Improvements relating to the Production, Regulation, and Utilization of Electric Currents of High Frequency, and to Apparatus therefor.
Year: 1896

page_text: Date of Application, 22nd Sept., 1896-Accepted, 21st Nov., 1896
[Communicated from abroad by NIKOLA TESLA, of 46 East Houston Street,-
New York, United States of America, Electrician.]
Improvements relating to the Production, Regulation, and
Utilization of Electric Currents of High Frequency, and to
Apparatus therefor.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent
Agents, 45 Southampton Buildings, in the County of Middlesex, do hereby
declare the nature of this invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement :-
This invention, subject of the present application, is embodied in certain
improvements in methods of and apparatus for producing, regulating and utilizing
electric currents of high frequency heretofore invented by Nikola Tesla, and
described in British Letters Patent No. 8575, dated May 19, 1891. The method
and apparatus referred to in said patent were devised for the purpose of converting,
supplying and utilizing electrical energy in a form suited for the production of
certain novel electrical phenomena which require currents of high potential and a
higher frequency than can readily or even possibly, be developed by generators of
the ordinary types or by such mechanical appliances as were theretofore known.
The invention referred to was based upon the principle of charging a condenser or
a circuit possessing capacity and discharging the same, generally through the
primary of a transformer, the secondary of which constituted the source of
working current, and under such conditions as to yield a vibratory or rapidly
intermittent discharge current.
The present invention, while aiming to simplify and render more efficient the
apparatus heretofore used, has for its object, primarily, to provide a means for
converting such currents as are generally and most readily obtainable from the
mains of ordinary systems of municipal distribution, into currents of the special
character referred to, and to regulate or control, and utilize such currents in a
simple, economical and efficient manner. The improvements are illustrated
herein in forms of apparatus adapted for use with existing circuits or systems, and
which while constructed and operating on the same general principles are modified
only as may be required by a direct or an alternating source of supply.
The apparatus by which the present improvements are carried out may be
described in general terms as comprising a circuit from a given source of supply,
in which is included or with which is connected any suitable device for making
and breaking such circuit in the manner desired, a condenser arranged so as to be
periodically charged by the said circuit through the instrumentality of the circuit
controller, and a circuit, through which the condenser discharges, of such character
that the discharge will take place in a series of rapidly recurring or intermittent
impulses.
In the drawings which illustrate the invention,
Fig. 1 is a diagram of circuits and apparatus employed with a source of direct
currents. Figs. 2 and 3 are modifications of the same.
Figs. 4, 5 and 6 illustrate the apparatus and circuit connections employed with a
source of alternating current. Figs. 7, 8, 9, 10 are similar views illustrating the
method of and apparatus for regulating the system.

page_text: Figs. 11, 12, 13, 14 and 15 are views illustrating a form of circuit controller for
use with the system and the manner of connecting up and using the same.
When the apparatus is to be employed for the purpose of converting a direct
current of comparatively low potential into one of high frequency, a device in
the nature of a choking coil is interposed in the circuit, in order that advantage
may be taken of the discharge of high electro-motive force, which is manifested
at each break of such circuit for charging a condenser.
It will be apparent from a consideration of the conditions involved, that were
the condenser to be directly charged by the current from the source and then
discharged into its local or discharging circuit, a very large capacity would
ordinarily be required, but by the introduction into the charging circuit of a high
self induction the current of high electro-motive force which is induced at ench
break of said circuit, furnishes the proper current for charging the condenser,
which may, therefore, be small and inexpensive.
Figures 1 and 2 illustrate that part of the improvement which relates to the
conversion of direct or continuous current. Referring to said figures, A designates
any source of direct current. In any branch of the circuit from said source, such,
for example, as would be formed by the conductore A" A" from the mains A' A',
and the conductors K K are placed self induction or choking coils B B and any
proper form of circuit controlling device as C. This device in the present instance
is shown as an ordinary metallic disk or cylinder with teeth or separated
segments D D, E E, of which one or more pairs as E E, diametrically opposite,
are integral or in electrical contact with the body of the cylinder, so that when
the controller is in the position in which the two brushes F, F, bear upon two
of said segments E E, the circuit through the choking coils B B will be closed.
