Diathermy apparatus with automatic tuning for applicator head

A diathermy apparatus has a power circuit operative at a selected, fixed frequency. An applicator head, for providing therapeutic treatment, has an irradiating portion. A transmission line connects the power circuit and applicator head, and is of a length so that, at the frequency, a selected minimum power is delivered to the applicator head when unloaded, the length further being such that a selected maximum amount of power is delivered to the applicator head when it is in a loaded position in close proximity to a patient load. The diathermy apparatus also includes a cabinet and portable base, wherein the portable base mounts the applicator head, and provides a carriage for the cabinet. The applicator head has an internal fan for cooling components of the applicator head. A display is provided for displaying the actual power consumed by the patient load. A processor independently controls the pulse modulator and power circuit in digital increments on a selected scale.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to a diathermy apparatus which 
therapeutically heats internal body tissue by irradiating the tissue with 
RF energy. In particular, the present invention discloses a method and 
apparatus for accurately measuring and controlling the amount of RF power 
being absorbed by the body tissue with the irradiating region of the 
diathermy apparatus. Specifically, the present invention relates to a 
diathermy apparatus which automatically tunes an applicator head of the 
apparatus. 
2. Description of the Related Art 
Medical diathermy involves the use of high frequency electric current for 
the therapeutic treatment of body tissue. This technique involves the 
transcutaneous transmission of high frequency energy to internal body 
tissues. The irradiated RF energy generates heat within the internal body 
tissue, having a therapeutic effect. This deep heating action produced by 
the diathermy apparatus is used to treat a number of varied ailments. 
A diathermy apparatus typically generates high frequency electric currents 
which are provided to an applicator head for controllable application to 
the body tissue to be treated. The high frequency currents produced in a 
diathermy apparatus typically have a standard frequency of 27.12 MHz, 
which is within the permissible frequency range allocated for diathermy 
service. At this frequency, nerves and muscles are not adversely 
stimulated by the radiated energy, and the temperature produced in the 
internal body tissue is well below that required to destroy the tissue or 
impair its vitality. 
Prior art diathermy machines typically are constructed of a single cabinet 
which houses the electrical circuitry and the display portion of the 
shortwave electrical therapeutic apparatus. Typically, a pair of movable 
arms extend outwardly from the cabinet, each of which positions a 
diathermy head at its outer end. 
The applicator head of the diathermy apparatus includes a radiating 
electrode which is comprised of an induction coil that generates 
electromagnetic and electrostatic energy in response to the high frequency 
electric currents flowing through the electrode. The generated 
electromagnetic and electrostatic energy is then controllably applied by 
the applicator head to the body of the patient. This energy causes heat to 
be generated in the internal body tissue, which is within the radiating 
region of the head. U.S. Pat. No. 3,800,802 entitled "Short-Wave Therapy 
Apparatus" to Berry, et al., issued Apr. 2, 1974, and U.S. Pat. No. 
4,210,152 to Berry entitled "Method and Apparatus for Measuring and 
Controlling the Output Power of a Shortwave Therapy Apparatus", issued 
Jul. 1, 1980, disclose diathermy machines which are utilized to apply RF 
energy to the human body for therapeutic purposes. These patents are 
incorporated herein by reference. 
Of the energy generated by a diathermy apparatus, only the electromagnetic 
energy is useful in therapy. The electrostatic energy field that is 
generated simply heats the surface area of the human skin without deep 
penetration, and is therefore undesirable. Electrostatic shields, of the 
type shown, in U.S. Pat. No. 4,068,292 to Berry, et al. entitled 
"Electrostatic Shield for Diathermy Treatment Head", issued Jan. 10, 1978, 
and U.S. Pat. No. 4,281,362 to Berry entitled "Electrostatic Shield for 
Diathermy Treatment Head", issued Jul. 28, 1981, are conventionally used 
to attenuate the electrostatic energy field. These patents are 
incorporated herein by reference. U.S. Pat. No. 4,510,937 to Rogers 
entitled "Method and Apparatus for Operating Dual Diathermy Applicator 
Heads in Close Proximity to One Another", issued Apr. 16, 1985, discloses 
a method and apparatus for simultaneously operating two diathermy 
treatment heads in close proximity without interference caused by phase 
and frequency differences. This patent is incorporated herein by 
reference. 
Elimination of the electrostatic field, through the use of an electrostatic 
shield, significantly improves the operating efficiency of the diathermy 
apparatus and the accuracy of the power measurement. Particularly, the 
interposition of an electrostatic shield between the generating electrode 
and the applicator head and the treated body tissue significantly reduces 
the electrostatic (capacitive) coupling between the body tissue and the 
applicator head, thereby making the reactive parameters of the head less 
responsive to the surface characteristics of the human load within the 
irradiating region of the applicator head. By eliminating capacitive 
coupling between the applicator head and the body tissue, the operating 
parameters of the diathermy apparatus no longer vary erratically in 
response to the surface characteristics of the load within the irradiating 
region of the head. Since the operating parameters of the device do not 
vary in response to the surface characteristics of the load, the level of 
power being provided to the applicator head only varies in response to the 
level of power actually being absorbed by the treated body tissue. While 
the introduction of body tissue into the irradiating region of the 
applicator head still causes some minor disturbances in the electrical 
operation of the power generating equipment, these disturbances are much 
smaller in magnitude and can be accurately measured. Furthermore, these 
minor disturbances are predictable and can be accounted for during the 
power computation. 
