Abstract: The subject invention discloses a method for non-destructively determining the thickness of layers deposited on a substrate by analyzing thermal waves generated in a sample. The methods are particularly suited for use with integrated circuit manufacturing. In the subject method, the sample is subjected to a focused periodic heat source which generates thermal waves. Either the magnitude or phase of the thermal waves generated in the sample are measured. The values obtained are normalized relative to a reference sample. The normalized values are analyzed with respect to a theoretical model of the sample to calculate the thickness of the unknown layers. In an alternate embodiment, thermal characteristics can be determined in a sample as a function of depth. The latter approach is useful for nondestructively determining dopant concentrations or lattice defects in semiconductor devices as a function of depth beneath the surface.

Abstract: An ultrasound transducer having an annular acoustic aperture is utilized in combination with an echo-ultrasound imaging system having an FM detector. The off-axis transfer function characteristics of the annular transducer substantially improve the lateral resolution of the imaging system as compared with prior art systems which utilized round or rectangular transducer apertures.

Abstract: An ultrasonic microscope displays an ultrasonic wave image of a sample relatively and two-dimensionally scanned with respect to an ultrasonic wave beam transmitted from and focused by a transducer including a piezoelectric element and an acoustic lens. The F number of the acoustic lens is variably changeable while the scan in one direction of the two-dimensional scan is substituted by a time axis scan of the received echo.

Abstract: An acoustic microscope comprising a transducer for transmitting acoustic signals towards the surface to be studied, and means for receiving at least one reflected signal from the surface; in many embodiments of the invention, signals are received from two separate points. The signals received are passed to a synchronous phase detection system for analysis. The signals may be received at the same phase detector input and separated according to their expected time of receipt relative to their time of transmission, or they may be received at separated points on the transducer related to their separated points of transmission. The separated return signals are compared on the basis of phase (and in certain embodiments, magnitude) differential either to each other or to an internally generated reference signal to analyze the surface characteristics of the material.

Abstract: A circuit for adjusting the sweep time provided by a sweep generator used in an ultrasonic test instrument is described. The adjustment takes into account three test parameters, i.e. the angle of propagation of the sound in the workpiece, the speed of propagation of sound in the workpiece, and the thickness of the workpiece. To this end, the quartz-stabilized frequency of an oscillator comprising an adjustable frequency divider is divided by the angle function value of the angle of sound propagation to which the test instrument is set. The divided frequency is fed to a frequency multiplier in a phase locked loop circuit, comprising an adjustable frequency divider by means of which the speed of propagation of the sound is adjusted. A succeeding time reference stage contains also an adjustable frequency divider by means of which the workpiece thickness is adjusted.

Abstract: An ultrasonic microscope is provided wherein a sample placed in a medium is irradiated with a focused ultrasonic wave from a focusing ultrasonic transmitting element and the focused ultrasonic wave is detected by a focusing ultrasonic receiving element. The sample (or the focusing transmitting element and the focusing ultrasonic receiving element) is moved within the X-Y plane, and either the focusing transmitting element or the focusing ultrasonic receiving element is vibrated toward the sample along the beam axis.

Abstract: A method of image display of a specimen by an ultrasonic wave microscope comprising an acoustic wave propagating medium, a piezoelectric member provided at one end of said medium for generating an ultrasonic beam, and an acoustic wave lens formed at an opposite end of said acoustic wave propagating medium and having a predetermined focal point, said method comprising the steps of two-dimensionally scanning a specimen disposed substantially at said focal point by said ultrasonic beam while moving one of said specimen and said beam relative to the other, and applied to said specimen repetitive stress selectively during the scanning of said specimen.

Abstract: The subject invention relates to a method of evaluating the quality of the bond achieved between two members utilizing thermoacoustic microscopy. More particularly, thermoacoustic microscopy is used to detect and/or image the plate-mode resonant signature of bonded members to determine the quality of the bond therebetween. The method is particularly suited for analyzing the integrity of a bond between an integrated circuit die and a substrate. The subject method takes advantage of the fact that the plate-mode signature of a securely bonded die and substrate combination and a poorly bonded combination will be different. Accordingly, by detecting and/or imaging the plate-mode resonant signature of the sample the integrity of the bond can be assessed. Two techniques for carrying out the subject method are disclosed.

