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V I O I ‘ I I ‘ r ' I , ‘ . . . Y . I , ' - ‘ I 3 , ' I I v I A l‘ ' I ’ I ~ I . I . . ' \ I O l I I ’ I l l . b u ' . . . _ . b. ‘ I l ’ ‘ ’ l I I ~ I . I n ‘ I V ,V . . ‘ I I V - _ _ . ' I . I u-v'v ‘ v-E‘_:g_-_9 ‘. .-~-_-' -4 ‘v v-.. a. t... -‘ 2—s- . “J. c :sll. 1 ‘ ‘VI—f '( .40 PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE "u... a. i .-K I->.|..|D . I‘I THE INFLUENCE CE EIGR RREQUEECI ALTERNATING CURRENT on ‘ VARIOUS FORMS 0R LITE T H E S I 8 SUBMITTED TO THE FACULTY OR THE MICHIGAN STATE COLLEGE CE AGRICULTURE AND AHMED SCIENCE IN RARTIAI. EULEILL- ‘ .MEUT 0E TEE REQUIREMEUTS EUR TEE DEGREE 0R MASTER CE SCIEBOE ' .\ ‘ t j '. V‘ I} I a. . s l'-. Rmmm fl mam August 1932 3‘ T A B L E 0 F C O N T E N T S P A R T I THEORETICAL ANALYSIS OF THE "PUSH-PULL" SELF EXCITED OSCILLATIBG beTEM. IKTROLUCTIOL 1 THEORETICAL EXTLARATION OE TEE SIBGLE TUBE [QSELE-EXCITED OSCILLATOR. 5 THEORETICAL EXILAIATION OF THE "PUSH-PULL" SELF-EXCITLD OdCILgaTIkG bYfiTfld. ‘6 GRAPHICALL fifllI'Aibb‘AflTa'BIOh 01." THE 51.301330th ELOW AND VOLTAGE WITH REDIECT TO THE TWO VACUUM TUNES AND THE L1 L2 0 CIRCUIT. 20 EXAMPLE ILLUSTRATING'METHOD OE CALCULATION. 22 SUMMARY AND CONCLUSIONS. 25 P A R T 11 THE BIOLOGIC ILELUENCE OF HIGH FREQUENCY DIS- PLACEMENT CUEHENTS UION ANIMALS AND BACTERIA. INTRODUCTION. 27 LITERATURE REVIEN. 29 APPARATUS. 56 ANIMAL EXPERIMENTS. 40 RESULTS OF ANIMAL EXPERIMENTS. . 42 BACTERIAL EXPERIMENTS. 49 BACTERICLOGICAL TECHNIQUE. RESULTS WITH BACTERIA 52 DISCUSSION 67 SUMMARY AND CONCLUSIONS ACLNONLEDQIEN TS {3534138 19 21 24 26 35 39 41 48 50 51 66 71 72 75 T A B L E O E C O N T E N T 8 (cont'd) BIBLIOGRAPHY 74 - 77 P.A R T I THEORETICAL ANALYSIS OR THE 'RUSH-EULL' SELE HIC‘ITED OSCILLATING SYSTEM I N T R O D U C T I O N The 'push-pull‘ oscillator was used as the source of energy for determining the influence of high-frequency alter- nating current upon the various forms of life. The Operation of a vacuum tube oscillator, or any sys- tem maintained in continuous oscillation, has certain un- usual teatures. In order for such a system to be uniform in operation or rise to the condition of stability, several elements must adjust thanselves until certain.necessary conditions are established.. In order to better understand how the above mentioned push-pull oscillator functions, one should first observe the manner in which a simple shingle vacuum tube oscillating system starts oscillating and how that oscillation is maintained and then observe hOW’B sys- tem such as used here establishes and maintains its con- tinuous oscillation. It is quite difficult many times to obtain a clear picture from.an equation of exactly what occurs when.the change in one quantity is accompanied by a general readjust- ment of all the others. The problem here is to depict from a physical stand- point, on.the basis or the electronic flow or current, exactly shat occurs in the circuits of the 'push-pull' self- exeited oscillating system, first: how energy is delivered or transferred to the Lc’ Circuit before this LC ‘oircuit is -in the oscillatory state, and second: has this energy, that was transferred to the Lchcircuit,'is the cause or more energy being supplied at proper intervals by virtue of its proper connection to the two vacuum tubes, and a possr source, thus maintaining the system in continuous oscilla- tion. (3) Pifll. sonnlargo DRAIIIG O BIIPEBIOSOILLATOR Grid condenser b 3 fl ...._ 0 '3?!- b;c l... O t--v I t:_d e. e rrn y s e r In "M‘ 1. (4) THEORETICAL EXPLANATION OF THE SINGLE TUBE SELF-EXCITED OSCILLATOR The following explanation of the action of the con- ductively coupled feed-back type oscillator circuit is given with the references illustrated in Fig. 1. In order to make clear the functioning of the tube as an oscillation generator we will suppose that the system is designed so that oscillations will build up immediately when the circuit is set in Operation. Assume all parts of the circuit closed except the key, Fig. l. The tube is filled with electrons which have been emitted from the filament. As the key is closed, making the plate positive with respect to the filament, electronic current will flow through the circuit from the filament to the plate through coil P, "B" battery and key to the filament. As this current rises from zero to a few milliamperes, a voltage will be induced in the secondary coil 3, such that the grid end G will be positive with respect to the filament end P during this growth of current in coil P. The grid thus being made positive with respect to the filament will further hasten the growth of current through coil P, which in turn causes the grid to become still more positive, until by this cycle of cause and effect all of the electrons that are given off from the filament are be- ing utilized. The growth of current through coil P thus having reached a lhmit, likewise the magnetic field about coil P will cease to grow, consequently, the positive and negative potentials induced in coil 3 by the increasing (5) magnetic field about coil P, will at once disappear. Coil 3 having lost its respective potentials, that is, point G falling to the potential of the filament, will cause the current through coil P to decrease. This decrease of current in coil P will cause the magnetic field about coil P to diminish, thereby inducing a voltage in the oppo- site direction in coil 8. The grid will then be made neg- ative with respect to the filamnnt further hastening the decrease in current through coil P. Again we have a cycle of cause and effect which works to the other extreme of practically zero current through the plate circuit. As soon as the current through P ceases to decrease, the mag- netic field about P will become constant and the induced voltage in 3 will be zero. The grid will then lose its negative potential and the current will begin to rise through P. The increasing magnetic field about P, by virtue of the rise of current, will induce a potential across the soil 8, the end G being positive. We have thus completed one cycle and are back to our starting po int . The period of oscillation of this system is determined hy the inductance and capacity in the grid circuit, coil 3 and Condenser C respectively. ('6) PAGE. SCHEMATIC DRAWING OF OSCILLATOR UXI85 TUBE 2 2 TUBE 1 01.852 FIGURE 2. le el (7) THEORETICAL EXPLANATION OF THE "PUSH-PULL" OSCILLATING SYSTEM. In the explanation of how this system functions as an oscillator we will first assume that the two tubes are identical, and that all other similar parts are identical. We will show that under these conditions no oscillation could occur and then show how any slight dissimilarity of tubes or associated parts of the circuit would result in the starting of an oscillation and how when it is once started, such.an oscillation is maintained. If the tubes and parts are identical, the plate current of tube 1, Fig. 2, flowing through L1 produces a potential difference between the ends of L1 directly proportional to the current intensity, and of such polarity as to make the filament and P of L1 positive with respect to the other end