Assessment of radio frequency radiation exposure in beauty care appliances
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Radiotaajuisen säteilyn altistuksen arviointi kauneudenhoidon sovelluksissa
The aim of this Master’s Thesis was to assess the radiofrequency exposure of beauty care appliances and to be able to evaluate the safety of the devices according to the limits issued in the regulations for the exposure of electromagnetic fields. The treatments with radiofrequency beauty care appliances are usually associated with some degree of local tissue heating, thus the effects of excessive heating might cause some thermal damage in tissues. In the literature survey of this Thesis, the principles of radiofrequency (RF) radiation and its interaction mechanisms with biological tissue, the properties of human tissues, the structure and operation of RF beauty care appliances and different dosimetric assessment methods of radiofrequency radiation exposure are studied. To study the operation and output power of the RF beauty care appliances, a moveable power measurement set-up was developed. In this set-up the RF power, which connects to resistors representing human body and its impedance, was determined from the output signal with an oscilloscope. A model simulating a human forearm made of cylindrical container and tissue simulating liquid was fed with radiofrequency power of RF beauty care device under review. The temperature increase in the liquid was measured below the RF treatment electrode. An output power of the device, which was obtained from the temperature increase measurements, was used as an output power when assessing the exposure in numerical simulations with Finite Difference Time Domain (FDTD) method in homogeneous and heterogeneous human models. The numerical simulation model was successfully validated with the temperature increase measurements. The dosimetry of the RF exposure was based on simulations with heterogeneous model. The simulations showed that the distribution of the specific absorption rate (SAR) in the heterogeneous tissue model was really superficial, and maximum 10 g average SAR value might exceed the public exposure limit values. This value was determined to be 650 W/kg ± 38 % (k=2), meaning that when considering the public exposure limits, the treatment electrode can be held in one place for 1,1 seconds in head and trunk area and 2,2 seconds in limbs. The power measurement set-up can be used for getting more information on the appliances for surveillance use, but it still needs to be developed further to obtain more reliable estimations on the exposure of the device being measured.