Abstract: A method for the location of shocks with a structure-borne sound monitoring system is used especially for pressurized enclosures in power plants, particularly nuclear power plants. Structure-borne sound monitoring systems were heretofore dependent upon assumptions regarding the propagation velocities of the structure-borne sound sensors. According to the invention an exact method of ascertaining the propagation velocities and the burst location is given. The invention begins with the realization that the frequency spectrum of the respective bursts of information for clarification of the dispersion behavior, for identifying the sound wave modes and for deriving the group velocity of these modes is self-evident. Burst signal-rise time differences, wave modes, especially s.sub.0 and a.sub.0 mode, as well as the pertaining group velocities are then ascertained.

Abstract: The invention relates to a method and a device for measuring a distance by means of an ultrasound. A drawback of this type of known methods for measuring a distance is that the transmitting and the receiving devices are separate, and they are designed to function according to whether they are positioned at a point of origin or at a target point of a measuring interval. For solving this problem, transmitter-receiver units (LVA, LVB) at the ends of a measuring interval are identical and interact continuously with each other so that the measuring result can be read in both devices.

Abstract: The position of a projectile travelling at a supersonic velocity is sensed by two triangular arrays of transducers 10,11 which are located below and close to the plane of a target area 14 through which the projectile passes. Signals from the transducers are processed to obtain data indicative of the direction of the trajectory from each array. This data can be processed to obtain the position of the trajectory in a cartesian coordinate system.

Abstract: A method and apparatus for use in a pulse-echo imaging or ranging system comprising means (32) for identifying the analytic signal from a received signal and means (34) for extracting ranging information from the analytic signal. The analytic signal can be obtained and processed by digital or by analog circuit means. One embodiment of the analog circuit means (32) includes means (90) for modulating the received signal on a carrier frequency, means (92) for obtaining a single sideband signal from the modulated signal and means (94) for envelope detecting the single sideband signal.

Abstract: A system for monitoring the safety and location of individuals includes a portable transceiver worn by each individual and a base control unit for sending interrogation signals to the individual units. The interrogation signals are transmitted through both air and water, and the individual units transmit a response through the medium through which the interrogation signal was received. The base unit measures both the elapsed time from transmission to reception and the incoming phase angles of the response signal, and converts these measurements to indications of distance and angle between the base unit and the individual transceivers.

Abstract: The minimum distance between a passing projectile and a training (dummy) target is ascertained by means of four shock wave responsive transducers in the target, two of which are aligned with the target's propagation and the transit time differential of receiving the shock wave from the projectile as well as measured distances to the projectile's trajectory are used to establish a set of possible projectile trajectories, one of them being the real one; all of them being arranged in rotational symmetry to the line established by the two transducers. This information suffices already to determine the minimum distance of fly by.

Abstract: For identifying the position of a movable body comprising a reflector, a primary transducer and a secondary transducer are utilized which transmit ultrasonic pulses to the reflector and, in turn, detect the ultrasonic pulses reflected by the reflector. A measuring device identifies a positional value assigned to the position of the reflector from the transit times of the ultrasonic pulses from both transducers. To this end, the measuring equipment has a primary control to which a calculator, a primary memory, a timer and a pilot control are coupled. Furthermore, the measuring equipment has a receiver, a transmitter and a transfer device which alternately connects the ultrasonic transducers to the measuring equipment.

Abstract: Disclosed is a method for measuring a distance by using a radio-wave and an ultra-sonic wave. The method includes the steps of generating a certain start pulse in the form of a radio-wave between a measuring position and a position to be measured from the measuring position, receiving the radio-wave at the position to be measured while simultaneously generating an ultra-sonic wave from the same measuring position, determining a time difference between the moment of generating the start pulse and the moment of receiving the ultra-sonic wave, and multiplying the obtained difference by the sonic velocity.The method of measuring distances by utilizing the radio-wave and the ultra-sonic waves is very accurate without false operation and is simple, brief and convenient to use.

Abstract: A new form of proximity sensor is described which enables sensing of magnetic and/or metallic objects over an extended region of space. The time-varying magnetic field necessary for proximity sensing is provided by a strain wave propagating at acoustic velocity in a waveguide composed of magnetized magnetostrictive material. The propagating strain wave carries with it a disturbance in the magnetic field in the region of the waveguide. A single, elongated sensing coil is located in the same plane as the acoustic waveguide and senses changes in the flux passing through the coil when magnetic and/or metallic objects or targets are present near the waveguide. The spatial location of the targets along the length of the proximity sensor can be determined by measuring the time interval from the initial application of the strain wave until the signal corresponding to the target is induced in the sensing coil. Multiple objects can be sensed by measuring the time interval for each signal.

