Gerald Diebold

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Verified

Gerald verified their affiliation via an institutional email.

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• Ph.D
• Professor Emeritus at Brown University

Although the photoacoustic effect is most commonly generated by pulsed or amplitude modulated continuous optical sources, it is possible to generate acoustic waves by moving a constant amplitude, continuous light beam. If the light beam moves at the speed of sound, an amplification effect takes place which can be used in trace gas detection. Here,...

The motion of an optically levitated, transparent sphere in an amplitude-modulated, Gaussian laser beam is shown to be described by Mathieu functions. Solutions to the equation of motion for the particle are found with and without the effects of viscosity for sinusoidal optical amplitude modulation. Solutions for step function changes in the amplit...

Photoacoustic waves can be detected by recording optical beam deflection as a result of density gradients inherent in the waves. Beam deflection can be recorded from a single laser beam placed at a distance from the source where data are generated as a function of time, or by recording beam deflections at a single time as the position of the probe...

Photoacoustic excitation of a fluid sphere generates an outgoing ultrasonic wave whose time profile permits determination of the density, sound speed, and diameter of the sphere. Experiments with pulsed laser beams have confirmed the major predictions of existing theory. With regard to acoustic waves generated within spheres, although mathematical...

Guest Editorial article for the special issue of the Journal of Applied Physics called "Photothermics". In this article we cover recent advances in the studies of photoacoustic and photothermal phenomena covered in this special issue.

When a modulated light beam is absorbed by an incompressible particle, the photoacoustic effect can take place through heat diffusion into the surrounding fluid followed by thermal expansion and the generation of sound. When two laser beams modulated at different frequencies irradiate a particle in aqueous solution, the effect of one laser is to mo...

When two different chromophores placed close to each other in water are optically excited by continuous light beams with intensities modulated at two different frequencies, the temperature change from heat diffusing from one chromophore affects the magnitude of the thermal expansion coefficient in the region of the other chromophore, owing to the f...

Precise measurement of temperature is significant to studies in chemical and biological systems as their reaction kinetics are sensitive to temperature variations. However, using conventional temperature probes will invade the systems vulnerable to exogenous disturbance, and thus introduce artifacts. Infrared pyrometry is a noninvasive technique fo...

The photoacoustic effect is governed by a wave equation with a source term proportional to the time derivative of the optical heat deposition per unit volume and time. Although the typical configuration for generation of the photoacoustic effect makes use of pulsed or amplitude modulated optical beams, the form of the source term in the wave equati...

The photoacoustic effect is usually studied in an isotropic medium on a laboratory scale. However, it is possible to use optical sources to launch pressure perturbations in the atmosphere consisting of both acoustic and gravity waves. Here photoacoustic theory is extended to incorporate the effects of a stratified atmosphere and a gravitational fie...

A method for directional emissivity determination by measurement of absorption through a photothermal effect is described. The experimental results found for Au, Al, and graphite show good agreement with the theoretical prediction of the electromagnetic theory. It is shown as well that complex refractive indices can be determined by fitting angular...

We show that emissivities in the near infrared can be determined relative to a reference surface employing the photoacoustic effect. The photoacoustic cell is equipped with two windows and a pair of synchronously moving chopping wheels so that the cell alternately views the test and the reference surface. The acoustic signals produced in the cell a...

The Ludwig-Soret effect, also known as thermal diffusion, refers to the separation of gas, liquid, or solid mixtures in a temperature gradient. The motion of the components of the mixture is governed by a nonlinear, partial differential equation for the density fractions. Here solutions to the nonlinear differential equation for a binary mixture ar...

Although the photoacoustic effect is typically generated by amplitude-modulated continuous or pulsed radiation, the form of the wave equation for pressure that governs the generation of sound indicates that optical sources moving in an absorbing fluid can produce sound as well. Here, the characteristics of the acoustic wave produced by a radially s...

The angular dependence of emissivity is obtained indirectly by measuring absorption through photothermal effect. Absorption of light induces thermal deformation and then electric charge generation. Angular dependence of emissivity of graphite and copper are given.

Although the photoacoustic effect is commonly produced through use of pulsed or amplitude-modulated radiation, it can also be generated by a steady source moving in space. Here, the properties of the photoacoustic effect generated by moving sources in three dimensions are investigated. The mathematics for the moving photoacoustic point source are s...