I. The plates of condenser Cl are connected directly across the ends of L1. Condenser Cl is therefore charged to a potential difference equal to the battery voltage minus the voltage drOp across L1 and r1. There is however no potential drop across the resistor r1 as long as the potential across L1 remains constant because no current flows through r1 unless Cl is in the process of charging or discharging. This same statement can also be made regarding tube 2, L2, 02 and r2. The system would under these conditions remain in equilibrium since both grid elements are at the same poten- tial as the filaments. Lland L2 are exactly alike, one coil with a center tap. Each tube has the same potential ap- (8) plied to it and passes the same amount of plate current. The potential drops across L1 and L2 are the same, thus imposing the same conditions on each tube. If tubes of the same rating were exactly the same and capable of functioning exactly alike, the above stated con- dition might be possible. Tubes are not made with this precision (1), hence it is reasonable to make an assumption based upon the idea of non-uniformity. The system is really of such a nature as to magnify any very small current vari- ation.that should occur. In this analysis Of how the self-excited "push-pull" oscillating system starts to feed energy into or drive the LC circuit, the electron theory of current will be used and not the conventional theory. Let us start with the filaments of both tubes lighted and plate current of each tube equal. Electrons will flow from.X to P and from Y to P, Fig. 2, which means that I and I are both negative with respect to P. Plates A and D of the respective condensers are then negative with respect to plates B and 0. Let us assume that the plate current of tube 1 decreases slightly. This is not an arbitrary assumption because the tubes used as the drivers of this oscillating system were tested over periods Of time and current fluct- uations were found to be almost cantinuous, a drifting above and below the normal. With current indicating devices in each plate circuit, in a parallel set-up, the current fluct- uations of the tubes occured infrequently at the same instant, consequently, power supply variations were not the sole cause (9) for the current changes, but the inherent characteristics of the tubes. With the apparatus set up as shown in Fig. 2, and the plate current of tube 1 diminishing, the difference of potential across L1 is therefore decreasing (3L1 Ip1 decreasing). Condenser 01 will discharge, electrons flowing in the direction A L1 P r1 B and a potential difference will be developed across r1, the grid end being positive with respect to the filament end. The grid of tube 2 is connected to B, consequently, it will become positive and the result will be an increase in.the plate current of tube 2. This increase in plate current flowing through L2 will increase the potential difference between P‘Y (3L2 Ipz increasing). Condenser 02 is connected across L2 to the points Y and P through r2. This increase of potential across L2, Y'becoming more negative with respect to P, will cause a charging elec- tronic current to flow in the direction C r2 L2 D in order to raise the condenser voltage to the new value of potential difference across L2. This charging electronic current flow- ing through r2 produces a potential difference across it, making the end C negative with respect to the filament end. The grid of tube 1 is connected to point C and the result of the charging current flowing through r2 will be to apply a negative potential to the grid of tube 1, which will produce a still further decrease in the plate current of tube 1. ‘At this point, it can be seen that regardless of Just what the current change may be, the nature of the system is to magnify that change. (10) In the state of equilibrium the points I and I were at the same potential, but as this assumed equilibrium condition was disturbed in accordance with the foregoing steps, the potential of point X with respect to the filament becomes less negative and approaches the potential of P. At the same time point Y becomes more negative with respect to the P which means that Y'becomes negative with respect to.I. This difference of potential is therefore applied to condenser C, and a charg- ing current will be flowing in the direction 1 L1 Lg Y’N..As the potential across L2 increases, energy will thus be stored in C, that is, electrons will be stored on plate N of condenser C, and this storing process will continue until the upper limit of the plate current curve or saturation point is reached. it this time, the current flowing through r1 and r2 will cease. Thus the grid of each tube will lose its respective potential, causing the plate current of tube 2 to decrease and the plate current of tube 1 to increase and a cycle of events will follow which result‘ in a reversal of the electron flow in the L1 L2 C circuit. We will now consider the oscillatory current in the 11 L2 0 circuit, its relation.to the current flowing through the vacuum tubes and its influence Upon.their action. It has been shown how it is possible for each of the vacuum tubes to cause some energy to be delivered to the L1 L& C circuit. If sufficient energy is given this circuit at the proper intervals, it will oscillate at a frequency given by the following equation (2): (11) I I - Elam-1+ 1-2) 0 Let us now analyze in detail the behaviour of this alternating or oscillating current in the circuit L1 L2 C, and its effect upon the current flowing through the two vacuum tubes in causing energy to be supplied at the proper intervals. The best method of treating the L1 L2 0 circuit and ’ the alternating current flowing in it, is to consider the vacuum tubes as a generator of’sn alternating e.m.f. which when applied to the L1 L2 C circuit causes alternating current to flow therein (5). This alternating voltage is the result of a varying voltage being impressed upon.the grid of the tubes (3) . The conditions under which.we begin the explanation is shown in.Pig. 3, that is, Ip2' has reached its maximum value, which as it has been shown, is determined by the character- istics of the tube and its grid pctential. Condenser C has been charged due to the potential across L2, that is, plate I being negative with reapect to plate I. The plate current of tube 1, Ipl' has reached its lowest value which might be zero. 