Dual-Band CPW Graphene Antenna for Smart Cities and IoT Applications.

In this paper, a dual-band graphene coplanar waveguide antenna is designed for smart cities and internet of things applications. A graphene film is chosen as the conductive material for the radiation patches and ground plane with a thickness of 240 µm and an electric conductivity of 3.5 × 105 S/m. The dielectric is glass with a dielectric permittivity of 6 and a thickness of 2 mm. The implementation of the antenna on glass permits the integration of the antenna in smart cities and IoT applications. This antenna is based on two trapezoidal patches that generate the dual-band behavior. The overall dimensions of the antenna are 30 mm × 30 mm × 2 mm. The reflection coefficient, gain, and radiation patterns were measured and compared with the simulations. The antenna covers two frequency bands; the lower band covers the 2.45 GHz ISM band, and the upper band range covers from 4 to 7 GHz.

Dielectric properties of litchi fruit (Litchi chinensis Sonn) at microwave frequencies.

The dielectric properties of litchi fruit were determined using the open-ended coaxial probe method. The measurements were performed in the frequency range from 0.5 to 20 GHz during 3 days of storage at room temperature (~  24 °C). The dielectric properties increased with storage time. Additionally, measurements at different temperatures (24, 30, 40 and 50 °C) were determined. The dielectric constant (ε') decreased with increasing temperature in a frequency range of 0.5-5 GHz; at higher frequencies, ε' increased with increasing temperature. The loss factor (ε″) value increased at frequencies higher than 2 GHz and decreased with increasing temperature. The results will be useful for further applications using microwaves, such as microwave-assisted drying, sensing of quality parameters, modeling, and heating to protect against molds or insects, among other applications.

Dielectric properties of cereals at frequencies useful for processes with microwave heating.

Dielectric properties of barley, corn (white and yellow), sorghum, and wheat at microwave frequencies for heating purpose were analyzed. Properties were determined at 915, 2450 and 5800 MHz with the free space transmission method in the cereals at 20, 30, 40, 50 and 60 °C. ε´ and ε"of all the cereals decreased with increasing frequency. ε´ slightly increased with temperature, while ε "remained practically constant for all the cereals in the temperature range from 20 to 60 °C. Penetration depth decreased with increasing frequency for all the samples, and increased with increasing temperature at 915 MHz, except for barley. These results are useful for further microwave heating applications for the studies on cereals.