Wave transmission lines and networks – Resonators
Reexamination Certificate
1998-01-19
2001-03-27
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Resonators
C333S0990MP, C505S210000, C505S700000, C505S866000
Reexamination Certificate
active
06208227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electromagnetic resonators, and more particularly to structures for distributing and dissipating heat generated in those resonators.
BACKGROUND OF THE INVENTION
Electromagnetic resonators are often used in filters in order to pass or reject certain signal frequencies. To optimize filter performance, the resonators should have a minimum of signal loss in the passed frequency range. Such losses in resonators can occur in a variety of modes, but all manifest themselves through the generation of heat caused by resistance to current flowing on the surfaces of conductive elements in the resonator. For that reason, conductors in resonators are usually chosen for their low-surface resistance. However, even with low-surface resistance metals, such as copper or silver, significant heating and signal losses may occur. The heating can further increase the surface resistance of the metal, thereby adding to signal loss.
In order to minimize losses in resonators, superconducting materials have been used. For instance, if a cavity resonator is used, the walls of the cavity or a resonant element located inside the cavity may be made from or coated with a superconducting material. While superconductors have a significantly lower surface resistance than ordinary conductors, a relatively small amount of heat will still be generated in a superconducting resonator. Dissipation of that heat may not be a significant problem if the power of the filtered signal is relatively low. Thus, when a superconducting resonator is used, for instance, as a component in systems receiving low-power radio frequency signals, heat build-up in the superconductor may not have significant adverse effects. However, if the superconducting resonator is used, for instance, as a component in a high-power signal transmission system, heat build-up in the superconducting material can result in serious performance degradation.
As heat builds up in a superconducting material, the temperature of that material may rise above its critical temperature. Once a superconductor rises above its critical temperature, it loses its superconducting properties, thereby increasing the surface resistance drastically, and further generating heat until the component completely fails. This phenomenon is known as thermal runaway. Therefore, removing heat from a resonator handling relatively high power signals, particularly when superconducting materials are used, may be required for effective resonator performance. Moreover, removal of heat must be accomplished without significantly increasing the overall loss of the resonator.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, an electromagnetic resonator includes a housing having walls and a resonant element. The resonant element is made of a layer of high-temperature superconducting material and a layer of thermally conductive material having a thermal conductivity above about 22.5 W/m·K at 77K. The resonant element is attached to the housing and spaced from the walls and experiences a momentary peak magnetic field above about 160 A/m without experiencing thermal runaway.
The resonant element may include a metallic substrate coated with a layer of thermally conductive material. The thermally conductive material may be silver, and the high-temperature superconducting material may be YBa
2
Cu
3
O
7−x
. The housing defines a cavity, and the resonant element may be located in the cavity, which may be filled with a thermally conductive gas.
The thermally conductive layer preferably has a thermal conductivity above about 100 W/m·K and more preferably above about 200 W/m·K at 77K. The resonator preferably does not exhibit thermal runaway at a momentary peak magnetic field strength of above about 270 A/m.
In accordance with another aspect of the present invention, a signal transmission system includes a signal-generating device emitting a signal having a power and an electromagnetic resonator for receiving a signal where the resonator includes a resonant element having a surface coated with a high-temperature superconducting material. A layer of thermally conductive material adjacent the high-temperature superconducting material disperses heat along the thermally conductive layer. The thermally conductive material has a thermal conductivity of above about 22.5 W/m·K at 77K and the power of the signal results in a peak magnetic field on the resonant element of above about 160 A/m.
In accordance with another aspect of the present invention, a signal transmission system includes a signal-generating device and an amplifier for increasing the power of a signal from the signal-generating device. The system includes a filter coupled to the amplifier and having a resonator with a layer of high-temperature superconducting material and a layer of thermally conductive material adjacent the high-temperature superconducting material. The system also includes a signal transmitter. The amplified signal has a power above about 5 watts and the thermally conductive material has a thermal conductivity above about 160 W/m·K at 77K.
The filter may have at least two resonators. Each resonator has a mounting mechanism and each mounting mechanism has a volume. At least one resonator mounting mechanism may have a volume different than the volume of at least one other resonator mounting mechanism.
In accordance with yet another aspect of the present invention, a resonator includes a housing having at least one wall defining a cavity and a resonant element located in the cavity. A mounting mechanism attaches the resonant element to the housing wall and is made of a dielectric material having a thermal conductivity above about 1 W/m·K at 77K.
The mounting mechanism may be made of polycrystalline alumina and is preferably 99.8% pure polycrystalline alumina. The mounting mechanism may include a post made of polycrystalline alumina, an epoxy and a polymer base, where the post and base are epoxied together. The post may be in contact with the wall, and the base attaches the stand to the wall.
In accordance with still another embodiment of the present invention, a resonator mounting mechanism for attaching a resonant element to a wall of a resonator cavity includes a post made of a thermally conductive dielectric material having a first end adapted to receive the resonant element and a second end having a flat-bottom surface. The mounting mechanism also includes a base connected to the post near the bottom surface of the post. The base holds the post to the cavity wall with the bottom surface of the post in contact with the wall to transmit heat from the resonant element, through the post, to the cavity wall.
In accordance with another embodiment of the present invention, an electromagnetic filter includes a first resonator having a first wall, a first resonant element, and a first mounting mechanism attaching the first resonant element to the first wall. The filter also includes a second resonator having a second resonant element, a second wall, and a second mounting mechanism attaching the second resonator to the second wall. The first mounting mechanism has a first volume and the second mounting mechanism has a second volume, and the first volume is different than the second volume.
Each resonator has a second harmonic mode, and the second harmonic mode has a location of its electric field maximum. Each mounting mechanism may be located adjacent the second harmonic mode electric field maximum. The first mounting mechanism and the second mounting mechanism may be made of a material having a dielectric constant above about three and more preferably above about nine.
In accordance with still another aspect of the present invention, an electromagnetic resonator includes a housing having at least one wall defining a cavity, a resonant element located in the cavity, and a mounting mechanism attaching that resonant element to the housing wall. The mounting mechanism is comprised of a dielectric material having a dielectric constant above ab
Freeman Edward A.
Hodge James D.
Ortenberg Nikolay
Remillard Stephen K.
Richied Donald E.
Illinois Superconductor Corporation
Lee Benny
Marshall O'Toole Gerstein Murray & Borun
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