'In.any'case the following explanation.need not be altered. At this time, calling this our starting point, condenser C begins to discharge, 'fhat is, electrons leave plate I traveling in the direction I P I I. Any charge condenser is held under a strain, seeking to relieve the tension immediately. Hence, because condenser C (12) is charged,it supplies a voltage to the circuit, causing electrons to flow in the direction Just stated. Thus, point Y’is negative with respect to point P, Pig. 5, and.the potential is greatest when the condenser first begins to dis- charge. The current through L1 and L2, because of this maximum potential, is changing or increasing at its greatest rate. While the current increases through L1 and ngthe magnetic lines of force produced by the current build up outward from the coil. This induces an electromotive force in the circuit which is counter to the condenser voltage. This counter voltage slows up the condenser current and represents the effect of self-inductance by tending to prevent the current from rising. It will be noticed by observing the curves of Pig. 3, that the current flowing through L2 at this time is composed of the electrons that were stored on plate B, condenser C and electrons that are flowing from the plate of tube 2. . Condensers Cl and Ca are connected across L1 and La as shown in Pig. 2. It should be clear at this point that as condenser C dischargeslits potential difference will be grow- ing less. Consequently, the potential difference across L2 will be growing less, point I becoming less negative with) respect to point P, and point I becoming more negative with respect to point P. Therefore, the potential of the grid of tube 1 is becoming less negative and the potential of the grid of tube 2 is becoming more negative with respect to the filament. The plate currents of tubes 1 and 2 will be increasing and (13) decreasing reapectively. ‘During this period the plate voltage of tube 2 is rising, becoming more positive, because of the voltage across L2 which is counter to the condenser voltage C. It is therefore approaehing the potential of the supply source. it the time when.the potential difference between H and N, condenser C, is equalized, the plate potential of both tubes will be the same. It can be seen at this time that it is this counter voltage set Up by L1 and L2 that is the cause for the change in plate potential. The magnetic field about L1 and L3 will reach its maximum value Just at the instant condenser C has become discharged or has given up its energy. At this instant the potential dif- ference between points x and Y is zero. Therefore, the grid of each tube will be at the same potential, namely, that potential resulting from the r1 181 and r2 182’ I81 and 188 being the respective grid current values. In further explanation it should be here said that in order to operate the vacuum tubes on the desired portion of the plate current grid potential curve, the proper steady grid biasing voltage is obtained by the use of the resistances r1 and r3, in connection with the grid blocking condensers as follows}. When the grid is positive, a anall current will flow from the filament to the grid, and because this current is not sinusoidal, but pulsating in one direction, it will have an average value, which.may be considered as a.direct current, thus resulting in a steady voltage on the grid. In order to obtain high efficiency the value of each resistance (14) is such that the potential drop across it is sufficient to bias the tube back beyond the cut-off point (4). The plate current will then be flowing only during the half cycle when the grid excitation voltage is positive. In the cycle of events ninty degrees removed from our starting point, when the magnetic field has reached its maximum value and the condenser has given up its energy, the magnetic field about L1 and L2 will instantly begin to recede. This action of the magnetic field upon L1 and L2 induces an electromotive force of the same polarity as that of condenser C before discharge. This new electromotive force generated by the receding magnetic lines of force about L1 and L2 con- tinues the electronic flow in the direction I P.X. In other words the self-inductance of L1 and L2 perpetuates the current thus tending to prevent any change in its value. As the magnetic field about L1 and L2 recedes, the magnitude of the current flowing in the direction I P1X through L1 and L2 will decrease because the condenser devOIOpes a counter or reactance voltage as the charge in it builds up. As this reactance voltage increases the rate of electron flow to condenser, plate I’diminishes. Thus’the point.x with re- spect to points P and If will become more negative and the voltage across condenser C will become opposite in polarity to the initial voltage condition. Hence’it can be seen that . it requires a definite length Of time to build up a magnetic ‘ field around L1 and L2 and to charge condenser C to its max- imum potential. This is how the element of time enters into the sequence of energy changes and determines the frequency (15) of these occurances. ‘ Condenser 01 through r1, is connected across L1, and because the magnetic field is receding in L1, a charging electronic current will flow in condenser C1 in the direction B r1 P A, thus making the grid of tube 2 negative. Its maximum negative potential will occur when the magnetic flux in L1 is changing at its greatest rate, namely, 180 degrees removed from our starting point. Likewise condenser Cg, be- cause cf its connection across L2 through r2, is going to be charged. Point I is becoming more positive with respect to point P and a charging current will flow through r2 in the direction D‘Y P r2 C, thus causing the grid of tube 1 to become positive with respect to the filament. The grid pd- tehtial of tube 1 will reach its maximum positive potential when the rate of change of the magnetic field about L8 is greatest. Likewise this occurs 180 degrees from our starting point. As the grid potential of tube 1 is becoming more positive, electrons flowing from the plate of the tube will travel to plate H of comenser C, because that is the path of least resistance. Plate l of condenser C is at a positive potential in.qficess of that of the supply source. The mechanical anal- ogy of this phase is that of comparing the inductance to some- thing having inertia and the condenser as being free from inertia; but the ease with which electrons flow into the con- . denser will be lessened as the charge inhreases. The process of charging a condenser is comparable to Torcing water into a chamber‘ having an elastic diaphragm fOr one of its walls. (16) As the quantity of water in the chamber increases, the elastic diaphragm exerts counter farce thus increasing the difficulty of forcing more water into it. Thus, condenser C acts as a reservoir for energy or electrons. Therefore tube 1 has delivered energy to the oscillating circuit fbr one quarter of the cycle, that is, during the period when the magnetic field about L1 is dininiahing from its maximum to its zero value, condenser C is being charged from its zero value of difference of potential between its plates to its mathmm value. ‘The vacuum tuber when it_is conducting current, this being detenuined by the grid excitation.or potential, delivers energy to condenser C which is to be used at a later instant to maintain or increase the amplitude of the current in the oscillatory circuit L1 Lg C. When the magnitude of the magnetic field about L1 and L2 has diminished to a zero value, the potential difference between the plates M and N of condenser C is a maximum. Thus the potential across L1 and L2 is’a maximum. Therefore, sans, the grid of tube 1 has its maximum positive value and the grid of tube 2 has its maximum negative value because of their connections across L1 and L2. The