United States Patent 1191
`Knapp et al.
`
`153116111 1811111111611
`1111
`[45] Date of Patent:
`
`4,877,999
`Oct. 31, 1989
`
`[54] METHOD AND APPARATUS FOR
`PRODUCING AN HF-INDUCED NOBLE-GAS
`
`[56]
`
`References Cited
`U S PATENT DOCUMENTS
`
`PLASMA
`
`,
`_
`[75] Invenmrs" cfuger KrPERAM'e” schau" b°th
`° W» “s m
`
`[73] Assignee: Anton Paar KG, Graz, Austria
`‘
`
`21 A L N _, 180 590
`[
`1
`pp
`°
`’
`_
`[22] F11¢d=
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`APr- 7, 1988
`
`[63]
`
`Related US. Application Data
`Continuation of Ser. No. 931,031, Nov. 17, 1986, aban
`doned.
`
`Foreign Application Priority Data
`[30]
`Nov. 15, 1985 [AT] Austria ............................... .. 3342/85
`
`[51] Int. Cl.‘ . . . . .
`
`. . . . . . . . . . . . . . . . . . . . . . . .. H01J 7/24
`
`[52] US. Cl. ............................. .. 315/248; 3l5/11l.21;
`315/267; 313/231.31; 313/570; 313/607;
`313/631; 333/24 C; 333/99 PL
`[58] Field of Search ................. .. 333/24 C, 99 PL, 32;
`315/248, 111.1, 111.2, 267; 313/362.1, 231.01,
`231.1, 231.3, 570, 574, 607, 631
`
`'
`'
`2,800,622 7/1957 1.1611 ............................. .. 315/248 x
`3,525,953 8/1970 1111111613611
`333/99 PLX
`3,569,777 3/1971 Beaudry ..
`315/111.21
`3,577,207 5/1971 K11j11311111 ................ .. 315/39
`3,600,712 8/1971 Williamson ......... ..
`315/39 x
`3,641,389 2/1972 Leidigh ................... .. 315/39
`3,671,195 6/1972 Bersin .......... ..
`3l3/231.01X
`3,783,419 1/1974 1.111611111111111.
`333/24cx
`3,946,272 3/1976 Young ................... .. 315/267
`4,115,184 9/1978 POlllSen ....... ..
`315/111.2x
`4,451,766 5/1984 Angle 61111 .............. .. 315/248
`4,629,940 12/1986 Gagne et a1. ................... .. 333/32 X
`Primary Examiner—James J. Groody
`Assistant Examiner-Mark R. Powell
`Attorney, Agent, or Firm—Bacon & Thomas
`[57]
`ABSTRACT
`The invention concerns a method and apparatus to
`produce a noble-gas plasma for excitation in optical
`emission spectrometry. The apparatus includes an hf
`generator feeding an oscillation circuit consisting of at
`least one inductor and one capacitor. The capcitor in
`cludes at least two capacitor plates which are so shaped
`and mutually arranged that they enclose a cavity in
`which the plasma may form.
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`16 Claims, 7 Drawing Sheets
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`1
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`METHOD AND APPARATUS FOR PRODUCING
`AN HF-INDUCED NOBLE-GAS PLASMA
`
`This application is a continuation, of application Ser.
`No. 931,031, ?led 11/17/86 now abandoned.
`
`15
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`BACKGROUND OF THE INVENTION
`1. Field of the Invention.
`The invention concerns an apparatus for producing a
`high-frequency induced noble gas plasma such as is used
`in particular in excitation in optical emission spectrome
`try. The excitation means employed is a high-frequency
`generator.
`_
`2. Description of Related Art
`The noble gas considered here is helium and/or
`argon that shall be used at normal (atmospheric) pres
`sure. In recent years such plasmas have assumed high
`signi?cance as radiation sources in emission spectrome~
`try. Diverse methods are known for producing the
`plasma. Besides plasma production by means of a DC
`arc (DCP), the other methods used in particular involve
`applying to the gas the energy required to produce the
`plasma in the form of high-frequency electromagnetic
`oscillations. A problem is incurred thereby expecially
`when coupling the electromagnetic power into the gas.
