US3790927A

US3790927A - Underwater sound signal discriminating system

Info

Publication number: US3790927A
Application number: US00767489A
Authority: US
Inventors: A Chwastyk
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1958-10-15
Filing date: 1958-10-15
Publication date: 1974-02-05
Anticipated expiration: 1991-02-05

Abstract

1. An underwater actuation system comprising means for detecting an underwater sound pressure wave and for developing an electrical signature signal correlative thereto, means for separating said signature signal into a plurality of different energy components, means for detecting the envelope of one of said energy components, means for deriving a signal corresponding to the logarithm of said detected envelope, means for deriving a signal representative of the first derivative of said logarithm signal, means for deriving a signal representative of the second derivative of said logarithm signal, means for developing a triggering signal corresponding to the product of said first and second derivative signals, means coupled to said triggering signal for developing an output, circuit means normally effective for preventing the application of said triggering signal to said output developing means, means coupled to said logarithm signal deriving means and to said one of said energy components for interrupting the passage of said one of said components within the actuation system, means for developing a control signal correlative to the ratio between the other of said energy components and the average value of said one energy component, and means coupled to said control signal for rendering said circuit means effective when a predetermined relationship between said control signal and said triggering signal is effected.

Description

Primary @rgminer- Bichard A. Farley Attorney, Agent, or Firm-R. S. Sc1asc1a & J. A. Cooke @hwastyk Feb. 5, 1974 UNDERWATER SOUND SIGNAL for developing an electrical signature signal correla- DISCRIMINATING SYSTEM tive thereto, means for separating said signature signal into a plurality of different energy components, means [75] Inventor at Chwmyk Sllver Spnng for detecting the envelope of one of said energy components, means for deriving a signal corresponding to [73] Assignee: The United States oi America as the logarithm of said detected envelope, means for derepresented by the Secretary all the riving a signal representative of the first derivative of Navy, Washington, DC. said logarithm signal, means for deriving a signal rep- [22] Filed. Oct 15 1958 resentative of the second derivative of said logarithm signal, means for developing a triggering signal corre- [21] Appl. No.: 767,489 sponding to the product of said first and second derivative signals, means coupled to said triggering signal 52 us. c1. 340/5 R 102/18 .devebping .Output, cir?uit.means [511 at (:1. .....,.........:........11.11:111111 ma 11/00 e for rg 3 F of sad mggermg slgna to sm output eve oping means, means cou- 5s Fleld or Search 340/5, 6, 102/18, 19.2 pled to Said logarithm signal deriving means and to [56] References Cited said one of said energy components for interrupting the passage of said one of said components within the UNITED STATES PATENTS actuation system, means for developing a control sig- 2,802,420 8/1957 MacDonald 102/18 nal correlative to the ratio between the other of said energy components and the average value of said one energy component, and means coupled to said control signal for rendering said circuit means effective when a predetermined relationship between said control signal and said triggering signal is effected.

16 Claims, 5 Drawing Figures 14 AC0 29 46 62 ,6? F u 1c BROAD BAND LOW-PASS SMOOTHING TRANSDUCER AMPLIFIER FILTER GATE DETECTOR FILTER 53 I "i DETECTOR LOGARlTHMIC CIRCUIT I men PASS FILTER SIGNAL LEvEL 14s SHIFTING CIRCUIT RATIO I 75 DETECTOR DIFFERENTIATOR I DELAY m l HI} |2s DIFFERENTIATOR GATE VOLTAGE 99 MULTIPLIER i 1 =5 MINE FIRING PATENTEU 5 74 SHEEY 2 BF 3 MINE FiRlNG CHANISM NdE O.

INVENTOR. ADOLPH. iVI. CHWASTYK ATTORNE Y3 UNDERWATER SOUND SIGNAL DISCRIMINATING SYSTEM The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates generally to an acoustic signal discriminating method and apparatus and more particularly to a passive acoustic signal detecting system for effecting actuation of an underwater ordnance weapon, such for example as a naval mine, or the like.

In modern naval mine warfare widespread use is being made of electronic circuitry for detecting the underwater acoustic signal developed by either a surface or submerged vessel within the proximate area, and in response thereto, for effecting detonation of the mine if the vessel comes within the desired firing radius of the mine. In the earlier acoustic firing systems, the mine actuating signal was almost entirely dependent on the amplitude of the acoustic signal, or signature, developed by the target ship. Because of the wide variation in sound output amplitude of various ships, a firing mechanism set to actuate the mine by the acoustic signature of a comparatively quiet vessel within the desired damage range may be actuated by the acoustic.

signature of a loud vessel outside the damage range. Moreover, the same loud vessel within the damage range may even result in countermining the mine rather than actuating it.

To overcome the hereinbefore described disadvantages of amplitude actuation, acoustic signal mine firing systems have been devised which are selectively responsive to the mathematical derivatives of the logarithm of the envelope of a target vesselssignature thereby resulting in mine actuation which is substantially dependent of the signal amplitude. An acoustic mine firing mechanism of this type is disclosed in the copending application of Lloyd D. Anderson, Ser. No. 487,001, filed Feb. 8, 1955, and of common assignee with this application.

