Design optimization of porous fibrous material for maximizing absorption of sounds under set frequency bands

In this paper, a methodology is proposed for designing porous fibrous material with optimal sound absorption under set frequency bands. The material is assumed to have a rigid frame and a hexagonal arrangement of fibers, and the analytical model derived by Johnson, Champoux and Allard (“JCA model”) is used to investigate the influences of the micro-structural parameters (fiber radius r and gap w) on sound absorption performance, and the macro-acoustic parameters used in JCA model is determined via finite element analysis for the hexagonal micro-structure. Moreover, a mathematical model is constructed to obtain the optimized micro-structure design, with fiber radius and gap as design parameters and average absorption performance of the porous fibrous material under set frequency band as target. Utilizing the constructed optimization model, the microstructure parameters are derived with optimal sound absorption under low frequency (20 ⩽ f < 500 Hz), medium frequency (500 ⩽ f < 2000 Hz) and high frequency (2000 ⩽ f < 15,000 Hz), respectively. On top of that, for a given thickness of porous fibrous material layer, the analytical relationship between fiber radius and optimal porosity under set frequency bands is constructed.     

Normal incidence sound transmission loss in impedance tube – Measurement and prediction methods using perforated plates

For the determination of the transmission loss of samples in an impedance tube, two different approaches is found in the literature, one based on determining the full transfer matrix (TM method) of the acoustic element, the other based on the wavefield decomposition theory (WD method). In this paper both methods are implemented and measured results are compared using samples which includes different types of perforated plates, also combined with porous material. Measurements are conducted in a tube of square cross section with dimensions 200 × 200 mm, thereby limiting the workable frequency range upwards to approximately 850 Hz. The main purpose of the paper is, however, to compare measured results with predictions using the transfer matrix method. For a bare plate with cylindrical apertures two models are compared as well; a “classical” one and another based on modeling the perforated plate as a porous material having a rigid frame. As for these transmission loss measurements, the two measurement approaches turn out to give identical results within the numerical accuracy. The fit between measured and predicted results are reasonably good with a maximum deviation mostly within 2 dB.     

High energy femtosecond OPA pumped by 1030 nm Yb:KGW laser.

We present a traveling-wave-type optical parametric amplifier (OPA) pumped at 1.03 μm by a Yb:KGW laser that produces tunable high-energy pulses of 6.5–4 μJ in the mid-infrared (mid-IR) region from 3.6 to 7 μm. Pumping with negatively chirped pulses generates nearly transform-limited (TL) mid-IR pulses of 300–330 fs length. Pumping with TL pulses of 200 fs not only decreases the output energy by a factor of 1.5, but also decreases the mid-IR pulse-length to 160 fs after additional compression. The compact and simple OPA setup is ideal for femtosecond infrared experiments in the fingerprint region.     

Thermoluminescence response of the larimar rocks

The aim of this paper is to evaluate the thermoluminescent (TL) response of a larimar, a variety of pectolite (NaCa₂Si₃O₈[OH]). It is a blue pectolite only found on the terrestrial crust of the province of Barahona, in the south-western region of the Dominican Republic. The larimar rock used in this study, presented a light-blue color with brown areas. X-ray powder diffractometry (XRD), showed that the light-blue portion of the rock is composed essentially by pectolite and the brown portion is composed by a mixture of minerals. Aliquots of 5 mg of light-blue portions were irradiated with gamma rays with doses from 10 to 10⁴ Gy and the TL glow curves were obtained from 50 to 400 °C. The glow curve showed a broad peak around 150 °C and a peak near 280 °C. Different pre-heat condition were used to remove the broad peak. The TL emission of the main peak appeared in the region of 580 nm. The TL response of the main peak showed a linear behavior up to 2500 Gy and a sub-linear behavior above this dose value. Studies of the 30 day fading effects in TL signal using a pre-heating temperature around 180 °C during 15 min were carried out and fading near 25% was observed.     

AC losses and transverse resistivity in filamentary MgB2 tape with Ti barriers

We measured and analyzed AC losses of MgB₂ tape with 19 filaments surrounded by Ti barriers and embedded in copper stabilization, exposed to external magnetic field with frequencies from 30 mHz up to 1.4 Hz and amplitudes up to 0.8 T at 4.2 K. Using the measured frequency dependence of the total AC losses we determined the contribution of hysteresis and coupling losses. The transverse resistivity determined from the coupling losses is considerably higher than that corresponding to the resistivity of copper stabilization before the tape processing due to diffusion of Ti. From the measured penetration field critical current densities were determined using results of theories for circular as well as rectangular filaments.     

