Field fuze
United States Patent Kalmus Apr. 15, 1975 FIELD FUZE March-April 1947; pp. 98 &amp; 99. [75] Inventor: Henry P. Kalmus, Washington, DC.  
  Primary Examiner-Benjamin A. Borchelt [73] Assignee: The United States of America as Assistant Examiner c. Jordan represented by the Secretary of the Army, Washington, DC.  
 [22] Filed: June 25, 1957 [21] Appl. No.: 667,997  
  52 0.8. CI. 102/70.2 P  
 [51] Int. Cl. F42c 13/00 [58] Field of Search 340/256, 258, 282; 102/702 P, 70.2; 343/5, 14  
 [56] References Cited UNITED STATES PATENTS 2,323,317 7/1943 Dunmore 102/702 2,403,567 7/1946 Wales, Jr...&#34; l02/70.2 P  
 2,403,955 7/1946 Schlesinger.. 340/258 2,490,238 12/1949 Simons 340/258 2,505,042 4/1950 Gourdon 102/702 2,514,359 7/1950 Allison 102/702 P 2,646,559 7/1953 Nutzler 340/258 2,660,718 11/1953 Summerhayes 343/5 2,711,133 l/1955 Rines 102/702 P 2,892,412 6/1959 Mullins et a] 102/702 P OTHER PUBLICATIONS C. H. Page et al. Survey of Proximity Fuze Development; American Journal of Physics; Vol; 15, No. 2;  
 I i n-- o Attorney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Saul Elbaum EXEMPLARY CLAIM l. A missile fusing system of the quasi-stationary field type, said system comprising in combination: an explosive missile having a case; two electrodes each extending through and insulated from the case of said missile and located at diametrically opposed positions around the periphery of said case; neutralizing means-for reducing the free space transfer capacitance between said electrodes in order to make the increase in transfer capacitance between said electrodes, as said missile approaches a target, a readily detectable portion of the total transfer capacitance; said neutralizing means including external electrostatic shielding means consisting of the case of said missile and internal electrostatic shielding means consisting of an internal projection of said case; balancing means for balancing out the remainder of said -free space transfer capacitance not eliminated by said neutralizing means; and means responsive to a predetermined increase in the transfer capacitance between said electrodes caused by target proximity to detonate said missile.  
 4 Claims, 5 Drawing Figures FIELD FUZE The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any roy alty thereon.  
  This invention relates to missile fuzing systems in general and more particularly to a fuzing system which causes detonation of the missile just prior to missile impact.  
  It is well known in the art that certain missiles are considerably more effective if they can be made to detonate just prior to missile impact (one-half foot to feet, for example). To accomplish this radar and doppler systems are unsuitable, and mechanical systems having devices extending from the missile are impractical for most applications.  
  The use of a fuzing system operating on quasistationary field concepts appears to be the only satisfactory solution for many applications. Such a fuzing system would not depend upon radiation but would use the capacitive effect resulting from target proximity. So far, the prior art has not been able to produce an adequate fuzing system based on quasi-stationary field concepts.  
  One type of quasi-stationary field fuzing system of the prior art uses two adjacent bodies in free space which are charged with respect to ground. If these two charged bodies approach the earth a d-c potential is developed which is employed as a signal. This system has two basic drawbacks: (1) during rain the charge can not be maintained, and (2) the signal is developed across a very high impedance making amplification difficult.  
  Other systems of the prior art use two adjacent bodies and utilize as a signal the increase in capacitance or transfer capacitance between these bodies caused by target proximity. The difficulty with such a system is that in free space a transfer capacitance exists between the electrodes having a value of 2 to 5 micromicrofarads in a practical set up. At a usable distance from the ground (about one-half foot) the value of transfer capacitance increase due to ground proximity is only of the order of to 10 micro-microfarads. For a practical missile fuzing system, therefore, the free-space transfer capacitance has to be kept stable within a ratio of about 1 part in 10 if a signal to noise ratio of 10 to l is desired. Although this may be possible in the laboratory, it becomes impossible in a practical design.  
