Abstract:
A method and apparatus is disclosed for monitoring an angular displacement, such as angle position and the direction of displacement. The method and apparatus includes at least one resonator placed in proximity to a electrodynamic profile and exciting within said resonator an alternating electromagnetic field. The electromagnetic field should be at a frequency at which the electromagnetic field contacts the electrodynamic profile and then variations of the electromagnetic field parameters are measured for the resonator caused by rotating the electrodynamic profile. Excitation of the resonator is by an electromagnetic field in the form of at least one slowed electromagnetic wave having a suitable energy distribution of the electric and magnetic fields for measuring the electromagnetic field parameters.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of U.S. patent application Ser. No. 09/134,056, filed Aug. 14, 1998, by Pchelnikov et al., for Electromagnetic Method of Liquid Level Monitoring. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the angular displacement monitoring, more specifically, to an electromagnetic method and apparatus for measuring angular position and a rotation speed of the axial parts of different mechanisms. 
     BACKGROUND OF THE INVENTION 
     The usefulness of the RF or microwave field application for angular displacement and rotation speed monitoring is recognized by the prior art. Such devices can operate with either RF or microwave excitation. When an electromagnetic field is excited near the rotating part of a mechanism, the parameters of the electromagnetic field, such as resonant frequency, phase or amplitude, vary with the change of angular position of the rotating part. The electromagnetic field parameters may be converted into angle, angular speed or rotation frequency. In particular the state of the art is shown in U.S. Pat. No. 3,939,406 “Sensing Rotational Speed by Amplitude Modulating a Continuous Microwave Signal,”/F. W. Chapman, F. E. Jamerson, and N. L. Muench, 1971, disclosing an electrodynamic sensor including two cavity resonators, one connected to a microwave generator, the other connected to microwave receiver, the two cavity resonators placed near a muff installed on the rotating part, said muff has identical slots in a cylindrical surface along generatrix and positioned periodically in the angular direction. The rotation of the slots influenced by the angular displacement of the muff, leads to a change in the electromagnetic connection between the resonators and, as a result, to the amplitude modulation of the signal passing from the microwave generator to the receiver. The modulation frequency is proportional to rotational speed. 
     A general discussion, see V. A. Viktorov, B. V. Lunkin and A. S. Sovlukov, “Radio-Wave measurements” [in Russian],  Moscow: Energoatomizdat,  1989, pp.148-153, states that a microwave resonator is placed near the rotating part, which surface electrodynamic property (“electrodynamic profile”) changes, in the azimuth direction and the resonator&#39;s frequency has a direct correlation to the angular position of the rotating part. 
     Slowed electromagnetic waves and slow-wave structures are also well known in the field of microwave engineering, see J. R. Pierce, “Traveling-Wave Tubes” D. Van Nostrand Company, Inc., Princeton, N.J., 1950. These waves are electromagnetic waves propagating in one direction with a phase velocity v p  that is smaller than the light velocity c in a vacuum. The relation c/v p  is named slowing or deceleration and is designated as n. In the most practically interesting cases, slowed electromagnetic waves are formed in slow-wave structures by coiling one or two conductors, for example, into a helix, or radial spiral (prior art), which increases the path length traveled by the wave. The curled conductor is named “impedance conductor,” the other is named “screen conductor.” Additional deceleration was also obtained due to positive electric and magnetic coupling in coupled slow-wave structures, which both conductors are coiled and have configuration of mirror images turned by 180° relatively to the plane of symmetry, see Yu. N. Pchelnikov, “Comparative Evaluation of the Attenuation in Microwave Elements Based on a Spiral Slow-Wave System,”  Soviet Journal of Communication Technology and Electronics,  Vol 32, #11, 1987, pp. 74-78. 
