# A Comprehensive Review of In-Body Biomedical Antennas: Design, Challenges and Applications
## 5 In-Body Antenna Applications
### Capsule Endoscopy  
Capsule endoscopy (CE) is the most common ingestible device, which is used for diagnosis and monitoring of different gastrointestinal (GI) disorders. A wide range of in-body antennas used for CE application over the last few years are described below.  
A planar meandering antenna fabricated on a 0.1 mm thick polyimide flexible substrate (with \(\varepsilon_{r}\) = 3.5 and tan \(\delta\) = 0.0027) with 0.035 mm copper thickness is presented in Ref. [104], as shown in Figure 21. The proposed antenna has dimensions of 28 mm \(\times\) 12 mm, working with an operation frequency of 433 MHz. The measured peak gain is \(-\)39 dBi.  
Figure 19: Planar implantable antenna for an UHF RFID-based orthopedic implant [101]. Copyright © _IEEE_.  
Figure 20: Folded loop wire antenna for a cochlear implant [102]. Reproduced with permission from Attribution-NoDerivates 4.0 International shared at CSEM archive.  
In Ref. [105], a circularly polarized (CP) helical implantable antenna is proposed. The proposed antenna operates at 2.4 GHz frequency with a gain of \(-19.83\) dBi and a bandwidth of 290 MHz. A perfect electric conductor (PEC) is used to build and simulate this antenna with a 6.6 mm diameter and 8.85 mm length, with an approximate wire thickness of 0.4 mm. Furthermore, the antenna covers the cylindrical shape of the capsule with a diameter of 7.06 mm and length of 25 mm.  
A 3D wireless power transfer receiver coil of 8.9 mm in diameter and 4.8 mm in thickness is presented in Ref. [61], as shown in Figure 22. The proposed 3D coil is built with a 0.2 mm copper wire. It achieves 0.7% power transfer efficiency (PTE) and a SAR of 66 mW/kg for 10 g of tissue at 1 MHz operation frequency.  
A conformal antenna with a frequency of 402, 433, 915 and 2450 MHz is presented with an achieved gain of \(-32.5\), \(-30.4\), \(-17.9\) and \(-19.0\) dBi, respectively [106]. The proposed antenna is printed on a 0.17 mm thick flexible Kapton substrate with \(\varepsilon_{r}=3.5\) and tan \(\delta=0.0027\). It has a size of 12 mm \(\times\) 6 mm. The bandwidth of the antenna is reported to be 2.95 and 3.33 GHz.  
A similar conformal differentially fed antenna with an operation frequency of 915 MHz is presented in Ref. [107]. The proposed antenna has dimensions of 32 mm \(\times\) 5.8 mm, as shown in Figure 23, and it is printed on a flexible polyimide substrate (with \(\varepsilon_{r}=3.5\) and tan \(\delta=0.008\)) of 0.15 mm in thickness. The antenna achieves a peak gain of \(-21\) dBi and a bandwidth of 8.9% tested in the phantom under 50 mm depth.  
Figure 21: Fabricated planar meandering antenna with SMA connection [104]. Reproduced with permission from an open-access article from _IEEE Access_ (CC-BY).  
Figure 23: Conformal differentially fed antenna built in a capsule [107]. Copyright © _IEEE_.  
Figure 22: Three-dimensional wireless power transfer receiver coil for capsule endoscopy tested in gel phantom [61]. Reproduced with permission from an open-access article from MDPI _Micromachines_ (CC-BY).  
Figure 24 shows a slot line fed antenna with the size of 7 mm \(\times\) 7 mm constructed on a silicon substrate of approximately 0.675 mm in thickness with \(\varepsilon_{r}\) = 11.9, which is presented in Ref. [108]. The proposed antenna is operating at a 915 MHz frequency. It can achieve a peak gain of \(-\)35.5 dBi and a bandwidth of 300 MHz, as tested in colon phantom. Furthermore, it achieves a SAR of 8 mW/kg for 1 g of colon tissue.  
A wideband multiple-input-multiple-output (MIMO) compact antenna for ingestible capsules is presented in Ref. [109], as shown in Figure 25. The size of the antenna is 5 mm \(\times\) 4.2 mm \(\times\) 0.12 mm, operating at a 2.45 GHz frequency. The proposed MIMO antenna is manufactured on a Rogers RO3010 substrate with \(\varepsilon_{r}\) = 10.2 and tan \(\delta\) = 0.0022. It maintains a peak gain of \(-\)20.6 dBi and a bandwidth of 25%. It can achieve a SAR of 2 W/kg for 10 g of tissue when the input power is 3.97 mW.