*Microwave Antennas Suggested for Biomedical Implantation DOI: http://dx.doi.org/10.5772/intechopen.101060*

polarization [43]. The design of the circular polarized (CP) antenna is difficult and needs to be miniaturized. Here, good circular polarization is achieved with a limited size [44]. Circular polarization has a special advantage in that it becomes insensitive between transmitter and receiver [45].

An Implantable patch antenna was first described with capacitive loading in [43], its axial ratio bandwidth is below 3 dB is narrow about 1.63%. [43]. In a circularly polarized helical antenna, measured impedance is 40% and axial radial bandwidth is 32.6% [46]. Similarly, in a loop antenna, simulated impedance and axial ratio bandwidth is 18.2%. [44]. Broadband CP implantable antenna exhibits its axial ratio bandwidth is 6.09% and wide impedance is 16.05% [45]. A miniaturized complementary split ring resonator (CSRR) was designed 915 MHz and its axial ratio bandwidth was 2.4% and impedance bandwidth is 12.2% [47]. Recent research on the CP ISM band antenna contained axial ratio 18.2% and impedance bandwidth 6.2% [48]. Recent work of CP ISM band at 915GHz consists axial ratio bandwidth and impedance band with 1.2 and 29% respectively [49]. **Table 2** shows all recent information about the circularly polarized antenna.

## **2.3 Capsule antennas**

Capsule endoscopy is a diagnostic technology for gastrointestinal (GI) imaging that complements conventional endoscopy. An ingestible electronic radio telemetry capsule, first developed in 1957, is used to measure pressure and temperature [50]. It consists of the ability to transmit detailed information in real-time like growing heatstroke among the athletes while transmitting information to the receiver it simultaneously monitoring body temperature [51]. The approximate size of the capsule is 11 26 mm, in this small size it consists CMOS imager, light-emitting diode, transmitter, batteries, antennas, detailed track of the digestive system. Also, for prevention conditions such as gastroparesis and iron deficiency anemia [52, 53].

Wireless telemetry is used for real-time diagnostics, which is easy for disease diagnosis. The capsule orientation is random, but a robust continuous communication link for biomedical telemetry is quite a challenge to develop stable and secure communication links for capsule devices. The antennas are designed and must be characterized electromagnetically [54, 55]. **Figure 1** shows in detail information about a biomedical capsule. It has eight different parts such as optical dome, lens holder, short focal length lens, light-emitting diode, CMOS Imager, batteries, radio telemetry transmitter, and antenna.

Various antenna designs for capsule antennas have been designed and developed in the literature, including multilayer spiral, multilayer helical, dipole, and complementary split resonator antennas. Antenna performance can be done with help of matching, radiation patterns, link budget, and characterization of wireless medical telemetry characterization. Wireless medical telemetry services (WMTS), industrial scientific and medical (ISM) band used for performance evaluation [56]. **Table 3** shows design techniques, operating frequency, the radiation performance of capsule antenna.

In [57] capsule is off-entered, the antenna operates in MedRadio 403 MHz and ISM 2.45 MHz bands and gain is for 403 MHz, [58] capsule is off-entered and distance to a surface is 10 mm. The bandwidth almost covers 403Mhz, ISM 434,868, 915, and 2.45GHz bands. The gain is about 434 MHz [61]. In [62] capsule is offcentered and the distance to a surface is 3 mm. The motivation is to improve the transmission range of a miniature in a body, but there are some difficulties such as poor radiation efficiency, strong coupling to biological tissues with loss and scattering, antenna impedance detuning, etc. Capsule antenna also considered for animal biotelemetry, electromagnetic properties of some animal tissue differ from humans. High robustness can reduce impedance detuning [63].


**Table 2.** *Circular polarized antennas for biomedical*

*applications.*

*Microwave Antennas Suggested for Biomedical Implantation DOI: http://dx.doi.org/10.5772/intechopen.101060*

**Figure 1.** *Detail digestive track of a biomedical capsule.*