Significance The photoacoustic effect refers to the generation of sound through a process of optical heat deposition followed by thermal expansion, resulting in a local pressure increase that produces outgoing acoustic waves. In the linear acoustic regime, a unique property of the photoacoustic effect in a geometry with symmetry in one dimension is...

Shock waves resulting from irradiation of energetic materials with a pulsed ultraviolet laser source have been shown to be an effective indicator for explosives detection. Here, the features of shock wave propagation are explored theoretically. The initial stage of the shock motion is simulated as a one-dimensional process. As the nonlinear wave ex...

In this paper, we examine a laser-based approach to remotely initiate, measure, and differentiate acoustic and vibrational emissions from trace quantities of explosive materials against their environment. Using a pulsed ultraviolet laser (266 nm), we induce a significant ( > 100 Pa ) photoacoustic response from small quantities of military-grade ex...

A photoacoustic cell containing an infrared active gas and equipped with a pair of infrared transmitting windows that alternately views two bodies at different temperatures through a pair of chopping wheels acts as a differential detector of the radiation emitted by the two bodies. A theory for the photoacoustic signal shows that the device acts to...

Although the photoacoustic effect is typically generated by pulsed or amplitude modulated optical beams, it is clear from examination of the wave equation for pressure that motion of an optical source in space will result in the production of sound as well. Here, the properties of the photoacoustic effectgenerated by moving sources in one dimension...

Although the photoacoustic effect is almost universally generated by radiation whose intensity is varied in time either by amplitude modulation of a continuous optical source or through the use of pulsed irradiation, it is possible to produce sound by movement of a continuous source in space. Here, the characteristics of sound production by movemen...

Irradiation of an optically thin layer immersed in a transparent fluid with pulsed laser radiation can generate photoacoustic waves through two mechanisms. The first of these is the conventional optical heating of the layer followed by thermal expansion, in which the mechanical motion of the expansion launches a pair of oppositely directed sound wa...

The wave equation for pressure that governs generation of the photoacoustic effect possesses a forcing term proportional to the time derivative of the energy delivered to the gas per unit volume and time. A positive pressure fluctuation, with its accompanying density increase, thus increases the optical absorption and provides a positive feedback m...

The sedimentation potential refers to the generation of a voltage in an ionic or colloidal solution as a result of motion of the ions or colloidal particles relative to the surrounding fluid. In the case of colloidal suspensions, where the density of the colloidal particles differs from that of the fluid, the effect of a body force on the suspensio...

Irradiation of an absorbing surface in contact with a transparent fluid with a pulsed laser can result in the generation of extremely large thermal gradients. For example, when a laser with a pulse width of 10 ns and a fluence of 1 J/cm(2) irradiates a region with an absorption of 1 cm(1) having the thermal properties of liquid water, a thermal gra...

Pulsed laser irradiation of a weakly absorbing fluid sphere in a transparent medium results in the production of a large thermal gradient at the surface of the sphere. The rapid transfer of heat from the sphere to the surrounding fluid as a result of the thermal gradient generates high frequency photoacoustic transients which affect the leading edg...

Irradiation of an absorbing surface in contact with a transparent fluid by a pulsed laser can result in generation of enormous thermal gradients. Here it is shown that the effect of such thermal gradients on photoacoustic waves is the production of fast transients that accompany the leading edge of the wave. Calculations show that the transients ca...

Absorption of high power laser radiation by aqueous carbon suspensions is known to result in the formation of highly compressed bubbles of hydrogen and carbon monoxide through the endothermic carbon-steam reaction. The bubbles expand rapidly, overreaching their equilibrium diameter, and then collapse tens to hundreds of microseconds after formation...

The ultrasonic vibration potential, which refers to the generation of voltages on the passage of sound through colloidal or ionic solutions, can be used as a method of imaging, where image contrast is governed by the presence of colloidal or ionic regions within a body. Here we derive an expression for the current in a pair of parallel electrodes p...

The wave equation for the photoacoustic effect in a three-dimensional spherically symmetric, or two-dimensional structure where the compressibility or density varies sinusoidally in space reduces to an inhomogeneous Mathieu equation. As such, exact solutions for the photoacoustic pressure can be found in terms of either Mathieu functions, integer o...