The segments D, D, are insulated, and while shown in the drawings as of
substantially the same length of are as the segments E E, this latter relation may
be varied at will to regulate the periods of charging and discharging.
The controller is designed to be rotated by any proper device, such for example,
as an electro-magnetic motor, as shown in Figure 2, receiving current either from
the main source or elsewhere.
Around the controller C or in general having its terminals connected with the
circuit on opposite sides of the point of interruption, is a condenser H, or a circuit
of suitable capacity, and in series with the latter the primary K of a transformer,
the secondary L of which constitutes the source of the currents of high frequency.
L' indicates the circuit from the secondary and may be regarded as the working
circuit.
It will be observed that since the self induction of the circuit through which
the condenser discharges, as well as the capacity of the condenser itself, may be
given practically any desired value, the frequency of the discharge current may
be adjusted at will.
In the operation of this apparatus the controller closes the charging circuit and
then interrupts the same. When the break occurs the accumulated energy in the
said circuit charges the condenser. Then while the charging circuit is again
completed the condenser discharges through the primary K, by a succession of
rapid impulses. These operations are maintained by the action of the controller.,
A more convenient and simplified arrangement of the apparatus is shown in
Figure 2. In this case the small motor G which drives the controller has its field
coils M M' in derivation to the main circuit, and the controller C and condenser H,
are in parallel in the field circuit between the two coils. In such case the field
coils M M take the place of the choking coils B.
In this arrangement, and in fact, generally, it is preferable to use two condensers
or a condenser in two parts, and to arrange the primary coil of the transformer
between them. The interruption of the field eircuit of the motor should be so
rapid as to permit only a partial demagnetization of the cores; these latter,
moreover, should in this specific arrangement, be laminated.
In lieu of connecting the field coils of the motor only with the charging circuit

page_text: This
to raise the self induction therein, the motor may be connected in other ways,
that is to say, its armature only may be connected with the circuit, or its field
and armature coils may be in series and both connected with such circuit.
latter arrangement is illustrated in Figure 3, in which a terminal of the circuit A¹¹
is connected to one of the binding posts of the motor from which the circuit is
led through one field coil M, the brushes and commutator C¹ and the other field
coil M, and thence to a brush F which rests upon the controller disk or cylinder C.
The other terminal of the circuit connects with a second brush F¹ bearing on the
controller, so that the current which passes through and operates the motor is
periodically interrupted.
As an illustration of the various uses to which the apparatus may be put, the
secondary I. is shown in this figure as connected to two plates P, P, of any
suitable character between which a current of air is maintained by a fan on the
shaft of the motor G, for developing ozone or for similar purposes.
When the potential of the source of current periodically rises and falls, whether
with reversals or not is immaterial, it is essential to economical operation that
the intervals of interruption of the charging circuit should bear a definite time
relation to the period of the current, in order that the effective potential of the
itopulses charging the condenser may be as high as possible. In case, therefore,
an alternating or equivalent electromotive force be employed as the source of
supply, a circuit controller is used which will interrupt the charging circuit at
instants predetermined with reference to the variations of potential therein.
A convenient, and probably the most practicable means for accomplishing-this
is a synchronous motor connected with the source of supply and operating a circuit
controller which first interrupts the charging current at or about the instant of
bighest intensity of each wave and then permits the condenser to discharge the
energy stored in it, through its appropriate circuit. Such apparatus, which may
be regarded as typical of the means for accomplishing this purpose, is illustrated
in Figures 4, 5 and 6.
In Fig. 4, A"A" are the conductors taken from the mains of any alternating
current generator A, and for raising the potential of such current a transformer is
employed represented by the primary B and secondary B¹.
The circuit of the secondary includes the energizing coils of a synchronous motor G,
and a circuit controller C fixed to the shaft of the motor.
An insulating arm O, stationary with respect to the motor shaft and adjustable
with reference to the poles of the fixed magnets, carries two brushes F F which
bear upon the periphery of the disk C. With the parts thus arranged, the secondary
circuit is completed through the coils of the motor whenever the two brushes rest
upon the uninsulated segments of the disk, and interrupted through the motor at
other times.
