Acoustic modeling of perforated concrete using the dual porosity theory

Perforated concrete shows nowadays a high potential for many construction and building engineering applications. This work is devoted to the analysis of the acoustic properties of perforated concrete made from arlite lightweight aggregates. Concrete produced from these materials is an environmentally friendly alternative to traditional materials and offers a higher durability, excellent strength-to-weight ratio and low cost. In particular, it is shown that the acoustic behavior of perforated concrete can be modeled using a dual porosity approach based on the knowledge of the non-acoustic properties of the matrix granular material and geometrical data. To this end, various non-perforated and perforated samples were prepared and characterized in an experimental test facility, their acoustic properties being determined through the transfer function impedance tube method. Experimental and estimated results related to the acoustic properties of a number of prepared specimens are presented, showing a good agreement. Results suggest that this approach is suitable for practical design of such materials as part of noise control systems.     

Evaluation of the acoustic and non-acoustic properties of sound absorbing materials using a three-microphone impedance tube

This paper presents a straightforward application of an indirect method based on a three-microphone impedance tube setup to determine the non-acoustic properties of a sound absorbing porous material. First, a three-microphone impedance tube technique is used to measure some acoustic properties of the material (i.e., sound absorption coefficient, sound transmission loss, effective density and effective bulk modulus) regarded here as an equivalent fluid. Second, an indirect characterization allows one to extract its non-acoustic properties (i.e., static airflow resistivity, tortuosity, viscous and thermal characteristic lengths) from the measured effective properties and the material open porosity. The procedure is applied to four different sound absorbing materials and results of the characterization are compared with existing direct and inverse methods. Predictions of the acoustic behavior using an equivalent fluid model and the found non-acoustic properties are in good agreement with impedance tube measurements.     

Acoustic impedance microscopy for biological tissue characterization

A new method for two-dimensional acoustic impedance imaging for biological tissue characterization with micro-scale resolution was proposed. A biological tissue was placed on a plastic substrate with a thickness of 0.5 mm. A focused acoustic pulse with a wide frequency band was irradiated from the “rear side” of the substrate. In order to generate the acoustic wave, an electric pulse with two nanoseconds in width was applied to a PVDF-TrFE type transducer. The component of echo intensity at an appropriate frequency was extracted from the signal received at the same transducer, by performing a time–frequency domain analysis. The spectrum intensity was interpreted into local acoustic impedance of the target tissue. The acoustic impedance of the substrate was carefully assessed prior to the measurement, since it strongly affects the echo intensity. In addition, a calibration was performed using a reference material of which acoustic impedance was known. The reference material was attached on the same substrate at different position in the field of view. An acoustic impedance microscopy with 200 × 200 pixels, its typical field of view being 2 × 2 mm, was obtained by scanning the transducer. The development of parallel fiber in cerebella cultures was clearly observed as the contrast in acoustic impedance, without staining the specimen. The technique is believed to be a powerful tool for biological tissue characterization, as no staining nor slicing is required.     

Growth characteristics and properties of ZnO:Ga thin films prepared by pulsed DC magnetron sputtering

Transparent conductive ZnO:Ga thin films were deposited on Corning 1737 glass substrate by pulsed direct current (DC) magnetron sputtering. The effects of process parameters, namely pulse frequency and film thickness on the structural and optoelectronic properties of ZnO:Ga thin films are evaluated. It shows that highly c-axis (0 0 2) oriented polycrystalline films with good visible transparency and electrical conductivity were prepared at a pulsed frequency of 10 kHz. Increasing the film thickness also enlarged the grain size and carrier mobility which will subsequently lead to the decrease in resistivity. In summary, ZnO:Ga thin film with the lowest electrical resistivity of 2.01 × 10⁻⁴ Ω cm was obtained at a pulse frequency of 10 kHz with 500 nm in thickness. The surface RMS (root mean square) roughness of the film is 2.9 nm with visible transmittance around 86% and optical band gap of 3.83 eV.     