Thermoluminescence response in gamma and UV irradiated Dy2O3 nanophosphor

Low temperature solution combustion method was employed to synthesize Dy₂O₃ nanophosphors using two different fuels (sugar and oxalyl dihydrazine (ODH)). Powder X-ray diffraction confirm pure cubic phase and the estimated particle size from Scherrer's method in sugar and ODH fuel was found to be 26 and 78 nm, respectively, and are in close agreement with those obtained using TEM and W–H plot analysis. SEM micrographs reveal porous, irregular shaped particles with large agglomeration in both the fuels. An optical band gap of 5.24 eV and 5.46 eV was observed for Dy₂O₃ for sugar and ODH fuels, respectively. The blueshift observed in sugar fuel is attributed to the particles size effect. Thermoluminescence (TL) response of cubic Dy₂O₃ nanophosphors prepared by both fuels was examined using gamma and UV radiations. The thermoluminescence of sugar used samples shows a single glow peak at 377 °C for 1–4 kGy gamma irradiations. When dose is increased to 5 kGy, two more shouldered peaks were observed at 245 and 310 °C. However, in TL of ODH used samples, a single glow peak at 376 °C was observed. It is observed that TL intensity is found to be more in sugar used samples. In UV irradiated samples a single glow peak at 365 °C was recorded in both the fuels with a little variation in TL intensity. The trapping parameters were estimated by different methods and the results are discussed.     

Effect of sodium chloride and food target properties on nonelectrostatic and electrostatic coating

Salts were coated on a variety of thick food targets. The best transfer efficiency, adhesion (>70%), and percent side coverage (100%) were obtained when small (<200 μm) and cohesive (Hausner ratio > 1.20) salt was used with electrostatic coating on targets with high a_w (>0.7), low resistivity (<9 × 10⁸ Ωm), and short charge decay time (<3.8 s). Shape of salt also affected the coating performance; porous cube provided significantly better transfer efficiency and adhesion than flake salt on some targets. There was no significant effect of KCl content on coating performance.     

Thermoluminescence,photoluminescence and EPR studies on Mn2+ activated yttrium aluminate (YAlO3) perovskite

Thermoluminescence (TL) measurements were carried out on undoped and Mn²⁺ doped (0.1 mol%) yttrium aluminate (YAlO₃) nanopowders using gamma irradiation in the dose range 1–5 kGy. These phosphors have been prepared at furnace temperatures as low as 400 °C by using the combustion route. Powder X-ray diffraction confirms the orthorhombic phase. SEM micrographs show that the powders are spherical in shape, porous with fused state and the size of the particles appeared to be in the range 50–150 nm. Electron Paramagnetic Resonance (EPR) studies reveal that Mn ions occupy the yttrium site and the valency of manganese remains as Mn²⁺. The photoluminescence spectrum shows a typical orange-to-red emission at 595 nm and suggests that Mn²⁺ ions are in strong crystalline environment. It is observed that TL intensity increases with gamma dose in both undoped and Mn doped samples. Four shouldered TL peaks at 126, 240, 288 and 350 °C along with relatively resolved glow peak at 180 °C were observed in undoped sample. However, the Mn doped samples show a shouldered peak at 115 °C along with two well defined peaks at ～215 and 275 °C. It is observed that TL glow peaks were shifted in Mn doped samples. The kinetic parameters namely activation energy (E), order of kinetics (b), frequency factor (s) of undoped, and Mn doped samples were determined at different gamma doses using the Chens glow peak shape method and the results are discussed in detail.     

Improvements to the Johnson–Allard model for rigid-framed fibrous materials

Measurements of the surface impedance and the physical parameters of seven glass wool samples and six polyester fibre samples with flow resistivities between 4100 and 69,900 Pa s m⁻² have been made. Comparisons of measured absorption coefficients and those predicted from the Johnson–Allard formulae using the measured and deduced physical parameters show discrepancies that exceed 20% for some samples and frequencies. By modifying the Johnson–Allard formula for effective density and by introducing a correction factor that is a function of flow resistivity based on data fitting, it has been found possible to improve the predictions. However, it has also been found that a similar modification of the formula for bulk modulus is necessary to reduce the discrepancies with data to below 5% in the frequency range between 800 Hz and 5 kHz.     

Thermoluminescence studies of thermally treated CaB4O7:Dy

Borate based thermoluminescence dosimeters (TLD) show high sensitivity and good TL characteristics. One of the promising material amongst the dosimeters is Dy doped CaB₄O₇. Spectrally resolved thermoluminescence of Dy doped CaB₄O₇ shows three glow peaks at about 50 °C, 240 °C and 380 °C, the intensity of the 240 °C glow peak being the maximum. All TL experiments were conducted on a high sensitivity TL spectrometer at Sussex University with a heating rate of 50 °C min^?1. Two main emissions associated with the Dy dopant are observed at ～480 and 580 nm. The samples were subjected to a series of treatments including excitation by X-rays and UV laser radiation. As part of the present research CaB₄O₇:Dy materials were subjected to two different heat treatments; quenching and slow cooling in order to investigate the changes in TL characteristics.     