By
Such a motor, if properly constructed, in well understood ways, maintains very
exact synchronism with the alternations of the source, and the arm may, there-
fore, be adjusted to interrupt the current at any deterinined point of its waves.
the proper relations of insulated and conducting segments, and the motor poles, the
current may be interrupted twice in each complete wave at or about the points of
bighest intensity.
In order that the energy stored in the motor circuit may be utilized at each break
to charge the condenser H, the terminals of the latter are connected to the two
brushes F F or to points of the circuit adjacent thereto, so that when the circuit
through the motor is interrupted the terminals of the motor circuit will be connected
with the condenser. The discharge of the condeuser takes place through the
primary K, the circuit of which is completed simultaneously with the motor circuit
and interrupted while the motor circuit is broken and the condenser being charged.
The secondary impulses of high potential and great frequency are available for the
operation of vacuum tubes P, single terminal lamps R, and other novel and useful
purposes.
It is obvious that the supply current need not be alternating, provided it be

page_text: converted or transformed into an alternating current, before reaching the controller.
For example, the present improvements are applicable to various forms of rotary
transformers as is illustrated in Figs. 5 and 6.
G¹ designates a continuous current motor, here represented as having four field
poles wound with coils E" in shunt to the armature. The line wires A" A" connect
with the brushes bb bearing on the usual commutator.
On an extension of the motor shaft is a circuit controller composed of a cylinder,
the surface of which is divided into four conducting segments c, and four
insulating segments d, the former being diametrically connected in pairs as showu
in Fig. 6.
Through the shaft run two insulated conductors ee from any two commutator
segments ninety degrees apart, and these connect with the two pairs of segments c,
respectively. With such arrangement, it is evident that any two adjacent
segments cc become the terminals of au alternating current source, so that if two
brushes F F be applied to the periphery of the cylinder they will take off current
during such portion of the wave as the width of segment and position of the brushes
may determine. By adjusting the position of the brushes relatively to the cylinder,
therefore, the alternating current delivered to the segments ac may be interrupted
at any point of its waves.
When
While the brushes F F are on the conducting segments the current which they
collect stores energy in a circuit of high self-induction formed by the wires fi,
self-induction coils SS, the conductors A A", the brushes and commutator.
this circuit is interrupted by the brushes FF, passing onto the insulating seg-
ments of the controller, the high potential discharge of this circuit stores energy
in the condensers H H which then discharge through the circuit of low self-induction
containing the primary K. The secondary circuit contains any devices as P, R,
for utilizing the current.
In some cases the energy delivered by the system may be readily and economically
regulated. It is well known that every electric circuit, provided its ohmic resistance
does not exceed certain definite limits, has a period of vibration of its own analogous
to the period of vibration of a weighted spring. In order to alternately charge a
given circuit of this character by periodic impulses impressed upon it and to
discharge it most effectively, the frequency of the impressed impulses should bear
a definite relation to the Trequency of vibration possessed by the circuit itself.
Moreover, for like reasons, the period of vibration of the discharge circuit should
bear a similar relation to the impressed impulses or the period of the charging
circuit. When the conditions are such that the general law of harmonic vibrations
is followed, the circuits are said to be in resonance or in electro-magnetic synchronism,
and this condition of the system is found to be highly advantageous.
In carrying out the invention, therefore, the electrical constants should be so
adjusted that in normal operation the condition of resonance is approximately
attained. To accomplish this, the number of impulses of current directed into the
charging circuit per unit time is made equal to the period of the charging circuit
itself, or, generally, to a harmonic thereof, and the same relations are maintained
between the charging and discharge circuit. Any departure from this condition
will result in a decreased output, and this fact is taken advantage of in regulating
such output by varying the frequencies of the impulses or vibrations in the several
circuits.
Inasmuch as the period of any given circuit depends upon the relations of its
resistance, self-induction and capacity, a variation of any one or more of these may
result in a variation in its period. There are, therefore, various ways in which
the frequencies of vibration of the several circuits in the system may be varied,
but the most practicable and efficient ways of accomplishing the desired result are
the following:
(a) Varying the rate of the impressed impulses or those which are directed from
the source of supply into the charging circuit, as by varying the speed of the
commutator or other circuit controller.

page_text: (b) Varying the self-induction of the charging circuit.
(c) Varying the self-induction or capacity of the discharge circuit.