Elimination of the electrostatic field also stabilizes the operation of the 
diathermy apparatus because the applicator head is less likely to be 
detuned from resonance on the introduction of a load into the irradiating 
region of the head. Therefore, it is easier to keep the current voltage 
locked in phase, thereby greatly enhancing the operation of the diathermy 
apparatus and improving the accuracy of the power measurement. 
In order to properly and efficiently utilize the electromagnetic field that 
is generated by the applicator head of the diathermy apparatus, the 
circuitry associated with the apparatus should be tuned and the power 
applied to the patient should be closely controlled at a desired level. As 
the patient moves, or the body temperature or circulation of the patient 
changes, the load can vary rather widely. To compensate for such expected 
changes in the load, tuning devices are desirable because they 
continuously maintain the head tuned to a resonate condition to assure 
maximum power transfer from the applicator head to the patient load. 
In the past, a variety of mechanical tuning components have been utilized 
for tuning the applicator head to a resonate condition. For example, 
variable capacitors have been utilized so that an operator of the 
diathermy apparatus could manually adjust the capacitor to maintain the 
device in a tuned state. Many such devices utilized a servo mechanism to 
achieve the tuning. Typically, the prior art utilizes a variable capacitor 
and a mechanical motor for physically driving the capacitor. The motor is 
coupled to a servo mechanism which controls a tuning element in the 
applicator head. The tuning element (e.g., variable capacitor) is varied 
in order to keep the applicator head in electrical resonance, thereby 
maintaining phase lock between the sensed current and voltage, and thus 
maintaining the amount of power being absorbed by the treated body tissue 
at a desired level. 
The mechanical tuning mechanisms utilized in the prior art which require 
the operator to continuously vary the power are undesirable because of the 
very requirement that the operator must continually monitor and adjust the 
device. Those prior art devices requiring variable capacitors, servo 
mechanism and motors are overly cumbersome, require multiple components, 
and increase the overall expense of the device, and are therefore 
undesirable. 
The need exists for a diathermy apparatus for generating and providing RF 
power in a simple manner. The need also exists for a diathermy apparatus 
which is more portable than prior art machines, and which automatically 
tunes the diathermy apparatus in a simple and efficient manner. The need 
also exists for a diathermy apparatus which easily and accurately displays 
on visual presentation of the actual power being used by a satellite load. 
These and other needs are met by the unique diathermy apparatus of the 
present invention while the foregoing and other drawbacks of the prior art 
are overcome. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an efficient diathermy 
apparatus. 
It is an object of the present invention to automatically tune an 
applicator head of a diathermy apparatus. 
It is an additional object of the present invention to provide a diathermy 
apparatus which is portable. 
It is a further object of the present invention to provide a diathermy 
apparatus which is easy to operate. 
It is another object of the present invention to visually display a 
representation of power generated by a diathermy apparatus and consumed by 
a patient load. 
It is an additional object of the present invention to provide a diathermy 
apparatus having a cabinet which is removable from a portable housing, so 
that the diathermy apparatus can be utilized in the field. 
These and other objects are achieved by a unique diathermy apparatus for 
applying RF energy to a load of human tissue for therapeutic purposes. The 
apparatus of the present invention has a cabinet for housing the control 
circuitry of the apparatus. A control panel is provided at one face of the 
housing for presenting display areas and input keys and switches. Each of 
a pair of handles is also provided on the control panel face for gripping 
by an operator or user when moving the housing. Each of a pair of 
transmission lines extends from the control circuitry within the housing 
to a respective applicator head located remotely from the housing. 
The diathermy apparatus of the present invention also provides a portable 
base constructed in the form of a generally rectangular box having an open 
top. Wheels, for portability, are provided at a lower portion of the 
portable base. A pair of movable arms extend outwardly from one side of 
the portable base. Each of the diathermy applicator heads is mounted on an 
outer end of a respective one of the arms. The open top of the portable 
base is dimensioned so as to snugly receive the diathermy cabinet. When 
inserted into the portable base, the control panel is accessible at the 
open top of the portable base. The handles on the face of the control 
panel may be grasped by an operator for insertion and removal of the 
cabinet. Such a construction permits the cabinet to be placed within the 
portable base, and the entire unit moved into a desired location. 
Alternatively, the cabinet can be removed from the base and put on a rack 
or shelf, possibly along with other medical electronic devices, leaving 
the portable base free to be moved into the desired location. 