     The slow-wave structure-based sensitive elements are known in the art, see V. V. Annenkov, Yu. N. Pchelnikov “Sensitive Elements Based on Slow-Wave Structures”  Measurement Techniques,  Vol. 38, #12, 1995, pp. 1369-1375. The slowing of the electromagnetic wave leads to a reduction in the resonant dimensions of the sensitive elements and this enables one, by using the advantages of electrodynamic structures, to operate at relatively low frequencies, which are more convenient for generation and are more convenient for primary conversion of the information signal, but sufficiently large to provide high accuracy and high speed of response. The low electromagnetic losses at relatively low frequencies (a few to tens of megahertz) also helps to increase the accuracy and sensitivity of the measurements. The slowing of the electromagnetic wave leads also to energy concentration in the transverse and longitudinal directions, that results in an increase in sensitivity, proportional to the slowing down factor n, see Yu. N. Pchelnikov, “Nontraditional Application of Surface Electromagnetic Waves” Abstract Book, First World Congress on Microwave Processing, 1997, pp. 152-153. 
     Both the prior art and the present invention measure one or more parameters of electromagnetic field. Some of the prior art methods and present invention use one or two resonators, placed near the rotating part, having an “electrodynamic profile.” The resonators are connected to a measuring circuit comprising an RF or microwave signal generator which is used to excite an electromagnetic field. The change in rotating part position causes a shift in the characteristics of the electromagnetic field in the resonators. See V. A. Viktorov, B. V. Lunkin and A. S. Sovlukov, “Radio-Wave measurements” [in Russian],  Moscow: Energoatomizdat,  1989, pp. 
     Devices used in the prior art exhibit several problems overcome by the present invention. Previous methods have low accuracy, sensitivity, and resolution at relatively low frequency, increasing only with frequency increase. However, the increase in frequency is accompanied by an increase in electromagnetic losses, such losses causing a loss of accuracy of the measurement. It is also known that the higher the frequency is, the higher the cost of electronics. The previous methods do not yield the direction of the rotation, and require complex and expensive equipment. Thus, there is a need in the art for an electromagnetic method and apparatus for monitoring rotation that has greater sensitivity, resolution, diversity and lower cost. 
     SUMMARY OF THE INVENTION 
     The present invention employs a slow-wave structure as a part of a resonator sensitive to position of the rotating surface, parameters of the electromagnetic field in the resonator being informative parameters of position, velocity and the like. The main advantages of such sensitive elements, in comparison to known ones, are: relatively low frequency, concentration of electromagnetic energy in a small volume, the independence of their electrodynamic parameters upon the electronic circuit parameters. 
     Frequency decrease is achieved due to slowing. Sensitivity increase is achieved due to electromagnetic energy concentration near the rotating surface and due to shifting the electric or magnetic field in the region between the resonator and rotating surface having special electrodynamic profile changing along the azimuth direction. The direction of rotating is obtained due to using non-symmetrical electrodynamic profile, or due to using of two identical resonators placed with angular shift one to another, and comparing electromagnetic parameters of both resonators. The simplicity and inexpensive construction are due to relatively low frequency which allows the printed-circuit processing application. The high accuracy and resolution are due to the resonators&#39; design: the slow-wave structure-based resonators are made, as a rule, on dielectric base, stable to temperature alteration and its electromagnetic parameters dependence on temperature is very small, contrary to, for example, cavity resonators. 
     The present invention teaches an electromagnetic method of measuring the position of rotating surface, rotation speed and its direction or other measurements that require high resolution wherein: an excited electromagnetic wave with a preset distribution of the electric and magnetic components of the electromagnetic field makes it possible to increase the sensitivity and accuracy of measurement, using relatively low frequencies. The method is implemented in an apparatus, for example, encoders, wherein: the structural form of the resonators, used as the sensing element and the electrodynamic profile of the rotating part allow increased sensitivity and accuracy. In the invention resonators include at least one section of a slow-wave structure sensitive to the electromagnetic parameters of the electrodynamic profile rotating with a monitored part. 
     It is known, that the dielectric or conducting materials, placed in the electromagnetic field, alter its parameters, for example, its velocity, that leads to the phase delay or resonant frequency alteration. The influence of dielectric, conducting, and magnetic material differs and depends on electric and magnetic fields distribution in the monitored volume, see V. A. Viktorov, B. V. Lunkin and A. S. Sovlukov, “Radio-Wave measurements” [in Russian],  Moscow: Energoatomizdat,  1989, pp. 148-153. Application of slow-wave structures makes it possible to alter electric and magnetic field distribution in the transverse and in the longitudinal directions both, including the electric and magnetic fields splitting. It leads, from one hand, to the sensitivity increasing, and, from the other hand, to electromagnetic field parameters dependence on electromagnetic parameters of conducting or non-conducting objects being in the field of a slow-wave structure-based resonator. 