  To reduce the value of the free space transfer capacitance the prior art has tried various types of neutralizing schemes within the fuze. These were unsuccessful because any neutralizing scheme which had the necessary suppression factor proved to be highly microphonic and hence impractical for use in missiles.  
  My invention overcomes the difficulties of the prior art by providing electrostatic shielding means between the sensing electrodes. In this way the free-space transfer capacitance is very greatly reduced and a simple, reliable and practical quasi-stationary field fuzing system now becomes possible. At first glance, the provision of electrostatic shielding means to reduce the freespace transfer capacitance between the sensing electrodes might erroneously appear to be an obvious solution to the problem, especially since my invention is quite simple. It should be noted, however, that there has been a great need in the art for a practical, simple and reliable quasi-stationary field fuzing sustem. Because of this need considerable research has been expended toward this end, but until my invention, no successful fuze of this type was known.  
  One object of this invention is to provide an improved fuzing system which causes detonation of a missile just prior to impact.  
  Another object is to provide an improved sensing configuration for a quasi-stationary field fuzing system.  
  A further object is to provide a practical, simple and reliable missile fuzing system operating on quasistationary field concepts.  
  An additional object of this invention is to provide a practical, simple and reliable fuzing system operating on quasi-stationary field concepts which utilizes the rotating properties of a rotating missile to improve performance.  
  The specific nature of the invention as well as other objects, uses and advantages thereof will clearly appear from the following description and from the accompanying drawing, in which:  
  FIG. 1 is a cross-sectional schematic representation of a symmetrical quasi-stationary field sensing configuration in accordance with my invention.  
  FIG. 2 is a schematic representation of one example of a quasi-stationary field fuzing system embodying the sensing configuration of FIG. 1.  
  FIG. 3 is a schematic representation of neutralizing means which can be used with the embodiment of FIG.  
  FIG. 4 is a schematic representation of a second example of a quasi-stationary field fuzing system embodying the sensing configuration of FIG. 1.  
  FIG. 5 is a cross-sectional schematic representation of a non-symmetrical quasi-stationary field sensing configuration in accordance with my invention which is advantageous for use with rotating missiles.  
  In&#39;FIG. l, a missile 10 is provided with diametrically opposed electrodes 15 and 16 extending through and insulated from the case 12 of the missile 10. The case 12 establishes circuit ground and provides external electrostatic shielding between the sensing electrodes 15 and 16. A metal plate 13 within the missile 10 provides internal electrostatic shielding. The internal circuitry within the missile 10 is not shown. The capacitances between each of the sensing electrodes 15 and 16 and the earth ll are represented by the dashed capacitors 18 and 19 respectively, and the free space transfer capacitance between the electrodes 15 and 16 is represented by the dashed capacitor 14. Transfer capacitance is a measure of the portion of the signal applied between one electrode and circuit ground which is transferred to the other electrode.  
  Using the sensing configuration of F IG. 1 in a practical missile fuzing system I have been able to reduce the value of the free space transfer capacitance 14 to less than 10 micro-microfarads. When the missile 10 comes within close proximity of the earth 11 the series combination of capacitances l8 and 19 add to the free space transfer capacitance 14 between the electrodes 15 and 16. In a practical system this increase in the transfer capacitance at a usable distance above the earth 11 is, of the order of 10&#39; to 10 micromicrofarads. Since the free space transfer capacitance is only of the order of 10 micro-microfarads a considerable proportionate change is obtained. With such a large proportionate change in transfer capacitance available, those in the art will readily see how a practical, simple and reliable quasi-stationary fuzing system is now possible. I have found that even without neutralization a fuzing system using the sensing configuration of FIG. 1 will provide a function height of foot. With moderate neutralization of say to 1, the function height can be increased to 1% feet.  
