A Study Of The Interaction Between Wearable Patch Antenna And Human Body

The interaction between the wearable patch antenna and human body in the frequency range of 860⁹60 MHz is investigated through the finite difference time domain (FDTD) method in this paper. The antenna in this paper can be used as tag antenna of ultra high radio frequency identification (UHF RFID) system. Six patch antennas with H-shaped slot are designed according to the differences of substrate permittivity and the contact geometry with the human body. There are two substrates with different relative permittivity, one is 9.6 and the other is 16. And there are three ways of contact, one regards the human body as ground plane, another touches the human body through an electric ground plane, the third one adds a kind of medium under the electric ground plane to touch the human body. The Zubal human body phantom which is widely used in relative researches is chosen. The building of the human body phantom includes calculating the geometric and electromagnetic parameters. According to the three-dimensional array built by professor Zubal et al., the human body phantom is parameterized through programming with C++ for the commercial software XFDTD. The electromagnetic parameters are calculated by solving the one-pole Debye equation, with parameters optimized in the frequency band of interest. Electromagnetic parameters of a single frequency and those from the Debye parameters of the wide band are determined.Based on the model of antenna and human body, the interaction of them is studied on two aspects. One is the influence of human body on the antenna, which is studied by the impendence, pattern, S11 parameter and activation distance of the antenna. First, we calculated the performance parameters for only the antenna and those under the effect of human body. Second, the influence of human body is analyzed on the performance parameters of six antennas to find the best antenna. The effect of the antenna position relative to the human body is also studied. Then, we study the radiation of the antenna on human body, which is quantified by the specific absorption rate (SAR) of human body tissues. First, the SAR values of six different antennas are given to find out the antenna with the minimum radiation dose. Then the influence of the relative position of the antenna and human body on SAR values is analyzed. Finally, through the comparative analysis of the obtained data, we find out the antenna with the best performance parameters and the lowest SAR. An application example is given.Through the analysis of these results, we can obtain the human body has significantly effect on the antennas'work. The performance parameters of six antennas are obviously changed under the action of the human body, especially the two antennas. Under the influence of the human body, the change of antenna impendence with frequency is slower, the radiation on human body is weaker, and the S₁₁ value is smaller. The change of the antenna position relative to the human body has no obvious effect on antenna pattern and activation distance, but has some effect on antenna impendence and S₁₁ parameter. When the antenna moves down 10 mm, the change rate of impendence is slower and the S₁₁ value is smaller. The change of the relative position also affects the SAR value of human body, so choose a reasonable location of the antenna can reduce the radiation dose to the human body. The comprehensive performances of the antennas regarding the human body as ground plane are better than the other four antennas. Their S₁₁ values are smaller in the frequency band 860₉60 MHz, activation distances are longer, and has weaker radiation on the human body. Under the action of the human body, the radiation patterns of the six antennas are almost the same.