Abstract: A method of reducing Rayleigh waves (ground roll) in land seismic exploration employs a unique combination of amplitude output from and spacing of the vibrator sources making up a land seismic exploration system. The velocity of the Rayleigh wave for the prospect to be explored is determined. At least one receiver is used and is spaced from the vibrator sources a distance sufficient to establish the receiver as being in the far-field. The output of each of the vibrator sources is locked in phase and frequency and known separations between the vibrator sources are maintained. The frequency is varied and the individual output amplitude of each vibrator source is varied at each frequency so that the resultant Rayleigh waves traverse the known separations resulting in out-of-phase Rayleigh waves between the sources.

Abstract: A power-actuated instrument for the impact excitation of mechanical structures includes means for producing a single impact force of variable magnitude and self-contained integrated electronic means for detecting, conditioning, and limit testing of the electronic representation of the impact force so delivered.

Abstract: An ultrasound transceiver providing enhanced imaging by selective filtering of the received signal to provide a variable frequency, constant bandwidth filtering of the received echo signals. The resulting signals are then detected to produce a signal, which when displayed, has a reduced number of false multiple images and enhanced signal quality from the deeper tissue discontinuities. Additionally, the received signal is detected in quadrature by reference to a simulated carrier pilot tone having a nonconstant frequency relationship to the transmitted signal. The resulting signal is post-processed to provide information which is used to display structural features, and in addition, the velocity profile of blood flow. The structure and velocity image information is superimposed to provide a composite signal wherein the static and dynamic characteristic of a patient is completely reported to the observer.

Abstract: A driver bar assembly for coupling together a shaker head 12 and a slip plate 34 carrying a test piece 60 to be vibration tested, the assembly comprising a driver bar 14 having a laterally extended locus of intersection (L-L, P-P) with the slip plate in the slip plate plane of test movement, and fastener means comprising a rigid pin 50 extending laterally within the locus of intersection in slip plate and bar interconnecting relation for transmission of shaker head vibration to the slip plate through the pin.

Abstract: The surface acoustic waves are generated by laser beam that is focussed onto a surface to irradiate it in an arcuate pattern as a partial annulus or as a still or moving fringe pattern. The arcuate pattern may be formed by a transmitting or a reflecting axicon, while the fringe pattern may be formed by splitting the laser beam into two beams and directing the two beams to the surface. In addition, a lens or a frequency shifting device may be placed in the path of one of the split beams to form a circular fringe or a moving fringe, respectively.

Abstract: A load dynamic compensation circuit for a servohydraulic control system for fixtures and specimens being tested operating in various degrees of freedom, for example in an environment to simulate earthquakes to test building specimens, or to provide road profile simulation for rail and automobile vehicles, or wind buffet loads for aircraft. A compensation circuitry compensates for specimen displacement disturbances in the control loop that are a function of the force exerted from the specimen and the acceleration of the test mass.

Abstract: In order to ensure that the vibrations of a system under test are in accordance with a reference spectral density Z(w), the system is driven by a signal x.sub.n (t) provided by an inverse discrete Fourier transform (IDFT) with random phases introduced by a function R.sub.n (w) and the response spectral density Y.sub.n (w) provided by a DFT is brought into agreement with Z(w) by a feedback loop. Moreover, in order to ensure that this is done in one iteration, X'.sub.n (w) is derived from x.sub.n (t) by a DFT and divided by Y.sub.n (w) and the quotient is multiplied with Z(w) to provide the new input x.sub.n (w) for the IDFT. The division cancels out the random factor which is present in both X'.sub.n (w) and Y.sub.n (w).The system thus equalizes both rapidly and stably.

Abstract: A series of pulses are transmitted to a first laser and the same series of ulses through a time delay network to a second laser. Each laser provides pulses of light through separate diagonal mirrors and through respective transparent holograms. Each light beam is then brought into convergence by respective sides of a wedge shaped reflector and brought into spacially coincident focus by an imaging lens onto the surface of a sample under test. The two hologram transparencies are imaged spacially coincident but separated in time on the face of the sample. Thermal elastic waves produced by laser heating at the sample surface transform into a desired acoustic beam pattern determined by the nature of the wavefronts which the hologram transparency represents. The position of the coincident image on the sample may be moved by varying the time between the two pulses.