  A consideration of electrostatic field theory reveals that for a symmetrical configuration between the case 12 and the electrodes and 16 as in FIG. 1, the function height will remain substantially the same regardless of how the missile 10 approaches the earth 11. The function height is the distance from the earth 11 to the center of a line drawn between the electrodes 15 and 16.  
  FIG. 2 shows one example of how the sensing configuration of FIG. 1 can be used to provide a quasistationary fuzing system. In FIG. 2 and a-c generator 22 applies a voltage between an electrode 16 and the case 12 which is circuit ground. The other electrode 15 is fed to the input of detonation means 27 which causes detonation of the missile 10 when a predetermined value of signal appears at the electrode 15.  
  The dashed capacitor 24 is the total transfer capacitance and consists of the sum of the free space transfer capacitance 14 and the series combination of the capacitances l8 and 19 resulting from proximity of the electrodes 15 and 16 with the earth.  
  As the missile 10 approaches the earth the increase in the total transfer capacitance 24 increases the signal transferred to the electrode 15. The missile 10 is detonated by the detonation means 27 when the signal transferred to the electrode 15 reaches a predetermined value.  
  FIG. 3 illustrates one type of neutralizing means within the missile which can be used with the embodiment of FIG. 2. In FIG. 3 the parallel combination of the capacitor 23 and the inductor 25 represents the tank circuit of an oscillator, the oscillator being used as the generator 22 in FIG. 2. The inductor 25 is centertapped to circuit ground. The capacitor 29 and the wire 31 comprise the neutralization circuits. A metal shield 37 around the wire 31 provides electrostatic shielding. With the neutralization circuit omitted the operation of the embodiment of FIG. 3 is as described in connection with FIG. 2, and the capacitor 14 represents the free space transfer capacitance between the electrodes 15 and 16.  
  Because of the free space transfer capacitance 14, an unwanted portion of the voltage applied to the electrode 16 is transferred to the electrode 15. One way of neutralizing this effect is to apply an equal and oppositely phased voltage to cancel out the free space voltage value. FIG. 3 shows a convenient way in which this may be accomplished. Since the inductor 25 is centertapped to circuit ground, the voltages at the ends of the tank circuit will be equal and l80 out of phase with one another. One end of the tank circuit is connected to the electrode 16 and the other end is connected to the electrode 15 through a capacitor 29 equal in value to the free space transfer capacitance 14. This causes a voltage to be applied to the electrode 15 which is equal and opposite to the voltage transferred to the electrode 15 by the transfer capacitance 14. The two voltages cancel, accomplishing the desired neutralization.  
  FIG. 4 shows a second example of how the sensing configuration of FIG. 1 can be used to provide a quasistationary fuzing system. In FIG. 4 an amplifier 33 uses the electrodes 15 and 16 in a positive feedback loop. The output of the amplifier 33 is fed to a detonation means 27, which causes detonation of the missile when the amplifier 33 breaks into oscillation. The amplifier 33 is adjusted so that in free space, transfer capacitance 14 is sufficiently small to keep the amplifier 33 stable. As the missile 10 approaches the earth 11, the total transfer capacitance 24 increases, increasing the positive feedback applied from the output to the input of the amplifier 33. Amplifier 33 breaks into oscillation when the positive feedback increases to a predetermined value. When the amplifier 33 begins to oscillate a signal is applied to the detonation means 27 causing detonation of the missile 10. It should be noted that neutralization means similar to those illustrated in FIG. 3 may also be used in the embodiment of FIG. 4.  
  The symmetrical sensing configuration of FIG. 1 is a useful application of my invention since it uses the case 12 of the missile 10 for electrostatic shielding. However, if so desired, a non-symmetrical sensing configuration may also be used. Furthermore electrostatic shielding may be provided by any other suitable means.  
