Search Results (17)

Graphene nanoplatelets (GNPs)/epoxy composites have been fabricated via gravity molding. The electrical and thermal properties of the composites have been studied with variable GNP type (C300, C500, and C750, whose surface areas are ~300, 500, and 750 m²/g, respectively), GNP loading (5, 10, 12, and 15 wt.%), and dispersion time via ultrasonication (0, 30, 60, and 120 min). By increasing the time of sonication of the GNP into the epoxy matrix, the electrical conductivity decreases, which is an effect of GNP fragmentation. The best results were observed with 10–12% loading and a higher surface area (C750), as they provide higher electrical conductivity, thereby preserving thermal conductivity. The influence of sonication over electrical conductivity was further analyzed via the study of the composite morphology by means of Raman spectroscopy and X-ray diffraction (XRD), providing information about the aspect ratio of GNPs. Moreover, electromagnetic shielding (EMI) has been studied up to 4 GHz. Composites with C750 and 120 min ultrasonication show the best performance in EMI shielding, influenced by their higher electrical conductivity. Full article

As a high-end medical technology, high-intensity focused ultrasound (HIFU) is widely used in cancer treatment and ultrasonic lithotripsy technology. The acoustic output level and safety of ultrasound treatments are closely related to the accuracy of sound pressure measurements. Heterodyne laser interferometry is applied to the measurement of ultrasonic pressure owing to its characteristics of non-contact, high precision, and traceability. However, the upper limit of sound pressure measurement is limited by the bandwidth of the interferometer. In this paper, a high-bandwidth heterodyne laser interferometer for the measurement of high-intensity focused ultrasound pressure is developed and tested. The optical carrier with a frequency shift of 358 MHz is realized by means of an acousto-optic modulator. The selected electrical devices ensure that the electrical bandwidth can reach 1.5 GHz. The laser source adopts an iodine frequency-stabilized semiconductor laser with high-frequency spectral purity, which can reduce the influence of spectral purity on the bandwidth to a negligible level. The interference light path is integrated and encapsulated to improve the stability in use. An HIFU sound pressure measurement experiment is carried out, and the upper limit of the sound pressure measurement is obviously improved. Full article

In order to meet the increasing demand of non-destructive testing (NDT) in engineering practice, a continuous terahertz NDT platform based on linear scanning has been developed, with a center frequency of 154 GHz and a bandwidth of 56 GHz. This system combines frequency modulation continuous wave (FMCW) radar technology with a continuous scanning structure, as well as a data acquisition platform to provide a non-contact detection method; this is highly efficient and compensates for the shortcomings of traditional methods such as microwave, X-ray, ultrasonic, and others in safety inspection and special detection. In addition, a signal processing method of spectral refinement and correction is proposed in this paper for accurate thickness measurement. The results show that the method has a high accuracy for ABS, PVC, and ceramic matrix composites. By extracting the characteristic parameters, the detection and imaging of prefabricated defects, such as debonding and bubbles in composite materials, have been successfully achieved. This helps to evaluate the internal state of the inspected object more intuitively and further meets the requirements of industrial NDT. Full article

The expanded uncertainty of the measured Brillouin scattering shift frequencies is essential in assessing the measurements of parameters of various materials. We describe the general operation principles of a Brillouin light scattering (BLS) spectrometer with a high-power laser and a scanning tandem Fabry–Pérot interferometer (TFPI) for material characterization. Various uncertainty components have been analyzed for the BLS spectrometer following the Guide to the Expression of Uncertainty in Measurement (GUM). The expanded relative uncertainty in the measured Brillouin frequency shift of 15.70 GHz for polymethyl methacrylate (PMMA) was estimated to be 0.26%. The calculated Brillouin frequency shift (based on material properties of PMMA) was determined to be 15.44 GHz with expanded relative uncertainty of 2.13%. It was shown that the measured and calculated Brillouin frequency shifts for PMMA agree within their expanded uncertainties. The TFPI-based BLS spectrometer can be used to measure the longitudinal modulus of materials with an expanded uncertainty of 1.9%, which is smaller than that of the ultrasonic velocity-based method (estimated to be 2.9%). Full article

