Abstract:
An apparatus for tuning and/or matching a RF coil in a NMR probe comprising a first variable capacitor electrically connected to the coil and a first motor capable of coupling to the first variable capacitor. The first motor when coupled to the first capacitor adjusts a capacitance associated with the first capacitor. The first motor is capable of operating in a strong magnetic field and is capable of not disturbing homogeneity of said magnetic field when said motor is not operating. The apparatus may further include a second variable capacitor and a second motor. The first motor is further capable of coupling to the second capacitor for adjusting a capacitance associated with the second capacitor. The second motor moves the first motor between coupling with the first capacitor and coupling with the second capacitor. The mechanism may be employed to manipulate variable inductive loads for tuning and/or matching.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to magnetic resonance. More particularly, the invention relates to tuning and matching radio frequency (RF) coils in a nuclear magnetic resonance (NMR) probe. 
     BACKGROUND OF THE INVENTION 
     Magnetic resonance may be used to analyze medical and/or chemical samples. Specifically, the diverse chemical constituents and/or the spatial distributions of such constituents of the sample may be analyzed through the application of the magnetic resonance phenomena. In general, the physical context of the invention is a NMR probe for nuclear magnetic resonance or magnetic resonance imaging. An idealized illustration is shown in FIG.  1 . 
     A magnet  10  having bore  11  provides a main magnetic field. In order to control the magnetic field with precision in time and direction, there are provided magnetic field gradient coils (not shown). The gradient coils are driven by gradient power supplies  16 ,  18  and  20 , respectively. Additionally, other shimming coils (not shown) and power supplies (not shown) may be required for compensating residual undesired spatial inhomogenities in the basic magnetic field. An object or fluid for analysis (hereinafter “sample”) is placed within the magnetic field in bore  11 ; typically, the sample is placed in a sample space of an NMR probe (not shown) and the NMR probe is placed within the bore  11 . The sample is subject to irradiation by RF power, such that the RF magnetic field is aligned in a desired orthogonal relationship with the magnetic field in the interior of bore  11 . This is accomplished through a transmitter coil  12  in the interior of bore  11 . Resonant signals are induced in a receiver coil, proximate the sample within bore  11 . The transmitter and receiver coils may be the identical structure, or separate structures. 
     As shown in FIG. 1, RF power is provided from transmitter  24 , and is amplified by an amplifier  31  and then directed via multiplexer  27  to the RF transmitter coil  12  located within the bore  11 . The transmitter  24  may be modulated in amplitude or frequency or phase or combinations thereof, either upon generation or by a modulator  26 . Transmitter and receiver coils are usually not concurrently used as such. The identical coil may be employed for both functions if so desired. Thus, a multiplexer  27  is provided to isolate the receiver from the transmitter. In the case of separate transmitter and receiver coils, element  27 , while not precisely a multiplexer, will perform a similar isolation function to control receiver operation. 
     The modulator  26  is controlled by pulse programmer  29  to provide RF pulses of desired amplitude, duration and phase relative to the RF carrier at preselected time intervals. The pulse programmer may have hardware and/or software attributes. The pulse programmer also controls the gradient power supplies  16 ,  18  and  20 , if such gradients are required. These gradient power supplies may maintain selected static gradients in the respective gradient coils if so desired. 
     The transient nuclear resonance waveform is processed by receiver  28  and further resolved in phase quadrature through phase detector  30 . The phase resolved time domain signals from phase detector  30  are presented to Fourier transformer  32  for transformation to the frequency domain in accordance with specific requirements of the processing. Conversion of the analog resonance signal to digital form is commonly carried out on the phase resolved signals through analog to digital converter (“ADC”) structures which may be regarded as a component of phase detector  30  for convenience. 
     It is understood that these resolved data signals from the phase detector  30  may be directly stored in a storage unit  34 . The Fourier transformer  32  may, in practice, act upon a stored (in storage unit  34 ) representation of the phase resolved data. This reflects the common practice of averaging a number of time domain phase resolved waveforms to enhance the signal to-noise ratio. The transformation function is then applied to the resultant averaged waveform. Display device  36  operates on the acquired data to present same for inspection. Controller  38 , most often comprising one or more computers, controls and correlates the operation of the entire apparatus. 