The photoacoustic effect for a one-dimensional structure, the sound speed of which varies sinusoidally in space, is shown to be governed by an inhomogeneous Mathieu equation with the forcing term dependent on the spatial and temporal properties of the exciting optical radiation. New orthogonality relations, traveling wave Mathieu functions, and sol...

We derive solutions to an inhomogeneous Mathieu equation that describes the photoacoustic effect in a one-dimensional phononic structure whose acoustic properties vary sinusoidally in space. Solutions show splitting of resonances, the space equivalent of subharmonic generation, and spatial confinement. Properties of the photoacoustic effect includi...

We derive an expression for the electric field at the image plane from the Kirchhoff-Fresnel integral for a grating in contact with an object in an x-ray, in-line imaging configuration that shows the grating to give a heterodyning effect. We also show how image contrast in a harmonic of the grating is enhanced depending on the first space derivativ...

Laser excited photoacoustic and photothermal waves can be generated in one-dimensional structures whose acoustic or thermal properties vary sinusoidally in space. The wave equations describing the pressure or the temperature in such structures can be shown to reduce to inhomogeneous Mathieu equations. Solutions of the Mathieu equation are obtained...

The generation of thermal waves in a one-dimensional structure with a sinusoidal variation in thermal diffusivity can be described by an inhomogeneous Mathieu equation. An exact solution to the frequency-domain Mathieu equation can be found by using a variation of parameters method to give the alternating component of the temperature along the stru...

An exact solution to the nonlinear differential equation describing thermal diffusion (the Ludwig-Soret effect) for a binary mixture in a linear temperature field is given. The differential equation of motion for the components of the mixture is reduced to a heat diffusion equation with boundary conditions that act as unbounded sources which grow i...

Refractive index gradients in materials or at material interfaces lead to x-ray diffraction. Interference of this radiation with adjacent x-ray waves causes phase contrast that can be used for imaging purposes if an x-ray source with sufficient spatial coherence is used. The imaging modality presented here uses hard x radiation diffracted at interf...

The Ludwig–Soret effect, also known as thermal diffusion, describes the separation of mixtures in the presence of a temperature gradient. Here, a solution to the nonlinear differential equation that describes the motion of components of a binary mixture in a linear temperature field is given for long times, when the distribution of the components i...

Generation of the photoacoustic effect through chemical reaction of particulate carbon in chemically reactive solutions is presented. Experiments are carried out using a Q?switched Nd:YAG laser to heat carbonnanoparticles, initiating chemical reaction which results in sound production. The amplitude of the photoacoustic signal from a carbonsuspensi...

We discuss the photoacoustic effect in one-dimensional phononic structures with sinusoidal modulation of its acoustic properties. The periodic structure is considered to have a modulation in its density or compressibility of the form 1-2γ(2πxa), where γ is the modulation factor and a is the periodic length of the phononic structures. The properties...

Irradiation of chemically reactive particulate suspensions by high power, pulsed laser radiation initiates reactions at the sites of the particles so that besides the absorbed optical energy, chemical energy is liberated. In addition to the release of chemical energy, chemical reaction can result in gas production both of which result in enhancemen...

The application of intense ultrasound to a liquid-gas interface results in the formation of an ultrasonic fountain and generates both mist and vapor from the liquid. Here, the composition of the vapor and aerosol above an ultrasonic fountain is determined as a function of irradiation time and compared with the results of sparging for five different...

There is widespread concern among health care professionals regarding the increase in HCC and the lack of optimal detection methods that lead to early diagnosis and treatment. It is hoped that early diagnosis may improve the prognosis of this almost uniformly fatal disease. There are substantial issues with false/negatives and false/positives and b...

If an absorbing medium is constructed so that its sound speed varies periodically in space, the photoacoustic effect takes on a different character than when it is generated in a homogeneous medium. The case considered here is where either the density or the compressibility of the medium varies sinusoidally in space. The wave equation for pressure...

The high resolution characteristic of in-line x-ray phase contrast imaging can be used in conjunction with directed ultrasound to detect small displacements in soft tissue generated by differential acoustic radiation pressure. The imaging method is based on subtraction of two x-ray images, the first image taken with, and the second taken without th...