potential of the plate of tube 1 has a value sufficient to overcome the space charge drop, and the potential of the plate of tube 2 has the supply ' battery potential plus that of Lg. We are now at a place in our cycle of events 180 degrees removed from our starting point. The magnetic flux about L1 and L2 is zero and condenser C is fully charged. As condenser C then begins to discharge" (17) electrons flow from plate M'in the direction X P'Y, causing e.magnetic field about L1 and L2 to build Up. This magnetic field induces in the circuit an electromotive force which is counter to the condenser voltage causing the potential difference across L1 and L2 to decrease. The plate potential of tube 1 willIthereforeIincrease and the plate potential of tube 2 will decrease. This change of potential across L1 and L2 causes the grid of each tube to be affected, that is, the potential of the grid of tube 1 becomes less positive and the grid of tube 2 becomes less negative. It can be seen at this time that the plate current of tube 1 is flowing through L1 supplying energy to L1 in the form of a magnetic field, this occuring for one quarter of a cycle. Thus tube 1 is capable of delivering energy first to the con- denser and then to the inductance. The total time of energy delivery is one half cycle. Therefore it is necessary to bias the grids sufficiently so that current will flow through each tube for only half cycle intervals, that is, when their re- spective grid potentials are positive. If either of the tubes conduct current for a greater period, inefficiency in opera- tion would result (6). Condenser C continues to discharge until the potential difference between its plates is equalized. When this happens, almost all of the energy previously in the electrostatic field will be in.the form of a.nagnetic field surrounding L1 and L2. At this instantfl the grid of both tubes are at the same potential, as was shown earlier in the cycle. If the two tubes “-9 a high negative bias potential,neither of the tubes sre,. Pea-ins any plate current. LLU) We are now 270 degrees removed from our starting point. Condenser C, having given up its stored energy, cannot now furnish additional current because the potential difference between its plates is zero. The result will be that the mag- netic field around L1 and L2 will instantly begin to recede. I The falling back upon the coil of this magnetic flux induced an electromotive forcex1causing the current to flow in the same direction that it did when condenser C was last dis- charging. This electrcmctive force will increase as the rate ' of change of flux increases, thus increasing the positive potential of point x with respect to point P. The grid of the respective tubes will be influenced accordinglyx causing thd plate current of tube 2 to rise and the plate current of tube 1 to decrease. Plate l of condenser C will act as a reservoir fbr electrons until such a time as they can pass through L2. This occurs when condenser C is charged to its maximum value and the magnetic field about L2 is depleted. The conditions Which must be fulfilled in order that the amplitude of the oscillations will increase are that n.e8, where J1 is the amplification constant of the tube and as is the grid excitation voltage, must be greater than and in phase withx the alternating voltage in the L1 L2 0 circuit (6). When use is equal to the alternating electromotive force in the L1 L2 C circuit, the oscillations will be sustained (6). The amplitude of the oscillations in the L1 L2 C circuit will increase until the grid voltage variations are such that the operating point of the tubes describes the entire portion of the characteristic curve lying between the upper and lower \J-VI bends. The amplitude will then stop increasing because a further increase of alternating grid potentials would no longer produce a corresponding or proportional increase of plate current. If the electromotive force e8 impressed upon the grid condensers is such that the equivalent plate electromotive. force.u e8 is smaller than.the electromotive force operating in the L1 L2 0 circuit, the oscillations will not be sustained; but will decrease in amplitude and the electromotive force across L1 Lg which affect the grids will decrease too. The oscillations will therefore be damped out. This damping is less than that of a free oscillation of L1 L2 0 circuit, because acme energy is supplied, but not a sufficient amount to compensate for the losses. 0) l7 l6 l5 )4 13 )a’ t) Figure 3. (21) CRAPHICAL REPRESENTATION OF THE ELECTRONIC FLOW AND VOLTAGE WITH RESPECT TO THE Two VACUUM TUBES ATP THE L1 L2 C CIRCUIT Curve 1, represents the electron flow corresponding to each tube as marked. Curve 2, shows the electron flow through L1 and L2 the direction.cf electronic flow is marked Upon.the curve. Curve 5, shows the electron flow from one plate of the ‘ condenser to the other. Of course the electron flow into the condenser is a combination of the electrons from the induct- ance plus that which the tube is supplying. This is shown be the current curve #1. Curve 4, represents the potential of point Y'with respect to point P and X, which is the potential across L2. This is the potential that is supplied to the grid of tube #1. It can be seen that this potential is in phase with the plate current of l. A condition which must be fulfilled if the system is to sustain oscillations. Curve 5, represents the potential of point I'with re- Qpect to point P, which is the potential across L1. It is this potential that is impressed upon the grid of tube 2. (This potential is in phase with the plate current of tube #2. A condition.which must be fulfilled if the system is to sustain oscillations (loc. cit.). (22) EXAMPLE ILLUSTRATING METHOD OE CALCULATION The rating of the two UK 852 tubes is 150 watts output, and the input to the plate circuit is 300 watts, an efficiency of 60%. The frequency will be 10 meg cycles, or a wavelength of 30 meters. The inductance of the coil (L1 and Lg) is 12.8 micro- henries. The capacity of the condenser (C) 20 micro micro farads. The reactance of the coil (L1 and Lg at a frequency of 10 meg cycles is:' XIII!“ L2 3 13wa ' 211 102105: .0000128 804 ohms 'Morecroft (2) has shown that the plate voltage of an oscillator must vary from nearly zero to nearly twice that of the supply potential. Then the plate voltage in our case will fluctuate from nearly zero to nearly 4000?. The effective plate voltage will then be: _ 2000 = 1418 Volts :2 '. as the voltage of our supply source is 2000 volts. If the value of the plate voltage rises to 4000 volts, the maximum grid potential must be sufficient to allow no current to flow during this period. The resistance values of r1 and rg must be such that the (23) grid potentials will stop the plate current in the tubes at a time in the cycle when commutation occurs. Therefore the product of the grid current multiplied by the resistance of either resitor should be EP R .3 Applied D. 0. plate potential. P ,1 Therefore in our problem the grid bias voltage should be Amplification constant. 