ABSTRACT:There has been a recent increase in public concern regarding human safety due to the exposure of humans to radio frequency (RF)
INTRODUCTIONAccording to the Office of the Telecommunications Authority in Hong Kong, the penetration rate of local mobile telephone services increased from 2. 3% in 19903% in to 85% in April 2002. Due to this rapid growth in the use of mobile phones and other wireless communication systems, public concern regarding the exposure of humans to radio frequency (RF) electromagnetic radiation has recently increased. This is particularly evident in the case of mobile telephone handsets and associated devices. As a result, many countries, such as Australia, Canada, Korea, and Japan, have provided various guidelines and standards that specify safety levels for such exposure to RF radiation. In the United States, the IEEE standard C95.1:1999 [2] specifies a recommended safety limit for human exposure to RF electromagnetic fields from 3 kHz to 300 GHz. In Europe, the International Commission on NonIonizing Radiation Protection (ICNIRP) has published guidelines, which are generally followed by the published standard EN50360: 2001 [3]. In Hong Kong, the mobile communications systems (GSM900, GSM1800) are similar to those in European countries. Therefore, the SAR limit of the European Standard will be used as a safety guideline for mobile phones. The European standards for testing mobile phones, EN50360:2001 and EN50361:2001, were published in July 2001. They specify the compliance of mobile phones with respect to SAR related to human exposure to electromagnetic fields ranging from 300 MHz to 3 GHz, including both basic restrictions on SAR and measurement methods.The specific absorption rate (SAR), used in the assessment of mobile phone handsets, is a measure of the amount of electromagnetic energy absorbed by biological tissue, particularly in the human body. For example, the SAR limit specified in IEEE C95.1: 1999 is 1.6 W/kg in a 1-g averaging mass, while that specified in the ICNIRP guidelines is 2 W/kg in a 10-g averaging mass. The induced SAR of a RF transmitting device is obtained by measuring the electric field in simulated human tissue in close proximity to the device, and is calculated by the formulawhere E i is the rms value of the electric field strength in the tissue V/m, is the conductivity of body tissue in S/m, and is the density of body tissue in kg/m 3 . The calculation of the SAR distribution in the human head, eye, and ear caused by a mobile phone using numerical methods has been discussed in various papers [4 -7].Products are available for SAR reduction which add external shields to mobile phones, particularly near the earpiece of the handsets. Materials, such as conductive mesh, conductive fabric, and conductive foam are now available and have been displayed in recent EMC exhibitions. These materials can also be applied to reduce the SAR of mobile phone handsets. There has also been some recent investigation into the shielding effectiveness of wiremesh screens and...
