US3594611A

US3594611A - Noise-free static discharger

Info

Publication number: US3594611A
Application number: US766113A
Authority: US
Inventors: Robert L Tanner; Robert Michael Tanner
Original assignee: Communications Technology Corp
Current assignee: Fluke Electronics Corp; Technology for Communications International
Priority date: 1968-10-09
Filing date: 1968-10-09
Publication date: 1971-07-20
Anticipated expiration: 1988-07-20
Also published as: DE1949649A1; GB1278947A; SE352999B; FR2020197A1

Abstract

A noise-free static discharger including a conductive structure connected to a body in which static voltage builds up, by a high resistance element to provide DC connection therebetween is disclosed. The conductive structure includes at least one discharge pin with a sharp discharge point, to which are connected one or more conductive members which provide paths for the flow of RF currents, inducted therein by corona discharges, taking place at the sharp discharge point. These conductors have lengths and spatial orientations such that the RF currents induced in them create a sum of dipole moments which cancels the dipole moments of the currents in the corona discharge and in the discharge pin. The conductive members, which have blunted or rounded free tips, are preferably covered with insulating material to limit all static discharging to occur at the sharp point of the discharge pin.

Description

United States Patent [72] Inventors Robert L. Tanner;

Robert Michael Tanner, lboth of Palo Alto,

l'lc L241;

3,370,200 2/1968 Heyletal ABSTRACT: A noise-free static discharger including a conductive structure connected to a body in which static voltage builds up, by a high resistance element to provide DC connection therebetween is disclosed. The conductive structure includes at least one discharge pin with a sharp discharge point, to which are connected one or more conductive members which provide paths for the flow of RF currents, inducted therein by corona discharges, taking place at the sharp discharge point. These conductors have lengths and spatial orientations such that the RF currents induced in them create a sum of dipole moments which cancels the dipole moments of the currents in the corona discharge and in the discharge pin. The conductive members, which have blunted or rounded free tips, are preferably covered with insulating material to limit all static discharging to occur at the sharp point of the discharge pin.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a static discharging system and, more particularly, to a static discharger from which noise radiation, caused by the static discharge, is substantially eliminated.

2. Description of the Prior Art The use of static discharging devices to minimize noise in radio receivers, especially those which are transported in a vehicle, such as an aircraft, are well known. The function of these devices is to reduce the adverse effect of noise, produced by the corona or static discharges, which occurat various locations onthe aircrafts frame, on the receiver antenna. Herebefore, the minimization of such adverse effects has been achieved, by controlling the geometrical relation between the static discharging device and the antennas radio frequency (RF) field. In such devices, the corona discharge causes the radiation of noise energy. However, due to the geometrical relation between the discharger and the antenna field the quantity of noise energy which is coupled to the antenna is greatly reduced, thus minimizing the adverse effect of the noise on the radio receiver.

Among prior art, static discharging devices are those described in US. Pat. Nos. 2,933,732 and 3,106,663, issued to applicant of the present application. In the device described in US. Pat. No. 2,933,732, the effect of noise energy in a radio receiving systemof a vehicle, such as an aircraft, is minimized by manipulating the RF fields of the receiving system's antenna so that a local null field region is created, and by causing the entire noise-producing static discharge process to occur at such localized null field region. As a result, hardly any coupling exists between the antenna and the static discharge and, therefore, theoretically, none of the noise energy, radiated by the static discharge, finds its way into the anten na's terminals. I

In the device, described in US. Pat. No. 3,106,663, the noise energy, which is radiated by a static discharger is prevented from reaching the antennas terminals by causing the direction of flow of the discharge current to be at right angles the antennas fields. I

The devices described in the aforementioned patents represented advances over the state of the art at the time they were invented. However, the dependence of their effectiveness on a fixed geometrical relation between them and the fields of an antenna, to produce decoupling between the noise energy and the antenna, has been found to represent a marked disadvantage, since any change in the required, fixed relationship or orientation greatly effects or destroys the decoupling between the noise energy and the antenna. A consequent disadvantage is the need for pins which project at right angles to the airstream in order to satisfy the fixed orientationrequirement. Such pin projection can only be achieved with rigid sharp pins which, in addition to being vulnerable to damage, represent a safety hazard to maintenance personnel and equipment. Attempts to alleviate such hazards by protecting the pins with plastic guards has been found to be only partially effective.

