Acoustic Spectroscopy Research Articles

Molecular dynamics parameters of liquid crystal mixtures with different chemical structures

Results of molecular parameters studies using methods of dielectric spectroscopy, acoustic spectroscopy and viscometry are compared. An influence of dipole-dipole interactions on the relaxation time, the coefficients of molecular friction and rotational diffusion of molecules has been established. An analysis of modern methods for determining the coefficient of molecular friction and rotational diffusion for liquid crystal mixtures of different composition is carried out. It is shown that currently there is no theory that can describe qualitatively and quantitatively the behavior of the molecular relaxation parameters of the liquid crystal mixtures.

Application of acoustic models for polydisperse emulsion characterization using ultrasonic spectroscopy in the long wavelength regime

Ultrasonic spectroscopy is a technique that often has been used for measuring the particle size distribution in suspensions and emulsions. The ability to analyze concentrated heterogeneous systems and optically opaque samples, without the need for dilution, is the major advantage over alternative technologies, such as light scattering method. Several physical models used to interpret the measured attenuation spectra have been applied considering monodisperse particles. However, the polydisperse particle distributions are found in many practical applications, for example, in crude oil emulsions during droplet coalescence or flocculation. The polydispersity effects are usually important and need to be incorporated into theoretical predictions. For this work, acoustic spectroscopy within the frequency range 6–14 MHz was used to measure the droplet size distribution of water-in-sunflower oil emulsions for a volume fraction range from 10 to 50 % and considering monomodal size distribution. The results obtained from experimental attenuation spectra have been compared with the predictions of acoustic models from simple and multiple scattering, extended multiple scattering, and other simpler models of propagation usually applied to the long wavelength regime. The droplet size distributions from theoretical and experimental attenuation spectra were calculated with a deconvolution algorithm. The size distribution results obtained by ultrasonic spectroscopy showed good agreement with those obtained by laser diffraction analysis. The findings indicate that the methodology employed in this study is suitable for polydisperse particle size characterization for moderate concentrations up to 20 %.

Determining the crystallographic orientation of hexagonal crystal structure materials with surface acoustic wave velocity measurements

Throughout our engineered environment, many materials exhibit a crystalline lattice structure. The orientation of such lattices is crucial in determining functional properties of these structures, including elasticity and magnetism. Hence, tools for determining orientation are highly sought after. Surface acoustic wave velocities in multiple directions can not only highlight the microstructure contrast, but also determine the crystallographic orientation by comparison to a pre-calculated velocity model. This approach has been widely used for the recovery of orientation in cubic materials, with accurate results. However, there is a demand to probe the microstructure in anisotropic crystals - such as hexagonal close packed titanium. Uniquely, hexagonal structure materials exhibit transverse isotropic linear elasticity. In this work, both experimental and simulation results are used to study the discrete effects of both experimental parameters and varying lattice anisotropy across the orientation space, on orientation determination accuracy. Results summarise the theoretical and practical limits of hexagonal orientation determination by linear SAW measurements. Experimental results from a polycrystalline titanium specimen, obtained by electron back scatter diffraction and spatially resolved acoustic spectroscopy show good agreement (errors of ϕ1=5.14° and Φ=6.99°). Experimental errors are in accordance with those suggested by simulation, according to the experimental parameters. Further experimental results demonstrate dramatically improved orientation results (Φ error <1°). Demonstrating the possibility of achieving results near the theoretical limit by strict control of the experimental parameters.

Acoustic attenuation spectroscopy and helium ion microscopy study of rehydration of dairy powder

Complete hydration is essential for the production of structured dairy products from powders. It is essential that the ingredients used hydrate completely. Determination of an end point of rehydration is non-trivial, but ultrasound-based methodologies have demonstrated potential in this area and are well suited to measuring bulk samples in situ. Here, acoustic attenuation spectroscopy (AAS) is used to monitor rehydration of skim milk powder, and recombined systems of micellar casein isolate with lactose and whey protein isolate. Dynamic light scattering, zeta-potential measurements and AAS as a function of pH characterise each component around its isoelectric point to assess its functionality. Scanning helium ion microscopy was used to image the dry powders, without any conductive coating, producing resolution equivalent to scanning electron microscopy, but with much larger focal lengths and fewer imaging artefacts. Imaging the powders provides information on particle size and morphology which can affect dissolution behaviour. Reconstituted skim milk powder and recombined samples were monitored showing there are changes occurring over several hours. Attenuation coefficients are shown to predict the end point of hydration. Model fitting is used to extract volume fractions and average particle sizes of large and small particle populations in recombined samples over time. AAS is demonstrated to be capable of tracking the dynamics in rehydrating dispersions over time. Physical parameters such as the volume fraction and particle size of the dispersed phase can be determined.