Additionally, in accordance with an aspect of the invention, the cabinet 
has connectors for receiving the diathermy arms. Accordingly, the cabinet 
can be removed from the portable base, the movable arms and diathermy 
heads can be removed from the portable base, and the cabinet, arms, and 
head can be placed in a carrying case. An operator can thus carry the unit 
into the field, and reconnect the diathermy arms directly to the cabinet. 
Each diathermy applicator head of the present invention has at least one 
capacitive element, and at least one inductive control element positioned 
within a case. An electrostatic shield serves as a cover for the case. In 
accordance with an aspect of the present invention, a small fan, including 
fan blades and a motor, is positioned within the applicator head case for 
cooling of the head and its components. 
Inside the housing, a processor and a crystal oscillator, operative at 
27.12 MHz, are connected to a pulse width modulator. The output of the 
pulse width modulator is connected in series through preliminary power 
amplifier circuits, having an output connected to a final power amplifier 
circuit. The final power amplifier includes a low pass filter, for 
filtering harmonics, and a bridge circuit for detecting standing wave 
ratios. The standing wave ratio bridge circuit has an output, connected by 
a transmission line, to an applicator head of the invention. The standing 
wave ratio circuit, which acts as a detector, is also connected in a 
feedback loop through an amplifier circuit and into a light bar display. 
The pulse width modulator is utilized to modulate the RF frequency provided 
by the crystal oscillator. Modulation of the frequency provides the rate 
at which power is to be applied during therapy to a patient load. 
In accordance with the principles of the present invention, the rate at 
which power may be supplied is variable in frequency from a first, minimum 
selected frequency, of 300 pulses per second, to a second, maximum 
selected frequency of 7,000 pulses per second. The processor is programmed 
to permit the rate to be varied by an operator on a digital scale from a 
minimum unit of one to a maximum unit of 12. Thus, a setting of one unit 
represents 300 Hz and a setting of 12 units represents 7,000 Hz. 
The processor also controls the power to be applied to the applicator head. 
The present invention is preferably constructed to permit variance in 
power output from a desired minimum power to a desired maximum power, 
preferably approximately 100 watts. The desired processor is programmed to 
permit an operator to vary the power on a digital scale from one unit to 
12 units, where one unit represents minimum power and 12 units represents 
approximately 100 watts. The processor also includes a timer to permit an 
operator to program the time duration of therapy. Preferably, the 
processor is constructed to permit time duration to be set in 5 minute 
increments, with 5 minutes being a minimum, and 60 minutes being a 
maximum. A display is connected to the processor for displaying digital 
read outs of the rate, power and time settings. A keyboard input, coupled 
to the processor, is utilized by an operator to change the display up or 
down, depending upon the desired rate, power, and time desired for a given 
diathermy treatment. 
The amount of power generated by the diathermy system is determined by the 
setting provided by the operator through the input means, and by the 
processor accordingly controlling the pulse width of each pulse. The RF 
energy leaving the pulse width modulator is amplified by the preliminary 
power amplifiers and applied to a final amplifier that amplifies the power 
to the desired power setting. 
The low pass filter, for filtering subharmonics, leads into a variable 
standing wave ratio (VSWR) bridge circuit that is used as a detector to 
detect the forward wave of power being delivered to the applicator head. 
The VSWR bridge output is also utilized to drive a light bar display 
showing representative power actually being delivered to the head, and 
thus ultimately to the patient. The light bar display is constructed of a 
plurality of light emitting diodes (LEDs), each of which represent a 
defined and selected incremental amount of power to the patient. In 
accordance with an aspect of the invention, the apparatus is calibrated so 
that each light bar represents an actual amount of power. Thus, the 
apparatus provides a unique visual display permitting an operator to 
visually ascertain whether the appropriate amount of power is being 
delivered to the patient. 
The diathermy apparatus of the present invention is also uniquely designed 
to maintain resonance, and therefore optimal coupling of the diathermy 
energy to the patient load, when the diathermy head is in a loaded, 
close-proximity position to the patient load. Similarly, the construction 
is such that removal of the applicator head from the load causes the 
apparatus to deliver a minimum or zero power to the applicator head. 
Particularly, each applicator head of the diathermy apparatus of the 
present invention includes an inductive element formed in a coil, and a 
capacitive element made up of a number of capacitive components. For 
example, the capacitive element of the applicator head is made up of 
physical aluminum plates located between the spiral wound inductor and the 
inside back portion of the aluminum case, a fixed, stray capacitance made 
up of the many different capacitor plates to case ground, and the stray 
capacitance between the inductor and the electrostatic shield utilized in 
the applicator head. As will be understood, a variable capacitance is also 
realized when the irradiating portion of the head is located in close 
proximity to a load of human tissue, thus absorbing the inductive heating 
present from the tuned circuit of the applicator head. 
In accordance with an aspect of the present invention, yet another 
capacitive element is obtained by designing the length of the transmission 
line cable, extending from the power amplifier final stage and coupling 
into the resonate circuit of the applicator head in a fashion that at a 
frequency of 27.12 MHz, the following parameters are realized. 