Another disadvantage of the prior art static discharging devices, which must assume an exact orientation in relation to the antenna 's field, is the requirement of using rigid relatively large diameter rods, capable of maintaining a fixed orientation. However, to act as effective dischargers such large diameter pins must be etched, to define fine points which become dull by repeated current discharges. Due to such disadvantages a need has arisen for a static discharging device whose principle of operation is not based on a fixed orientation, between a point therein at which noise energy is produced and the field of signal-receiving antenna. It has been determined that such a need can be satisfied by providing a static-discharging device which radiates a minimal quantity of noise energy so that regardless of its orientation that amount of noise energy which may be coupled to the antenna is greatly minimized.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of the present invention to provide a new improved static-discharging device.

Another object of the invention is to provide a staticdischarging device, whose principle of operation is not based on its fixed orientation with respect to the RF field of an antenna.

A further object of the invention is to provide a staticdischarging device which radiates a minimum of noise energy.

I Still a further object of the invention is the provision of a relatively simple, easily constructable, inexpensive staticdischarging device from which effectively no noise energy is radiated.

These and other objects of the invention are achieved by providing a static-discharging device, hereafter also referred to as the discharger, which includes a conductive structure, shaped to define a first member in the form of a discharge pin and at least a second conductive member, oriented with respect to the pin, so that a component of induced current therein flows in a direction opposite to the direction of flow of current in the discharge pin. Consequently, the dipole moment of the second member is of a polarity opposite that of the discharge pin dipole moment. These dipole moments tend to cancel one another resulting in a substantial reduction in the net dipole moment of the discharger which accounts for the radiated noise energy. Since as is appreciated by those familiar with the art, the amount of noise energy which radiate from a discharger is directly related to the dischargers total dipole moment, by reducing its net dipole moment, the noise energy radiated therefrom is reduced, proportionately.

'The discharger may, in addition to the discharge pin, include a plurality of conductive members whose lengths and geometric orientations are chosen so that the current induced therein create dipole moments which together cancel the dipole moment due to the current induced in the discharge pin and the corona discharge so that the net dipole moment of the discharger is essentially zero and therefore no noise energy radiates therefrom.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified cross-sectional view of one embodiment of the invention;

FIGS. 2 and 3 are cross-sectional views of two other embodiments of the invention;

FIG. 4 is a combination isometric and cross-sectional view of yet another embodiment of the invention; and

FIGS. 5 and 6 are cross-sectional views of additional embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Attention is now directed to FIG. 1, which is a simplified diagram of one embodiment of the discharger of the present invention, and which will be used to explain the principle of operation of the novel discharger. Therein, numeral 10 designates an electrically conductive structure of the discharger. Structure 10 includes a discharge member or pin 12 which is sharpened to define a point 14 at one end thereof. The other end of pin 12 is connected to a base member or portion 16 of structure 10. The structure is physically and electrically connected to an aircraft frame, represented in FIG. I by a wing 18, by means of a high resistance member 20. The latter provides a direct current DC or static connection between wing 18 and structure 10 so that the static voltage existing on wing lSwill cause a high static field to be present at point-l4 ofpin-lZ. i

The structure further includes a conductive member 22 which, as shown in FIG. 1, is larger than pin 12 and is parallel thereto. Member 22 is connected to base member 16 by a perpendicular conductive member 24. Structure 10 may be thought of as an electrically conductive rod sharpened at one end (point 14) and having a bent-back portion (member 22) which is parallel to and exceeds the length of an upper portion (pin 12) near the pointed end.

