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Carbon nanofibers (CNFs) is a typical electrical loss material with strong permittivity that has been widely used in the field of electromagnetic shielding, attenuation, and reception. However, studies have demonstrated that the unstable anisotropic EM behavior exhibited by CNFs in the terahertz domain hinders its application in the tremendously high frequency domain. In this study, ZnO is used to perform surface modification of CNFs based on the sputtering method, which effectively eliminate the anisotropic EM behavior of CNFs at different irradiation angles in the sub-terahertz band. ZnO coated the surface of fiber wall comprehensively in the form of nano-scale. The results show that after the surface modification, the composite sample exhibits a stable isotropic EM response in the sub-terahertz band of 500-750 GHz. Also, in the frequency range of 551-563 GHz (bandwidth: 12 GHz), ZnO not only acts as a stabilizer, but also enhances the absorption performance of the original CNFs by 6%, which is up to 92%. In the frequency range of 660-690 GHz (bandwidth: 30 GHz), the composite sample and the pure CNFs sample have similar wave absorption performance with about 75%, the maximum difference is less than 5%, and the minimum is about 2.6%.

SiCN thin film is one of the most attractive silicon-based materials due to its excellent electrical, mechanical and optical properties. In this study, SiCN thin films have been prepared by the radio frequency reactive magnetron sputtering method under different sputtering power, pressure, and substrate temperature. The microstructure, morphology, and the optical and field emission properties of SiCN thin films were performed. The results indicated that the high-quality SiCN thin films have been successfully prepared and it is proved that these properties can be tailored by the preparation conditions. A main near ultraviolet light emission line at around 370 nm in SiCN thin films makes it suitable for the development of optoelectronic devices. This study can provide novel guidance for the controlled preparation of high-quality SiCN thin films by magnetron sputtering.

Textile Reinforced Cementitious (TRC) sandwich technology generate lightweight elements with satisfactory loadbearing capacity. The non-corrosive nature of the textiles allows for concrete cover reductions, and therefore energy savings and lower carbon emissions when compared to a steel reinforced concrete sandwich, or steel reinforced concrete elements. However, due to its composite nature, TRC sandwich elements have a complex damage behavior, and bad interlaminar bond, might cause premature debonding, and drastically reduce the loadbearing capacity of the composite. Non-Destructive Testing (NDT) Techniques allow to inspect and monitor structural elements without affecting their behavior. In this study, MMW Spectrometry, Acoustic Emission, and Digital Image Correlation are used simultaneously to monitor quasi static four-point bending tests of TRC sandwich panels, and similar elements with an artificially destroyed interlaminar bond.

As the fabrication scale of graphene continues to expand, the limitations of existing mass characterization techniques such as Raman spectroscopy, AFM, and other microscopic characterization techniques for large-scale homogeneity characterization of graphene films become more and more prominent. Although the line-shaped defects (primarily grain boundaries and folds) distributed on the graphene film can be observed using the above techniques, it is difficult to comprehensively evaluate their distribution state on the entire film surface using these instruments. Based on this background, the author’s group has been aiming at the above problems by combining terahertz vector network analysis technology with the detection of large-area homogeneity of graphene films and quantitative characterization of line-shaped defects on the film surface, to explore a quality inspection technology that can be used in the production line of graphene films. The results demonstrate that the terahertz transverse electric (TE) wave is extremely sensitive to the variation of local thickness and electrical conductivity, which can be used in the homogeneity testing for the graphene; distributed line-shaped defects on graphene surface can exhibit anisotropic EM behavior with respect to THz TE waves, which can be exploited to identify the defect distribution states.

