# Design and SAR Analysis of a Dual Band Wearable Antenna for WLAN Applications
## 3 Results
### Specific Absorption Rate (SAR) Analysis of Conventional Dual Band Antenna  
Whenever an antenna is installed on a human body, a part of the electromagnetic waves (EMW) radiated by that antenna is absorbed into the human body in the form of side and back lobes. The specific absorption rate (SAR) is the term used for the evaluation of the absorption of these EM waves by the wearer's body. The SAR value must be in the RF exposure limit to ensure the wearer's safety. However, for the frequency range of 400 MHz to 6 GHz, the ICNIRP and IEEE Std C95.1 TM-2019 specifies the restriction in term of specific energy absorption (SA) of any 10-g cubic mass, where SA is restricted to 7.2 \([0.05+0.95(\frac{t}{80})^{0.5}]\) kJ kg\({}^{-1}\) for the head and torso and 14.4 \([0.025+0.975(\frac{t}{80})^{0.5}]\) kJ kg\({}^{-1}\) for limb exposure, where t  
Figure 21: On-body directivity patterns at (**a**) 2.5 GHz and (**b**) 5.2 GHz. Figure 22: On-body gain patterns at (**a**) 2.5 GHz and (**b**) 5.2 GHz. is the exposure interval in seconds. Note that for this specification, exposure from any pulse, group of pulses, or subgroup of pulses in a train, as well as from the total (sum) of exposures (including non-pulsed EMF), delivered in t seconds, must not exceed the limit (in order to ensure that the temperature thresholds are not exceeded) [41; 42]. Table 5 illustrates that when the conventional antenna is worn on a child's arm (worst case), a small amount of reduction in maximum gain and directivity occurrs for the lower frequency band. This means that some amount of power is consumed in the child's arm to increase the SAR level at the lower frequency band as compared to the upper frequency band. However, as shown in Figure 23, it is still in the SAR limit (<2 W/kg) because of the small amount of absorption of energy (demonstrated by the small reduction in gain and directivity at the lower resonance frequency (Table 5, 4 th column). There is an increase in the maximum gain and directivity at the upper frequency band when the conventional antenna is worn on a child's arm. Thus, as shown in Figure 24, the SAR value at the higher frequency band is much lower than that at the lower frequency band. The SAR values at both the resonance frequencies for the conventional antenna placed on a flat body phantom are given in Figure 22. These values are 0.332 W/kg and 0.234 W/kg averaged over 10 g of tissue for the lower and upper resonance bands, respectively. In case of the conventional antenna wrapped around the rounded body parts, the worst condition (child arm) among all bending conditions gives an SAR value of 1.89 W/kg and 0.462 W/kg taken over 10 g of tissue at 2.5 GHz and 5.2 GHz, respectively, as shown in Figure 23. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Conventional Antenna**} & \multicolumn{2}{c}{**Conventional Antenna**} \\  & \multicolumn{2}{c}{**without Body**} & \multicolumn{2}{c}{**Bern Around**} \\  & \multicolumn{2}{c}{**Arm of Radius 40 mm**} \\ \hline Frequency (GHz) & f1 = 2.5 & f2 = 5.196 & f1 = 2.508 & f2 = 5.224 \\ \hline Gain (dBi) & 8.08 & 8.74 & 6.68 & 9.01 \\ \hline Directivity (dB) & 8.39 & 9.01 & 7.7 & 9.29 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Maximum gain and directivity comparison between conventional antenna without a body and with a child’s arm. Figure 23: Conventional antenna SAR value on a flat body phantom at (**a**) 2.5 GHz and (**b**) 5.2 GHz. The SAR analysis of the conventional dual band antenna shows that in all conditions, i.e., an antenna placed over a flat body phantom and an antenna wrapped around rounded body parts (when simulating a lower band of 2.5 GHz, a maximum allowable power of 5.7 mW and 53.8 mW was used for 1 g and 10 g, respectively; similarly, for the higher band of 5.2 GHz, a maximum allowable power of 10 mW and 90 mW was used for 1 g and 10 g, respectively), the obtained SAR value is within the RF exposure limit (<2 W/kg (European standard)) at both resonance frequencies.