# A Comprehensive Review of In-Body Biomedical Antennas: Design, Challenges and Applications
###### Abstract  
In-body biomedical devices (IBBDs) are receiving significant attention in the discovery of solutions to complex medical conditions. Biomedical devices, which can be ingested, injected or implanted in the human body, have made it viable to screen the physiological signs of a patient wirelessly, without regular hospital appointments and routine check-ups, where the antenna is a mandatory element for transferring bio-data from the IBBDs to the external world. However, the design of an in-body antenna is challenging due to the dispersion of the dielectric constant of the tissues and unpredictability of the organ structures of the human body, which can absorb most of the antenna radiation. Therefore, various factors must be considered for an in-body antenna, such as miniaturization, link budget, patient safety, biocompatibility, low power consumption and the ability to work effectively within acceptable medical frequency bands. This paper presents a comprehensive overview of the major facets associated with the design and challenges of in-body antennas. The review comprises surveying the design specifications and implementation methodology, simulation software and testing of in-body biomedical antennas. This work aims to summarize the recent in-body antenna innovations for biomedical applications and indicates the key research challenges. biocompatibility; capsule endoscopy; frequency band; implantable; ingestible; injectable; SAR 1  
K. [PERSON], K.  
device is the wireless endoscopic capsule, which was originally discovered in the year 2000 [8]. Currently, wireless ingestible capsules are equipped with cutting-edge abilities, which can also monitor the side effects of pharmaceuticals [9]. Lastly, injectable devices [10] are micro-sized devices, which can be injected into the human body using needles. Recently, these devices have been commonly used for important sensing and neurostimulation applications [10]. The primary components of an IBBD are the antenna, battery, the processing system and sensors [11]. The reliability and strength of the wireless link between the external and internal device largely depend on the antenna mounted on an IBBD. Therefore, the antenna is a key construction block of an IBBD, as the primary working requirement of signal reception and transmission depends mainly on the performance of the antenna. Furthermore, the overall size and weight of the IBBD can also be affected by it. In IBBDs, the antenna is primarily used for wireless communication and data transfer [12; 13], wireless power transfer (WPT) [14] and sensing [15; 16], which lead to a wide range of medical applications, including continuous pressure measurements, dental antenna for remote healthcare, intracranial pressure monitoring, glucose level check, insulin pump, radiometer/heating therapy, pacemaker connection, endoscopic capsule and blood pressure measurements [17]. The design of an in-body antenna is challenging, as it is mostly situated in electromagnetically harsh and lossy environments inside the human body. The electromagnetic (EM) wave passing through the lossy heterogeneous tissue inside the human body can cause significant absorption of most of the antenna radiations [18]. Such inhomogeneous human organ structure is the primary reason for the impedance mismatch, which makes the radiation performance inefficient. This also affects the antenna efficiency significantly [19]. The powering of an in-body antenna attached to an IBBD inside the human body is another key research challenge. The commonly used batteries in IBBDs are bulky in size with limited capacity and can complicate the system design process [20]. Recently, in-body antennas for WPT have become a great research interest [14]. WPT necessitates an appropriate selection of the frequency band, which is a vital component of the in-body antenna system for biomedical applications. The operation frequency band of an in-body antenna must avoid EM interference with the current terrestrial frequency bands [21].