     In conducting NMR experiments, the coil  12  must be tuned to the resonant frequency of the nuclei to be observed. Additionally, the impedance of the coil  12  should be electrically matched to the impedance of the transmission line  19  which is optimally coupled through the multiplexer  27  to the receiver  28  to obtain the maximum transfer of energy and to obtain the best signal to noise ratio (SNR). To tune and match the coil  12 , conventional NMR coils have variable capacitors. Typically, at least one variable capacitor is adjusted to tune the coil to the desired resonant frequency and at least another variable capacitor is adjusted to match the impedance of the coil. To adjust the capacitance of the variable capacitors, mechanical linkages are coupled to variable capacitors in the coil. 
     The probe is a critical component in NMR data acquisition. Among other functions, the NMR probe provides mechanical support for the sample and coil, and the NMR probe provides electrical connections between the coil and the NMR apparatus. The NMR probe is placed into the bore  11  to position the sample and coil in a preselected position along the center of the bore  11 . FIG. 2 illustrates the mechanical structure of one example of a contemporary NMR probe  50 . Briefly, the NMR probe  50  includes a box  52 , three tuning rods  54   a ,  54   b  and  54   c  and a pair of board levels  56   a  and  56   b . The coil (not shown) is located above the board level  56   a  e.g; axially beyond board level  56   a . The sample is placed within the interior volume defined by the coil and typically in the center of the coil. For example, the coil may be a simple LC circuit with variable capacitors connected to the coil (not shown). The variable capacitors are typically located on the opposite side of the board level  56   a  as the coil. 
     To adjust the capacitances of the variable capacitors, the tuning rods  54   a ,  54   b  and  54   c  each comprise an assembly of concentric rods  58   a  and  58   b . The concentric rods  58   a  and  58   b  are mechanical linkages that are coupled to the variable capacitors. The inner rod  58   a  rotates to adjust one of the variable capacitors on the board level  56   a , and the outer rod  58   b  rotates to adjust another variable capacitor on the board level  56   a . The box  52  supports the tuning rods  54   a ,  54   b  and  54   c  and the board levels  56   a  and  56   b . Additionally, the box  52  houses connectors to the NMR probe that link the coil to the NMR apparatus described above. Furthermore, an outside shield tube (not shown) surrounds the tuning rods  54   a ,  54   b  and  54   c , the board levels  56   a  and  56   b , the variable capacitors and the coil. 
     When NMR experiments are performed, the box  52  is positioned outside the bore  11  the of magnet  10 , and the board levels  56   a  and  56   b  are within the bore  11 . To tune and match the coil for the NMR experiment, an operator manually rotates the mechanical nubs  60  associated with each concentric rod at the base of each tuning rod. Rotating the mechanical nubs  60  rotates the respective concentric rod of the tuning rod which adjusts the capacitance of the associated variable capacitor. 
     One shortcoming of the contemporary NMR probe is that the manual adjustment of the mechanical nubs  60  is inconvenient and inefficient. Because the NMR probe  50  is positioned largely within the bore  11  for experiments, the mechanical nubs  60  need to be adjusted by hand at the bore  11  away from the control console and display  36  of the NMR apparatus. The manual adjustment is also time consuming and troublesome. 
     Thus, it is desired to develop a NMR probe that may be tuned and matched remote from the probe. It is also desired to develop a NMR probe that may be efficiently and conveniently tuned and matched without interfering with the magnetic field of the NMR apparatus. Additionally, it is desired to develop a feedback system that enables automatic tuning and matching without aid from the operator. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided an apparatus for tuning a RF coil in a NMR probe comprising a variable capacitor electrically connected to the coil and a motor. The motor is coupled to the variable capacitor for adjusting a capacitance associated with the variable capacitor. The motor is capable of operating in a strong magnetic field and does not disturb homogeneity of the magnetic field when the motor is not operating. 
     In accordance with another aspect of the present invention, there is provided an apparatus for tuning and matching a RF coil in a NMR prove comprising a first variable capacitor, a second variable capacitor, a first motor and a second motor. The first motor is capable of coupling to the first variable capacitors to adjust a first capacitance associated the first capacitor and is capable of coupling to the second variable capacitor to adjust a second capacitance associated with the second capacitor. The second motor is capable of coupling the first motor to either the first capacitor or the second capacitor. The first motor and the second motor are capable of operating in a strong magnetic field and are of a type that does not disturb homogeneity of the magnetic field when the motors are not operating. The apparatus may further including a third variable capacitor with the first motor being capable of coupling to the third capacitor to adjust a third capacitance associated with the third capacitor. Additionally, the second motor is capable of moving the first motor to couple with the third capacitor. The second motor may linearly move the first motor between the coupling with the first capacitor and the coupling with the second capacitor. Alternately, the second motor may rotationally move the first motor between the coupling with the first capacitor and the coupling with the second capacitor. The coupling between the first motor and the first and second capacitors is through a mechanical linkage and gear system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other aspects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. 