As is known in the art, noise energy radiates from a corona discharger because the discharger has a net dipole moment.

The noise energy is proportional to the square of the total dipole moment. Moreover, when the corona, designated in FIG. 1' by numeral 25, leaves the pin I2 at point 14 it induces currents on the discharger pin 12 itself, which adds to the total dipole moment and therefore to the total radiated noise energy. In the particular embodiment, shown in FIG. 1, the corona 25 leaving pin 12 induces currents in

conductive members

12, 22 and 24. The flow directions of currents induced in pin 12 and

members

22 and 24 are represented by

arrows

12c, 22c and 24c, respectively. Y

In the particular embodiment,.the total dipole moment of the discharger maybe thought of as being a function of the v dipole moment of the corona discharge itself as well as, the

dipole moments due to the currents in pin 12 and

members

22 and 24. However, as seen in FIG. 1, the current in member 22 flows in a direction opposite that of the current direction in the corona dischargeitself and the induced current in pin 12. Consequently, the dipole moment, due to the current in member 22, is opposite to that of the dipole moments of the corona discharge and the pin 12. I

The magnitude of the current in member 22 is smaller than the current in the discharge 25 or in member 12 because the induced current drops off with increasing distance (as measured along the axis of the rod) from the point 14, dropping to 'zero at the outermost tip of 22. However, by suitably adjusting the length of member 22 so thatits increased length compensates for the smaller value of current flowing in it, its dipole moment may be made equal and opposite the sum of the dipole moments of the current in the corona discharge 25 and the pin 12 so that the only remaining dipole moment would be due the current in perpendicular member 24. Such a dipole moment may be made to be very small to minimize the net dipole moment of the discharger and thereby minimize, if not completely eliminate, the radiation of noise energy therefrom.

The amount of noise energy radiated due to the dipole moment of verticalrnember24 may be eliminated altogether by incorporating instructure 10 an additional vertical member flows in a direction (arrow 28c) opposite the direction (arrow 24c) 'of current flow in member 24. The division of current flow between pin 12 and

members

22, 24 and 28 is approximately proportional to their lengths. Member 22 is longer than pin 12 so that the dipole moment, due to the current therein, is sufiicient to. cancel both the dipole moments due to the 'corona discharge current and the current in pin 12. Consequently, the current flowing in member 24 is substantially greater than the current in member 28. However, cancellation of the dipole moments due to currents in the two

vertical members

24 and 28 may be achieved by making member 28 longer than member, as shown in FIG. 2.

The length of vertical member 28 may be made equal to that of vertical member 24 b extending, from the former, a

member 30, oriented in a direction parallel to pin 12 and herein. The direction or current flow in member 30 is designated by arrow 30c. The structure 10 in FIG. 3 may be thought of as a bifurcated structure, symmetrical with respect to pin 12, unlike structure 10 in FIGS. 1 and 2 which are unsymmetrical. The lengths of

members

22 and 30 which are assumed to be equal are adjusted so that the dipole moments due to the currents therein cancel the dipole moments due to the corona discharge current and the current induced in pin 12. By making

members

24 and 28 to be of equal lengths, currents of equal magnitude, though of opposite polarities, flow therein. Consequently, the dipole moments due to these currents cancel one another. As a result, the discharger of such an embodiment of the present invention has a net dipole moment equal to zero and therefore no noise energy radiate therefrom.

As shown in each of FIGS. 1, 2 and 3, herebefore referred to, the structure 10 is connected to the aircraft frame, such as wing 18, by the high resistance member 20 in order to provide a DC or static connection between the two so that the static voltage existing on the aircraft will cause a high static field at point 14 of pin 12. The distributed resistance of member 20 must be high enough to make the structure 10 appear isolated at the radio frequencies of interest, yet provide the necessary DC connection to the aircrafts frame.

