Abstract: A sector scanner having an oscillating transducer element includes a motor and rotating shaft, a crank attached to an end of the shaft, and a linkage connecting the crank and the oscillating transducer element whereby rotation of the shaft is translated to oscillation of the transducer element. Vibration from the oscillating transducer element is minimized by reducing the mass of the oscillating element and employing harmonic motion of the transducer element.

Abstract: The apparatus comprises a base and two movable opposite centers, one of which is fastened to a rotatable axle, while the other is fastened to a screw by means of a bearing, and mounted in two opposite parallel plates. Between the plates there is disposed a tank filled with an acoustic medium, and underneath it there is mounted a sensor which is connected to a measuring system. Two parallel guides are transversely fastened to the plates. The base is suspended on the parallel guides with a collar fastened to it. The base is provided with a driving screw and a handle. A spring, within the collar and attached to it, is fastened rigidly to a guiding sleeve. To this sleeve there is fastened the tank, on which there are seated parallel rotating rollers. A limiting sleeve of the sensor is mounted inside a guide by means of a locking nut, which is pressed against a second nut fastened to the guiding sleeve.

Abstract: An ultrasonic scanning apparatus has a housing which includes the apparatus which has a cylindrical body extending along a central axis thereof and a window at a distal end of the cylindrical body. A transducer is disposed in the vicinity of the window to transmit an ultrasonic beam in a direction perpendicular to the central axis of the housing, and a reflecting member is disposed to guide the ultrasonic beam to the outside through the window. A continuously rotating motor is disposed such that an output shaft thereof is parallel to the central axis of the housing. A swinging mechanism is coupled to the output shaft of the motor so as to swing the reflecting member within a predetermined angular range.

Abstract: An ultrasonic probe for accurately determining angular location includes a rotating mobile assembly with at least one angular location track placed thereon. The angular location track is inscribed with location data arranged in a succession of pulses. As the mobile assembly rotates, the track traces a path in space. A fixed reading unit is provided at a point along the path to read the data inscribed on the track. The read data contains information corresponding to the angular position of the mobile assembly at any given point in time.

Abstract: An ultrasound device for sector scanning which includes an ultrasound transmitting/receiving system. The system is housed in a compact cylindrical applicator housing which contains ultrasound transducer heads and associated ultrasound transducer elements at both ends of the applicator housing. Each of the two ultrasound transducer heads is rotatable within the applicator housing for performing sector scanning. A single drive mechanism rotates or swivels reciprocally both transducer heads so that undesirable inertial forces are cancelled or compensated. A guiding element pivotally supports the applicator housing so that the housing can be rotated and one or the other of the two ultrasound transducer heads be used. The guiding element also provides the enclosure for the electronics associated with the ultrasound applicator.

Abstract: In an improved method for determining the position of a measuring sensor or probe (1), such as a probe for ultrasonic examination of an object (2), use is made of at least two mutually crossing bars (3a, 3b, 3c) of electrically conducting material in constant sliding, electrical contact with each other. At least one bar (3a) is kept fixed in relation to the object (2) to be examined, and at least one bar (3b, 3c) is kept fixed in relation to the probe (1). By measuring the electrical voltage drops in the bars, the positions of the crossing points (4ab, 4ac) between these bars and thereby the actual position of the probe in relation to a reference system (x, y) on the surface of the object are determined. By using at least three bars, it is possible to determine the position coordinates (x, y) as well as the angular direction (v) of a freely movable probe in relation to objects to be examined having plane, cylindrical or double-curved surfaces.

Abstract: A transducer drive assembly is disclosed having particular application for use in medical diagnostic imaging systems. The drive assembly includes a rotor coupled to drive means for rotation about its longitudinal axis. The rotor is formed such that it includes an integrally formed contact plate which extends upwardly from a generally flat rotor face at a given angle. A transducer is carried in a cradle which is mounted for pivotal movement, and includes a lower base portion having a generally cylindrical cross section. The lower base portion of the cradle is disposed such that it is maintained in physical contact with the rotor contact plate at all times. The rotation of the rotor applies force to the lower base of the cradle resulting in the oscillation of the cradle about the pivot points. The transducer is thereby oscillated back and forth about the pivot points in a uniform and continuous movement so long as the rotor continues to rotate.