     FIG. 1 is a schematic illustration of an NMR apparatus for the context of the invention. 
     FIG. 2 is a perspective of the mechanical structure of one example of a contemporary NMR probe. 
     FIG. 3 is a block diagram of a system for tuning and matching a RF coil of an NMR probe. 
     FIG. 4 is a perspective of one embodiment of the present invention for tuning and matching the coils of an NMR probe. 
     FIG. 5 is a perspective of an NMR probe of the present invention for tuning and matching the coils of the NMR probe. 
     FIG. 6 is a cross section of the NMR probe of FIG. 5 along line  6 — 6 . 
     FIG. 7 a  is a cross section of the NMR probe of FIG. 5 along line  7   a — 7   a.    
     FIG. 7 b  is a cross section of the NMR probe of FIG. 5 along line  7   b — 7   b.    
     FIG. 7 c  is a cross section of the NMR probe of FIG. 5 along line  7   c — 7   c.    
     FIG. 8 a  is a cross section of a clutch of the NMR probe of FIG.  5 . 
     FIG. 8 b  is a cross section of another clutch of the NMR probe of FIG.  5 . 
     FIG. 9 is an electrical schematic diagram of a coil circuit. 
     FIG. 10 shows a motor driven probe adjustment apparatus of the present invention that may be directed to the adjustment of tuning paddles of the NMR probe. 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of the specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined in the appended claims. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, FIG. 3 illustrates a simplified block diagram of the present invention for remotely tuning and/or matching a RF coil in an NMR probe. To remotely tune and/or match the NMR probe, the capacitance values of variable capacitors of the coil on the NMR probe must be adjusted. As depicted in FIG. 3, a small motor  104  in the NMR probe  100  is mechanically coupled to a variable capacitor  102 . The motion of the motor  104  adjusts the capacitance value of the variable capacitor  102 . To control the capacitance of the variable capacitor  102 , a controller  106  controls the motion provided by the motor  104 . 
     The motor  104  on the NMR probe that adjusts the variable capacitor  102  must meet stringent requirements not met by ordinary electric motors. When the motor  102  is not running, the motor  102  must not disturb the homogeneity of the applied magnetic field in the bore  11 . 
     Additionally, the motor  102  must be able to operate in a strong magnetic field. Furthermore, for NMR probe coils using high temperature superconducting materials, the motor should be able to operate in a vacuum environment. 
     In one embodiment of the present invention, the motor on the NMR probe is an iron-free d.c. motor. The iron-free d.c. motor uses the strong magnetic field of the NMR magnet as a constant unidirectional field typically supplied by a field coil. If this field is vertical, the iron-free d.c. motor&#39;s armature with several coil pairs would rotate about a horizontal axis. The rotatable coils are coupled through brushes similar to conventional motors. By applying a d.c. current, the armature will rotate. Reversing the direction of the d.c. current reverses the direction of rotation. The iron-free d.c. motor coupled to the variable capacitor rotates to adjust the capacitance for tuning and/or matching of the coil. During the acquisition of an NMR spectrum and after the tuning and/or matching of the coil, no current flows in the iron-free d.c. motor, thus, the iron-free d.c. motor produces no disturbances to the applied field. 
     In a preferred embodiment of the present invention, the motor on the NMR probe is a piezoelectric motor. The piezoelectric motor may provide either linear or rotational motion. In the piezoelectric motor, an oscillating electrical voltage applied to a piezoelectric material produces a moving or rotating wave. The moving or rotating wave is coupled to a friction plate causing the plate to move or rotate. The piezoelectric motor will operate at a relatively low speed and will provide a substantial force or torque. Additionally, the piezoelectric motor has a small size that will occupy little space on the NMR probe. An example of the piezoelectric motor is those sold by Shinsei. 
     In one embodiment, the controller  106  drives the piezoelectric motor  104  with an ultrasonic frequency (greater than 20 kHz) oscillating electrical voltage. In the preferred embodiment, the controller  106  comprises two 50 kHz sources that are 90° out of phase to each other. The controller  106  controls the speed of the motor  104  with the voltage applied to the motor  104 , and the controller  106  controls the direction of the motor rotation with the electrical phase of the drives. 