When the applicator head is resting in an open case position--that is, no 
power is being delivered to the load--then, transmission line connecting 
the power amplifier final stage and the resonate circuit of the applicator 
head reflects an open voltage or high impedance to the amplifier, 
resulting in a selected minimum power (or no power) being utilized by the 
diathermy apparatus. Thus, the apparent net capacitance at the end of the 
transmission line is a minimum value which allows the resonate point of 
the final power amplifier to increase to a frequency of approximately 
27.16 to 27.18 MHz, thereby unloading the final power amplifier and the 
power supplies that feed DC voltage and current into the final power 
amplifier. 
When, however, the applicator head is placed in close proximity to a 
patient load, the variable capacitance element starts to increase, thus 
increasing the capacitance at the end of the transmission line. Variable 
standing wave ratios, indicative of the capacitance increase, reflect back 
into the final power amplifier, causing the amplifier to adjust to 
increase the current supplied to the applicator head, thus increasing the 
power to the selected level. Thus, when the applicator head is unloaded, 
the load presented to the final RF power amplifier is a high impedance. 
Under such a condition, the final power amplifier requires only minimal 
power from the switching power supply. Additionally, under such a 
condition, the preliminary power amplifier becomes unloaded.

DETAILED DESCRIPTION OF THE INVENTION 
With reference initially to FIG. 1, a diathermy apparatus of the present 
invention is denoted generally by reference numeral 10. Diathermy 
apparatus 10 has a cabinet 12, for housing electronic components of the 
apparatus 10. As illustrated, housing 12 is preferably generally 
rectangular in configuration, having four sides, a bottom and a top. In 
the preferred embodiment, the top face 14 of cabinet 12 includes a control 
panel for controlling the electronic circuitry of the diathermy apparatus 
10. The central panel includes input keys 15 and display areas 17. Top 
face 12 has a pair of handles 16, each of which is located proximate an 
outer side edge of the cabinet 12. 
Diathermy apparatus 10 of the present invention also includes a portable 
base, designated generally by reference numeral 20. Portable base 20 
serves as a carriage for cabinet 12. As illustrated, portable base 20 of 
diathermy apparatus 10 is preferably constructed in a generally 
rectangular box configuration, with an open top. Specifically, portable 
base 20 has first and second outer side walls, or faces 22, 24, and front 
and rear faces or walls, 26, 28, respectively. Portable base 20 has an 
open top, designated by reference numeral 30. In the preferred embodiment 
shown, portable base 20 includes a pair of support brackets 32 positioned 
at the bottom of portable base 20. Each support bracket 32, preferably 
positioned on the bottom of portable base 20, extends outwardly past the 
front face 26 of the portable base 20. An outermost end 34 of each 
supporting bracket 32 angles inwardly, toward the other support member 32, 
as illustrated. Castor wheels 36 are positioned on the bottom side surface 
of each support 32 at outer ends thereof, as illustrated. 
Front wall 26 of portable base 20 mounts a pair of outwardly extending, 
movable arms 38. Each movable arm 38 is mounted to front wall 26 of 
portable base 20 by a mounting support 40. Each movable arm 38 is 
extendable and supports an induction applicator head 42 thereon. 
Particularly, in the preferred embodiment, each extendable arm 38 is 
formed of three sections, designated by 38a, 38b, and 38c, rotationally 
attached to each other at pivot points 44. Each arm 38 is attached to its 
respective mounting support 40 by a similar rotational attachment 44. Each 
movable arm 38 is hingedly attached to its respective mounting support 40, 
such that the arm 38 can be swung sideways relative to the front wall 26 
of support base 20. Similarly, as will be readily appreciated, each 
movable arm may be pivoted upwardly and downwardly relative to front wall 
26 of portable base 20. Additionally, as illustrated in FIG. 1, each 
applicator head 42 is pivotally attached to its respective movable arm 38, 
such that the heads 42 can be moved between horizontal and vertical 
positions. The entire unit is constructed so that the movable arms 38 will 
remain in a substantially preset positioned, but may be pivotally moved, 
and thus swung, extended, or contracted, with a controllable amount of 
force. The construction illustrated gives the applicator treatment heads 
42 a great deal of movement for optimum positioning with respect to the 
patient or patient's body (or patients' bodies). 
With reference still to FIG. 1, each diathermy applicator head 42 is 
connected by a coaxial transmission line 46 to the electrical circuitry of 
the diathermy apparatus located inside the housing formed by cabinet 12. 
In this regard, each coaxial cable 46 extends through a front wall 48 of 
cabinet 12 to connect with the electrical circuitry of diathermy apparatus 
10, as described in greater detail below with reference to the schematic 
electrical diagrams. Each coaxial transmission line 46 also connects with 
the circuit inside the respective diathermy applicator head 42, as 
described in greater detail below. 