  For a rotating missile advantageous use may be made of the non-symmetrical sensing configuration of FIG. 5. In FIG. 5 external electrostatic shielding means 40 located between the electrodes 15 and 16 provides a nonsymmetrical sensing configuration between the case 12 and the electrodes 15 and 16. The plate 13 provides internal electrostatic shielding between the electrodes 15 and 16. The external circuitry within the missile 10 is not shown. As the rotating missile 10 approaches the earth 11, the total transfer capacitance 24 will vary periodically with missile rotation, the maximum value of the transfer capacitance increasing as the missile 10 gets closer to the earth 11. Because of this periodic variation due to missile rotataion it is possible to discriminate between the signal obtained because of target proximity and the free space signal or other unwanted signals. Means for providing such discrimination are well known in the art. For example, if the sensing configuration of FIG. 5 were used in the embodiments of FIGS. 2 and 4, the detonation means 27 could be designed to be responsive only to signals having the predetermined modulation frequency caused by missile rotation. The use of discrimination means of this type will provide a safe system and make possible an increase in the operating function height. Neutralization means similar to those illustrated in FIG. 3 may be included if so desired.  
  At this point my invention will be reviewed in order to more clearly point out its inventive features which might be overlooked because of the great simplicity which is achieved. From the foregoing description of the construction and operation of a number of embodiments of this invention it can be seen that the invention operates upon the change in the transfer capacitance between two sensing electrodes mounted to the missile as the missile approaches the earth or some other suitable target. The difficulty with prior art missile capacitance detection schemes, which operate on a similar principle, is that because the transfer capacitance between the electrodes on the missile is so large as a result of the restrictive missile environment, changes caused in the transfer capacitance by approach of the missile to the earth are so small as to be incapable of reliable measurement. The prior art has never been able to satisfactorily overcome this problem of large free space transfer capacitance so as to make practicalthe use of a capacitance-detection fuzing system on a. missile. Neutralization schemes were attempted, but were unsuccessful because the necessary suppression factor could not be maintained in the presence of the microphonics produced by missile vibration. As a result, the use of capacity detection missile fuzing systems were discarded, until my invention showed how a practical system could be provided.  
  My invention overcomes the problem of high initial free-space transfer capacitance by providing a construction and arrangement which reduces the free-- space transfer capacitance to a very low value without the use of the complex and microphonic neutralization schemes unsuccessfully tried in prior art systems. This is accomplished by making use of the discovery that simple electrostatic shielding means provided between the sensing electrodes results in an unexpectedly large decrease in the free-space transfer capacitance. The fact that this electrostatic shielding means can be provided in an amazingly simple manner by the case of the missile itself in the embodiments of FIGS. 1 and 3, and by a projection from the missile case in the rotating missile embodiment of FIG. 5 is of considerable practical importance.  
  It was found that as a result of the large reduction in transfer capacitance provided by these simple electrostatic shielding means, a simple and stable type of neutralizing means as illustrated in FIG. 3 having a relatively small suppression factor may be employed to provide a further reduction in the free space transfer capacitance between the electrodes. Since only a relatively small suppression factor is required, it will be understood that the neutralization provided will not be materially affected by the microphonicsproduced by missile vibration. If electrical energy is applied to one electrode and the other electrode serves as a receiver in a system such as shown in FIG. 2, the amount of energy transferred to the receiver electrode will be dependent upon the transfer capacitance. Because of the presence of a free space transfer capacitance an initial and unwanted amount of energy will be transferred to the receiver electrode when the missile is in free space. To cancel out this initial amount of unwanted energy neutralization is provided by feeding a signal to the receiver electrode (as shown in FIG. 3) which has a value exactly equal, but opposite in phase, to the initial voltage transferred to the receiver electrode through the free-space transfer capacitance. The resultant energy transferred to the receiver electrode will therefore be essentially zero when the missile is in free space. As the missile approaches the earth, the transfer capacitance between the electrodes increases, increasing the amount of energy transferred to the receiver electrode.  