`Illustratively, the operative frequency range from 13 to
`100 MHz must be selected for the generally known
`inductive coupling, and the power applied then is be
`tween 500 w and several kw (ICP method). If the cou
`pling is capacitive (CMP method), a high frequency
`signal at 2,450 MHz is used and the power is 0.5 -3 kw.
`In both cases, the power to be coupled therefore is
`exceedingly high.
`_
`A further method operating at 2,450 MHz is known,
`where a power of 50-200 w suf?ces to produce the
`plasma, however this method (MIP) causes difficulties
`in obtaining a uniformly arcing plasma when different
`probes are introduced. In this instance, the plasma tends
`to form ?lamentary arcing channels which strongly
`degrade the measurements (see for instance D. Kollot
`zek, Spectrochimica Acta, Vol. 37B, #2, pp 91-6, 1982).
`The initially cited methods (DC arcs, ICP, CMP) are
`suitable for comparatively large specimens, but in view
`of their high performance they are initially costly.
`Moreover, the consumption of noble gas in such appara
`tus is between 5 and 20 liter/ / minute, which entails high
`operational costs. On the other hand, the above-cited
`MIP method is comparatively more economical in pur
`chase cost and furthermore requires a lesser consump
`tion of noble gases (less than 1 liter/minute). However,
`besides the above mentioned dif?culties and lack of
`plasma uniformity, a further problem is encountered,
`namely that the plasma occasionally extinguishes and
`always must be re-?red externally by means of primary
`ions, for instance by an arc discharge.
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`hf potential at a frequency corresponding to the reso
`nant frequency of the oscillating circuit. Advanta
`geously, the oscillating circuit shall be driven at a reso
`nant frequency approximately between 10 and 100
`MHz.
`The method can be carried out by an apparatus which
`is characterized in that the high frequency (ht) genera
`tor of this apparatus is connected to an oscillating cir
`cuit which it feeds, this oscillating circuit comprising at
`least one inductor and at least one capacitor element,
`this capacitor element including at least two capacitor
`plates which are so shaped and mutually arranged that
`they enclose a cavity wherein the plasma can form.
`The method and/or the apparatus of the invention
`assure that essentially the entire energy transmitted into
`the oscillating circuit shall be transmitted into the gas
`and after this gas’ ?ring into the plasma because the gas
`or the plasma in some sense is a component of the en
`ergy transmission system. When the cavity between the
`capacitor plates is suitable shaped, a homogeneous ?eld
`may be created therein, whereby the plasma arcs uni
`formly and does not form channel-?laments. Contrary
`to the case for the above cited CMP and MIP methods,
`the method and/orapparatus of the invention allow
`using excitation frequencies that are lower by one or
`two orders of magnitude than in the conventional case.
`Advantageously a tube (illustratively, 6 mm in diame
`ter with a wall thickness of l-li mm) is made of an
`electrically non-conducting and high~temperature resis
`tant material such as quartz, or quartz glass, aluminum
`oxide or boron nitrite and is mounted in such a manner
`between the capacitor plates that it encloses the cavity
`(less the wall thickness). Thereby the capacitor plates
`are separated from the gas or plasma and the gas can be
`fed in a simple manner to the cavity between the capaci
`tor components. To prevent overheating resulting from
`extended operation of the capacitor plates, cooling
`means, in particular water cooling elements, are pro
`vided in the capacitor plates.
`The apparatus can be manufactured in expecially
`simple manner if the cavity is essentially cylindrical, the
`generated electric ?eld then being very homogeneous in
`this cavity. In other preferred embodiments of the in
`vention, the tube is ?attened, being cylindrical with
`illustratively an elliptical cross-section, the homogene
`ous region of the ?eld being enlarged thereby and the
`feed of aerosol being facilitated. The term “?attened”
`or “cylindrically ?attened” means a tube of which two
`mutually opposite and axially extending sidewalls are
`?attened or pressed ?at.
`In a preferred embodiment of the invention, at least
`one of the capacitor plates is provided with an aperture
`directed essentially toward the center of the cavity
`whereby plasma radiation can pass through this aper
`ture to be analyzed outside the apparatus. In this way it
`is possible to utilize both the radiation emitted from the
`apparatus along the tube axis (together with the gas)
`and also the radiation portion emitted by the plasma in
`the other directions. Such a system illustratively may be
`operated in a closed circuit after a specimen has been
`inserted into the noble gas and the spectroscopic test
`results can be determined over a substantial length of
`time, whereby on one hand the gas consumption is
`minimized and the signal-to-noise ratio of the test results
`is increased, and on the other hand, the required amount
`of specimen is lowered.
