Abstract:
Disclosed is a probe unit for nuclear magnetic resonance. The probe unit includes a cylindrical outer conductor, a cylindrical central conductor concentrically disposed in the outer conductor, and fluid paths guiding the flow of fluid in the space between the central and outer conductors. By applying a RF current between the outer and central conductors, a sensing magnetic field is generated in a radial direction. Accordingly, it is possible to detect in real time and in situ, variations of characteristics of a fluid under reaction and/or passing through the fluid paths as well as spatial distribution changes of the sample fluid species in the space between the central and outer conductors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 from Korean Patent Application No. 10-2006-0020083 filed on Mar. 2, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    The present invention disclosed herein relates to probe units for nuclear magnetic resonance. In particular, the present invention relates to a probe unit for nuclear magnetic resonance, using toroid cavity. 
         [0003]    A probe coil used for nuclear magnetic resonance (NMR) generates a sensing magnetic field (B 1 ) of radio frequency (RF) therein. When the frequency thereof matches with a specific nuclear spin resonance frequency of a sample, RF energy is absorbed into the nuclear spins of the sample. Then, the probe coil detects a variation of inductive magnetization during relaxation of the nuclear spins excited by the RF energy. 
         [0004]    The probe coil is generally classified into various kinds widely used for nuclear magnetic resonance, e.g., solenoid coil, saddle coil, Helmholtz coil, and toroid cavity. Toroid cavity can produce a series of spatially resolved NMR spectra of a sample as a function of radial distance from a central conductor. In electrochemical applications, the central conductor may function as a working electrode as well as part of a RF coil. 
         [0005]    However, according to conventional technology, the measurement of various properties is possible only for a stationary sample contained in a probe unit without being continuously supplied thereto or discharged therefrom. Thus, it is hard to detect in real time and in situ, spatially resolved variations of characteristics of a fluid (liquid or gas) sample in a system requiring continuous supply and discharge of fluid. 
       SUMMARY OF THE INVENTION 
       [0006]    For purposes of solving the aforementioned problems, the present invention is directed to a probe unit for NMR, capable of detecting variations of properties as well as spatial distribution of fluid(s) in situ and in real time. 
         [0007]    The present invention provides a probe unit for nuclear magnetic resonance. The toroid cavity includes flow paths through which gas or liquid flows. The probe unit comprises a cylindrical outer conductor including an opening at one end to a central axis, and a hollow inside; a central conductor placed concentrically in the outer conductor; a membrane assembly disposed adhesively to the central conductor, between the outer and central conductors; a first flow path, guiding a flow of fluid, extending from one end of the conductor toward the other end along the central axis, adjacent to the membrane assembly; and a cap connecting the ends of the central and the outer conductor. A sensing magnetic field is generated by applying a RF current between the outer and central conductors. 
         [0008]    The central conductor may further comprise a first furrow extending from one end of the outer surface of the conductor toward the other end along the central axis. In this embodiment, the first furrow constitutes the first flow path in a space formed by the membrane assembly and the first furrow. 
         [0009]    The probe unit may further comprise a tube including a second furrow on the inner surface of the tube at a position matching with the first furrow, being disposed adhesively to an outer surface of the membrane assembly. 
         [0010]    The membrane assembly for an electrochemical cell comprises an electrolyte membrane, anode and cathode electrodes that are attached to inner and outer surfaces of the membrane, respectively. The electrodes are made of a carbon cloth and metallic catalysts coated on the surface of the carbon cloth. 
         [0011]    Methanol and oxygen gas may flow through the first and second fluid path, respectively, in the application of the probe for a methanol direct fuel cell. 
         [0012]    The probe unit further comprises a current collector that is disposed between bottom ends of the central and the outer conductors, and connected to the outer electrode of the membrane assembly. 
         [0013]    A further understanding of the nature and advantages of the present invention herein may be achieved by referring to the remaining portions of the specification and the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0014]    Non-limiting and non-exhaustive embodiments of the present invention will be described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
           [0015]      FIG. 1  is a sectional view illustrating a probe unit according to the present invention; 
           [0016]      FIG. 2  is a sectional view illustrating a central conductor according to the present invention; 
           [0017]      FIG. 3  is a sectional view illustrating a tube according to the present invention; 
           [0018]      FIG. 4  is an enlarged sectional view of the part A in  FIG. 1  including a membrane assembly according to the present invention; 
           [0019]      FIG. 5  is a sectional view illustrating a modified central conductor according to the present invention; and 
           [0020]      FIGS. 6A and 6B  are sectional views of a tube for a modified central conductor according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    Preferred embodiments of the present invention will be described below in more detail with the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the technology. In the figures, the dimensions of elements are exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout. 