Although the later developed underwater acoustic signal firing systems have performed satisfactorily under operational conditions, recent technological advances in countermining and mine sweeping techniques have reduced the operational effectiveness of these improved acoustic systems. More specifically, methods and apparatuses for generating an acoustic countermining signal sufficiently simulative of the signature of a target vessel have been developed for effecting a premature and non-target destructive detonation of a naval mine. Examples of these apparatuses are hammering mechanisms, underwater explosions, and the intermittent sound pressure wave generating device,

disclosed in the copending application of Norman Taslitt and William Byrd, Jr., Ser. No. 565,747, filed Feb. 15, 1956, now U.S. Pat. No. 3,052,205 and ofcommon assignee with this application. To provide protection against the premature firing, or misfiring of a naval mine by the presence of an artificially produced underwater acoustic signal, anti-countermine circuitry have been included in the presently available acoustic firing systems for rendering them insensitive to the countermining signals. Although these present day anticountermine circuits have functioned satisfactorily under most countermining conditions, they have been found to exhibit certain inherent undesirable characteristics which have seriously limited their operational usefulness. A principal limitation lies in the relatively long time duration that the firing channel of the mine firing system is maintained blocked, or insensitive after the expiration of the countermining signal. It has been found that this operational limitation will allow for the safe passage of a target vessel by the periodic transmission of an underwater countermining signal. Another major shortcoming of the protective circuitry provided in the present day passive acoustic firing systems is their inability to more readily and positively discriminate between an artifically generated and target generated signature. Still another disadvantage of present day anti-countermine circuitry lies in their inability to provide for normal operation of an acoustic firing system during the concurrent presence of a target and countermine signal by reason of which a proximate target vessel employing countermining techniques will pass safely by the mine.

Accordingly, it is a principal object of the present invention to provide a new and improved underwater acoustic signal responsive system.

Another object of this invention is the provision of a new and improved passive acoustic responsive actuating apparatus for an underwater ordnance weapon.

Still another object of the present invention resides in the provision of an underwater acoustic signal detection circuit having improved signal discrimination capabilities.

A further object of the instant invention is to provide new and improved anti-countermining circuitry for use in an underwater acoustic signal responsive mine detonating system.

A still further object of this invention is to provide a new and improved underwater acoustic firing system, wherein the relationship between the various energy components of an underwater acoustic signature are compared and utilized for effecting discrimination between the signature generated by a proximate target vessel and a countermining device.

Another still further object of this invention is the provision of a new and improved underwater sound signal discrimination method.

Other objects and many of the attendant advantages of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. la is a graphical illustration-of the energy distribution in the underwater acoustic signature of a target vessel;

FIG. lb is a graphical illustration of the energy distribution in an artificially produced underwater acoustic signature;

FIGS. 2a and 2b show a detailed schematic diagram of the passive acoustic firing system according to the present invention; and, FIG. 3 is a block diagram of the entire system.

Referring now to the drawings,and more particularly to FIGS. la and 1b thereof, the curves 1] and 12 thereon respectively designate the high and low frequency energy distribution in the acoustic signatures of a proximate target vessel and a relatively distant countermining device of the types hereinbefore described. The curves show that the acoustic signatures of a vessel or countermining device consists of an energy distribution over a relatively wide range of frequencies and magnitudes. A consideration of curves 11 and 12 readily shows the existence of various distinctions in the energy content of the two acoustic signals. One significant distinction between the signatures is the much larger ratio of the energy in the high frequency band; i.e., above 100 cps, and the energy in the low frequency band; i.e., between 15 and 60 cps, for the acoustic signature generated by a target vessel. Another significant distinction lies in the coincidence of the peaks of the high and low frequency energy components of the signature of a proximate vessel and the non-coincidence of the energy peaks of the countermining signal. This phenomenon is caused by the dual paths traveled by the different energy components of an underwater acoustic signal. More specifically, the high frequency energy travels the direct water path while the low frequency energy travels through the sea bottom thereby arriving at a remote listening point ahead of the more slowly transmitted high frequency energy. It will be apparent therefore that the more distant the source of the acoustic energy signal from the acoustic signal detector, the greater the time delay of arrival, A t, FIG. lb, of the high frequency energy peak after the low frequency energy peak.

In accordance with the general concept of the present invention discrimination between a target and countermine signatures is obtained by detection of the aforedescribed dissimilitudes between the energy content of the divers signatures. In a generalized form of the method and apparatus of the instant invention, a sound signal is picked up by a hydrophone and passed through an amplifier stage as required to provide necessary gain for the succeeding plurality of operations to which the detected signal is subjected in order to obtain the desired signal source discrimination. The detected signature is separated into its componential high and low frequency energy contents. The low frequency energy content is suitably amplified and detected. The logarithm of the low frequency envelope is taken, the first and second derivatives thereof obtained, and a triggering signal corresponding to the product of the two derivatives developed. The ratio of the peak to the average value of the low frequency energy signal is detected and the transmission of the low frequency signal within the system regulated accordingly. The sequence further includes detection of the ratio between the high and the average of the low frequency energy signals as well as detection of the time duration of the detected ratio thereby to provide for selective utilization of the triggering signal by the mine initiator. Circuitry is also provided for effecting optimum response of the overall firing system to the acoustic signature of a particular type target vessel.