Abstract: Real time image zoom is obtained by sampling electrical signals corresponding to reflected ultrasonic waves at a sampling frequency whereby display data is obtained only in an area of interest. The sampling is delayed to eliminate signals from areas not of interest. Ultrasonic pulse repetition rate is selected so that internal resolution in the area of interest is optimized.

Abstract: The scanhead uses a shaft mounted, oscillating rotor driven by a shaft mounted rotor. Energy storage and repulsive means, provided by magnetic "bumpers" helps to reverse the direction of motion of the rotor at the end of the scan angle.

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: A method and apparatus for ultrasound tomography for use in clinical diagnostics, the apparatus comprising paired couples of transmission transducers (3) and reflection transducers (5,6), the paired couples of transducer means being independently operable within a container (1) of ultrasound transmission medium to provide data capable of processing by computational methods for mathematical reconstruction of the distribution of specific values of acoustic data to permit separate comparative and synergistic examinations of the data thus obtained to classify the internal structure of a body.

Abstract: Low pressure turbine disc rims are inspected by a method in which an ultrasonic beam is directed into a disc rim steeple from a location on the disc rim web. Reflected waves are received and signals indicative thereof are produced for display. A predetermined time window is established on the display, based on the time-of-flight difference between the top of the steeple and the disc rim. The presence of signals within the time window on the display is determined to indicate the presence of a crack. Cracks located along the steeple serrations and oriented in a generally tangential direction to the steeple cross section are detected by producing an ultrasonic beam directed along a line normal to the bottom of a steeple. Cracks located at the bottom of a blade groove at the steeple root and oriented in a generally radially direction can be detected by producing an ultrasonic beam skewed at an acute angle relative to the line normal to the bottom of a steeple.

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: An ultrasound probe includes an acoustical mirror that deflects an ultrasound beam generated by an ultrasound crystal toward an object under examination. The probe includes a thin flat motor whose rotor is controlled by a control system. The control system creates commutating signals that are applied to stator coils of the motor. An error signal that is related to the difference between the actual and desired positions of the object rotated by the motor is applied to the commutating signals to alter their amplitude or polarity to change the torque developed by the motor.

Abstract: A fixture for mounting an ultrasonic transducer against the end of a threaded bolt or stud to test the same for flaws. A base means threadedly secured to the side of the bolt has a rotating ring thereon. A post rising up from the ring (parallel to the axis of the workpiece) pivotally mounts a variable length cross arm, on the inner end of which is mounted the transducer. A spring means acts between the cross arm and the base to apply the testing transducer against the workpiece at a constant pressure. The device maintains constant for successive tests the radial and circumferential positions of the testing transducer and its contact pressure against the end of the workpiece.

Abstract: In ultrasonic flaw inspection for determining the size of a flaw by emitting an ultrasonic wave to a subject via a probe and receiving an ultrasonic echo from said flaw existing inside said subject, changes in the propagation distances of the ultrasonic echoes before and after movement of said probe through a micro-small distance are compared with each other and the ultrasonic echoes are determined to result from the same flaw if the change width falls within a predetermined value determined by the angle of incidence of the ultrasonic wave and the directional angle.

Abstract: An ultrasonic flaw detector device including axial and circumferential fixed tracks located in a space defined between a pressure vessel of a nuclear reactor and a heat insulating wall surrounding the vessel and arranged axially and circumferentially respectively of the pressure vessel of the nuclear reactor. A rotary track is located at a junction of the axial fixed track and the circumferential fixed track and moved in rotary movement by a chain and has its angle of rotation restricted by a pair of stoppers. A carrier member supporting an ultrasonic probe is moved on the tracks to effect ultrasonic flaw detection to detect any flow that might be present in the pressure vessel. To transfer the carrier member from the axial fixed track to the circumferential fixed track, the carrier member is first transferred from the axial fixed track to the rotatable track, and after the rotary track is rotated, the carrier member is transferred from the rotatable track to the circumferential fixed track.

Abstract: A conventional ultrasonic B-scan image is converted into a volume backscatter image by accounting for four propagation effects: dispersion of transmitted energy, beam width and beam intensity variations, inhomogeneous attenuation of ultrasonic energy, and signals resulting from specular reflections at interfaces. These images are a two-dimensional map of backscatter efficiency, are independent of details of the measurement system, and are quantitative images of an intrinsic property of tissue and other materials.

