Buffer Rod Research Articles

Cross pressure and temperature derivatives of selected elastic moduli for olivine from gigahertz ultrasonic interferometry

Techniques have been developed to measure the cross pressure and temperature dependence of elastic moduli of olivine using the gigahertz ultrasonic interferometric method in a gas pressure vessel (to 500 MPa) equipped with an internal heater (to 500 K). Special attention has been drawn to the effect of the bond which couples the sample to the buffer rod. We obtained ∂2C22/∂P∂T = (2.8 ± 0.9) × 10−3 K−1 for a San Carlos olivine sample with a lapped contact. Selective values of ∂2KT/∂P∂T (0, 0.5 × 10−3, 1.0 × 10−3 K−1) are used to calculate their effect on cell volume, bulk modulus, and bulk sound velocity for olivine at pressures to 14 GPa and temperatures to 1800 K (410‐km depth), using the high‐temperature form of the Birch‐Murnaghan equation of state. The largest difference between the cell volumes for ∂2KT/∂P∂T = 1 × 10−3 K−1 and for ∂2KT/∂P∂T = 0 is about 0.6% at the highest pressure and the highest temperature (14 GPa, 1800 K). Therefore PVT data with precision at least better than 0.6% are required to distinguish between the extreme values of ∂2KT/∂P∂T for olivine if the pressure and temperature data are free of errors. If the cross pressure and temperature derivative term is neglected (∂2KT/∂P∂T = 0) in extrapolating laboratory elasticity data to mantle pressure and temperature conditions, the bulk modulus of olivine can be underestimated by as much as 10% and the bulk sound velocity by 3% at the 410‐km seismic discontinuity. Thus the present study highlights the need to measure elastic properties of mantle candidate minerals at the P‐T conditions of the mantle transition zone in order to establish a more precise model of the mantle mineralogy.

Elastic wave velocity measurement in multi-anvil apparatus to 10 GPa using ultrasonic interferometry

Elastic wave velocities of dense fine-grained polycrystalline Al 2O 3 were measured to 10 GPa at room temperature by ultrasonic interferometry within a multi-anvil apparatus. This technique features the use of a WC cube as the acoustic buffer rod allowing the location of 40 MHz LiNbO 3 transducers in a stress-free environment, an in-situ pressure indicator (Bi and/or ZnTe), and a wide frequency range (20 to 70 MHz) for precise (10 −3) measurement of travel times. The specimens recovered from the high-pressure experiments are undamaged and re-usable; and the travel times measured during successive pressure cycles are reproducible within 0.4%. Room pressure velocity measurements for Lucalox alumina yield V P = 10.92 ± 0.05 km s −1 and V S = 6.39 ± 0.03 km s −1. The average pressure derivatives of P and S wave velocities are dV P dP = 5.4 × 10 −2 km s −1 GPa −1 and dV S dP = 2.2 × 10 −2 km s −1 GPa −1 in the pressure range of 3–9.6 GPa, which are consistent with previous results from single-crystal and polycrystal specimens at much lower pressures. This study demonstrates the feasibility of measuring the acoustic wave velocity of mantle minerals at the pressures corresponding to the Earth's transition zone using ultrasonic interferometry in multi-anvil apparatus.

Ultrasonic properties of tendon: Velocity, attenuation, and backscattering in equine digital flexor tendons

Ultrasound velocity, attenuation, and backscattering were measured in vitro in samples of equine digital flexor tendon sandwiched between plane, parallel rexolite buffer rods. The buffer rods were coupled to transmitting and receiving transducers (nominally 10 MHz) mounted in-line and facing one another on the jaws of a digital caliper. Six superficial digital flexor (SDF) tendons and six deep digital flexor (DDF) tendons were measured in three orthogonal directions: along the long axis of the tendon (D), and across the tendon in the dorsal-volar (C), and lateral (L) directions. Substantial anisotropy was apparent in all the measured properties. The velocity data, which in both tendons showed a higher velocity along the fibers than across (e.g., in the DDF tendon at 0 degrees C: 1713 +/- 9 m/s in the D direction compared with 1650 +/- 5 m/s in the C direction), were consistent with a composite comprising stiff fibers embedded in a less stiff medium of lower speed. The apparent backscattering coefficient adjusted for the tissue's frequency-dependent attenuation (e.g., in the C direction of the DDF tendon at 0 degrees C: 7.4 x 10(-3) cm-1 sr-1), was independent of frequency in both transverse directions and larger than that measured along the long axis of the tendon (e.g., in DDF tendon at 0 degrees C: 1.2 x 10(-3) cm-1 sr-1 at 7 MHz) in which direction the apparent backscattering coefficient increased with frequency as f4.0 +/- 1.2. The frequency-independent backscattering was thought to be due to specular reflection from the boundaries between the fascicles, i.e., the bundles of fibers making up the tendon, while backscattering along the axis was due to structures of unknown origin, but of a size much smaller than 45 microns. Attenuation of ultrasound directed along the fibers was higher than that across (at 7 MHz in DDF tendon at 0 degrees C: 58 dB/cm in the D direction compared with 11.3 dB/cm in the C direction). Calculations indicated that the attenuation was primarily caused by absorption rather than scattering.

