# Wearable Flexible Antenna for UWB On-Body and Implant Communications
## 1 Introduction  
Currently, healthcare devices have attracted the interest of many antenna designers [1, 2, 3, 4]. The continuous monitoring of a patient can interfere with the freedom of movement, which complicates the use of continuous monitoring. Thus, currently, healthcare systems aim to devise innovative wearable devices for wireless diagnosis, monitoring, and following-up of the patient's health status, involving the motion activity [5]. Among the technological devices currently in a clinical use, we can find several wearable antennas implemented in those systems. Such antennas are mounted on the patient by means of attachment belts and the communication is established wirelessly with internal or external devices with respect to the human body [6, 7, 8]. To ensure good performance and safety of these connected devices, many issues should be taken into the account during the design stage [9, 10, 11]. The antenna radiating properties close to a human body should be investigated, as well as the antenna on-body matching at different body locations. The design of new, sophisticated antennas for different body area applications has been an active research topic for several years [12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]. Recently, there has been recognized a need for especially flexible, wearable antennas for biomedical applications. A coupleof recently published surveys on flexible antennas and their materials [26, 27, 28] give a comprehensive overview on the previously published flexible antennas having different sizes, shapes, materials, properties, and their intended uses. One can find several flexible antennas designed especially for industrial, scientific, and medical (ISM) bands or ultra-wideband (UWB) [29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55]. However, published studies for flexible on-body antennas have emphasized on-body communications, leaving aside the implant communications. Only a few initial flexible antenna studies have been presented for the in-body applications: for tumor detection [52, 53, 54], brain hemorrhage detection [35], or in general head imaging [36]. These proposed antennas operate at least partially on UWB band or ISM band. In general, a very limited number of flexible antenna studies can be found covering the whole UWB band as well as ISM band 2.45 GHz. When considering practical applications, the size of the antenna is crucial. Several wearable flexible antennas covering ISM bands 2.45 GHz or lower UWB bands are approximately at least 30 mm on the shorter side and even 50 mm on the longer side [26]. Antenna total efficiency, which is a ratio of the power delivered to the antenna relative to the power radiated from the antenna, is usually rather low with flexible antennas at UWB frequencies, approximately \(-20\) dB [51], since the antenna operates less efficiently in proximity to the human body. The closer the antenna is to the skin surface, the weaker the total efficiency. To the authors' best knowledge, wearable flexible antennas for in-body communications for the entire UWB band, as well as ISM bands, have not yet been reported. This paper addresses this uncovered issue in flexible antenna design for medical monitoring and diagnosis applications by presenting for the first time in-body propagation results with the wearable flexible antenna. As an example case, the suitability of this flexible antenna for implant communications and gastrointestinal track monitoring, e.g., for wireless capsule endoscopy (WCE), is studied by evaluating frequency domain radio channel characteristics between this antenna and a UWB capsule endoscope antenna. Furthermore, the antenna is shown to be feasible for on-body communications as well. The study is carried out using electromagnetic simulations as well as measurements with a hand phantom and a volunteer.