     FIG. 4 illustrates another embodiment of the present invention for motor driven tuning and/or matching RF coils in an NMR probe  110 . A pair of motors  112  and  114  work together to adjust several variable capacitors  116 ,  118 ,  120  and  122  in the NMR probe. In many cases, such as 2-D, 3-D NMR experiments, more than two variable capacitors need adjustment. Since the motors are expensive and space is limited within the NMR probe, it is desired to use the least number of motors possible to adjust the capacitors. The embodiment of FIG. 4 uses a switching motor  112  to mechanically switch an adjuster motor  114  between a number of capacitors  116 ,  118 ,  120  and  122 . The names of the motors  112  and  114  serve only to help identify the function of the motor, namely the switching motor  112  moves the adjuster motor  114  into position to enable the adjuster motor  114  to change the capacitance of one of the variable capacitors. Once the switching motor  112  moves the adjuster motor  114  into position corresponding to the capacitor to be adjusted, the adjuster motor  114  rotates to adjust that capacitance. 
     As depicted in FIG. 4, the pair of motors  112  and  114  operate together to adjust several capacitors  116 ,  118 ,  120  and  122 . The adjuster motor  116  rotates an adjuster shaft  124  containing an adjuster drive gear  126 . The adjuster drive gear  126  is capable of engaging the adjuster driven gear  128 ,  130 ,  132  and  134  on each ofthe variable capacitors  116 ,  118 ,  120  and  122  respectively to adjust the capacitance of each variable capacitor  116 ,  118 ,  120  and  122 . To protect the variable capacitors from breaking when they have been driven to their mechanical ends, the adjuster shaft  124  may include a clutch  142 . 
     The switching motor  112  has a switching shaft  136  which raises and lowers the adjuster motor  114  to allow the adjuster drive gear  126  of the adjuster motor to mesh with the adjuster driven gear of each variable capacitor. As depicted in FIG. 4, using the switching motor  112  to select the capacitor to be adjusted and the adjuster motor  114  to adjust that capacitor&#39;s capacitance allows the four capacitors to be adjusted. Alternatively, more capacitors can be added with additional adjuster driven gears. Similar to the controller  106  described above with conjunction with FIG. 3, a controller  138  controls the motion of the switching and adjuster motors  112  and  114 . 
     The NMR probes with motor driven tuning and matching of the RF coils of the above embodiments provide several advantages over the contemporary NMR probes. First, the motor driven NMR probes provide remote tuning and matching eliminating the manual adjustments of the conventional NMR probes. Instead of the operator manually adjusting the mechanical nubs of the conventional NMR probe by hand at the bore away from a control console and display of the NMR apparatus, the present invention enables the operator to tune and match the coils of the NMR probe at the control console of the NMR apparatus through inputs to the controller  138 . 
     This not only is more convenient for the operator but it is more efficient and less time consuming. 
     Additionally, FIG. 4 depicts a computer  140  connected to the controller  138 . The computer  140  together with the controller  138  may make automatic adjustments to the variable capacitors  116 ,  118 ,  120  and  122  for automatic tuning and matching of the coil. Using amplitude and phase information from the RF voltages used to activate the tuning circuits, capacitances may be automatically adjusted to match and tune the coil. An expert system trained by an operator could be used to optimize the tuning and matching controls automatically. 
     Furthermore, using a switching motor  112  to move the adjuster drive gear  126  between capacitors  116 ,  118 ,  120  and  122  and the adjuster motor  114  to rotate the adjuster drive gear  126  to adjust the selected capacitor simplifies the design of the NMR probe. The two motor system is capable of adjusting numerous capacitors to tune and/or match multi-frequency probes. 
     In one embodiment, a series of microswitches (not shown) may be used to indicate which capacitors are engaged at a particular time. 
     Moreover, the use of the two motor system frees up space in the critical regions of the NMR probe. This is particularly important in cryoprobes which are NMR probes that operate in a vacuum environment and at a low temperature of approximately 25 K. The conservation of space provided by the two motor system is essential for cyroprobes because these probes require additional space for the heat transfer system used to cool the probe coils. In addition, it is desirable to keep the number of heat paths to a minimum between the cold probe coils and the outside world. By using only one adjuster shaft  124  to select and control all of the variable capacitors  116 ,  118 ,  120  and  122  as illustrated in FIG. 4, the number of undesirable heat paths is minimized. 
