Patent Application
20110018668
1. Field of the Invention
The present invention relates to inductors. More specifically, the present invention relates to a variable inductor having a non-magnetic core, and a method of manufacturing same.
2. Related Art
Inductance is a fundamental property of an electrical circuit or circuit element, whereby an electromotive force is induced in the circuit or element as the result of a changing magnetic flux (e.g., a change in magnetic flux due to an alternating current flowing through a coil). Often, it is desirable to change the inductance of a circuit so as to alter the resonant frequency of the circuit. For example, in radio frequency (RF) applications, it is often necessary to tune a circuit to a desired frequency in the radio spectrum. This is often accomplished by altering the inductance of the circuit, using a device known as an inductor.
Inductors can be fixed or variable. A fixed inductor is a coil of wire wrapped around a core, which can either be a dielectric (e.g., air, plastic, etc.) or a metal (e.g., soft iron, etc.). Fixed inductors provide a specific, pre-defined, non-variable level of inductance. Variable inductors, on the other hand, can provide a range of inductance levels, and can be adjusted as desired. One type of variable inductor is a coil of wire wrapped around a dielectric core, and a magnetic, metallic core positioned coaxially within the dielectric core. The position of the core can be adjusted with respect to the coil to alter the resonant frequency of the coil, by rotating the core with respect to the coil.
The present invention relates to a variable inductor having a non-magnetic core. The coil includes a dielectric core having a helical thread on an outer surface thereof for receiving the coil, and a non-magnetic element positioned coaxially within the core. The non-magnetic element could be provided in the form of a bushing or a solid rod, and could be manufactured from any suitable, non-magnetic metal, such as copper, brass, etc. The dielectric core is preferably manufactured from a dielectric material having a low coefficient of friction (e.g., polytetrafluoroethylene, sold under the trademark TEFLON), to allow for precise adjustment of the inductor.
The present invention also relates to a method for manufacturing a variable inductor. The method includes the steps of forming a dielectric core having a helical thread on an outer surface thereof and a recess coaxial with the central longitudinal axis of the dielectric core; forming a non-magnetic element; positioning the non-magnetic element within the recess of the dielectric core; and forming a coil of wire about the dielectric core.
The foregoing features of the invention will be apparent from the following Detailed Description of the Invention, taken in connection with the accompanying drawings, in which:
The present invention relates to a variable inductor, as discussed in detail below in connection with
It is noted that any desired number of turns of wire could be provided in the coil 18 (and, the thread 14 of the dielectric core 12 could be lengthened or shortened to accommodate such number of turns), to provide a device having a inductance range. Table 1, below, provides a list of sample operating characteristics of the variable inductor 10 of the present invention, corresponding to various turns of wire in the coil 18:
The core 12 is preferably made from polytetrafluoroethylene material (sold under the trademark TEFLON) conforming to American Society for Testing and Materials (ASTM) Standard D 1710 or equivalent. Such material is a lightweight, dielectric material having a low coefficient of friction, which facilitates easy operation of the inductor 10, i.e., reduced friction when the core 12 is rotated within the coil 18. Of course, other dielectric materials could be used, such as plastic, ceramic, etc., without departing from the spirit or scope of the present invention. A slot 26 could be provided on one end of the core 12 for receiving a tool (e.g., a flat-blade screwdriver) for rotating the core 12.
As mentioned above, the core 12 of the present invention could be provided in various lengths to accommodate a desired number of turns of the coil 18, so as to provide a variable inductor having desired operating characteristics. For example, as shown in
It is expressly noted that the dimensions set forth herein are illustrative in nature, and are not intended to limit the scope of the present invention.
The present invention could be manufactured using the following process. First, the dielectric core 12 is fabricated from a length of PTFE stock, such that the helical thread 14 is formed on an outer surface thereof by machining or milling. Then, the recess 28 is formed coaxial with the central longitudinal axis of the core 12 by drilling to a depth sufficient to accommodate the non-magnetic element 16. The non-magnetic element 16 is then formed from copper or brass, using conventional milling or machining techniques and, optionally, conventional drilling techniques (in the case of the hollow bushing version of the element). Once formed, the non-magnetic element 16 is inserted into the recess 28. Optionally, an adhesive could be applied to the inner surfaces of the recess 28 prior to insertion of the non-magnetic element 16. Finally, the coil 18 is formed around the core 12 from a length of wire, and ends of the wire are bent at desired angles to form the terminal ends 20a, 20b. A protective coating could be provided on the coil 18, and it is noted that the terminal ends 20a, 20b could also be pre-tinned, such that a thin coating of solder is applied to the ends 20a, 20b after the protective coating on the coil 18 is abraded off the terminal ends 20a, 20b in order to facilitate soldering of the present invention to a circuit board.
Having thus described the invention in detail, it is to be understood that the foregoing description is not intended to limit the spirit or scope thereof. What is desired to be protected is set forth in the following claims.
