US3882781A

US3882781A - Capacitance fuze

Info

Publication number: US3882781A
Application number: US237764A
Authority: US
Inventors: Philip Krupen
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1962-11-14
Filing date: 1962-11-14
Publication date: 1975-05-13
Anticipated expiration: 1992-05-13

Abstract

1. A proximity fuze comprising: A. A FIRST CONDUCTING BODY AND A SECOND CONDUCTING BODY, SAID FIRST CONDUCTING BODY SEPARATED FROM SAID SECOND CONDUCTING BODY, SAID FIRST AND SECOND CONDUCTING BODIES LYING SUBSTANTIALLY IN AN EDGEWISE RELATION ON THE OUTER SURFACE OF A PROJECTILE, B. A SOURCE OF DIRECT CURRENT POTENTIAL CONNECTED BETWEEN SAID FIRST CONDUCTING BODY AND SAID SECOND CONDUCTING BODY, SAID SOURCE OF DIRECT CURRENT POTENTIAL ESTABLISHING AN ELECTRIC FIELD BETWEEN SAID BODIES WITH A POSITIVE CHARGE ON SAID FIRST CONDUCTING BODY AND A NEGATIVE CHARGE ON SAID SECOND CONDUCTING BODY, SAID ELECTRIC FIELD EXTENDING INTO THE MEDIUM SURROUNDING SAID CONDUCTING BODIES, AND SAID PROJECTILE, C. DETONATING CIRCUIT MEANS INCLUDING VACUUM TUBE MEANS HAVING AN ANODE, A CATHODE, AND A GRID, SAID FIRST CONDUCTING BODY CONNECTED TO SAID GRID, AND SAID SECOND CONDUCTING BODY CONNECTED TO SAID CATHODE, SAID DETONATING CIRCUIT MEANS BEING RESPONSIVE TO A TIME RATE OF CHANGE IN THE CHARGE ON SAID BODIES RESULTING FROM A CHANGE IN THE ELECTRIC FIELD CONFIGURATION SURROUNDING SAID CONDUCTING BODIES AND SAID PROJECTILE.

Description

United States Patent [191 Krupen May 13, 1975 CAPACITANCE FUZE [75] Inventor: Philip Krupen, Silver Spring, Md.

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

22 Filed: Nov. 14, 1962 21 Appl. No.: 237,764

[52] U.S. Cl. l02/70.2 P [51] Int. Cl. F42c 13/00 [58] Field of Search 102/702, 70.2 P, 18, 19.2,

[56] References Cited UNITED STATES PATENTS 2,998,775 9/1961 Craft 102/702 R 3,001,476 9/1961 Boykin 102/702 R Primary Exanziner-Benjamin A. Borchelt Assistant ExaminerC. T. Jordan Attorney, Agent, or FirmNathan Edelberg; Robert P. Gibson; Saul Elbaum EXEMPLARY CLAIM l. A proximity fuze comprising:

a. a first conducting body and a second conducting body, said first conducting body separated from said second conducting body, said first and second conducting bodies lying substantially in an edgewise relation on the outer surface of a projectile,

b. a source of direct current potential connected between said first conducting body and said second conducting body, said source of direct current potential establishing an electric field between said bodies with a positive charge on said first conducting body and a negative charge on said second conducting body, said electric field extending into the medium surrounding said conducting bodies, and said projectile,

c. detonating circuit means including vacuum tube means having an anode, a cathode, and a grid, said first conducting body connected to said grid, and said second conducting body connected to said cathode, said detonating circuit means being responsive to a time rate of change in the charge on said bodies resulting from a change in the electric field configuration surrounding said conducting bodies and said projectile.

1 Claim, 2 Drawing Figures PATENTED MAY 1 31975 DE-TONATOR /w l I //V VENTOE DETONATOR 56 PH/z/P Ker/PEN CAPACITANCE FUZE 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 to me of any royalty thereon.

This invention relates to proximity fuzes, and more particularly to a non-radiating capacitance fuze.

In firing an explosive projectile at a target it is difficult to time the explosion so that it will occur at the most advantageous position with respect to the target.