Abstract: In an acoustic microscope device using an acoustic surface wave, a plurality of interdigital electrodes are provided on an acoustic surface wave propagating medium in a linear or circular manner, and these electrodes are selectively connected to a transmitting signal source via a multiplexer and respective delay lines having such delay times that the acoustic surface waves generated from the selected electrodes are focused at a focal point on the medium. The selection of the electrodes and the delay times of the delay lines are so changed that the focal point is moved two-dimensionally over the medium surface. The acoustic surface waves reflected at the focal points are received by the selected electrodes and electric signals from the electrodes are summed through the delay lines to derive an image signal at the relevant focal point. In this manner, a tomographic image of a specimen near its surface which is made in contact with the medium is formed.

Abstract: The invention relates to an ultrasonic imaging system for diagnostic use or non-destructive testing. The system comprises a first array of ultrasonic transducers coupled to the object space wherein objects under examination are located or distributed; a second array of ultrasonic transducers coupled to a reconstitution space wherein the acoustic images of the objects are to be replicated; and time inversion means. The time inversion means has a set of waveform memories which first captures the ultrasonic signals from said objects, typically echos produced in response to suitable excitation, via said first array of ultrasonic transducers with suitable amplification and preconditioning as necessary. Then readouts of these signals are provided inversely in time which drive the second array of ultrasonic transducers with said time inverted signals to reproject inversely propagating ultrasonic wavetrains forming replicated acoustic images of the objects.

Abstract: An acoustic microscope using a line-focus acoustic beam is disclosed. The line-focus acoustic beam is generated by an acoustic transducer head having an acoustic transducer electrode applied on a flat end surface of a sapphire rod, in the opposite end surface is formed a cylindrical concave surface. The acoustic transducer head is arranged fixedly above a mechanical stage on which a specimen is placed. The mechanical stage is movable in a Z axis, i.e. an axis of the line-focus acoustic beam and is also rotatable about the Z axis. By moving the stage in the Z-axis, a V(z) curve is obtained and a phase velocity of a leaky surface-acoustic wave is calculated from a repetition period of the V(z) curve. Then the V(z) curve measurement is repeated while the stage is rotated, and it is possible to obtain anisotropies of the specimen expressed by a relation between the rotational angle and the phase velocity of the leaky surface-acoustic wave.

Abstract: The insonification apparatus is designed for the examination of an object, preferably for medical examinations. The apparatus contains an ultrasonic wave-generating transducer for emitting ultrasonic waves toward an examination plane, and an imaging device having principal planes for passing ultrasound waves received from the examination plane toward an imaging plane. The acoustic image formed in the imaging plane is received by a receiving transducer and transferred into electrical signals. The apparatus also contains an ultrasound condensing device such as a lens, a mirror, or a combination of such elements. This condensing device forms an ultrasonic image of the wave-generating transducer in the aperture of the imaging device. Thus, an increased uniformity of the intensity distribution in the image plane and an increased image contrast for high-spatial frequency information are obtained.

Abstract: An acoustic scanning microscope includes a specimen table for supporting a specimen illuminated by an ultrasonic wave. The specimen table is supported in a non-contacting manner under aerostatic pressure or alternatively magnetic repulsion.

Abstract: A method and apparatus for electronically focusing and electronically scanning microscopic specimens are given. In the invention, visual images of even moving, living, opaque specimens can be acoustically obtained and viewed with virtually no time needed for processing (i.e., real time processing is used). And planar samples are not required. The specimens (if planar) need not be moved during scanning, although it will be desirable and possible to move or rotate nonplanar specimens (e.g., laser fusion targets) against the lens of the apparatus. No coupling fluid is needed, so specimens need not be wetted. A phase acoustic microscope is also made from the basic microscope components together with electronic mixers.

Abstract: An acoustic coupling device for use in a scanning acoustic microscope consists of an acoustic lens which has a concave focusing surface, and an acoustic coupler having a convex surface on which a convergent beam of acoustic radiation is normally incident. The coupler has a coupling surface which conforms to the shape of a test object; the coupler may be disposable. The spacing between the concave and convex surfaces may be varied to give a variable-focus device.