    
    
     DESCRIPTIONS OF THE DRAWINGS 
     For further understanding of the nature and objects of the present invention, reference should be had to the following figures in which like parts are given like reference numerals and wherein: 
     FIG. 1 illustrates a preferred embodiment of the present invention in which a resonator is placed inside a rotating part; 
     FIG. 2 illustrates a preferred embodiment of the present invention in which a resonator is placed outside a rotating part; 
     FIG. 3 illustrates a preferred embodiment of the present invention in which a resonator is placed from the side of a rotating part; 
     FIG. 4 illustrates a preferred embodiment of the present invention in which a resonator is placed between electrodynamic profiles; 
     FIG. 5 illustrates the measuring circuit of the preferred embodiment of the present invention; 
     FIG. 6 illustrates a preferred embodiment of the present invention in which two resonators are installed outside an electrodynamic profile; 
     FIG. 7 illustrates a two-conductor slow-wave structure scheme of prior art; 
     FIG. 8 illustrates a helical slow-wave structure of prior art; 
     FIG. 9 illustrates an interdigital combs of prior art; 
     FIG. 10 illustrates a preferred embodiment of the present invention in which an electrodynamic profile is made as a metal ring with a changing width installed on a dielectric body; 
     FIG. 11 illustrates a preferred embodiment of the present invention in which an electrodynamic profile is made as a metal ring with a configuration of a meander line installed on a dielectric body; 
     FIG. 12 illustrates a preferred embodiment of the present invention in which an electrodynamic profile is made as a row of metal members installed on a dielectric body; 
     FIG. 13 illustrates a preferred embodiment of the present invention in which one resonator is used for scalar monitoring of an angular displacement; 
     FIG. 14 illustrates a preferred embodiment of the present invention in which two resonators are placed diametrically opposite to the rotation axis; 
     FIG. 15 illustrates a preferred embodiment of the present invention in which one resonator is used for a small angular displacement monitoring; 
     FIG. 16 illustrates a preferred embodiment of the present invention in which two resonators are placed with 90° shift from the side of the symmetrical electrodynamic profile; 
     FIG. 17 illustrates the resonance frequencies of the resonators in FIG. 16; 
     FIG. 18 shows the relations between the average frequency and frequencies of vertically and horizontally placed resonators; 
     FIG. 19 illustrates an electric and magnetic fields distribution for in-phase type wave in the resonator of the preferred embodiment of the present invention; 
     FIG. 20 illustrates an electric and magnetic fields distribution for anti-phase type wave in the resonator of the preferred embodiment of the present invention; 
     FIG. 21 illustrates coupled arithmetic spirals; 
     FIG. 22 illustrates the preferred circuit of the preferred embodiment of the present invention for the phase delay converting into a generator&#39;s frequency; 
     FIG. 23 illustrates the preferred circuit of the preferred embodiment of the present invention to confer alteration of a resonant frequency to a generator&#39;s frequency; 
     FIG. 24 is an illustration of the resonator of the preferred embodiment of the present invention; 
     FIG. 25 illustrates a multi-pole of the preferred embodiment of the present invention, coiled into a ring; 
     FIG. 26 illustrates a non-contact matching plug placed near the multi-pole of the preferred embodiment of the present invention; 
     FIG. 27 shows a general scheme of a matching plug of the preferred embodiment of the present invention; 
     FIG. 28 shows the preferred embodiment of the present invention in which a transmission line of a matching plug is formed by coupled helices; 
     FIG. 29 illustrates a resonator wherein: a transmission line is replaced by two inductors; 
     FIG. 30 illustrates an resonator wherein: a transmission line is replaced by two capacitors; 
     FIG. 31 shows the sequence connecting of the resonator into a measuring circuit; 
     FIG. 32 illustrates a general model of the multi-pole in the present invention; 
     FIG. 33 demonstrates a multi-pole formed by meander line and a tape, both curled into rings; 