Abstract: A keyboard apparatus has a plurality of elastically deformable elastic members disposed on a board in a predetermined positional relationship, a plurality of push members each disposed above each of said plurality of elastic members and adapted to push said elastic member to cause the same to elastically deform and produce an acoustic signal. At least three pickups are disposed on the board at different positions for sensing arrival of the acoustic signal. A detecting circuit determines for detecting the keyed position in response to the output from each of the pickups based upon the differences between arrival times of the acoustic signal at these pickups.

Abstract: An assembly for identifying the results of a specimen analysis wherein such specimen analysis occurs in an array of discrete cells. The assembly includes a housing having top, bottom, end walls, and sidewalls. An array receiving recess is provided on the top wall for receiving and holding in a fixed position the array of the discrete cells. An ultrasonic signal producing stylus is provided for selectively producing an ultrasonic signal adjacent a cell in the array in which the results of the analysis are to be identified. A first ultrasonic signal transducer is provided on the top wall for converting the ultrasonic signal from the ultrasonic signal generator to a first electrical signal. A second ultrasonic signal transducer is provided on the top wall for converting the ultrasonic signal from the ultrasonic signal generator to a second electrical signal.

Abstract: Method and apparatus for estimating the location of an unknown sound source in a structure to be monitored, wherein sounds from at least three known sound sources are detected by a plurality of detectors. At least one of peak value data and signal arrival time data derived from the outputs of the detectors are classified for each of the known sound sources and stored in a storage. Pattern differences from each of the known sound sources to a number of predetermined positions respectively, are calculated to prepare for each of the known sound sources a correspondence table indicating relationships between the calculated pattern difference and the real distances from the known sound source positions to the predetermined positions, the correspondence table being stored in a storage. The pattern differences for each of the known sound source positions are calculated on the basis of the sound signal data derived through detection of a sound from an unknown sound source and the data stored in the storage.

Abstract: An obstacle sensing area ahead of a mobile robot is divided into a plurality of sensing regions. A number of ultrasonic transmitters and plural receivers on the robot cooperate to detect the presence of obstacles in the sensing regions. Coordinates representing four corners of each sensing region, and time data representing a time period from emission of ultrasonic waves from selected transmitters to reception of the waves by each receiver when the waves are reflected by an obstacle at each corner point, are prestored in data ROMs. The data ROMs are retrieved by a CPU in response to obtained time data, and precise position data of the obstacle in the sensing area is determined.

Abstract: An ultra-sonic distance sensor system includes means for measuring the elapsed time between transmission of ultra-sonic waves and receipt of the return wave reflected by an object which reflects ultra-sonic waves and the distance to which is to be measured. A correction value is derived on the basis of the rate of change of the signal level of a receiver signal output by an ultra-sonic receiver. On the basis of the derived correction value, the resultant distance value or the measured elapsed time value is corrected to ensure accurate measurement of the distance to the object can be ensured. This allows more precise height control for a vehicle when the distance detector is applied to a height control system of an automotive vehicle.

Abstract: Hydrophone systems in which the direction of acoustic waves impinging on an array of hydrophones is determined from measurements of the periods between successive zero-crossings of waves detected by the two hydrophones of each several different pairs of the hydrophones, allowance being made for the fact that the start and finish of such a period may be due to zero-crossings of different waves. In one embodiment the hydrophones are arranged in two linear groups disposed at right angles to one another, with unequal spacing between adjacent pairs of hydrophones in each group. In another embodiment the hydrophone array consists of five hydrophones disposed at the corners of a regular pentagon.

Abstract: An apparatus for determining an angle of incidence of a received signal utilizes two widely spaced interferometers with equal length crossing baselines. The time differential of a signal arrival between the two elements of each interferometer is established and the difference between the two time differentials is determined. Multiplying this difference by a predetermined constant provides the desired angle.