`In an especially preferred embodiment of the inven
`tion, at least one of the components forming the oscillat
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`SUMMARY OF THE INVENTION
`In the light of the above state of the art, it is the object
`of the present invention to create a method and an appa
`ratus whereby it is possible to produce in simple manner
`an essentially uniformly arcing plasma.
`This problem is solved by the invention in that the
`energy required for ?ring and maintaining of the plasma
`is coupled into the gas through two mutually opposite
`capacitor plates between which the plasma is formed or
`located, these capacitor plates together with an induc
`tor forming an oscillating circuit and being fed with an -
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`ing circuit includes means to tune its impedance. In this
`rarily, and the regulating circuit is designed to be of
`manner, the oscillating circuit-of which the resonant
`corresponding inertia. This is very easily done because
`frequency is basically determined by the geometric and
`system changes take place only very slowly or take
`electrical properties of the cavity (for instance its ?ller
`place mainly when the apparatus is turned on. This
`material—can be tuned to a predetermined supply fre
`self-regulating system is especially advantageous when
`quency of the hf-generator. Illustratively this will be
`the hf generator must be operated, on the grounds al
`required when the hf generator must operate at of?
`ready discussed above, at a ?xed frequency.
`cially prescribed frequencies or when it must operate at
`In another preferred embodiment of the present in
`a frequency set by the design (resonance ampli?er). In
`vention, the hf generator includes an internal regulating
`such a case, the oscillating circuit advantageously in
`circuit designed in such a manner that the generator
`cludes an adjustable capacitor in series or preferably in
`output frequency is automatically set to that value at
`parallel with the capacitor component. Such tunable
`which maximum power is accepted by the oscillation
`capacitors are commercially available and accordingly
`circuit. In this case, therefore, the oscillation circuit is
`the apparatus design is substantially simpli?ed and made
`not tuned, instead the generator output frequency is
`cheaper.
`tuned (within a predetermined range) to the arbitrary
`If the osciallating circuit is a series or parallel circuit,
`resonant frequency of the oscillation circuit.
`then an increased hf voltage is set up between the ca
`As regards all the above stated embodiments of the
`pacitor plates, resulting in plasma ?ring. Accordingly,
`present invention, advantageously the hf generator will
`no separate energy of ?ring need be applied after the hf
`include a voltage-controlled oscillator as the oscillating
`generator is turned on, rather the plasma is self-?ring.
`element. Such voltage-controlled oscillators are com
`20
`It is especially advantageous in the above embodi
`mercially available and by means of slight circuitry
`ment, wherein the oscillation circuit is tunable, that the
`modi?cation can be designed to form highly frequency
`impedance timing means he remote controlled. In such
`stable generators, and furthermore, no phase jumps will
`a case the oscillation circuit can be tuned automatically.
`occur if there is switching between various frequencies.
`In a preferred embodidment of the invention, the
`It is especially advantageous for the above stated
`impedance tuning means then include a test circuit to
`systems that a sensor be mounted near the inductor to
`measure the power damping of the oscillation circuit
`measure the magnetic ?eld generated by this inductor
`and further a regulation circuit connected to the test
`and make it available as an (electrical) output signal. In
`circuit and so designed and so connected to a setting
`this case, the sensor in no way affects the system con
`member acting on the impedance tuning means that the
`sisting of generator and oscillation circuit and delivers a
`oscillation circuit is automatically tuned to the supply
`signal that is substantially proportional to the power in
`frequency of the hf generator. This automatic tuning
`the oscillation circuit. A coil or a Hall element or the
`assures that following changes within the apparatus, for
`like is especially well suited as such a sensor.
`instance when changing the tube or the like, the appara
`In a further preferred embodiment of the invention,
`tus after being switched on will automatically adjust
`the hf generator includes a power regulating circuit
`itself to the resonant frequency of the oscillation circuit.