Abstract: A scanner for periodically scanning an object to be examined with a beam of ultrasonic radiation. A transducer mounted within a housing emits a beam of ultrasonic radiation. The beam is guided and deflected respectively to a continuously rotating scanning reflector which is disposed opposite a stationary object reflector, from which the beam is directed to the object. The beam propagation path further includes a first focussing member adapted to focus the beam to a focal point within the housing, and a second focussing member adapted to focus the beam to a focal point within the object. In a preferred embodiment the first focussing member can be selectively adjusted. Thereby the focal area of the beam in the object can be conveniently shifted.

Abstract: An ultrasonic scanning system is provided in which an ultrasonic transducer is oscillated for scanning purposes by a piezoelectric bender. One end of the bender is fixedly mounted in a sector scanner head, while the other end is connected to the ultrasonic transducer. The bender is deflected through the application of a drive voltage to electrodes plated on the piezoelectric material, causing the bender to deflect by a distance which is proportional to the applied voltage. The transducer is thereby caused to oscillate or rock by the motion of the bender.

Abstract: A method of ultrasonically inspecting the internal structure of a multi-ply composite material using ultrasonic transducers includes the steps of positioning an ultrasonic transmitter in acoustical contact with one surface of the material, directing a beam of acoustic energy into the material with the angle of incidence of the beam with respect to the surface being less than the second critical angle for the material but greater than normal to the surface, and receiving the reflected energy. In one embodiment, the transmitting and receiving transducers are positioned with their axis perpendicular to the orientation of the reinforcing fibers within the ply being inspected. In another embodiment, the transmitter and receiver are aligned at equal angles on either side of a line which is perpendicular to the orientation of the fibers. The receiver may be located on the same or the opposite side of the material from the transmitter.

Abstract: A rotating scanner for use in ultrasonic echoscopy has a linearly scanned transducer arrangement, for transmitting beams of ultrasonic energy into an object (and receiving reflected ultrasonic echoes from the object). The transducer arrangement is rotated about an axis passing through the center or one end of the linear scan. The linear scanning may be mechanical scanning, or by electronic switching of an array of transducer elements.

Abstract: An X-Y scanner is illustrated which utilizes an eddy current or ultrasonic current test probe for detecting surface defects in small flat plates and the like. The apparatus includes a scanner C which travels on a pair of slide tubes (20) in the X-direction. The scanner is, in turn, carried on a carriage B which slides in the Y-direction. The scanner C is driven in the X-direction by means of a helix shaft (44) having a closed-loop helix groove (46) in which a follower pin 38 carried by scanner C rides. The carriage B is moved incrementally in the Y-direction upon the completion of travel of the scanner back and forth in the X-direction by means of an indexing means E which includes an indexing actuator (54) and an indexing gear (50). Actuator (54) is in the form of a ratchet which engages ratchet gear (52) upon return of the scanner to the indexing position whereupon the indexing gear (50) is rotated a predetermined increment along a rack gear (48) to move carriage B incrementally in the Y-direction.

Abstract: A locomotion unit is remotely controlled to advance stepwise through a passageway by frictional engagement with the surfaces of the passageway walls. A support section is mounted on the locomotion device to bring special tools to bear at predetermined positions within the passageway to which the support is brought by the locomotion unit.

Abstract: In a mechanical sector scanner, a first bevel gear is mounted on the end of an output shaft of a motor, and an ultrasonic transducer is rotatably supported for rotating about a scanning axis transverse to the output shaft. A second bevel gear engaging the first bevel gear is mounted on the back surface of the transducer. The output shaft oscillates about an output axis. Oscillations of the output shaft are coupled to the transducer by the bevel gears. The second gear has a plurality of teeth arranged in an arc less than completely around the scanning axis, and the second gear is so disposed that the back surface of the transducer is nearer to the scanning axis than the teeth.

