6.6 CHAPTER SUMMARY
This chapter has traced the physical progression from source emissions, through external exposure and internal fields and energy absorption, to biological response. The corresponding assessment activities are source characterization, exposure assessment, RF dosimetry, and biological-effects assessment. Chapter 6 has addressed the first three; Chapter 7 addresses the fourth.
Source characterization establishes what an RF source emits and how the emission is distributed in frequency, time, and space. Natural RF sources provide a useful background for comparison, while human-made sources span communications, radar, industrial, medical, scientific, and domestic applications. Rated power, average power, peak power, PEP, ERP, and EIRP describe different source characteristics but must not be treated as interchangeable measures of exposure.
Exposure assessment determines the electric and magnetic fields, or incident power density, present where a person may be located. The result depends on frequency, antenna gain and radiation pattern, beam direction, duty cycle, distance, field region, reflections, shielding, and the person's position. Exposure may be whole-body or localized and may occur under general-public or controlled occupational conditions.
Modern RF guidelines link readily measured external quantities to basic restrictions on quantities induced or absorbed within the body. Compliance with an applicable reference level demonstrates compliance with the corresponding basic restriction. Exceeding a reference level does not necessarily mean that a basic restriction has been exceeded, but it may require a more detailed assessment.
RF dosimetry determines the internal electric fields and the power or energy absorbed by tissues. Coupling between an external field and the body depends on frequency, polarization, field distribution, near-field or far-field conditions, body size and posture, and the frequency-dependent electrical properties of tissues. Consequently, identical external field strengths need not produce identical internal distributions.
The principal dosimetric quantities are induced electric-field strength, whole-body and localized SAR, specific energy absorption, absorbed power density, and absorbed energy density. They apply over different frequency ranges and averaging intervals and are not interchangeable. Experimental dosimetry uses calibrated instruments and tissue-equivalent phantoms, while computational dosimetry uses validated numerical models such as FDTD and FEM. Both approaches require appropriate averaging, validation, and uncertainty analysis. Their results describe internal physical conditions; the biological meaning of those conditions is considered in the next chapter.