Abstract: A small non-colinear transducer array for omnidirectional acoustic emission monitoring is disclosed. The small transducer array consists of four piezoelectric sensor elements of sufficiently small diameter as to function as essentially point receivers and of sufficient frequency response as to be sensitive to the signals to be detected. The sensor elements of the transducer array are close together and are non-colinear so that the signals received by them can be used for determining the group velocity of acoustic waves on solid plates and on plate-like structures such as shells and pipes, and to permit determination of both the source direction and distance.

Abstract: The disclosure is directed to an apparatus for determining position in a data space. A generally flat tablet is provided, the tablet being formed of a solid acoustically-conductive material. A movable element, such as a stylus, is adapted to be manually movable over the tablet surface, the movable element having a tapered tip which contacts the surface of the tablet. An acoustic transducer is coupled to the tip of the movable element. Fixed transducer means are coupled to the tablet. Means are provided for energizing acoustic energy to propagate in either direction between the transducer of the movable element and the fixed transducer means. The midrange frequency of the energy is selected such that the wavelength of the energy mode propagating parallel to the tablet surface is a function of the tablet thickness. Means are provided for determining the time of propagation of the acoustic energy travelling, in either direction, between the transducer of the movable element and the fixed transducer means.

Abstract: A passive method for obtaining target data from a sound source disposed in a nonsolid medium by means of a sound receiver remote from the sound source, by the steps of: providing, as the sound receiver, first and second sound-to-electrical signal transducers constituted and positioned to each respond to a respective one of two sound waves propagated from the sound source to the sound receiver at respectively different propagation speeds; and deriving, by means of an electrical signal processing system connected to receive output signals from the transducers, target data from the sound source by determining the frequencies of, or the difference in reception time between, the sound waves emitted by the source and to which the two transducers respond.

Abstract: An acoustic sensor and method of using same for determining the position of a tool from a workpiece are disclosed in which a piezoelectric transducer having a curved surface emits a sound wave which strikes the workpiece and is reflected back to the sensor. The sensor and tool are positioned relative to one another so that the workpiece will be near the focal point of the curved surface when the tool is operating. This positioning substantially overcomes the attenuation problems of high frequency sound waves transmitted through air.

Abstract: Acoustic positioning device for a vessel comprising N transponders (B.sub.1 . . . B.sub.i . . . B.sub.N).A fixed acoustic transmitting means (E) periodically transmits acoustic pulses at frequency f. The responses of the transponders (B.sub.1 . . . B.sub.i . . . B.sub.N) are received by the acoustic array (A.sub.1, A.sub.2) of the vessels. The time origins are transmitted by a radio antenna to the surface vessel. In the case of submarines, two stable clocks are used, one of which is on board the submarine. Processing circuits make it possible to know the position of submarines.Application to the positioning of vessels in an oil production field or for oceanographic research.

Abstract: An apparatus for use in a firing range, in which transducers located adjacent the target area detect the airborne shock wave from supersonic projectiles. The position at which each projectile passes through the target plane is determined from the relative time of arrival of the associated shock wave at the transducers. A visual display of the target and the projectile position is provided for the use of range personnel.

Abstract: An apparatus for use in a firing range, in which transducers located adjacent the target area detect the airborne shock wave from supersonic projectiles. The position at which each projectile passes through the target plane is determined from the relative time of arrival of the associated shock wave at the transducers. A visual display of the target and the projectile position is provided for the use of range personnel.

Abstract: A pulse generator is provided for transmitting individual acoustic pulses which can be sensed by an audio surveillance device and retransmitted as modulated electromagnetic information. Circuitry is associated with the pulse generator for controlling the time when a first acoustic pulse is generated relative to the detection of an unmodulated carrier frequency. This circuitry further provides for the generation of a second acoustic pulse in the event that a modulated carrier frequency is detected during the interval when it can be expected that the first pulse has resulted in modulation of the previously unmodulated carrier frequency. Means are included in the circuitry for comparing the respective periods between the times the first and second acoustic pulses are generated and when modulation on the carrier frequency occurs within the predetermined intervals following such pulse generations.

Abstract: Sound monitoring device for an industrial installation to detect possible impacts of stray bodies including at least one set of two sound detectors arranged in contact with the wall of the installation or in its vicinity, and a measuring and alarm circuit. The detectors are connected to this measuring circuit which includes a device for measuring the separation in time between the reception of the sound waves at one and the other detector, a comparator for this separation with at least one set of two predetermined values, and an alarm which is triggered if the separation in time falls between the two predetermined values. The invention is particularly useful for surveillance of the primary circuit of a pressurized water nuclear reactor.