Military munitions, such as bombs and mortar shells which are used in great quantities, rely on proximity fuzes to cause detonations that have a maximum destructive effect.

Proximity fuzes may be broadly classified either as radio systems or as non-radio system. The normal radio system ultimately depends on the receipt of a radio signal for detonation. Such systems, while highly developed, tend to be complicated and expensive. Also they require extensive protective circuitry in order to be relatively immune from enemy jamming. Non-radio systems are, in general, simple, inexpensive, and inherently less susceptible to enemy jamming. Non-radio systems, however, which use A.C. circuitry in their detection operation radiate electromagnetic energy, providing an opening through which enemy jamming can operate.

It is an object of this invention to provide a novel compact, light weight, low cost fuze.

Another object of the invention is to provide a nonradiating proximity fuze.

A further object of this invention is to provide a direct current operated detection device for a fuze.

A still further object of this invention is to provide a novel non-radiating fuze which is relatively insensitive to weather conditions.

The invention, deceptive in its simplicity, consists in its elemental form merely of two conducting bodies separated by a dielectric medium, a source of direct potential, and a resistance connected in series. As will be more fully developed later in the specification, current flow through the resistor generates the detonating voltage when the capacity between the conducting bodies changes due to an onrushing target.

As is well known, two conducting bodies forming a capacitor have what may be termed a fringe effect, that is, the electrostatic field between the two conducting bodies which form the capacitor will bulge out along the edges. Any change in the dielectric constant of the material in this fringe field will result in a change in the effective capacitance between the conducting bodies. It is a target causing a change in the dielectric constant of the fringe field, which is used in accordance with the teaching of this invention, to produce a firing signal.

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 drawings in which:

FIG. 1 is a simplified schematic drawing of a fuze embodying the principles of this invention.

FIG. 2 is a schematic drawing of a specific embodiment of the invention.

Referring to FIG. 1, there is shown one embodiment of the simple, direct current operated, non-radiating fuze of this invention. The fuze consists principally of two conducting bodies 11 and 12 separated by a dielectric medium, with a source of potential 13 and a resistor 14 connected between them. A detonator or detonating circuit 15 shown in block diagram form, is connected across resistor 14. The detonating signal is developed in the resistor 14.

The operation of the fuze illustrated in FIG. 1 may be analyzed as follows. Equilibrium is established before the fuze approaches a target 16 so that a potential difference V, equal to the source potential 13, exists between the conducting bodies 11 and 12 across an effective capacitance C which exists between them. At equilibrium there is no current flow in the resistor 14 and the circuit is governed by the equation;

Q=VC

where Q is the charge on the bodies 11 and 12, V is the source voltage 13, and C is the total capacitance between the bodies 11 and 12 including the capacitance due to the fringe field. As the munition approaches a target 16 the capacitance C, between the bodies 11 and 12 increases due'to a change in the fringe field caused by the entry of the target. The equation governing the circuit in this case is;

where, AC is the change in capacitance due to the change in the fringe field," and AQ is the resultant change in charge. To maintain equilibrium the charge AQ flows through the resistance 14, and this results in an IR drop, AQ/At X R. The resulting IR drop is detected by the circuit 15 which causes the fuze to function.

The maximum signal for small values of AC is given y v,,, V AC /C Applicant has determined that to a first approximation on a large munition system that 0 artisan/9 I -I 'f where s is the separation between the bodies 11 and 12, and h is the height above the target.

FIG. 2 shows a specific embodiment of the invention constructed in accordance with the principles described in connection with FIG. 1. A non-rotating frontal approach munition 20 is provided with the nonradiating, direct current operated fuze of this invention. Two conducting

bodies

21 and 22 are provided which form the forward outer surface of the munition 20, and correspond to 11 and 12 of FIG. 1. A piece of insulating material 23 serves to separate the

bodies

21 and 22 while giving mechanical support and maintaining the structural integrity of the munition. The insulating material 23 may, if desired, be allowed to extend beyond the conducting

bodies

21 and 22 in order that rain drops in the atmosphere cannot bridge the gap between

bodies

21 and 22. Also the area of the conducting

bodies

21 and 22 should be made as large as practicable relative to the edge dimension in order to increase the ratio,AC,,/C A direct current supply, corresponding to supply 13 of FIG. 1, is provided by a charged capacitor 24 which is charged shortly before the projectile is fired. The firing signal is developed across the internal grid-cathode resistance of the tube 25, corresponding to resistor 14 of FIG. 1, as will be described.