FIG. 3 of the drawings discloses a block diagram of this novel system. The acoustic signal is picked up by some suitable acoustic transducer such as shown by 13. The resulting electrical signal produced by the transducer is fed to broad band amplifier 14. The output of this amplifier is supplied to both low pass filter 29 and high pass filter 31. Filter 31 produces a voltage containing only the high frequency components of the signal picked up by transducer 13.

The output of filter 29 containing only the low frequency components of the signal picked up by the transducer 13 is connected to gate 46 and signal level shifting circuit 105. Gate 46 passes the output of the filter 29 whenever the output of detector 53 reaches or exceeds a certain predetermined value. A voltage indicative of the average value of the output of gate 46 is obtained by detector 62, smoothing filter 67 and logarithmic circuit 71 which are series connected to the gate 46. The signal produced by the logarithmic circuit is fed to signal level shifting circuit 105 wherein a voltage commensurate with the ratio of the peak value to the average value of the output of filter 29 is produced. This ratio signal is fed through amplifier 99, condenser 1 10 and detector 53 to control the operation of gate 46 in the manner previously mentioned. The values of resistor 126 and capacitor 113 are chosen so as to prevent this ratio signal from affecting the output of multiplier 111. The voltage produced by logarthmic circuit 71 is supplied to differentiator 75. One output of differentiator 75 is fed directly to voltage multiplier 1 11 and the other output is differentiated a second time by circuit 95. The signal developed by differentiator is supplied to multiplier 111 by way of amplifier 99. The value of capacitor is chosen so as to prevent passage of this differentiated signal to detector 53. The first and second derivative signals are multiplied together in circuit 1 11 and fed into the mine firing mechanism as long as the high frequency signal developed by filter 31 is of sufficient value to maintain gate 171 open. The operation of differentiators 75 and 95 as well as multiplier 1 1 1 produces a sharp, short duration pulse to actuate the mine firing mechanism as disclosed in the aforementioned application of Anderson.

High pass filter 31 and logarithmic circuit 71 are connected to ratio detector which produces a voltage indicative of the ratio of the peak value of the high frequency portion of the signal received at transducer 13 to the average value of the low frequency portion of said input signal. The voltage developed by detector 145 is fed into delay means 167 to open gate 171 and allow passage of the signal from the multiplier to the mine firing mechanism. This takes place when the value and time of occurrence of the peak of the high frequency portion of the received signal with respect to the low frequency portion of said signal is as shown in FIG. 1a. The signatures of FIG. lb will not detonate the mine because the high frequency peak occurs substantially after the low frequency peak. When an actuation pulse is produced by the multiplier in response to the low frequency peak, the gate remains closed because the value of the high frequency signal at that time is insufficient to actuate it.

The detailed circuit diagram of this invention is shown in FIGS. 2a and 2b wherein the passive acoustic signal mine firing system is shown as including an underwater transducer, or crystal hydrophone 13 which converts an acoustic pressure wave impinging thereon into an electrical signal having an instantaneous magnitude proportional to the instantaneous intensity of the pressure wave. The electrical signature of the impinging pressure wave is amplified to a desired level by a first signal amplifier stage 14. The voltage amplifier 14 consists of a relatively broad band input filter network, which includes

condensers

15, 16 and resistors 17, 18 selected in a well known manner to pass only the portion of the frequency spectrum of an underwater acoustic signal representative of a particular class ships signature. The amplifier stage 14 also includes an electron tube 19, the plate and screen electrodes of which are connected to a unidirectional potential energy source B through

individual dropping resistors

21 and 22, re-

spectively, and the filament of which is connected to a unidirectional potential energy source, such for example as a l.5 volt A battery. A condenser 23 is included to provide a suitable by-pass to ground 24 for the screen grid of electron tube 19. A clamping network consisting of

semiconductor diodes

25 and 26 is connected between the positive side of the filament supply A and the negative side of a bias potential supply source, such for example as a 6 volt C battery, to provide peak-to-peak amplitude limiting of the amplified output signature to a preselected magnitude, such for example as 7.5 volts, as will be more fully explained hereinafter. The amplified output signature is simultaneously applied through

coupling condensers

27 and 28 to a low frequency pass filter 29 and a high frequency pass filter 31 whereby the low and high frequency energy components of the amplified acoustic signature are separated. It is to be understood that filters 29 and 31 may constitute plug-in units, each of which is especially responsive to the energy components of the signature generated by a particular type target vessel.