Effect of change in pulsed DC frequency on indium-tin oxide anode on J-V-L performance of built-up organic light emitting diode during facing-target sputtering

Investigations were carried out on the changes in the electrical and optical properties and surface roughness of the indium-tin oxide (ITO) anode as a function of DC pulse frequency during facing-target sputtering. The current density-voltage-luminescence (J-V-L) characteristics of organic light emitting diodes (OLEDs) developed on the anodes were measured and analyzed in relation to the properties of ITO. When the pulsed DC frequency was less than 120 kHz, the resistivity of ITO was maintained well below 4.3 × 10⁻⁴ Ω cm and the optical energy band gap was greater than 4.1 eV, but these properties changed abruptly at 150 kHz with the morphological transition from columnar to equi-axed. Meanwhile, the surface roughness decreased continuously with increasing pulsed DC frequency up to 150 kHz. The J-V characteristics of the built-up OLED deteriorated slightly as the pulsed DC frequency increased to 120 kHz and then deteriorated rapidly at 150 kHz. The L-V curves, however, showed an improvement of luminescence as the frequency increased up to 120 kHz. These J-V-L characteristics imply that ITO which is more conductive and with a higher band gap can be obtained at the lower pulsed DC frequencies, which is desirable for higher current flow; however, better luminescence is closely related to smoother surfaces. Therefore, for the optimized J-V-L performance of OLEDs, a moderate pulse DC frequency, below the morphological transition of ITO, is desirable.     

Experimental study of the line mixing coefficient for 118.75 GHz oxygen line

The oxygen fine structure line 1− at 118.75 GHz was studied by two spectrometers at low (0.2-3.5 Torr) and high (atmosphere) pressures in air and pure oxygen. Improvement in the spectrometer with BWO and acoustic detector included use of a powerful (more than 40 mW) radiation source. Improvement in the modern resonator spectrometer included exclusion of apparatus function by sample substitution and a wider (110-130 GHz) scanned frequency range. As a result, the 1− oxygen line was observed by both spectrometers with high (up to 450) signal-to-noise ratio which permitted precise measurements of the line parameters. The investigation separated linear- and quadratic-with-pressure displacement of the line center. The line mixing coefficient responsible for apparent quadratic dependence of the center frequency on pressure was measured experimentally for the first time for this line. The line mixing coefficient was measured at 297 K as −4.62(38)×10⁻⁵ Torr⁻¹ for pure oxygen and −5.9(29)×10⁻⁵ Torr⁻¹ for air, compared to the previously calculated value −3.1×10⁻⁵ Torr⁻¹. Linear dependence of the line center frequency on pressure does not exceed ±20 kHz/Torr for air and ±10 kHz/Torr for pure oxygen. Refined values of line broadening were obtained. Integral intensity of the line was measured. A comparison with the previous investigations is presented. Inconsistencies in published data about pressure line shifts of oxygen molecule spectral lines are discussed.     

Giga-bit optical receiver for plastic optical fibre

An optical receiver with high sensitivity and linearity specially designed for Giga-bit communications over small-bandwidth high-attenuation multimode plastic optical fiber is presented. An automatic gain control transimpedance amplifier and linear post amplifiers are used to maintain a good performance with multilevel modulation. Using multilevel signaling and large-diameter integrated photodiodes make the presented optical receiver suitable for large core plastic optical fiber. For a wavelength of 675 nm, a sensitivity of −26.3 dB m (BER = 10⁻⁹) at 500 Mb/s is presented by a binary signal. A data rate of 1 Gb/s and a sensitivity of −19.8 dB m (BER = 10⁻⁹) are achieved with four-level pulse amplitude modulation.     

Magnetic properties of iron-based soft magnetic composites with MgO coating obtained by sol-gel method

Soft magnetic composites with a thin MgO insulating layer were produced by a sol-gel method. Energy dispersive X-ray spectroscopy, X-ray analysis, Fourier transform infrared spectroscopy, density measurement and compositional maps confirmed that thin layers of MgO covered the iron powders. Coercivity measurement showed that the stress relaxation and reduction of hysteresis loss efficiently occurred at 600 °C. At this temperature, the phosphate insulation of commercial SOMALOY^TM samples degrade and their electrical resistivity, magnetic permeability and operating frequency decreases noticeably. The results show that the MgO insulation has a greater heat resistance than conventional phosphate insulation, which enables stress-relief at higher temperatures (600 °C) without a large increase in eddy current loss. The results of annealing at 600 °C show that the electrical resistivity and ferromagnetic resonance frequency increased from 11 μΩ m and 1 kHz for SOMALOY^TM samples to 145 μΩ m and 100 kHz for the MgO insulated composites produced in this work.     