In accordance with an aspect of the present invention, cabinet 12, housing 
the electrical components of the diathermy apparatus 10, is insertable 
into, and removable from, portable base 20. Particularly, an operator may 
grasp each handle 16 on the top face of cabinet 12, and lower cabinet 12 
through the opening 30 of portable base 20 into the interior of portable 
base 20 defined by walls 12, 22, 24, 26, and 28 of the portable base 20. 
As illustrated, a pair of support brackets 50 are fixedly located in the 
interior space of portable base 20, and connect to inside surfaces of 
front and rear walls 26, 28, respectively. When inserted into portable 
base 20, the bottom of cabinet 12 rests on the top of support brackets 50. 
Preferably, when cabinet 12 is fully inserted into portable base 20, the 
top face 14 of cabinet 12, having the control panel, is either flush with 
the top of portable base 20, or extends slightly above the top of portable 
base 20. As shown, front wall 26 of portable base 20 has a cut-out area 
52, at a central, upper portion thereof, so that coaxial transmission 
lines 46, as well as a power supply line 54, entering into front wall 48 
of cabinet 12, may extend from cabinet 12 and pass portable base 20 in an 
uninterrupted fashion. 
The physical construction of diathermy apparatus 10 permits it to be easily 
moved into an optimum position with respect to a patient load for 
operation of the apparatus 10. Additionally, cabinet 12 may be removed 
from portable base 20 and placed on a fixed shelf unit or rack, while 
portable base 20 may still be positioned as desired. Portable base 20, 
without cabinet 12 located in its interior, is much lighter and more 
easily moved. Moreover, the construction of the present invention permits 
the cabinet 12 to be located, for instance, on a rack and the portable 
base 20 moved from room to room or location to location, as needed. 
Alternatively, portable base 20 could remain in a particular hospital 
room, for instance, and the removable cabinet 12 could be relocated and 
utilized in conjunction with a second portable base 20 at another 
location. Additionally, the unique construction of the diathermy apparatus 
10 makes the electrical components far more accessible for serviceability 
than in prior art constructions. 
With reference now to FIG. 2, a diathermy applicator head 42 of the present 
invention is shown and described in detail. 
Applicator head 42 of the present invention has a casing 54, preferably 
formed of aluminum and covered by plastic. Casing 54 has a rear face 56 
and a peripheral side wall 58. Peripheral side wall 58 has a plurality of 
spaced apart slots 60 positioned as shown. A plurality of capacitor plates 
62, having a known capacitance, are positioned inside casing 54. An 
inductive coil element 64, having a known inductance, is also positioned 
within casing 54. 
A small fan, denoted generally by reference numeral 66 includes a motor, 
located inside a motor housing 68, and an impeller formed of a number of 
fan blades 70, rotatably mounted to an output shaft of the motor at a hub 
72. The fan 66 is positioned centrally within the casing 54 on the inside 
surface of rear face 56 of casing 54. Fan 66 is powered by a power supply, 
and is operated to cool the components of applicator head 42. 
An electrostatic shield 74 serves as a front cover for applicator head 42. 
As described above, the electrostatic shield 74 eliminates, or at least 
drastically reduces, the electrostatic energy emitted from applicator head 
42, thereby significantly improving the operating efficiency of the 
diathermy apparatus 10. Coaxial transmission line 46 connects electrical 
circuitry within cabinet 12 with the circuit formed of capacitor plate 62 
and inductive coil element 64. 
With reference now to FIG. 3, a block diagram illustrating the electrical 
circuitry associated with diathermy apparatus 10 of the present invention 
is shown and described. 
Diathermy apparatus 10 includes a central processing unit (CPU), designated 
generally by reference numeral 80 and referred to herein as a processor. A 
plurality of code switches, for coding processor 80 are designated 
generally by reference numeral 82, and are utilized for encoding processor 
80. A display 84 is connected to processor 80. Display 84, as described in 
greater detail below, preferably includes a plurality of display modules 
for displaying rate, power, and time settings selected by an operator of 
diathermy apparatus 10. Processor 80 is connected to a pulse width 
modulator 86. An RF crystal oscillator, designated by reference numeral 
88, operates at a frequency of 27.12 MHz and is used to provide an 
accurate means for supplying the RF frequency of the diathermy apparatus 
10. As will be readily understood, the high frequency electrical currents 
induced in diathermy apparatus 10 will thereby have a standard frequency 
of approximately 27.12 MHz, which is within the permissible frequency 
range allocated for diathermy service. 
Pulse width modulator 86 outputs into a preliminary power amplifier formed 
of a pair of preliminary power amplifiers 90, 92 connected in series. 
