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In this study, the whole-body specific absorption rate (SARw) and tissue average specific absorption rate (SARa) of rats under alternatively incident microwave exposure (1.5 GHz and 9.4 GHz) were calculated by finite-difference time-domain (FDTD). The effects of combined and alternating microwave exposures on the SARw and SARa values of rats were discussed and compared with those of single frequency irradiation. Numerical simulation of electromagnetic exposure revealed that under double-source alternating irradiation, both SARw and SARa values of rats were affected by the combined incidences. With the increment in the duration of alternating exposure, both SARw and SARa tended to increase nonlinearly. On comparison with SARw and SARa values obtained from single frequency irradiation, it was found that the SARw value of double-source alternating irradiation was limited within the two SARw values that were determined by two individual irradiation frequencies, corresponding to 1.5 GHz and 9.4 GHz. However, the SARa value of testis tissues that back-incident short-axis polarization of double-source alternating irradiation is 31.2% higher than the maximum SARa value of the two wave sources acting alone. The SARa value (1.5 GHz, long-axis polarization; 9.4 GHz, short-axis polarization) of the spleen is 18.9% higher than the maximum SARa value of the single-wave source when the double-source is incident back.

To provide experimental evidence that defines the safety limits of electromagnetic exposure, the effects of long-term and low-dose electromagnetic irradiation during the developmental stage of free-move behaving Sprague Dawley (SD) rats on their learning and cognitive abilities were investigated. A 1.8 GHz electromagnetic wave was used as the irradiation source, and the absorbed dose was set at 0.40 W/kg during the 8-hour working time and 0.08 W/kg during the rest time of the day, the whole irradiation was continuously administered for 4 weeks. The water maze experiment was performed to detect the learning and memory ability of the rats. The chemical colorimetric method was used to measure the level of cholinergic markers, the level of monoamine neurotransmitters, the activity of antioxidant enzymes, and the concentration of oxidative stress products in the hippocampus of the rats. In addition, the hippocampal tissue was sectioned, stained, and observed under an optical microscope. The results showed that the hippocampal tissue in the brain of the exposed group was not significantly different from that of the sham group, but the content of cholinesterase was reduced and the content of acetylcholine and the activity of acetylcholine transferase were increased in the exposed group. The contents of the neurotransmitter dopamine and serotonin (5-HT) were also significantly higher in the exposed group than those in the sham group. The water maze test results showed that there was no significant change in the behavior of rats in the exposed group. Although long-term and low-dose electromagnetic radiation can cause disorders of the cholinergic system and neurotransmitter levels in SD rats, the changes in these indicators did not cause a decline in the learning and memory ability of rats, and the levels of cholinergic system markers and neurotransmitters returned to normal after 14 days.