The low frequency band pass network 29 consists of an inductance 32, preferably exhibiting a band pass characteristic of cps i 1 octave for selectively passing only the low frequency energy content of the amplified acoustic signature. For the purpose of obtaining equal loading on amplifier stage 14, a parallel network consisting of resistor 33 and condenser 34 and inductance 35 may be shunt connected across the output of the filter network 29 through coupling condenser 36.

The low frequency energy signal output of filter network 29 is simultaneously applied across two parallel voltage divider networks. One network consists of a serial arrangement of a potentiometer 37 and a resistor 38, while the other network includes a serial arrangement of a blocking condenser 39, a potentiometer 41, and resistor 42. The juncture of potentiometer 41 and resistor 42 is connected to the negative terminal of the C potential source through resistor 43.

A portion of the low frequency energy signal, the level of which is controlled by the setting of potentiometer 37, is applied to the control grid of an electron tube 44 of a second signal amplifier stage 45 across a gating circuit 46. As shown, the gate 46 includes a serial arrangement of dropping resistor 47 and condensers 48,49 in the low frequency signal path between potentiometer 37 and electron tube 44. The juncture of condensers 48,49 is connected through semiconductor rectifiers 51,52 between the C potential supply and a detector stage 53 which develops an output potential corresponding to the varying ratio between the peak and average of the low frequency signal, as will be explained more fully hereinafter. The low frequency signal gate 46 will permit transmission of the low frequency signal to the control grid of tube 44 when the level of the output potential signal of detector 53 is above a preselected level, such for example, as the level of the negative reference potential provided by source C. Under this operating condition, rectifiers 51, 52 offer a high impedance path to the low frequency signal. However, when the output potential of detector 53 is more negative than the reference potential, rectifier 51 becomes a low impedance path to the low frequency signal and most of the signal will be dropped across resistor 47, whereupon no signal is transmitted to elec' tron tube 44. A shunting resistor 54 is provided across rectifier 51 to maintain the juncture point at the negative bias potential level thereby to minimize the amplitudes of transients developed by the opening and closing operations of gate 46.

Assuming for purposes of description that the gate 46 is open, the low frequency signal is impressed upon the control grid of tube 44 and amplified to a preselected level as determined by the tube bias as established by a voltage dividing network consisting of

resistors

55,56 and 57 connected across the bias potential supply. Suitable operating potentials are applied to the plate and screen grid of tube 44 from the B supply through

individual dropping resistors

58 and 59, while condenser 61 provides an a.c. by-pass to ground for the screen grid.

The amplified low frequency signal output of amplifier stage 45 is applied to a voltage doubling and rectifying stage 62 consisting of semiconductor diodes 63,64 and

condensers

65,66. During the positive halfcycle of the applied signal, current flows from ground 24 through diode 62, charging condenser 65 to approximately the peak of the input voltage. Diode 63 prevents current flow through condenser 66 during this half-cycle. During the negative half-cycle of the applied signal, the current path is through condenser 64 and diode 63 thereby charging condenser 66 to approximately twice the peak applied signal voltage. The rectified and doubled output signal of stage 62 is applied through a smoothing filter network 67, consisting of resistor 68 and condenser 69, to a logarithmic signal developing stage 71. The logarithmic circuit 71 consists of a serially connected resistor 72 and a varistor 73, the effective resistance of which is proportional to a loga rithmic function of the current passing through it. To obtain an extended operational range of logarithmic stage 71, the varistor 73 is connected to the B source through a dropping resistor 74. The potential output signal of stage 71, which approximates the logarithm of the envelope of the applied input signal to stage 71, is simultaneously applied to the high frequency band pass filter 31 and to a differentiating network 75 through a smoothing circuit consisting of resistor 76 and condenser 77. The differentiating circuit 75 includes condenser 78 and

resistors

79 and 80 the magnitudes of these elements being selected in a well known manner to have a time constant characteristic suitable for developing an output differentiated signal corresponding to the first derivative of the logarithmic signal.

The first derivative signal developed by differentiator 77 is applied directly to the control grid of electron tube 81 of a third signal amplifier stage 82 wherein the level of amplification is dependent upon certain environmental conditions, such for example, as the depth at which the associated mine is planted. The necessary operating potential is provided from the B supply to the screen grid of tube 81 through resistor 83, while the plate thereof is connected to the B supply through a depth compensator 84. Suitable operating bias is provided for the tube 81 by a voltage divider consisting of

resistors

80,85 connected across the C potential source. The depth compensator includes a voltage divider consisting of serially connected resistor s 85,86, 87 and a pair of hydrostatic pressure operated

electrical switches

88,89 normally shunted across

resistors

86 and 87, respectively. Inasmuch as hydrostatic pressure switches 88 and 89 are not part of the present invention they are not disclosed in detail. As the mine sinks in the water wherein it is planted, the switches are adapted to be sequentially operated at varying water depths to an open position thereby resulting in the application of a larger portion of the amplified first derivative signal. A resistance 91 shunting both

switches

88 and 89 may be provided to prevent development of spurious electrical signals which may arise from the intermittent operation of the switches. It is to be understood from the foregoing that the depth compensator provides for automatic regulation of the over-all sensitivity of the acoustic firing mechanism correlative with the planting depth of the mine.