A Fresnel–Kirchhoff integral can be used to calculate x-ray phase contrast images when the transmission function is known. Here expressions for image intensity are derived for objects with axial symmetry for an x-ray source with non-vanishing dimensions. An expression for the image intensity is given for an x-ray source whose intensity distribution...

Imaging with the ultrasonic vibration potential is based on voltage generation by a colloidal or ionic suspension in response to the passage of ultrasound. The polarization within a body arising from the oscillatory displacement in the ultrasonic field produces a current in a pair of external electrodes that is measured as a function of time or fre...

The Journal of Applied Physics edited a special topic section in the general area of applied biophysics in 2007 to encourage submission of manuscripts in the concerned field. The effort also focused on expanding the application of applied biophysics in new and significant area of applied physics, while increasing its international recognition. P. J...

We report a new preparative method for providing contrast through reduction in electron density that is uniquely suited for propagation-based differential x-ray phase contrast imaging. The method, which results in an air or fluid filled vasculature, makes possible visualization of the smallest microvessels, roughly down to 15 microm, in an excised...

Absorption of high power laser radiation by colloidal suspensions or solutions containing photoreactive chemicals can result in bubble production. Here, transient grating experiments are reported where picosecond and nanosecond lasers are used to initiate photoinduced processes that lead to bubble formation. Irradiation of colloidal Pt suspensions...

Imaging with the ultrasonic vibration potential is based on recording current from a time varying polarization generated by a colloidal or ionic solution irradiated by ultrasound. Here, potential distributions between two parallel grounded electrodes are calculated for colloidal infinite layers, upright cylinders, and spheres. The calculations are...

Thermodynamic arguments show that a sonoluminescing bubble that acts as a black body can absorb energy from a high power, pulsed laser beam. The mechanism for increasing the temperature of a sonoluminescing bubble is discussed and experiments with a frequency doubled, pulsed Nd:YAG laser are described. A bound for the amount of radiation absorbed i...

. Irradiation of colloidal suspensions with the output of a high power, pulsed laser can give rise to chemical reactions and phase transitions that are linked to the production of ultrasound. Transient grating experiments, which record both photoacoustic and photothermal processes, show the effects of the concentration of heat at the sites of...

An ultrafast, laser-driven x-ray source with a liquid mercury target has been used for phase contrast imaging of an excised murine liver and for computed tomography of an electronic component. The x-ray spectrum emitted at 5 kHz repetition rate is found to be similar to that of a 2.5 W, 30 kV microfocus x-ray tube with a tungsten anode. The images...

In-line, x-ray phase-contrast imaging is responsive to both phase changes and absorption as the x radiation traverses a body. Expressions are derived for phase-contrast imaging of objects having transmission functions separable in Cartesian coordinates. Starting from the Fresnel–Kirchhoff integral formula for image formation, an expression is found...

Research has been directed towards detection of tumors using a new imaging modality based on an electrokinetic effect known as the ultrasonic vibration potential. Major accomplishments include completion of a theory for image formation for a colloidal object, such as a pool of blood, development of instrumentation for recording images, and testing...

We report the use of an inline holographic x-ray imaging technique for medical purposes. In contrast to conventional x-ray radiography a phase-sensitive x-ray imaging method is employed. This phase-contrast x-ray imaging is fundamentally different from conventional x-ray shadowgraphy because the mechanism of image formation does not rely on differe...

The ultrasonic vibration potential refers to the voltage generated when ultrasound traverses a colloidal or ionic fluid. The theory of imaging based on the vibration potential is reviewed, and an expression given that can be used to determine the signal from arbitrary objects. The experimental apparatus consists of a pair of parallel plates connect...

The in-line x-ray phase-contrast imaging method relies on changes in index of refraction within a body to produce image contrast. In soft tissue, index of refraction variations arise from density changes so that phase contrast imaging provides a map of density gradients within a body. An intense, short pulse laser beam that is differentially absorb...

Frequency domain, ultrasonic vibration potential imaging can be carried out by irradiating a colloidal object with a plane ultrasonic wave and recording the magnitude and phase of the current in a pair of electrodes as a function of the frequency. The method is applied to imaging of objects with symmetry in one dimension including a thin layer, a t...