2000 3 166.5 volts. The maximum excitation voltage upon the grid should be 2 Ep 1L 2 x 2000 s 333 volts the effective value is then 333 a 235 volts. by assuming a reasonable power factor (2%) the high frequency resistance of the circuit is about 7 China. If 150 watts are to be delivered to the oscillating circuit and its resistance is 'I owe the current flowing than. L1 and L2 will be, a 4.62 anperes The reactance from mid-point on the coil L1 and Lg to (24) either end is 402 ohms, the reactance drop<1>L1 L = eL 1 2T!“ 10 x 1061.0000064 x 4.62 = 1850 volts. It can be seen from the above calculation that the reactance drop across either L1 or 12 is more than sufficient to give ample grid excitation voltage. The reactance drop across about one sixth of L1 or L2 is theoretically required according to the calculation. However, because of the voltage drop across the grid blocking condenser, a higher voltage will be required. It has been found that by using the voltage across about one third of L1 and L2 will give ample excitation voltage. (25) S‘U M MIA R Y A N D C O N C L‘U S I 0 N Summarizing the analysis briefly, we can say that during the period the first tube is carrying current its anode po- tential has a small value sufficient to overcome the space charge. The oscillating circuit has a sinusoidal voltage, and the potential of the anode of the second tube is equal to the space charge voltage plus that of the oscillating circuit voltage. During the period the second tube is carrying current, a reversal of the above condition exists. The conducting path shifts from one tube to the other when the oscillating circuit voltage is zero, that is’when the current through L1 and L2 is a maximum. It can be seen that the function of the plate filament circuit through the vacuum tube is to connect a sinusoidal and a steady voltage source together at a time when the volt- ages are nearly equal. If they were exactly equal, there would be nothing left to overcome the space charge drop in the tube. The energy supplying operation is thise fit a time in the cycle when the current is a minimum, the voltage is a maximum, consisting of the direct current voltage plus the peak value of the alternating voltage. When the total plate potential is lowest, current flows into the oscillating system, thus supplying energy, one tube operating one half cycle and the other tube Operating the other half cycle. The period during Which.either tube conducts current de- pends upon the grid excitation. The voltage used for excitation (2'5) is supplied by the oscillating system Li I2 C._and_will_be-: sinusoidal. The steady voltage for bias_in order to 99°?fite on the desired portion of the plate current gridLPthbtial curve is obtained by. the. use of a grid leal; and a grid blocka. ing condenser. 'These are r1 r2 and Ci D2.resnectively_in Fig. 2. The sinusoidal voltage is derived from.the reactance drop '..7. across L1 and L2 and is applied to the large blocking condensers. When the grid is positive. a.small current will flow to the grid; and because this current is not sinusoidal. but pulsating in one” direction, it will have an average value. This may be considered as a direct current, and will be forced to pass through ri,_fl Which produces a steady voltage on the grid. The same is true of re with respect to its grid. PART II P A R T II THE BIOLOGIC INFLUENCE ’ or HIGH FREQUENCY DIsPLAcEMEnr cuaaaurs ‘U P O N A H I M A L S A N D B A C T E,R I A I N T R O D'U C T I 0 N The influence of various forms of energy upon life has always been an attractive field for the biologist. As soon as the physicist has made available methods by which these different forms of energy may be applied, the biologist has made use of them in his field. Thus in turn he has studied gamma rays, Z~rays, ultra-violet rays and infra-red rays as well as light rays, all of which differ in wave-length. Be- yond the infra-red are the longer waves of the spectrum used by the radio and now commonly called lertzisn or electric waves. The vacuum tube has made possible short radio waves. The physicist has, therefore, placed at the disposal of the biologist a vast field of radiation the possibilities of which have been but little investigated by him. This region extending from the near infra-red to a theoretical infinity is so inconceivably vast that it would appear like a hopeless task to explore it. However, there are certain limitations due to mechanical and practical consider- ations that restrict the working field of the biologist to (28) wave-lengths of from approximately 1 to 100 meters. Even the possibility of thoroughly studying this restricted field would entail a considerable amount of work. In the present investi- gation three wave-lengths were selected and studied. The wave- length chosen were 20, 30 and 40 meters. The biologic influ- ence of these waves upon certain species of animals and upon bacteria was studied. Bacteria are ideal forms of life with which to work out the more fundamental biological aspects of the lethal effect of high frequency displacement current since they are unicellular, simple in organization and reflect more nearly the fundamental character of the biological effect of the dielectric in which they are placed. (29) LIITERATURE REVIEW. d'Arsonval (7) (B) in 1893 was the first worker to study the influence of high frequency currents on animals. The observed effects on animals he considered to be due to an increase in their temperature and metabolism. Later in the sens year (9) he described the apparatus which was used to generate the high frequency currents and together with Charrin (10) reported the specific biologic effect on color production in Pseudomonag agrugipgsg of a current oscillating at the rate of 800,000 cycles per second. They (11) next studied the influence of continuous and intermittent electric currents of high potential on the toxins of Pseudomonas aeroginosa and Qggynebacterium diphtheriae and found that they attenuated the toxins. Their next series of experiments (12) were conducted with high frequency currents of 200,000 cycles per second and a wave-length of 1,500 meters. In these eXperiments the temperature never exceeded 18° 0. They found that the irradiated toxins were attenuated and had special immunizing properties. After the work of d'Arsonval and Charrin there seems to have been no further important studies made of the biologic ~effects of short electric waves of high frequency currents for over a quarter of a century. With the advent of the radio and the development of vacuum tube oscillators, research work in this field was resumed. MMch of the recent work has been done with plants and animals or with plant and animal tissues and not with bacteria. Gosset, Gutman, Lakowsky and Magrou (13) demonstrated (so) that tumors of plants produced by Bacterium Lgmgfggigng'were destroyed by electric waves of 2 meters oscillating at a rate of 150,000,000 cycles per second. Schereschewsky (14) working with mice at frequencies of 8,300,000 to 135,000,000 cycles per second found the physiolgic effect most marked_in a certain band of frequencies extending from F . 