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Cu2SnSe3 has been considered as a potential thermoelectric material owing to its tunable transport properties and its phonon-glass-electron-crystal (PGEC) characteristics. Here, p-type pure and In-doped Cu2SnSe3 samples are synthesized by the solid-state sintering technique. Cubic structure with $$F\overline{4}3m$$ F 4 ¯ 3 m space group is maintained for all the samples, and a linear increase in lattice parameter with increasing In concentration has been observed. The nature of electrical resistivity changes from semiconducting to metallic behavior for samples with x > 0.10. The decrease in both electrical resistivity and Seebeck coefficient with an increase in x is attributed to the increased hole concentration. Such a scenario is confirmed from the room-temperature Hall effect measurements. Indium doping also reduces the thermal conductivity of the Cu2SnSe3 system as a result of increased phonon scattering due to the mass fluctuation. Concurrently, enhancement of thermoelectric power factor (PF) and figure of merit (ZT) is achieved with In doping at Sn site of Cu2SnSe3. The maximum ZT of 0.04 has been exhibited by the sample with x = 0.25 at 400 K, which is six times higher than that of the undoped Cu2SnSe3.

In order to obtain ultra-compact and ultra-narrow bandstop performances, the work presents a terahertz filter based on graphene cavities, which consists of four graphene cavities and a graphene waveguide on SiO 2 /Si substrate. To demonstrate the feasibility of the approach, numerical simulation performed with the aid of the finite-element method is used to evaluate the terahertz performance of the proposed device. The structure rejects the signals at the frequencies from 5.9978 to 6.002 THz with >20 dB suppression. The high-Q band-rejection terahertz wave filter with four graphene cavities provides of 1500. The dimensions of the presented terahertz wave band-stop filter are of 22.5 μm × 18.0 μm. The high-performance, compact-size, and low-cost filter is designed for reducing the interference in future terahertz systems.

We report the structural and thermoelectric properties of the Cu2Se compound with a systematic substitution of Se by Te atom. The bulk polycrystalline Cu2Se1-xTex samples for the Te concentrations of x = 0.00, 0.02, 0.04, 0.06, and 0.08 were prepared by the solid-state reaction method. The room-temperature XRD studies revealed that the studied samples possess a monoclinic crystal structure. The oxidation state and electronic structure are confirmed by employing X-ray photoemission spectroscopy (XPS). The hardness of the samples increased systematically with an increase in Te doping concentration. The electrical resistivity of the doped samples was found to be increased in comparison to the pure sample. The Seebeck coefficient was positive throughout the temperature range under investigation, indicating that holes are the majority charge carriers in the studied compounds. The thermal conductivity of the doped samples decreased, which is presumably attributed to the point defect scattering. The systematic evolution of thermoelectric properties via substitution of Se by Te over the range (0.00 ≤ x ≤ 0.08) concludes that the overall thermoelectric power factor (PF) and figure of merit (ZT) decrease with Te substitution compared to the pristine Cu2Se compound.

In the study, we deal with the effects of Bi doping on the thermoelectric properties in a series of Cu2Sn1-xBixSe3 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) compounds. The pristine and Bi-doped Cu2SnSe3 samples are synthesized by the solid-state sintering technique. Cubic structure with F 4 ‾ 3 m space group is maintained for all the samples. FESEM analysis indicated that the average grain size increases with an increase in Bi concentration. It is found that the characteristics of electrical resistivity changes from semiconducting in the case of the pristine sample to metallic behavior for the doped samples. The decrease in both electrical resistivity (ρ) and the Seebeck coefficient (S) with an increase in x is attributed to the increased hole concentration. The highest power factor (PF) of ~348 μW/mK2 has been achieved for the x = 0.08 sample at 350 K, which is four times larger than that of the pristine sample. The thermal conductivity (κ) of the doped samples is observed to be higher than that of the pristine Cu2SnSe3, attributed to the increased grain size and electronic thermal conductivity. As a combined effect on the values of PF (= S2/ρ) and thermal conductivity, a maximum figure-of-merit (ZT) of ~0.027 for the x = 0.08 sample is attained at 350 K, about twice that of the pristine sample.

To investigate the thermoelectric properties, we have attempted to tune selenium content in Cu2SnSe3-δ (−0.04 ≤ δ ≤ 0.1) compounds synthesized via the conventional solid-state reaction. Electrical and thermal properties are presented in the low and near room temperature regime (10–350 K). The lowest electrical resistivity is observed for the compound with δ = 0.08. The electron-phonon coupling and the presence of small polarons are experimentally validated from temperature-dependent electrical and thermal transport data. A decrease in the Seebeck coefficient along with carrier concentration is observed, verifying the linear electron band dispersion. A downward shift of the Fermi level deep into the valence band is realized in the case of non-stoichiometric samples, thereby reducing the Seebeck coefficient. A maximum power factor of ~50 μWmK−2 is achieved for the sample with δ = 0.04, which is about twice that of the pristine compound. The highest ZT of ~0.01 is obtained for the compound with δ = 0.08. The observed results suggest that stoichiometry plays a vital role in tuning the thermoelectric properties in the Cu2SnSe3 compound.

In order to extend to 3-bit encoding, we propose notched-wheel structures as polarization insensitive coding metasurfaces to control terahertz wave reflection and suppress backward scattering. By using a coding sequence of "00110011…" along x-axis direction and 16 × 16 random coding sequence, we investigate the polarization insensitive properties of the coding metasurfaces. By designing the coding sequences of the basic coding elements, the terahertz wave reflection can be flexibly manipulated. Additionally, radar cross section (RCS) reduction in the backward direction is less than -10dB in a wide band. The present approach can offer application for novel terahertz manipulation devices.

A small size monopole antenna with a matching network for WWAN/LTE bands in the tablet computer is presented. With the aid of the matching network, the bandwidths of the antenna's lower and higher bands have been widened. The numerical and experimental results demonstrated that the proposed antenna satisfies the requirement of 6dB return loss for the impedance bandwidth of the WWAN/LTE bands (670MHz∼980MHz/1650MHz∼2660MHz). The antenna efficiencies are about 48%∼69% and 53%∼77% over the lower and higher bands with the peak gains of 1.28dBi and 3.48dBi, respectively. The total size of the presented antenna is of 30×10mm2. Details of the proposed antenna are described and the experimental results are discussed.

A dual-band bandpass filter using two embeded stepped impedance resonators is proposed. To validate the proposed structure, the prototype filter has been fabricated and measured. Two stepped impedance resonators are embedded in a half-wavelength resonator and thus the proposed filter is compact in size. The results show the passbands with 3dB fractional bandwidth of 15.2% and 14.5% at 1.65GHz and 2.75GHz, respectively. The measurement results agree well with the full wave electromagnetic designed responses.