A colloid is a suspension of charged particles in a liquid, with each particle surrounded by a counter charge. When ultrasound propagates through a colloid where the particles have either a higher or lower density than that of the surrounding fluid, the amplitude and phase of the particle motion, owing to the difference in inertia between the parti...

We report measurements of thermal diffusivity of several room-temperature ionic liquids (RTILs) using the transient grating method. Measurements are carried out using ionic liquids with small concentrations of an inert dye that is excited by the 532 nm output of a Nd:YAG laser in a grating with a fringe spacings of (92 and 104) µm. The experiments...

The ultrasonic vibraton potential refers to the production of a voltage that varies in time when ultrasound passes through a colloidal or ionic solution. The vibration potential can be used as an imaging method for soft tissue by recording its phase, time of arrival, and magnitude relative to the launching of a burst of ultrasound. A theory of the...

We show that the radiation pressure exerted by a beam of ultrasound can be used for contrast enhancement in high resolution x-ray imaging of tissue. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. The...

We show that the radiation pressure exerted by a beam of ultrasound can be used for contrast enhancement in high resolution x-ray imaging of tissue. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. The...

Expressions for the time dependence of the state variables in a transient grating experiment carried out on suspensions of particles can be determined by integration over space of the solutions for the temperature and photoacoustic pressure for a single particle. The method relies on independent computation of the thermal and acoustic modes of wave...

We show that the radiation pressure exerted by a beam of ultrasound can be used for contrast enhancement in high resolution X-ray imaging of tissue. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of X-ray phase contrast imaging to density variations. The...

Thermal diffusion, also known as the Ludwig-Soret effect, refers to the separation of mixtures in a temperature gradient. For a binary mixture the time dependence of the change in concentration of each species is governed by a nonlinear partial differential equation in space and time. Here, an exact solution of the Ludwig-Soret equation without mas...

We show that ultrasound can be used for contrast enhancement in high-resolution x-ray imaging of tissue and soft materials. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to density variations. We have performed preliminar...

The ultrasonic vibraton potential refers to the production of a time varying voltage when ultrasound passes through a colloidal or ionic solution. The vibration potential can be used as an imaging method for soft tissue by recording its phase, time of arrival, and magnitude relative to the launching of a burst of ultrasound. A theory of the effect...

Recording of an ultrasonic vibration potential when a burst of ultrasound traverses a body containing a colloidal object can be used as the basis for an imaging method. The fundamentals of the theory of signal production and experimental demonstration of the imaging method are given. In a second imaging method, the use of ultrasound to modify x-ray...

The Ludwig-Soret effect or thermal diffusion, which refers to the separation of liquid mixtures in a temperature gradient, is governed by a nonlinear, partial differential equation in space and time. It is shown here that the solution to the nonlinear differential equation for a binary mixture predicts the existence of shock waves completely analog...

The current in a circuit produced by a time-varying polarization generated by an object within a body in response to the passage of ultrasound (US) is found through solution to Maxwell's equations. Current generation is modelled in a body with uniform dielectric constant and conductivity where a finite region within the body produces an ultrasonic...

Thermal diffusion, also known as the Ludwig-Soret effect, refers to the separation of mixtures in a temperature gradient. For a binary mixture the time dependence of the change in concentration of each species is governed by a nonlinear partial differential equation in space and time. Here, an exact solution of the Ludwig-Soret equation without mas...

We show that the radiation pressure exerted by a beam of ultrasound can be used for contrast enhancement in high-resolution x-ray imaging of tissue and soft materials. Interfacial features of objects are highlighted as a result of both the displacement introduced by the ultrasound and the inherent sensitivity of x-ray phase contrast imaging to dens...

We report the use of ultrasonic radiation pressure with phase contrast x-ray imaging to give an image proportional to the space derivative of a conventional phase contrast image in the direction of propagation of an ultrasonic beam. Intense ultrasound is used to exert forces on objects within a body giving displacements of the order of tens to hund...

An ultrasonic wave traversing a colloidal suspension causes distortion of the charge distributions at the sites of individual colloidal particles producing a voltage known as the ultrasonic vibration potential. We show how imaging of colloidal regions within a body can be carried out using a beam of ultrasound to produce a radio frequency vibration...