To regulate the output of a single circuit which has no vibration of its own, by
merely varying its period would evidently require, for any extended range of
regulation, a very wide range of variation of period. But in the system described,
a very wide range of regulation of the output may be obtained by a very slight
change of the frequency of one of the circuits when the above mentioned rules
are observed.
Figs. 7, 8, 9 and 10 illustrate some of the more practicable means for effecting
the regulation, as applied to a system deriving its energy from a source of direct
currents.
In each of the figures A"A" designate the conductors of a supply circuit of
continuous current, & a motor connected therewith in any of the usual ways, and
operating a current controller C which serves to alternately close the supply
circuit through the motor or through a self-induction coil, and to connect such
motor circuit with a condenser H, the circuit of which contains a primary coil K,
in proximity to which is a secondary coil L serving as the source of supply to the
working circuit or that in which are connected up the devices P R for utilizing
the current.
In order to secure the greatest efficiency in a system of this kind, it is essential,
as before stated, that the circuits, which mainly as a matter of convenience are
designated as the charging and the discharge circuits, should be approximately in
resonance or electro-magnetic synchronism. Moreover, in order to obtain the
greatest output from a given apparatus of this kind it is desirable to maintain
as high a frequency as possible.
The electrical conditions, which are now well understood, having been adjusted
to secure, as far as practical considerations will permit, these results, the regulation
of the system is effected by adjusting its elements so as to depart in a greater or
less degree from the above conditions with a corresponding variation of output.
For example, as in Figure 7 the speed of the motor, and consequently of the
controller, may be varied in any suitable manner, as by means of a rheostat R¹ in
a shunt to such motor, or by shifting the position of the brushes on the main
commutator of the motor or otherwise. A very slight variation in this respect by
disturbing the relations between the rate of impressed impulses and the vibration
of the circuit of high self-induction into which they are directed, causes a marked
departure from the condition of resonance and a corresponding reduction in the
amount of energy delivered by the impressed impulses to the apparatus.
A similar result may be secured by modifying any of the constants of the
local circuits as above indicated. For example, in Figure 8 the choking coil B
is shown as provided with an adjustable core N', by the movement of which
into and out of the coil the self-induction, and consequently the period of the
circuit containing such coil, may be varied.
As an example of the way in which the discharge circuit or that into which
the condenser discharges, may be modified to produce the same result, there is
shown in Figure 9 an adjustable self-induction coil R" in the circuit with the
condenser, by the adjustment of which coil the period of vibration of such circuit
may be changed.
The same result would be secured by varying the capacity of the condenser,
but if the condenser were of relatively large capacity this might be an objectionable
plan, and a more practicable method is to employ variable condenser in the
secondary or working circuit, as shown in Figure 10. As the potential in this
circuit is raised to a high degree, a condenser of very small capacity may be
employed, and if the two circuits, primary and secondary, are very intimately and
closely connected, the variation of capacity in the secondary is similar in its effects
to the variation of the capacity of the condenser in the primary. As a means well
adapted for this purpose two metallic plates S¹ S₁ adjustable to and from each
other and constituting the two armatures of the condenser are shown.

page_text: The description of the means of regulation is confined herein to a source of
supply of direct current, for to such it more particularly applies, but it will be
understood that if the system be supplied by periodic impulses from any source
which will effect the same resuits, the regulation of the system may be effected by
the method herein described.
The circuit controller or the device which ensures the proper charging and
discharging of the condenser may be of any construction that will perform the
functions required of it. In illustration of the principle of construction and mode
of operation, reference has been made only to forms of mechanism that make and
break metallic contacts, but there need be no actual metallic contact, if provision
be made for the passage of a spark between separated conductors. Such a device
is illustrated in Figs. 11 to 15.
A designates, in Fig. 11, a generator having a commutator a' and brushes all
bearing thereon, and also collecting rings 6, 61, from which an alternating current
is taken by brushes b¹ in the well understood mauner.
The circuit controller is mounted, in part, on an extension of the shaft c¹ of the
generator, and in part on the frame of the same, or on a stationary sleeve
surrounding the shaft. Its construction, in detail, is as follows:-
el is a metal plate with a central hub e" which is keyed or clamped to the
shaft c. The plate is formed with segmental extensions corresponding in number
to the waves of current which the generator delivers. These segments are
preferably cut away, leaving only rims or frames, to oue of the radial sides of
which are secured bent metal plates i which serve as vanes to maintain a
circulation of air when the device is in operation.