Accurate measurement of elastic constants in thin films is still an important issue to understand the scale behavior of nanosized materials. In the present study, we introduced an advanced non-destructive method, picosecond ultrasonics (PU), for measuring the out-of-plane elastic modulus of thin chromium (Cr) films. The femtosecond light pulse is focused on the Cr film to excite the longitudinal acoustic phonons (LAP), which propagate along the thickness direction and repeat reflections inside the Cr film. Then, the propagation/distribution of LAP is detected by the time-delayed probe light pulse through the photoelastic effect. Therefore, we can determine the out-of-plane modulus by measuring the periodic pulse echoes or the breathing mode vibrations within the Cr film. For most Cr films, the determined modulus is smaller than the corresponding bulk value and decreases with the decreasing thickness, while for some Cr films, it closes and may exceed the bulk value. This work describes the thickness-dependent elasticity of thin Cr films and provides evidence of the stiffness enhancement in Cr films on the Si substrate. In addition, since LAP with central frequency up to 310 GHz is excited in Cr films on the SiO₂ substrate, we also demonstrate the potential of Cr films as high-frequency photoacoustic transducers. Full article

Electromagnetic waves show rapid development in electronics, telecommunications, and the military. One of the efforts to overcome the effects of electromagnetic interference is by developing microwave-absorbing materials. Barium hexaferrite is the best candidate for development as an absorber material. Microwave absorption in barium hexaferrite can be increased through Mg-Al doping and reducing the particle size. This study aimed to analyze sonication parameters to reduce the particle size by combining destruction methods using mechanical alloying followed by high-power ultrasonic irradiation. Barium hexaferrite was synthesized through mechanical alloying by mixing stoichiometric BaCO₃, Fe₂O₃, Al₂O₃, and MgO (Sigma-Aldrich p.a 99%) (Mg-Al 0.4%wt). The samples continued the sintering process at 1200 °C for 2 h to grow crystal embryos. The optimal parameters for ultrasonic destruction were using a transducer:reactor diameter ratio of 1:10, a particle density of 5 g/250 mL, and adding a non-ionic surfactant of 0.01% at an amplitude of 55% and a sonication time of 8 h. These methods resulted in the saturation magnetization of 18.50 emu/g and a coercivity of 0.08 Tesla. The reduction in the particle size of BHF doped with Mg-Al was successfully up to 21 nm, resulting in a reflection loss of up to −40.8697 dB at 11.896 GHz (x-band, 8–12 GHz). The BHF nanoparticles doped with Mg-Al effectively absorbed up to 99.99% electromagnetic waves. Full article

Water being one of the foremost needs for human survival, conservation, and management of the resource must be given ultimate significance. Water demand has increased tremendously all over the world from the past decade due to urbanization, climatic change, and ineffective management of water. The advancement in sensor and wireless communication technology encourages implementing the IoT in a wide range. In this study, an IoT-based architecture is proposed and implemented for monitoring the level and quality of water in a domestic water tank with customized hardware based on 2.4 GHz radiofrequency (RF) communication. Moreover, the ESP 8266 Wi-Fi module-based upper tank monitoring of the proposed architecture encourages provide real-time information about the tank through internet protocol (IP). The customized hardware is designed and evaluated in the Proteus simulation environment. The calibration of the pH sensor and ultrasonic value is carried out for setting the actual value in the prototype for obtaining the error-free value. The customized hardware that is developed for monitoring the level and quality of water is implemented. The real-time visualization and monitoring of the water tank are realized with the cloud-enabled Virtuino app. Full article

Superparamagnetic ZnFe₂O₄ spinel ferrite nanoparticles were prepared by the sonochemical synthesis method at different ultra-sonication times of 25 min (ZS25), 50 min (ZS50), and 100 min (ZS100). The structural properties of ZnFe₂O₄ spinel ferrite nanoparticles were controlled via sonochemical synthesis time. The average crystallite size increases from 3.0 nm to 4.0 nm with a rise of sonication time from 25 min to 100 min. The change of physical properties of ZnFe₂O₄ nanoparticles with the increase of sonication time was observed. The prepared ZnFe₂O₄ nanoparticles show superparamagnetic behavior. The prepared ZnFe₂O₄ nanoparticles (ZS25, ZS50, and ZS100) and reduced graphene oxide (RGO) were embedded in a polyurethane resin (PUR) matrix as a shield against electromagnetic pollution. The ultra-sonication method has been used for the preparation of nanocomposites. The total shielding effectiveness (SE_T) value for the prepared nanocomposites was studied at a thickness of 1 mm in the range of 8.2–12.4 GHz. The high attenuation constant (α) value of the prepared ZS100-RGO-PUR nanocomposite as compared with other samples recommended high absorption of electromagnetic waves. The existence of electric-magnetic nanofillers in the resin matrix delivered the inclusive acts of magnetic loss, dielectric loss, appropriate attenuation constant, and effective impedance matching. The synergistic effect of ZnFe₂O₄ and RGO in the PUR matrix led to high interfacial polarization and, consequently, significant absorption of the electromagnetic waves. The outcomes and methods also assure an inventive and competent approach to develop lightweight and flexible polyurethane resin matrix-based nanocomposites, consisting of superparamagnetic zinc ferrite nanoparticles and reduced graphene oxide as a shield against electromagnetic pollution. Full article