Abstract: The probe has a casing provided with an ultrasonically transmissive window and containing a couplant liquid in which are immersed a piezoelectric disc, an electric motor and a mechanical coupling between the motor shaft and the disc. The mechanical coupling comprises a connecting rod driven at one end by the shaft in a conical motion about the shaft axis, which is at right angles to the disc and to the window. The disc is rotatably supported about a diametrical axis which is fixedly positioned with respect to the casing. A yoke which has a bracket secured to the connecting rod at the opposite end thereof, is rotatably supported about an axis which is fixedly positioned with respect to the disc and at right angles to the diametrical axis. The mechanical coupling transmits an oscillating motion to the disc about the diametrical axis.

Abstract: A real-time ultrasonic transducer for use in a scanning system and a novel drive circuit therefor are provided. The transducer includes a housing and a transducer assembly mounted therein for movement in a predetermined manner. An electromagnet causes the transducer assembly to move in such a predetermined manner. The drive circuit reverses the polarity of the voltage applied to the electromagnet when the transducer assembly reaches a predetermined limit of movement thereby reversing the direction of movement thereof. The drive circuit and the transducer assembly are located within the transducer housing. The drive circuit includes a set-reset (R-S) flip-flop that reverses the polarity of the voltage applied to the electromagnet. The two conventional collector resistors of the flip-flop are each replaced by a transistor circuit thereby providing the R-S flip-flop with power amplification capability.

Abstract: In ultrasonic equipment for generating section images, wherein a sector of a section surface is scanned, the angle of swing of the sound head carrier and the angular width of the sector-shaped section image can be adjusted to different values by adjusting means. For this purpose a crank mechanism is provided, which comprises a connecting rod, which is pivoted on an axis spaced from the geometric axis of rotation of the motor. The connecting rod is mounted in a bearing member, which is disposed adjacent to the axis of rotation and which is pivoted to the sound transducer head carrier on a transverse axis. The adjusted angle between the axis of the connecting rod and the axis of rotation of the motor and the angle of swing of the sound transducer head carrier can be adjusted by an alteration of the ratio of the effective length of the connecting rod to the distance from the axis of the motor to that end of the connecting rod that is nearer to the motor (FIG. 1).

Abstract: The present invention provides an ultrasonic scanning transducer for use in an ultrasonic scanning system that examines an object by directing a series of ultrasonic waves into the object, receiving electrical signals related to the echoes generated by the ultrasonic waves when they strike acoustical interfaces within the object, and displaying the information borne by the electrical signals relating to the nature and location of acoustical interfaces within the object. The ultrasonic scanning transducer includes transducer elements secured to a permanent magnet mounted for rotational movement within the housing of the transducer and a stator assembly for rotating the transducers and magnet continuously in a single direction. The stator assembly receives a periodic signal having a zero average value and creates therefrom a unidirectionally rotating magnetic field which exerts a force on and rotates the permanent magnet.

Abstract: In the exemplary embodiments, the apparatus comprises: an ultrasonic transducer arrangement; a drive arranged to pivotably displace the transducer arrangement within a predetermined angular range; an actual-value generator for supplying a signal (F.sub.I (.rho.) dependent upon the angular position of the transducer arrangement within the said range; a desired-value generator for supplying a signal (F.sub.S (.rho.)) representing a desired angular position of the transducer arrangement within the said range; and a control for controlling the drive in dependence upon such signals from the actual-value and desired-value generators. The actual-value and desired-value generators are adapted to supply respective signals having the same or similar forms over a relatively large signal range within the said range.

Abstract: A position sensor for sensing the angular position of an oscillatory member includes a magnetic element which is permanently magnetized in a predetermined direction and is mounted as a unitary structural part of the oscillatory member for oscillatory movement therewith. A Hall plate sensor is positioned adjacent the magnetic element to detect changes in the magnetic field presented thereto by changes in position of the magnetic element. When the magnetic element is oscillated with the transducer, the magnetic field presented to the Hall plate is varied accordingly. This, in turn, produces an electrical signal as an output of the Hall plate which is a function of the instantaneous position of the magnetic element and hence of the oscillatory transducer. That electrical signal may then be used to produce synchronization signals for the imaging apparatus.

Abstract: An insert section of an ultrasonic probe device which is bendably coupled by means of a hinge with two rotation shafts rotatably disposed within an insert section that is coupled to a universal joint. The distal tube can be bent freely by operating a control knob at a control section, so that an ultrasonic transducer member at the tip of the distal tube may be brought closely into contact with the body wall.