Evaluation of Elastic Properties and Conductivity of Chitosan Acetate Films in Ammonia and Water Vapors Using Acoustic Resonators.

Novel bio-materials, like chitosan and its derivatives, appeal to finding a new niche in room temperature gas sensors, demonstrating not only a chemoresistive response, but also changes in mechanical impedance due to vapor adsorption. We determined the coefficients of elasticity and viscosity of chitosan acetate films in air, ammonia, and water vapors by acoustic spectroscopy. The measurements were carried out while using a resonator with a longitudinal electric field at the different concentrations of ammonia (100–1600 ppm) and air humidity (20–60%). It was established that, in the presence of ammonia, the longitudinal and shear elastic modules significantly decreased, whereas, in water vapor, they changed slightly. At that, the viscosity of the films increased greatly upon exposure to both vapors. We found that the film’s conductivity increased by two and one orders of magnitude, respectively, in ammonia and water vapors. The effect of analyzed vapors on the resonance properties of a piezoelectric resonator with a lateral electric field that was loaded by a chitosan film on its free side was also experimentally studied. In these vapors, the parallel resonance frequency and maximum value of the real part of the electrical impedance decreased, especially in ammonia. The results of a theoretical analysis of the resonance properties of such a sensor in the presence of vapors turned out to be in a good agreement with the experimental data. It has been also found that with a growth in the concentration of the studied vapors, a decrease in the elastic constants, and an increase in the viscosity factor and conductivity lead to reducing the parallel resonance frequency and the maximum value of the real part of the electric impedance of the piezoelectric resonator with a lateral electric field that was loaded with a chitosan film. This leads to an increase in the sensitivity of such a sensor during exposure to these gas vapors.

Revealing in real-time a multistep assembly mechanism for SV40 virus-like particles

Many viruses use their genome as template for self-assembly into an infectious particle. However, this reaction remains elusive because of the transient nature of intermediate structures. To elucidate this process, optical tweezers and acoustic force spectroscopy are used to follow viral assembly in real time. Using Simian virus 40 (SV40) virus-like particles as model system, we reveal a multistep assembly mechanism. Initially, binding of VP1 pentamers to DNA leads to a significantly decreased persistence length. Moreover, the pentamers seem able to stabilize DNA loops. Next, formation of interpentamer interactions results in intermediate structures with reduced contour length. These structures stabilize into objects that permanently decrease the contour length to a degree consistent with DNA compaction in wild-type SV40. These data indicate that a multistep mechanism leads to fully assembled cross-linked SV40 particles. SV40 is studied as drug delivery system. Our insights can help optimize packaging of therapeutic agents in these particles.

The sound of tablets during coating erosion, disintegration, deaggregation and dissolution.

This research aims to address a gap in our understanding of the mechanisms by which pharmaceutical tablets achieve highly reproducible and predictable drug release. The present industrial and regulatory practice is centred around tablet dissolution, i.e. what follows disintegration, yet the vast majority of problems that are found in formulation dissolution testing can be traced back to the erratic disintegration behaviour of the medicinal product. It is only due to the distinct lack of quantitative measurement techniques for disintegration analysis that this situation arises. Current methods involve costly, and time-consuming test equipment, resulting in a need for more simple, green and efficient methods which have the potential to enable rapid development and to accelerate routine solid drug formulation dissolution and disintegration testing. In this study, we present a novel approach to track several sequential tablet dissolution processes, including coating erosion, disintegration, deaggregation and dissolution using Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS). BARDS, in combination with minimal usage of UV spectroscopy, can effectively track these processes. The data also show that a solid oral dose formulation has an intrinsic acoustic signature which is specific to the method of manufacture and excipient composition.