Acoustic characterization of a new trisacryl contrast agent. Part I: In vitro study

The objective of the study was to acoustically characterize trisacryl polymeric microparticles (TMP), which are derived from biocompatible embolic agents.With significant acoustic properties, these polymeric particles could be potentially used as targeted ultrasound contrast agents, directed towards a specific site, with ligands conjugation on the polymeric network surface. In the in vitro study, a pulser/receiver (PRF of 1 kHz), associated to different transducers (5, 10 and 15 MHz), was used to measure the acoustic properties of the TMP inserted in a Couette flow device. Acoustic characterization according to TMP concentration (0.12-15.63 mg/ml), frequency (4.5-17 MHz, defined by each transducer bandwidth), ultrasound pressure (137-378 kPa) and exposure time (0-30 min) was conducted. Particle attenuation was also evaluated according to TMP concentration and emission frequency. Backscattering increased non linearly with concentration and maximum enhancement was of 16.4 dB ± 0.89 dB above 7.8 mg/ml. This parameter was found non-linear with increasing applied pressure and no harmonic oscillation could be noticed. Attenuation reached approximately 1.4 dB/cm at 15 MHz and for the 15.6 mg/ml suspension.The TMP have revealed in vitro ultrasound properties comparable to those observed with known contrast agents, studied in similar in vitro systems. However, such set-ups combined with a rather aqueous suspending medium, have some limitations and further investigations need now to be conducted to approach in vivo conditions in terms of flow and blood environment.     

The acoustical properties of consolidated expanded clay granulates

The paper presents a systematic study of acoustic and non-acoustic properties of consolidated porous samples of expanded clay granulates. The effect of the particle size on the acoustic performance of consolidated expanded clays is investigated experimentally and theoretically. This work involves a comparison of the measured and predicted values of the absorption coefficient and normalised acoustic surface impedance data. It is demonstrated that the values of tortuosity and standard deviation in the pore size distribution do not depend significantly on the size of the material aggregate. An empirical expression which links the flow resistivity of the consolidated granular mix has been derived from the measured data. These results pave the way for the development of a simple practical model which will be able to link the acoustic properties of a consolidated granular mix with the characteristic particle dimension and the porosity data. These materials are structurally robust and easy to integrate in buildings and highway structures to control the levels of environmental noise and improve the acoustic quality of spaces.     

Attractive microwave absorption and the impedance match effect in zinc oxide and carbonyl iron composite

The flower-like ZnO and ZnO/carbonyl-iron composite have been prepared by a sonochemical route and ball-milling process, respectively. For ZnO/carbonyl-iron composite, a reflection loss (RL) exceeding −20 dB was obtained in a broad frequency range of 8.4-17.9 GHz with a thin thickness of 1.2-2.3 mm. An optimal RL of −61 dB was found at 11.7 GHz for an absorber thickness of 1.91 mm. It is demonstrated that the attractive microwave-absorption properties are a consequence of a proper electro-magnetic impedance match and geometrical cancellation at the air-material interface. In addition, an impedance mismatch function was proposed, which provides an effective method to determine the microwave absorbing properties from the intrinsic materials constants. The calculated value of matching frequency and thickness is well consistent with the experimental data. The method also provides a simple theoretical graphic aid for determining the absorption characteristics and the location of the matching conditions in the frequency domain.     

Surface textured ZnO:Al thin films by pulsed DC magnetron sputtering for thin film solar cells applications

Transparent conducting thin films of ZnO:Al (Al-doped ZnO, AZO) were prepared via pulsed DC magnetron sputtering with good transparency and relatively lower resistivity. The AZO films with 800 nm in thickness were deposited on soda-lime glass substrates keeping at 473 K under 0.4 Pa working pressure, 150 W power, 100 μs duty time, 5 μs pulse reverse time, 10 kHz pulse frequency and 95% duty cycle. The as-deposited AZO thin films has resistivity of 6.39 × 10⁻⁴ Ω cm measured at room temperature with average visible optical transmittance, T_total of 81.9% under which the carrier concentration and mobility were 1.95 × 10²¹ cm⁻³ and 5.02 cm² V⁻¹ s⁻¹, respectively. The films were further etched in different aqueous solutions, 0.5% HCl, 5% oxalic acid, 33% KOH, to conform light scattering properties. The resultant films etched in 0.5% HCl solution for 30 s exhibited high T_total = 78.4% with haze value, H_T = 0.1 and good electrical properties, ρ = 8.5 × 10⁻⁴ Ω cm while those etched in 5% oxalic acid for 150 s had desirable H_T = 0.2 and relatively low electrical resistivity, ρ = 7.9 × 10⁻⁴ Ω cm. However, the visible transmittance, T_total was declined to 72.1%.     