 &#39; Since the energy transferred to the receiver electrode by the neutralization means remains always the same, it will be seen that a large proportionate increase is obtained in the resultant energy received at the receiver electrode as the missile approaches the earth, thereby making it relatively easy to detect when the missile approaches the earth (since as is well known in the art a large proportionate change is easily detectable).  
  It can thus be seem that it is my realization and discovery of the need, practicality, and the unexpected desirable effect of providing electrostatic shielding in a missile capacity-detection scheme which makes possible a practicaland reliable missile fuzing system. Some additional realizations important to my system are as follows; 1 The realization that the missile casing itself may be employed as-adequate electrostatic shielding means, thereby providing a considerable simplification in the system; and (2) the realization that two sensing electrodes mounted diametrically opposed on the missile will experience substantially the same increase in transfer capacitance as the missile approaches the earth regardless of the axial position of the missile. It will be understood that this latter feature is of considerable importance in a practical system for use on a nonrotating missile.  
  It should be noted. that although the earth was used as the target for the illustrative embodiments of FIGS. 1-4, my invention will also operate satisfactorily over practically any other type of target. The important feature is that a sufficient increase in the transfer capacitance be obtained at a usable distance from the target. Furthermore, my invention may be used in applications other than ordnance fuzes. It will be apparent to those skilled in the art that my invention can be applied to any system in which the detection of the close proximity of an object is desired. Some examples are: airplane landing systems, automobile object sensing devices, and electric eye type systems.  
  It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.  
 I claim as my invention:  
  1. A missile fusing system of the quasi-stationary field type, said system comprising in combination: an explosive missile having a case; two electrodes each extending through and insulated from the case of said missile and located at diametrically opposed positions around the periphery of said case; neutralizing means for reducing the free space transfer capacitance between said electrodes in order to make the increase in transfer capacitance between said electrodes, as said missile approaches a target, a readily detectable portion of the total transfer capacitance; said neutralizing means including external electrostatic shielding means consisting of the case of said missile and internal electrostatic shielding means consisting of an internal projection of said case; balancing means for balancing out the remainder of said free space transfer capacitance not eliminated by said neutralizing means; and means responsive to a predetermined increase in the transfer capacitance between said electrodes caused by target proximity to detonate said missile.  
  2. The invention in accordance with claim 1 wherein said means responsive to the increase in the transfer capacitance between said electrodes comprises: an a-c generator applying a signal between one of said electrodes and circuit ground; and detonation means connected between the other of said electrodes and circuit ground, said detonation means detonating said missile when a signal having a predetermined value is applied to said detonation means; whereby upon approach of said missile to a target, the transfer capacitance between said electrodes increases causing a portion of the signal from said generator to be transferred to said detonation means, detonation of said missile taking place when target proximity increases the signal applied to said detonation means to said predetermined value.  
  3. The invention in accordance with claim 1 wherein said means responsive to the increase in the transfer capacitance between said electrodes comprises: an amplifier having a positive feedback loop in series with said electrodes, said amplifier being adjusted to be stable in free space; and detonation means connected to said amplifier, said detonation means causing detonation of said missile when said amplifier breaks into oscillation; whereby upon approach of the missile to a target the transfer capacitance between said electrodes increases, increasing the positive feedback within said amplifier, detonation of said missile taking place when target proximity increases the positive feedback to a value which causes said amplifier to break into oscillation.  
  4. In a rotating explosive missile having a case, a missile fuzing system of the quasi-stationary field type, said system comprising in combination: two electrodes which extending through and insulated from the case of said missile, said electrodes being located asymmetrically with respect to said case so that the approach of the case of said missile extending between said electrodes and internal electrostatic shielding means consisting of an internal projection of said case; balancing means for balancing out the remainder of said free space transfer capacitance not eliminated by said neutralizing means; and means responsive only to said predetermined rate of variation of transfer capacitance to cause detonation of said missile when target proximity increases the maximum value of the periodically varying transfer capacitance to a predetermined value.