Abstract: The disclosure is directed to a microprocessor-based apparatus and method for determining the distance between an object and a reference position. An embodiment of a graphical digitizer is set forth in which a microprocessor system is adapted to generate and store a count that depends upon the number of instruction cycles that the microprocessor system performs during a time interval that is a function of the travel time of acoustic wave energy traveling between the object and the reference position. In a disclosed embodiment, acoustic receivers are mounted with their axes parallel, and each receiver has a generally circular receptivity pattern.

Abstract: Disclosed is an apparatus for training in marksmanship. The apparatus uses a computer to determine the position of strike of a projectile on a target and further detects a hit on the target, especially in the region of the edge of the target where the projectile position determination computer may produce some errors. The physical hit detection system of the present invention will "override" the computer in those instances where the projectile barely touches the edge of the target and the computer "sees" the projectile as having missed the target or vice versa.

Abstract: A number of sound detectors are provided on an external enclosure of a pressure vessel of a nuclear reactor. Output signals produced from the individual detectors are combined into a pattern in terms of time difference of the detector output signals relative to the time point at which the detected signal is first produced in response to the sound signal and relative peak values of the detector output signals relative to the magnitude of the output signal produced by the detector which detects the sound signal with the highest sensitivity. The pattern thus obtained is then compared with patterns which have been previously prepared by intentionally producing the sound signals at locations in interest within the pressure vessel, to thereby estimate the location within the pressure vessel at which the sound is produced.

Abstract: Disclosed is an apparatus for indicating the location in a measurement plane through which a projectile passes. The apparatus includes an array of at least three transducers responsive to the airborne pressure wave produced by the projectile and positioned at predetermined locations along a line parallel to the movement plane. The apparatus further includes a device for measuring the velocity of the projectile and another for measuring the velocity of sound in air in the vicinity of the transducers. A computing means, responsive to the array of transducers, the velocity measuring means and the propagation of sound determination is provided which determines the location in the measurement plane through which the projectile passed and provides an output indicating that location. Also disclosed is a means, in combination with the position detecting means, for detecting and providing a positive indication of a projectile hit on a target member.

Abstract: Disclosed is an apparatus for use in marksmanship training. The apparatus includes means for detecting and indicating a position in a measurement plane in the vicinity of a target through which a projectile passes. In addition, the apparatus includes means for measuring the velocity of the projectile in the vicinity of the target. The measured velocity is compared with a predetermined expected velocity to determine if the projectile passed through the measurement plane in free flight or if it had ricocheted prior to passing through the measurement plane. The apparatus will then afford the marksman both an indication of where the projectile passed relative to the target and an indication of whether the projectile has struck the target on a ricochet.

Abstract: A curved, elongate transducer assembly contacted by a shock or pressure wave transmits the resultant vibrations to the ends of the member, the vibrations at the respective ends being converted to output signals from which a time difference signal is produced. A computer calculates from the time difference signal the inclination angle of the projectile trajectory relative to a reference line. Two of the curved, elongate transducer assemblies at spaced locations permit calculation of two such inclination angles and, therefrom, the location at which the projectile trajectory passes through a reference plane. The transducer assembly may be a rigid bar with transducer elements at each end, or a single piezoelectric member with pickup electrodes at each end.

Abstract: A hit detection device for use in a marksmanship evaluation device for providing positive and negative reinforcement of shooting techniques immediately after each shot is fired. The hit detection device comprises a transducer spaced apart from a target member and detects and provides a hit indication output when the target is hit. In a preferred embodiment, the transducer in combination with electronic circuitry provide discrimination such that a hit indication output is only provided when the target member is actually hit by a projectile directly and no output is provided if the target is hit by a ricochet or is disturbed by any other external source such as the wind, sonic booms, etc. In a further preferred embodiment, the target member is three-dimensional and at least partially surrounds the transducer to shield the same from air pressure disturbances caused by projectiles passing by but not actually hitting the target member.