The segmental disk and vanes are contained within a close insulated box or
case mounted on the bearing of the generator, or in any other proper way, but
so as to be capable of angular adjustment around the shaft. To facilitate such
adjustment, a screw rod /, provided with a knob or handle, is shown as passing
through the wall of the box. The latter may be adjusted by this rod, and when
in proper position may be held therein by screwing the rod down into a depression
in the sleeve or bearing as shown in Fig. 11.
Air passages 9 g are provided at opposite ends of the box through which air is
maintained in circulation by the action of the vanes.
Through the sides of the box f, and through insulating gaskets h, when the
material of the box is not a sufficiently good insulator, extend metallic terminal
plugs 1, 1, with their ends in the plane of the conducting segmental disk e' and
adjustable radially towards and from the edges of the segments.
Devices of this character are employed in the manner illustrated in Fig. 13.
A, in this figure, represents any source of alternating current, the potential of
which is raised by a transformer of which B is the primary and B¹ the secondary.
The ends of the secondary circuit s are connected to the terminal plugs 1, 1, of
an apparatus similar to that of Figures 11 and 12, and having segments rotating
in synchronism with the alternations of the current source, preferably, as above
described, by being mounted on the shaft of the generator, when the conditions
so permit.
The plugs 1, 1, are then adjusted radially so as to approach more or less the path
of the outer edges of the segmental disk, and so that during the passage of each
segment in front of a plug a spark will pass between them, which completes the
secondary circuit, s. The box, or the support for the plugs 1, is adjusted angularly
so as to bring the plugs and segments into proximity at the desired instants
with reference to any phase of the current wave in the secondary circuit, and
fixed in position in any proper manner.
To the plugs L, l, are also counected the terminals of a condenser or condensers,
so that at the instant of the rupture of the secondary circuit & by the cessation
of the sparks the energy accumulated in such circuit will rush into, and charge,
the condenser.
A path of low self-induction and resistance, including a primary K of a few

page_text: turns, is provided to receive the discharge of the condenser, when the circuit s
is again completed by the passage of sparks, the discharge being manifested as a
succession of extremely rapid impulses.
By means of this apparatus effects of a novel and useful character are
obtainable, but to still further increase the efficiency of the discharge or working
current, there may be in some instances provided a means for further breaking
up the individual sparks themselves. A device for this purpose is shown in
Figures 14 and 15.
The box or case in these figures is fixedly secured to the frame or bearing
of the generator or mctor which rotates the circuit controller in synchronisni
with the alternating source. Within said box is a disk e fixed to the shaft c'
with projections d' extending from its edge parallel with the axis of the shaft..
A similar disk el on a spindle d" in face of the first is mounted in a bearing in
the end of the box f with a capability of rotary adjustment.
The ends of the projections d' are deeply serrated or several pins or narrow
projections placed side by side, as shown in Fig. 14, so that as those of the
opposite disks pass each other a rapid succession of sparks will pass from the
projections of one disk to those of the other.
The invention is not limited to the precise devices or forms of the devices shown
and described. For example, when the source of supply is a circuit of high self-
induction no special choking coils or the like need be employed. So, too, the
condenser as a distinctive apparatus may be dispensed with when the capacity of
its circuit is sufficiently great to accomplish the desired result. The circuit
controller may, as already explained, be very greatly modified and varied in
construction and principle of operation without departure from the invention.
In the illustrations given of the circuit controller, the contacts and insulating
spaces are arranged for charging and discharging a single condenser, but it is.
obvious that a single motor and circuit controller may be used to operate more than
one condenser, by charging one while discharging the other or others.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is:-
1. The apparatus herein described for converting electric currents of the kind
generally obtainable from municipal systems of electric distribution, into currents
of high frequency, comprising in combination a circuit of high self-inductior, a
circuit controller adapted to make and break such circuit, a condenser into which
the said circuit discharges when interrupted, and a transformer through the primary
of which the condenser discharges, as set forth.