A Vector Network Analyzer (VNA) is an indispensable piece of equipment for the electromagnetic characterization of materials. With continuous development, the testing frequency band of the VNA has entered the terahertz domain. Previous studies have shown that carbon nanofibers (CNFs) prepared by the vapor method have excellent absorbing characteristics for both the microwave and the millimeter wave. This study is the first to characterize CNFs using a VNA in the 500–750 GHz band. The results show that CNFs with a random orientation distribution have an obvious polarization-sensitive absorption behavior in the 500–750 GHz band test, and this effect also causes a phenomenon of polarized reflection. As a comparison, the CNF sample was also tested in the W-band by the same test method. However, the result tested in the W-band showed a strong absorbing characteristic without any polarization response. The mechanism of the above phenomena was analyzed from the perspective of crystal growth and the principle of the antenna and polarizer. For further exploration and proof, CST Microwave Studio was used for the first time to model and simulate CNFs according to the actual parameters of the CNF sample.

This review presents an overview of previously reported non-invasive intra-abdominal pressure (IAP) measurement techniques. Each section covers the basic physical principles and methodology of the various measurement techniques, the experimental results, and the advantages and disadvantages of each method. The most promising non-invasive methods for IAP measurement are microwave reflectometry and ultrasound assessment, in combination with an applied external force.

Background:: Synthetic compounds with pharmaceutical applications in brain disorders are daily designed and synthesized, with well first effects but also seldom severe side effects. This imposes the search for alternative therapies based on the pharmaceutical potentials of natural compounds. The natural compounds isolated from various plants and arthropods venom are well known for their antimicrobial (antibacterial, antiviral) and antiinflammatory activities, but more studies are needed for a better understanding of their structural and pharmacological features with new therapeutic applications. Objectives:: Here we present some structural and pharmaceutical features of natural compounds isolated from plants and arthropods venom relevant for their efficiency and potency in brain disorders. We present the polytherapeutic effects of natural compounds belonging to terpenes (limonene), monoterpenoids (1,8-cineole) and stilbenes (resveratrol), as well as natural peptides (apamin, mastoparan and melittin). Methods:: Various experimental and in silico methods are presented with special attention on bioinformatics (natural compounds database, artificial neural network) and cheminformatics (QSAR, drug design, computational mutagenesis, molecular docking). Results:: In the present paper we reviewed: (i) recent studies regarding the pharmacological potential of natural compounds in the brain; (ii) the most useful databases containing molecular and functional features of natural compounds; and (iii) the most important molecular descriptors of natural compounds in comparison with a few synthetic compounds. Conclusion:: Our paper indicates that natural compounds are a real alternative for nervous system therapy and represents a helpful tool for the future papers focused on the study of the natural compounds.

The grown interest in healthcare applications has made biomedical engineering one of the fastest growing disciplines in recent years. Photoplethysmography (PPG) has gained popularity in recent years due to its versatility for noninvasive monitoring of vital signs such as heart rate, respiratory rate, blood oxygen saturation and blood pressure. In this work, an adjustable PPG-based educational device called PPG EduKit, which aims to facilitate the learning of the PPG technology for a wide range of engineering and medical disciplines is proposed. Through the use of this educational platform, the PPG signal can be understood, modified and implemented along with the extraction of its relevant physiological information from a didactic, intuitive and practical way. The PPG Edukit is evaluated for the extraction of physiological parameters such as heart rate and blood oxygen level, demonstrating how its features contribute to engineering and medical students to assimilate technical concepts in electrical circuits, biomedical instrumentation, and human physiology.

Textile Reinforced Cementitious (TRC) composites have gained recent attention due to several advantages compared to traditional steel-reinforced concrete, such as concrete usage reductions and design freedom. The implementation of this technology on a sandwich design offers light-weight and slender structural elements with superior mechanical performance. Despite their advantages, they exhibit a complicated structural and fracture pattern rendering their monitoring essential, as only detailed information on the damage modes will lead to understanding their failure behaviour. This review paper reports on NDTs’ application, working principle and configuration, performance and accuracy. Potential future lines of research and advances are discussed.

