S/m , mass density ρ = 1040 kg/m 3 \rho = 1040\text{ kg/m}^3 ρ = 1040 kg/m 3 , and specific heat capacity c t = 3600 J / ( kg ⋅ ∘ C ) c_t = 3600\text{ J}/(\text{kg}\cdot^\circ\text{C}) c t ​ = 3600 J / ( kg ⋅ ∘ C ) ) is subjected to an internal RMS electric field of E int = 22 V/m E_{\text{int}} = 22\text{ V/m} E int ​ = 22 V/m at 144 MHz 144\text{ MHz} 144 MHz .

Calculate the local Specific Absorption Rate (SAR) in W/kg \text{W/kg} W/kg .

Determine the initial rate of temperature rise ( Δ T / Δ t \Delta T / \Delta t Δ T /Δ t ) in degrees Celsius per hour ( ∘ C/h ^\circ\text{C/h} ∘ C/h ), assuming no circulatory heat removal.

Assuming this value represents a 10 g cubic average in head or torso over 6 minutes, compare it with local SAR limits. Determine whether it also establishes whole-body compliance.

Step 1: Calculate the local SAR: SAR = σ ∣ E int ∣ 2 ρ \text{SAR} = \frac{\sigma |E_{\text{int}}|^2}{\rho} SAR = ρ σ ∣ E int ​ ∣ 2 ​

Substitute the known values: ∣ E int ∣ 2 = ( 22 V/m ) 2 = 484 V 2 / m 2 |E_{\text{int}}|^2 = (22\text{ V/m})^2 = 484\text{ V}^2/\text{m}^2 ∣ E int ​ ∣ 2 = ( 22 V/m ) 2 = 484 V 2 / m 2 SAR = 0.85 S/m × 484 V 2 / m 2 1040 kg/m 3 = 411.4 1040 ≈ 0.3956 W/kg \text{SAR} = \frac{0.85\text{ S/m} \times 484\text{ V}^2/\text{m}^2}{1040\text{ kg/m}^3} = \frac{411.4}{1040} \approx 0.3956\text{ W/kg} SAR = 1040 kg/m 3 0.85 S/m × 484 V 2 / m 2 ​ = 1040 411.4 ​ ≈ 0.3956 W/kg

Step 2: Calculate the initial rate of temperature rise:

Using SAR = c t Δ T Δ t \text{SAR} = c_t \frac{\Delta T}{\Delta t} SAR = c t ​ Δ t Δ T ​ : Δ T Δ t = SAR c t = 0.3956 W/kg 3600 J / ( kg ⋅ ∘ C ) ≈ 1.099 × 10 − 4 ∘ C/s \frac{\Delta T}{\Delta t} = \frac{\text{SAR}}{c_t} = \frac{0.3956\text{ W/kg}}{3600\text{ J}/(\text{kg}\cdot^\circ\text{C})} \approx 1.099 \times 10^{-4}\ ^\circ\text{C/s} Δ t Δ T ​ = c t ​ SAR ​ = 3600 J / ( kg ⋅ ∘ C ) 0.3956 W/kg ​ ≈ 1.099 × 1 0 − 4 ∘ C/s

Convert seconds to hours ( 3600 s/h 3600\text{ s/h} 3600 s/h ): ( Δ T Δ t ) hour = ( 1.099 × 10 − 4 ∘ C/s ) × 3600 s/h ≈ 0.396 ∘ C/h \left(\frac{\Delta T}{\Delta t}\right)_{\text{hour}} = (1.099 \times 10^{-4}\ ^\circ\text{C/s}) \times 3600\text{ s/h} \approx 0.396\ ^\circ\text{C/h} ( Δ t Δ T ​ ) hour ​ = ( 1.099 × 1 0 − 4 ∘ C/s ) × 3600 s/h ≈ 0.396 ∘ C/h

Step 3: Regulatory comparison:

Under the stated 10 g/6 minute assumption, 0.396 W/kg 0.396\text{ W/kg} 0.396 W/kg is below both the occupational head/torso limit of 10 W/kg 10\text{ W/kg} 10 W/kg and the public limit of 2 W/kg 2\text{ W/kg} 2 W/kg . It does not establish whole-body compliance: that requires absorbed power averaged over the whole body and 30 minutes. The no-cooling temperature rate is an initial estimate, not a prediction of sustained body temperature.

Worked Example 2: Reference Level Evaluation at 144 MHz

An amateur operator measures E = 42 V/m E=42\text{ V/m} E = 42 V/m at a shared boundary 20 metres from a 144 MHz Yagi whose largest dimension is 4 metres. Assume the unperturbed field is constant over time and approximately uniform over the whole-body space. The class-licence far-field boundary is the larger of 2 D 2 / λ ≈ 15.4 m 2D^2/\lambda\approx15.4\text{ m} 2 D 2 / λ ≈ 15.4 m and 0.5 λ ≈ 1.04 m 0.5\lambda\approx1.04\text{ m} 0.5 λ ≈ 1.04 m , so this location is in the far field.

Calculate the equivalent plane-wave power density S S S in W/m 2 \text{W/m}^2 W/m 2 .

Determine whether this location complies with ARPANSA Occupational reference levels.

Determine whether this location complies with ARPANSA General Public reference levels.

Step 1: Calculate plane-wave power density: S = E 2 Z 0 = ( 42 V/m ) 2 377 Ω = 1764 377 ≈ 4.68 W/m 2 S = \frac{E^2}{Z_0} = \frac{(42\text{ V/m})^2}{377\ \Omega} = \frac{1764}{377} \approx 4.68\text{ W/m}^2 S = Z 0 ​ E 2 ​ = 377 Ω ( 42 V/m ) 2 ​ = 377 1764 ​ ≈ 4.68 W/m 2

Step 2: Evaluate against Occupational Reference Levels:

At 144 MHz, RPS S-1 whole-body occupational reference levels are:

  • E limit, occ = 61 V/m E_{\text{limit, occ}} = 61\text{ V/m} E limit, occ ​ = 61 V/m
  • S limit, occ = 10.0 W/m 2 S_{\text{limit, occ}} = 10.0\text{ W/m}^2 S limit, occ ​ = 10.0 W/m 2

The field is below the occupational whole-body reference levels, 61 V/m 61\text{ V/m} 61 V/m or 10 W/m 2 10\text{ W/m}^2 10 W/m 2 . At 144 MHz the local occupational values are also higher, so this constant, uniform field is below those values. Occupational exposure still requires the controlled conditions defined by the standard.

Step 3: Evaluate against General Public Reference Levels:

At 144 MHz, RPS S-1 whole-body public reference levels are:

  • E limit, pub = 27.7 V/m E_{\text{limit, pub}} = 27.7\text{ V/m} E limit, pub ​ = 27.7 V/m
  • S limit, pub = 2.0 W/m 2 S_{\text{limit, pub}} = 2.0\text{ W/m}^2 S limit, pub ​ = 2.0 W/m 2

The field exceeds the whole-body public reference levels, 27.7 V/m 27.7\text{ V/m} 27.7 V/m or 2.0 W/m 2 2.0\text{ W/m}^2 2.0 W/m 2 . Its power-density ratio is 4.68 / 2.0 = 2.34 4.68/2.0=2.34 4.68/2.0 = 2.34 . Because this boundary is publicly accessible, the class-licence condition is not met. Reduce exposure, change the installation or prevent public access, then reassess; passing an occupational comparison does not authorize public exposure.