Patent Publication Number: US-2022224304-A1

Title: Balun

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional patent application no. 63/136,715, filed on Jan. 13, 2021, which is incorporated by this reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to baluns. 
     BACKGROUND 
     In certain applications, baluns are tuned to a frequency of −16 db or less and are place around a coil cable to reduce shield currents. 
     SUMMARY 
     Certain challenges presently exist. For instance, currently, baluns are constructed using a Teflon base. This Teflon base is porous and over time can warp. The machining process of the Teflon is a two-step process and is time consuming and costly. The baluns are also plated with a copper plating. Ideally, the copper plating process should produce a consistent thickness of copper over the surface of the Teflon base. However, the plating is hard to hold to the current dimensional requirement and many failures occur. Accordingly, this disclosure describes an improved balun design. 
     For example, in one aspect there is provided a balun comprising a three-dimensional (3D) printed base (e.g., the base may have been printed using a resin-based printing process such as the Digital Light Synthesis (DLS) printing process). In some embodiments, the balun further comprises a piece of electrically conducting tape (e.g., copper tape) adhered to an outer surface of the 3D printed base. In some embodiments, the balun further comprises a capacitor directly connected to the electrically conducting tape. 
     In another aspect there is provided a method for making a balun. In one embodiment, the method includes: using a three-dimensional (3D), resin-based printer to print a 3D base; attaching an electrically conducting tape to an outer surface of the 3D base; and connecting a capacitor to the copper tape. In some embodiments, the 3D resin-based printer uses a Digital Light Synthesis (DLS) printing process to print the 3D base. In some embodiments, attaching the tape to the outer surface of the 3D base comprises using an adhesive to adhere the tape to the outer surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a balun base according to an embodiment. 
         FIG. 1B  illustrates a cross-sectional view of the balun base shown in  FIG. 1A . 
         FIG. 2  illustrates a piece of copper tape after it has been die stamped. 
         FIG. 3  illustrates a balun base after copper tape has been applied to the outer surface of the base. 
         FIG. 4  illustrates the performance of a balun according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, the Teflon base is replaced with a 3D printed base; for example a 3D printed base obtained using a resin-based printing process that cures liquid plastic resin into a solid part using light (e.g., ultraviolet (UV) light). In one embodiment, the resin-based 3D printing process works by projecting light through an oxygen-permeable window into a reservoir of UV-curable resin. One such resin-based printing process is known as the Digital Light Synthesis (DLS) printing process. The DLS printing process uses digital light projection, oxygen permeable optics, and liquid resins to produce desired 3D products. A printer for producing a DLS 3D printed balun base may be obtained from Carbon® (see, e.g., www.carbon3d.com). 
     For the 3D process, one can 3D print all the features in the balun base eliminating the need for the two-step machining process.  FIG. 1A  illustrates an example DLS 3D printed balun base  100 , and  FIG. 1B  is a cross-sectional view of the base  100  along axis A. As shown in  FIG. 1A and 1B , the DLS printed base  100  can be printed with all the necessary pockets (e.g., pocket  102 ), grooves (e.g. groove  104 ), and thread holes (e.g., holes  106  and  108 ). By printing the base  100  with all of the necessary features (e.g., pockets, grooves, thread holes), this eliminates the machining process, which is a large advantage over using a Teflon base as the Teflon baes requires a two stage machining process. The printed base  100  is very accurate and one can adjust any dimension to nominal. Additionally, no additional steps are required for a finished base balun. Also, the base  100  has been tested and passed Proton Emissions Testing. 
     Additionally, the copper plating process is replaced by using a copper tape, thereby eliminating the inconsistent plating thickness issue. In one embodiment, the copper tape that is used is the EMI Copper Foil Shielding Tape made by 3M (UPC 05400727470).  FIG. 2  illustrates a piece of copper tape  200  after it has been die stamped to remove potions of the tape corresponding to the packet(s), groove(s), and thread hole(s) formed on the surface of base  100 . This piece of copper tape, which has copper on one side and an adhesive on the opposite side is adhered to the base  100 , as shown in  FIG. 3  which illustrates the balun base after the copper tape has been applied to the outer surface of the base. An advantage of using copper tape is that the thickness of the copper layer is consistent, thereby reducing scrap and providing a consistent tuning result. After the copper tape is applied, one or more capacitors are directly connected (e.g., soldered) to the copper tape.  FIG. 3  further illustrates a capacaitor  302  that has been electrically and physically connected to the copper tape  200 . 
     These design changes described above has produced a balun with better test results than the current Teflon balun. The testing average of the Teflon balun is −16 db, the new DLS 3D printed design is yielding on average −17 db (see  FIG. 4 ). 
     While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. 
     Additionally, while the processes described above and illustrated in the drawings are illustrated as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.