`designed and connected in such a manner with the sen
`Also during operation the changes in the electrical con
`sor that the output power of the hf generator is kept at
`ditions (resonant frequency) are automatically compen
`a preselected value. Obviously, the sensor also can be
`sated.
`mounted directly in the output line of the hf generator.
`In a preferred embodiment of the invention, adjust
`Such a power-regulated system allows to keep the
`ment means are so arranged in the hf generator that the
`power constant in the plasma with other conditions, for
`output frequency of the hf generator can assume three
`instance gas supply, being kept constant.
`different and essentially constant values. In that case the
`Advantageously the supply connected from the hf
`regulating and test circuits are so connected to the ad
`generator to the oscillation circuit is implemented by
`justment means that the setting member tunes the oscil
`means of at least one coil tap of the inductor. In this
`lation circuit to a higher resonant frequency when the
`manner it is possible to use a generator with standard
`power in the oscillation circuit at the highest frequency
`output impedance (for instance 50 ohms) and with a
`is higher, and the power at the lowest frequency is
`correspondingly standard transmission cable as well as
`lower than the power in the oscillation circuit at the
`the conventional connector materials (BNC cables and
`center frequency. In the reverse case, that is when the
`connectors) and to achieve nevertheless i'elatively re
`power in the oscillation circuit at the lowest frequency
`?ection-free coupling to the oscillation circuit. As there
`is higher, and the power at the highest frequency is
`may be nevertheless re?ections in the cable at different
`lower than the power at the center frequency, the oscil
`plasma impedances and hence voltage shifts (interfer
`lation circuit is moved to a lower resonant frequency.
`ence radiation), advantageously the feed connection
`When the frequency spacings between the lowest and
`shall be balanced. In that case, the re?ections only
`center or between the center and the highest frequency
`occur at the inner conductors of the (double conductor,
`are equal (logarithmically), no change in the resonant
`shielded) cable and are substantially self-compensated.
`frequency of the oscillation circuit is undertaken if the
`BRIEF DESCRIPTION OF THE DRAWINGS
`highest and lowest supply frequency of the hf generator
`cause the same test result for the damping/power mea
`FIG. 1 shows the circuit diagram of a ?rst, preferred
`surement. In that case the center frequency will be
`embodiment of the invention with unbalanced coupling;
`precisely at the resonant frequency of the oscillating
`FIG. 2 shows a circuit diagram similar to FIG. 1 but
`circuit. Therefore in this preferred embodiment of the
`with balanced coupling;
`invention, the hf generator is driven at three ?xed fre
`FIG. 3 is a schematic side view of an embodiment of
`quencies, the center frequency being the actual opera
`the invention;
`tional one while the two other frequencies diverging
`FIG. 4 is a top view of the apparatus of FIG. 3;
`from it are merely used as test frequencies. Accord
`FIG. 5 is a cut-away top view of a capacitor with a
`ingly, the test frequencies need be present only tempo
`tube located between the plates;
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`then it will be heated by the electrical ?eld between the
`FIG. 6 is a side view of the apparatus of FIG. 5;
`capacitor plates 10,11. If a plasma 9 is formed in the tube
`FIG. 7 is a sectional view of apparatus similar to that
`of FIG. 5 but provided with apertures in the capacitor
`11, then in principle the ?eld lines shown in FIGS. 5 and
`plates;
`6 will be set up. This ?eld within the plasma 9 is essen
`tially homogeneous and accordingly the plasma “?res”
`FIG. 8 is a partly sectional side view of the apparatus
`uniformly. The radiation (of a specimen in the thing gas
`of FIG. 7;
`helium-argon) excited in the plasma together with the
`FIG. 9 is a ?rst preferred embodiment of the inven
`gas leaves the tube 13 in the direction of the arrow A,
`tion with a regulating circuit;
`arriving therefore in the direction of the tube axis in the
`FIGS. 10 and 11 are two preferred embodiments of
`tuned oscillation circuits;
`free space, where by means of a suitable detector it can
`be converted into an electrical signal and be processed
`FIGS. 12 through 14 are plots of frequency vs. ?eld
`further.
`intensity of the apparatus of the invention in various
`operational modes;
`In a preferred embodiment of the invention shown in
`closer detail in FIGS. 7 and 8, the capacitor plates 10,11
`FIG. 15 is a further preferred embodiment of the
`invention with automatic frequency tuning; and
`are provided with apertures or boreholes 14,15 located
`essentially centrally in the capacitor plates 10,11. The
`FIG. 16 is a preferred embodiment of a power
`regulated hf generator.