Abstract: A target apparatus, having a framework covered by sheets of material to form a chamber the sheets of material being penetrable by a projectile, such as a bullet, fired at the target. A plurality of transducers are positioned at respective spaced-apart locations within the chamber and lying on an arc of a circle, for detecting shock or pressure waves in the chamber caused upon penetration of the sheets of material by the projectile. Time differences between instants of detection of a shock or pressure wave by the transducers are measured, the location at which the projectile penetrated the sheet of material being determined from the time differences. Preferably, a bull's-eye or aiming mark is provided on the target, the center of which is aligned with the center of the circle on which the transducers lie. Apparatus is also disclosed for determining the speed of sound in air within the chamber, enabling the projectile penetration point to be determined with particular accuracy.

Abstract: Probe method and means are disclosed for guiding and positioning a robot-actuated tool, such as a gripper or a welding head, through at least one transceiver for generating and sensing focused shockwaves, the probe being associated with the tool for relative movement with respect to the object or objects being sensed, without physically contacting the same.

Abstract: Indicator apparatus for determining the miss distance of a projectile in relation to a fixed or moving target, comprising pressure-sensing transducers intended to sense the pressure wave generated by the projectile in at least four points, and means for generating corresponding electrical signals therefrom. The apparatus further comprises computer circuits, calculating the distance to the point of origin of the wave, i.e. the so-called "bang generation point", in response to the characteristics of the pressure wave. This distance has been called the "miss distance" in previously known indicator apparatus, but in accordance with the invention the miss distance is defined as the shortest distance between the projectile and target, and one object of the invention is to indicate this distance and the exact position of the projectile when it is at the miss distance from the target.

Abstract: A device for determining the position of a sound source includes a plurality of sensors disposed on an object for which the sound source is to be detected and organized in the form of a matrix with N rows and M columns. The sensors are connected in parallel through respective uni-directional transmission elements with a common terminal for each row and each column. A signal processing circuit amplifies and carries out a designated output waveform generation process on detected signals produced by the sensors.

Abstract: In a target equipment in which transducers are provided to detect the pressure wave generated by a projectile the transducers being connected to a timing and calculating device adapted to calculate from the time delays between the instants of reception of the pressure wave the trajectory of the projectile, a signal transmitter, comprising a spark generator, is used to transmit sonic signals which are detected by the transducers. The signal transmitter can be used to indicate the precise location or shape of the target and this information is stored in the computer memory.

Abstract: 1. Apparatus for protecting a vessel from a waterborne missile launched urwater by air pressure, comprising means for continuously listening to port and to starboard at three spaced locations at predetermined progressive distances astern of the vessel for any waterborne wavefront radiated as a consequence of a waterborne missile launching, and for detecting the passage of such wavefront across each of said spaced locations, means for signalling aboard the vessel the passage of such wavefront across any of said locations, and means for recording on a time base the instants that such wavefront crosses each of said locations and the approximate arrival direction of the wavefront in terms of port or starboard, whereby proper evasive action for the vessel may be determined and taken.

Abstract: The method and apparatus for computing the range to and depth of a submerged object that either emits or reflects pulses of acoustic energy, wherein a detecting array and related data handling apparatus measure as a function of time the apparent angles of arrival of the acoustic energy associated with each such pulse. This data is then translated into actual multipath arrival angles and multipath travel time differences which are utilized to solve mathematical equations, the solutions of which result in the calculation of the range to and depth of the submerged source of acoustic energy.

Abstract: In a target equipment in which transducers are provided to detect the pressure wave generated by a projectile the transducers being connectead to a timing and calculating device adapted to calculate from the time delays between the instants of reception of the pressure wave the trajectory of the projectile, a signal transmitter, comprising a spark generator, is used to tansmit sonic signals which are detected by the transducers. The signal transmitter can be usd to indicate the precise location or shape of the target and this information is stored in the computer memory.

Abstract: The invention relates to the determination of the position of a self-contained operating apparatus movable along any line of displacement over any immersed structure.A follower apparatus is associated with the operating apparatus, and the position of this follower apparatus, along a line of displacement chosen as the reference line, is determined at any instant. The follower apparatus is displaced by the operating apparatus by servo-control means, and at any instant the transverse distance between the operating apparatus and the follower apparatus is monitored.

Abstract: Apparatus for training in marksmanship which provides positive and negative reinforcement of shooting techniques immediately after each shot is fired. The reinforcement may take a number of forms, preferably comprising a plurality of indications concerning each shot fired. The indications may comprise at least an approximate indication of where a projectile fired at a target has passed relative to the target and/or a positive indication of whether the projectile has actually hit the target and/or whether the projectile has ricocheted prior to reaching the zone of the target. Specific apparatus for performing each of these functions is disclosed. Indication may also be given concerning whether the trainee marksman is correctly gripping the weapon being fired.