Zinc oxide (ZnO), a wide direct band gap semiconductor, has attracted extensive attention for its potential optoelectronic applications, such as coherent ultraviolet light emitters. Pure one-dimensional ZnO, structures such as nanorods and nanowires, etc. inevitably have some crystal defects, which makes them to emit not only in the ultraviolet region but also in the visible range. Photoluminescent ZnO‑carbon nanocomposites are an emerging class of nanomaterials that has spurred a lot of interests due to its attractive optical properties. It has been shown that these composite structures yield an enhanced ultraviolet to visible emission ratio due to improved surface plasmon emission and a new defect emission mechanism. Hence, a novel one-dimensional structure of ZnO and carbon nanofibers composite material has been designed and prepared. The scaly ZnO is completely coated with carbon nanofibers. This new composite structure has strong ultraviolet emission photoluminescence characteristics in combination with low visible emission.

We propose a novel strategy for applying compressed sensing (CS) to stepped frequency continuous wave synthetic aperture radars. The measurements are performed by adhering to a sequential measurement strategy. The sensor autonomously adapts, on the fly, the number of samples needed to reconstruct the reflectivity function and guarantees an imposed reconstruction quality. The measurements obtained at the previous scanning positions are added as side information into the reconstruction of the reflectivity function sensed by the radar at the current radar position. The algorithm attributes autonomous weights to each of these side information depending on the similarity with the signal to reconstruct. This approach is tested and evaluated on a series of simulated and real through-the-wall imaging radar measurements for detecting static human targets hidden behind a wall. The experiments first prove that the frequency sampling rate can be decreased far below the bound obtained by the common CS approach and, second, that the algorithm allows determining an accurate upper bound for the reconstruction error, and thus to autonomously decide online on the number of samples.

In the study of the blue-violet emission properties of SiCN thin films, the emission intensity depends on the crystal structure of thin films. The annealing process is widely used in the preparation process of thin films as one of the effective means to remove defects and improve crystal quality. In this study, SiCN thin films were prepared by RF magnetron sputtering method utilizing sintered silicon nitride and graphite targets on Si/SiO2 substrates. Then, the samples were separately annealed from 600 to 1000℃ with an argon ambient for 30 min to optimize the photoluminescence performance of the blue-violet emission. The characterization results of XRD spectra show that the crystallinity of the SiCN sample with 900 °C annealing temperature is the best. The chemical bonds, and the surface morphology of the samples changed greatly after annealing. The RMS roughness of the SiCN samples increased from 1.9 nm to 20.19 nm before and after annealing at 900 °C. Also, the results of PL spectra show that the intensity of blue-violet emission at 365 nm reinforced 28.6 times after annealing at 1000 °C. It makes the SiCN film be a candidate of phosphor for blue-violet LEDs.

The mechanical properties of Textile Reinforced Cementitious (TRC) composites have been extensively investigated in recent years. This material is constituted by a fine-grained cementitious matrix and a continuous textile reinforcement, a combination that has proven to be a lightweight, durable, and sustainable alternative for reinforced concrete. TRC is capable of generating curved slender components, offering the versatility to produce complex geometries not previously possible with reinforced concrete. The mechanical behavior and durability of these materials are highly affected by manufacturing and curing conditions. Non-Destructive Techniques (NDT’s) can provide a powerful reliable tool to monitor early age TRC without affecting nor compromising its properties. Along this manuscript, in order to provide an accurate assessment on the TRC mechanical and physical changes occurring during curing, Ultrasound Wave Reflection (UWR), Ultrasound Pulse Velocity (UPV) and Millimeter Wave (MMW) spectrometry are combined in an attempt to exploit the capabilities of elastic and electromagnetic waves for material characterization and monitoring. Experimental results evidence that UPV effectively monitors the development of stiffness in the material, while MMW spectrometry is more sensitive to evaporation of water and chemical reactions involved in the hydration of cement. Additionally, the applicability and resolution of these two contact and non-contact (US and MMW Spectrometry) techniques are discussed.