     FIG. 34 illustrates a multi-pole formed by coupled meander lines curled into rings; 
     FIG. 35 illustrates the preferred embodiment of the present invention in which the multi-pole is formed by coupled radial spirals with the sector form; 
     FIG. 36 illustrate a multi-pole in a form of a segment on a cylindrical surface; 
     FIG. 37 illustrates a multi-pole in the form of a closed ring on the cylindrical surface. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 1-3, an electrodynamic profile  1  may be mounted on the rotating part  2  inside (FIG.  1 ), outside (FIG.  2 ), or from the side (FIG. 3) of the rotating part  2 , said rotating part  2  having stationary axis  3  of rotation. It can be two electrodynamic profiles  1 , mounted from both sides of the resonator  4  (FIG.  4 ). The arrow A in figures lies in the rotation plane. In parallel to the electrodynamic profile  1  a resonator  4  is mounted on a stationary base (not shown in figures). The resonator  4  includes a matching plug  5  through which it is connected to the measuring circuit  6 . Circuit  6  comprises (FIG. 5) a generator  7  of electromagnetic oscillations at microwave or RF frequency, primary transducer  8 , converting the electromagnetic parameters of the resonator  4  into an electromagnetic informative signal, for example, frequency of the generator  7 , and converter  9 , converting electromagnetic informative signals into information about the part  2  angular position, angular velocity, etc. 
     Two or more identical resonators  4  may be placed in parallel to electrodynamic profile  1  in the same rotational plane and at the same distance from the rotation axis  3  (FIG.  6 ). Each of resonators  4  can be connected to the identical measuring circuits  6  or to one measuring circuit  6  (not shown in figures), which generator  7  is a sweep generator or noise generator, see Author&#39;s Certificate #1049795 (USSR),/Pchelnikov et al.//Published in B. I. #39, 1983. 
     At least one slowed electromagnetic wave is exited in the resonator  4  at a frequency at which the electromagnetic field penetrates into electrodynamic profile  1 . This means that the distance δ between electrodynamic profile  1  and resonator  4  should not exceed the so called “thickness of the energy concentration” which is approximately equal to λ/2 πn, where λ is the said slowed wave wavelength in a vacuum, n is a slowing of said wave, defined by relation 
     
       
         n=c/v p .  
       
     
     Here c is the light velocity in a vacuum, v p  is a phase velocity of a slowed wave. 
     The slowed electromagnetic wave can be formed by so called slow-wave structure, see Dean A. Watkins “Topics in Electromagnetic Theory,” John Willy &amp; Sons, Inc. Publishers). Two-conductor slow-wave structures (FIG. 7) are preferably used the most though three-conductor slow-wave structures can be used also, see V. V. Annenkov, Yu. N. Pchelnikov “Sensitive Elements Based on Slow-Wave Structures”  Measurement Techniques,  Vol. 38, #12, 1995, pp. 1369-1375. One of the slow-wave structure  10  conductors is a so called “impedance conductor”  11 , the other is a screen conductor  12 . For example, in a helical slow-wave structure (see L. N. Loshakov, Yu. N. Pchelnikov “Traveling Wave Tube Theory and Amplification Calculation”  Moscow: Radio,  1964.) a helix is an impedance conductor  11 , a metal cylinder is a screen conductor  12  (FIG.  8 ). Both conductors of slow-wave structures could be impedance conductors  11 ,  13 , for example in the case of an interdigital combs, shown in FIG.  9 . Thus, a slow-wave structure may be quadripole, hexapole, or multi-pole. It can be connected to a measuring circuit by both its ends or from one end only as a dipole, three-pole, etc. 
     In the present invention the part of resonator  4  facing the electrodynamic profile  1 , and sensitive to its rotation is formed by slow-wave structure  10 , which is called in future “multipole.” 
     The electrodynamic profile  1  is characterized by changing of, in the azimuth direction (arrow A), at least one of its electromagnetic parameter (conductivity, permittivity, or permeability), or changing its dimensions. The simplest way to change electromagnetic property of the electrodynamic profile  1  which influence the electromagnetic field in the resonator  4  is to change radius r of the electrodynamic profile  1  or its width w, as shown in FIGS. 2 and 3, respectively. 