Transducers and measurements at high temperatures using resonant ultrasound spectroscopy.

Resonant ultrasound spectroscopy (RUS) measurements of material properties at high (above 150 °C) temperatures have been directed mainly at materials of geological interest, but a wide variety of other applications exists for high temperature RUS measurements. These include physical properties (phase transitions, elastic moduli) of novel solid state materials and understanding and control of processing parameters for industrial materials such as ceramics and steels. A RUS measurement system has been developed which operates to 600 °C without buffer rods. A description of the materials used and the transducer construction will be presented with some results from measurements on perovskite‐type crystal structures and magnetic materials. A discussion of the limits of the present system and possible techniques for bufferless transducers with operating temperatures to 1000 °C will be presented. [Work supported by the U.S. Department of Energy.]

Measurements for pressure and temperature dependencies of elastic moduli by the resonant sphere technique, RST.

The resonant sphere technique, RST, has been developed for measurements of elasticity and anelasticity of small crystal specimens. This method has advantages over other methods, especially in high‐temperature and high‐pressure measurements. New methods of data acquisition have made it convenient to measure resonance frequency at high temperatures (using a buffer rod), making a 1 K temperature interval measurement possible; this opens up many possibilities in the determination of physical properties of solids. Preliminary measurements of resonance frequency were performed by RST up to 100 MPa, which showed interference of vibration modes between the specimen and the pressure medium, even for helium gas as the pressure medium. This interference may become more serious at higher pressures or under liquid pressure. In order to evaluate such effects, the cavity resonance method was developed by Ohno in 1993, with a spherical shell structure with a spherical specimen at the center. This gives clear boundary conditions in the wave equations. Theoretical evaluation of the resonant frequency on such a system shows the necessity of correction to pressure derivatives of elastic moduli, even in measurements up to 100 MPa.

Hertzian contact transducers for nondestructive evaluation

Hertzian, dry, pointlike contacts are used to couple ultrasonic energy efficiently to plate wave modes in anisotropic solid plates. A new transducer configuration using a piezoelectric PZT-5H transducer and a quartz buffer rod is realized for this purpose. In particular, the lowest order antisymmetric Lamb wave (A0) mode is excited and detected in anisotropic plates at a frequency of 200 kHz and with signal-to-noise levels exceeding 65 dB. Time delay measurements and FFT techniques are used to obtain dispersion and anisotropy curves of phase velocity in anisotropic plates. The accuracy of the method is limited mainly by the distance measurements. In (001) silicon plates the agreement between theory and experiments is obtained with an accuracy of ±0.08%. Anisotropic phase velocity measurements are also performed for uniaxial graphite/epoxy composite plates and the results are compared with the theoretical model to derive the elastic constants of the composite. Through accurate phase velocity measurements, it is possible to detect delamination defects in composite plates with high resolution operating at 200 kHz. Using the surface impedance approach, a model is also developed to predict the effects of delaminations on phase velocity and the results are verified by experiments.

VHF/UHF range bioultrasonic spectroscopy system and method

A new system and method for characterizing biological tissues in vitro and liquids in the VHF and UHF ranges is described. Bulk acoustic properties such as the sound velocity, attenuation, acoustic impedance, and density are determined in reflection and transmission modes, with the biological tissue/liquid specimen sandwiched between the parallel surfaces of synthetic silica glass buffer rods having ZnO piezoelectric film transducers on their opposite ends. The method is an ultrasonic transmission line comparison method wherein the reference medium is distilled water, for which all acoustic properties are known. Measurement errors due to diffraction losses in the acoustic media and to mode conversion at the buffer/sample interfaces are corrected. Special techniques for achieving precise parallelism between the two rod surfaces, for movement to adjust the gap distance, and for signal processing are employed in order to obtain high measurement accuracy. Attenuation and reflection coefficients are determined using the gated pulse echo method. The sound velocity is determined with the gated pulse interference method by sweeping the ultrasonic frequency, or by changing the gap distance. Results of measurements on castor oil, cottonseed oil, silicone oil, and bovine liver, in the frequency range from 10 to 500 MHz, are presented and compared with results of earlier reports.