Thermo,Iono and photoluminescence properties of 100 MeV Si7+ ions bombarded CaSiO3:Eu3+ nanophosphor

This paper reports on the thermo (TL), iono (IL) and photoluminescence (PL) properties of nanocrystalline CaSiO₃:Eu³⁺ (1–5 mol %) bombarded with 100 MeV Si⁷⁺ ions for the first time. The effect of different dopant concentrations and influence of ion fluence has been discussed. The characteristic emission peaks ⁵D₀→⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions was recorded in both PL (1×10¹¹–1×10¹³ ions cm^?2) and IL (4.16×10¹²–6.77×10¹² ions cm^?2) spectra. It is observed that PL intensity increases with ion fluence, whereas in IL the peaks intensity increases up to fluence 5.20×10¹² ions cm^?2, then it decreases. A well resolved TL glow peak at ～304 °C was recorded in all the ion bombarded samples at a warming rate of 5 °C s^?1. The TL intensity is found to be maximum at 5 mol% Eu³⁺ concentration. Further, TL intensity increases sub linearly with shifting of glow peak towards lower temperature with ion fluence.     

High pressure AC resistivity and compressibility study on Al2(WO4)3

The effect of pressure on the resistivity and compressibility on Al₂(WO₄)₃ has been investigated. AC resistivity measurements have shown that the resistance values are strongly frequency dependent and show an anomalous change at about 5 kbar. Compressibility measurements also show an inflection at about 5 kbar in the pressure derivative of the volume compression data, which is found to be reversible. Both the measurements indicate the occurrence of a reversible phase transformation in Al₂(WO₄)₃ at about 5 kbar.     

Re-Active Passive devices for control of noise transmission through a panel

Re-Active Passive devices have been developed to control low-frequency (<1000 Hz) noise transmission through a panel. These devices use a combination of active, re-active, and passive technologies packaged into a single unit to control a broad frequency range utilizing the strength of each technology over its best suited frequency range. The Re-Active Passive device uses passive constrained layer damping to cover relatively high-frequency range (>150 Hz), reactive distributed vibration absorber to cover the medium-frequency range (50–200  Hz), and active control for controlling low frequencies (<150 Hz). The actuator was applied to control noise transmission through a panel mounted in the Transmission Loss Test Facility at Virginia Tech. Experimental results are presented for the bare panel, and combinations of passive treatment, reactive treatment, and active control. Results indicate that three Re-Active Passive devices were able to increase the overall broadband (15–1000 Hz) transmission loss by 9.4 dB. These three devices added a total of 285 g to the panel mass of 6.0 kg, or approximately 5%, not including control electronics.     

Carrier transport properties in high resistivity polycrystalline CdZnTe material

The electrical properties of polycrystalline CdZnTe (Zn = 4%) having high resistivity (3.3 × 10⁹ Ω cm) were investigated by using the time-of-flight technique. We have found that the average drift mobility of as-deposited polycrystalline CdZnTe samples is 1.21 cm²/V s and the electron trapping time is 4.6 μs. In a comparison of annealed samples at different conditions, the variation of resistivity in polycrystalline CdZnTe is considered to be mainly related to the fluctuation of carrier concentration, which originates from the change of density in deep level.     

Low frequency properties of micro power generator using a gold electroplated coil and magnet

Micro power generating devices were fabricated by using a gold electroplated coil and a permanent magnet. The electrical power was generated when the magnet reciprocated on the fabricated electroplated coil. The output power was increased as a function of vibration frequency. A measurement system, which convert a rotational motion of a motor into a linear motion, was designed and fabricated. The purpose of this work is to develop the micro power generating devices which convert the ambient vibration or oscillating energy into useful electrical energy. With changing vibration frequency from 0.5 to 8 Hz, the generated power increased linearly. The generated voltage was 106 mV at 3 Hz and 198 mV at 6 Hz. After using the step up circuit, the measured voltage was 81 mV at 3 Hz and 235 mV at 6 Hz. From above the frequency of about 4.5 Hz, the gain obtained by using the quadrupler circuit becomes larger than the loss without using that circuit.     