Preliminary power amplifier 92 outputs into a final power amplifier 
circuit, designated generally by reference numeral 94, and formed 
generally of final power amplifiers 96, 98 connected in parallel, as 
illustrated. Final power amplifier 94 includes a low pass filter 100 for 
filtering off subharmonics in a known manner. Low pass filter 100 outputs 
into an SWR circuit designated by reference numeral 102. SWR circuit 102 
outputs into an applicator head 42. As described in greater detail below, 
SWR circuit 102 reflects standing wave ratios back into final power 
amplifier 94. SWR circuit 102 also reflects forward waves of power through 
line 104, through an amplifier 106, and into a litebar display 108. 
Litebar display 108 is preferably formed of a plurality of light emitting 
diodes 109 (LEDs), wherein each diode 109 represents an actual amount of 
power delivered to the applicator head 42, and hence a patient load. 
It should be understood that diathermy apparatus 10, as illustrated in FIG. 
1, preferably includes a pair of applicator heads 42. Each applicator head 
42 is independently controlled, having its own associated circuitry as 
illustrated in FIG. 3. 
Applicator head 42 is illustrated as having a fixed capacitance C2 
(approximately 36 pF and a fixed inductance L2 (approximately 950 nH). 
Fixed capacitance C2 represents the capacitance of the capacitor plate 62, 
as illustrated in FIG. 2, while fixed inductance L2 represents the 
inductance of inductor coil element 64, as set forth in FIG. 2. Also, fan 
66 (see FIG. 2) is connected as shown. It will be understood by those with 
skill in the art that applicator head 42, in addition to the physical 
aluminum capacitance plates 62 and the physical inductive element, 
comprised of coil 64, includes an additional fixed capacitance. The 
additional capacitance is made up of the many different capacitor plates, 
to case ground, as well as the stray capacitance between the inductor 
element 64 and the electrostatic shield 74. As will be described in 
greater detail below, a variable capacitance is realized when the 
radiating portion of applicator head 42 is located close to human tissue, 
thus absorbing the inductive heating resulting from the tuned circuit 
condition of the present invention. Additionally, in accordance with an 
aspect of the invention, another important capacitive element is obtained 
by designing the length of the coaxial cable comprising transmission line 
46, in a fashion that at the fixed frequency of 27.12 MHz certain 
parameters, as described above and as set forth in greater detail below, 
are realized. 
In operation, upon activation of diathermy apparatus 10, electrical power 
is provided to the apparatus, and the processor 80 is initialized. In 
accordance with the desired diathermy therapeutic treatment, the operator 
utilizes keys 15 on the control panel of the diathermy apparatus to enter 
a desired power setting, rate of application, and time duration. 
Particularly, each key 15 on the control panel corresponds with one of the 
code switches 82. In the preferred embodiment, switch 82a corresponds to 
"power up". Switch 82b corresponds to "power down". Switch 82c corresponds 
to "rate up". Switch 82d corresponds to "rate down". Switches 82e and 82f 
correspond to "stop" and "start", respectively. Switches 82g and 82h 
correspond to "time up" and "time down", respectively. Accordingly, upon 
initialization of diathermy apparatus 10, the operator utilizes switch 82a 
and/or 82b to enter a preferred power. As discussed above, processor 80 is 
programmed to accept input from switches 82a and 82b to correlate 
operation of the switches with a programmed digital scale. Preferably, 
processor 80 is programmed with a digital "power scale" from 1-12, with 
one representing a desired small amount of power, while a unit of 12 
represents a maximum amount of power, which is preferably approximately 
100 watts. Accordingly, switches 82a and 82b are utilized by the operator 
to incrementally or decrementally alter the desired power set. Switches 
82c, 82d are similarly used to vary the rate, or frequency of application 
of the power. In the preferred embodiment, the processor is programmed to 
accept rate variations on a digital scale from 1-12. Preferably, a unit of 
one represents 300 Hz, while a unit of 12 represents 7,000 Hz. As will be 
understood by those skilled in the art of diathermy apparatus, molecules 
in a patient's blood are excited at a different rate, depending upon the 
rate setting for application of power. This can become important, 
depending upon the particular patient receiving therapy. For example, a 
high power setting corresponds with deep penetration into the patient 
load, and therefor deep therapeutic benefit. However, in a patient having 
poor circulation, a high power setting along with a high rate setting 
could very likely begin to burn the surface of the patient's skin. 
Therefore, it is common practice to reduce the rate of power application 
to prevent burning, while keeping power at a high setting for good 
therapeutic benefit. Switches 82g and 82h are utilized to select the time 
duration of therapy, while switches 82e and 82f are utilized to start and 
stop, respectively, application of therapy with diathermy apparatus 10. 
By way of an example in accordance with the preferred operating principles 
of the diathermy apparatus 10 of the present invention, when diathermy 
apparatus 10 is turned on, the digital read outs on the display areas 17, 
read 12-12-5, representing rate of 12, power of 12, and time of 5 minutes. 
