US 2707223 A
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P 6 1955 H. E. HOLLMANN 2,707,223
ELECTRIC RESISTOR Filed June 15, 1949 2 Sheets-Sheet l F 37 1g4 I O 0 Fig./ 36 7. kn
INVENTOR. .HANS E. HOLLMANN TTORNEYS April 6, 1955 H. E. HOLLMANN 2,707,223
ELECTRIC RESISTOR Filed June 15, 1949 2 Sheets-Sheet 2 lgUTPUT Fig. /0
IN PUT INVENTOR.
HANS E. HOLLMANN BY 4 i zs-w bm United States Patent ELECTRIC RESISTOR Hans E. Hollmann, Camarillo,
United States of America as retary of the Navy Calif., assignor to the represented by the Sec- This invention concerns polar mixtures of a fluid, semifluid, or solid state of aggregation, consisting of an insulating and originally fluid or semi-fluid carrier material mixed with semi-conductive particles whose dielectric constant differs substantially from that of the carrier material. Such a mixture, when subjected to an electric polarizing field, even when thickening, solidifying, or coagulating during this treatment, assumes an electric over-all conductivity which is nonlinear, i. e. which depends on the momentary polarizing field strength. The invention is more particularly concerned with the uses of such nonlinear mixtures in various fields of electric engineering. The interspace between a plurality of electrodes is filled with the fluid or semi-fluid mixture or a plurality of electrodes is immersed or embedded in the coagulating mixture, so that there results a non-linear resistor which can be controlled by external or internal signals; such as additional electric or magnetic field signals, mechanical, vibrational, strain, compressional, bending forces, turbulent signals applied or produced in the liquid carrier material, electromagnetic radiation signals, impinging particles signals, or combinations of such signals.
An object of the present invention is to provide a nonlinear polar mixture wherein the overall conductivity of the mixture may be controlled by external or internal signals of various types applied to the polar substance thereof.
Another object is to provide a nonlinear resistor wherein the resistance thereof varies nonlinearly with respect to the voltage impressed thereon.
A further object of the invention is to provide polar tubes utilizing a polar mixture and operating in a manner similar to corresponding vacuum tubes.
These and further objects and aspects of the invention will become more apparent through the following description, taken with reference to the accompanying drawings which are intended to be illustrative only of the broader principles underlying the invention. Since the peculiar properties of the polar resistors seem to contradict common conceptions, it may be emphasized that the invention is the result of extensive research carried on for many years and that its versatility is satisfactorily proven by numerous experiments. In order to disclose the broad scope of the invention, it may be noted that the invention opens an entirely new field of electrical engineering, most of which, heretofore, has been confined exclusively to electronics.
Before describing the various forms of the instant invention in greater detail, it is necessary to explain the basic properties of the polar mixtures on which the invention is based. The polar mixture, according to the invention, is ranged in between two well known suspensions, namely the Magnetic Oil (Technical News Bulletin of the National Bureau of Standards volume 31, pp. 5460, 1948) on the one side and the Electrostatic Oil (U. S. Patent 2,417,850) on the other side. Since the colloidal suspension is the easiest to describe and comprehend, it is given below in preference to polar fluids or substances which are based on the same philosophy.
Figure 1 shows the irregular distribution of dielectric particles in a neutral suspension;
Figure 2 indicates the formation of dielectric chains resulting when the suspension is subjected to a polarizing field;
Figure 3 shows the incremental voltage drop along the dielectric chains;
Figures 4, 5, and 6 indicate suitable electrode arrangements of polar resistors;
Figures 7 and 8 are typical characteristic explanations of the function and operation of the invention;
Figure 9 indicates a polar triode; and
Figure 10 shows a modification in the form of a polar beam tetrode.
The polar fluid, suspension, mixture, or substance, according to the invention, consists of an insulating and more or less viscous carrier material in which fine powder of semi-conductive particles is suspended, preferably in colloidal dispersion. This carrier material may be an insulating oil, e. g. transformer oil, transformer insulating fluids, mineral oils, such as olive oil, castor oil, or silicone oils. Furthermore, the carrier material may consist of insulating pastes such as Vaseline and other greases. Finally, the carrier material may be fluid or semifluid only at the beginning of the production of a polar mixture, solidifying or coagulating, after intermixing of the powder, either by cooling, evaporation, polymerization, or chemical reaction. For example, there may be used paraflin or waxes, glues such as the well known household-cement, kaurite-glue, or resins, the best of which is acrylate-resin, or finally ordinary rubber which polymerizes under the influence of heat treatment.