,It should be appreciated that for the proper performance of .the discharger, disclosed herein, it is necessary to limit discharge to occur at point 14 of pin 12, rather than at the free ends or tips of members, such as

members

22 and 30. Any discharges occuring at the tips of such members would induce currents having relatively high dipole moments and would therefore radiate significant noise energy. Since these free tips of

member

22 and 30 typically project beyond point 14, at which the corona discharge occurs in order to effect the required dipole moment cancellation, these ends are subjected to high fields. Consequently, discharges would normally tend to occur at these tips, in preference to point 14 of pin I2, unless such tendency is purposely inhibited. This may be accomplished by shaping the free tips of the

outer members

22 and 30 to be blunt and that of point 14 to be very sharp. As a result, the static electric field is concentrated at point 14 rather than at the tips of the outer members so that any static discharge occurs at point 14, as required. Inhibiting the occurrence of static discharge at the tips of the outer members may also be achieved by covering at least the outer members, such as 22 and 30, with an insulating'sheath of material 32, while leaving the pin 12 bare with its very sharp point 14. In this way all discharging is forced to occur at point 14.

Preferably the tips of the outer members are shaped to be blunt even though they are covered by the insulating material 32. Although such insulating material is shown only in the embodiment diagrammed in FIG. 3, it should be apparent that it may and should be assumed to be incorporated in any one of the embodiments of the novel discharger disclosed herein.

The discharger embodiments, diagrammed in FIGS. 1 and 2, include single outer member 22 parallel to pin 12, while the embodiment in FIG. 3 includes two

such members

22 and 30. It should be appreciated that if desired, more than two outer members may be incorporated in the structure 10. For example, as shown in FIG. 4, to which reference is made herein, three parallel axially aligned outer members designated 22, 30 and 34 with three

transverse members

24, 28 and 36 are incorporated in structure 10 to form a trifurcated, symmetrical arrangement about pin 12.

It should further be pointed out that the teachings of the present invention are not limited to a discharger with a conductive structure in which the outer members must be parallel to the discharge pin and connected to the base member 16 by members, perpendicular to the pin I2. Rather, any symmetrical or unsymmetrical structural configuration may be employed as long as the various members of the structure are oriented with respect to pin I2 and, with respect to one another, so that the currents induced therein, have components which flow in directions so as to minimize, if not completely eliminate, the net dipole moment of the discharger.

For example, the structure may assume the shape of a V, formed by

outer members

42 and 44 which are diagrammed in FIG. 5 to which reference is made herein. Each of these members is connected at one end at base member 16 from which the pin 12 extends. The directions of current flow in the two members are designated by arrows 42c and 440. The lengths of these two members and the angles which they form with the pin l2 are chosen so that the components of the currents in the two members in a direction parallel to pin 12 have magnitudes which produce dipole moments, sufficient to cancel the dipole moments due to the corona discharge current and the current induced in pin 12.

Another embodiment of the invention, in which structure 10 includes outer members which are not parallel to pin 12, is diagrammed in FIG. 6. Therein, the structure 10 includes two rounded

outer members

46 and 48 which together form a semicircle, with pin 12 shown in radial alignment.

in all of the embodiments of the invention, herebefore 20 described, a single discharge pin 12 is shown. if desired, a plurality of pins, each with its separate sharp discharge tip or point, may be included. In such an arrangement, a separate group of one or more outer members would have to be included to balance or cancel the dipole moment produced by the discharge current and the current induced in the discharge pm.

In summary, in accordance with the teaching disclosed herein, a novel noise-free static discharger is provided which comprises a conductive structure having one or more pins with sharp discharge points. Each pin is associated with at -least one and preferably a plurality of conductive members which provide paths for the flow of radio frequency currents induced therein by the corona discharge which takes place at the sharp point of the pin with which they are structurally associated. These conductive members have length and spatial orientations such that the radio frequency currents induced therein have components in directions which create a sum of dipole current moments of the corona discharge current and the current induced in the pin with which they are associated.

