Abstract:
A thermocouple produced by removing insulation from a distal end of each of at least first and second thermocouple conductors, forming a thermocouple junction at the distal ends of the at least first and second thermocouple conductors, placing the thermocouple junction into the heat shrinkable polymer material by sliding a second end of the tube of heat shrinkable polymer material over the thermocouple junction and sealing the thermocouple junction by heating and melting the polymer material.

Description:
RELATED APPLICATIONS 
   As provided under 35 U.S.C. § 119(e), this patent application claims the benefit of related U.S. Provisional Application No. 60/366,435 filed Mar. 21, 2002, which is hereby incorporated by reference in its entirety. 

   TECHNICAL FIELD 
   This patent application relates to thermocouple devices, and in particular, to a thermocouple device produced by encapsulating a thermocouple junction with a heat-shrinkable polymer coating. 
   BACKGROUND 
   A thermocouple is a bimetal junction that provides a voltage proportional to temperature. Temperature probes are often formed using thermocouples. Many applications requiring temperature probes require extremely small size. 
   One application for extremely small temperature probes is in the medical device industry; especially for use in catheters. For example, ablation catheters are used in non-invasive treatment of heart abnormalities. The ablation catheter is able to identify abnormal tissue growth and uses heat to remove the tissue causing the additional conduction paths. Thermal feedback is required when removing the tissue to prevent blood clotting or blood boiling during the procedure. In using a temperature probe to provide this feedback, the probe must be small enough to get as near an ablation electrode as possible. Also, when used in catheters, it is desirable that a temperature probe not rupture a catheter sleeve by tearing or abrasion. Further, a probe should be electrically insulated to allow in vivo operation. 
   It is apparent that uses for extremely small temperature probes beyond the medical field are possible. An extremely small probe would be useful in any field where a measurement of a localized temperature variation is desired, such as for example, the field of electronics. 
   What is needed is an insulated thermocouple device of extremely small size. 
   SUMMARY 
   This document discusses an insulated thermocouple device of extremely small size. The thermocouple is produced by removing insulation from distal ends of two thermocouple conductors and then forming a thermocouple junction at the distal ends of the two thermocouple conductors. A tube of heat shrinkable polymer material is placed over the thermocouple junction. The entire thermocouple junction is then sealed by heating and melting the polymer material. 
   The resulting thermocouple and seal fall within a reproducible confined shape, where the height of the confined shape falls within a range of about 0.003 to 0.010 inches and the width of the confined shape falls within a range of about 0.005 to 0.0110 inches. 
   This summary is intended to provide an overview of the subject matter of the present application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the subject matter of the preset patent application. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings like numerals refer to like components throughout the several views. 
       FIG. 1  is a drawing of one embodiment of the micro-thermocouple. 
       FIG. 2  is a flowchart showing one method for forming the micro-thermocouple. 
       FIG. 3  is a drawing of showing fused embodiments of the micro-thermocouple. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and specific embodiments in which the invention may be practiced are shown by way of illustration. It is to be understood that other embodiments may be used and structural changes may be made without departing from the scope of the present invention. 
   As stated previously, the present application is concerned with materials and techniques used to create a sealed thermocouple of extremely small size.  FIG. 1  shows one embodiment of a micro-thermocouple  100 . The thermocouple junction  130  is formed from joining conductors  120 ,  122  of dissimilar metals. The metals comprise any of the standard metal combinations defined by the American Society of Testing and Materials (A.S.T.M.) for thermocouples. The size of the thermocouple conductors generally fall with a range of about 30 awg (0.010 inch diameter) to about 50 awg (0.0009 inch diameter). In one embodiment conductors  120 ,  122  are joined to form a thermocouple junction  130  by soldering using lead-free solder  135 . In another embodiment, conductors  120 ,  122  are welded and  135  represents a welded bead or seam. Beyond the thermocouple junction  130 , the conductors  120 ,  122  are electrically insulated with commonly used insulating material  140  such as nylon, polyurethane, or polyimide. A heat shrinkable polymer material is then used to form an electrically insulating seal  150  over the micro-thermocouple  100 . To create the seal  150 , a tube is slid over the thermocouple junction. In one embodiment, the tube is slid over the thermocouple junction and the seal  150  is then formed by heating the tube of polymer material to the point of melting onto and over the thermocouple joint  130  and onto the insulation  140 . Melting the polymer material onto the thermocouple conductor insulation  140  provides a seal around the insulation  140 . The melting also forms a domed shape  155  on the end of micro-thermocouple  100 . This domed end  155  is advantageous if the thermocouple is used in a catheter as it results in the micro-thermocouple  100  being resistant to abrading or tearing a catheter sleeve. In another embodiment, the tube of heat shrinkable polymer material is first sealed on one end by melting the end and forming the domed end before the tube is slid over the thermocouple junction. After the tube is slid over the thermocouple junction  130 , further heating and melting provides the insulating seal  150 . Other embodiments involve sealing the end while it is placed over the thermocouple junction  130 . 
   The length (l)  160  of the resultant seal  150  is within the range of about 0.05 inches to 0.5 inches. The overall length (L)  165  of the micro-thermocouple  100  is within the range of about 20 inches to 78 inches. One embodiment of the micro-thermocouple  100  uses polyethylene terephthalate (PET) as the polymer material. Another embodiment uses fluorinated ethylene propylene (FEP). The seal  150  is moisture resistant and electrically insulating. The insulation resistance of the seal is greater than 100 Mega-ohms when measured at 50 Volts(DC). 
     FIG. 1  also shows a cross section  110  of micro-thermocouple  100 . The width (w)  170  of the micro-thermocouple  100  falls within a range from about 0.005 inches to 0.011 inches. The height (h)  175  of the micro-thermocouple  100  falls within a range of about 0.003 inches to 0.01 inches. Thus, it can be seen that the micro-thermocouple can be formed within a reproducible confined shape having a height  175  less than about 0.01 inches and a width  170  less than about 0.011 inches. The final dimensions of the confined shape is determined in part by the gauge of the thermocouple conductors used. Providing the insulation by the technique described herein adds about 0.0005 inches to the width and height dimensions of a formed thermocouple junction. 
     FIG. 2  shows a flowchart of one embodiment of a method  200  of forming micro-thermocouple  100 . At  210 , insulation  140  is removed from a distal end of thermocouple conductors  120 ,  122 . At  220 , a thermocouple junction  130  is formed at the distal end of the conductors  120 ,  122 . At  230 , the tube of polymer material is slid over the thermocouple junction  130 . At  240 , a seal  150  is formed over the thermocouple junction  130  by heating and melting the polymer material. 
     FIG. 3  shows fused embodiments of the micro-thermocouple  100 . A fused thermocouple prevents the possibility of recycling or reusing the thermocouple if the micro-thermocouple  100  is used in a medical device. In one embodiment a fuse  390  is placed in a thermocouple conductor  120  between a proximal end of the conductor  120  and the thermocouple joint  130 . Exceeding the rating of the fuse breaks the electrical connection between the proximal end of conductor  120  and the thermocouple joint. In another embodiment, a fuse  395  is formed by placing within the thermocouple junction  130 . Exceeding the rating of the fuse  395  across the thermocouple conductors  120  causes the device to lose the properties of a thermocouple. 
   Although specific examples have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement calculated to achieve the same purpose could be substituted for the specific example shown. This application is intended to cover any adaptations or variations of the present invention. Therefore, it is intended that this invention be limited only by the claims and the equivalents shown.