As discussed, keyboard type entry is utilized by the operator to change 
the digital display up or down, depending upon the desired rate, power, 
and time for a given diathermy treatment. In the example given, with a 
digital display reading of 12-12-5, upon pressing the start key 82f, 
diathermy apparatus 10 will deliver a rate of 7,000 pulses per second, and 
approximately 100 watts of power for a time of 5 minutes. Thus, data 
indicative of a desired power of 100 watts, at the rate of 7,000 pulses 
per second, is generated by processor 80 and applied to pulse width 
modulator 86 (FIG. 3) so as to modulate (e.g., turn on and off) RF crystal 
oscillator 88, thereby generating the desired approximately 100 watts of 
power. The RF energy leaving the pulse width modulator 86, enters the 
preliminary power amplifier 90. In accordance with the preferred 
principles of the present invention, preliminary power amplifier 90,92 
amplify the signal to a 15 watt level. The RF energy is then applied to 
final power amplifier 94, where it is amplified to the desired 100 watt 
level. Thus, crystal oscillator 88 stabilizes the frequency at 27.12 MHz. 
The preamplifier amplifies the signal the first time, while the final 
power amp amplifies the signal to the desired level. Pulse width modulator 
86 generates a square pulse, based upon data indicative of the desired 
rate and power provided by processor 80, depending upon what was keyed 
into the keyboard. As the energy passes through the final power amplifier 
94, it passes through a low pass filter which filters off the second, 
third, fourth, and fifth harmonics of the fundamental. The energy then 
passes through SWR bridge 102, and passes along transmission line 46 to 
applicator head 42. 
In accordance with an aspect of the present invention, the total line 
length of the transmission line 46, extending between the final amplifier 
to the tune circuit of applicator head 42, is critical to give the needed 
variable capacitance at the end of the transmission line 46. Thus, the 
hardware components of the circuitry, including those components having an 
inductance and a capacitance at the applicator head, as well as the 
transmission line, are utilized to effect change in the capacitance from, 
in the preferred embodiment, approximately one-half (1/2) picofarad(Pf) to 
approximately 31/2 Pf. This change in capacitance represents the desired 
amount of capacitance change on the applicator head 42 to change its 
tuning from roughly 250 ohms of effective impedance, down to approximately 
50 ohms of effective impedance. When 50 ohms of effective impedance is 
reached, the amplifier 94 draws approximately 12 amps of current and 
output approximately 100 watts of power when the head is in a loaded 
position in close proximity to a patient load, and a maximum power setting 
is selected at the controller. In contrast, if the head is unloaded, and 
thus removed from its position in close proximity to the patient load, the 
capacitance's value at the end of the transmission line is down to 
approximately 1/2 Pf, and the final power amplifier 94 sits at an idle 
current of approximately 3 amps in the preferred embodiment, and is 
delivering very little power out to the applicator head 42, and thus the 
patient load. In the preferred embodiment, a minimal amount of power 
output to the applicator head represents loss in the circuit elements. 
As will now be understood, changing the effective capacitance at the end of 
the transmission line 46, and thus at the applicator head 42, from 
approximately 1/2 Pf to 31/2 Pf represents tuning of a tuned circuit, 
which represents going from a low load condition wherein the applicator 
head 42 is removed from a patient load to a loaded condition, wherein the 
applicator head 42 is located in close proximity to a patient load. 
As diathermy apparatus 10 is operated, an applicator head 42 is placed in 
close proximity to a patient load, thereby changing the effective 
capacitance at the applicator head to the desired maximum amount, the 
selected amount of power is output through applicator head 42 into the 
patient load. The unique design of the present invention is such that the 
line length is selected to produce the desired results at the selected 
fixed frequency, in this case 27.12 MHz. As power is transmitted to the 
patient load, SWR bridge circuit 102 reflects standing wave ratios back to 
the final power amplifier 94. Final power amplifier 94 responds to the 
received standing wave ratio, and current is increased or decreased 
accordingly to maintain power at the desired level. As conditions at the 
patient load changes, such as may be caused by movement of the patient 
closer to or farther away from the applicator head 42, or as may be caused 
by a rise in temperature of the patient load, the condition of the 
electrical circuit also changes, as will be readily understood. In 
practice, as the inductance at the load increases, final power amplifier 
94, based upon reflected standing wave ratios, will adjust to output less 
electrical current, and hence less electrical power. In contrast, as the 
capacitance at the load increases, the final power amplifier 94 will 
adjust to increase electrical current, and thus increase the electrical 
power transmitted through applicator head 42 to the patient load. In other 
words, the final power amplifier 94 receives reflected standing wave 
ratios and works as a tank circuit to maintain resonance while the 
applicator head 42 is in close proximity to the patient load. 
By way of a specific example, when applicator head 32 is placed in close 
proximity to a human load, variable capacitance starts to increase at the 
end of transmission line 46. In the preferred embodiment, transmission 
line 46 is a 50 ohm line and thus, the line is considered matched (or 
flat) when the load is 50 ohms and the driving source is 50 ohms. In other 
words, the variable standing wave ratio is 1 to 1. In contrast, the 
transmission line 46 is mismatched when the variable standing wave ratio 
is increased to 15 to 1. A .lambda..sub.m of line length is given by the 
following formula: 
##EQU1## 
Where .lambda..sub.m equals wave length in meters, f equals frequency in 
MHz and e.sub.r equals coefficient of dielectric constant for the cable 46 
in the design (preferably 67%). 