66 x 106 cycles to F = 18.3 x 105 cycles, the effect diminishing as the frequency was raised to F : 135 x 106 or lowered to F : 9 x 105. He continued his work (15) upon trans- planted mouse sarcoma and tranSplanted foul sarcoma. In this work he used 68,000,000 to 66,000,000 cycles per second and found the action of the electrostatic field highly inimcal to tumor growth and development. Kahler, Chalkley and Voegtlin (16) used Paramoscium caudatum in their studies of high-frequency electromagnetic and electrostatic fields. Wave-lengths of 4 and 30 meters were used. Their results showed that when the solutions were cooled to 30° C. or below, there was no injurious effects noted. The rate of multiplication was unimpaired. MCKinley (l7) exposed the seeds of Golden Bantam corn to the action of a high frequency electrostatic field and found that an exposure of 30 to 40 seconds accelerated germination of the corn while an exposure of one minute slightly retarded their growth, Exposures of from 5 minutes to 1 hour were highly lethal to the seeds. Week old rats (18) killed by means of the electro- static field and by external heat of an oven did not show the same microsc0pica1 picture. The body temperature in both cases was kept below 46° C. In his work he was able to show that the lethal action of the electrostatic field varied with the amount of nervous tissue present. In the case of holometabolous insects as Tenebris molitor, the adult was killed in 1 minute and 19 seconds, while the larva was killed in 7 minutes and 38 seconds. The nervous organization is more highly developed in the adult than in the larva for this group of insects. For the hemimetabolous insects the lethal time was approximately the same for the adult and the nymph. Here there is no marked difference in the nervous organization of the two. He also noted a difference between the action of the electrostatic field and external heat on the nerves of the sciatic plexas of a frog. They believed that high frequency and heat are not symonymous in their action, and that while some of the effects of the electrostatic field may be attributable to heat, that there is another reaction, which is as yet little understood. The effects noted may be due, they postulate, to the destruction of delicate cell balances by ionic displacements or to the differences in absorption between the different body tissues. Headlee and Burdette (19) likewise found a relation between the nervous system and the production of heat. The more specialized the nervous system the greater the increase in speed of reaction. They measured the heating rate of many organic compounds and found that cholesterol had the most rapid heating rate of those tested. There seems to be a difference of opinion among various investigators who have worked with high frequency radiation ‘. to whether the observed biological effects produced are due to (:52) the action of the current which produces chemical complexes in the cell or to the action of heat induced by the current. Schereschewsky (14) as a result of his work concluded that frequency was the sole differentiating characteristic and was a determining factor in the mode of action upon living organisms. He confirmed this view in his work on chicken and mouse sarcoma and states, "The hypothesis that the frequency at which these currents are produced may have the specific quality of attacking certain cells more then others is interesting and worthy of future experimentation." Ohristie and Loomis (20) in their work on mice showed that the lethal nature of the radiations was proportional to the intensity of the field up to 50,000,000 cycles. At frequencies higher than this the lethal effect of the radi- ations appeared to diminish. They explained this by the fact that the standard of the current strength was the intensity of the electromagnetic field and not necessarily the amount of current induced in the mouse. They believed that the changes in the dielectric constant of the mouse caused a diminuation in the amount of current induced in it. At wave-lengths less than.6 meters e.mouse behaved in a different manner than an electrolyte. from their work they concluded that the results they obtained were due to the production of heat in the mice generated by the resistance of the tissues and the dielectric loss. Their results were directly at variance with those obtained by Schereschewsky. They believed that the method which he used to measure the intensity of the electrostatic \vvl field was incorrect, and, therefore, he did not obtain a true picture of the output of energy at the different frequencies which he was using. In order to measure more accurately the amount of energy between the condenser plates at different frequencies, Christie and Leonie used a saline thermometer. This method was like- wise subJect to error as was demonstrated by the work of Isrshall (21), Boomer (22) and Richards and Loomis (23) who showed that the heat effect depends upon the frequency and that it varies with the different electrolytes. Furthermore that for the different electrolytes there exists a specific concentration at which.maximum heating occurs if the wave- length is constant. The results of.Kahler et al (16) would indicate that the lethal effect upon.paraéicimm was proportional to the rise in temperature whether the temperature was induced by the magnetic or electrostatic fields or by the application of heat to water. Schliephake (24) (25) (26) in his work made a comparison of the action of ordinary diathermic currents with the action of short electric waves, 2.8 meters. He used the rate of cutaneous heating as the standard of comparison.and found that there was selective heating of various tissues. The short ‘waves heated the liver and bone most and the diathermy hosted the adipose tissue to the greatest extent. Continuing his work, Schliephake (27) found in the case of a human leg that the heating effects of high frequency radiation of a wave-length from 3 to 20 meters was dependent on the position of the condenser plates on the leg. He per- formed another interesting experiment on the heating effects (34) of high frequency currents upon a block of dough. When the condenser plates was touching the dough, the heating effect was similiar to that observed in diathermy. When, however, the condenser plates were not touching the dough it was heated uniformly throughout. In this same paper Schliephake reports experimental work conducted with the tubercle bacillus and staphylococci. The growth in subcultures of tubercle bacilli which had been irriadiated for 30 minutes was retarded from 12 to 14 days over those of unexposed controls. Staphylococci irridated between the condenser plates died more quickly than control cultures exposed to the same degree of heat in a water bath. Ssymanowski and Hicks (28) worked with three bacterial toxins, diphtheria, tetanus and botulinus, in raw broth filitrates. They were able to attenuate them by subjecting them to wave-lengths of 1.9 to 3.7 meters. In their work they controlled the temperature so that the attenuation of the toxins was not due to the heat factor. They advanced a theory that the attenuation of the