The amplified first derivative logarithmic output signal of signal amplifier stage 82 is split between two paths. In one path the first derivative signal is applied to an L filter section 92, consisting of resistor 93 and condenser 94, the time constant of which has been selected in a well known manner to remove any ripple voltage riding on the first derivative signal. The first derivative signal is then applied to a differentiating network 95. Differentiating network 95 consists of condenser 96 and

resistors

97,98, the magnitudes of these elements being selected in a well known manner to have a time constant characteristic suitable for developing an output signal corresponding to the second derivative of the first derivative logarithmic signal applied thereto.

The slowly varying second derivative logarthmic output signal of differentiating network 95 is applied to a fourth signal amplification stage 99. Amplifier stage 99 consists of electron tube 100, the plate and screen grid of which are energized from the B source through dropping resistors 101,102, respectively. A suitable bias potential is applied to the control grid from the negative side of the C source by a voltage divider consisting of

resistors

97, 98, and 103. Condenser 104 provides an a.c. by-pass to ground 24 for the screen grid of tube 100. In addition to amplifying the second derivative signal, amplifier stage 99 also amplifies an a.c. blocking signal applied to the control grid of tube 100 from an automatic signal level shifting network 105 through a coupling condenser 106. Compensating network 105 includes condenser 39, potentiometer 41,

resistors

42, 43, 107 and semiconductor diode 108. The level of the applied a.c. blocking signal is controlled by the variation in the impedance exhibited by rectifier 108 in response to divers potentials applied thereacross, as will now be more fully described.

A portion of the low frequency energy content of the detected target signature, as preselected by the setting of potentiometer 41, is applied through resistor 107 to the anode of the rectifier 108, while the smoothly varying average logarithmic signal developed across condenser 77 is applied to the cathode thereof. The average value of the logarithmic signal developed for a relatively remote target vessels will be of a small negative value, whereupon rectifier 108 will present a high impedance to the low frequency signal across potentiometer 41. Under this condition substantially all of the low frequency signal, which will be of a low amplitude due to the remoteness of the target vessel is applied to the control grid of tube 100. As the target vessel distance lessens, the average value of the logarithmic signal becomes more negative and the impedance presented by the semiconductor diode 108 diminishes whereupon the low frequency signal will be by-passed to ground 24 through rectifier 108 and condenser 77. If a high amplitude sound impulse, such as would be developed by a nearby countermine device, is superimposed on the low frequency signal, the rectifier becomes a high impedance path and this portion of the impulse signal is fed to the control grid of tube 100. A resistor 109 is interposed between

coupling condensers

96 and 106 to provide for decoupling between the two signals being applied to electron tube 100. It is to be understood that the magnitude of the a.c. blocking signal is representative of the peak to average relationship in the low frequency energy portion of the detected acoustic signature.

Both the slowly varying second derivative signal and the a.c. blocking signal are amplified in amplifier stage 99 and appear at the output thereof. The output of amplifier stage 99 is simultaneously fed to the ratio detector 53 through coupling condenser 110, and to a voltage multiplier section 111 through coupling condenser 1 12. The magnitude of condenser is selected in the well known manner to pass only the amplified a.c. blocking signal, while the magnitude of condenser 112 is selected to pass the amplified second derivative signal. A condenser 113 is included within the multiplier stage 11 1 to by-pass to ground 24 any of the a.c. blocking signal passing through condenser 112.

The low frequency signal ratio detector 53 is composed of a voltage peaking and rectifying network, which includes condensers 110, 114 and semiconductor diodes 115,116, and an R-C network, consisting of resistor 117 and condenser 118. A resistor 119 is shunted across condenser 114 to permit rapid variations in the potential charge appearing thereacross. The operation of the peaking and rectifying network is analogous to that of the voltage doubler stage 62, hereinbefore more fully described. Detector stage 53 develops a negative envelope signal having an amplitude correlative to the magnitude of the a.c. blocking signal, which signal is representative of the peak to average energy relationship of the low frequency componential signal. The componential elements of the ratio detector 53 are selected in a well known manner to develop a negative output signal of a magnitude below the negative potential level of the C source when the peak low frequency energy exceeds the average low frequency energy in the a.c. blocking signal by a certain ratio, thereby to close gate 46 in a manner as described hereinbefore. For a ratio less than the preselected discriminating ratio level, negative output signal above the bias potential source will be applied to gate 46 thereby maintaining the gate open. In view of the relatively high peak value and relatively low average value of the low frequency energy component of a proximate countermine signature, the discriminating ratio level may be pre-established by potentiometer 144. The sensitivity of ratio detector stage 53 is basically dependent upon the average logarithmic signal developed across condenser 77. Consequently as the target vessel more closely approaches and the amplitude of its associated acoustic signature increases, the logarithm of the low frequency energy component increases in a negative direction and the ratio detector becomes less sensitive to nearby countermining signals occurring concurrently with a close-in target vessels signature. By reason of this operational feature, the acoustic firing system can anti-countermine during the presence of a countermine signal and a target vessels signature when the vessel is beyond the lethal range of the mine but will not anti-countermine when the vessel is within the mines destructive radius.