     FIGS. 5-8 illustrate a NMR probe  150  of another embodiment of the present invention. 
     In FIG. 5, instead of the switching motor linearly moving the adjuster motor, the motion is rotational. The NoM probe  150  depicted in FIG. 5 includes a box  152 , three tuning rods  154   a ,  154   b  and  154   c  and a pair of board levels  156   a  and  156   b . The coil (not shown) is located on top of the board level  156   a  and the sample would be positioned in the middle of the coil at the top of the board level  156   a . The tuning rods  154   a ,  154   b  and  154   c  each comprise a pair of concentric rods  158   a  and  158   b . The inner concentric rod  158   a  is coupled to a variable capacitor  162  on the board level  156   a . The outer concentric rod  158   b  is coupled to a pair of variable capacitors  164   a  and  164   b  on the board level  156   a . The variable capacitors  162 ,  164   a  and  164   b  are electrically connected to the coil. FIG. 9 illustrates one example of the coil circuit with variable capacitors  162 ,  164   a  and  164   b . The variable capacitor  162  is for matching, and the variable capacitors  164   a  and  164   b  are for tuning. Other coil circuit arrangements are possible as known to one skilled in the art. 
     At the top board level  156   a , the outer concentric rod  158   b  includes a rod drive gear  166  engaging a pair of rod driven gears  168   a  and  168   b  associated with the variable capacitors  164   a  and  164   b  respectively. The rotation ofthe inner rod  158   a  adjusts the capacitance of the variable capacitor  162 , and the rotation of the outer rod  158   b  adjusts the capacitance of the variable capacitors  164   a  and  164   b  through their associated rod driven gears  168   a  and  168   b . Because the tuning rods  154   a ,  154   b  and  154   c  have identical platforms of variable capacitors and mechanics for adjusting those capacitors, only one of the tuning rods  154   a  will be described in detail. 
     The box  152  supports the tuning rods  154   a ,  154   b  and  154   c  and the board levels  156   a  and  156   b . Additionally, the box  152  houses the mechanics for adjusting the capacitance of the variable capacitors  162 ,  164   a  and  164   b  by rotating the concentric rods  158   a  and  158   b  which is best viewed in FIG.  6 . To rotate each of the concentric rods  158   a  and  158   b  of the three tuning rods  154   a ,  154   b  and  154   c , a switching motor  170  moves an adjuster motor  172  between each of the concentric rods  158   a  and  158   b  ofthe three tuning rods  154   a ,  154   b  and  154   c . The switching motor  170  and the adjuster motor  172  may be piezoelectric motors with an appropriate controller as described above. 
     As depicted in FIG. 6, the switching motor  170  is mounted on a top plate  176  in the box  152 . The switching motor  170  has a switching drive shaft  178  that drives a switching drive gear  180 . The switching drive gear  180  is position below a bottom plate  182  in the box  152 . The switching drive gear  180  meshes with a driven hub gear  184  such that when the switching drive shaft  178  rotates the switching drive gear  180  in a clockwise direction, the driven hub gear  184  rotates in a counter-clockwise direction. The adjuster motor  172  is mounted to the driven hub gear  184 , so when the driven hub gear  184  rotates, the adjuster motor  172  moves with the driven hub gear  184 . When the driven hub gear  184  rotates counter-clockwise, a position gear  186  rotates clockwise because the position gear  186  is meshed with the driven hub gear  184 . The position gear  186  connects to an absolute angular encoder  188  through a position shaft  190 . The absolute angular encoder  188  is mounted to the bottom plate  182 , and the rotation of the position gear  186  provides the absolute angular encoder  188  with the position of the adjuster motor  172 . 
     In one embodiment, a controller (not shown), similar to the one described in conjunction with FIG. 4, receives the position information from the absolute angular encoder  188 . 
     Each of the tuning rods  154   a ,  154   b  and  154   c  have an adjuster gear assembly  192  that works with the adjuster motor  172  to adjust the variable capacitors associated with the tuning rod on the board level  156   a . Only one of the adjuster gear assemblies  192  will be discussed because they each have identical structure and operation. The adjuster gear assembly  192  comprises a driven inner gear  194  connected to the inner concentric rod  158   a , a driven outer gear  196  connected to the outer concentric rod  158   b , and an outer adjuster assembly  198 . The outer adjuster assembly  198  comprises a driven bottom gear  200  connected to an upper drive gear  202  by a shaft  204  having an outer clutch  206 . The upper drive gear  202  meshes with the driven outer gear  196 . For the adjuster motor  172  to cooperate with the gear assembly  192 , the adjuster motor  172  has adjuster shaft  208  connected to a adjuster drive gear  210 . 
