US2312498A - Signal translating apparatus - Google Patents

Description

March 1943- A. M. SKELLETT 2,312,498

SIGNAL TRAIiSLATING APPARATUS Filed April 16, 1941 INVENTOR MSKELLETT ATTORNEY Patented Mar. 2, 1943 SIGNAL TRANSLATING APPARATUS Application April 16, 1941, Serial No. 388,786

7 Claims.

This invention relates to signal translating apparatus and more particularly to such apparatus including electron discharge devices having one or more secondary electron emissive electrodes and commonly known as electron multipliers.

Electron multipliers comprise, in general, a source of primary electrons, a collector electrode or anode, and one or more secondary electron emissive electrodes for amplifying the primary electron current by electron multiplication whereby the electron current to the collector electrode or anode is several times as great as the primary electron current. In such devices, one of the problems encountered is the dispersion of the electrons in flowing from one electrode to the next succeeding one. For example, in electron multipliers comprising substantially coplanar electron emitting surfaces, the electrons emanating from the primary cathode'sufier a dispersion normal to their direction of flight to the secondary electron emissive electrode nearest thereto and also in the direction of their flight. In such multipliers, a similar dispersion effect occurs with the secondary electrons emanating from one secondary electron emissive surface and flowing to the next succeeding electrode of the device. Hence, some of the electrons flowing between successive electrodes may not impinge upon the electrode to which they are intended to flow or may impinge upon such electrode at a portion thereof at which the fields are not conducive to eificient electron multiplication.

Furthermore, electron multipliers including one or more secondary electron emissive electrodes operated at a positive potential with respect to the next preceding electrode are effectively direct current amplifiers. Hence, when in such devices, the initial or primary electron current is varied in accordance with an alternating current signal both the direct current and alternating current components of the primary electron stream are amplified by the device so that the output current of the device includes a relatively large direct current component in relation to the alternatin current component thereof.

One object of this invention is to effectively focus the electron stream emanating from each electron emissive surface in an electron multiplier upon a restricted area of the next succeeding electrode.

Another object of this invention is to improve the operating characteristics and efficiency of electron multipliers operable as alternating ourrent amplifiers. More specifically, another object of this invention is to enable the attainment of a large amplification of the alternating current component of the primary electron current in an electron multiplier, in relation to the amplification of the direct current component thereof.

In one illustrative embodiment of this invention, an electron multiplier comprises a primary cathode, a collector electrode element, and a plurality of aligned coplanar secondary electron emissive electrodes or cathodes mounted between the primary cathode and the collector electrode element, the secondary electron emissive electrodes or cathodes being adapted to be maintained at successively higher positive potentials whereby the electrons emanating from each of the cathodes are subjected to an electric field accelerating them toward the next succeeding electrode.

In accordance with one feature of this invention, means are provided for producing adjacent each of the cathodes a curved or semicylindrical magnetic field symmetrical with respect to the axis of alignment of the several cathodes and concave downward with respect to the emissive surfaces thereof, whereby the electrons emanating from each cathode are focused upon the corresponding area of the next succeeding electrode.

In accordance with another feature of this invention, an electron multiplier is provided with two rows of coplanar secondary electron emissive electrodes arranged in pairs and mounted on opposite sides of an axis extending between the primary cathode and the collector electrode element, and means are provided for deflecting the primary electron stream in accordance with a signal to be amplified whereby the primary electron current is divided between the secondary electron emissive electrodes nearest the primary cathode, in accordance with the instantaneous magnitude of the signal whereby push-pull amplification is effected.

In accordance with a further feature of this invention, the secondary electron emissive electrodes in each pair are coupled to each other through impedances of such character that a potential difierence is established therebetween when an electron stream impinges thereupon, whereby the deflection of the stream flowing away therefrom, with reference to the deflection of the impinging stream, is increased and the gain of the multiplier is increased.

The invention and the above-noted and other manner of operating the electron discharge device shown in Fig. 1;

that the magnetic field lines are substantially semicircular, symmetrical with respect to the medial plane between the two rows of secondary cathodes and substantially coextensive laterally with the secondary cathodes.

As illustrated in Fig. 2, each pair of the secondary cathodes is biased at the same potential with respect to the preceding cathode of the device as by a battery 36, the secondary cathodes .in each pair being connected to each other through equal resistances 31. For example, the

' secondary cathodes 20a and 20b may be biased Fig. 3 is a diagrammatic viewishowing the form and direction of the magnetic field produced in the device illustrated in Fig. 1 and the relation thereof to the emissive electrodes in the device; and

Fig. 4 is a diagrammatic view illustrating another electron discharge device constructed in accordance with this invention, the enclosing vessel of'the device being shown in phantom.