toxins was due to rapid agitation of the molecular dipoles of the toxins in the high frequency field and the resistance to this motion due to the viscosity of the fluid. Hichs and Ssymanowski (29) continued their work on a larger variety of biologic substances. ‘Most of the work reported in this paper was done at a 2.5 meter wave-length. Their work covers the action of the high frequency currents on.bacteria-streptococci, staphylococci and the diphtheria bacillus; on bacteriophage; on the precipitating antibody (so) for the pneumoooccus; on the course of the experimental in- fection in animals; on specific desensitization; and on immunization by irradiated toxins. The temperature was likewise controlled in these experiments. They concluded that under the conditions of their experiments ultrahigh frequency fields had no biologic action on the substances studied. Carpenter and Beak (30) in their work on experimental syphilis in rabbits found that exposure to a field of 30 meter radio waves oscillating between two aluminum plates entirely altered the usual character of syphilis infection in such laboratory animals. The rectal temperature was raised from 3 to 5° F. They believed that the results were due to an increase in temperature in the rabbits when placed between the aluminum plates. (36) A P P A R.A T'U 3 The 'push-pull' self excited oscillator and the reson- ating circuit for the utilization of its energy in connection with a combination cooler and condenser are shown in Fig. 4, diagrammatically. OSCILLATOR:” The filaments of the two'Ux 852 vacuum tubes were heated by a transformer whose secondary potential is 10 volts. The plate circuit is fed by a full wave rectifier, using a General Electric transformer, whose secondary winding delivers 2000 volts on each side of the center tap working into two I J 28 General Electric hot cathode mercury vapor rectifier tubes. The rectified current then passes through a filter system as shown in Pig, 4. An.Amertran transformer whose secondary winding delivers 10 amperes at 2.5 volts was used to heat the cathodes of the mercury vapor rectifier 'tubes. The inductance in the main oscillatory circuit was of such a value that the reactance drop across half of it was sufficient to supply the proper grid and plate excitation voltage. (5'7) 1' I l‘ I RR 110V.” 1 2.5 l q re .pere s condary w 18 h '4 < chok ' P I so HOT cumin mount fir. VAPOR RETIFIE TUBE O W .i T oils rlecder 2W ‘ UK 852 comma scmmc helium: 171mm 4 . ‘T'J -JA-U.J.. ffifr COITBIIIATION COOLER A121) COED //I////Il////////lll/¢ III/I’ll} ,////////////A ; xfill/IIIxxlzlllllllllllllllI’ll/IIII/IIIII/////// 9 Fromm 5. I. 8. 3. 4. 5. 6. 7. 8. 9. (39) Key to Figure 5. Mercury . 'Pyrex test tube. Connections to the plates of the condenser. Inoculated nutrient broth chamber. Electrode (constituting plate of condenser) surrounded ‘with pyrex glass. Circulating water inlet. Pyrex mounting insulator and stand. water chamber. later outlet. (40) A H-I‘M A L ' E X P E R IVM.E N T S The animals (see table 1) that were used in this exper- iment were placed between the plates of the condenser in.the main oscillating circuit, thus exposing them to an electric field. The inside faces of the condenser plates were insulated in order to prevent the animals being burned by electrons either passing into or out from the animals' bodies to the metallic circuit. Even though the animal body was insulated from the con- denser plates, they were subjected to an electric current since llaxwell has shown (31) that any change in the electric: induction in aumedium is an electric current. When electrons leave one plate of the condenser and pass to the other plate, the current in the wires to the plates represents the rate at which electrons are leaving one plate and pass on to the other plate. Considering the plates as having unit area the charge on each plate is equal to the surface density J“and the current i flowing from one plate to the other through the inductance is: i - d<7 "d?- Btarling (31) has shown that the electric displacementlb in the dielectric is equal to--.- Figure 8. (65) Figure 9. (55) Figure 10. .1'“ meg stud ter the me: im 08 (67) D 1 S C U S S I 0 N It is apparent from these data that a frequency of 10 meg cycles per second is by far the most effective frequency studied. This Was true both for the animals studied and bac- teria. The data as given in tables 2, 5 and 4, would indicate that the reason for the greater effectiveness of the diaplace- ment current at this frequency was due to its ability to increase the temperature. The nutrient broth used for the bacterial experiments had approximately 0.65 per cent NaCL, 1 per cent peptone together with meat extractativee of unknown chemical com- position. 13 this was added bacteria of unknown chemical composition. This solution constituted part of the dielectric of the condenser. It has been shown by a number of investigations (22) (23) that the heating of an electrolytic dielectric subjected to high frequency diSplacement current is a direct function to the salt concentration, likewise it varies for various salts at the same frequency. It has also been shown (21) that there is a considerable difference between inorganic and organic salts as well as collodial and non-collodial material in their heating when made a part of the dielectric of a condenser in a high frequency circuit. When a solution such as was used is made a part of the dielectric of a condenser in a high frequency circuit, the disturbance in this solution is due to the potential difference between the plates of the condenser causing electronic or ionic displacement which in turn produces heat 0 Richards and Loomis (23) have shown that the power loss in a condenser having an electrolytic dielectric manifests itself as heat and is a function of the conductivity of the electrolyte and frequency of the current in the external circuit. A simple means of measuring the power loss would therefore be to measure the heat produced in the dielectric. Since the temperature rise, table 2, Fig. 9, in the dielectric at 7.5 meg cycles per second was less than for either of the other two frequencies studied, table 3 and 4, Fig. 9, it would indicate that the power loss in the condenser was less. This would account for the observed lethal effect at this frequency. At a frequency of 10 meg cycles per second the temperature rise of our dielectric was greater than for 7.5 or 15 meg cycles per second, which would indicate that the power loss was greater at this frequency than at either 7.5 or 15 meg cycles per second, Fig. 9. This offers a rational explanation of the observed facts in those experiments where the temperature was not controlled. However, when the dielectric was cooled to 19° C. by means of circulating water, thereby controlling the temperature factor, it is apparent that some other factors are involved. Influence of size of bacteria on radiation. It is a well known fact that the amount of heat radiated from a body depends, among other factors, upon the amount of surface area. It is also a well known fact that bacteria due to size have a large area in prOportion