Robust Wearable UHF Antennas for Security Applications

by Jovanche Trajkovikj

Institution: EPFL
Year: 2015
Keywords: Wearable antennas; security services; Ultra High Frequency (UHF); Planar Inverted F Antenna (PIFA); polydimethylsiloxane (PDMS); copper meshes; robustness; flexibility; waterproof; Specific Absorption Rate (SAR)
Record ID: 1085627
Full text PDF: http://infoscience.epfl.ch/record/207629


Wearable electronics are occupying an increasing portion of our daily activities. The span of wearable applications extends from purely medical, over different security services to various sports and fashion devices. Antennas play one of the most important roles in wearable networks as they have a key contribution to the overall efficiency of a wearable wireless link. This work focuses on the design and practical realization of robust wearable antennas intended for voice communication inside the Ultra High Frequency (UHF) band. The proposed antennas are mainly envisioned for security services such as military, police or rescue services. To this aim, several questions have been addressed while analyzing and designing the proposed antennas. The on-body environment significantly affects the characteristics of an antenna. The coupling between the antenna and the host body influences both the antenna and the body characteristics. On one hand, the complex lossy nature of the hosting body tends to deteriorate the radiation performances of the wearable antenna, while on the other hand, the radiation from the antenna can cause an increase of the temperature of the wearer’s body (localy and/or of the entire body). The wearability aspect also requires that the size and the profile of the antenna are appropriate so that it can be easily integrated into the wearer’s garment. The size of the wearable antennas becomes more critical at lower frequencies (for instance UHF), where the wavelengths become comparable with the size of the body, thus adding an additional limitation while selecting the type of the antenna. A Planar Inverted F Antenna (PIFA) was selected as an appropriate antenna candidate addressing the introduced specifications. In parallel with the antenna prototype, a suitable technology, combining flexible conductors and stretchable substrates, has been proposed. The suggested technology also enables an adjustment of the electric properties of the designated substrate materials. Several antenna prototypes were successfully designed, fabricated and characterized. Finally, a set of tests in realistic everyday conditions were performed, thus validating the performance of the proposed antenna concepts along with the proposed technology and assessing their potential of being used for commercial purposes. We believe that the obtained results provide useful guidelines for future design of robust flexible wearable antennas.