Referring now to the drawing, the electron discharge device shown in Fig. 1 comprises an elongated, evacuated enclosing vessel I 0 having a plane base wall and provided adjacent one end with a tubulature I2 in which a cathode I3 is supported. The cathode I3 may be ofthe equipotential type and comprises a metallic cupshaped member the outer surface I4 of the base of which is coated with thermionic material which is heated to the desired emission temperature as by a heater filament I5, shown in Fig. 2.

Mounted at the other end of the vessel II] are a pair of coplanar collector electrodes or anodes I6a. and I6!) supported by lead-in conductors II, only one of which is shown in Fig. 1, sealed in the side walls of the enclosing vessel I0. I A screen grid I8 is mounted opposite and in parallel relation to the collector electrodes or anodes I6, by a leading-in conductor I9 sealed in one side wall of the enclosing vessel I0.

A plurality of pairs of coplanar secondary electron emissive electrodes or cathodes 20 to 24; inclusive, are mounted in two parallel rows on opposite sides of an axis extending between the cathode I3 and the gap between the anodes Ilia and I 6!), the secondary cathodes in each pair at a potential of the order of 100 volts positive with respect to the primary cathode I3, and each of the other pair of cathodes may be biased at a potential of the order of 100 volts positive with i respect to the next preceding pair of secondary being designated in the drawing by the same 7 numeral followed by the letter a or b. These secondary cathodes are supported by individual leading-in conductors 25 sealed in the side walls of the vessel I0 and are arranged parallel to the base wall I I of the vessel I0 and in immediate proximity thereto.

Mounted on opposite sides of the cathode I3, equally spaced therefrom and coplanar with the surface I4 and the secondary cathodes 20 to 24 are a pair of deflector plates 26a and 26b which are supported by leading-in conductors 21 sealed in the side walls of the enclosing vessel I0.

A plurality of field plates 28 to 33,'inclusive, are supported in coplanar relation parallel to the secondary cathodes by individual leading-in conductors 34, each of the field plates 29 to 33 overlying and being aligned with one pair of the secondary cathodes and the field plate 28 overlying'and being aligned with the deflector plates An elongated U-shaped permanent magnet 35 is positioned with its poles in immediate proximity to the base wall II of the enclosing vessel, opposite the secondary cathodes'and in alignment with the two rows thereof. The relation of the magnet poles and the secondary cathodes. is illustrated in Fig. 3 from which it will be seen cathodes. Each of the field plates 28 to 32, inclusive, is connected to and biased at the same potential as the pair of cathodes next succeeding the pair it overlies, and the field electrode 33 is connected directly to the screen grid I8 and maintained with it at a positive potential higher than that of the secondary cathodes'24a and 24b. The deflector plates 26a and 2617 are connected across the secondary winding 38 of an input transformer T1, the mid-point of which winding is connected to the cathode I3. The collector electrodes or anodes I6a and I6!) are connected across the primary winding 39 of an output transformer T2, the midpoint of which winding is connected to the battery 36 so that the collector electrodes or anodes are maintained at a positive potential, for example of the order of volts, with respect to the secondary cathodes 24a and 24b.

The electrons emanating from the emissive surface I4 of the cathode constitute an electron stream having, inthe vicinity of this surface, a cross-section of substantially the same form and dimensions as the surface I4. These electrons come under the influence of electric fields due to the potential difference between the cathode I4 and the field plate 28 and secondary cathodes 20a and 20b, and are caused to traverse arcuate paths which, in the absence of a potential difference between the deflector plates 26a and 261), would pass through the plane of the cathodes 20a and 20?) at points adjacent the medial plane between these cathodes, some of the electrons passing between these cathodes and other impinging thereon to cause the release of secondary electrons. These secondary electrons, in number greater than the impinging primary. electrons, are similarly directed along arcuate paths toward the secondary cathodes 2Ia and 2Ib where a further electron multiplication occurs. This action is repeated at each of the succeeding secondary cathodes and the secondary electron current emanating from the cathodes 24a and 24b, which may be many times as great as the primary electron current, flows to and is collected by the anodes IBa and IBb.