Abstract: An ultrasonic test instrument includes a pulse generator, a receiver, a cathode ray tube screen display and a time gate means providing a gated time interval for viewing only echo signals which arise from a predetermined workpiece region under test. The time gated interval is shown as a horizontal gate bar display on the screen and the length of the bar being indicative of the gated time interval. Circuitry provided generates a reference signal to cause the gate bar to appear at a height commensurate with the echo signal received in the gated intervals having the highest peak amplitude. Unless reset, the amplitude of the gate bar remains at this peak value although subsequent echo signals may have a lower amplitude.

Abstract: An acoustic microscope and method are disclosed in which an object under investigation is excited by two energy sources. Acoustic waves are propagated from the heated area of the object and the waves are detected and analyzed.

Abstract: A system for the non-invasive inspection of a living organism utilizes two ultrasonic fields, one of which is produced by a perturbing beam transmitting transducer to perturb an internal region of tissue at a focal region which may be subject to movement. The second ultrasonic field consists of a set of ultrasonic beams, constituting a sense beam and reference beams, and which may be portions of a single beam or a plurality of separate beams and which are directed through and near the focal region of the perturbing field before and/or after perturbation. The time of flight differences of the sense beam and reference beams are detected by a plurality, preferably at least three, receiving transducers whose outputs are processed by a digital computer system, interacting with the signal analysis electronics, to derive information concerning the internal tissue of the living organism.

Abstract: An ultrasonic microscope is formed with an impedance matching layer composed of a chalcogenide glass film on a spherical lens portion of an ultrasonic condensing lens which contacts with an acoustic field medium.

Abstract: An ultrasonic diagnosing apparatus comprising a probe for radiating ultrasonic wave beams toward a target and converting ultrasonic echo data reflected from the target into electrical signals indicative of a tomogram of the target, an ultrasonic wave transmission and reception circuit for controlling the probe to radiate the ultrasonic wave beams in predetermined ultrasonic field patterns, a processor for processing the electrical signals in accordance with correlations among the ultrasonic echo data, which depend upon the ultrasonic field patterns to eliminate artifact components of the tomogram from the electrical signals, a display device for displaying the tomogram of the target in response to the output signal of the processor, and a system pulse generator for generating a system synchronizing pulse supplied to the transmission and reception circuit and processor.

Abstract: An array of acoustic receiving transducers is placed next to the body to be imaged. Acoustic energy is initially projected through the body, picked up by these receiving transducers, and processed to determine any time domain deviations which exist in the paths actually followed by that energy from those paths which would have been followed if the body were substantially homogeneous and the transducer array substantially fixed. Further acoustic energy is also picked-up by the transducers, after reflection within the body to be imaged. The image of any given point within the body is then formed by selecting from each transducer output signal that portion which corresponds to the image forming energy emanating from that point, as corrected in accordance with the previously determined deviations.

Abstract: In an acoustic microscope wherein a piezoelectric transducer disposed on one face of an ultrasonic wave focusing lens radiates an ultrasonic wave into the lens and also converts into an electric signal a reflected wave from a specimen arranged on the side of the other face of the lens, a reflected wave from the interface of the lens and the reflected wave from the specimen are caused to interfere with each other.

Abstract: In an ultrasonic sector scanner in which display control data is obtained from beam reflection vectors for controlling television display pixels, missed pixels in a display horizontal scan line between two vectors are filled by interpolating known pixel values in the two vectors. By property weighting the known pixel values an improved picture is presented in a display of a digital scanner system.

Abstract: An improved still or frozen picture is provided in an ultrasonic sector scanner by generating and displaying two frames. The first frame is identical to the frame generated for dynamic real-time display. The second frame is generated from vectors lying intermediate vectors of the first frame with the same reflected signal data applied thereto. Accordingly, the pixel data is doubled in the still or frozen picture.

Abstract: An ultrasound visualization system, and certain aspects of the electronics that are incorporated therein. A scan conversion system which includes means for converting the ultrasound scan signal into a stream of single bit digital data in which each bit is indicative of the relative amplitude of the ultrasound scan signal as compared to the amplitude indicated by previously converted digital data. The single bit digital data is inputted and stored alternately into two full screen buffers. As the data is read into one of the two full screen buffers, the stored data in the other buffer is being simultaneously converted into an analog television video signal. The digital to analog conversion is accomplished by varying an analog television video signal in response to the relative amplitude indicated by each bit in comparison with the amplitude indicated by previously converted digital data.

