Acoustic properties of multiferroic BiFeO<Subscript>3</Subscript> over the temperature range 4.2–830 K

The longitudinal acoustic wave velocity and attenuation in BiFeO₃ ceramics have been measured by ultrasonic pulse-echo technique at a frequency of 10 MHz in the temperature range from 4.2 K to 830 K. The anomalies observed in the sound velocity and attenuation behavior versus temperature are attributed to the assumed relaxation in the temperature range 200–500 K and antiferromagnetic phase transition at higher temperatures. Order parameter fluctuations along with magnetostriction are discussed as the factors determining the acoustic wave velocity anomaly in the vicinity of the antiferromagnetic phase transition point.     

Precise measurements of bulk-wave ultrasonic velocity dispersion and attenuation in solid materials in the VHF range

A general method was established for precisely measuring velocity dispersion and attenuation in solid specimens with acoustic losses in the very high frequency (VHF) range, using the complex-mode measurement method and the diffraction correction method. Experimental procedures were presented for implementing such a method and demonstrated this measurement method in the frequency range of 50-230 MHz, using borosilicate glass (C-7740) as a dispersive specimen and synthetic silica glass (C-7980) as a nondispersive standard specimen. C-7980 exhibited no velocity dispersion; velocity was constant at 5929.14 +/- 0.03 m/s. C-7740 exhibited velocity dispersion, from 5542.27 m/s at 50 MHz to 5544.47 m/s at 230 MHz with an increase of about 2 m/s in the measured frequency range. When frequency dependence of attenuation was expressed as alpha = alpha(0)f(beta), the results were as follows: alpha0 = 1.07 x 10(-16) s2/m and beta = 2 for C-7980 and alpha0 = 5.16 x 10(-9) s(1.25)/m and beta = 1.25 for C-7740.     

非晶态快离子导体(AgI)x(Ag4P2O7)1-x的声学性质

用液氮骤冷方法制备了(AgI)_x(Ag₄P₂O₇)_1-x系列非晶态快离子导体。对AgI摩尔浓度x=0.50,0.60,0.67,0.75,0.80的样品,在77—300K温度范围及2,5,10,15MHz的频率上测量了纵波和横波的超声衰减和声速。发现在200—240K附近存在一个异常强的弛豫型超声吸收峰,随AgI含量的增加,该峰的位置向低温方向移动,且峰的高度增大。在实验的温度范围内,观察到纵波和 关键词：     

Acoustic anomalies in SrTiO<Subscript>3</Subscript>−BiFeO<Subscript>3</Subscript> solid solutions

The results of acoustic investigations of solid solutions SrTiO₃?BiFeO₃ in the temperature range from 100 to 650 K have been presented. The measurements of the velocity and attenuation of the longitudinal ultrasonic mode at a frequency of 10 MHz were carried out by the pulse-echo method. The observed anomalies in velocity and attenuation correlate with the maxima of the dielectric constant in the temperature range of the relaxor state. In addition, the attenuation peaks in the temperature range 400–600 K, which define Burns and T* temperatures, which are characteristic of relaxors, have been identified. The obtained results have allowed the clarifying of the phase diagram of the solid solution system SrTiO₃?BiFeO₃.     

Ultrasonic measurements on polycrystalline YBa2Cu3O7

Temperature dependent ultrasonic attenuation data of polycrystalline YBa₂Cu₃O₇ at 10 MHz show a plateau between 220 and 250 K, and slope changes at 263, 135 and 97 K. The attenuation does not display a sharp decrease at T_c as would be described in the BCS theory. Around 255 K, the sound velocity in the sample increases from its room temperature value by more than 10%.     

Ultrasonic attenuation in the intermediate state of indium

Ultrasonic attenuation has been measured in the intermediate state of high purity single crystals of indium of different sizes over the frequency range 10–30 MHz. Oscillations in the temperature dependence of attenuation of longitudinal ultrasound have been observed and are discussed here in the light of a recent theory.     