     In most cases it is more convenient to change electromagnetic property by changing a configuration of metal coating  14  on the dielectric body  15  of the electrodynamic profile  1  (FIGS.  10 - 12 ). The metal coating  14  may form a solid ring with changing in the azimuth direction width, as shown in FIG. 10, or form a periodic row of conducting members connected one to another (FIG.  11 ), or not connected (FIG.  12 ). In most cases the metal coating  14  faces the sensitive part of the resonator  4  the multi-pole  10 . 
     The electromagnetic parameters of the electrodynamic profile  1  facing the multipole  10  influence on the electromagnetic field in the resonator  4  that leads to its electromagnetic parameters changing, for example, the resonant frequency ƒ r . The electrodynamic profile  1  angular position alteration leads to electromagnetic parameters alteration also. 
     In the case of a scalar monitoring, when the displacement direction should not be measured) the electromagnetic property of the profile  1  may change symmetrically relative to one axis in the rotation plane (axis  16 ), and one resonator  4  can be used, as shown in FIG.  13 . In this case the displacement to be measured may not exceed (180°−α/2), where α is the angular dimension of the resonator  4 . 
     The accuracy of the scalar monitoring can be increased by the using of two resonators  4  placed diametrically opposed relative to the axis  3  (FIG.  14 ). In this case the measured electromagnetic parameters of resonators  4  can be summed to eliminate the error caused by mechanical errors, for example, by the profile  1  vibration. 
     If a relatively small angular displacement φ is to be monitored, the preferable sensitivity can be achieved by using a periodic metal coating  14 . In this case the resonator  4  faces the whole area of coating  14  (FIG.  15 ). 
     Two resonators  4  placed with an angular shift, for example 90° (FIG.  16 ), make it possible to monitor not only an angular displacement value but also the displacement direction. Comparing a dependence, for example, of the resonant frequency ƒ 1  (curve  17  in FIG. 17) of the vertically placed resonator  4 , and a dependence of the resonant frequency ƒ 2  (curve  18  in FIG. 17) of the horizontally placed resonator  4  upon angular displacement φ relative to vertical, one can find an angular position of the profile  1  and a rotation direction. Indeed, the curves  17  and  18  are shifted one relative to another on 90° that makes it possible to define the electrodynamic profile  1  position by calculating the average frequency (ƒ 1 +ƒ 2 )/2 and comparing this value with frequency ƒ 0  that corresponds to such position of the coating  14  when the point  19  at the narrowest part of the coating  14  and point  20  at the widest its part are equally removed from the considered resonators  4 . 
     Let us consider the angle φ=0 when the axis  16  is vertically oriented and the point  19  of the metal coating  14  faces the middle of the vertically placed resonator  4 . If the width of the coating  14  increases the resonance frequency of resonator  4  also increases. This is demonstrated by curves  17  and  18  in FIG.  17 . It is shown also in FIG. 18 that the point  19  is in the upper part of the circle (−π/2&lt;φ&lt;π/2) if 
     
       
         ƒ 1 &lt;ƒ 0 ,  
       
     
     and is in the lower part of the circle (π/2&lt;φ&lt;3π/2) if 
     
       
         ƒ 1 &gt;ƒ 0 ;  
       
     
     the point  19  is in the right part of the circle (0&lt;φ&lt;π) if 
     
       
         ƒ 2 &gt;ƒ 0 ,  
       
     
     and in the left part of the circle if 
     
       
         ƒ 2 &lt;ƒ 0 .  
       
     
     The frequency ƒ 1  decreasing while point  19  lays in the left part of the circle means the clockwise rotation, the frequency ƒ 1  increasing while point  19  lays in the right part of the circle means the clockwise rotation also. 
     Four resonators  4  placed with 90° shift one to another make it possible to increase accuracy, similar to that shown in the case of a scalar measurement with help of two resonators  4  placed diametrically opposite. 
     The angular position and direction of rotation can be measured by using of one resonator  4  only. In this case the electromagnetic property of the profile  1  should be changed monotonously (increases or decreases only) for the most part of the profile, for example as shown in FIG. 2, where the radius r of the profile  1  alters monotonously from its maximum to its minimum value and after has a discontinious change or jump to its maximum value. If the profile  1  has a dielectric property, the radius r increasing is followed by the resonant frequency of the resonator  4  decreasing. Thus, in the case shown in FIG. 2, a monotonous frequency increasing means rotating in the arrow A direction. 