Abstract: A scanning acoustic microscope comprises transducer means (10, 12, 14) to provide a convergent beam of acoustic radiation; means (20, 22) to cause relative movement in the focal plane of the focus of the beam and a sample (16); transducer means (10, 12, 14) to receive acoustic radiation modulated by the sample near the beam focus; and means (30) to supply a pressurized gas to a volume surrounding the transducer means and the sample.

Abstract: The results of the non-destructive testing of objects with a beam of ultrasonic energy is enhanced by generating display control signals commensurate with a precisely defined region in the test object. These region related signals may be displayed as a "gate" bar on the screen of a cathode ray tube simultaneously with the display of echo related signals. Echo related signals having a magnitude greater than a threshold level, as also defined by the "gate" bar, are detected and may be employed to energize an alarm.

Abstract: An ultrasonic imaging system includes a linear array of transducers of which a group of successively arranged transducers is selected and successively shifted to the next by at least one transducer. The transducers of the selected group are successively activated at respective delay times to transmit a radial scan beam which appears to emanate from a hypothetical point source located behind the transducer array. A scan converter is provided for conversion of analog echo signals in sector scan format to digital echo data in raster format for visual display.

Abstract: Echo related signals, commensurate with the results of the non-destructive testing of an object with a beam of ultrasonic energy, are presented along with or alternately with textual information on the screen of a cathode ray tube. The textual information is derived from data permanently stored in a memory of a computer and combined with variable data also stored in a memory of the computer.

Abstract: Display of the results of non-destructive testing with a beam of ultrasonic energy is enhanced by exercising precise control over the horizontal sweep voltage which is applied to the deflection plates of a cathode ray tube on which the test information is displayed. The sweep voltage generator produces a sawtooth waveform which has a precisely selectable slope. The sawtooth voltage waveform slope may be adjusted by selecting the capacitance, which is charged from an adjustable constant current source, and by varying the charging current. A microprocessor, which stores information commensurate with various waveform slopes, will control the adjustment of the sawtooth waveform slope by comparison of the stored information with keyboard entered data corresponding to a desired slope.

Abstract: A process is disclosed for recording an ultrasonic exposure pattern employing an ultrasonographic element containing a support and a recording layer unit. The recording layer unit is placed into contact with a transport liquid and imagewise ultrasonically exposed to accelerate imagewise diffusion from the recording layer unit to the transport liquid, thereby producing in the recording layer unit an ultrasonographic record. Diffusion is further accelerated imagewise by establishing a temperature differential within the transport liquid adjacent the recording layer unit.

Abstract: In an exemplary embodiment, an examination object is scanned line-by-line with an ultrasonic beam and the developing echo signals are correspondingly recorded line-by-line on an image recording installation to form a visible image. The echo recording is to ensue amplitude-compressed without a simultaneous deterioration of the resolution or of the image sharpness. To this end, a preselectable plurality of echo lines (Z.sub.n through Z.sub.n+3) which preferably determine the breadth of a surround field for echoes to be depicted together with a current line (Z.sub.n+4) are always written into intermediate memories. Subsequently, the stored and, under certain conditions, current echo signal information are supplied to an evaluation installation. During a specific section time, which determines the depth (.tau.) of the surround field, a mean value of the echo intensity in the surround field is here at least approximately comprehended.

Abstract: A method and apparatus employing zero order Raman-Nath diffraction information to visualize the longitudinal character of an acoustic field. The method includes the steps of directing a first portion of a beam of coherent light at normal incidence to a reflective mirror, propogating an acoustic field within a medium to interact with the first portion of the beam, detecting signals derived from the acousto-optical interaction from which phase change and amplitude change information in the reflected zero order diffraction component of the laser beam can be derived after its return pass through the acoustic field and then generating a two-dimensional raster scan representation of the acoustic field from the detected light signals.

Abstract: An acoustic apparatus and method for microscopic imaging and spectroscopy. The apparatus includes a plurality of devices for exciting an object of interest so that acoustic waves are propagated from the object. These devices include lasers, x-ray sources, microwave generators, ultraviolet sources, and electric current generators. The acoustic waves propagated from the object of interest are detected and the object of interest and the acoustic wave detector are moved with respect to each other in a raster scanning pattern. The magnitude of the detected acoustic waves and the corresponding raster pattern of the object are recorded so that a visual image of the object can be obtained. In addition, the frequency of the exciting electromagnetic radiation that excites the object can be varied so that both the absorption spectra and the Raman frequency mode of the object can be determined.