Features of high-frequency ultrasound propagation in the temperature range of structural and magnetic phase transitions in La1−x SrxMnO3 (x=0.175) manganite

The propagation of ultrasonic waves at a frequency of 770 MHz in a La_0.825Sr_0.175MnO₃ single crystal is investigated in the temperature range 350–150 K. It is found that the velocity, attenuation, and mode composition of ultrasonic waves change at temperatures of 315–280 and 220 K. These changes correlate with the structural and magnetic phase transitions and can be explained in terms of the Jahn-Teller distortions of the crystal lattice.     

Frequency dependence of acoustic parameters of freshly excised tissues of Sprague Dawley rats

A modified version of the pulse echo technique was used to measure the velocity of propagation and attenuation of ultrasound in excised tissue of young-adult Sprague-Dawley rats. The measurements were made at ultrasonic frequencies of 1.0, 2.25, 5.0, 7.5 and 10.0 MHz. The temperature of the tissues was monitored continuously to within ± 0.1°C of the ambient temperature. The acoustic parameters were measured in the liver, kidney, cardiac muscle and gastrocnemius muscle. All measurements were carried out in the near field region of the ultrasonic beam. It was observed that the velocity of propagation in tissues showed a slight dispersion with frequency. The attenuation in tissues increased with increasing frequency.     

Exvivo ultrasound attenuation coefficient for human cervical and uterine tissue from 5 to 10 MHz

Attenuation estimation and imaging in the cervix has been utilized to evaluate the onset of cervical ripening during pregnancy. This feature has also been utilized for the acoustic characterization of leiomyomas and myometrial tissue. In this paper, we present direct narrowband substitution measurement values of the variation in the ultrasonic attenuation coefficient in ex vivo human uterine and cervical tissue, in the 5-10 MHz frequency range. At 5 MHz, the attenuation coefficient values are similar for the different orientations of uterine tissue with values of 4.1-4.2 dB/cm, 5.1 dB/cm for the leiomyoma, and 6.3 dB/cm for the cervix. As the frequency increases, the attenuation coefficient values increase and are also spread out, with a value of approximately 12.6 dB/cm for the uterus (both parallel and perpendicular), 16.0 for the leiomyoma, and 26.8 dB/cm for the cervix at 10 MHz. The attenuation coefficient measured increases monotonically over the frequency range measured following a power law.     

Ultrasonic attenuation due to resonant interaction with a distribution of level splittings of the ground state of shallow acceptors in Ge

The ultrasonic attenuation in Ge (Ga, In) has been measured in the frequency range from 500 MHz to 2.5 GHz, and from room temperature down to 1 K. Below 10 K the attenuation rises as ω²/T. For the first time saturation of the attenuation has been observed for ground state of a shallow acceptor. These results can be interpreted as due to resonance interaction with level splittings of a broad distribution with width of about 0.1 meV.     

Ultrasonic evidence for short-range charge-ordering state in the low-doping regime of La1– x Sr x FeO3 (1/3 ≤ x ≤ 0.45)

The longitudinal ultrasonic velocity (V) and attenuation at a frequency of 10?MHz, as well as magnetization and resistivity, have been measured in the single-phase polycrystalline La_{1– x} Sr _x FeO₃ (x?=?1/3, 0.4, 0.45). Upon cooling down from high temperature, a slight softening in V and dramatic stiffening are observed in all samples, and this stiffening is coincided with a big attenuation peak. The relative increase of V is proportional to the Sr concentration, which implies that this anomaly is strongly correlated with Fe⁴⁺. However, no obvious changes in magnetic and electric properties are found at this temperature range. The analysis suggests that this feature may be caused by the Jahn–Teller effect of Fe⁴⁺ and correspond to the formation of short-range charge-ordering state.     