Kinetic and Activation Characteristics of Structure Rearrangement Processes in Ethoxylated Isononylphenol Derivates

The paper presents the calculation results of the kinetic and activation characteristics of fast and ultrafast structure rearrangement processes in liquid hydroxyethylated derivates of isononylphenol (ОНФn). Parameters were calculated using the relaxation theory of acoustic spectroscopy of liquids based on the analysis of the acoustic spectra of speed and sound absorption of the hydroxyethylated derivates of isononylphenol. The paper shows that two simple regions of acoustic dispersion can describe the acoustic spectra in the frequency range from 12 MHz to 2 GHz and the temperature range from 253 K to 323 K. The dispersion region data in the hydroxyethylated derivates of isononylphenol correspond to the interconnected reactions of OH ... O bonding and breaking in chain associates and spatially branched network structures. It is noted that the change in the spatial structure of liquid hydroxyethylated derivates of isononylphenol can be considered as a set of the large number of independent (for non-collective processes) and interconnected (for collective processes) local rearrangements of the liquid structure as a result of the thermal motion of molecules. The proposed molecular mechanism of acoustic relaxation and the kinetic model of fast and ultrafast structure rearrangement processes of the hydroxyethylated derivates of isononylphenol made it possible to explain the main experimental results and to calculate the kinetic and activation characteristics of the structure rearrangement processes of the hydroxyethylated derivates of isononylphenol. This model and the kinetic and activation parameters of the hydroxyethylated derivates of isononylphenol can find application in development of various technologies for using nonionic surfactants.

Acoustic spectroscopy of functionalized carbon nanotubes in magnetic fluid

Acoustic spectroscopy is used to study the rearrangements of multi-walled carbon nanotubes (MWCNTs) functionalized by Fe3O4 magnetic nanoparticles dissolved in transformer oil under the influence of a magnetic field at various temperatures. Three methods for the application of the magnetic field are used: a jump change, a linear increase or decrease and a constant magnetic field with a change of its orientation to the acoustic wave. The rearrangements of MWCNTs/Fe3O4 to new structures (chains) by the influence of a magnetic field is confirmed by changes in the acoustic attenuation. From the measurement results, the lifetime of the chains after the switch-off of the magnetic field is less than 30 s. Such a rapid change is due to the fact that the nanotube chains are held by magnetic forces, resulting from the same direction of the magnetic moments of bound magnetic nanoparticles. A temperature-dependent hysteresis effect is observed with a linear change of the magnetic field. From our experiments, it follows that the reorientation of MWCNTs by magnetic nanoparticles with the magnetic field was gradual. The effect of the anisotropy of the acoustic attenuation is observed at a magnetic flux density of 200 mT and at various temperatures. Three MWCNT/Fe3O4 concentrations diluted in the transformer oil are used for the measurements and their influences on the structural changes with various developments of the magnetic field are discussed.

ІДЕНТИФІКАЦІЯ ОБ’ЄКТІВ МАШИНОБУДУВАННЯ ЗА КІЛЬКОМА КІЛЬКІСНИМИ ОЗНАКАМИ ОДНОЧАСНО

Показано, що діагностика об'єктів машинобудування передбачає обґрунтування розширення застосовуваних фізичних ефектів, орієнтованих, в першу чергу, на неруйнівного контролю параметрів продукції машинобудування. На підставі досліджень, які показують перспективність експериментальних і теоретичних доказів, доведена доцільність пошуку підтвердження інформативності частотних спектрів резонансних акустичних сигналів досліджуваних об'єктів, порушених широкосмуговими резонаторами рівній амплітуди в акустичному діапазоні. Надані прикладі застосування широкосмугових випромінювачів наноамплітудних впливів на досліджувані об'єкти з метою акустичної спектроскопії для створення їх ідентифікаційних моделей. Для практичного використання експериментальних результатів для ідентифікації розмірних і фізико-механічних характеристик станів діагностованих об'єктів авторами застосовані нейромережні моделі. Такі моделі служать практичним цілям діагностики станів об'єктів на основі частотних спектрів власних резонансних коливань. Доведено, якщо діагностика об'єкта проводиться щодо опорного сигналу у вигляді широкосмугового впливу постійної амплітуди, то такий підхід дозволяє нормувати вихідні діагностичні сигнали щодо опорного сигналу. представлені ідентифікаційні моделі, побудовані на нейромережному базисі, показали реальну можливість їх використання для створення системи діагностики об'єктів за кількома кількісними ознаками. Причому, кількість таких ознак, які можна контролювати одночасно, практично, не обмежена. Авторами роботи проведені додаткові дослідження, які показали можливість одночасного контролю не тільки геометричних характеристик об'єктів, а й їх фізико-механічних характеристик, включаючи показники напруженого стану, твердості і т.ін..