Abstract: A method for producing a visible image of an object is disclosed in which a fermental plate is illuminated with ultrasonic waves and a latent image of the object is therefore produced therein which is developed using a solution of chromogenic substrates, comprising, for example, hydrogen peroxide and a water-soluble aromatic amine. An apparatus to practice the disclosed method comprises an ultrasonic generator to generate ultrasonic waves illuminating the object, a fermental plate to receive and convert the ultrasonic waves passed through the object to a visible image, and a tray filled with a developer to develop the latent image of the object in the fermental plate.

Abstract: Method and apparatus for thermoacoustic or thermal wave microscopy to detect surface and subsurface information from a material on a microscopic scale. A thermal wave is generated in a material by causing periodic, localized heating at a microscopic spot by focusing intensity modulated light, or electromagnetic radiation or particle beam, on the spot. The thermoacoustic signal produced provides information about material composition, structure, and the presence of energy deexcitation processes such as fluorescence, photochemistry and photovoltaic processes. The sample is scanned as a two-dimensional array of microscopic spots. Full depth-profiling of the material is provided by varying the modulation frequency of the energy source.

Abstract: An ultrasonic transducer system comprising a transducer array, control circuit and display system wherein the control system is able to actuate the transducer elements in groups of N and N+1 elements, actuate the groups in non-sequential order, actuate groups of selectively different sizes, subject the actuation signals to and the echo signals from the transducers to pre-programmable delay periods, compress the echo signals into a logarithmic representation, transform the echo signals into plural simultaneous visual displays on a standard TV monitor in split screen format, and transform the display of discrete points in the visual display into continuous lines. Further, each transducer element in the array may consist of a split or paired set of transducers.

Abstract: An ultrasonographic exposure apparatus is disclosed. An ultrasound transducer is positioned in a reservoir so that it is immersed in a transport liquid within the reservoir. An ultrasonographic element is positioned in contact with the transport liquid, and a damper is located to form an interface with the transport liquid adjacent the ultrasonographic element remote from the ultrasound transducer.

Abstract: The invention relates to ultrasonic systems for the visual display of a thin section of a body. The subject of the invention is a system wherein the multi-element scanning probe which picks up or transmits the ultrasonic energy cooperates with an array of elastic-surface-wave transducers and with a group of frequency converter circuits in order to constitute an ultrasonic lens. The invention is more particularly applicable to the non-destructive examination of bodies permeable to ultrasonic energy such as is practiced for example in medicine and when industrial goods are being checked.

Abstract: A method of sensing changes in an object comprising irradiating the object with a focused beam of acoustic radiation excited by a first alternating electric signal; receiving a beam of acoustic radiation modulated in phase and amplitude by the object in the vicinity of the focus and deriving a second alternating electric signal therefrom; providing a reference electric signal derived from the first alternating electric signal and at a known phase; mixing coherently the second signal and the reference signal to derive a first in-phase signal; mixing the second signal with the reference signal altered in phase by between 80.degree. and 100.degree.

Abstract: A diagnostic method and apparatus for ultrasound imaging utilizes Rayleigh backscatter of ultrasound waves directed to an object for creating an image of the object. The apparatus includes an ultrasonic generator for generating a pair of waves of slightly different frequencies which are directed through the object and, after their individual detection upon return from the interior of the object, the two signals representing the two frequencies are differentially amplified in order to emphasize the scattered waves returned from various regions of the object and minimize specular reflections, thereby characterizing the acoustical scattering properties of the interior of the object based upon regional scattering properties.

Abstract: A real-time display device or fast imager for ultrasonic echography comprises a first electroacoustic transducer array 2 for periodically and simultaneously emitting a multiplicity of parallel ultrasonic wave trains toward a body O to be examined and receives from it reflected ultrasonic wave trains which it converts into electrical echo signals. These signals are transmitted through respective amplifiers 4 to a second electroacoustic transducer array 3 or 30 which retransmits them in the form of regenerated ultrasonic waves to an acousto-optical converter including a transparent tank 5 which contains a piezo-optical liquid 6, serving as an acousto-optical interaction medium, wherein the regenerated waves are focused by one or two focalizing elements, i.e. acoustic lenses and/or mirrors or simply by an arcuate shape of the second transducer array 30.