Ultrasonic investigation of amorphous carbon in various frequencies at low temperatures from 2.1 to 300 K

Using pulse echo overlap measurement, the elastic behavior of amorphous carbon has been studied at ambient and low temperatures. The smaller ratio B/G of the bulk modulus to shear modulus and smaller Poisson's ratio σ at room temperature indicate that there is an intrinsic stiffening of transverse acoustic phonons in the amorphous carbon. The acoustic velocity and attenuation for longitudinal modes have been measured between 2.1 and 300 K at three frequencies of 7, 21 and 35 MHz, respectively. Their frequency and temperature dependence are observed. The elastic constant C₁₁ increases with decreasing temperature and show enhanced stiffening at low temperatures. In the 130-220 K region, the abnormal change and effect of longitudinal velocity and attenuation with temperature and frequency, and a phase transition associated with structure relaxations are discussed.     

High frequency attenuation measurements of lipid encapsulated contrast agents

A number of recent studies have indicated the potential of ultrasound contrast agent imaging at high ultrasound frequencies. However, the acoustic properties of microbubbles at frequencies above 10 MHz remain poorly understood at present. In this study we characterize the high frequency attenuation properties of (1) BR14, (2) BR14 that has been mechanically filtered (1 and 2 microm pore sizes) to exclude larger bubbles, and (3) the micron to submicron agent BG2423. A narrowband pulse-echo substitution method is employed with a series of four transducers covering the frequency range from 2 to 50 MHz. For BR14, attenuation decreases rapidly from 2 to 10 MHz and then more gradually from 10 to 50 MHz. For 2 microm filtration, the attenuation peaks between 10 and 15 MHz. For 1 microm filtration, attenuation continues to rise until 50 MHz. The agent BG2423 exhibits a diffuse attenuation peak in the range of 15-25 MHz and remains high until 50 MHz. These results demonstrate a strong influence of bubble size on high frequency attenuation curves, with bubble diameters of 1-2 microm and below having more pronounced acoustic activity at frequencies above 10 MHz.     

Absorption and velocity dispersion due to crystallization and melting of emulsion droplets

The influence of droplet crystallization and melting on the ultrasonic properties of oil-in-water emulsions has been investigated. The ultrasonic velocity and attenuation were measured in a series of 3 wt% n-hexadecane-in-water emulsions as a function of frequency (0.3–4 MHz), droplet diameter (0.4 and 1 μm) and temperature (0–25°C). The emulsified n-hexadecane crystallized at about 5°C due to supercooling effects and melted at about 18°C. As solid and liquid n-hexadecane have significantly different ultrasonic properties, an appreciable change in the velocity and attenuation is observed during the phase transition. This behaviour is modified significantly in systems where the emulsion droplets are partially crystalline because the temperature fluctuations associated with the ultrasonic wave can perturb the phase equilibria solid liquid causing excess attenuation and velocity dispersion. The magnitude of this effect depends on the ultrasonic frequency and the average droplet size.     

Measurement of the acoustic properties of a nerve-muscle preparation as a function of physiologic state

Nerve-muscle preparations of Sprague Dawley rats were exposed to low dosage ultrasound. The objectives were to measure the velocity of propagation and attenuation of ultrasonic energy in both the relaxed and contracted states. A tension-measuring system and associated ultrasonic instrumentation were designed to measure the tension developed in stimulated muscle and its corresponding acoustic parameters, ie the attenuation coefficient, (db cm^-1) and the velocity of propagation, c (ms^-1). Each test was performed at ultrasonic frequencies 3.1, 5.35, and 7.68 MHz and with the preparation maintained at 23 ± 0.5° C. Attenuation of ultrasonic energy was observed to increase by 10 ± 0.5% in the active state from its value in the relaxed state. The relation between the attenuation and the acoustic frequency was found to be approximately linear over the frequency range tested. The velocity of propagation in the active state did not change appreciably from its value in the relaxed state and was observed to be independent of the acoustic frequency in the range used.     