The tunability of graphene’s surface conductivity attracts tremendous interests in electromagnetic applications. This proposing feature enables graphene one of the ideal materials for reconfigurable antenna designs. In this paper, a new dipole antenna with two integrated graphene sheets operating in terahertz frequency is proposed and its reconfiguration of radiation properties is investigated. The two graphene sheets are deposited at the feeding positions of the two dipole arms, which increases the tunable freedoms of the dipole antenna’s impedance up to two degrees. The tunable two-degree freedom of the dipole antenna enables antenna’s operating frequency reconfigurable in a wide frequency range from 0.65 to 1 THz, and total radiation efficiency change from 13% to 89% when graphene chemical potential is electrically tuned from 0 eV to 0.5 eV. At 1 THz frequency, the realistic gain can be tuned from 1.6 dB to -8.7 dB. The more than 10 dB difference of the realistic gain makes the dipole antenna switchable. The fancy reconfigurable properties of the dipole antenna can be applied for multi-functional wireless THz systems and beam-forming THz antenna arrays.

This paper reports on the performance of a sub-THz liquid sensor tool coupled to a microfluidic platform. Non-invasive, non-destructive and on-line measurements are demonstrated for the determination of ethanol concentration and for controlling via micromixer device. We have developed a label-free chemical sensing methodology coupling a sub-terahertz sensor technology in microfluidic devices fabricated on glass and polydimethylsiloxane. The concept of sensor in micromixer applications operating at 60 GHz for known ethanol concentration ranging 0% to 100%, with a corresponding dynamic range of 2.79dB. The sensor allowed establishing the correlation between the mass flow rate and the ethanol concentration in the microfluidic system, where two-stream lines form the mixture in laminar flows, with Reynolds number < 13.54 and Peclet number > 25700. We demonstrated on-line sensing and linear control of ethanol concentration on demand with a small variation of 0.32% (v/v) between measured and required ethanol concentration.

Controlling the number of graphene layers is crucial in graphene synthesis for the development of graphene-based electronics. Numerous investigations have found that a reasonably designed binary alloy can effectively overcome the defects of pure metal and activate the self-limited growth of a monolayer of graphene. Graphene films were prepared on the Ni@Cu substrate by a chemical vapor deposition method. Ni@Cu is a novel Cu based substrate whose surface is alloyed with Ni atoms. In this paper, the advantages of graphene film synthesis on this new substrate were demonstrated through experiments, including the influence of the fast cooling process on the growth of graphene film, the influence of the proportion of Ni on the growth thickness of graphene film, and the transfer process of graphene film from this substrate.

Millimeter (mm) waves are of interests to monitor the properties of interest (POIs) of food products which are opaque for optical and infrared frequencies as they not suffer from all the atomic and intermolecular absorption processes situated in the latter bands of the Electromagnetic (EM) spectrum. They also offer a higher penetration depth into water containing products than the IR domain. With respect to the microwave domain, they are less perturbed by ionic contributions of food products, hydration shell effects and finally they offer a higher spatial resolution compared to microwaves. In the considered mm-wave frequency range, the dipole moment of free water molecules plays a dominant role compared to the other constituents, hence the electromagnetic interaction depends mainly on the amount and phase state of free water present in food products. These features make mm-wave based sensors an appealing alternative for monitoring and quality control of food processes. However, the effectiveness of mm-wave sensing solutions has not yet been explored in the food industry. In this paper, we present a real time, contactless and non-destructive sensor methodology based on mm-waves to monitor food processes. An analytical model is developed to estimate the dielectric properties of food products with varying POIs and to establish the relation between the mm-wave sensor's output and the POIs. A drying and freezing process of potato slabs are monitored by measuring the transmission and reflection coefficients by means of mm-wave sensors. The theoretical and experimental results are compared and validated. It will be proven that mm-wave based sensors are a promising real time, contactless and non-destructive monitoring tool for food quality control.