`radiation also can be emitted through these boreholes
`14,15 in the direction of the arrow B (FIG. 4) and'thus
`DETAILED DESCRIPTION OF THE
`leave the apparatus. Moreover, the radiation can be
`PREFERRED EMBODIMENTS
`emitted from the apparatus in the direction of the arrow
`20
`C, that is between the two capacitor plates 10,11. Obvi
`The basic design of the apparatus is described below
`ously, this is only the case if the material of the tube 13
`in closer detail in relation to FIG. 1. As shown by FIG.
`is of a suitable nature (for instance, quartz glass).
`1, a hf generator 8 consisting of an oscillator 21, a pre
`A preferred embodiment of the invention with regu
`ampli?er 25 and a power ampli?er 26 is connected by a
`lation is described below in greater detail in relation to
`cable 7 to an oscillation circuit 1. The oscillation circuit
`25
`FIG. 9. As shown by FIG. 9, the hf generator 8 includes
`1 consists of an inductor L to the tap of which is applied
`the signal, and of a variable capacitor C2 parallel to the
`a voltage controlled oscillator (V CO) 21 of which the
`output signal is ampli?ed by a power ampli?er 24. The
`inductor L. Two capacitor plates 10,11 are connected in
`gain of the ampli?er 24 is adjustable (V GC) by means of
`parallel to the two components and together bound a
`cavity 12. The capacitor plates 10 and 11 form the ca
`a control line. As already described in relation to FIGS.
`pacitor C1. By feeding an hf signal to the oscillation
`1 through 4, the oscillation circuit 1 comprises a vari
`able capacitor C2. In this case, however, the capacitor
`circuit 1, an electrical ?eld is generated between the
`capacitor plates 10 and 11, that is in the cavity 12,
`C2 is adjusted by a setting member 18, for instance a
`whereby the gas contained in the cavity 12 can be
`servomotor in response to an electrical signal. The ser
`heated into the plasma state.
`vomotor 18 is connected to the output of a regulating
`In the embodiment of the invention shown in FIG. 2,
`circuit 17. A sensor 22 is mounted next to the inductor
`L and picks up the intensity of the magnetic ?eld gener
`the hf generator 8 consists of an oscillator 21 followed
`by a pre-ampli?er 25, the pre-ampli?er feeding two
`ated by the coil L which it then feeds in the form of an
`electrical signal both to the regulating circuit 17 and to
`power ampli?ers 26,26’ in a push-pull. The outputs of
`a power regulating circuit 23. Another output of the
`the power ampli?ers 26,26’ are applied to a balanced
`line 7 coupled through balanced taps of the coil L to the
`regulating circuit 17 is connected to an adjustment cir
`oscillation circuit 1. In this design the re?ections caused
`cuit 19 in the generator 8 which in relation to the re
`ceived input signals from the regulating circuit 17
`by mismatching the oscillation circuit 1 to the wave
`makes available three different (precise) voltage values
`impedance of the cable 7 or of the generator 8 are re
`to the voltage controlled oscillator 21.
`duced.
`The design of the power regulating circuit 23 is such
`The mechanical design of the apparatus of the inven
`that when the ?eld intensity generated by the coil L
`tion is discussed below in relation to an illustrative em
`bodiment (FIGS. 3 through 6). This discussion in partic
`differs from a nominal value, the gain of the ampli?er 24
`ular concerns the design of the capacitor C1. As shown
`increases, while in the reverse case it is decreased. In
`by the FIGS. 3 through 6, the capacitor C1 is formed by
`this manner, the power fed into the oscillation circuit 1
`two condensor plates 10,11 which are held in place by
`can be kept constant.
`The system frequency tuning is described in further
`means of the arms of a capacitor base 4. The capacitor
`plates 10,11 are supplied by (omitted) duets with cool
`detail below in relation to FIGS. 12 through 14, inde
`pendently of the oscillation circuit 1 designed as shown
`ing water and are cooled. The capacitor plates are
`in FIG. 9 or designed as shown by FIGS. 10 and 11 as
`shaped in the manner of the stator of an electric motor
`a series oscillation circuit with either tuning inductor
`so that they de?ne between them an essentially annular
`(FIG. 10) or capacitor (FIG. 11).