To prevent static discharging from occuring at the free tips of these conductive members, their tips are blunted or rounded and/or the members are covered with a sheath of insulating material. The conductive structure is connected to an aircraft frame or other structure, for which RF noise protection is desired, by a resistive member whose resistance is high enough to make the conductive structure appear electrically isolated at the radio frequencies at which noise protection is desired. The resistive member however, must provide a static or DC connection between the conductive structure and the structure which is being protected.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What we claim is:

l. A noise free static discharger for a body which collects static electricity comprising:

a conductive structure defining a base portion, a substantially straight first member having one end connected to said base portion, and an opposite pointlike end, and at least a second member extending from said base portion in a direction whereby a radio frequency current induced in said second member by corona discharge at aid pointlike end has a current component flowing in a direction which is opposite the direction of the flow of current which is induced in the first member by the corona discharge at said pointlike end, said second member having a first end connected to said base portion and an op-.

posite rounded end to inhibit corona discharge from occurring thereat, the spacing between the rounded end and said base portion in a direction parallel to said first member being greater than the length of said first member; and

resistive means coupled to said body and to said structure for providing an electrical path therebetween and for supporting said structure spaced from said body with the pointlike end pointed away from said body.

2. A noise-free static discharger for a body which collects static electricity comprising:

a conductive structure defining a base portion, a substantially straight first member having one end connected to said base portion, and an opposite pointlike end, and at least a second member extending from said base portion in a direction whereby a radio frequency current induced in said second member by corona discharge at said pointlike end has a current component flowing in a direction which is opposite the direction of the flow of current which is induced in the first member by the corona discharge at said pointlike end with said second member being enclosed in a sheath of insulating material; and

3. A noise-free static discharger for a body which collects static electricity comprising:

a conductive structure defining a base portion, a substantially straight first member having one end connected to said base portion, and an opposite pointlike end, and at least a second member extending from said base portion in a direction whereby a radio frequency current induced in said second member by corona discharge at said pointlike end has a current component flowing in a direction which is opposite the direction of the flow of current which is induced in the first member by the corona discharge at said pointlike end with the length of said second member being related to the dipole moments created by the corona current and the current flowing in said first member; and

4. A noise-free static discharger as recited in claim 3 wherein said second member has one end connected to said base portion and an opposite rounded end.

5. A noise-free static discharger as recited in claim 4 wherein said second member is enclosed in a sheath of insulating material.

6. A noise-free static discharger as recited in claim 1 wherein said structure includes said first member and n secondary members, at least one secondary member being fixedly positioned in a direction whereby a current induced in said at least one secondary member by a corona discharge at said pointlike end of said first member includes a component flowing in a direction opposite the direction of current flow in said first member the end of said at least one secondary member remote from said base portion being rounded and at a distance from said base portion in a direction parallel to said first member which is greater than the length of said first member, and said structure further includes at least one secondary member in which a component of the current induced therein flows in a direction perpendicular to the direction of induced current flowing in said first member.

7. A noise-free static discharger as recited in claim 1 wherein said structure include said first member, n substantially straight second members each having a first end connected to said base portion and a second end spaced from said first end in a direction perpendicular to the direction of said first member, said structure further including at least one additional straight second member having a first end connected to said second end of one of said n members, said additional second member further defining a second end spaced from the first end thereof in a direction substantially parallel to the direction of said first member, the second end of said additional second member being spaced from said base portion a distance in a direction parallel to said first member which is greater than the length of said first member.

8. A noise-free=static discharger for a body which collects static electricity comprising:

' resistive means connected to said body and to said conductive member for providing an electrical path therebetween and for supporting said conductive member spaced from said body with the end portions pointed away from said body.

-9. A noise-free static discharger as recited in claim 8 wherein all of said endportions-of said conductive member except said shorter end portion which terminates in a point are enclosed in a sheath of insulating material.

