**5.2 Impact of tissue type on antenna performance**

As mentioned earlier in this chapter, interaction of the electromagnetic wave with the tissue depends on the operating frequency and the dielectric properties. Thus, it is expected that the antenna of the implanted device behaves differently based on which part of the body the device is implanted as well as depending on the frequency of the EM. In [33], a dual band flower-shaped antenna is proposed for wireless implanted devices as shown in **Figure 10**.

The performance of the antenna at different part of the body was recorded for both frequency bands as summarized in **Table 3** below. It is clearly observed that the performance of the antenna is changed when placed at different parts of the body. It was also noticed that the bandwidth is higher at 2.45 GHz frequency band compared with 928 MHz, however, the gain was smaller. Thus, there is a tradeoff between the gain and the bandwidth depends on the application of the wireless implanted device.

**Figure 10.** *The proposed flower-shaped antenna [33].*


*Implantable Wireless Systems: A Review of Potentials and Challenges DOI: http://dx.doi.org/10.5772/intechopen.99064*

**Table 3.**

*Summarized performance parameters (bandwidth and gain) of the proposed flower-shaped antenna [33].*

#### **Figure 11.** *The proposed dipole and loop UHF antennas [34].*

The antenna type play an important role in the wireless implanted system. Thus, it is important to study different antenna types at different parts of the human body and compare the performance. In [34], a comparison is made between dipole and loop antennas, where several dipole and loop antennas were designed as shown in **Figure 11**.

Recent study showed that the loop topologies provide higher gain than dipole topologies with achieving miniaturized size, while dipole antennas exhibits better impedance matching properties [34]. In addition, the dipole antennas showed a better ability to increase the gain and less sensitivity changes in tissue structure. The variation of antenna gain at different parts of the body is plotted in **Figure 12** [34] for both topologies (i.e. dipole and loop).

Another studies investigated the impact of tissue location on the return loss of the antenna at high frequencies as shown in **Figure 13** [35]. It was observed that the resonant frequency and the bandwidth can be changed by placing the antenna at another body part such as hand, heart, chest and head.