The intermixed powder, in addition to being semiconductive, must have a dielectric constant which differs substantially from that of the carrier material. Powdered substances such as cuprous oxide (cuprite), Rochelle salt, coal, or ordinary graphite create the desired nonlinear effects with more or less eflicient results. It is probable that some carrier materials and other agents which are still untried will give even better results than any so far experimented with. This may be the case especially when using very high frequencies, where the high frequency conductivity and dielectric constant, in connection with the depth of infiltration, play a decisive role.
A control of colloidal suspensions or even of rough mixtures is basically known. As mentioned before, there exist two types, namely: the so-called Magnetic Oil and its counterpart in the field of electrostatics, the socalled Electrostatic Oil. Both are put to ingenious uses by utilizing their increasing viscosity when subjected to a suitable control field: the magnetic oil to a magnetic field, and the electrostatic oil to an electric field. The ferromagnetic particles of the magnetic oil become magnetized and the dielectric particles of the electrostatic oil become polarized; both types of particles attract each other and arrange themselves in the form of magnetic or dielectric chains. Regardless of the type of chains, the viscosity of both suspensions increases when subjected to their associated fields. This viscosity effect is utilized, in the prior art, for transferring mechanical forces or torques in a magnetic or electric viscosity clutch.
The polar mixture according to the instant invention fits between these two previously known extremes. Whereas the viscosity effect requires either ferroor paramagnetic particles in the one case, and dielectric particles in the other case, the nonlinear mixture or substance according to this invention requires semi-conductive particles whose dielectric constant differs substantially from that of the carrier material. For special purposes, namely for magnetic control, the particles, in addition to their semi-conductivity and dielectric constant, must be paramagnetic, so that a control of the dielectric chains can be achieved by means of an additional magnetic field. A powder which has been found to operate very satisfactorily, is ferri-ferro-oxide. The new mixtures, according to this invention, display a nonlinear conductivity under electric or magnetic fields, but only slight variation in viscosity, contrary to the aforementioned extreme cases of the electrostatic and magnetic oils.
The process of the formation of dielectric chains is explained in greater detail by means of the Figures 1, 2, and 3. Referring to Fig. l, the dielectric, semi-conductive particles 30, in general, are distributed at random throughout the carrier material 31, undergoing a random molecular movement. However, as soon as a direct or alternating voltage is applied across the two electrodes 32 and 33 in Fig. 2, i. e. as soon as the neutral mixture is subjected to a direct or alternating electric field (produced e. g. by the battery 34) the dielectric particles 30 become polarized and form the chains shown in Fig. 2. This chain effect produces an electric linkage or connection between the electrodes 32-33 and makes the mixture semi-conductive. Since the conductivity of the particles can be obtained only at the expense of the dielectric constant, the polar mixtures display only a very weak viscosity effect (contrary to the prior art magnetic and electric oils, aforementioned), and noticeable mechanical moments or torque moments cannot be transferred with the mixture of the instant invention.
Once the virgin state of the polar mixture is affected at a certain threshold field, or in other Words, once the mixture is converted from its virgin state corresponding in Fig. 1 into its polarized state as shown in Fig. 2, the conductivity increases further with increasing field strength. In a pure physical sense, the polar mixture assumes a nonlinear conductivity, and the resistance between the electrodes becomes nonlinear. This particular phenomenon may be explained by reference to Fig. 3. The semi-conductivity of the dielectric particles effects an incremental voltage drop along each individual chain in such a way that the partial fields appear preponderantly in steps at the transition resistances between every two particles whereas the conductivity of the particles prevents higher voltage drops across the particles themselves. On the other hand, the dielectric constant of the particles must have a certain minimum value for assuring an initial chain formation. Consequently, the dielectric constant and conductivity of the particles on one hand, and the dielectric constant of the carrier material on the other hand assume great significance for obtaining the desired nonlinearity effect. Furthermore, the high electric fields created in the transition regions, where the particles touch each other, produce strong electrostatic forces of attraction. As a result, the dielectric chains are reinforced at increasing field strength or electrode voltage so that the increasing over-all conductivity may be considered as being caused by the action of innumerable fluctuating contacts between the innumerable links. An important result of this electrostatic attraction is a very high frequency response even extending into the microwave range.
One practical example of the polar resistor, namely two flat or even cylindrical electrodes, has already been shown in Fig. 2. The simplest form, however, consists of a drop of the polar mixture suspended between two closely situated wire electrodes by adhesion only. Another example consists of a glass tube closed at both ends and occupied by the polar mixture or substance. A wire electrode is immersed in each side extending into the polar mixture or substance. Varying the gap between the wires or varying the entire length of the glass tube permits the resistance to be changed within very large limits and to a be matched to any desired voltage range.