Application of the flexoelectric effect in liquid crystals to create acousto-optic transducers

The flexoelectric effect in nematic liquid crystals was studied using acoustic modulation spectroscopy. A cell consisting of three plates separated by spacers was used. The movable plate made shear oscillations in the plane of the cell. We studied thin layers of liquid crystals with homeotropic orientation of molecules with a thickness of from 20 to 100 microns. The frequency of exposure is 1 kHz. In the framework of the de Gennes model, near the phase transition liquid crystal - isotropic phase, the resulting signal has a flexoelectric nature and is due to a dipole mechanism. In this work, the temperature dependences of the flexosignal, the temperature effect on the value of the average constant angle of inclination (θc) and the amplitude of the oscillations of the director (θd) of a liquid crystal are investigated. The dependences of flex coefficients e33 on temperature are obtained. It was found that dipole and quadrupole mechanisms contribute to the observed molecular orientational polarization. The results of this study are proposed to be used to create liquid crystal transparencies of the new generation, as well as acousto-optic transducers for automated vibration control systems, since the use of liquid crystals provides a number of advantages (lightweight construction, low power consumption and overall dimensions, low cost).

Thiophene Determination in Liquid Hydrocarbons by In-line Acoustic Measurements

Introduction.Petroleum is a complex mixture of hydrocarbons. Sulphur is the most common heteroatom in pe-troleum and petroleum products. Its content in oil can reach 14 %. The determination of sulphur in oil and its removal is of great importance, since sulphur compounds adversely affect the quality of petroleum products and pollute the environment. Desulphurization of hydrocarbons is important in the processing of petroleum products, which needs in usage of accurate and simple methods for the sulphur-containing components determination. Most of developed methods are difficult to apply for flow online analysis, which can create difficulties in using them to monitor the content of sulphur-containing heteroatomic components in real time. Acoustic sensors are one of the possible solutions. In term of sensing of flammable liquids, the use of the acoustic methods is attractive since the analyte is not a part of an electrical measuring circuit and it is only acoustically coupled that prevents an occurrence of a spark.Objective.The purpose of the work is to study the possibilities of online flow analysis of sulphur-containing heteroatomic components using acoustic measurements. The challenge is the development of a resonator system integrated with the pipe.Materials and methods. Thiophene and oil fraction with the boundary boiling point of 100–140 oC were used to prepare the mixtures. Thiophene is a representative of sulphur-containing components, which may be included in the composition of petroleum and its derivatives. Experimental measuring equipment includes impedance analyzer, a developed sensor structure integrated with a liquid-filled pipe, a pump and a tank with a measured liquid. A theoretical analysis of sensor structure was carried out on the basis of numerical simulation using COMSOL Multiphysics software.Results.The sensor structure was designed as a combination of 2D and 1D pipe periodic arrangements to achieve high Q-factor of acoustic resonance in the flow system. The eigenmodes of the sensor structure with a liquid analyte were carried out. The characteristic of sensor structure is determined. The sensor shows good sensitivity to the thiophene content with high resolution in-line analysis. This result is achieved by limiting the energy losses of acoustic resonance in radiation along the pipe by creating a periodic structure.Conclusion. The study of acoustic properties of solutions prepared on the basis of thiophene and oil fraction with boundary boiling point 100–140 °C was performed. It shows that methods based on acoustic spectroscopy make it possible to accurately determine the concentration of heteroatomic components in gasoline mixtures, since the presence of heteroatomic components leads to a change in mechanical properties of liquid hydrocarbons mixtures. Possible applications for developed acoustic sensor are flow analysis for monitoring the quality of oil products.

Effects of spraying surfactants in a fluidised bed on the rehydration behaviour of milk protein isolate powder

Milk protein isolate (MPI) powder is a difficult to rehydrate powder displaying poor wettability and slow dissolution. In this study, MPI powder was top-sprayed with surfactants (Tween 80 and lecithin) in a fluidised bed to investigate the effect of surfactants on the rehydration behaviour. The wetting behaviour of MPI covered by the surfactants was greatly improved except for 4% lecithin. The wetting time of lecithinated MPI decreased to 42 s compared with MPI of 36 min. The Tween coated powders and larger size fractions displayed faster wetting attaining a minimum wetting time of 15 s. The rate of dissolution was not influenced by the presence of the surfactants as the particles continued to slowly dissolve. Broadband acoustic resonance dissolution spectroscopy (BARDS) showed that the gas release behaviour of surfactant covered MPI was totally altered and accelerated in comparison to the MPI powder, especially for Tween 80.

