Eberhart's Manual of High Frequency
Noble M. Eberhart
Types of Apparatus; D’Arsonval Type; Tesla Transformers; Impedance;
Direct D’Arsonval Currents; Auto-Conduction; Auto-Condensation; Resonator
of Oudin; Tuning Coils; Measuring the Current.
Types of Apparatus. There is no intention
on the part of the author to encumber this volume with lengthy descriptions
of apparatus. For such information, the reader is referred to the
manufacturers of electrical outfits.
All high frequency instruments, however, are constructed
along two principal types -- that of D’Arsonval and that of Tesla -- and
these should be understood by the high frequency operator, since all machines
represent one or the other or a combination of these types.
In connection or combination with them, a third instrument,
the resonator of Oudin, is in such common use that it also calls for special
description. In speaking of high frequency currents, to be specific,
we should always state the form of current used, as D’Arsonval high frequency,
or Tesla high frequency, etc.
Fig. 11 and 12 - Portable Coils.
The D’Arsonval type of apparatus as it is manufactured
today consists of a combination of the D’Arsonval solenoid and an improved
type of the Oudin resonator. The Oudin current derived from this
type of apparatus serves to energize vacuum electrodes, the spray electrode,
the so-called “static spark” electrode, the portable ozone inhaler, and
also is the current which is utilized for obtaining the “cold” fulguration
spark. The D’Arsonval solenoid in this instance delivers a comparatively
low potential and high milliamperage current.
Fig. 13 - Diagram of D’Arsonval Type.
The Tesla type of apparatus is designed along the same
general lines as is the D’Arsonval and has the same wide range of usefulness,
but the general characteristics of the current are different in that the
Tesla type of apparatus delivers a high potential, low milliamperage current.
If every physician employing high frequency apparatus
was aware of this difference it is the author’s opinion that many cases
of misunderstanding and dissatisfaction would be cleared away.
In other words, the milliamperage reading of the meter
is not an indicator of the capacity or power of the apparatus. This
means that 500 milliamperes of Tesla high frequency current is just as
capable of producing deep constitutional effects as 1,500 milliamperes
on a D’Arsonval high frequency apparatus.
The relative merit of the “Tesla” versus the “D’Arsonval”
apparatus more particularly as regards auto-condensation and diathermy
has been the subject of numerous discussions among electro-therapeutists.
The thickness of the di-electric (auto-condensation cushion) has also entered
into this discussion. It has been proved that either type is capable
of producing results and in consequence thereof the author does not feel
capable of choosing himself as the sole arbitrator in deciding which is
better. He however, for the past three years has been employing the
Tesla type of apparatus in his individual practice and has been deriving
eminent satisfaction from its use. He employs a cushion of approximately
three inches in thickness– this size being endorsed by the standardization
committee of the American Electro-Therapeutic Association.
As will be stated in Chapter VI, the author originated
the thin cushion as well as the portable thick pad, and the method of making
these different forms is given. He bows to the ruling of the committee
referred to above and now employs only the thicker cushion.
The D’Arsonval Current is one of high frequency, not very
high voltage, and high amperage.
It is administered as a bi-polar method, thereby producing
constitutional effects. D’Arsonval started with an induction coil
attached to the direct current. The terminals of the secondary coil
were attached to the inner layers of two Leyden jars, thereby charging
one of them positively and the other negatively. In the circuit between
these two layers was placed an adjustable spark gap. Between the
outer layers of the jars was placed a solenoid or coil consisting of fifteen
to twenty turns of coarse copper wire. This combination of condensers
connecting on one side through a spark gap, and on the other through a
coil of wire, is an absolute necessity in order to obtain the D’Arsonval
current, and it therefore constitutes this type. See Fig. 13.
When the positive layer of the first receives a sufficiently
high charge, it jumps across the spark gap to neutralize the negative charge
in the second jar. Immediately the positive charge on the outer layer
of the second jar is released and passes through the coil of wire to neutralize
the negative charge on the outer layer of the first jar, and as it passes
through this coil or solenoid, it produces a high frequency current, keeping
in mind the fact that the oscillation back and forth through the condensers
exists as described in Chapter II. The patient is connected on that
side of the condensers that discharges through the coil and is really on
a shunt or switch from that part of the circuit, and the reason the patient
receives any current at all, is because the solenoid possesses the property
known as self-inductance, which impedes the passage of the current, allowing
part of it to go through the lesser resistance in the patient’s circuit.