Aside from the electrode separation, which determines the voltage sensitivity or nonlinearity, the power dissipation can be adjusted by varying the surface of the electrodes. A very practicable type of polar resistor is indicated in Fig. 4. Two wires 35 and 36 are wound bifilarly on a supporting member 37 of mica, Plexiglas, ceramic, or other suitable insulator of any arbitrary shape. The entire device is immersed in a suitable container filled with the liquid mixture. Another modification is obtained by covering the electrode arrangement with a thin layer of the liquid mixture, after which the entire device can be wrapped with insulating or Scotch tape.
Referring to Fig. there is shown another modification of a polar resistor which resembles a mica capacitor. It comprises two sets of foil electrodes 38 and 39 with insulating sheets 40, e. g. of mica, inbetween. These mica sheets are perforated and the perforations are filled with the polar mixture before assembling.
If a high voltage sensitivity at relatively low power dissipation is required, the polar resistor shown in Fig. 6 is convenient. It comprises a glass mirror 41 whose silver layer is cut with a sharp knife or razor blade, so that two electrodes 42 and 43 result with a minute gap of only a few thousandths of an inch. This very fine gap is bridged by a drop of the polar mixture and is protected by a small piece of mica before the entire resistor is wrapped with tape. Various modifications can be derived from the three types shown in Figs. 4, 5, and 6.
Until now, the polar mixture according to the invention has been described preponderantly as a liquid, semiliquid, or more or less in a consistent state of aggregation. A further improvement is obtained by converting the liquid or consistent mixture into a solid state thus changing all previously described examples of polar resistors into dry types.
The simplest way to produce such dry resistors is by means of wax such as paraffin. The paraffin is heated in a container until it melts. Then, a certain amount of graphite powder, for instance 20 per cent by volume, is intermixed and carefully stirred up. One of the electrode arrangements described before is immersed into the hot paraflin-graphite suspension or the hot mixture is poured over the electrode arrangements shown in Figs. 4 and 6. Since the high temperature does not disturb the chain formation, the hot resistor is formed just as the previous cold resistors with the aid of an electric polarizing field between its electrodes. The paraffin cools slowly under the continuous influence of the electric field so that the electric nonlinearity is retained until the paraffin reaches its solid state, i. e. until it becomes dry paraflin intermixed with graphite. In this manner an artificial polar substance and dry polar resistors can be produced.
During the cooling and coagulating of the hot paraffin, the over-all conductivity and, at the same time, the electric nonlinearity decreases considerably because the paraffin shrinks. This shrinking effect causes the dielectric chains to be compressed so that the frozen mixture is under an internal compressional bias.
This disadvantage can be avoided by utilizing a carrier material which coagulates without shrinking or evaporation. Liquids with this special property are, e. g. kauriteglue, Khotinsky-cement, and acrylate resin. All these substances are composed originally of two separate fluids which, after being intermixed, solidify due to chemical reactions without noticeable shrinking. Consequently, a polar substance and dry polar resistors can be produced by intermixing the semi-conductive powder with one of the initial solutions and slowly adding the binding reactor until the combined suspension, while under the continuous influence of a polarizing field, becomes completely hard, similar to the cold parafiin mixture. The hardening process of such polar resistors is considerably accelerated if the polarizing field is produced by means of high frequency voltages which, at the same time, produce a diathermy field accelerating the chemical binding reaction.
Another carrier material which assures a well pronounced electric nonlinearity and, furthermore, particular applicability, is rubber. A polar rubber is produced, according to the invention, by intermixing the semi-conductive, dielectric powder with liquid rubber and by polymerizing this liquid mixture by heat while under the continuous influence of a sufficiently strong polarizing field. Although the aforementioned polar substances show a more or less pronounced sensitivity to vibrational or compressional forces, the polar rubber with its included semi-conductive chains, because of its elasticity, is much more sensitive to any compression or dilation, because together with the rubber the incorporated chains are compressed or extended. As a result, the over-all conductivity increases or decreases to a very high amount by compressing or extending the polar rubber.
All practical requirements concerning power dissipation and voltage sensitivity can be fulfilled by selecting and adjusting the size of the supporting member or the surface of the electrodes, respectively, and the distance inbetween.
