Inductor devices – With deformable or distortable coil and/or core
Reexamination Certificate
1999-12-06
2001-08-14
Donovan, Lincoln (Department: 2832)
Inductor devices
With deformable or distortable coil and/or core
Reexamination Certificate
active
06275131
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to variable inductors, and more particularly to variable inductors whose shape and inductance can be changed by the application of internal or external heat and without significantly increasing the inductor's series resistance as related to the Quality Factor (Q) of said inductor.
BACKGROUND
As is well known in the art, an inductor, such as an inductor used in an RF tunable circuit, shows an inductive value based on its physical characteristics of length, diameter, number of turns and wire thickness. Once those physical characteristic were set, changing the tuned frequency of the circuit required changing a circuit component such as the circuit inductance or capacitance. Changing the inductance requires switching to a new inductor or altering the properties of the inductance in some other way such as changing the magnetic properties of the inductor core by adding a magnetic material into the inductor's core, such as soft iron, or increasing the separation between the individual coils of the inductor. These physical changes were managed by moving a magnetic material into or out of the inductor core, manually separating the coil windings, or by switching inductors into or out of a tuned circuit, upon command or manually, resulting in additional components, or larger size requirements for tuned circuits.
Even where a single value inductor is used, changes in temperature, for example, may alter the physical characteristics of an inductor in a RF tuned circuit, requiring re-calibration, re-tuning, or even rebuilding the circuit to accommodate the ambient temperature around the inductor.
Therefore, there exists a need to resolve these problems with the prior art and to significantly improve the way the value of inductors in tuned circuits may be altered, without the need to add components to the tuned circuits.
SUMMARY OF THE INVENTION
The invention disclosed according to its inventive principles, permits the use of a single coil as a variable inductor in a tunable circuit. According to the inventive principles as disclosed in connection with the preferred embodiment, a tuned circuit's reactive characteristics, such as frequency, may be altered by changing the circuit's inductance. This change in inductance may be achieved by applying external heat or internal heat to alter the inductor's size and hence, its inductive value. However, as is well known to those of ordinary skill in the art, heat generated in a conductor is proportional to the conductor's series resistance which, in the case of a prior art inductor, is also a measure of the Quality Factor (Q) of a circuit. The higher series resistance reduces circuit Q value and the efficiency of the circuit when it is used as an RF tuning device. According to the inventive principles, an elastic element is used as a support for the inductor. The elastic element is in the shape of an inductor coil and the inductive element is formed as a layer on the elastic coil support. By incorporating the elastic element for supporting and altering the shape of the layered inductor element, as two separate elements in one combined system, with an insulating layer between, the heating of the elastic element does not substantially alter the series resistance of the layered inductor element. The combined system, as shown and described according to the example of the preferred embodiment, uses a elastic material having a memorized state which is created when the coil is being formed. The material of the coil may be of the composition Nickel Titanium (NiTi) and its alloys, as are commercially available. For example, an inductor support may be made in the shape of a coil from NiTi and heated according to manufactures perscription until that coil shaped memory state is set. According to the inventive principles as disclosed in connection with the preferred embodiment, the coil is then coated with an insulator such as polyurethane, as would be known to one of ordinary skill in the art. The insulating coating of polyurethane preserves the elastic properties of the NiTi coil when the conductive element which becomes the operative inductor element, is added to the system as a low resistance conductor, for example in the form of an electroplated gold coating applied to the insulating layer.
The elastic element in the system is the NiTi coil which may be altered in shape for example by sending a heating current through the coil. The RF operative element of the system is the conductive plating incorporated in the system but separated from the heat responsive elastic element by the insulating layer. As would be known to one skilled in the art, high frequency current such as current at radio frequencies travels at the surface of the conductor. As the RF operative element of the system is attached to but insulated from the heated elastic NiTi coil, it changes in shape in response to change in the shape of the NiTi coil but is insulated from the heat produced in the coil. At the same time, because of the insulation, the material used for the operative inductive element in the system can be made of a different material than used as the elastic material, such as a material having the highest conductive properties and least responsive to heat induced resistive changes. In the example shown for the preferred embodiment, the coating is a gold or gold alloy. However, as would be understood by those skilled in the art, other materials may be used in the practice of this invention.
Accordingly, what is shown and described is a system for a heat responsive variable inductance, incorporating an elastic element having a coil shape responsive to changes in applied heat and temperature, with a conductive element layered on the coil and separated from the elastic element by a layer of insulation. The inductive element, formed from a conductor layered on the insulation, is insulated from the elastic heat responsive element and has a shape and inductance responsive to the change in shape of the heat responsive system element.
REFERENCES:
patent: 3152312 (1964-10-01), Johnson
patent: 3648205 (1972-03-01), Bunch et al.
patent: 4825184 (1989-04-01), Bloch et al.
patent: 5012125 (1991-04-01), Conway
patent: 5889340 (1999-03-01), Miller et al.
Koskan Patrick D.
Liebman Henry F.
Swope Charles B.
Donovan Lincoln
Motorola Inc.
Nguyen Taylor T.
Scutch, III Frank M.
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