         [0022]      FIGS. 1 ,  2 , and  3  are sectional views illustrating a probe unit  100 , a central conductor  140 , and a tube  120  according to the present invention, respectively. 
         [0023]    Referring to  FIGS. 1 and 2 , the probe unit  100  is comprised of a cylindrical outer conductor  110  that has a hollow inside and an opening at one end to the direction of a central axis, a central conductor  140  concentrically placed in the outer conductor  110 , a membrane assembly  130  interposed between the outer conductor and the central conductor, and a cap covering the open ends of the central and outer conductors simultaneously. The outer conductor is in a shape of two tubings with different diameters concentrically attached end to end. 
         [0024]    The central conductor  140  is comprised of a first furrow  142  on the outer surface of the conductor extending from one end toward the other end along the central axis, guiding a fluid flow through the first furrow. The central conductor  140  may be built in a cylinder shape with one open end and the other end closed. The central conductor  140  includes a hollow  141  extending from the open end and has an inlet unit  144  for supplying the fluid, and an outlet unit  145  for exhausting the fluid. Supplying and exhausting fluid may pass through the hollow of the central conductor. A cap  150  is placed to close the hollow  141  and to cover the open ends of the central and outer conductor simultaneously and to connect them electrically. Alternatively, the cover  150  may include an opening  152  to open the hollow  141  while the cover  150  still keeps the electric contact between the central and outer conductors. An electric lead of solid wire type  146  is attached to the closed end of the central conductor  140 . 
         [0025]    The membrane assembly  130  is installed in contact with the outer surface of the central conductor  140 , covering a first furrow  142  that guides the flow of fluid through a first fluid path F 1 . 
         [0026]    Referring to  FIGS. 1 and 3 , according to the present invention, the probe unit  100  may have a tube  120  with the inner surface engraved with a second furrow  122  for a second fluid path F 2  at a position and area matching with the first furrow  142 , placed adhesively to the outer surface of the membrane assembly  130 . An inlet unit  124  for supplying the fluid and an outlet unit  125  for exhausting the fluid are installed at each end of the tube  120 . The tube  120  is preferred to have a very big skin depth or be made of a nonmetallic material such as glass epoxy laminate in order to minimize distortion of the sensing magnetic field. The first and second furrows  142  and  122  are constructed to cover wider areas parallel to the central axis in order to make the more fluid exposed to the constant sensing magnetic field, and hence increasing NMR signal strength thereof. With this structure, the probe unit  100  generates a sensing magnetic field (B 1 ) with the flow of RF current between the central conductor  140  and the outer conductor  110 . The strength of the sensing magnetic field in a space between the central and outer conductors is inversely proportional to a distance along a radial direction from the central conductor. The direction of the sensing magnetic field for NMR is orthogonal to the central axis of the central conductor  140 . The central conductor  140  may be connected also with an external apparatus (e.g., a potentiostat). The fluids passing through the fluid furrows  142  and  122  are exposed to the sensing magnetic field. Therefore, it is possible to detect in situ and in real time, the variation of various characteristics due to chemical reactions and spatial redistribution of the chemical constituents of a fluid, by NMR. 
         [0027]      FIG. 4  is an enlarged sectional view of the part A, including the membrane assembly  130 . Referring to  FIGS. 1 and 4 , according to a modification of the present invention, the membrane assembly  130  may be prepared with an electrolyte membrane  132  of an electrochemical cell, an anode  134  and a cathode  136  that are attached each to the inner surface and outer surface of the membrane  132 . In this structure, the fluids are forced to flow through the first and second furrows  142  and  122 , in contact with the membrane  132 . The anode  134  or the cathode  136  may be installed either the outer surface or the inner surface of the membrane  132 . 