The electric function of the polar resistor, or, more generally, of the polar mixture or substance, is disclosed in the characteristics shown in the qualitative Figures 7 and 8. If a direct or alternating voltage is impressed upon the two electrodes of a polar resistor, either in liquid or dry form, the passing current increases nonlinearly with increasing voltage thus yielding nonlinear transfer characteristics of the form indicated in Fig. 7. Since the polarity is of no consequence, the characteristic is symmetrical. The polar resistance changes from a certain zero value R0, characterized by the slope of the dotted initial tangent in the zero point, to a very much lower saturation value Rs, characterized by the dashed end-tangent. At this extreme state of saturation all links c ntribute to the saturation conductivity because they all are strongly pressed together along all chains. For the sake of completeness it must be emphasized that the full state of saturation, under practical conditions, cannot be reached but only approached because the oil becomes overloaded and unstable.
The nonlinear transition between R0 and Rs is more clearly disclosed by the nonlinear resistance characteristic shown in Fig. 8. It is obtained by plotting the voltageto-current ratio V/I=R against the applied voltage V. A more general physical picture is obtained by considering the conductivity in relation to the polarizing field E= V/e=V where e is the electrode gap, under the present assumption of setting e: 1.
In addition a differential resistance Rdifi must be taken into consideration whenever the polar resistance is controlled by an alternating voltage superimposed on a certain bias. Obviously the differential resistance also is nonlinear.
Without going into further details it may be mentioned that RS depends primarily on the conductivity of the particles as well as on the mixture ratio. hand R0 and the transition region is determined not only by the pure electric properties of the polar mixture or substance but also by its previous history, which means, by the momentary state of the chains as they are formed under the influence of a certain bias or alternating voltage. This effect may be compared roughly to the peculiar behavior of ferromagnetics and polar dielectrics displaying Rochelle-salt properties especially in its virgin state, and hysteresis.
In order to distinguish the polar resistor over well known devices, it may be mentioned that it has a certain analogy to the obsolete coherer. However, whereas the latter operates, so to speak, only as an off-on device because its resistance fluctuates only between infinity and zero, the polar resistor displays a shaded transition between R0 and Rs. As long as RS is not attained, the polar resistor requires no external reduction to its initial condition as is necessary for the coherer by means of mechanical shocks. Only under special conditions, namely when the polar resistors become overloaded, do the dielectric particles fuse together, just as do the metal particles in the coherer. In this special case the welded chains remain intact even at decreasing fields and can be destroyed only by stirring up the mixture or by strong vibrations. Once the dry paraffin resistor is overloaded, it must be heated again or subjected to even stronger overloading currents until the paraffin melts, so that a new chain formation can be accomplished. The completely dry resistors, made of Kaurit, acrylate or rubber, cannot be repaired, once damaged by overloading.
On the basis of this new philosophy many practical applications are obvious to one skilled in the art. All applications are based on the important phenomenon that the linkage strength of the dielectric chains and, therefore the over-all conductivity, can be controlled by external or internal signals of various types applied to the polar substance or suspension. In general such signals may be of one or more of the following forms: additional electric or magnetic fields, mechanical vibrations or strains, compressional or bending forces, sound or supersonic waves, turbulences in the fluid mixture caused by a stream of the latter or by moving electrodes, electromagnetic radiation covering a large portion of the whole spectrum, or impinging particles. It is therefore apparent that many types of transducers may be constructed utilizing an electrically nonlinear polar mixture according to the present invention.
In contrast to all previously known devices operating with various types of colloidal suspensions, i. e. with magnetic or electrostatic oil, the change in resistance, according to this invention, produces corresponding fluctuations of the direct or alternating currents flowing through the polar resistor in series with a load impedance.
According to the invention a further feature is that the dielectric chains are controlled by the aid of additional electric control fields which are generated between auxiliary control electrodes and the output electrodes, or only between two or more control electrodes. Referring to Fig. 9, the simplest device for obtaining a pure electrical control, similar to that of a vacuum triode, contains two output electrodes, which, in analogy to a vacuum triode, may be called cathode 118 and anode 119. The grid electrode 120 is arranged between both main electrodes and the entire interspace is occupied by the polar mixture in liquid or in dry form. Provided the over-all conductivity of the polar mixture,
On the other I depending on the substance of the dielectric particles, the mixture ratio, and the chain-forming plate field, is not so high that a noticeable control field around the grid is neutralized or suppressed-a condition resembling the existence of a very high space charge in a vacuum tube-the chains extending between cathode 118 and anode 119 are strengthened or weakened under the influence of the fluctuating grid fields. As a result the liquid triode has a mutual transconductance similar to that of an electronic tube, although this comparison is subjected to certain limitations. However, favorable operational conditions, such as suitable electrode separations, mixture ratios, etc., assure an over-all performance largely analogous to a vacuum triode so that the latter for many purposes, can be replaced by liquid triodes. The simplicity of its construction, i. e., no thermionic emission and no vacuum, gives the polar tubes an overwhelming superiority over the electronic tubes in many respects, especially so since not only small and sensitive tubes but also big power tubes can be manufactured at very low cost.