`space. This annular space is bounded by a tube 13 on
`which the capacitor plates 10,11 rest in essentially her
`In FIG. 12, the curve K1 denotes the ?eld intensity
`(as a function of frequency) before the plasma has ?red,
`metic manner.
`the curve K2 denotes the ?eld intensity when the plasma
`A generator 8 and its output cable 7 with a corre
`already has ?red. Thus, this plot shows that by lowering
`sponding connector is coupled by means of the BNC
`the resistance Rp representing the effective cavity resis
`jack 27 to the apparatus shown in FIGS. 3 and 4 in such
`tance, the system is damped. The system resonant fre
`a manner that the signal is fed through a further cable
`quency changes only slightly after the plasma ?res. The
`segment 7’ to the coil L. The oscillation circuit is tuned
`by means of the rotary knob 3 of the capacitor C2 in
`regulation takes place as follows: the oscillator 21 is
`alternatinvgly supplied with three different voltages by
`such a manner that its resonant frequency coincides
`with the supply frequency. If the gas from a supply
`the adjustment means 19 so that its output frequency
`corresponds to the frequencies f0, f1 and f2; when the
`conduit 5 (FIG. 3) is made to pass through the tube 13,
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`oscillation circuit 1 is precisely tuned to the center fre
`We claim:
`quency f0 (about 10-100 MHz) of the generator 8, the
`1. An apparatus for producing an HF-induced noble
`gas plasma, comprising:
`positions of the three frequencies shown in FIG. 12 are
`obtained. On the other hand, if, as shown by FIG. 13,
`an HF generator for generating a high frequency
`output signal; and
`the oscillation circuit is tuned to a resonant frequency
`which is too low, then the curve of FIG. 13 is obtained.
`an oscillation circuit including an inductor and at
`This curve shows that the ?eld intensity is highest at the
`least one primary capacitor, said oscillation circuit
`lowest oscillator frequency f1, but is lowest at the high
`receiving said high frequency output signal, and
`est oscillator frequency fz. Such conditions are commu
`said primary capacitor comprising at least two
`nicated by the sensor 22 to the regulating circuit 17,
`capacitor plates positioned with respect to one
`whereupon same so controls the setting member 18 that
`another so as to de?ne a cavity therebetween
`the capacitance of the capacitor C2 is lowered, hence
`through which a noble gas flows at substantially
`the curve of FIG. 13 is shifted in the direction of the
`atmospheric pressure.
`arrow Y toward higher values. In the reverse case
`2. An apparatus as claimed in claim 1, further com
`shown in FIG. 14, the setting member 18 is driven into
`prising a tube formed from an electrically non-conduc
`the opposite direction. Obviously, the “test frequen
`tive material said tube positioned in the cavity defined
`by the capacitor plates.
`cies” f1, f2 need be fed only intermittently to the system
`to achieve essentially proper tuning of the frequency. In
`3. An apparatus as claimed in claim 1, wherein said
`particular, the system must be tuned when being turned
`capacitor plates de?ne a cylindrical cavity.
`on, when possibly the generator 8 or the output ampli
`4. An apparatus as claimed in claim 1, wherein at least
`?er 24- is operated at low power insufficient for ?ring
`one of said capacitor plates comprises an aperture sub
`the plasma as the system resonant frequency-in the
`stantially directed at the center of said cavity so as to
`manner already discussed above-does not signi?cantly
`permit radiation to exit from said cavity de?ned by said
`plates.
`change (see FIG. 12). The supply voltage for the capac
`itor plates is approximately 1-3 kv.
`5. An apparatus as claimed in claim 1, wherein said
`Alternatively, the generator 8 need not be controlled,
`primary capacitor discharges during an increase in the
`but the oscillation circuit 1 is tuned in some other man
`hf voltage between said capacitor plates.
`ner. As shown by FIG. 15, a sensor 22 may be provided
`6. An apparatus as claimed in claim 1, further com
`in the oscillation circuit 1, for instance a magnetic ?eld
`prising means for tuning the impedance of said oscilla
`pickup near the coil L. The output signal from the sen
`tion circuit.