Negative dispersion in bone: the role of interference in measurements of the apparent phase velocity of two temporally overlapping signals

In this study the attenuation coefficient and dispersion (frequency dependence of phase velocity) are measured using a phase sensitive (piezoelectric) receiver in a phantom in which two temporally overlapping signals are detected, analogous to the fast and slow waves typically found in measurements of cancellous bone. The phantom consisted of a flat and parallel Plexiglas plate into which a step discontinuity was milled. The phase velocity and attenuation coefficient of the plate were measured using both broadband and narrowband data and were calculated using standard magnitude and phase spectroscopy techniques. The observed frequency dependence of the phase velocity and attenuation coefficient exhibit significant changes in their frequency dependences as the interrogating ultrasonic field is translated across the step discontinuity of the plate. Negative dispersion is observed at specific spatial locations of the plate at which the attenuation coefficient rises linearly with frequency, a behavior analogous to that of bone measurements reported in the literature. For all sites investigated, broadband and narrowband data (3-7 MHz) demonstrate excellent consistency. Evidence suggests that the interference between the two signals simultaneously reaching the phase sensitive piezoelectric receiver is responsible for this negative dispersion.     

Acoustic analysis of the composition of human blood serum

New acoustic methods of determining total protein, protein fractions, and lipid components of the human blood serum are presented. Acoustic methods are based on high-precision measurements of velocity and temperature dependences and frequency and temperature dependences of ultrasound absorption. Acoustic characteristics of the blood serum were measured using the method of a fixed length interferometer in acoustic cells ～80 mcl in volume in the temperature range from 15 to 40°C and the 4–9 MHz frequency range with the acoustic analyzer developed by BIOM company. An error in measuring ultrasound velocity in the blood serum was 3 × 10^?5; that of absorption, 2 × 10^?2. The developed acoustic methods were clinically tested and recommended for application at clinical diagnostic laboratories with RF treatment-and-prophylactics establishments.     

Acousto-induced structural change in amorphous As2S3

The acoustic flux injection method was applied to amorphous As₂S₃. The velocity and the attenuation constant for shear wave at ～ 100MHz were measured through the observation of the Brillouin scattering of the light beam from a He-Ne laser. The optical transmission around absorption edge was found to change after the injection of acoustic fluxes. It was also found that the sound velocity decreased with increasing injection time of acoustic fluxes and the amount of the change of the sound velocity reached ～ 20% after 10⁵ injections. The changes in the optical transmission and the sound velocity tended to be erased by annealing below the glass transition temperature. These phenomena are considered to be due to structural changes caused by the injection of strong acoustic fluxes.     

Ultrasonic properties of a suspension of microspheres supporting negative group velocities

The ultrasonic attenuation coefficient, phase velocity, and group velocity spectra are reported for a suspension that supports negative group velocities. The suspension consists of plastic microspheres with an average radius of 80 microm in an aqueous medium at a volume fraction of 3%. The spectra are measured using a broadband method covering a range from 2 to 20 MHz. The suspension exhibits negative group delays over a band near 4.5 MHz, with the group velocity magnitude exceeding 4.3 x 10(8) m/s at one point. The causal consistency of these results is confirmed using Kramers-Kronig relations.     

Ultrasonic characterization of heavy metal TeO2–WO3–PbO glasses below room temperature

The longitudinal ultrasonic attenuation measurements have been made using pulse echo method at fundamental frequencies of 2, 4, 6 and 8 MHz in 20WO₃–(80−x) TeO₂–xPbO ternary tellurite glasses (x=10, 12.5, 15, 17.5 and 20 mol%) in the temperature range 160–280 K. The results showed the presence of a broad peak which shifts to higher temperature with increasing frequency. The ultrasonic attenuation peaks suggest that the experimental behavior is controlled by thermally activated structural relaxations. The internal friction, acoustic activation energy, deformation potential, relaxation strength, number of loss centers and density of state have been calculated both as a function of temperature and PbO content. The acoustic activation energy was found to decrease from 0.156 to 0.135 eV with the increase of PbO content. The results showed that both the number of loss centers and their activation energy decrease with the atomic ring size. An increase in the density of state is observed with addition of PbO content at the same frequency in the whole range of temperature which is associated with structural units formed when PbO is added.