It is to be noted primarily, that the theory and behavior of the polar tubes differs in several respects from that of vacuum tubes which depend on their freely operating electrons. An important feature is the plate reaction resulting from the nonlinearity of the plate resistance. Consequently, the alternating output voltages, in relation to the direct plate supply voltage, are limited because intolerable distortions would otherwise occur in the plate circuit. A low-impedance plate load, there fore, is preferable. If a high voltage amplification is to be obtained, a step-up transformer 121 (Fig. 9) may be used similar to the aforementioned polar detector and polar transducer. A regenerative feed-back, i. e. the output voltage leading back to the grid, immediately produces a polar oscillator whose frequency is determined in the usual manner by a tuned-plate and/or a tuned-grid circuit.
Fig. 10 differs from Fig. 9 by transversal control fields being generated between interleaved grids 122 and 123 which are fed in push-pull by the center-tapped input transformer 124. The grid wires, at the same time, may be shielded by insulating strips 125 against cathode and anode so that the effective chains extend throughout the interspace between these strips. The grid bias is permitted to adjust automatically by means of the capacitor 126 in accordance with the direct voltage drop between cathode and anode. This results in a type of a polar beamtetrode whose current lines, represented by the dielectric chains, are concentrated preponderantly in a transverse direction. The power gain of such a polar beam-tetrode considerably exceeds that of the simple polar triode.
As can be seen by means of these few examples the invention opens the field for a completely new technique in liquid or even dry tubes whose design and performance can be taken from current electronic practice.
As noted previously, the bipolarity of the colloidal resistor makes direct rectification impossible. However, a power rectification can be obtained by means of polar tubes together with auxiliary rectifiers such as selenium rectifiers or thyratrons, etc. which control the grid potential in such a manner that the polar tube is closed only during one-half cycle. In this way, one or more polar tubes operate only as high power relays whereas only small rectifiers are required for producing the desired grid control. In connection with the foregoing descriptions and explanations this procedure is well understood in analogy to common rectifier technique.
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.
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.
What is claimed is:
l. A nonlinear resistor having a plurality of spaced electrodes, the interspace being occupied by a polar mixture which consists essentially of an insulating carrier material and semi-conductive particles whose dielectric constant differs substantially from that of said carrier material, the particles being effective under the influence of a polarizing electrostatic field to become polarized and thereby to arrange themselves in the form of semi-conductive chains electrically linking said electrodes.
2. A nonlinear resistor which comprises a plurality of spaced electrodes, the interspace being occupied by a polar mixture which consists essentially of an insulating carrier material and semi-conductive particles suspended therein in the form of semi-conductive chains electrically linking said electrodes, said particles having a dielectric constant differing substantially from that of said carrier material.
3. A nonlinear resistor as defined in claim 2, said carrier material is an insulating fluid.
4. A nonlinear resistor as defined in claim 2, said carrier material is an insulating solid.
5. A nonlinear resistor as defined in claim 2, said carrier material is resilient.
6. A nonlinear resistor as defined in claim 2, said carrier material is acrylate resin.
7. A nonlinear resistor as defined in claim 2, wherein said semi-conductive particles are graphite particles.
8. A transducer which comprises a nonlinear resistor having a plurality of spaced electrodes, the interspace being occupied by a polar mixture which consists essentially of a solid insulating carrier material and semi-conductive particles embedded therein in the form of semiconductive chains electrically linking said electrodes, said particles having a dielectric constant differing substantially from that of said carrier material.
wherein wherein wherein wherein 9. An electrical device which comprises a nonlinear resistor having a pair of spaced electrodes, the interspace being occupied by a polar mixture which consists essentially of an insulating carrier material and semi-conductive particles suspended therein in the form of semi-conductive chains electrically linking said electrodes, and a third electrode in said mixture intermediate said pair of spaced electrodes, said particles having a dielectric constant1 differing substantially from that of said carrier materia References Cited in the file of this patent UNITED STATES PATENTS 1,325,889 Curtis a- Dec. 23, 1919 1,822,742 McEacheron Sept. 8, 1931 1,919,053 Brinton July 18, 1933 1,989,187 Fitzgerald Jan. 29, 1935 2,418,516 Lidow Apr. 8, 1947 2,469,569 Ohl May 10, 1949 2,500,953 Libman Mar. 21, 1950 2,532,157 Evans Nov. 28, 1950 FOREIGN PATENTS 22,142 Great Britain of 1901