2. The combination with a circuit of high self-induction and means for making
and breaking the same, of a condenser around the point of interruption in the
said circuit, and a transformer the primary of which is in the condenser circuit, as
described.
3. The combination with a circuit having a high self-induction, of a circuit
controller for making and breaking said circuit, a motor for driving the controller,
a condenser in a circuit connected with the first around the point of interruption
therein, and a transformer the primary of which is in circuit with the condenser, as
set forth.
4. The combination with an electric circuit of a controller for making and
breaking the same, a motor included in or connected with said circuit so as to
increase its self-induction and driving the said controller, a condenser in a circuit
around the controller, and a transformer through the primary of which the
condenser discharges, as set forth.
5. The combination with a circuit of direct current, of a controller for
making and breaking the same, a motor having its field or armature coils or
both included in said circuit and driving said controller, a condeuser connected

page_text: with the circuit around the point of interruption therein, and a transformer, the
primary of which is in the discharge circuit of the condenser, as set forth.
6. The method herein described of converting alternating currents of relatively
low frequency into currents of high frequency, which consists in charging a
condenser by such currents of low frequency during determinate intervals of
each wave of said current, and discharging the condenser through a circuit of
such character as to produce therein a rapid succession of impulses, as set forth.
7. The combination with a source of alternating current, a condenser, a circuit
controller adapted to direct the current during determinate intervals of each wave
into the condenser for charging the same, and a circuit into which the condenser
discharges, as set forth.
8. The combination with a source of alternating current, a synchronous motor
operated thereby, a circuit controller operated by the motor and adapted to
interrupt the circuit through the motor at determinate points in each wave, a
condenser connected with the motor circuit and adapted on the interruption of the
same to receive the energy stored therein, and a circuit into which the condenser
discharges, as set forth.
9. The combination with a source of alternating current, a charging circuit in
which the energy of said current is stored, a circuit controller adapted to interrupt
the charging circuit at determinate points in each wave, a condenser. for receiving,
on the interruption of the charging circuit, the energy accumulated therein, and a
circuit into which the condenser discharges when connected therewith by the circuit
controller, as set forth.
10. The method of regulating the energy delivered by a system for the production
of high frequency currents, and comprising a supply circuit, a condenser, a circuit
through which the same discharges, and means for controlling the charging of the
condenser by the supply circuit and the discharging of the same, the said method
consisting in varying the relations of the frequencies of the impulses in the circuits
comprising the system, as set forth.
11. The method of regulating the energy delivered by a system for the production
of high frequency currents comprising a supply circuit of direct currents, a condenser
adapted to be charged by the supply circuit and to discharge through another
circuit, the said method consisting in varying the frequency of the impulses of
current from the supply circuit, as set forth.
12. The method of producing and regulating electric currents of high frequency
which consists in directing impulses from a supply circuit into a charging
circuit of high self-induction, charging a condenser by the accumulated energy
of such charging circuit, discharging the condenser through a circuit of low
self-induction, raising the potential of the condenser discharge and varying the
relations of the frequencies of the electrical impulses in the said circuits, as set
forth.
13. The combination with a source of current, of a condenser adapted to be
charged thereby, a circuit into which the condenser discharges in a series of rapid
impulses, and a circuit controller for effecting the charging and discharge of said
condenser, composed of conductors movable into and out of proximity with each
other, whereby a spark may be maintained between them and the circuit closed
thereby during determined intervals, as set forth.
14. The combination with a source of alteruating current, of a condenser adapted
to be charged thereby, a circuit into which the condenser discharges in a series
of rapid impulses, and a circuit controller for effecting the charging and discharge
of said condenser composed of conductors movable into and out of proximity
with each other in synchronism with the alternations of the source, as set forth.
15. A circuit controller for systems of the kind described, comprising in com-
bination a pair of angularly adjustable terminals and two or more rotating
conductors mounted to pass in proximity to the said terminals, as set forth.
16. A circuit controller for systems of the kind described, comprising in

page_text: combination two sets of conductors, one capable of rotation and the other of
angular adjustment whereby they may be brought into and out of proximity to
each other at determinate points and one or both being subdivided so as to present.
a group of conducting points, as set forth.
Dated this 22nd day of September 1896.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.