'10. A noise-free static discharger as recited in claim 8 wherein the dipole moments of the respective end portions, in the presence of current flow as established by their respective lengths, are equal.

11. A noise-free static discharger as recited in claim 8 wherein said conductive member has the form of a conductive rod with a plurality of end portions extending away from a base portion, one of said end portions being shorter than the other end portions and terminating in at least one point, the other end portions being longer than said one end portion, being symmetrically disposed around said one end portion, and terminating in rounded ends. I

12. A noise-free static discharger as recited in claim 12 wherein all of said end portions of said conductive member except said shorter end portion terminating in at least one point is encased in a sheath of insulating material.

Claims

1. A noise free static discharger for a body which collects static electricity comprising: a conductive structure defining a base portion, a substantially straight first member having one end connected to said base portion, and an opposite pointlike end, and at least a second member extending from said base portion in a direction whereby a radio frequency current induced in said second member by corona discharge at aid pointlike end has a current component flowing in a direction which is opposite the direction of the flow of current which is induced in the first member by the corona discharge at said pointlike end, said second member having a first end connected to said base portion and an opposite rounded end to inhibit corona discharge from occurring thereat, the spacing between the rounded end and said base portion in a direction parallel to said first member being greater than the length of said first member; and resistive means coupled to said body and to said structure for providing an electrical path therebetween and for supporting said structure spaced from said body with the pointlike end pointed away from said body.

2. A noise-free static discharger for a body which collects static electricity comprising: a conductive structure defining a base portion, a substantially straight first member having one end connected to said base portion, and an opposite pointlike end, and at least a second member extending from said base portion in a direction whereby a radio frequency current induced in said second member by corona discharge at said pointlike end has a current component flowing in a direction which is opposite the direction of the flow of current which is induced in the first member by the corona discharge at said pointlike end with said second member being enclosed in a sheath of insulating material; and resistive means coupled to said body and to said structure for providing an electrical path therebetween and for supporting said structure spaced from said body with the pointlike end pointed away from said body.

3. A noise-free static discharger for a body which collects static electricity comprising: a conductive structure defining a base portion, a substantially straight first member having one end connected to said base portion, and an opposite pointlike end, and at least a second member extending from said base portion in a direction whereby a radio frequency current induced in said second member by corona discharge at said pointlike end has a current component flowing in a direction which is opposite the direction of the flow of current which is induced in the first member by the corona discharge at said pointlike end with the length of said second member being related to the dipole moments created by the corona current and the current flowing in said first member; and resistive means coupled to said body and to said structure for providing an electriCal path therebetween and for supporting said structure spaced from said body with the pointlike end pointed away from said body.

8. A noise-free static discharger for a body which collects static electricity comprising: a conductive member; said conductive member having the form of a rod with a base portion and at least two end portions extending away from the base portion, one of said end portions being shorter than the other end portion and terminating in a point, the other end portion having a rounded termination to inhibit corona discharge from occurring thereat, the termination being at a distance from said base portion along a direction parallel to said first member which is greater than the length of said first member; and resistive means connected to said body and to said conductive member for providing an electrical path therebetween and for supporting said conductive member spaced from said body with the end portions pointed away from said body.

9. A noise-free static discharger as recited in claim 8 wherein all of said end portions of said conductive member except said shorter end portion which terminates in a point are enclosed in a sheath of insulating material.

10. A noise-free static discharger as recited in claim 8 wherein the dipole moments of the respective end portions, in the presence of current flow as established by their respective lengths, are equal.

11. A noise-free static discharger as recited in claim 8 wherein said conductive member has the form of a conductive rod with a plurality of end portions extending away from a base portion, one of said end portions being shorter than the other end portions and terminating in at least one point, the other end portions being longer than said one end portion, being symmetrically disposed around said one end portion, and terminating in rounded ends.