The voltage multiplier circuit 111, to which the first derivative output signal of amplifier stage 82 and the second derivative output signal of amplifier stage 99 is simultaneously applied, although invertedly phased, consists of coupling condensers 122,112, between which is a serial arrangement of resistors l23,l24,125,126, semi-conductor diodes 127,128 and a voltage network, which includes resistors 129, 130 and potentiometer 13, connected between the negative potential source and ground 24. A thermistor 132 may be included in the voltage divider to provide suitable temperature compensation for the multiplier circuit 1 1 1. The first derivative input signal is fed through coupling condenser 122 and dropping resistor 123 across rectifier 127 while the second derivative input signal is fed through coupling condenser 112 and dropping resistor 126.

The characteristics of

rectifiers

127 and 128 will provide for the development of signals thereacross corresponding to the logarithm of the applied derivative signals.

Resistors

133 and 134 may be shunted across

rectifiers

127 and 128, respectively, for the purpose of increasing the logarithmic response range thereof. The logarithmic signals developed across the semiconductor diodes 127,128 are then added across resistors 124,125 and the sum thereof is applied as a triggering signal to the control grid of an electron tube 135 which is part of a firing relay amplifier stage 136. The setting of potentiometer 130 determines the floating d.c. level of the multiplier stage and therefore controls the magnitude of the triggering signal developed by the multiplier circuit 11 1. It is to be understood that by judicious presetting of potentiometers 41,47,130 and 144, certain distinctive characteristics of the acoustic signature of a particular class of vessels can be emphasized thereby resulting in the optimum operation of the acoustic system in response to a particular type target at a preselected lethal distance from the mine.

As shown in FIG. 2b of the drawings, relay amplifier 136 includes a relay 137 in the anode circuit of tube 135, which relay is operated in response to the application of a suitable triggering signal from the multiplier stage 111. Operation of relay 137 results in the operation of a mine firing mechanism and a consequent detonation of the mine. Operating potentials are applied to the anode and screen of tube 135 via the coil of relay 137 and a resistor 138, respectively.

As hereinbefore disclosed, the high frequency energy component of the amplified output of signal amplifier stage 14 is applied to a high pass band filter 31 through coupling condenser 28. Filter network 31 consists of resistors 139,140,141 and condensers 142,143, the magnitudes of which are selected in a well known manner to pass only the high frequency energy portion of the detected acoustic signature, such for example as signals of a frequency of 100 cps and above. A potentiometer 144 is also included to adjust the amplitude level of the high frequency signal. The high frequency signal passed by filter network 31 is compared with the average logarithmic low frequency signal in a ratio detector stage 145, consisting of semiconductor diode 146 and resistor 147. The ratio signal output of stage 145 is then applied through coupling condenser 148 to the control grid of an electron tube 149 which comprises the active circuit element of a fifth signal amplifier stage 150. The magnitude of the ratio signal developed by detector stage is largely determined by the effective a.c. impedance presented to the high frequency signal by rectifier 146 and resistor 147. The effective a.c. impedance of the path through rectifier 146 and resistor 147 is dependent upon the magnitude of the potential difference thereacross, which in turn is a function of the nature of the detected acoustic signature. As shown in FIG. 1a, in a target vessels sound signature the peak of the high frequency energy occurs concurrently with and is substantially larger, than the peak of the low frequency energy for the particular plug in

filter networks

29 and 31 employed. Under this condition, the semiconductor diode 146 will be biased in the forward direction and will offer a relatively small impedance to the high frequency signal. Under this condition, a substantial portion of the high frequency signal will be dropped across isolation resistor 147 and only a small portion thereof appear on the control grid of electron tube 149. As shown in FIG. 1b, in the acoustic signature generated by a countermining device, particularly a distant countermining device, the peak of the high frequency signal is delayed, or completely alternated, while due to the bottom effect, as hereinbefore described, the peak of the low frequency signal component is extended. Under this condition, the ratio between the two signal components of the artifically generated sound signature will be of a minimum value and a high impedance path will be presented by rectifier 146 whereupon substantially all of the high frequency signal will be applied to tube 149 of amplifier stage 150.