Abstract: The claimed invention is directed to seismic exploration wherein an earth surface vibrator sweeps through a frequency range with varies with time as a function of frequency.

Abstract: The disclosure concerns an electromagnetic exciter for striking the wheels of moving railroad cars undergoing acoustic signature inspection. The apparatus comprises a pivotally mounted impact member which is accelerated by a solenoid through only a portion of its impact stroke and then moves onward to impact solely as a result of the kinetic energy imparted to it during the initial acceleration period. The solenoid is controlled by an electronic drive circuit which responds to an input signal from a wheel presence detector and delivers to the solenoid coil a burst of energy whose size and duration may be adjusted to yield the greatest sound pressure level while allowing the field of the coil to relax quickly enough to reset the apparatus for the next car wheel.

Abstract: Driver bar assembly for vibration test apparatus, comprising a bar element and a retainer element separably connected thereto; the bar element having a normally vertically disposed base attachable to a pivotally mounted shaker head and a normally horizontally disposed flange adapted to lie in a common plane with and spaced from a slip plate to be driven by the shaker head; the retainer element having a first bracket in which the bar element flange is bracketable, and a second bracket in which the slip plate is bracketable opposite the bar element flange, whereby the flange and slip plate spacing is bridged in vibration transmitting relation between the shaker head and the slip plate; the retainer element being separable from the slip plate and the bar element flange without relative movement of the slip plate and shaker head, the bar element and shaker head being freely angularly movable relative to the slip plate in the separated condition of the retainer element and the bar element.

Abstract: A method and apparatus for determining at least one component of a sample of a particulate material, such as grain or seed, on the basis of a permittivity value of the sample. Before measuring the permittivity value the sample is compacted to a predetermined degree, preferably by vibrating the sample. Preferably, the sample is vibrated while being introduced into a sample container or receptacle in which the sample is exposed to an alternating electric field for determining said permittivity value.

Abstract: A position measuring head, especially for locating proximity to a surface of an object to be detected, is mounted on a support and can be displaced relative to this surface. A small vibration is imparted to the head and changes in the mode of vibration on contact or approach to the surface are detected to produce an output signal.

Abstract: A method for visually indicating the natural frequencies of a vibrating member utilizing an improved instrument strobed through suitable frequency pick-ups such as accelerometers indiscriminately placed on the vibrating structure to be analyzed.

Abstract: A falling weight deflectometer operates with a falling weight, transmitting shock energy upon its fall to an intermediate weight and to a holder for a pressure plate engaging the ground. Between the falling weight and the intermediate weight is interposed a shock absorber of elastically yieldable material such as shock absorbing rubber, and a corresponding shock absorber is interposed between the intermediate weight and the holder.

Abstract: Apparatus for creating vibratory forces in a specimen in which the specimen is positioned within a carrier which is rotated about a remote axis, preferably vertical, to generate centrifugal forces directed radially outward from the remote axis. The carrier is also rotated about an axis perpendicular to the direction of the radial centrifugal force so that the force on any particle is cyclically reversed at a frequency determined by the frequency of the rotation about the perpendicular axis. The rate of rotation about the remote axis may be varied to vary the amplitude of the centrifugal force and the rate of rotation about the perpendicular axis may be varied to vary the frequency of the vibratory force generated by this combination. The specification discloses an apparatus in which a solid specimen may be mounted for the generation of cyclically-varying vibration forces and also an apparatus for receiving a liquid which may be subjected to cyclically-varying vibrational forces.

Abstract: The entrance angle of an ultrasonic beam into a test object results from refraction at the interface thereof with water. The physical orientation of the transducer directing a beam towards the object is maintained, but the refraction angle is varied through controlled adjustment of the water temperature.