Fig. 9. Simulated broad side gain of the original adhesive-bandage-like
antenna design (no edge extension) and the design with an 8 mm extended
shielding ground conductor. Both designs were tested in free space.
gain when it was bent into a curved shape. The reactive nearfields
of a small antenna can interact with the body [1], therefore,
the on-body effect when the two designs were mounted on
the tissue-equivalent phantom were investigated. A columnar
phantom was used because the antenna was bent into a curved
shape, as shown in Fig. 10. The tissue-equivalent phantom exhibited
a relative permittivity Er = 40.5 and conductivity low = 1.2 S/m
at 1.45 GHz [32]. The antennas and tissue-equivalent
phantoms were spaced 1 mm apart. The simulation results
showed that the modified design with the edge extension exhibited
less frequency deviation (fphantom/f0 ) when it was
brought close to the tissue-equivalent phantom. The simulated
broad side gains for the designs with and without the edge extension
were 0.28 dBi and -3.04 dBi, respectively. The simulated
radiation efficiency of the design with the edge extension
was 34.7%, whereas the radiation efficiency of the original design
was only 18.7%, which was attributed to the resonant frequency
deviation. These results are listed in Table III, which are
calculated at their free space resonant frequency when bent into
curved shape.
IV. SAR EVALUATION
Wearable devices for WBANs can be used to facilitate
automatic medical treatment or remote monitoring of patient
health. Medical telemetry devices are typically worn on the
body of a patient, therefore, the safety of the human body is
of a higher priority to these systems than it is to other wireless
systems. The SAR must be considered to protect human
tissue. The SAR of the proposed design was evaluated using
a simulation model. A method for lowering the average SAR