Fabrication and characterisation of aluminium clad aluminium–copper alloy cored rod

The Ohno continuous casting process was successfully applied to cast cored rod with Al–Cu alloy as a core material and Al as a clad material. Good metallurgical bonding was observed at the core/clad interface. Ultrasonic characterisation and pulse–echo measurements were performed to assess the suitability of the material as an acoustic buffer rod. Acoustic velocity profiles across the rod diameter and acoustic anisotropy were measured using a 225 MHz line focus beam scanning acoustic microscope. Longitudinal wave measurements with excellent signal/noise ratios were obtained.MST/3154

Ultrasonic in situ monitoring of sintering in alumina: P. Komarenko et al (University of Florida, Gainsville, USA), Int. J. Powder Metallurgy, Vol 30, No 1, 1994, 67–76

Ultrasonic waves were successfully employed to continuously monitor the presence and level of residual porosity in pure alumina samples during high temperature sintering. An alumina sample with initial porosity 29% was sintered at 1400°C for 4 hours. The magnitude of longitudinal velocity of 100 kHz pulsed ultrasound was continuously monitored throughout the sintering cycle. Measurements were accomplished in situ using a pulse-echo/through-transmission buffer rod waveguide technique employing magnetostrictive transducers and pressure friction acoustic coupling to the sample. A tungsten buffer rod protected a brazed Remendur magnetostrictive transducer rod from the temperature of the sintering furnace by keeping it near ambient temperature. With the present method, porosity can be determined to within ±1% of the absolute level

Acoustic double-reflection and transmission at a rough water–solid interface

The double interaction of a wave with a rough interface is important in many acoustic measurements. An acoustic beam that reflects twice from a rough water–solid interface is considered. The second reflection from the rough surface is accomplished after the transducer’s buffer rod is used as an acoustic mirror. Changes in the spatially averaged specular reflection are related to the phenomenon of ‘‘enhanced backscatter,’’ previously observed for diffuse scattering. Simple, approximate closed-form analytic formulas for the strength of the specular double reflections are given as a function of frequency and the stand-off distance of the transducer. As one application of the analytic results, a method is proposed for determining the surface correlation function from the specular double reflections. The same physics (and appropriately modified analytic formulas) apply to doubly transmitted waves. Experimental measurements have been made of acoustic double reflection with a normally oriented broadband piezoelectric transducer near a rough water–solid interface. Measurements of (1) the wave reflected once from the rough interface, and (2) the wave reflected twice from the rough interface are given. The strength of the specular reflections was measured as a function of frequency and the transducer’s distance from the surface. It was observed that for large distances between the transducer and the rough surface and at low frequencies the scattering-induced loss of the doubly reflected wave was twice the loss of a singly reflected wave. However, for small distances between the transducer and the surface and at high frequencies the scattering-induced loss of the doubly reflected wave was four times the loss of a singly reflected wave.

A modified ultrasonic interferometer for sound velocity measurements in molten metals and alloys

An ultrasonic interferometer has been developed for measuring compressional wave velocity (VP) and attenuation (or conversely, quality factor QP) in molten Fe, Fe-Ni, Fe-Ni-S, and Fe-Ni-Si alloys. Results for pure molten Fe are presented. A radio frequency (rf) induction technique is used for heating that allows a ±1 K temperature stability at 1973 K. The effects of the electromagnetic field interaction with the molten conductive metal are discussed in terms of applicability to VP and QP measurements. Considerations of acoustic impedance and thermal absorption are presented to discuss the high-temperature use of polycrystalline Al2O3 buffer rods for velocity and attenuation measurements. Viscoelastic theories, when applied to pure molten Fe, predict an extremely small acoustic coefficient of attenuation. Suggestions are made to circumvent the experimental difficulties encountered in attenuation measurements.

