Two ground radiation antennas with polarisation diversity performance were proposed for MIMO WLAN applications in wearable devices. The antennas can simultaneously excite the vertical mode and horizontal mode of the ground plane and the phase difference between the two modes can be controlled by utilising an inductor‐loaded metal strip in the ground plane, generating circular polarisation. A 3:1 VSWR bandwidth of 140 MHz with high isolation (above 17 dB) and a 3 dB axial ratio bandwidth of 100 MHz was obtained. The opposite rotations generated by the two antennas resulted in good diversity performance, which was verified by the measured envelope correlation coefficient.

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Solid solutions of magnesium silicide and magnesium stannide were recently reported to have high thermoelectric figure-of-merits (ZT) due to remarkably low thermal conductivity, which was conjectured to come from phonon scattering by segregated Mg2Si and Mg2Sn phases without detailed study. However, it is essential to identify the main cause for further improving ZT as well as estimating its upper bound. Here we synthesized Mg2(Si,Sn) with nanoparticles and segregated phases, and theoretically analyzed and estimated the thermal conductivity upon segregated fraction and extraneous nanoparticle addition by fitting experimentally obtained thermal conductivity, electrical conductivity, and thermopower. In opposition to the previous speculation that segregated phases intensify phonon scattering, we found that lattice thermal conductivity was increased by the phase segregation, which is difficult to avoid due to the miscibility gap. We selected extraneous TiO2 nanoparticles dissimilar to the host materials as additives to reduce lattice thermal conductivity. Our experimental results showed the maximum ZT was improved from ∼0.9 without the nanoparticles to ∼1.1 with 2 and 5 vol % TiO2 nanoparticles at 550 °C. According to our theoretical analysis, this ZT increase by the nanoparticle addition mainly comes from suppressed lattice thermal conductivity in addition to lower bipolar thermal conductivity at high temperatures. The upper bound of ZT was predicted to be ∼1.8 for the ideal case of no phase segregation and addition of 5 vol % TiO2 nanoparticles. We believe this study offers a new direction toward improved thermoelectric performance of Mg2(Si,Sn).

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