Transparent conducting molybdenum-doped zinc oxide films deposited by RF magnetron sputtering

A new transparent conducting oxide (TCO) film with low resistivity and high transmittance in the visible range, molybdenum-doped zinc oxide (MZO), was successfully prepared by RF magnetron sputtering method on glass substrates at room temperature. The structural, electrical, and optical properties as a function of film thickness were investigated. All the samples have a preferred orientation with the (0 0 2) planes parallel to the substrates. The resistivity initially decreases and then shows an increase with the increase of the film thickness. When the thickness is 400 nm, the film has its best crystallinity and lowest resistivity 9.2 × 10⁻⁴ Ω cm with a Hall mobility of 30 cm² V⁻¹ s⁻¹ and a carrier concentration of 2.3 × 10²⁰ cm⁻³. The average transmittance in the visible range exceeds 84% for all thickness films.     

Carotid atherosclerotic plaque characterisation by measurement of ultrasound sound speed in vitro at high frequency, 20 MHz

This study aimed to utilise a tissue mimicking material (TMM) in order to embed in vitro carotid plaque tissue so that its acoustic properties could be assessed. Here, an International Electrotechnical Commission (IEC) agar-based TMM was adapted to a clear gel by removal of the particulates. This clear TMM was measured with sound speed at 1540 ms⁻¹ and an attenuation coefficient of 0.15 dB cm⁻¹ MHz⁻¹. Composite sound speed was then measured through the embedded material using a scanning acoustic microscope (SAM). Both broadband reflection and transmission techniques were performed on each plaque specimen in order to ensure the consistency of the measurement of sound speed, both at 21 °C and 37 °C. The plaque was measured at two temperatures to investigate any effect on the lipid content of the plaque. The contour maps from its associated attenuation plots were used to match the speed data to the photographic mask of the plaque outline. This physical matching was then used to derive the sound speed from the percentage composition seen in the histological data by solution of simultaneous equations. Individual speed values for five plaque components were derived; TMM, elastin, fibrous/collagen, calcification and lipid. The results for derived sound speed in the TMM were consistently close to the expected value of soft tissue, 1540 ms⁻¹. The fibrous tissue showed a mean value of 1584 ms⁻¹ at 37 °C. The derived sound speeds for elastic and lipid exhibited large inter-quartile ranges. The calcification had higher sound speed than the other plaque components at 1760–2000 ms⁻¹. The limitations here lay in the difficulties in the matching process caused by the inhomogeneity of the plaque material and shrinkage during the histological process. Future work may concentrate on more homogeneous material in order to derive sound speed data for separate components. Nevertheless, this study increases the known data ranges of the individual components within a plaque. This information may be used help to assess the mechanical properties and structural integrity and its associated vulnerability or risk of embolization in future diagnostic ultrasound techniques.     

Acoustic properties of unconsolidated granular mixes

Simple empirical relations have been proposed to relate a limited number of directly measurable non-acoustic properties of an unconsolidated granular mix to its characteristic acoustic impedance and propagation constant. These properties are: characteristic particle dimension, porosity, tortuosity and the density of the grain base. It is believed that the model accounts heuristically for the mechanical friction between the elements of the rigid frame, the absorption in the frame micro-pores, and the degree of compaction. These effects can be important and are linked to the value of material density. This work presents practical applications of the proposed model for the prediction of the acoustic characteristics of hard-backed layers of loose granular mixes which can be used for acoustic absorption and insulation. It is shown that the predictions are in excellent agreement with the measured data for a representative range of loose granular mixes. A comparison of the results of the 4-parameter Attenborough model for the acoustic properties of porous media and the experimental data is made also. This model is used extensively to predict the acoustic properties of porous ground and granular media. The accuracy of this model with respect to loose granular materials is discussed.     

Dip-coated HNR120 photoresists thin-film optical waveguides

We report on our systematic and detailed study of fabrication and characterization of HNR120 photoresists thin-film optical waveguides. Various waveguide properties, such as refractive index, optical losses as a function of temperature, waveguide thickness, dispersion and birefringence have been studied. The optical loss are found to be <1.4 dB cm⁻¹.     

Bonding and impedance matching of acoustic transducers using silver epoxy

Silver epoxy was selected to bond transducer plates on glass substrates. The properties and thickness of the bonding medium affect the electrical input impedance of the transducer. Thus, the thickness of the silver epoxy bonding layer was used as a design parameter to optimize the structure for the transducer input impedance to match the 50 Ω output impedance of most radio frequency (RF) generators. Simulation and experimental results show that nearly perfect matching is achieved without using any matching circuit. At the matching condition, the transducer operates at a frequency band a little bit below the half-wavelength resonant frequency of the piezoelectric plate. In experiments, lead titanate (PT) piezoelectric plates were employed. Both full-size, 11.5 mm × 2 mm × 0.4 mm, and half-size, 5.75 mm × 2 mm × 0.4 mm, can be well matched using optimal silver epoxy thickness. The transducer assemblies demonstrate high efficiency. The conversion loss from electrical power to acoustic power in soda-lime glass is 4.3 dB. This loss is low considering the fact that the transducers operate at off-resonance by 12%. With proper choice of silver epoxy thickness, the transducer can be matched at the fundamental, the 3rd and 5th harmonic frequencies. This leads to the possible realization of triple-band transducers. Reliability was assessed with thermal cycling test according to Telcordia GR-468-Core recommendation. Of the 30 transducer assemblies tested, none broke until 2900 cycles and 27 have sustained beyond 4050 cycles.     

