Calculating Total Exposure Ratios for Co Located Transmitters in Handheld Equipment
Multi-radio handheld exposure compliance requires summing normalized SAR values across concurrent transmitters to verify the total exposure ratio stays below unity.
Human Phantom Fluid
Meaning
Liquid mixture designed to mimic the dielectric properties of human tissue enables accurate electromagnetic exposure testing in laboratory environments. Used inside hollow plastic models of the human head or body during testing, human phantom fluid simulates how radio frequency energy is absorbed by the human body. This allows repeatable, standardized measurements of the specific absorption rate of a wireless device.
Composition Control
Chemical recipes for these mixtures use specific ratios of water, salt, sugar, and cellulose to achieve the targeted electrical permittivity and conductivity. Different formulations are required for each operating frequency band because the electrical response of human tissue changes with frequency. The mix must be carefully adjusted to match standard values specified by international electrotechnical commissions.
Measurement Application
During the specific absorption rate testing process, a robotic arm moves a miniature electric field probe through the liquid-filled container while the device is transmitting. The probe measures the localized electric field strength, allowing the system to calculate the energy distribution within the simulated tissue. This assessment must be completed under controlled ambient temperature to prevent density shifts in the fluid.
Any deviation in the temperature of the laboratory environment can alter the viscosity and electrical parameters, leading to incorrect exposure readings.
Maintenance Protocol
The liquid must be regularly checked for evaporation or contamination that would alter its dielectric parameters. Measurements of the dielectric constant and conductivity should occur before each test run. Storing the fluid in sealed containers slows down the degradation of the mixture over time.