In amplifier stage 150 the necessary operating potentials for the plate and screen of tube 149 are applied thereto from the B source through dropping resistors 151 and 182, respectively, while the control grid thereof is provided with a suitable bias potential through grid dropping resistor 153 and resistors 154,155 of a voltage dividing network connected across the bias potential source. Condenser 156 provides a suitable a.c. by-pass for the screen grid. The amplified high frequency output signal of stage 150 is applied to a voltage doubler and detector network 157, consisting of

condensers

158, 159, semiconductor diodes 161,162, and resistor 163 connected across the diodes. Resistor 163 functions as a bleeder path for the charge accumulated across condenser 159. The amplified high frequency envelope signal developed by network 157 is applied to a voltage limiting network 164, consisting of a serially connected resistor 165 and a semiconductor diode 166 which prevents the envelope signal from exceeding a preselected level, such for example as +0.5 volts with respect to ground 24. The high frequency envelope signal is then applied to an R-C timing network 167 consisting of resistor 16S and 169. The componential circuit elements of timing network 167 are selected in the well known manner to have a time constant characteristic whereby a charge of suitable magnitude to bias a semiconductor diode gate 171 in the reverse direction is developed across condenser 169 only upon the application of an envelope signal thereto for a preselected duration, such for example as twenty seconds. During the period when the diode gate 171 is biased in the reverse direction, it will'present a high impedance path to the triggering signal developed by multiplier circuit 111, and consequently, the triggering signal will be impressed upon the control grid of tube 135 thereby to actuate the mine firing mechanism. If the high frequency signal applied to electron tube 149 is interrupted prior to the expiration of the preselected time interval, the triggering signal will take the low impedance path through the normally closed gate 171 to condenser 169, which under this condition will be at a negative potential, such for example as -4 volts. A semiconductor diode 172 is shunted across resistor 168 to provide a low impedance path for the rapid discharge of condenser 169 under these conditions. The time duration requirement obviates the possibility of mine detonation in response to a remote target vessel signature or a repetitive short duration countermining signal, which may possibly duplicate the overall energy characteristics of a proximate target signature.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

2. An underwater mine actuation system comprising transducer means for developing an audio signature signal correlative to a sound pressure wave detected thereby, means for separating said signature signal into its low and high frequency energy components, means for selectively detecting the envelope of a preselected portion of the low frequency energy component, normally open gating means for effecting passage of said low frequency energy component from said filtering means to said last recited means, said gating means being closed upon application thereto of a control signal representative of a preselected peak to average relationship of the energy'in said low frequency energy component, means for deriving a signal corresponding to the logarithm of said detected envelope, means for deriving a signal representative of the first derivative of said logarithm signal, means for deriving a signal representative of the second derivative of said logarithm signal, means for developing a blocking signal correlative to the relationship between said logarithm signal and a portion of said low frequency energy component,

means for comparing the peak to average energy relationship in said blocking signal to develop said control signal correlative to said relationship, means for deriving a triggering signal corresponding to the product of said first and second derivative signals, mine actuation means coupled to said triggering signal means for producing an output signal, normally closed gating means for preventing the application of said triggering signal to said mine actuation means, means for developing an output signal corresponding to the ratio between a preselected portion of said high frequency energy component and said logarithm signal, means for selectively amplifying said output signal and for detecting the envelope thereof, and means for opening said normally closed gating means in response to the continuous application of said last recited envelope for a preselected time duration.

3. A system according to claim 2 wherein said transducer means comprises a crystal hydrophone.

4. A system according to claim 2 wherein said signature signal separating means comprises a high band pass filter and a low band pass filter.

5. A system according to claim 2 wherein said logarithm signal deriving means includes a varistor.

6. A system according to claim 2 wherein said first derivative signal deriving means comprises an R-C differentiating network.

7. A system according to claim 2 wherein said second derivative signal deriving means comprises an R-C differentiating network.

8. A system according to claim 2 wherein said blocking signal developing means includes a variable impedance network for preselectively varying the portion of said low frequency energy component.

9. A system according to claim 2 wherein said blocking signal developing means includes a semi-conductor diode element.

10. A system according to claim 2 wherein said peak to average energy relationship comparing means comprises a voltage doubler and detector network, and an R-C network coupled thereacross having a preselected time constant characteristic.

11. A system according to claim 2 wherein said triggering signal deriving means includes a variable biasing network for preselectively establishing the operational level thereof.

12. A system according to claim 2 wherein said normally closed gating means comprises a semi-conductor diode.

13. A system according to claim 2 wherein said output signal developing means includes a semi-conductor diode and a variable impedance.

14. A system according to claim 2 wherein said output signal amplifying and envelope detecting means comprises a voltage doubler and detector network.

15. A system according to claim 2 wherein said opening means comprises a R-C network having a predetermined time constant characteristic.

