A Comparative Study of the Effects of Substrate Composite Materials on External and Internal Handset Antenna EM Absorption
Cellular phones are used in the vicinity of a human head, which absorbs power from antenna radiation. This investigation analyzes the effects of antenna substrate materials on electromagnetic (EM) absorption in a human head. Antennas are used in analysis with four different dielectric substrate materials, which are Bakelite, FR4 glass epoxy, Rogers R04003, and Taconic TLC. Moreover, two different thicknesses of each substrate are considered in the experimental setup. The EM absorption associated with two types of cell phone antennas is evaluated in the closed vicinity of the human head model. One of them is planar inverted-F antenna (PIFA), which is used as the internal handset antenna and another one is helical antenna, which is used as external handset antenna. This investigation consists of two different operating frequency bands, GSM 900 MHz and DCS 1800 MHz. The EM absorption in the human head is presented using the peak specific absorption rate (SAR) and total absorbed power (TAP) by the user. The finite-difference time-domain (FDTD) method based on Computer Simulation Technology (CST) Microwave studio is utilized in this investigation. The obtained results show that the substrate materials do not effect SAR and TAP values considerably for both antennas, but substrate thickness affects the SAR and TAP values significantly. In addition, the substrate thickness affects the SAR and TAP values significantly in most of the cases Moreover, PIFA produces lower SAR than that of a helical antenna significantly for both GSM and DCS frequency band.
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