The increasing needs of free licensed frequency bands like Industrial, Scientific, and Medical (ISM), Wireless Local Area Network (WLAN), and 5G for underwater communications required more bandwidth (BW) with higher data transferring rate. Microwaves produce a higher transferring rate of data, and their associated devices are smaller in comparison with sonar and ultrasonic. Thus, transceivers should have broad BW to cover more of a frequency band, especially from ultra-wideband (UWB) systems, which show potential outcomes. However, previous designs of similar work for underwater communications were very complicated, uneasy to fabricate, and large. Therefore, to overcome these shortcomings, a novel compact elliptical UWB antenna is designed to resonate from 1.3 to 7.2 GHz. It is invented from a polytetrafluoroethylene (PTFE) layer with a dielectric constant of 2.55 mm and a thickness of 0.8 mm. The proposed antenna shows higher gain and radiation efficiency and stability throughout the working band when compared to recent similarly reported designs, even at a smaller size. The characteristics of the functioning antenna are investigated through fluid mediums of fresh-water, seawater, distilled water, and Debye model water. Later, its channel capacity, bit rate error, and data rate are evaluated. The results demonstrated that the antenna offers compact, easier fabrication with better UWB characteristics for underwater 5G communications. Full article

The measurement and analysis of the arterial pulse wave provides information about the state of vascular health. When measuring blood pressure according to Riva-Rocci, the systolic and diastolic blood pressure is measured non-invasively with an inflatable pressure cuff on the upper arm. Today’s blood pressure monitors analyze the pulse wave in reference to the rising or falling cuff pressure. With the help of additional pulse wave analysis, one can determine the pulse rate and the heart rate variability. In this paper, we investigated the concept, the construction, and the limitations of ultrawideband (UWB) radar and continuous wave (CW) radar, which provide continuous and non-invasive pulse wave measurements. We integrated the sensors into a complete measurement system. We measured the pulse wave of the cuff pressure, the radar sensor (both UWB and CW), the optical sensor, and ultrasonic Doppler as a reference. We discussed the results and the sensor characteristics. The main conclusion was that the resolution of the pulse radar was too low, even with a maximum bandwidth of 10 GHz, to measure pulse waves reliably. The continuous wave radar provides promising results for a phantom if adjusted properly with phase shifts and frequency. In the future, we intend to develop a CW radar solution with frequency adaption. Full article

Pillar-shaped Gallium arsenide (GaAs) micromechanical resonators are fabricated, and the feasibility to measure the inside of the pillars in the axial direction with laser-induced GHz ultrasound based on picosecond ultrasonics is tested. Measurements on the pillars with head sizes in the µm range show excellent agreement with theoretical predictions. Full article