Weighted Laguerre finite-difference time-domain (Laguerre-FDTD) method is an efficient and unconditionally stable time-domain numerical method. The complex frequency-shifted perfectly matched layer (CFS-PML) is the main absorbing boundary condition in the Laguerre-FDTD method. The implementations of CFS-PML in the Laguerre-FDTD method, which have been reported, include the use of auxiliary variables and auxiliary differential equations. These implementations make CFS-PML sensitive to its parameters and timescale parameter s of weighted Laguerre polynomials and result in potential instability and poor absorption issues in numerical simulations. In this paper, we proposed an efficient and stable implementation of CFS-PML based on recursive convolution in the Laguerre-FDTD method. The accuracy of the proposed implementation is theoretically validated. Its numerical dispersion is theoretically derived for choosing the key parameters of CFS-PML in the Laguerre-FDTD scheme. The numerical dispersion demonstrates that the timescale factor s needs to match the simulated signal frequency and the CFS-PML parameter $\alpha $ is chosen as $0.5s\varepsilon _{0}$ to obtain the minimum dispersive error. Numerical examples validate the theoretical predictions and verify that the proposed implementation of CFS-PML is robust and retains the advantages of CFS-PML in classical FDTD method, such as effectively absorbing evanescent as well as guided waves. It requires nonsplits of electromagnetic field components, no auxiliary variables, and no modifications when applying it to inhomogeneous, lossy, and dispersive media. The CFS-PML formulas can directly be converted into computer codes of the Laguerre-FDTD method.

Characterizing and understanding carbon nanotube (CNT)-based polymer composites plays a crucial role for the ability to customize their properties. The (an)isotropy of CNT networks inside a composite can have significant effects on the final material's properties. However, characterizing the (an)isotropy of seemingly random CNT networks can be difficult using standard techniques. In this letter, we show that terahertz polarization sensitive measurements can provide a reliable, noninvasive and fast way of identifying anisotropy in seemingly homogenous CNT networks as based on criteria by standard techniques.

The development of millimeter-wave (mm-wave) technology has enabled the study of bio-molecular interactions by means of electromagnetic waves with frequencies between 30 and 300 GHz. In this study, an attempt has been made to exploit the possibility of mm-wave technology as alternative detection technique for liquid chromatographic (LC) systems. The goal is to design and fabricate a label-free mmwave detector that is compatible with LC systems. As proof-of-concept experiments, the UV absorbing compounds praziquantel and trans-stilbene-oxide as well as a non-UV absorbing compound sorbitol are injected in an open capillary as well as a capillary with stationary phase and measured by both mm-wave and UV detectors. The in-house developed mm-wave detector is capable of detecting all compounds without the need for labelling. Although the detection limit of such detector still needs to be verified and occasionally improved in the future, it already shows great potential as an additional detection technique for LC systems. for LC systems.

Transient Radar Method (TRM) was recently proposed as a novel contact-free method for the characterization of multilayer dielectric structures including the geometric details. In this paper, we discuss and quantify the intrinsic and systematic errors of TRM. Also, solutions for mitigating these problems are elaborated extensively. The proposed solution for error correction will be applied to quantify experimentally the thickness of several single-layer dielectric structures with thicknesses varying from larger to smaller than the wavelength. We will show how the error correction method allows sub-wavelength thickness measurements around &lambda, /5.

Zinc oxide (ZnO), a wide direct band gap semiconductor, has attracted extensive attention for its potential optoelectronic applications, such as coherent ultraviolet light emitters. Pure one-dimensional ZnO, structures such as nanorods and nanowires, etc. inevitably have some crystal defects, which makes them to emit not only in the ultraviolet region but also in the visible range. Photoluminescent ZnO‑carbon nanocomposites are an emerging class of nanomaterials that has spurred a lot of interests due to its attractive optical properties. It has been shown that these composite structures yield an enhanced ultraviolet to visible emission ratio due to improved surface plasmon emission and a new defect emission mechanism. Hence, a novel one-dimensional structure of ZnO and carbon nanofibers composite material has been designed and prepared. The scaly ZnO is completely coated with carbon nanofibers. This new composite structure has strong ultraviolet emission photoluminescence characteristics in combination with low visible emission.

The dispersion equation for waveguide modes of rectangular metal waveguides containing a dielectric buffer/graphene/air gap layered structure has been derived in the approximation of perfectly conducting metal waveguide walls. Dispersion dependences of TE0m modes for sub-terahertz frequencies were analysed against buffer layer thickness and Fermi energy level of graphene electrons. For the first time, it is demonstrated that the waveguide modes can be substantially modulated by tuning the electron Fermi energy level in graphene, especially near the regions of strong waveguide mode modifications. This enables the potential for future designs of amplitude and phase modulators for sub-THz waves in metal waveguides filled with an integrated graphene structure.