     To adjust the inner variable capacitor  162 , the adjuster motor  172  rotates the inner concentric rod  158   a . To rotate the inner concentric rod  158   a , the switching motor  170  rotates the driven hub gear  184  to position the adjuster motor  172  such that the adjuster drive gear  210  meshes with the inner driven gear  194 . Once the adjuster drive gear  210  engages the inner driven gear  194 , the adjuster motor  172  rotates its adjuster drive shaft  208  and adjuster drive gear  210  to rotate the inner driven gear  194  which in turn rotates the inner concentric rod  158   a.    
     To adjust the outer variable capacitors  164   a  and  164   b , the adjuster motor  172  rotates the outer concentric rod  158   b . To rotate the outer concentric rod  158   b , the switching motor  170  rotates the driven hub gear  184  to position the adjuster motor  172  such that the adjuster drive gear  210  engages the bottom driven gear  200 . Once the adjuster drive gear  210  engages the bottom driven gear  200 , the adjuster motor  172  rotates its adjuster drive shaft  208  and adjuster drive gear  210  to rotate the bottom driven gear  200  and top drive gear  202 . Because the top drive gear  202  meshes with the outer driven gear  196 , the rotating adjuster motor  172  rotates the outer driven gear  196  which rotates the outer concentric rod  158   b.    
     As depicted in FIG. 6, the switching drive shaft  178  between the switching motor  170  and switching drive gear  180  has a switching clutch  212 . FIG. 8 b  illustrates the switching clutch  212  which includes a wave washer  214 . The wave washer  214  performs as a slip clutch that slips when too much torque is applied to minimize mechanical stress. As similarly depicted in FIG. 6, the portion of the inner concentric rod  158   a  between the top plate  176  and bottom plate  182  has a inner rod clutch  216 . The inner rod clutch  216  is identical to the outer clutch  206  on the outer adjuster assembly  198 . FIG. 8 a  illustrates the inner rod clutch  216  which includes a spring  218 . The clutch  216  has a spring  218  that prevents the variable capacitors  162 ,  164   a  and  164   b  from breaking when reaching their mechanical end. If the adjuster motor  172  rotates the inner rod  158   a  when the variable capacitor has reached its mechanical end, the torque provided by the motor  172  may break the mechanical end of the variable capacitor. To prevent this breaking, the spring  218  provides friction and absorbs the torque. 
     It will be appreciated that the present invention has generally been described with reference to a particular embodiment of the NMR probe  150  illustrated in FIGS. 5-8. The present invention is not limited to the particular embodiment described herein. For example, any number and arrangement of variable capacitors is possible. Additionally, the tuning rods and mechanical linkages for adjusting the variable capacitors may vary from those depicted and probe adjustments other than capacitive adjustments may be employed. For example, frictionally coupled contact rollers may be used in lieu of toothed gears where appropriate. 
     In another embodiment shown in FIG. 10, the motor driven probe adjustment apparatus of this invention, may be directed to the adjustment of tuning paddles  314  for an NMR probe coil and especially for cryogenic probe coils  312 . The tuning paddle  314  is a conductive member, or plate, which is disposed in proximity to cryogenic probe coils  312  being a superconductive coil. 
     This serves as an inductive load which perturbs the field distribution of the coil. The paddle position relative to the coil is varied by rotation (as described above for capacitor adjustment), translation or a combination of translation and rotation, if desired. Translatory motion  316  is easily derived from the above described mechanisms by provision of a ball nut  318 , for example, with paddle fixed thereto. In addition to the mechanical motion control of a tuning paddle, matching of probe impedance to an external signal source or sink is obtained in similar fashion. A typical arrangement for this purpose would provide for the movement of a coupling loop  320 . By the same arrangement, capacitor adjustment may take the form of relative translation of capacitor plates of a linear variable capacitor. Other mechanisms for obtaining rotation or translation are within the purview of a probe equipped as here described with a motor(s)  322  which do not disturb the homogeneity of the surrounding field. 
     While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations will be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.