Coupling Medium Research Articles

Scanning acoustic microscope — has microwave transducer to direct beam through sapphire backed lens with pointed tip immersed in coupling medium : IBM Corp. European Patent No. 198, 944 (29 Oct. 1986)

Scanning acoustic microscope — has microwave transducer to direct beam through sapphire backed lens with pointed tip immersed in coupling medium : IBM Corp. European Patent No. 198, 944 (29 Oct. 1986)

Nondestructive characterization of texture and plastic strain ratio of metal sheets with electromagnetic acoustic transducers

All the lowest-order independent CODF (crystallite orientation distribution function) coefficients W400, W420, and W440 of rolled steel sheets, with thickness less than 1 mm, have been obtained nondestructively by using the known single-crystal elastic constants and the relative ultrasonic velocities measured with EMATs (electromagnetic acoustic transducers). The ultrasonic velocities of all the waves, longitudinal waves, shear waves propagating in the through thickness direction, and SH0 (shear horizontal) plate waves, were measured by the EMATs. No acoustic coupling medium was necessary, making possible quick, accurate, and reproducible measurements. It is shown that the CODF coefficients can be obtained as the solutions of three linear equations in which the measured relative ultrasonic velocities are included. There was an overall correspondence between the ultrasonic pole figures drawn using the obtained CODF coefficients and x-ray pole figures. All nine elastic constants of a steel sheet were also calculated. Average Young’s modulus Ē and planar variation in Young’s modulus dE calculated using the nine elastic constants were consistent with average plastic strain ratio r̄ and planar variation in plastic strain ratio dr, respectively, showing that the ultrasonic method here is well adapted for practical use.

Theoretical investigation of a phased-array hyperthermia system with movable apertures

A four-applicator phased-array hyperthermia system with movable apertures (MA) is compared with an eight-applicator annular phased-array hyperthermia system with fixed apertures (AA) in terms of the HEP (hyperthermia equipment performance) values, based on two-dimensional models and the bioheat transfer equation. A hybrid element method is used to calculate the zeta-directed two-dimensional electric field with the inhomogeneities in tissue properties taken into account. The amplitudes and phases of each applicator are then optimized with the objective of uniform power deposition in the tumour and no power deposited in normal tissues. The temperature distributions under different blood flow conditions are obtained by solving the bioheat transfer equation using the finite element method. It is found that among the seven patient models studied, the MA and AA in general perform equally well when the tumour has zero blood flow, or equally poorly when the tumour has a blood flow larger than 5 ml/100 g per min. The performance of AA is often significantly better than that of MA when the tumour blood flow is 2.7 ml/100 g per min. The effects of different weighting functions are evaluated. We show that even if uniform absorbed power density (ARD = absorption rate density) could be achieved in the tumour volume with zero ARD in normal tissue the entire tumour would still not be brought to 43 degrees C or greater. However, it is found that the performance of uniform ARD in the tumour is on average far better than either the AA or MA, and choosing the uniform ARD as the objective function improved 35% of the cases for AA and 16% for MA. The optimization formula includes a weighting function that can be varied for different tissues. By decreasing the weights in regions of high blood flow the HEP values can sometimes be improved quite noticeably. Finally, the importance of the locations of applicators is studied. The results obtained indicate that the applicators should be placed about 5 cm or more away from the patient body (assuming water is the coupling medium) to ensure good HEP ratings.

Immobilization of α‐chymotrypsin onto hydrolyzed poly(ethylene)‐g‐co‐hydroxyethyl methacrylate

Abstractα‐Chymotrypsin has been immobilized onto partially hydrolyzed poly(ethylene)‐g‐co‐hydroxyethyl methacrylate (120% graft), using 1‐cyclohexyl‐3‐(2‐morpholinoethyl)‐carbodiimide‐p‐toluene‐sulphonate (CMC) as the activating agent. The influence of the enzyme concentration, the carbodiimide concentration, and the coupling medium on the immobilization reaction was studied. A system with 160 mg of coupled enzyme per gram copolymer, providing 126 mg of active enzyme per gram of copolymer was obtained. The KM, Vmax, and the optimum temperature profile and optimum pH value for the free and immobilized α‐chymotrypsin were determined.

Pressurized Superfluid 4He Acoustic Microscopy

An acoustic microscope has been developed which makes use of pressurized super fluid helium as an acoustic coupling medium. Acoustic micrographs were taken using pure super fluid 4He under saturated vapor pressure at 0.2 K and under 25 atm at 0.2 K and 1.9 K, for the frequency of 400 MHz. By pressurizing liquid 4He, the acoustic attenuation decreases, the efficiency of the antireflection coating increases, and the power level of saturation caused by nonlinearity of the super fluid 4He is raised. A good signal-to-noise ratio of imaging is thus obtained.