     Alteration of each resonator  4  electromagnetic parameters, for example resonant frequency, caused by angular displacement of the profile  1 , can be converted by the measuring circuit  6  to the position of rotating part  2  in the real time. Comparing of said positions allows calculation of the angular velocity, direction of rotation, and number of revolutions made by part  2 . 
     The slowed electromagnetic wave in the sensitive slow-wave structure  10  can be excited with electric or magnetic field shifted in the region  21  between resonator  4  and electrodynamic profile  1  (FIGS. 19,  20 ,). In the first case the profile  1  having dielectric property or conducting property increases slowing n of the slowed wave, in the second case, the profile  1  having conducting property decreases the slowing n. The electrodynamic profile influence change (distance, width, conductivity, etc. change) leads to the slowing n change, and, as a result, also to resonance frequency of the resonator  4  change. 
     The electric field shifting in the region  21  can be achieved by the in-phase slowed wave excitation in the multi-pole  10  (FIG.  19 ), the magnetic field shifting can be achieved by the anti-phase slowed wave excitation (FIG.  20 ). The electric field shifting means that the electric-field energy is presented predominately in the monitored region (region  21  in the invention), the magnetic field shifting means that the magnetic-field energy exceeds the electric field energy in region  21 , see V. V. Annenkov, Yu. N. Pchelnikov “Sensitive Elements Based on Slow-Wave Structures”  Measurement Techniques,  Vol. 38, #12, 1995, pp. 1369-1375. 
     If the electromagnetic properties of the element  1  are represented by the metal coating  14  and the distance δ between this coating and the resonator  4  can be made relatively small, the sensitivity can be increased by the presentation of the slowed wave field in the region  21  by the first minus and plus space harmonics. For example, the magnetic field in a meander line and the electric field in interdigital combs are presented by first space harmonics, see Yu. N. Pchelinikov, V. T. Sviridov, “Microwave Electronics” [in Russian],  Moscow: Radio i Svjaz,  1981. In this case the “thickness of the energy concentration” is restricted by the condition 
     
       
         δ&lt;T/2π,  
       
     
     where T is a period of the considered slow-wave structure. 
     One or more types of slowed waves at one or different frequencies can be excited in the sensitive slow-wave structure simultaneously, their number being equal to the number of conductors minus 1, see Le Blond A., Mourier G. “L&#39;etude des Lignes a bareux a structure periodique pour les tubes electroniques U.H.F.”  Ann. Radioelektr.,  1954, 9, #38, p. 311 or Z. I. Taranenko, Ya. K. Trochimenko “Slow-Wave Structures” [in Russian]  Kiev,  1965, p.57. The more waves that are excited in the resonator  4 , the more informative parameters can be obtained. 
     As was mentioned above, the slowed electromagnetic wave is excited in resonator  4  with distribution of the electric and magnetic components of the field required for the best sensitivity. Usually, the field distribution is defined by the slowing n and the frequency ƒ. As it follows from theory, see L. N. Loshakov and Yu. N. Pchelnikov, “Theory and Amplification Calculation of Traveling-Wave Tube,”  Moscow: Radio,  1964, the electric and magnetic field distribution near the multi-pole  10  (near the resonator  4  surface facing the electrodynamic profile  1  in the present invention) can be changed as by slowing n change or by frequency ƒ change. Thus, one can obtain different distribution of the field in the same resonator, exciting, for example, two or more slowed waves at different frequencies, or exciting different modes (in-phase or anti-phase). 
     The field distribution can be changed essentially in so called coupled slow-wave structures (see V. V. Annenkov, Yu. N. Pchelnikov “Sensitive Elements Based on Slow-Wave Structures”  Measurement Techniques,  Vol 38, #12, 1995, pp. 1369-1375), which impedance conductors  11 ,  13  have configuration of turned through 180°, mirror images of one another, for example, oppositely directed radial spirals, shown in FIG.  21 . Here impedance conductors  11 ,  13  with similar dimensions are placed on the opposite surfaces of a thin dielectric substrate  22 . When an in-phase wave is excited in the coupled slow-wave structure, the electric field is shifted outside conductors  11  and  13  and the magnetic field is concentrated between these conductors as shown in FIG.  19 . When anti-phase wave is excited in the same coupled slow-wave structure the electric energy concentrates between conductors  11 ,  13  and magnetic field concentrates outside these conductors as shown in FIG.  20 . 
