Thermal and Electromagnetic Properties of Polymer Holey Structures Produced by Additive Manufacturing

Multifunctional 3D-printed holey structures made of composite polymers loaded with nanocarbon were designed to serve simultaneously as GHz-radiation absorbing layers and heat conductors. The geometry of the structures was devised to allow heat to be easily transferred through, with special attention paid to thermal conductivity. Numerical calculations and a simple homogenization theory were conducted in parallel to address this property. Different structures have been considered and compared. The electromagnetic shielding effectiveness of the produced holey structures was measured in the microwave range

Short-length carbon nanotubes as building blocks for high dielectric constant materials in the terahertz range

Due to the high polarizability of finite-length carbon nanotubes (CNTs) in the quasi-static regime, they can be considered as building blocks for the fabrication of high dielectric constant material. Our theoretical estimations, based on an effective medium approach and solutions of a boundary value problem for individual CNT, predict that composite materials comprising short-length CNTs can have very high dielectric constants (up to 300) and low dielectric loss tangents (below 0.03) in the terahertz range. In order to prove this, 500–1000 nm thick films comprising single- and multi-walled CNTs of both long (0.5–2 μm) and short (0.1–0.4 μm) lengths have been fabricated. The analysis, based on the time-domain terahertz spectroscopy in the range 0.2–1.0 THz, demonstrated a decrease in the dielectric loss tangents of the CNT-based materials with a reduction in CNT length. In the terahertz range, the films comprising short-length CNTs had a relative effective permittivity with a large real part (25–136) and dielectric loss tangent (0.35–0.60)

How effectively do carbon nanotube inclusions contribute to theelectromagnetic performance of a composite material? Estimation criteria from microwave and terahertz measurements

Screening effect in finite-length carbon nanotubes (CNT) and their agglomerates hinders significantly the electromagnetic interaction in composite materials. Screening effect is strong in the microwave range, and it decreases with increasing frequency resulting in a strong frequency dependence of the effective conductivity of the composite. Since screening effect is rather small in the terahertz range, the effective conductivity in this range is determined directly by the intrinsic conductivity of the inclusions. The ratio of the microwave to terahertz effective conductivities was proposed as a parameter to estimate how effectively carbon nanotube inclusions contribute to the electromagnetic performance of composite materials in the microwave range. CNT film was considered as a material where maximal possible interaction of the CNTs with EM field occurs. Single-walled CNT films and CNT-based composite materials, as well as hybrid film comprising mixtures of WS2 nanotubes and CNTs were fabricated and measured in the microwave and terahertz ranges. The electromagnetic field interaction with the inclusions has been estimated for all the samples fabricated

Influence of nanotube length and density on the plasmonic terahertz response of single-walled carbon nanotubes

We measure the conductivity spectra of thin films comprising bundled single-walled carbon nanotubes (CNTs) of different average lengths in the frequency range 0.3-1000 THz and temperature interval 10-530 K. The observed temperature-induced changes in the terahertz conductivity spectra are shown to depend strongly on the average CNT length, with a conductivity around 1 THz that increases/decreases as the temperature increases for short/long tubes. This behaviour originates from the temperature dependence of the electron scattering rate, which we obtain from Drude fits of the measured conductivity in the range 0.3-2 THz for 10 $\mu$m length CNTs. This increasing scattering rate with temperature results in a subsequent broadening of the observed THz conductivity peak at higher temperatures and a shift to lower frequencies for increasing CNT length. Finally, we show that the change in conductivity with temperature depends not only on tube length, but also varies with tube density. We record the effective conductivities of composite films comprising mixtures of WS$_2$ nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1 THz, finding that the conductivity increases/decreases for low/high density films as the temperature increases. This effect arises due to the density dependence of the effective length of conducting pathways in the composite films, which again leads to a shift and temperature dependent broadening of the THz conductivity peak.Comment: Submitted to Journal of Physics D. Main manuscript: 9 pages, 8 figures. Supplementary material: 5 pages, 6 figure

A deep learning approach to organic pollutants classification using voltammetry

This paper proposes a deep leaning technique for accurate detection and reliable classification of organic pollutants in water. The pollutants are detected by means of cyclic voltammetry characterizations made by using low-cost disposable screen-printed electrodes. The paper demonstrates the possibility of strongly improving the detection of such platforms by modifying them with nanomaterials. The classification is addressed by using a deep learning approach with convolutional neural networks. To this end, the results of the voltammetry analysis are transformed into equivalent RGB images by means of Gramian angular field transformations. The proposed technique is applied to the detection and classification of hydroquinone and benzoquinone, which are particularly challenging since these two pollutants have a similar electroactivity and thus the voltammetry curves exhibit overlapping peaks. The modification of electrodes by carbon nanotubes improves the sensitivity of a factor of about x25, whereas the convolution neural network after Gramian transformation correctly classifies 100% of the experiments

Fluorination as effective method for tuning the electromagnetic response of graphene

Fluorinated graphene (FG) has been obtained by a fluorination of thermally exfoliated graphite fluoride C2F layers using a gaseous mixture of BrF3 and Br2 at room temperature. Comparative study of electromagnetic (EM) response of thin FG films after recovering their conductivity via different methods is presented in microwave (GHz) and terahertz (THz) frequency ranges. We discovered that fluorination can be used as promising tool for producing tunable EM interference (EMI) shielding materials, combining reflective and absorptive layers

Transport mechanisms and dielectric relaxation of epoxy nanocomposites in DC to microwave range

Using several methods we measure the effective complex permittivity of epoxy composites realized by shear mixing and filled with carbonaceous carbon black (CB), single wall CNT (SWCNT), and multiwalled carbon nanotube (MWCNT) over nine decades of frequency. The spectral analysis of permittivity of these nanocomposites is in good agreement with Jonscher's modelling. We point out, taking these examples, that the experimental frequency dependence of the effective permittivity has a range of interesting properties. Likely transport mechanisms responsible for the dielectric relaxation in these samples can be modeled by the dipolar relaxation and anomalous low frequency dispersion (LFD) below and above percolation, respectively

DAMPAK BERMAIN GAME ONLINE DALAM MEMPERLUAS RELASI SOSIAL PADA PEMAIN GAME ONLINE DOTA 2

This research was conducted in order to find out the impact in social relations in DOTA online game players. The method used in this research is qualitative research methods using a phenomenological approach, namely research taken based on phenomena that exist in society. The researcher used interviews and observation as a method of retrieving data. The subjects of this study were 3 students of Soegijapranata Catholic University Semarang, playing online game Dota 2 and able to communicate well. The data analysis method that the researcher uses is inductive, which is an analysis of data based on the data that has been obtained, and then developed into general conclusions. The research results obtained, namely playing online games can have a positive impact on social relations such as expanding the social relations of the players. In addition, researchers also found that there was a negative impact from playing online games on social relations in the parent subject, namely the time to communicate was reduced. Keywords: online games, social relations, the impact of playing online games