In the absence of the magnetic field, between each pair of cathodes a dispersion of the electron occurs and the dispersion increases at each successive multiplying stage in the device. Thus, for example, if the emissive surface I4 is circular in form, the primary electron stream would have at the plane'of the secondary cathodes 20a and 20b an oval cross-section with axes greater than the diameter of the surface I4. At each of the succeeding electrodes, the arriving electron stream would be in cross-section an oval with greater axes than those of the oval cross-section at the preceding: electrode. Consequently; .atithec later: stages 'ofzthezdevice-some'of the:arrivingielectrons woul dl faillto: impinge. upon secondary icatha ode .to:.which they 'wereadirecte'd. whereby? ailo'ssg. a reduction in operating efiiciency'ofthe'device and non-uniform operating characteristicstwouldl.be: occasioned.

In: devices. constructed: in accordance with. a: feature-ofthisinventiomhowever, suchdispersion': of: the electrons. in the: various? streamsaflowingbetween successive. electrodes is. prevented; so that at. the-.plane'of. each of the secondary cathodes; thearriving electron stream hasisubstantially'ther same: cross-section as. it had when: leaving: the' preceding electrode. Stated in. another'wamin: devices-constructed in accordance with a.feature1 of thisinvention, all of the-electrons:leavingzanyr particular area of one. electrode arerfocusedmporr the corresponding area ofthe next succeeding electrode. This result. will. be understood from: the following considerations with particular ref.- erence to Fig. 3.-

Each electron emanating from the emissive" surface I4 of the cathode has a: componentxof. velocity normal to the medialplane between" the deflector plates 26a and 261), i. e. in the X direction indicated in Fig. 3 and travels along, an arcuatev path toward the secondary cathodes 20a'and'i20b; The-magnetic field, however, becauseof. itsrform:

changes the direction. ofthe :0. component of elec'-'- tron velocity after the electron hasv passed the; highest point in its arcuate path and, inasmuch. as this. field is symmetrical with respect. to? the medial plane between the deflector plates, each; electron, under the influence of the magnetic field, will. arrive in the plane of the-secondary cathodes 20a and 201) at a point corresponding; in relation to the medial plane, to the pointrat' which it left the surface I4; Hence; all. ofzthe: electrons emanating from the surface l4 willbe focused upon a corresponding area in the plane' of the secondary cathodes 20a and 20b. A-similar' focusing action is produced between each pair of succeeding secondary cathodes.

When the deflector plates ZBa-and 26bare-tat. the same potential, that is when no signalisiiinpressed upon the input transformer, equal por'-'- tions of the primary electron current impinge upon the secondary cathodes 20a; andIDb and': equal multiplied currents are supplied to the collector electrodes or anodes IBa'and. 16b. However, when an. alternating current signal, for example, is impressed upon the input transformer T1, the primary electron stream will be deflected during one half cycle of the signal toward one of the secondary cathodes 20a and 20b to an extent proportional to the magnitude of the input signal so that the primary electron current to one of these cathodes is increased and that to the other of these cathodes is decreased. Hence, the multiplied current flowing to one anode will be increased and that to the other decreased. During the other half cycle of the signal, the condition will be reversed. Honce, there will be produced in the winding 39 of the output transformer T2 an alternating current corresponding to but of much greater magnitude than the signal impressed upon the input transformer T1.

It will be noted that the number of secondary electrons leaving any one of the secondary cathodes is proportional to and greater than the number of primary electrons impinging thereon. Hence, when the beam is deflected in accordance with a signal so that, for example, more primary electrons flow to the secondary cathode 202) than ondary cathode 20a. Consequently-,nthe secondary electron" streamileaving'i the secondary cathcathodes: 20a; anct: 201)..

at. each? succeeding. pain of' secondary: cathodes:

Hence. it will; be: seen; that a.- high; amplification:

of the alternating;current component. of the. primary electron stream is achievedwith relatively. low. amplification of. the: direct. current com-- ponent thereof;

It .maycbe noted. that eachstageof thezmultie plier is'regenerativei to some extent inasmuch asthe difference of potential. between eachpair of. secondary cathodes iseffective in both direc tions. The regenerative effect, however, mayr-be made negligibly small without appreciably'afiect ing; the gain, by; spacing.v the cathodesof: each pair so that-the-electron streamthereto impinges:

. cathodes to collect theseelectronswhich dov not impinge upon the cathodes, these electrodes functioningv somewhat analogously to screen:

grids.