Abstract: An improvement to a pulse-echo ultrasonic-imaging system, which permits the displaying of a three-dimensional representation of internal structure such as the soft tissue within the body of a living human being. The improved system includes a focusing device, such as an acoustic lens or an acoustic axicon, which provides a depth of field for the scanning focused beam which is several times the focused spot size of the scanning focused beam and which is at least as great as the depth dimension of the structure.

Abstract: An improved pulse-echo ultrasonic-imaging system for scanning, in real time, objects such as soft tissue within a living human body. It employs a transducer including first and second parallel wave-energy generating electrodes extending linearly in a first direction and a linear array of image-spot detecting electrodes also extending in this first direction and is situated half-way between the first and second electrodes. Scanning in a second direction orthogonal to the first direction is provided by counter-rotating Risley prisms rotating at a predetermined rate. The distance between each of the first and second electrodes and the linear array is related to this predetermined rate such that reflected wave energy is always directed to the linear array.

Abstract: An improvement to a pulse-echo ultrasonic-imaging system employing an acoustic focusing device occupying a fixed aperture to both illuminate internal structure of a visually opaque object with a scanning focused beam of ultrasonic energy and for returning a reflected signal portion of the scanning focused beam passed therethrough for detection. The improvement accomplishes real time scanning by scanning all of the image samples within a group of such samples in a time period not much longer, at most, than the round-trip travel time delay of the focused beam required to receive the reflected signal portion of only a single sample for detection. By way of example, this may be accomplished by a phased-array transducer arrangement.

Abstract: An acoustic focusing device occupying a fixed aperture is used to both illuminate internal structure of a visually opaque object with a scanning focused beam of ultrasonic energy and for returning a reflected signal portion of the scanning focused beam passed therethrough for detection. The use of such a fixed-aperture focusing device permits deep soft tissue of a living human being to be displayed with high resolution for medical diagnostic purposes in a manner compatible with a real time frame rate.

Abstract: An improvement to a pulse-echo ultrasonic-imaging system employing an acoustic focusing device occupying a fixed aperture to both illuminate internal structure of a visually opaque object with a scanning focused beam of ultrasonic energy and for returning a reflected signal portion of the scanning focused beam passed therethrough for detection. The improvement makes it possible to employ a large numerical aperture spherical lens exhibiting aberration as the focusing device by utilizing a corrector plate. The corrector plate causes the lens to image a flat transducer in a flat image field. Were it not for the corrector plate, the lens aberration would provide an undesired curved image field. The improved system is suitable for displaying deep soft tissue of a living human being for a medical diagnostic purpose.

Abstract: N elementary transducers are distributed regularly along a line of scanni An ultrasonic frequency receiver is associated with phase lag means. The distribution over n successive elementary transducers of the phases corresponding to focusing at a predetermined distance or several successive distances from the line is stored. That distribution corresponds to several Fresnel zones. Switches first connect a generator to a group of n' transducers corresponding to the central Fresnel zone of said stored distribution and later connect a group of n transducers to the receiver direct and via the phase lag means according to the stored distribution(s). The groups of n' and n elementary transducers are shifted along the line at intervals of time. The phase lag means may consist of inverter means causing a phase angle of .pi..

Abstract: An apparatus for detecting ultrasonic energy comprises a chamber, partially filled with a colored liquid, having two sides separated by spacing no greater than about 25 millimeters and having a transparent section allowing for visual observation of the height of the liquid therein. A method of detecting the energy level of a beam of ultrasonic energy being propagated through a fluid comprises positioning the apparatus in the fluid so that the beam of energy strikes the liquid at the surface thereof, whereby the beam generates a visible arc-shaped spray having an amplitude proportional to the energy level of the beam.

Abstract: Short bursts of ultrasonic energy are directed through a three-dimensional specimen to determine the spatial distribution of those structures within the specimen capable of affecting the waveform of the energy. Transducers are placed in spaced positions about the periphery of the specimen to measure the affected parameters (such as attenuation and delay time) of the energy as a result of passing through the specimen along paths between the spaced transducers. The output signals containing this transit time and energy absorption information are retained in a data storage device. Through conventional programming techniques, a computer processes the data and calculates a velocity or absorption profile for each path. The profiles are collectively used to reconstruct two-dimensional or three-dimensional images of the specimen.