The science of transmission line theory teaches if a 1/4 wave line is open 
at one end, a short or very low impedance will be present at the other 
end. In other words, a high voltage, low current at one end, produces a 
low voltage, high current at the other end. This principal is used in the 
design and construction of the present invention, including the several 
elements of applicator head 42. For example, the exact diameter of the 
coil to obtain the desired inductance for inductive element 64, the exact 
coupling capacity from the end of the line 46 to the fixed capacitance 
plates to obtain a portion of the desired capacitance are determined. 
Importantly, the exact length of the line 46 is selected to match the 
elements in the applicator head to the final power amplifier so as to 
obtain a high impedance, typically 250 ohms or more when the head is in an 
unloaded position, and a low impedance, preferably 50 ohms when the 
applicator head is positioned in close proximity to a human load. In the 
loaded position, the final power amplifier will deliver power, at the 
selected rate, for the selected time, to the human load. A 50 ohm load is 
reflected from the applicator head 42 to the final power amplifier, via 
the coaxial transmission line 46. The ratio of approximately 15 to 1 in 
power consumption can be realized by apparatus 10 utilizing the foregoing 
principles. For example, a switching power supply capable of delivering 
150 watts (12 volts at 13 amps) will deliver the 150 watts when the load 
(applicator head in close proximity to the body) is matched (e.g., 50 ohms 
to 50 ohms). Conversely, the apparatus will deliver only approximately 5 
watts when the applicator head is unloaded (e.g., 250 ohms at the end of 
the line). 
Additionally, during operation of diathermy apparatus 42, standing wave 
ratio bridge circuit 102 reflects forward power via line 104 to litebar 
display 108. Particularly, SWR circuit 102 detects RF energy at the 
applicator head. Thus, the time constant selected by components of SWR 
circuit 102 are selected so that the detector sees only the peak energy, 
so that the detection will also fall off before the next energy pulse 
comes along. The detected peak energy is scaled through an operational 
amplifier 106 and sent to litebar display 108, for illuminating an 
appropriate number of LEDs 109, representative of the actual power being 
delivered to applicator head 42. This unique display technique provides 
the operator or technician with a constant visual representation of the 
actual power delivered to the patient load. In accordance with the 
preferred aspects of the present invention, each LED 109 represents a 
selected, actual amount of power, such as 10 watts. Thus, ten LEDs 109, 
all illuminated, would indicate that a full 100 watts of power was being 
delivered to the patient load, whereas, for instance, only 3 LEDS 
illuminated would indicate that only approximately 30 watts were being 
delivered to the patient load. 
In some situations, it may be desirable to place the diathermy apparatus on 
a flat surface such as a table. The construction of the present invention 
provides this option. As shown in FIG. 4, the arms 38 can be detached from 
the base and attached to the front wall 48 of the cabinet 12. This is 
accomplished by removing the mounting supports 40 for the arms from the 
base 20 and securing them in openings 40a and 40b (FIG. 1) formed in wall 
48. The cabinet 12 can then be used with its back resting on a table 
surface (or other flat) and its front wall 48 facing upwardly in the 
position shown in FIG. 4. 
As illustrated and described, diathermy apparatus 10 is uniquely 
constructed so that cabinet 12 is removable from portable base 20. In use, 
cabinet 12 may be removed from portable base 20 and placed in a carrying 
case (not shown). Additionally, movable arms 38 and diathermy heads 42 may 
be removed from their mounting position on portable base 20, and located 
in the carrying case. In such a manner, the cabinet 12, arms 38, and heads 
42 may be carried out of the field for use. Thus, the construction of the 
present invention permits the diathermy unit to be conveniently 
transported to a patient, rather than requiring the patient to come to the 
diathermy apparatus. In use in the field, diathermy apparatus 10 is placed 
on a flat surface in the position as shown in FIG. 4, and mounting posts 
40 of respective movable arms 38 are pivotally positioned within 
respective openings 40a, 40b, and movable arms 38 are pivoted as needed to 
located diathermy heads 42 in the desired location relative to a patient. 
FIG. 4 also illustrates elapsed timer indicators 41a, 41b, which record 
the total time diathermy 10 has been on. 
From the foregoing it will be seen that this invention is one well adapted 
to attain all ends and objects hereinabove set forth together with the 
other advantages which are obvious and which are inherent to the 
structure. 
It will be understood that certain features and subcombinations are of 
utility and may be employed without reference to other features and 
subcombinations. This is contemplated by and is within the scope of the 
claims. 
Since many possible embodiments may be made of the invention without 
departing from the scope thereof, it is to be understood that all matter 
herein set forth or shown in the accompanying drawings is to be 
interpreted as illustrative, and not in a limiting sense.