16. An acoustic mine firing system comprising a hydrophone for detecting an underwater sound pressure wave and for developing an electrical signature signal correlative thereto, a tuned amplifier coupled to said hydrophone for amplifying a desired portion of said signature signal, a low pass filter network coupled to said tuned amplifier for passing the low frequency energy portion of said signature signal, a high pass filter network coupled to said tuned amplifier for passing the high frequency energy portion of said signature signal, a first amplifier coupled to said low pass filter network for amplifying said low frequency energy portion, a first gating circuit interposed between said high pass filter network and said first amplifier normally effective to allow passage of said low frequency energy portion to said first amplifier, a first doubling and detector network coupled to said first amplifier for developing a first unidirectional envelope signal representative of the amplified low frequency energy portion, a nonlinear responsive network coupled to said doubling and detector circuit for deriving a signal corresponding to the logarithm of said envelope signal, a first differentiating section coupled to said non-linear responsive network for deriving a first derivative signal of said logarithm signal, a second differentiating section coupled to said first differentiating section for deriving a second derivative signal of said logarithm signal, a voltage divider network coupled to said low pass filter network for providing a preselected magnitude of said low frequency energy portion, circuit means including a semiconductor diode element for developing a blocking signal correlative to the ratio between said preselected magnitude of said low frequency energy portion and the average of said logarithm signal, a signal multiplier network coupled to said first and second differentiating sections for deriving a triggering signal corresponding to the product of said first and second derivative signals, mine actuation means responsive to the application of said triggering signal, circuit means for rendering said first gating circuit ineffective in response to a preselected peak to average energy relationship in said blocking signal, circuit means including a semiconductor diode element coupled to said high pass filter network and said non-linear responsive network for developing a control signal correlative to the ratio between said high frequency energy portion and the average of said logarithm signal, a second doubling and detector network coupled to said last recited circuit means for developing a second unidirectional envelope signal representative of said control signal, a timing network coupled to said second doubling and detector network for developing an output signal having a magnitude correlative to the duration and magnitude of said envelope signal, and a second gating circuit intercoupling said mine actuation means and said timing network for normally by-passing said triggering signal from application to said mine actuation means and in response to an output signal of a preselected magnitude for effecting application of said triggering signal to said mine actuation means.

Claims

2. An underwater mine actuation system comprising transducer means for developing an audio signaturE signal correlative to a sound pressure wave detected thereby, means for separating said signature signal into its low and high frequency energy components, means for selectively detecting the envelope of a preselected portion of the low frequency energy component, normally open gating means for effecting passage of said low frequency energy component from said filtering means to said last recited means, said gating means being closed upon application thereto of a control signal representative of a preselected peak to average relationship of the energy in said low frequency energy component, means for deriving a signal corresponding to the logarithm of said detected envelope, means for deriving a signal representative of the first derivative of said logarithm signal, means for deriving a signal representative of the second derivative of said logarithm signal, means for developing a blocking signal correlative to the relationship between said logarithm signal and a portion of said low frequency energy component, means for comparing the peak to average energy relationship in said blocking signal to develop said control signal correlative to said relationship, means for deriving a triggering signal corresponding to the product of said first and second derivative signals, mine actuation means coupled to said triggering signal means for producing an output signal, normally closed gating means for preventing the application of said triggering signal to said mine actuation means, means for developing an output signal corresponding to the ratio between a preselected portion of said high frequency energy component and said logarithm signal, means for selectively amplifying said output signal and for detecting the envelope thereof, and means for opening said normally closed gating means in response to the continuous application of said last recited envelope for a preselected time duration.

16. An acoustic mine firing system comprising a hydrophone for detecting an underwater sound pressure wave and for developing an electrical signature signal correlative thereto, a tuned amplifier coupled to said hydrophone foR amplifying a desired portion of said signature signal, a low pass filter network coupled to said tuned amplifier for passing the low frequency energy portion of said signature signal, a high pass filter network coupled to said tuned amplifier for passing the high frequency energy portion of said signature signal, a first amplifier coupled to said low pass filter network for amplifying said low frequency energy portion, a first gating circuit interposed between said high pass filter network and said first amplifier normally effective to allow passage of said low frequency energy portion to said first amplifier, a first doubling and detector network coupled to said first amplifier for developing a first unidirectional envelope signal representative of the amplified low frequency energy portion, a non-linear responsive network coupled to said doubling and detector circuit for deriving a signal corresponding to the logarithm of said envelope signal, a first differentiating section coupled to said non-linear responsive network for deriving a first derivative signal of said logarithm signal, a second differentiating section coupled to said first differentiating section for deriving a second derivative signal of said logarithm signal, a voltage divider network coupled to said low pass filter network for providing a preselected magnitude of said low frequency energy portion, circuit means including a semiconductor diode element for developing a blocking signal correlative to the ratio between said preselected magnitude of said low frequency energy portion and the average of said logarithm signal, a signal multiplier network coupled to said first and second differentiating sections for deriving a triggering signal corresponding to the product of said first and second derivative signals, mine actuation means responsive to the application of said triggering signal, circuit means for rendering said first gating circuit ineffective in response to a preselected peak to average energy relationship in said blocking signal, circuit means including a semiconductor diode element coupled to said high pass filter network and said non-linear responsive network for developing a control signal correlative to the ratio between said high frequency energy portion and the average of said logarithm signal, a second doubling and detector network coupled to said last recited circuit means for developing a second unidirectional envelope signal representative of said control signal, a timing network coupled to said second doubling and detector network for developing an output signal having a magnitude correlative to the duration and magnitude of said envelope signal, and a second gating circuit intercoupling said mine actuation means and said timing network for normally by-passing said triggering signal from application to said mine actuation means and in response to an output signal of a preselected magnitude for effecting application of said triggering signal to said mine actuation means.