Study of ultrasound stiffness imaging methods using tissue mimicking phantoms

A pilot study was carried out to investigate the performance of ultrasound stiffness imaging methods namely Ultrasound Elastography Imaging (UEI) and Acoustic Radiation Force Impulse (ARFI) Imaging. Specifically their potential for characterizing different classes of solid mass lesions was analyzed using agar based tissue mimicking phantoms. Composite tissue mimicking phantom was prepared with embedded inclusions of varying stiffness from 50 kPa to 450 kPa to represent different stages of cancer. Acoustic properties such as sound speed, attenuation coefficient and acoustic impedance were characterized by pulse echo ultrasound test at 5 MHz frequency and they are ranged from (1564 ± 88 to 1671 ± 124 m/s), (0.6915 ± 0.123 to 0.8268 ± 0.755 db cm^-1 MHz^-1) and (1.61×10⁶ ± 0.127 to 1.76 × 10⁶ ± 0.045 kg m^-2 s^-1) respectively. The elastic property Young’s Modulus of the prepared samples was measured by conducting quasi static uni axial compression test under a strain rate of 0.5 mm/min upto 10 % strain, and the values are from 50 kPa to 450 kPa for a variation of agar concentration from 1.7% to 6.6% by weight. The composite phantoms were imaged by Siemens Acuson S2000 (Siemens, Erlangen, Germany) machine using linear array transducer 9L4 at 8 MHz frequency; strain and displacement images were collected by UEI and ARFI. Shear wave velocity 4.43 ± 0.35 m/s was also measured for high modulus contrast (18 dB) inclusion and X.XX m/s was found for all other inclusions. The images were pre processed and parameters such as Contrast Transfer Efficiency and lateral image profile were computed and reported. The results indicate that both ARFI and UEI represent the abnormalities better than conventional US B mode imaging whereas UEI enhances the underlying modulus contrast into improved strain contrast. The results are corroborated with literature and also with clinical patient images.     

Automated acoustic seabed classification of multibeam images of Stanton Banks

Dividing sidescan images into regions that have similar seabeds is often done by expert interpretation. Automated classification systems are becoming more widely used. This paper describes techniques, based on image amplitudes and texture, that lead to useful and practical automated segmentation of multibeam images. Seabed (or riverbed or lakebed) type affects amplitudes and texture, but so do system operating details and survey geometry. Effects of the last two must be compensated to isolate the effects of seabed type. Images from multibeam surveys are accompanied by bathymetric data from which grazing angles of all sonar footprints can be calculated. By compiling tables of amplitude against range and grazing angle, systematic changes in amplitude with these two variables can be removed consistently. Classification, based on a large number of features, is done in image space to avoid artifacts common in mosaics. Unsupervised segmentation requires clustering, in which records are divided into their natural classes. An objective clustering method using simulated annealing assigns points to classes based on their Bayesian distances from cluster centres. Stanton Banks is a rocky area 100 km north of County Donegal, Ireland, that rises about 100 m above the ocean floor at 180 m. Multibeam images and data from an 80-km² survey were classified into regions of acoustic similarity. Assigning labels of physical properties to these regions requires non-acoustic ground truth, which was obtained from a series of 105 photographs. Photographic geological assignments were found to correlate well with the acoustic classes.     

Practical optical frequency measurement system around 1.5 μm based on an acetylene-stabilized laser-locked optical frequency comb

We have developed a practical and precise frequency measurement system at 1.5 μm telecommunication band. An electro-optic-modulator based optical frequency comb is phase-locked to a dither-free acetylene-stabilized laser to realize an optical frequency comb with frequency uncertainty of 10 kHz (5 × 10⁻¹¹) and the linewidth of 15 kHz. The present frequency comb can be also used as an optical frequency reference grid defined by ITU-T (International Telecommunication Union, Telecommunication Standardization Sector). Using the present frequency measurement system, we have demonstrated the first optical frequency measurement of ¹²C¹⁶O overtone absorption lines around 1.56 μm with the uncertainty of lower than 900 kHz.