Wireless medical devices are utilized to obtain physiological signals from the human body to an external monitoring device. The in-body antenna plays a crucial role in ensuring the transmission of physiological signals for implantable or ingestible wireless medical devices. One of the wireless medical devices that involve implantable and ingestible antennas is capsule endoscopy. The implantable one is to be implanted surgically into the human body while the ingestible one is swallowed like a multi-vitamin to perform a wide variety of diagnostic and therapeutic functions in the gastrointestinal (GI) tract. A review of both antennas and their application is presented. Besides, the design of such in-body antenna in the wireless capsule endoscopy especially in current technologies (e.g Wi-Fi, WLAN, Bluetooth, IoT) is extremely challenging and intriguing owing to it deals with the challenges related to the selection of operating frequency band, type of antenna design, and antenna miniaturization technique. Most of the antenna is facing the issue with bandwidth, transmission rate, the robustness of the communication links, size constraint, components arrangement in capsule, and others that could directly affect the patient safety and performance of capsule endoscopy in the human body. Nevertheless, the application of such implantable and ingestible antenna in wireless capsule endoscopy is incessant and rapid growth along with the evolution of technology, thus eliminating any concerns related to the aforementioned challenges and their invasive nature. In this paper, comparative reviews on the design consideration of the in-body antennas are discussed.