`'
`sor 22 then is fed to a regulator 17 of which the output
`7. An apparatus as claimed in claim 4, wherein said
`is connected to a setting member 18 tuning the capacitor
`oscillation circuit further comprises an adjustable ca
`C2. In this embodiment of the invention, the reference
`pacitor in a parallel circuit with said primary capacitor.
`value fed to the regulator is set between three different
`8. An apparatus as claimed in claim 4, wherein said
`values (in relation to the ?xed output frequency of the
`means for impedance tuning is remote controlled.
`generator 8) as already explained in relation to FIGS. 12
`9. An apparatus as claimed in claim 8, wherein said
`through 14. The test results are used similarly to the
`means for impedance tuning comprises:
`case of the previous embodiment to adjust the capacitor
`a test circuit for measuring power damping in said
`C2. In this case, therefore, there is no switching of the
`oscillation circuit; and
`generator output frequency, rather the oscillation cir
`a regulation circuit connected to said oscillation cir
`cuit 1 is tuned to three different frequencies until its
`cuit for actuating said impedance tuning means so
`center frequency corresponds to the generator output
`as to automatically tune the supply frequency of
`frequency.
`'
`said hf generator.
`A further preferred embodiment for frequency tuning
`10. An apparatus as claimed in claim 8, wherein:
`the generator 8 is shown in FIG. 16. In this case, the
`said impedance tuning means comprise means for
`output power from the generator 8 is detected by a
`producing three distinct, constant frequency values
`sensor 16 and fed to the input of a regulator 20. The
`(f1. f0, f2); and
`output of the regulator 20 is connected to the control
`a test regulation circuit for tuning said oscillation
`input of the VCO 21 of which the output is connected
`circuit to a higher resonance frequency if the
`to the input of the power ampli?er 26. Similar to the
`power in the oscillation circuit at the highest fre
`regulator 17, the regulator 20 includes a subsequent
`quency (f2) is greater than the power in the oscilla
`adjustment means 19. But the essential difference with
`tion circuit at the center frequency (f()) which is
`respect to the circuit of FIG. 9 is that instead of the
`greater than the power in said oscillation circuit at
`resonant frequency of the oscillation circuit 1, it is the
`the lowest frequency (f1), said test regulation cir
`center frequency f0 together with the two different
`cuit tuning said oscillation circuit to a lower reso
`frequencies f1 and f2 which are shifted for tuning.
`nant frequency if the power in the highest resonant
`The principles, preferred embodiments and modes of
`frequency (f2) is less than the power in the center
`operation of the present invention have been described
`resonance frequency (f()) which is less than the
`in the foregoing speci?cation. The invention which is
`power in the lowest resonance frequency (f;).
`intended to be protected herein should not, however, be
`11. An electric apparatus as claimed in claim 1,
`construed as limited to the particular forms described,
`wherein said hf generator comprises an internal regula
`as these are to be regarded as illustrative rather than
`tion circuit that adjusts said hf generator so that said
`restrictive. Variations and changes may be made by
`output frequency has a center frequency (f0) at which
`those skilled in the art without departing from the spirit
`said oscillation circuit accepts maximum power.
`of the invention. Accordingly, the foregoing detailed
`12. An apparatus as claimed in claim 1, wherein said
`description should be considered exemplary in nature
`hf generator comprises a voltage-controlled oscillator.
`and not as limiting to the scope and spirit of the inven
`13. An apparatus as claimed in claim 9, further com
`tion set forth in the appended claims.
`prising a sensor positioned near said inductor to pro
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`LAM Exh 1004-pg 12
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`duce a signal proportional to the magnetic ?eld pro
`said inductor comprises at least one coil tap; and
`said high frequency output signal of said hf generator
`duced by said inducton
`is supplied to said oscillation circuit through said at
`14. An apparatus as claimed in claim 13, wherein said
`hf generator comprises a power regulating circuit con
`least one coil tap of said inductor.
`16. An apparatus as claimed in claim 1, wherein said
`nected to said sensor to maintain the output power
`output signal of said hf generator is balanced with said
`contained in said output signal from said hf generator at
`oscillation circuit.
`a predetermined value.
`15. An apparatus as claimed in claim 1, wherein:
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