Monitoring the evolution of snow on the ground and lake ice—two of the most important components of the changing northern environment—is essential. In this paper, we describe a lightweight, compact and autonomous 24 GHz frequency-modulated continuous-wave (FMCW) radar system for freshwater ice thickness and snow mass (snow water equivalent, SWE) measurements. Although FMCW radars have a long-established history, the novelty of this research lies in that we take advantage the availability of a new generation of low cost and low power requirement units that facilitates the monitoring of snow and ice at remote locations. Test performance (accuracy and limitations) is presented for five different applications, all using an automatic operating mode with improved signal processing: (1) In situ lake ice thickness measurements giving 2 cm accuracy up to ≈1 m ice thickness and a radar resolution of 4 cm; (2) remotely piloted aircraft-based lake ice thickness from low-altitude flight at 5 m; (3) in situ dry SWE measurements based on known snow depth, giving 13% accuracy (RMSE 20%) over boreal forest, subarctic taiga and Arctic tundra, with a measurement capability of up to 3 m in snowpack thickness; (4) continuous monitoring of surface snow density under particular Antarctic conditions; (5) continuous SWE monitoring through the winter with a synchronized and collocated snow depth sensor (ultrasonic or LiDAR sensor), giving 13.5% bias and 25 mm root mean square difference (RMSD) (10%) for dry snow. The need for detection processing for wet snow, which strongly absorbs radar signals, is discussed. An appendix provides 24 GHz simulated effective refractive index and penetration depth as a function of a wide range of density, temperature and wetness for ice and snow. Full article

In this paper, the influence of burial depth of crack on stress measurement of laser cladding coating with the critical refracted longitudinal wave (L_cr wave) was discussed based on the L_cr wave acoustoelastic effect. The regular rectangular slots with different depths that were used to simulate the burial crack in coating was based on the equivalent theory. The experimental system including an ultrasonic wave generator, digital oscilloscope (2.5 GHz sampling rate), and two L_cr wave transducers (2.5 MHz center frequency) was used to collect the L_cr wave under different tensile loads, and the L_cr wave was denoised by using wavelet analysis technology, then the fracture morphology was observed using SEM. The results show that after the denoising by wavelet analysis technology, the signal-to-noise ratio of L_cr wave becomes bigger and the mean square deviation of L_cr wave becomes smaller. When the tensile load is within the turning point load, the difference in time of flight between L_cr wave increases linearly as the tensile load increases, and the deviation of the experimental results becomes obvious as the tensile load increases. When the tensile load is the same, as the burial depth of the slot increases, the nominal L_cr wave acoustoelastic coefficient decreases and tends to be stable gradually. At last, the experimental results are discussed based on the L_cr wave acoustoelastic effect and deformation theory, and it is analyzed that the uneven deformation caused by the interface in coating, anisotropic microstructure, and the burial crack is considered as the main reason. Full article

Prior opto-mechanical techniques to measure vibrational frequencies of viruses work on large ensembles of particles, whereas, in this work, individually trapped viral particles were studied. Double nanohole (DNH) apertures in a gold film were used to achieve optical trapping of one of the smallest virus particles yet reported, PhiX174, which has a diameter of 25 nm. When a laser was focused onto these DNH apertures, it created high local fields due to plasmonic enhancement, which allowed stable trapping of small particles for prolonged periods at low powers. Two techniques were performed to characterize the virus particles. The particles were sized via an established autocorrelation analysis technique, and the acoustic modes were probed using the extraordinary acoustic Raman (EAR) method. The size of the trapped particle was determined to be 25 ± 3.8 nm, which is in good agreement with the established diameter of PhiX174. A peak in the EAR signal was observed at 32 GHz, which fits well with the predicted value from elastic theory. Full article

The global spread of bacterial resistance to antibiotics promotes a search for alternative approaches to eradication of pathogenic bacteria. One alternative is using photosensitizers for inhibition of Gram-positive and Gram-negative bacteria under illumination. Due to low penetration of visible light into tissues, applications of photosensitizers are currently limited to treatment of superficial local infections. Excitation of photosensitizers in the dark can be applied to overcome this problem. In the present work, dark antibacterial activity of the photosensitizer Rose Bengal alone and in combination with antibiotics was studied. The minimum inhibitory concentrations (MIC) value of Rose Bengal against S. aureus dropped in the presence of sub-MIC concentrations of ciprofloxacin, levofloxacin, methicillin, and gentamicin. Free Rose Bengal at sub-MIC concentrations can be excited in the dark by ultrasound at 38 kHz. Rose Bengal immobilized onto silicon showed good antibacterial activity in the dark under ultrasonic activation, probably because of Rose Bengal leaching from the polymer during the treatment. Exposure of bacteria to Rose Bengal in the dark under irradiation by electromagnetic radio frequency waves in the 9 to 12 GHz range caused a decrease in the bacterial concentration, presumably due to resonant absorption of electromagnetic energy, its transformation into heat and subsequent excitation of Rose Bengal. Full article