to their volume. This is well illustrated in the case of Escherichia_goli. For example, the average size of Escherichia coli is 0.8 u I 1.5 n. For shnplicity of calculation if we assume the cell to be a cylinder, the area of its surface would be 4.77 pa and its' volume 0.73 as. This gives a ratio of volume to area of one to six. Therefore, bacteria suspended in a dielectric of a condenser in a high frequency circuit would rapidly radiate the heat produced within the cell. Experiments with bacteria indicate (32) that the order of death in bacteria due to physical and chemical agents such as heat, light,drying, chemicals, etc. is an orderly process. The definition that the rate of death is proportional to the number of living cells, is a simple statement of the facts. This regular order of death makes a general mathematical treatment possible. This order of death from a mathematical standpoint is similiar to the monomolecular reactions in chemistry and may be stated mathematically by the following K :'1 lo a - 10 'b -e 5.355 Where a equals the initial number of cells, b equals the equation: number of cells surviving after an exposure for a given time interval and X represents the death rate in.deoimal logarithms. Rahn (33) has computed a general formula for the order of death for any number of reacting molecules which it is necessary to inactivate in order to produce death. When the logarithms of the surviving bacteria are plotted against time, a straight line indicates that death is brought about by the inactivation of only one molecule. When death is produced by the inactivation of more than one molecule, then the line is distinctly bulging. A comparison of the death rates of higher organisms with those of bacteria show that the survivor curves of all living things except unicellular organs are 0v bulging while bacteria show either a straight line or a survivor curve sagging below the line. The lethal effect upon bacteria of the various frequencies of displacement current used, shows that when the logarithm of the number of bacteria surviving at the end of two hour intervals was plotted against time, a typical survivor curve resulted, Fig. 10. Since the logarithmic curves are linear, it would indicate that death was caused by the disruption of one molecule in the cell. However, in these studies 24 hour cultures of Escherichia coli_were used. It has been shown that when cultures of uniform resistance are used the survivor curve is linear, but in cultures having various degrees of resistance the curve sags. The greater the difference in resistance the greater the sag of the curve. It is evident then that either the bacterial cells were of uniform resistance or that the displacement current was of such a nature that the resistance of individual cells was not a factor. In conclusion it may be stated that in the experiments where the temperature was not controlled, that heat was undoubtedly the principle factor in producing the pronounced lethal effects noted. Even when the temperature of the culture was controlled, the displacement current generated heat within the cell due to the intense electronic and ionic linear agitation. Under these conditions the bacteria were able to radiate a greater amount of heat because of the high ratio of their area to their volume. This would account for the length of time they survived in this environment as compared to the invironment where the temperature was not controllgd:w”" (71) Szymanowski and Hicks (28) explained the attenuation of toxins, which made up the dielectric of a condenser in a high frequency circuit, as due to the rapid agitation of the molecular dipoles and the resistance apposed to their motion by the viscosity of the fluid. This rapid agitation being due to the rapidly changing polarity of the condenser plates. In the animal experiments a diaplacement current at 10 meg cycles per second had the greatest effect on the animals of any of the frequencies studied. The next most lethal frequency was 16 meg cycles per second while the 7.5 meg cycles current was the least effective. In the case of animals we were dealing with a more highly developed mechanism which is subject to a greater variety of factors. It has been shown (17) (19) for example that the more highly developed the nervous system in an animal the greater the influence of high frequency current upon them. It has also been shown (24) (25) (26) that different tissues within the animal have different specific heating effects. Another factor of importance in this connection is the ratio of surface area to volume in animals. This would influence the rate at which the heat was radiated from their body. Presumably one or more or all of these factors are important in determining the lethal effect of the current depending upon the complexity of the animal. SUMMARY AND CONCLUSION Different species of animals responded differently to high frequency displacement current. Without exception a current of 10 met cycles produced the greatest lethal effect at the intensity used. A high frequency displacement current at 15 meg cycles was the next most lethal, while 7.5 meg cycles had the least effect on the animals studied. Bacteria as represented by Escherichia 231;,were more resistant to the lethal effect of high frequency displacement current at the same intensity than were any of the animals studied. In a high frequency displacement current of 10 meg cycles and an intensity of 0.08 amperes the number of Escherichia,ggli increased nearly 300 per cent during a period of three hours. When the intensity of the displacement current was increased approximately 10 times, the lethal effect of the current became evident. * Of the three frequencies studied, 7.6, 10 and 15 meg cycles, 10 meg cycles is the most effective, 7.5 meg cycles is the least effective while 15 meg cycles occupies an intermediate position. I The high frequency displacement currents produced a regular order of death inbacteria. When the logarithm.of the number of bacteria surviving at regular intervals was plotted against time, a typical survivor curve resulted, Fig. 10. The most probable explanation of the observed results is that the displacement current generated heat within the cells due to the intense electronic and ionic linear agitation. J‘s A C KIN O W L E D G M'E I T 8 It is with deep appreciation that I acknowledge the assistance and constructive criticism offered by Prof. O. L. Snow of the Physics Department in the preparation of Part I; and to Dr. F. W. Fabian of the Bacteriology Department for his guidance and untiring energy in the preparation of Part II. .’\ B I B L I O G’R A P H Y 1. Charton, W. Vacuum tube performance VS manufacturing tolerances. Electronics 4: Feb. 1932. 44-45. 2. Morecroft, J. H. Principles of Radio Communication. 2nd ed. New York; John Wiley and Sons, Inc. 1927. 1.! , 3. Prince, D. C. and Vogdes, F. B. Vacuum tubes and oscillation generators. General Electric publication; GED 272. 4. Prince, D. C. High Efficiency Circuits. General Electric Review. May 1932. 5. Prince, D. C. and Vogdes, F. B. 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