         [0028]    The membrane assembly  130  may constitute a direct methanol fuel cell (DMFC), then, Fluid  1  (methanol) and Fluid  2  (oxygen gas) flow through the first and second fluid paths F 1  and F 2 , respectively, or alternatively F 2  and F 1 , depending on the disposition of the anode  134  and the cathode  136 . The arrows in  FIG. 4  represent flow directions of the fluids. The electrode  134  and/or  136  is made of a carbon cloth or paper and metallic catalysts coated on the surface of the carbon cloth or paper. The anode  134  on the inner surface of the membrane  132  is connected to an external apparatus by way of the central conductor  140 , while the cathode  136  on the outer surface of the membrane  132  is connected to the external apparatus by way of a current collector which will be described later. The anode  134  and the cathode  136 , at each side of the membrane  132 , react with methanol and oxygen gas, respectively, which are supplied through the inner and outer fluid paths, F 1  and F 2 , respectively, and generate a current passing through a current path (not shown) connected through the external apparatus. During this electrochemical reaction, methanol and oxygen gas may be transformed into other chemicals as shown in the following reaction formula. The probe unit is able to detect the reaction reagents, intermediates, and products, and their spatial distribution in real time and in situ. 
         [0029]    Anode: CH 3 OH+H 2 O=CO 2 +6H + +6e −   
         [0030]    Cathode: 3/2O 2 +6H + +6e − =3H 2 O 
         [0031]    The membrane assembly  130  may have cylindrical gaskets  138  that are installed at both ends of the membrane assembly in order to block leakage of fluids flowing through the first and second fluid paths F 1  and F 2 . 
         [0032]    The probe unit  100  may be additionally comprised of the collector  160  interposed between the ends of the central and outer conductors  140  and  110  and connected to one of the electrodes of the membrane assembly  130 . The collector  160  may electrically connect the cathode  136  to the external apparatus. 
         [0033]    The present invention is not restrictive to the aforementioned chemical cell in application. Rather, for instance, the present invention also provides a technique capable of measuring fluid reaction and chemical redistribution across a membrane film under osmotic pressure, in real time, by properly modifying the configuration of the membrane assembly  130 . Further, it is able to monitor real-time reaction of gas, which flows through a specific one of the fluid paths, by a metallic catalyst that is provided to the membrane assembly  130 . 
         [0034]    Meanwhile, the first and second fluid furrows  142  and  122  may be arranged in a form differently configured from the one winding orthogonal to the central axis of the central conductor  140 . One of possible modifications is described in  FIG. 5  according to the present invention. The same reference numerals as in  FIGS. 1 through 3  may denote the same elements with the same functions but different in configuration. 
         [0035]      FIG. 5  is a sectional view illustrating a modified central conductor  140  according to the present invention. Referring to  FIG. 5 , the modified central conductor  140  is comprised of the first furrow  142 , on the outer surface of the conductor, extending from one end toward the other end along the central axis. A fluid flows through the first furrow  142 . In the central conductor  140 , the inlet unit  144  is provided for supplying the fluid, and the outlet unit  145  is for exhausting the fluid. An electric lead of solid wire type  146  is attached to the closed end of the central conductor  140 .  FIGS. 6A and 6B  illustrate assembly parts,  120   a  and  120   b , of the tube  120  for the fluid flow through the outer furrow  122  according to modifications of the present invention, in which the upper illustrations show the top views while the lower illustrations show the side views. The parts,  120   a  and  120   b , join with each other to form the tube  120 . The tube  120  is comprised of the second furrow  122  on the inner surface at the position matching with the first furrow  142 . The first and second furrows  142  and  122  are constructed to wind parallel to the central axis. The inlet unit  124  for supplying the fluid, and the outlet unit  125  for exhausting the fluid are installed in the tube  120 . 
         [0036]    Meanwhile, the first and second fluid paths may be formed by means different from furrows of the above specification. For example, the first fluid paths may be made with a film patterned and sandwiched between the central conductor and the membrane assembly. The second fluid paths may be made with a film patterned and sandwiched between the tube and the membrane assembly. 
         [0037]    According to the present invention as aforementioned, it is possible to detect real-time and in situ chemical reactions occurring at the interface between fluid and solid, and spatial distribution variation of chemicals across the interface. Furthermore, it is able to detect reaction variations of a fluid when reaction environmental factors such as current, voltage, temperature, and flux are changed. 
         [0038]    The above-disclosed subject matter is to be considered illustrative, not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.