The process of interfering with the current as a result of the self-inductance
is called impedance.
The Tesla Transformer and Coil. Tesla started
with the alternating current, and by referring to our definition of high
frequency currents (Chapter I), it is seen that all that was required was
the increasing of the frequency to a point which we properly call high.
To do this, he used as a primary , a coarse coil of wire consisting of
a few turns only, while the secondary coil consisted of an extraordinary
number of turns of very fine wire–the result being that the current induced
therein was of very high tension and very high frequency. The Tesla
transformer or coil is especially adapted to the alternating current.
It is employed in all of the portable high frequency apparatus on the market.
The Tesla primary resembles the D’Arsonval current except the amperage
is less. Fig 14 shows one method of evolving the various currents.
Fig. 14 - Diagram of Tesla Type
Administration of the D’Arsonval Current.
There are three principal ways in which this current is applied to the
body; first, the direct bi-polar method, which has also been subdivided
into two or three forms; second, auto-conduction, and third, auto-condensation.
In the first method, the patient is directly connected to the terminals
of the apparatus. Whether the patient holds the two electrodes, or
whether he is attached on one pole, while the other pole is connected with
an electrode in the hands of the operator, the method is still called direct
application. It should be borne in mind that the direct D’Arsonval
current is also known under several other terms, such as diathermy, electro-coagulation
and thermo-penetration. See Chapter XI. Referring back for
a moment to the component elements of the D’Arsonval apparatus. It is seen
that solenoids and condensers are fundamental parts. In the elementary
D’Arsonval type we have one set of condensers and one solenoid. It
would appear, therefore, that the inventor said to himself; “If one solenoid
gives a current of high frequency, let us add another solenoid and see
what that will do.” Thus the second type, auto-conduction, is constructed,
and a large solenoid is connected in the shunt which forms the patient’s
circuit, and it is made so large that the patient may be placed within
this coil or cage when it is found that as the high frequency currents
traverse the coil, other high frequency currents are induced in the body
of the patient. This is auto-conduction.
Auto-condensation. Again reverting to our
elementary type instead of using the second solenoid, the next arrangement
was the use of an extra condenser, and the current passes from one terminal
into one plate of the condenser, while the other plate was formed by the
body of the patient, hence the term auto-condensation.
Fig. 15 - Diagram of Oudin Resonator.
Oudin’s Resonator. Oudin discovered that
with a coil of wire properly tuned or adjusted to the coarse coil or solenoid
of D’Arsonval, the electrical currents of the latter produced currents
of such strength that they might be taken from the terminal of the larger
solenoid and applied to the body. They are of high frequency, high
voltage and low amperage, resembling the Tesla secondary. As ordinarily
constructed, the D’Arsonval apparatus and the resonator are combined in
one instrument; the resonator proper consisting of a large coil of fine
wire placed above the coarse solenoid of the D’Arsonval machine.
See Fig. 15.
Tuning coils. The best results in resonance
are obtained when the coils are properly adjusted and attuned to one another.
To facilitate this, the wire that passes from one side of the solenoid
is attached to a sliding metal finger, which may be moved up or down on
the solenoid, and thereby increase or decrease the number of turns of wire
employed. This permits proper adjustment of the coils, at the same
time it is found that the greater the number of turns included, the sharper
the resulting spark, and vice versa.
Measuring High Frequency Currents. High frequency
currents cannot be measured with an ordinary meter. For D’Arsonval
currents the method customarily employed is the use of a hot wire meter.
This is really a thermostat instead of an electrical device. It is
based upon the fact that the passage of the high frequency current gives
rise to heat and this heat causes expansion in a platinum wire and thereby
deflects the needle in proportion. Hot wire meters are faulty, but
give a relative idea of dosage when employed on the same apparatus.
One is shown in Fig. 16. Other methods of measuring these currents
are by Gaiffe and Meylon’s induction amperemeter, which “measures the repulsive
force between the original current and the current which it induces in
a coil attached to the indicator.”
Fig. 16 - Hot Wire Meter.
Fig. 16a - Air Cooled and Air Cleaned Spark Gap.
Fig. 17 - Large Combined Tesla, Oudin and D’Arsonval Type Coil.