Adaptive antenna at the cellular mobile handset for reduced deposition of power in human head

Abstract

Wireless communication is experiencing the fastest growth in the period of history. The next generation mobile services will offer variable bandwidth, desktop/multimedia with mobility and service personalization. To enable this, new technologies and systems is put in use viz; wideband receivers, advanced power amplifiers, advanced modems, adaptive antenna systems, space time coding techniques, radio resource management etc. The spatial processing is considered to be the last frontier in the battle of improved cellular system technology and smart antennas is emerging as the enabling technique that exploits available resources of the physical layer. The application of adaptive techniques to wireless communication has been shown to offer wide range of benefits including interference rejection, increased coverage and spectral efficiency. The use of adaptive antenna at handset can help in eliminating co-channel interference (CCI), multi-access interference (MAI), multipath fading and other effects has been discussed in various papers. In this paper the use of adaptive antennas in reducing radiation hazards has been discussed. The effect of high frequencies on human head has been discussed by taking a simple model of head i.e. by considering it to be a stack of skin, bone, fat, muscle and brain. The power reaching various tissues of the head has calculated by first considering an omni directional antenna. Next, the power reaching brain by use of adaptive antenna at handset is found. The adaptive antenna is adaptively forming a broad null in the direction of head. The power radiated by adaptive antenna towards head is very small as compared to omni directional antenna. The power absorbed by various tissues of head viz, skin, bone, fat, muscle and brain has been compared for omni directional as well as adaptive antenna. The study has been made at in the range 1 MHz to 10 GHZ. It has been found as frequency increases less power reaches brain. From the model developed it is found that from 1 GHz to 6 GHz, the human head absorbs about 47% of the power. Further it is shown that 6% of the incident power is reaching brain at 1900 MHz as compared to 13% at 900 MHz. At 6 GHz only 0.04% of the incident power is reaching brain. By using adaptive antenna at die handset decreases the power radiated towards human head thereby decreasing the power absorbed by head as now less power is directed towards human head.