The circuit shown in FIG. 2, including the tube 25 is of the two tube, directly heated hot cathode type, and provides both the functions of detecting and triggering. The circuit comprises hot cathode pentode 25 with its number 2 grid connected to the conducting body 22 by lead 26 and its number 1 grid connected to the positive side of the cathode forming an accelerating grid for the electrons emitted from the hot cathode. The primary purpose of the pentode 25 is to match the high impedance of the projectiles proximity signal to the relatively low impedance of the trigger tube, thyratron 27. Pentode 25 may also provide amplification.

The plates of pentode 25 and thyratron 27 are connected to a source of B supply 28, which may be a charged capacitor 34. A plate load resistor 29 is provided for the tube 25. The plate of the tube 25 is also connected to the control grid 31 of the thyratron 27 through a coupling capacitor 32. The control grid 31 is held below below cutoff potential by a suitable negative bias voltage 33. Across the thyratron trigger tube 27 are the capacitor 34, a resistor 35 a detonator 36 and an arming switch 39. As is well known in the art, when the tube 27 fires, the capacitor 34, which at equlibrium had been at the potential of 28, discharges through and actuates the detonator 36 if the switch 39 is closed and the resistance of resistor 35 is sufficiently high.

The supply voltage for the hot cathode supply is provided by a battery 37. Additionally, there is provided a setback switch 38 and the arming switch 39 to make the munition safe for handling and firing in the manner well known in the art.

A short time after the munition is launched, the

switches

38 and 39 will close and equlibrium will be established. At this time, with no target in close proximity, the signal voltage difference between the number 2 grid and the cathode of the pentode 25 will be zero. This will place all the grids of the pentode 25 at low potential with respect to the cathode resulting in a small anode current in the anode circuit. Although small, this anode current flowing through the large anode resistor 29 sets the equilibrium voltage at the anode of the tube 25 to a low value. As previously mentioned, the thyratron 27 is held below cutoff by the negative bias source As a target comes in close proximity to the munition 20 the capacitance between the

plates

21 and 22 will increase appreciably causing a current I =dQ/dt to flow between the number 2 grid and the cathode of pentode 25. The current flow is such as to make the number 2 grid negative with respect to the cathode. This causes a reduced anode current and a rise in the anode potential, of tube 25 which is coupled through the capacitor 32 to grid 31 of the thyratron 27 overcoming the negative bias 33 causing the thyratron to fire. As previously described, capacitor 34 discharges through thyratron 27 producing a pulse sufficient to actuate detonator 36, and the munition is exploded.

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 proximity fuze comprising:

b. a source of direct current potential connected between said first conducting body and said second conducting body, said source of direct current potential establishing an electric field between said bodies with a positive charge on said first conducting body and a negative charge on said second conducting body, said electric field extending into the medium surrounding said conducting bodies and said projectile,

Claims

1. A proximity fuze comprising: a. a first conducting body and a second conducting body, said first conducting body separated from said second conducting body, said first and second conducting bodies lying substantially in an edgewise relation on the outer surface of a projectile, b. a source of direct current potential connected between said first conducting body and said second conducting Body, said source of direct current potential establishing an electric field between said bodies with a positive charge on said first conducting body and a negative charge on said second conducting body, said electric field extending into the medium surrounding said conducting bodies and said projectile, c. detonating circuit means including vacuum tube means having an anode, a cathode, and a grid, said first conducting body connected to said grid, and said second conducting body connected to said cathode, said detonating circuit means being responsive to a time rate of change in the charge on said bodies resulting from a change in the electric field configuration surrounding said conducting bodies and said projectile.