Although in the construction. illustrated. in

a Fig... 1 one field plate has been shown fori each.

pairof cathodes, pairs. of.- such field: plates, one

pair: overlying1a corresponding: pair of cathodes In such'case, each fieldplate is connected to theor the deflector plates.;may be employed.

next succeeding; secondary cathode in. the. row which. it overlies. Thus, if the field plate 28 comprised two' parts, each overlying a. corre sponding one-of the-deflector plates 26a and; 26b, thetfield? plate overlying: the deflector plate 260.

would. be: connected to the secondary cathode? 20a, and the other field plate WOllldbBf connected to theisecondary'cathode 29b; Each'fieldplate,

then; .would ;vary: in potentialiwith .thesecondary cathodeto.whichitis'connected so that thedeflection, and, hence the amplification, would be increased;

The magneticfocusing' described hereina'bove may be utilized also in multistage multipliers including a single row of secondary cathodes, as illustrated in Fig. 4. The multiplier shown in this figure comprises a photoelectric primary cathode 50, which may be energized by a beam of light emanating from the lamp 5|, a collector electrode or anode 52, and a plurality of secondary electron emissive electrodes 53, the several electrodes being substantially coplanar as shown. A magnet 35 is provided for producing a field symmetrical with respect to the axis of alignment of the electrodes and concave downward with respect to the emissive surfaces of the cathodes, whereby all of the electrons emanating from each of the cathodes are focused upon the corresponding area of the succeeding electrode in each case.

Although specific embodiments of this invention have been shown and described, it will be understood, of course, that they are but illustrative and that various modifications may be made therein without departing from the scope tor. the. secondary. catIiode-.-. 2022; the: secondary cathode 2022 will be more positive:than..theisec andlspirit of'this invention as defined in the appended claims. I

What is claimed is:

1. Electron discharge apparatus comprising an electrode havingan electron emissive surface, a second electrode having an electron receiving surface substantially parallel to and in edge-toedge relation with said first surface, and means adjacent said surfaces for producing a curved magnetic field adjacent said surfaces having its lines of force transverse with respect to the electron path between said electrodes and. concave downward with respect to said surfaces.

2.'An electron multiplier comprising means including an electron emissive surface for producing an electron stream, secondary electron emissive means substantially coplanar with said emissive surface and in alignment therewith, electron receiving means adjacent said electron emissive means, and means for focusing electrons emanating from said surface upon a corresponding area in the plane of said electron emissive means comprising means adjacent said surface and said electron emissive means for producing a substantially semicylindrical magnetic field adjacent said surface and said electron emissive means, concave downward with respect to said surface, and symmetrical with respect to the axis of alignment of said surface and said emissive means.

3. Electron discharge apparatus comprising an elongated substantially plane electrode having an electron emissive surface, electrode means adjacent thereto for energizing said surface to produce electron emission therefrom, an electron receiving means having opposite surfaces one of which is substantially coplanar with said emissive surface and opposite one of the longer sides thereof, said electron receiving means having end portions on opposite sides of a median line extending through said emissive surface and said electron receiving means, and a U-shaped magnet'having its poles opposite said end portions and in f-ace-to-face relation with the other of said opposite surfaces of said electron receiving means.

4. Electron discharge apparatus comprising a series of substantially plane electron emissive means mounted in alignment in coplanar edgeto-edge relation, electrode means adjacent thereto for energizing the first means in said series, a collector electrode in electron receiving relation with the last'means in said series, and means adjacent said emissive means for pro ducing'a semicylindrical magnetic field adjacent said emissive means, said'field being symmetrical with respect to the axis of alignment of said the surfaces in each pair together, and electrode means'adjacent said cathode means for deflecting said stream to vary its division between the surfaces energized thereby.

6. An electron multiplier comprising a plurality of pairs of electrodes having secondary electron emissive surfaces, mounted side by side in two parallel rows, a plurality of field electrodes one opposite each of said pairs of surfaces, a U-shaped magnet having one pole opposite one row of said electrodes and its other pole opposite the other row of said electrodes, means adjacent one end of said rows for producing an electron stream, collector electrodes at the other end of said rows, and means in cooperative relation with said first means for deflecting said stream transversely to the longitudinal axis of said rows, whereby the division of said stream between the pair of electrodes nearest said first means is varied.

7. An electron multiplier comprising a primary cathode, a plurality of substantially coplanar secondary electron emissive surfaces mounted in pairs in two rows on opposite sides of an axis passing through said primary cathode, a pair of collector electrodes in cooperative relation with the pair of said surfaces furthest removed from said cathode, field plates opposite said emissive surfaces, a pair of deflector plates on opposite sides of said axis, adjacent said cathode and substantially coplanar with said surfaces, means adjacent said cathode and said surfaces for producing a substantially semicylin drical magnetic field symmetrical with respect to said axis and concave downward with respect to said surfaces, and, impedance means connecting the surfaces of each of said pairs.

ALBERT M. SKELLETT.

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