Design and Development of a Multi-Functional Antenna With Reactive Impedance Surface for Smart Helmets/Caps

This paper presents an antenna consisting of a bent monopole and a reactive impedance surface (RIS) reflector for smart helmets that can be used by rescue personnel for disaster management. The bent monopole and RIS concepts are introduced to achieve multiband performance with improved radiation characteristics. The bent monopole's resonant modes and the RIS reflector, which operates in its inductive region, are combined to produce hepta-band behavior. Unlike perfect electrical conductors (PECs) and perfect magnetic conductors (PMCs), RIS can operate over a wide frequency range with reflection phases ranging from 0° to 180°. Therefore, the challenges associated with PEC/PMC, such as focused image contribution and low efficiency, can be mitigated using RIS. The phase distribution can be controlled by varying the array size of the RIS. To achieve multiband performance, a RIS of array size of 18 × 21, with periodic square patches, is placed underneath the bent monopole. The designed antenna functions at the GPS L5 (1.176 GHz), GSM (1.8 GHz), LTE (2.6/3.7 GHz), WLAN (5.5/5.8 GHz), and MBAN (7.2 GHz) bands. The addition of the metasurface layer increases the gain of the antenna significantly over all resonant bands. With the RIS layer, the antenna achieves a peak gain of 8.7 dBi. The total efficiency values obtained at the seven resonating bands are 97.21%, 97.35%, 97.49%, 97.7%, 98.12%, 98.33%, and 98.81%, respectively. The monopole and RIS reflector are fabricated separately on the RT/duroid 5880 substrate with permittivity of 2.2. Also, a thick foam (λ₀/8) is sandwiched between the antenna and the RIS reflector to simulate (outer and inner surfaces) a realistic helmet scenario.