Study of a new Lif:Mg,Cu,P formulation with enhanced thermal stability and a lower residual TL signal

This paper presents results obtained for a new LiF:Mg,Cu,P (HMCP) preparation with modified Mg and Cu concentrations. The shape of the HMCP glow curve shows minimal differences for annealing in the range from 523 to 543 K for 10 min. The thermoluminescence (TL) readout value remained stable when annealed in the range from 513 to 543 K for 10 min. The new formula allows heating of the material to higher temperatures than that originally employed for the well-known GR-200A dosemeter, practically without losses in sensitivity. The TL sensitivity is approximately half of that for the GR-200A, and still 29-fold greater than that for the TLD-100 dosemeter, and the residual signal is approximately five-fold lower than for the GR-200A. These results indicate that the new TL material shows enhanced thermal stability and a lower residual TL signal at a small TL sensitivity cost. The heat treatment temperatures are related to concentrations of Mg and Cu in LiF:Mg,Cu,P.     

Preparation and characterization of highly conducting and transparent Al doped CdO thin films by pulsed laser deposition

Highly conducting and transparent aluminum doped CdO thin films were deposited using pulsed laser deposition technique. The effect of growth temperature on structural, electrical, and optical properties was studied. It is observed that the film orientation changes from preferred (1 1 1) plane to (2 0 0) plane with increase in growth temperature. The electrical resistivity of the films was found to increase with increase in growth temperature. The low resistivity of 4.3 × 10⁻⁵ Ω cm and high transparency (∼85%) was obtained for the film grown at 150 °C. The band gap of the films varies from 2.74 eV to 2.84 eV.     

Boron-doped nanocrystalline silicon germanium thin films for uncooled infrared bolometer applications

In this paper, boron-doped nanocrystalline Si_0.78Ge_0.22:H thin film is assessed for use as resistive sensing layer in uncooled infrared bolometer applications. The silicon germanium thin films were deposited by PECVD (plasma enhanced chemical vapor deposition) through decomposition of silane, germane and diborane diluted with argon at substrate temperature of 230 °C. Under optimum deposition parameters, the sensing films with modulate electrical resistivity (<10⁴ Ω cm) and high temperature coefficient of resistance (TCR) (>−3%/K) were obtained at room temperature. 1/f noise character in the form of the normalized Hooge parameter was measured in the frequency range of 1–64 Hz, resulting in a lower 1/f noise compared to other materials currently used for device application.     

Characterization of nanoporous carbon fibrous materials obtained by chemical activation of plane tree seed under ultrasonic irradiation

An ultrasonic irradiation was applied for the impregnation by chemical agents in the chemical activation process of new type of active carbon precursor. Plane tree seed, due to the unique fibrous structure and low cost is a promising eco-friendly raw material for the preparation of activated carbon materials. Ultrasonic irradiation was used for the impregnation step allowing the chemical activation by different agents: potassium or sodium hydroxide, hydrogen peroxide and pyrogallol. The porous structures were examined by nitrogen adsorption/desorption isotherms at 77 K and electrochemically by cyclic voltammetry. The textures of these materials were observed by scanning electron microscopy. The application of ultrasonic irradiation in the impregnation step increased surface area of the final material more than two times in comparison to the material which impregnation in the activation process was by conventional stirring. Ultrasonic irradiation enhances the chemical activation process and the activated carbon fibrous materials with nanoporous structure were obtained by impregnation of seeds with alkaline hydroxides. Total surface areas of these samples were 976 m² g⁻¹ and 1130 m² g⁻¹. These fibers have total specific capacitance as high as 125 F g⁻¹ and 53 F g⁻¹ which major fraction in both cases originate from internal micropores structure.     

Segments of a commercial Ge-doped optical fiber as a thermoluminescent dosimeter in radiotherapy

Optical fibers have been proposed as dosimeters in both diagnostic and radiotherapy applications. A commercial germanium (Ge)-doped silica fiber with a 50 μm core diameter which showed good thermoluminescence (TL) properties was selected for this study. The radiation sources used were a high dose rate brachytherapy iridium-192, MV photon and MeV electron beams from a linear accelerator. The coating of the fiber was chemically removed and then annealed at 400 °C for 1 h prior to irradiation. After irradiation, the fiber was read on a Harshaw Model 3500 TLD reader. The optical fiber had one well-defined glow peak at 327 ± 2 °C at all the radiotherapy energies. The dose response was linear within the clinical relevant dose for all these energies. Reproducibility was mainly within 4–6% (one standard deviation) for high energy photons and electrons. The fiber was found to be energy independent within the MV photon energy range. At room temperature the fading up until 1 month was around 6% which was within the 6% uncertainty of the sensitivity calibration of the fiber. Re-using the fiber four times did not significantly alter the sensitivity factor. The optical fiber was found to be dose rate as well as angular independent. Central axis depth dose curves of both 10 MV photons and 12 MeV electrons using the fiber showed relatively good agreement to standard depth dose curves in water within 4%. The Ge-doped fiber is a promising TL dosimeter but improvements have to be made to reduce the reproducibility within 3% for high energy photons and electrons.