What Are Tissue-Equivalent Phantoms?
How Can RF Absorption Be Measured Without Exposing a Person?
A tissue-equivalent phantom is a physical model used to represent selected electromagnetic properties of the human body during radio-frequency testing. It allows internal fields, absorbed power, or related quantities to be measured under controlled conditions without exposing a person.
A phantom may represent the whole body, the head, a limb, or another region. Its shape can be anatomically recognizable or deliberately simplified, depending on the standardized test method and the quantity being assessed.
The phantom contains or is made from tissue-equivalent material formulated to reproduce specified dielectric properties, particularly relative permittivity and electrical conductivity, over the test frequency range. No material reproduces every tissue property at every frequency.
For specific absorption rate testing, a probe may scan a tissue-equivalent liquid inside a shell while the transmitting device operates in prescribed positions. The measured electric field is converted to SAR and spatially averaged over the mass required by the applicable procedure.
Other systems use solid or semisolid materials, thermal measurements, electric-field sensors, or current measurements. The phantom, source position, separation, accessories, operating mode, scanning system, and averaging procedure together define the test configuration.
Before use, the phantom material and measurement system must be characterized, calibrated, and validated. Temperature, material composition, probe dimensions, boundary effects, positioning, drift, and interpolation can contribute to measurement uncertainty.
A phantom is a standardized representation, not an exact replica of every individual. Results are meaningful only for the stated method and configuration. Computational human models complement phantom measurements by examining anatomies, postures, tissues, and source positions that are difficult to reproduce physically.
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