Abstract: An ultrasonic transducer probe for testing workpieces exhibiting compound surfaces includes a molded plastic body which precisely fits to the shape of such workpiece surfaces. Moreover, the body includes, as an integral part thereof, an indexing portion for accurately locating the transducer probe in relation to a predetermined workpiece test area to cause the transducer element embedded in the molded body to transmit ultrasonic energy in the predetermined test area. The transducer probe is secured to a manipulator for remote operation.

Abstract: In a steam generator an ultrasonic probe is used to measure the accumulation of sludge between the tubes. A ribbon-like probe carrier is fed into the vessel and deflected by a carriage placed in alignment with a lane of tubes at 90.degree., the probe head being advanced in the lane to measure vertically and sideways the distance to the surface of the sludge. The probe carrier consists of two steel tapes held face-to-face by a plastic tube which has been heat shrunk. The conductors for the transducers are contained in the space between concave tapes. An adaptor mounted at the end of the probe carrier is amovably connected to the probe head. Probe head, adaptor and probe carrier are sealed so that measurement can be conducted inside the steam generator supposedly filled with water.

Abstract: An improvement in an ultrasonic imaging system is disclosed, enabling determination of volume and/or shape of three-dimensional portions of bodily tissue or the like.

Abstract: A method and apparatus for determining the position of a sensor with respect to a color screen are disclosed. The screen is colored with first and second colors in such a way that the intensity of each color varies from a minimum to maximum along a respective direction lying in the plane of the screen, the two respective directions being oblique to each other. As a result, each point on the screen is characterized by a unique pair of color intensities. The sensor is provided with means for measuring the intensity of each color at the point on the colored surface corresponding to the location of the sensor. In one advantageous application of the invention, one surface of a screen is colored as described above, and the screen is placed over an object to be ultrasonically inspected.

Abstract: Apparatus for early detection of fatigue cracks in aircraft structure surrounding fasteners and the like.An ultrasonic scanner manipulating apparatus is provided with various types of replaceable tips which are used to establish the center of a given fastener, adjustable support legs which provide stability and maintain a proper distance for an ultrasonic transmitting/receiving head assembly to be rotated 360.degree. about the centerline of the fastener, and a liquid filled boot attached to the transmitting/receiving head assembly to assure a reliable signal path between the head and the structure being evaluated.

Abstract: A method and apparatus for determining the position of a sensor with respect to a color screen are disclosed. The screen is colored with first and second colors in such a way that the intensity of each color varies from a minimum to maximum along a respective direction lying in the plane of the screen, the two respective directions being oblique to each other. As a result, each point on the screen is characterized by a unique pair of color intensities. The sensor is provided with means for measuring the intensity of each color at the point on the colored surface corresponding to the location of the sensor. In one advantageous application of the invention, one surface of a screen is colored as described above, and the screen is placed over an object to be ultrasonically inspected.

Abstract: In a method of plotting section images of objects subjected to ultrasonic examination, a section surface of the object is scanned with a sound beam and echoes generated in response to the pulses of the sound beam are converted into echo signals which are plotted on a plotting surface, such as a fluorescent screen or a record carrier, to form a section image. The sound beams scans the section surface at a varying velocity. The pulse repetition period of the sound pulses is varied so that the section surface is scanned with a uniform transverse resolution. In equipment for carrying out the method, the pulse repetition frequency of the sound pulses is controlled by a trigger which generates trigger pulses at times which are functionally related to the scanning movement of the sound beam. The trigger may comprise programmed memory.

Abstract: A manually operable scanner includes a rectangular frame having suction cups or other mounting devices connectable to a casting or other body to be scanned with a carriage being mounted on the frame for reciprocation in a first direction. A scanner such as an ultrasonic transducer is mounted on the carriage for reciprocation in a direction perpendicular to the direction of movement of the carriage with movement of the carriage and the scanner being sensed by first and second rotary encoders each of which provides an output signal to a display indicative of the position of the transducer with respect to the rectangular frame so that upon a detection of a fault in the body being scanned, the coordinates of location of the fault are immediately available from a visual readout of the coordinates from the display means.