     The currents induced on the surface of the electrodynamic profile  1 , for example on the metal coating  14 , decrease the magnetic field and increase the electric field of the multi-pole  10 , the first resulting in the slowing n decreasing, the second resulting in the slowing n increasing. Thus it is important to shift in the region  21  electric field only, or magnetic field only. This purpose may be achieved, as shown above, by anti-phase or in-phase wave exciting in the coupled slow-wave structures, or by screening the electric or magnetic field by the screen conductor  12  with anisotropy conductivity, see V. V. Annenkov, Yu. N. Pchelnikov “Sensitive Elements Based on Slow-Wave Structures”  Measurement Techniques,  Vol. 38, #12, 1995, pp. 1369-1375. 
     The variation of the slowing n in the multi-pole  10  can be converted into generator  7  frequency alternation Δƒ. This can be done by the resonator  4  serial connection in the feedback network  23  of amplifier  24  (FIG.  22 ). Filter circuits  25  and  26  in feedback  23  can be inserted to increase stability of the generator  7 . In this case the generator  7  acts as a primary transducer  8 , converting a phase delay variation into the frequency variation. 
     The resonator  4  resonance frequency ƒ r  depends on slowing n and other elements included in the resonator  4 . The resonance frequency ƒ r  and its variation can be measured by a standard frequency meter or other devices. In transducers the resonance frequency can be converted in the generator  7  frequency ƒ g . It is convenient to use for this purpose the Schmitt trigger (see “The Penguin Dictionary of Electronics,” second edition, p. 505). FIG. 23 shows the version of such generator. Here the resonator  4  is connected between the inverting input  27  of an operational amplifier  28  and the ground. Simultaneously, the inverting input  27  is connected through a resistance  29  to the output  30  of the amplifier  28 , which non-inverting input  31  is connected through a resistance  32  to the output  30  and is connected through a resistance  33  to the ground. The signal from the output  30  has meander configuration with frequency near the resonance frequency of the resonator  4 . 
     As discussed above, the apparatus for an angle displacement monitoring comprises the electrodynamic profile  1 , mounted on the rotating part  2 , and at least one resonator  4 , connected to a measuring circuit  6  (FIGS.  1 - 4 ), the last including a generator  7  of electromagnetic oscillations, a transducer  8 , connected to a converter  9 , converting an electric signal to indicate the measured parameters, such as the angular position, velocity, the number of revolutions, etc. (FIG.  5 ). 
     The resonator  4  (FIG. 24) includes at least one multi-pole  10 , and at least one matching plug  5 . The multipole  10  is connected with one its end (end  34  in FIG. 24) to the matching plug  5 , the other its end (end  35  in FIG. 24) can be free. 
     In some cases, when, for example, small displacement is monitored, the maximum sensitivity has resonator with the multipole  10 , curled into a ring (FIG.  25 ). In this case the multipole  10  has no ends and the matching plug  5  can be connected to the multi-pole  10  in any section. 
     The matching plug  5  can be made as a non-contacting device (loop, probe, etc.). The preferred embodiment of the non-contact plug  5  in the present invention is the section of a slow wave structure  36 , which impedance conductor  37  configuration (FIG. 26) is a turned through 180° mirror image of the impedance conductor  11  of the multi-pole  10 . The screen conductor  38  of the slow-wave structure  36  can be made as a tape or a plate. 
     The preferred embodiment of the matching plug  5  of the present invention is the section of a two-conductor transmission line  39  (FIG.  27 ), The matching plug  5  may include also additional element  40  including capacitor or inductor or both of them (not shown in FIG.  27 ). The conductors  41  and  42  of the transmission line  39  may form a coupled slow-wave structure, for example coupled helices, shown in FIG.  28 . Here conductor  41  is wound on a dielectric rod  43  and is isolated from conductor  42  by a thin dielectric tube  44 . 