Abstract: An improved ballistic impact sensing and display system is provided for use in conjunction with land or water ordnance ranges. A plurality of sensors placed around the target area detect the shock wave created by the impact or passage of the ballistic projectile. The sensors drive electronic timing means which record the time intervals between activation of the sensors by the propagating shock wave. Storage registers within the timing means drive a gridwork of display buses arranged along hyperbolic curves. A matrix of indicators bridging the points of intersection of the hyperbolic buses display the compartment within the target area in which the impact occurred. Additional indicators around the periphery of the matrix of indicators display the sector by which a projectile passed if it missed the target area.

Abstract: A target device for ascertaining the proximity of a hit to the target center comprises a plurality of transducers separated from one another in a space behind the target surface and positioned to respond to the impact shock at times determined by the sound propagation velocity in the air of this compartment. To increase the accuracy of the device, means is provided to provide an essentially constant temperature gradient (or uniform temperature) in the space or compartment and/or one sensor more than that required for determining the position of impact when the sound propagation velocity is known, is used.

Abstract: An apparatus for use in a firing range, in which transducers located adjacent the target area detect the airborne shock wave from supersonic projectiles. The position at which each projectile passes through the target plane is determined from the relative time of arrival of the associated shock wave at the transducers. A visual display of the target and the projectile position is provided for the use of range personnel.

Abstract: The height to which the forks of a lift truck are raised is measured by an ultrasonic height measuring arrangement including a downward facing transmitting transducer, positioned on the truck platform in fixed position with respect to the forks, and a downward facing ultrasonic receiving transducer which receives ultrasonic acoustic energy waves reflected by an upward facing parabolic reflector. The receiving transducer is positioned in a casing substantially at the focal point of the parabolic reflector and is mounted by means of springs which provide vibration isolation between the casing and the transducer.

Abstract: An output distance signal related to the distance between an ultrasonic transmitting transducer and an ultrasonic receiving transducer is provided by an apparatus including a reference oscillator and a burst generator responsive to the reference oscillator which periodically generates ultrasonic burst signals. The ultrasonic transmitting transducer is responsive to the generator for providing an ultrasonic acoustic energy burst in response to each of the ultrasonic burst signals. An ultrasonic receiving transducer receives the ultrasonic acoustic energy bursts and generates detection signals in response thereto. A range window circuit is responsive to detection of an acoustic energy burst by the receiving transducer, for providing a range window signal at a time period lagging the detection signal such that a range gate will be opened for passage of the next following detection signal.

Abstract: A pulse generator is provided for transmitting an acoustic pulse which is sensed by an audio surveillance device and retransmitted as modulated electromagnetic information. Associated with the pulse generator is a timing arrangement and display. The timer is triggered into operation by the generation of the acoustic pulse. The operating speed of the timer is established to be a function of the speed of sound. Means are provided to stop the timer upon receipt of a demodulated signal representative of the retransmitted pulse whereby the display indicates the distance to the surveillance device.

Abstract: A device which detects a displaced position by generating an ultrasonic signal in a magnetostrictive wire and measuring the propagation time of the signal generated. The device includes an exciting means to generate an ultrasonic signal in a magnetostrictive wire, first and second receiving means to receive the ultrasonic signal generated in the magnetostrictive wire by the exciting means, a means for changing the distance between the exciting means and each of the first and second receiving means in accordance with a mechanical displacement, and a circuit means for producing a signal representative to the time periods required for the generated ultrasonic signal to reach the first and second receiving means.

Abstract: A hit detection device for use in a marksmanship evaluation device for providing positive and negative reinforcement of shooting techniques immediately after each shot is fired. The hit detection device comprises a transducer spaced apart from a target member and detects and provides a hit indication output when the target is hit. In a preferred embodiment, the transducer in combination with electronic circuitry provide discrimination such that a hit indication output is only provided when the target member is actually hit by a projectile directly and no output is provided if the target is hit by a ricochet or is disturbed by any other external source such as the wind, sonic booms, etc. In a further preferred embodiment, the target member is three-dimensional and at least partially surrounds the transducer to shield the same from air pressure disturbances caused by projectiles passing by but not actually hitting the target member.