Abstract: A housing for an acoustic transducer includes means for dispersing internal reflections within the housing to minimize the incidence of such internally reflected acoustic pulses on the transducer itself, thereby avoiding the generation of spurious electrical signals for transmission to the translating circuitry.

Abstract: A support for a transducer for emitting and/or receiving ultrasonic signals in a given angular sector, comprising a series of substantially coaxial, loop-shaped elements which are axially arranged one behind the other. The first element can be arranged on a surface of an object to be examined, while the transducer is secured in the last element. Every two successive elements can pivot through a given angle with respect to each other. The total angular distance of the assembly formed by the elements at least equals the chosen angular sector. When the orientation of the transducer changes with respect to the surface, the distance between the transducer and the surface is not substantially varied.

Abstract: An ultrasonic-scan head is mounted by means of an articulated arm assembly; a swivel extension arm supports the assembly for rotation about a vertical central axis. Such vertical central axis is the isocenter for body sections to be scanned by the ultrasonic scan head. The construction of such an apparatus is desired which is particularly simple to handle during sectional plane selection. In particular, the apparatus mass to be moved is to be small so that a rotation of the entire scan system can also be conducted directly at the working location by the examining individual without requiring an assistant.

Abstract: Equipment is disclosed which serves to trace B-scan section displays of specimens and comprises a sound transducer head, which is oscillated by a scanning mechanism and projects sound beams, which scan the section to be displayed. The echoes which originate in response to these sound beams are displayed on a fluorescent screen at locations which are associated with the locations at which said echoes have originated. The sound transducer head comprises two sound transducers, the axes of which in the plane in which they are oscillated include an angle which is not in excess of the angular range of oscillation. As a result, the pitch with which the section to be displayed is scanned by ultrasonic beams is decreased and/or the angular velocity of the sound transducer head may be decreased.

Abstract: Electronic means, including an analog-to-digital converter responsive to samples of the output from an analog angle sensor directly coupled to an immersed oscillated transducer, is used to trigger the energization of the transducer at each of a predetermined number of equal increments in angle position during each cycle of oscillation of the transducer, with the triggered angle positions during a certain half-cycle of oscillation being interlaced with the triggered angle position during the other half-cycle of oscillation.

Abstract: A method and apparatus for determining the position of a sensor with respect to a color screen are disclosed. The screen is colored with first and second colors in such a way that the intensity of each color varies from a minimum to maximum along a respective direction lying in the plane of the screen, the two respective directions being oblique to each other. As a result, each point on the screen is characterized by a unique pair of color intensities. The sensor is provided with means for measuring the intensity of each color at the point on the colored surface corresponding to the location of the sensor. In one advantageous application of the invention, one surface of a screen is colored as described above, and the screen is placed over an object to be ultrasonically inspected.

Abstract: A high resolution, ultrasound imaging system is disclosed having a transducer which produces a diverging beam of ultrasound energy of sufficiently large angle so as to impinge on the sound-reflecting object from substantially all positions along the transducer scan path.

Abstract: Transducer completely immersed in ultrasonic propagating liquid can be oscillated back and forth at a high rate, without producing significant turbulence in liquid, if oscillation velocity varies as a predetermined smooth continuous function of time.

Abstract: There have been proposed ultrasonic scanners in which a transducer is laterally scanned relative to a body known arrangements with lead screws for example can give rise to much vibration and have a high power requirement. It is proposed to scan with a linear motor drive. The scanning part including the transducer is put in an oil bath and the oil flow is balanced to act as a counterweight. The scanning part should, therefore, have neutral buoyancy, with the centers of gravity and buoyancy substantially coincident.

Abstract: In detecting, characterizing or studying flaws in work whose surface is irregular by acoustic imaging in which a holographic pattern is produced the irregular surface is scanned by acoustic energy focussed on or near the irregular surface and the reception of the acoustic energy resulting from echoes from flaws is controlled for each scanned elemental area so as to reduce to a negligible magnitude the effects or variations in the acoustical path caused by the irregularties at different elemental areas in accordance with the irregularity at that area. The control may be effected by filling in the depressions in the irregular surface with an acoustic energy absorbing material such as butyl rubber or with a material, such as wax, which is not wetted by the liquid through which the acoustic energy is propagated to the surface.