Single-Impact Nonlinear Resonant Acoustic Spectroscopy for Monitoring the Progressive Alkali–Silica Reaction in Concrete

Alkali–silica reaction (ASR) is a ubiquitous cause of concrete degradation. The reaction produces an expandable gel that may cause internal over-stressing and cracking. This paper demonstrates the utility of single-impact nonlinear resonant acoustic spectroscopy (SINRAS) for monitoring the progress of ASR over the course of a standard ASR-susceptibility test. In SINRAS, the transient softening and subsequent recovery of resonance frequency due to one strong impact are analyzed. The performance of SINRAS in monitoring ASR is compared to that of multi-impact nonlinear resonant acoustic spectroscopy (MINRAS), where the gradual resonance frequency shifts caused by impacts of increasing intensity is measured. The changes in standard linear expansion and linear resonance frequency are recorded in parallel. Finally, the sensitivity of measured parameters to sample temperature is investigated. Our findings indicate that SINRAS, while being much simpler and faster to conduct, yields results that strongly correlate to those from MINRAS and even gives an additional parameter describing the rate of recovery. The extracted nonlinearity parameters exhibit good sensitivity and clearly differentiate between concrete with reactive and non-reactive aggregates. Further, this study suggests that the influence of sample temperature on the nonlinearity parameters depends on the level of ASR progression and has to be taken account.

Real-Time Assembly of Viruslike Nucleocapsids Elucidated at the Single-Particle Level.

While the structure of a multitude of viral particles has been resolved to atomistic detail, their assembly pathways remain largely elusive. Key unresolved issues are particle nucleation, particle growth, and the mode of genome compaction. These issues are difficult to address in bulk approaches and are effectively only accessible by the real-time tracking of assembly dynamics of individual particles. This we do here by studying the assembly into rod-shaped viruslike particles (VLPs) of artificial capsid polypeptides. Using fluorescence optical tweezers, we establish that small oligomers perform one-dimensional diffusion along the DNA. Larger oligomers are immobile and nucleate VLP growth. A multiplexed acoustic force spectroscopy approach reveals that DNA is compacted in regular steps, suggesting packaging via helical wrapping into a nucleocapsid. By reporting how real-time assembly tracking elucidates viral nucleation and growth principles, our work opens the door to a fundamental understanding of the complex assembly pathways of both VLPs and naturally evolved viruses.

Three acoustic microresonator quartz-enhanced photoacoustic spectroscopy for trace gas sensing

Quartz-enhanced photoacoustic spectroscopy (QEPAS) based on three acoustic microresonators (AmRs) of on-beam structure is developed and experimentally investigated. The three AmRs arranged two sides of the quartz tuning fork (QTF) vertically along the QTF prong exhibits a strong laser enhancement between the AmR and the QTF, which results in a 31.15 times increasement compared with the construction of the bare QTF. Six fiber collimators were placed the two ends of every AmR to collimate and collect the laser. Moreover, a fiber reflector connected into the output fiber collimator offered a 1.39 times enhancement further by increasing laser power which passing through QTF again. The configuration was investigated by the water vapor at 1368.597 nm, achieving the minimum detection limits (MDL) of 166 ppb and the excellent R-square values 0.9967 in the concentration range from 400 ppm to 2000 ppm.

A rapid in-process control (IPC) test to monitor the functionality of taste masking polymer coatings using Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS).