The relationships between the velocities, attenuations and petrophysical properties of reservoir sedimentary rocks1

AbstractWe have measured the velocities and attenuations of compressional and shear waves in 29 water‐saturated samples of sandstones and shales at a confining pressure of 60 MPa and at frequencies of about 0.85 MHz. The measurements were made using a pulse echo method in which the samples (diameter 5 cm, length 1.5 cm to 2.5 cm) were placed between perspex buffer rods inside a high‐pressure cell. The velocity of each seismic wave was determined from the traveltime difference of equivalent phase points (corrected for diffraction effects) of the signals reflected from the top and from the base of each sample. Attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals. The attenuation data are presented as ‘quality factors’: Qp and Qs for compressional and shear waves respectively. The results show that Qs is strongly correlated with Vs, that Qp is weakly correlated with Vp, and that Qp is strongly correlated with Qs. Qp is strongly dependent on the volume percentage of the assemblage of intra‐pore minerals, whether they are clays or carbonates. It is concluded that the attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra‐pore mineral assemblage, which is a result of their very different elastic moduli.

Materials for high temperature acoustic and vibration sensors: A review

The industrial and scientific communities have expressed a real need for the capability of pressure, acoustic, and vibration sensing at elevated temperatures. This review compares the various commercial methods and materials for acoustic transduction, identifying their advantages and limitations. Techniques and devices include simple piezoelectric sensors, accelerometers, strain gauges, proximity sensors, fiber optics and buffer rods. Sensors with operating temperatures in excess of 650°C are readily available from commercial sources. Of the mechanisms investigated, the piezoelectric approach offers several advantages, including design cost and simplicity. Therefore, the bulk of this review concentrates on piezoelectric materials, both those that are already available commercially, and those that are presently under development. The new materials include perovskite layer structure ferroelectric ceramics, which possess the highest known Curie temperatures, and thin film AlN, which has been reported to be piezoactive at 1150°C.

Method and apparatus for thermoacoustimetry: applications to polymers and glasses

A method and a convenient inexpensive apparatus are described for carrying out thermoacoustic analysis (TAA) of materials from room temperature to about 350 degrees C by monitoring the changes in the ultrasonic velocity in the sample as a function of temperature with the heating rate as a user-defined variable parameter up to 10 degrees C min-1. The thermoacoustimetric apparatus described is readily constructed from commercially available components with minimum workshop machining. The sample is loaded by sandwiching it between two identical glass buffer rods, one of which is stationary and the other vertically movable, without the need to attach transducers and thermocouples directly to the sample. The ultrasonic velocity is obtained from the time difference between the through signal at the receiving end and the echo at the transmitter end. The apparatus was used to measure the glass transition temperatures of polycarbonate, polyphenylenesulphide in matrix form as part of an aramid fibre-PPS matrix composite, poly(methyl methacrylate) and near stoichiometric As2Se3 glass from the break point of the semilogarithmic plot of the ultrasonic velocity against the temperature as in the case of thermomicrohardness measurements. The measurements, where possible, have been compared with those obtained from conventional differential scanning calorimetry and thermomicrohardness analysis.

One-point contact measurement of spherical resonances

Ceramic bearing balls are desirable for use in high-temperature and nonlubricative environments because of their ability to retain high mechanical strength and reduced wear. However, because ceramics are brittle, it is very important to inspect ceramic parts for the existence of small (1–10 μm) surface defects. The contact–contact resonant sphere technique has been shown to be able to detect the presence of surface defects in spherical objects. This technique, however, has certain limitations that are especially important when inspecting small spheres. In this letter we present a true one-point-contact technique to circumvent these limitations. We excite resonances of spheres at both low and high frequencies. Resonances are generated by forming a one-point Hertzian contact between the sphere and a spherical depression in a buffer rod with a transducer. The resonance spectrum is detected from the opposite pole of excitation using an optical interferometer. At low frequencies, bulk resonances of the sphere are excited, and material properties are determined. At high frequencies, surface-wave resonances of the sphere are excited, and the dispersion relation of the waves is measured. The measured dispersion relation of the sphere is correlated to the surface wave velocity on the sphere and to the presence of surface defects.