An analysis of a planar optical directional coupler with a lossless Kerr-like coupling medium

The nonlinear all-optically controlled coupling characteristics are studied analytically and numerically for two planar optical waveguides coupled through a lossless Kerr-like slab. The exact dispersion equation for this waveguiding structure is derived in terms of Jacobian elliptic functions. The optical intensity-dependent coupling length is described as a combination of symmetriclike and antisymmetriclike modes of propagation, derived from the nonlinear combination of the independent modes of the structure. A simple analytical formula is derived for the critical power, defined as the power above which the antisymmetric mode disappears and complete energy transfer between the two waveguides is no longer possible. The analysis provides insight into the complicated nature of the waveguiding structure behavior, and it shows one possible approach to solving difficult propagation problems in nonlinear optical waveguides of this or similar configuration.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sensor for acoustic shock wave pulses

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Cross-polarization two-beam coupling in optically active photorefractive media

We present a theoretical description of the coupling of energy and polarization between two beams in an optically active photorefractive medium. We apply this analysis to the problem of cross-polarization two-beam coupling and determine the dependence of the cross-polarization coupling gain on the input polarization states of the interacting beams and the properties of the coupling medium. In particular, we show that by a proper choice of the input polarization states, the cross-polarization gain seen in typical optically active photorefractive materials may be increased by more than 2 orders of magnitude over that previously observed. As a test of our theoretical treatment, we also apply it to standard two-beam coupling in Bi12SiO20 and obtain close numerical agreement with earlier experimental results in this material.

Waveguides in medical ultrasonics: an experimental study of mode propagation

Experimental results of ultrasound of varying frequency (0.8–5.0 MHz) propagating in cold drawn wires of stainless steel and aluminium ranging in diameter from 0.25 to 1.21 mm are in close agreement with theoretical predictions. This agreement is maintained when the coupling medium between the wire and the ultrasound source is a short distance of water. Similar measurements for brass and copper wires are in less close agreement with theory due, probably, to the effect of greater anisotropy.

Sonographic Piezoelectric Lithotripsy: More Bang for Your Buck*

The four major components required in any lithotripter are an energy source to generate the shock wave, a focusing device to focus the shock wave toward the focal point, a coupling medium to couple the shock wave to the patient, and a stone localization system to allow the focal point of the shock wave to be aligned precisely on the stone. The development of second-generation lithotripters has resulted in modifications of these four lithotripsy components. All second-generation machines have done away with the large water bath first used by Dornier in the HM3 device, and all new models utilize either a fluid-filled membrane or a small pool of degassed water.

Coupled cw dye lasers using intracavity four-wave mixing

An experimental investigation of laser-oscillator frequency locking by a four-wave interaction was conducted. An experiment was performed that successfully demonstrated the locking of two cw dye lasers using this concept with Na vapor serving as the nonlinear (coupling) medium.

Nondestructive measurement of texture and nine elastic constants of rolled metal sheets by EMAT

All the lowest-order independent coefficients W400, W420, and W440 for the crystallographic orientation distribution function were obtained nondestructively for thin rolled steel sheets by measuring ultrasonic wave speeds and making use of the known values of the single-crystal elastic constants. All the ultrasonic wave speeds were measured by EMAT so that no acoustic coupling medium was necessary, and the measurements were done quickly and with very good reproducibility. Pole figures were calculated using the obtained coefficients W400, W420, and W440 and the results were quite similar to the pole figures obtained by the x-ray diffraction method. It is well known that a rolled steel sheet can be modeled as an orthorhombic continuum having nine different elastic constants. It is also known that only six of the nine constants are independent when the sheet is a polycrystal of cubic crystallites and assuming that the macroscopic properties can be predicted by an averaging scheme. All these nine constants were calculated using the obtained W400, W420, W440, and the known single-crystal elastic constants. Young's moduli in the plane of the rolled steel sheet were also calculated and compared with the measured plastic strain ratio. Good relations were obtained between the average Young's modulus E and the average plastic strain ratio r.

Theoretical and experimental study of ultrasonic surface modes at a solid-fluid periodic interface

The generation of ultrasonic surface waves on a solid-liquid periodic interface is demonstrated. Characterization of leaky Stoneley modes and leaky Rayleigh modes is obtained by looking at the reflected and the transmitted broadband spectra. It is shown both experimentally and theoretically that the frequency and amplitude of such surface resonances are significantly affected, not only by the spatial periodicity of the profile, but also by the peak-to-valley height of the roughness. As a result, the practical problem of measurement of the geometrical parameters of the periodic surface, knowing the ultrasonic velocities in the coupling medium, is addressed. Conversely, we discuss a method to estimate the surface wave velocities on a given known profile.

Application of the sinc basis moment method to the reconstruction of infinite circular cylinders

A solution of the ultrasonic scattering and inverse scattering problem has been obtained by solving the inhomogeneous Helmholtz wave equation by the sinc basis moment method. In this numerical study, the algorithm of S.A. Johnson and M.L. Tracy (1983) has been applied to the reconstruction of an infinite circular cylinder that is subject to an incident cylindrical wave of ultrasound and is surrounded by a homogeneous coupling medium. For weak scattering cylinders, successful reconstructions have been obtained using the known exact solution for the scattered field as the input data for the algorithm. A detailed discussion of sampling requirements for this algorithm is presented, and the threshold derived correlates well with results of a numerical study of variation of the sampling density. Effects of varying object contrast, object size, grid size, sampling density, and method of iteration are investigated. Because the algorithm is slow, optimization of computation is described.