Monitoring of the coating end-point of functional coatings during the coating application process is desirable. Since currently available PAT methods require expensive test equipment, there is a need for a rapid test that can easily be applied without major investment. BARDS is a novel technique that has the potential to economise the production process of these kinds of pellet and tablet formulations. The thickness of a controlled release coating is a key factor that determines the release rate of the drug in the gastro-intestinal tract or other targeted functionalities such as taste masking or moisture protection. Correspondingly, the amount of drug per unit mass of pellets decreases with increasing thickness of the functional coating. In this study, the functional polymer loading of the coating process is investigated by testing pellets via BARDS technology (Broadband Acoustic Resonance Dissolution Spectroscopy). The technique offers a rapid approach (<200 s) to characterising functional coatings at-line during their manufacture. Measurements are based on reproducible changes in the compressibility of a solvent during dissolution which is monitored acoustically via associated changes in the frequency of induced acoustic resonances. In case of enteric coatings a steady state acoustic lag time is associated with the erosion of the enteric coatings in acidic dissolution test media. This lag time is indicative of the coating layer thickness, assuming that the quality of the film coating is high. BARDS represents a possible future surrogate test for IPC testing, as a PAT method and possibly also for conventional USP dissolution testing. BARDS data correlate directly with the thickness of the functional coating, its integrity and also with the drug loading as validated by UV-Vis spectroscopy.

Laser-ultrasonic nondestructive evaluation of porosity in particulate reinforced metal-matrix composites

In this work, we propose the laser-ultrasonic method for nondestructive evaluation of porosity in particulate reinforced metal-matrix composites fabricated by stir and in-situ reactive casting techniques. The method is based on the influence of porosity on dispersion of the phase velocity of longitudinal acoustic waves, which is measured by the broadband acoustic spectroscopy with laser excitation of ultrasound (laser-ultrasonic spectroscopy). We studied stir cast hypereutectic aluminum-silicon alloy A336 matrix composites reinforced with the SiC micro particles (3.3–13.5 vol%) and in-situ reactive cast Al/Al3Ti composites reinforced with the Al3Ti intermetallic particles (4–11.5 vol%). In the spectral range of 3–40 MHz, the phase-velocity dispersion in both types of composites was observed: the high-frequency velocity in the range of 20–40 MHz increases with the increase of the reinforcement content independent of porosity, whereas the low-frequency velocity in the range of 3–10 MHz decreases with the increase of porosity independent of the reinforcement content. As a result, the relative dispersion grows up with the increase in the composite porosity independent of the variation in the reinforcement content. The empirical dependence between the porosity in a scanning composite region and the relative phase-velocity dispersion in this region is approximated by the same unified function. For the first time, such unified porosity-phase velocity functional relationship is obtained for particulate reinforced metal-matrix composites completely different in fabrication techniques as well as in chemical composition and elastic properties of reinforcing particles.

Application of Acoustic Spectroscopy to the Characterization of Surfactant Solutions, Emulsions, and Microemulsions: d–Limonene–Water–C12EO7–Isopropanol System

AbstractThe application of acoustic spectroscopy to the characterization of binary C12EO7—water system was studied. It was discovered that the size of micelles in aqueous surfactant solutions could not be determined, but it was possible to determine the size of water nanodomains existing in the surfactant‐rich systems. It was suggested that in colloidal systems, the energy of ultrasonic waves is dissipated only by interfaces existing between condensed phases. The characterization of Winsor transitions by acoustic spectroscopy in water/d‐limonene system stabilized by a mixture of nonionic surfactant and isopropyl alcohol (cosolvent) was also explored. In one study, systems with a constant d‐limonene to water weight ratio obtained in the course of titration of d‐limonene‐in‐water emulsion with increasing amounts of surfactant+alcohol were investigated. In another study, a balanced d‐limonene/water microemulsion was sequentially diluted with water and d‐limonene. The transition between Winsor I and Winsor IV systems was monitored in both cases. Droplet size distributions were calculated using different models for dispersed and continuous phase composition. It was demonstrated that the magnitude of acoustic scattering played a significant role in the ability to reliably determine droplet size distributions, and in particular to simultaneously observe nanometer‐size and micron‐size droplets in Winsor I systems. An attempt was made to account for intrinsic attenuation of surfactant and alcohol by associating them with the aqueous phase, but this approach was shown not to be applicable in the case of Winsor IV microemulsions.

The Possibility of Using Nonlinear Acoustic Spectroscopy with a Single Excitation Signal for Testing of Concrete Elements Damaged by High Temperature

This paper focuses on the use of nonlinear acoustic spectroscopy with one excitation signal for NDT of concrete parts exposed to high temperature. The rate of the temperature rise, the highest achieved temperature, time of exposure to elevated temperature and the cooling rate has an influence on the overall damage of concrete structures affected by fire. The test specimens described in this paper have been heated for various periods of time and at a different temperature. Nonlinear acoustic spectroscopy method was performed before and after heat load.