In this paper, ZnO films were deposited on the surface of few-layer graphene films by RF magnetron sputtering and its photoluminescence performance was studied. Large-area few-layer graphene films were prepared on a Cu substrate by CVD. To improve the crystalline quality and c-axis preferred growth orientation of ZnO films, we systematically optimized the process parameters (RF power, working pressure, substrate temperature, the flow ratio of Ar and O2) of growing ZnO on graphene films. After optimizing the growth process of ZnO on the graphene surface, the enhancement effect of graphene film on the PL properties of the ZnO layer was studied. We explored the influence of ZnO thickness on the PL performance. On the one hand, the optimal process parameters of growing ZnO on the surface of graphene films by magnetron sputtering were investigated; on the other hand, the sputtering time was optimized to make the composite films have the strongest UV emission performance with the lowest visible range.

Graphene-based terahertz (THz) devices, such as modulators, detectors, and absorbers, play important roles in terahertz applications due to graphene’s effectively tunable terahertz absorption. The features of these terahertz devices are greatly related to the THz absorption of graphene. However, the monolayer graphene shows limited absorption to terahertz waves. In this paper, we demonstrated a new graphene composite with a double circular metal ring array deposited on graphene to enhance the absorption. The graphene composite consists of a double circular metal ring array, a monolayer graphene, silicon dioxide, and silicon substrates. The double circular metal ring array locally enhances the electromagnetic field on graphene and further increases graphene’s absorption. It shows that the peak absorption of the proposed graphene composite is increased to 95% for graphene Fermi level 0 eV at room temperature, which is more than seven times larger than that of the graphene composite without the double circular metal ring array. The enhanced terahertz absorption of the proposed graphene composite shows the potential ability of improving modulation depth and insertion loss of a THz reflection modulator.

Ground penetrating radars (GPRs) for mine detection can profit from the many advantages that compressed sensing can offer through random subsampling in terms of hardware simplification, reduced data volume and measurement time, or imagery simplification. An intrinsic antenna-ground model is used, canceling the undesired reverberation effects and the very strong reflection from the air–soil interface, producing higher detection rates, or even unmasking shallowly buried mines. Extensive Monte Carlo simulations on real GPR measurements (800–2200 MHz) show an increase in the probability of detection, yielding globally promising exploitable results, whenever the principal component analysis technique is used a as preconditioner, as well as providing lower random subsampling bounds for frequency and spatial measurements (cross range), whether applied individually or combined.

Passive radars based on DVB-t transmissions can benefit from the outstanding advantages that compressed sensing offers in terms of less acquired data, hence potentially reducing hardware requirements, and achieving reconstructed scene simplification. Adequate signal modeling enables sparse scene reconstructions which can be complemented with side information from previously known scene conditions and, thus, further reducing the amount of required data to achieve similar performances or even improve them.

The increased interest in the separation of peptides, proteins, immunoglobulins, and polynucleotides, led to an increased demand for appropriate analytical methodologies and instrumentation. CE, because of its unique separation mechanism and high efficiency, is frequently used in the analysis of those molecules. In this study, a CE method for the separation of six angiotensin analogues was developed in the first step. In the second step, the method was transferred to a CE instrument of another brand, taking into account guidelines defined earlier about the interinstrumental transfer of CE methods. Although previously successful, the application of these guidelines during this study was not able to maintain the baseline separation. Further research on the instrumental differences revealed that the electrical resistance on both instruments differed. At constant current, the electrical resistance, generated voltage, and separation efficiency on the Agilent instrument were lower than on the Beckman instrument. Increase of the electrical resistance, by reducing the capillary temperature, leads to an increased applied voltage and separation efficiency on the Agilent system. The guidelines developed earlier were, therefore, updated with an additional step equalizing the electrical resistances, which led to a successful interinstrumental analytical method transfer for the separation of six angiotensin derivatives.