The ultrasonic vibration potential refers to the generation of a potential when ultrasound traverses a colloidal or ionic solution. The vibration potential can be used for imaging of tissue by sending a burst of ultrasound into a body and recording the vibration potential on the surface of the body with a pair of electrodes attached to a preamplifi...

A microphone consisting of a flexible membrane coupled to a Helmholtz resonator can be constructed to have a resonance at a specific frequency making it, unlike conventional broadband microphones, a frequency selective detector of sound. The present device uses a laser beam reflected from the membrane and directed onto a split photodiode to record...

Separation of liquid mixtures in a thermal gradient, known as the Ludwig-Soret effect or thermal diffusion, is governed by a nonlinear, partial differential equation. It is shown here that the nonlinear differential equation for a binary mixture can be reduced to a Hamiltonian system of equations and that a solution can be obtained for the linear p...

This paper presents quantities, terminology, and symbols of terms related to photothermal phenomena and used in photothermal and related spectroscopies. The terms used in the literature to describe photothermal phenomena and methods are reviewed, and a glossary of terms is given. The origins of photothermal phenomena, as well as the relations among...

The quantum-cascade laser can be used as an infrared source for a small portable photoacoustic trace gas detector. The device that we describe uses a quantum-cascade laser without collimating optics mounted inside an acoustic resonator. The laser is positioned in the center of a longitudinal resonator at a pressure antinode and emits radiation alon...

The diffracted-light signals produced in transient grating experiments by phthalocyanine dyes, candidates for photodynamic therapy agents, are shown to be strongly dependent on the presence of oxygen in solution. Data indicate a facile transfer of energy from the excited dye to oxygen in solution to form excited 1Δg oxygen. The efficiency of excite...

The properties of photoacoustic waves generated outside acoustically reflecting boundaries can be found using Green’s function solutions to the wave equation for pressure. Here, Green’s functions are used to calculate the time profiles of photoacoustic waves generated in the fluid surrounding an incompressible sphere with a vanishing thermal expans...

An incompressible sphere with a vanishing thermal expansivity suspended in a fluid can generate a photoacoustic effect when the heat deposited in the sphere by a light beam diffuses into the surrounding liquid causing it to expand and launch a sound wave. The properties of the photoacoustic effect for the sphere are found using a Green's function s...

We report on laser-initiated chemical reactions in colloidal carbon suspensions. Irradiation of carbon particles ranging in size from 13 to 75 nm in diameter suspended in water, toluene, and benzene with high power nanosecond, picosecond, and femtosecond laser pulses leads to the formation of a number of gaseous hydrocarbons as well as a series of...

Hohe Antitumor-Aktivität zeigt das erste sterisch gehinderte (nichtplanare), perhalogenierte Zink-Phthalocyanin (Pc), [F64PcZn(Aceton)2], im Vergleich zu planarem Zinkperfluorphthalocyanin (siehe Struktur: F grün, N blau, O rot, C grau). Die Perfluorisopropyl-Substituenten erhöhen die Löslichkeit, stabilisieren die axialen Liganden (wie die koordin...

The transient grating method acts as a monitor of the evolution of thermal energy following optical excitation of an absorbing molecule. The signals produced by a photodynamic therapy agent are shown to be strongly dependent on presence of oxygen in solution indicating transfer of energy from a triplet state of the dye to form excited 1(Delta) g ox...

We investigate the photoacoustic effect generated by heat deposition at a point in space in an inviscid fluid. Delta-function and long Gaussian optical pulses are used as sources in the wave equation for the displacement potential to determine the fluid motion. The linear sound-generation mechanism gives bipolar photoacoustic waves, whereas the non...

We investigate the production of photoacoustic waves from a point source including the effects of heat diffusion. Solutions to wave equation for the displacement potential are found for an expansion coefficient depending linearly on the temperature. Solutions are found for delta function heating pulses in time as well as for long laser pulses.

An ultrasonic vibration potential is generated when an acoustic wave propagates in an ionic or colloidal suspension. Measurement of the potential as an ultrasonic wave propagates in a body offers the possibility of a method of imaging. The resolution of the method ultimately is limited by the wavelength of the ultrasound; the contrast of the techni...