     Changing the parameters of the slow-wave structure  39  (diameter and pitch of impedance conductors  41 ,  42 , the tube  44  thickness and its material permittivity) one can change the wave impedance Z 1  of the matching plug  5 . As a rule, the wave impedance of the matching plug  5  should differ by at least three times (to exceed or to be less) from the wave impedance Z 2  of the multipole  10 . It depends on multipole  10  loading. When multipole  10  is terminated to relatively large resistor or is open ended the wave impedance Z 1  should exeed the wave impedance Z 2 , and contrary. It allows one to split electric and magnetic energy between the multipole  10  and the plug  5 , and to decrease the sizes of the resonator  4 , see Yu. N. Pchelnikov and A. A. Elizarov “Quasiresonators Using Slowing Down Systems”  Radioelectronics and Communications Systems,  Vol. 34, #10, 1991, pp. 68-72.) 
     If the resonator  4  is open ended or terminated to an inductor  45 , as it is shown in FIG. 29, the slow-wave structure  39  may be replaced by two inductors  46  and  47 . 
     If the resonator  4  is short ended or terminated to a big capacitance  48 , as shown in FIG. 30, the slow-wave structure  39  may be replaced by two capacitors  49 ,  50 . 
     When resonator  4  is connected to the measuring circuit  6  in sequence, the multi-pole  10  is connected to two identical or different plugs  5 , as shown in FIG.  31 . 
     The multi-pole  10  includes at least one impedance conductor  11 , fashioned as a row of conducting members  51  arranged in series in the direction of the slowed wave propagation and connected to one another with spacing  52 , and a screen conductor  12 , made as a tape, plate, cylinder, etc. (FIG.  32 ). 
     Also, as discussed above, multi-pole  10  can include two or more impedance conductors ( 11 ,  13  in FIG.  24 ). The impedance conductors  11 ,  13  may lay on the same surface, forming, for example interdigital comb, shown in FIG. 9, or lay on the opposite surfaces of a dielectric plate, tube, etc., forming a coupled slow-wave structure. 
     The multipole  10  design (configuration and number of conductors) varies depending on the measurement to be done. If, for example, two waves should be excited, two impedance conductors  11 ,  13  and one screen conductor  12  should be in the multi-pole  10 . 
     For relatively small angular displacement the impedance conductor  11  may form a meander line and the screen conductor  12  may form a tape, both curled into a ring and placed on opposite surfaces of a dielectric substrate  22  (FIG.  33 ). The electrodynamic profile  1  in this case may be formed by the coating  14  with configuration of a meander line with the same period T as the impedance conductor  11  (FIG.  11 ), or may have the configuration shown in FIG. 12 with the same period T. The maximum measured angular displacement φ in this case does not exceed T/4R, where R is the average radius of the meander line, forming the conductor  11 . 
     The currents in the neighboring conductors of the meander line have opposite direction. If currents induced in the coating  14  by currents in the impedance conductor  11  form a closed ring, the magnetic field in the screen conductor will decrease, and, as a result, the slowing n will decrease also. The profile  1  displacement changes the amplitude of the currents induced in the coating  14 , and can be monitored, for example, by the resonant frequency of the resonator  4  measurement. The same result can be achieved when both conductors of the multi-pole  10  are impedance conductors and form a coupled meander lines shown in FIG.  34 . The profile  1  in this case may have the coating  14  on the dielectric body  15 , shown in FIG.  12 . 
     The preferred design of the multipole  10  for continuous monitoring of an angle displacement is shown in FIG.  35 . Here multipole  10  comprises impedance conductors  11 ,  13 , forming coupled spirals with segment configuration and placed on the opposite surfaces of the dielectric substrate  22 , both having configuration of turned through 180° mirrow image. The profile  1  has metal coating  14  on a dielectric body  15 , the coating  14  forming a symmetrical ring with a changing width w shown in FIG.  16 . 
     When the profile  1  is made as coating  14  on the cylindrical surface of a dielectric body  15 , the multi-pole  10  may be done as the segment (FIG. 36) or as a cylinder (FIG.  37 ).