## 3 Results
### Design Characteristics  
In Table 1, the center frequencies and other characteristics of the designs as well as some reported implantable antennas are presented. It is observed that the first and the third designs are smaller in size than most of the other samples. All designs have better BW in at least 2 bands of operation in comparison with other reported samples. Among our designs, the comb antenna has the best BW, and it can be used in all new Wi-Fi bands, including indoor, outdoor, and the 5 to 6 GHz range. Since samples are dual-band implantable antennas, some cells in the Table do not have entries.  
SAR limit is another important criterion in implantable antennas for the safety concern of the human body. The IEEE standard [8] restricts the Specific Absorption Rate (SAR) averaged over 1 g of tissue is less than 1.6 W/kg and over 10 g of tissue is less than 2 W/kg. In our simulations, the peak SAR in 1 g of the tissue was less than 300 W/Kg for 0.5 W stimulation power in three antennas, therefore, to observe the SAR limits, the input power should not exceed 2.5 mW to preserve a SAR of less than 1.6 W/Kg. Calculated SAR from 1 w input power for all antennas are shown in Table 2. Since in implantable applications, the antenna is communicating with an indoor communication point, such as Wi-Fi, this input power is sufficient for the intended biotelemetry applications and the indoor communication ranges. For example, most Wi-Fi or Bluetooth transceivers can easily communicate with signal levels of \(-\)70 dbm to \(-\)80 dbm. Assuming an input power of 2.5 mw and an average antenna gain of \(-\)15 db at 2.4 GHz frequency band, we can have up to a 10 m to 25 m distance for effective indoor communication. For 400 MHz and 5.7 GHz bands, the available distance for effective communication will be, respectively, higher and lower than the 2.4 GHz band due to the quadratic relationship between the free-space path loss and the wavelength. At 400 MHz the antenna can communicate to further distances but at a lower data rate because of lower bandwidth.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Antennas**} & **Center** & \multirow{2}{*}{**BW**} & **Gain** & **Center** & \multirow{2}{*}{**BW**} & **Gain** & **Center** & \multirow{2}{*}{**BW**} & **Gain** & **Dimensions** \\  & **Frequency** & **(MHz)** & **(dB)** & **Frequency** & **(MHz)** & **(dB)** & **(GHz)** & **(MHz)** & **(dB)** & **(dB)** & **(dB)** \\ \hline Antenna I & 0.414 & **53** & \(-\)**45** & 2.445 & **90** & \(-\)**18** & 5.63 & **300** & \(-\)**14** & **1.4 mm \(\times\) 10 mm \(\times\) 10 mm \\ Antenna II & 0.4 & **53** & \(-\)**40** & 2.447 & **237** & \(-\)**15** & 5.58 & **350** & \(-\)**13.5** & **3.04 mm \(\times\) 10 mm \(\times\) 17.25 mm \\ Antenna III & 0.412 & **120** & \(-\)**35** & 2.356 & **320** & \(-\)**10** & 5.63 & **1200** & \(-\)**16** & **1.4 mm \(\times\) 12 mm \(\times\) 12 mm \\ Sample [33] & 0.396 & **38.7** & \(-\)**39** & 2.43 & **69.2** & \(-\)**22** & \(-\) & \(-\) & 0.65 mm \(\times\) 7.6 mm \(\times\) 7.6 mm \\ Sample [34] & 0.404 & **30** & \(-\)**36.7** & 2.48 & **168** & \(-\)**27.1** & - & - & 1.27 mm \(\times\) 22 mm \(\times\) 23 mm \\ Sample [35] & - & - & - & 2.46 & **80** & \(-\)**25** & - & - & - & 0.5 mm \(\times\) 10 mm \(\times\) 10 mm \\ Sample [36] & - & - & - & 0.9 & **32** & **29** & - & - & - & 1.27 mm \(\times\) 15 mm \(\times\) 15 mm \\ Sample [37] & 0.4