Fabrication and characterization of continuously cast clad metallic buffer rods

The fabrication, characterization, and ultrasonic measurements of clad metallic ultrasonic buffer rods are presented. The core and the cladding consist of tin/lead alloy and pure tin, respectively, produced by a vertical continuous casting technique. The acoustic velocity profiles across the rod diameter are measured using a 225-MHz line focus beam scanning acoustic microscope. A schlieren visualization system confirms the concentration of acoustic energy in the core. Spherical acoustic lenses have been fabricated at the ends of the rods. Focused and unfocused ultrasonic measurements at frequencies between 2 to 10 MHz and signals with excellent signal to noise ratios have been obtained.

Nonlinear attenuation of 10- to 25-MHz ultrasonic waves in argon at pressures up to 10 MPa.

A large dynamic range (70 dB) ultrasonic measurement system has been developed to investigate the technology and the phenomonology of finite-amplitude high-frequency (10–25 MHz) acoustic waves in gases at pressures up to 10 MPa (100 bar). Transmission measurements of velocity and attenuation are made using two efficient lithium niobate transducers set onto quartz buffer rods, with variable separation from less than 1 to 25 mm. In this paper, data will be presented that show nonlinear phenomena as a gated tone burst (20 cycles) of finite amplitude acoustic waves propagated in argon. The received signals are digitized and analysis is performed in the time domain and using a Fourier transform. For low powers, linear attenuation with distance is observed. For finite amplitude waves, excess nonlinear attenuation and significant second harmonic generation are observed. The nonlinearity parameter at various combinations of pressure, temperature, and frequency is reported for argon.

Laboratory measurements of the seismic properties of sedimentary rocks

Abstract A laboratory technique for the measurement of compressional and shear wave velocities and attenuations (quality factors) of sedimentary rocks at pressures up to 70 MPa and at frequencies up to 1 MHz was published by Winkler and Plona in 1982. In the method the rock sample is enclosed between buffer rods. The arrival times and amplitudes of the signals reflected from its top and base are compared. A similar technique has been used for many years in the non-destructive testing of metals and plastics. This paper describes the use of a single-frequency pulsed sine wave for the velocity and attenuation measurements, in addition to the transient pulse used in the Schlumberger method. Measurements were made on samples with accurately known compressional and shear wave properties and on replicated rock samples. The results demonstrate that the determinations of velocities are accurate to ± 0.3%, and that the determinations of attenuation are accurate to ±0.1 dB/cm at 0.85 MHz.

Sonic velocity and attenuation in wet compact cow femur for the frequency range 5 to 100 MHz

Ultrasonic studies on bone have not been done as intensively as other tissues, probably because there is less opportunity to examine bone in vivo by this modality. There is considerable interest in using ultrasonics to learn about the material properties of bone for which purpose the sonic spectrum may be useful. The longitudinal sonic velocity and attenuation have been found for several sections from one sample of wet cow femur for both the axial and radial directions over the frequency range of 5 to 100 MHz. The basic technique was solid-to-solid contact using a fused quartz buffer rod coupled to the bone specimen. There is clear evidence of velocity dispersion which Lakes et al. (1986) did not find over a frequency range up to 16 MHz. While there seems to be a peak in both velocity and attenuation at 70 MHz, it is necessary to obtain measurements at higher frequencies to make sure this is not an artifact. The axial sonic velocity varied from 4.29 km/s at 5 MHz to 4.447 km/s at 50 MHz, while the radial velocity was 3.45 km/s at 5 MHz and increased to 3.62 km/s at 50 MHz. The attenuation coefficient axially started at a mean value of 3.5 db/mm at 5 MHz and increased to a mean of 19 db/mm at 100 MHz. The corresponding radial attenuation coefficients are 5.2 and 26, respectively.

Technique for measuring ultrasonic velocity and attenuation changes in attenuative materials at temperature such as during sintering processes

This paper describes a PC-based automatic measuring system for ultrasonic velocity and attenuation changes in highly attenuating green-body ceramics during sintering temperatures. The system uses pulse-echo/through-transmission buffer rod technique and records pulse-echo and through-transmission waveforms at programmed time or temperature intervals. Data can be taken without interruption during temperature schedules lasting many days. Archival files of the waveform data are saved on disks for later analysis. Accuracy of the technique is demonstrated for solid fused silica for which dynamic resonance and Brillouin scattering data of the longitudinal velocity are compared at temperatures up to 1200 °C. The system has been used successfully for measuring longitudinal velocity and attenuation changes at 5 MHz during sintering of ZnO-based varistor materials and YBa2Cu3Ox superconducting ceramics.