Lithotripter systems

Lithotripsy in its various forms has revolutionalized the treatment of kidney and ureter stones. In extracorporeal lithotrips, pulsed acoustic shock waves are generated outside the body and focused via a coupling medium to the concrement. The location of the focus is controlled by fluoroscopy of ultrasound imaging. Starting from simplified models, two methods for generating shock wave pulses are described: (a) point-like supersonic emitters; and (b) two-dimensional emitters of finite amplitude waves. The principles and performance of a spark-gap emitter with a focusing ellipsoid, an electromagnetic acoustic source with a focusing lens, and a spherical concave piezoceramic source are described and discussed. Commercial lithotripter systems and their components for coupling, imaging, patient handling, and triggering are described and their performance is discussed. >

Solid-phase peptide synthesis using tert.-butyloxycarbonylamino acid pentafluorophenyl esters.

Boc-amino acid pentafluorophenyl esters have been successfully used in solid-phase peptide synthesis. The coupling rates and the purity of the products are comparable to those with the symmetrical anhydrides. These active esters require modified Merrifield resin, polar medium for coupling and in some cases, base catalysis.

Application of the sinc basis moment method to the reconstruction of infinite circular cylinders

A solution to the ultrasonic scattering and inverse scattering problem has been obtained by solving the exact inhomogeneous Helmholtz wave equation via the sinc basis moment method. In this numerical study, the algorithm of Johnson and Tracy [Ultrason. Imag. 5, 361–375 (1983)] has been applied to the reconstruction of an infinite circular cylinder which is subject to an incident cylindrical ultrasonic wave and is surrounded by a homogeneous coupling medium. For weak scatterers, successful reconstructions have been obtained using the known exact solution for the scattered field in the case of a circular object function as the input data for the algorithm. Five percent noise does not affect performance, nor does transmitter and receiver distance to the object for a loss‐less coupling medium. Also for weak scatterers and exact field data, the reconstruction quality improves for cylinders when the grid size increases because the discretized shape becomes more nearly circular. Use of either the discrete scatte...

Ray trace calculations of ultrasonic fields

A computer code has been written to calculate realistic ultrasonic fields in solids. The program calculates the field due to a transducer coupled to the solid through either a fluid medium such as water or a solid medium such as a plastic shoe with a thin layer of fluid couplant. In this technique the transducer face is divided up into many small areas, each of which is assumed to be a source of spherical waves. A ray is traced from each source point, through the coupling medium and into the solid to the requested field point. The vector sum of the fields of each of the rays is then calculated to find the total incident field at that point for a particular frequency. The calculations have been compared to the fields predicted by the models of Thompson and Gray [R. B. Thompson and T. A. Gray, “Analytic Diffraction Corrections to Ultrasonic Scattering Measurements,” in Review of Progress in QNDE 2, edited by D. O. Thompson and D. E. Chimenti (Plenum, New York, 1983), pp. 567–586] and Thompson and Lopes [R. B. Thompson and E. F. Lopes, “The Effects of Focusing and Refraction on Gaussian Ultrasonic Beams,” J. Nondestruct. Eval. 4, 107–123 (1984)] and with experimental results. [Work supported by the U. S. Department of Energy, Office of Energy Research, Office of Basic Energy Sciences, under DOE Contract No. DE‐AC07‐76ID01570.]

Theoretical analysis of the angle beam ultrasonic testing method of unidirectional graphite/epoxy composite material

The reflection and refraction of an ultrasonic beam on the boundary of separation between a coupling medium and a unidirectional composite material is studied. The composite material is considered as an anisotropic material of hexogonal symmetry. Two variants of the coupling are studied: first is the immersion variant, when the ultrasonic beam is incident from the liquid; second is the contact variant, when the ultrasonic beam is incident from an isotropic solid wedge and the slip boundary condition, between the solid wedge and the composite material, is used. The energy reflection and refraction coefficients are analyzed as a function of the angle of incidence, with the angle of the orientation of the fibers relative to the incidence plane as a parameter. Principal attention is given to critical‐angle behavior and the deviation of the energy flux from the wave normal in the composite material.

High‐frequency acoustic systems for robotic applications

High‐frequency ultrasonic systems, operating in the 200‐kHz to 1‐MHz frequency range and using air as the acoustic coupling medium are an effective complement to optical systems for robotic and industrial measurement applications. An air‐coupled ultrasonic system was developed which produces well damped and focussed ultrasonic beams with good spatial resolution. Tests show that distance measurements with a resolution of 0.001 in. can be made through several inches of air at a rate of several hundred Hz. Focused transducers can reduce the effective area of measurement to below 0.05 in. at the focal point. The system was employed in several applications, including parts profiling, thickness testing, and the detection of missing parts. The apparent advantages that acoustic devices have over optical systems include lower cost by a factor of 5 or 10, and a higher speed of operation by perhaps 2 orders of magnitude.