This invention relates to a mode stirrer, in particular, a mode stirrer for use in microwave ovens.
Microwave ovens are an effective means of delivering heat to food products, imparting heat directly to the product via radiated waves. These waves are generated by a magnetron, fed down a waveguide, and then delivered directly into the oven cavity by a waveguide opening.
The most common problem of microwave ovens is uneven heating of products. Due to the nature of microwaves themselves interacting with food products, hot and cold spots occur. The non-uniform distribution of waves, along with the changes in the food product properties as it heats make hot and cold spots a certainty.
In the prior art, turntables have been one of the most common methods for improving uniformity of microwave heating. Other methods are the use of directional antennas to direct the desired pattern for producing uniform heating. These antenna arrays are usually more successful for certain types of foods, but not for others, with the result being inconsistent cooking/heating results.
Mode stirrers are another attempt to create random microwave fields within the heating cavity. These provide some improvement, but are usually only marginally effective. Mode stirrers change the standing wave pattern inside a microwave cavity by any or all of the following methods . . . changing the point of introduction of microwave energy into the cavity, changing the effective shape/size of the cavity and/or changing the oscillation frequency of the magnetron (load pulling). The changing oven cavity modes will result in a changing electro-magnetic field around the food item being cooked. A simple rod shaped antenna, by rotating inside the oven cavity, changes the point of introduction of microwave energy. This rotation results in excitation of different modes inside the cavity. Mode stirrers with large holes or with the presence or absence of a large area of metal will effectively change the geometry of the oven as the mode stirrer rotates.
There is not found in the prior art a mode stirring apparatus that improves the effectiveness by utilizing two mode stirrers in opposite walls of the oven wherein the stirrers rotate in a counter-rotating manner and wherein the stirrer has a unique curved shape, which permits a smaller sized stirrer.
It is an aspect of the invention to provided an improve microwave mode stirring apparatus that enables a more effective heating pattern in the food that is to be cooked in the oven. In order to improve the effectiveness of a single mode stirrer, this oven utilizes two mode stirrers located in opposite walls of the oven. Each mode stirrer is independently driven by a small gear motor that causes the mode stirrer to rotate in only one direction. The result of this mounting configuration is that the mode stirrers rotate in a counter-rotating fashion in relation to the food being cooked. The mode stirrer in this invention has a combination of radiating slots (which behave like a rod shaped dipole antenna) and large areas of angled/displaced metal.
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Residential microwave ovens generally have only one magnetron but most commercial ovens have two or more. The purpose in having two magnetrons is to have more microwave power. A single magnetron having greater power could be used, but the cost of a single magnetron of sufficient power is greater than the cost of having two lesser power magnetrons. Also, the use of two mode stirrers eliminates the problem of excessive heating on one side of the cooking cavity without the need for a rotating turntable that is found typically in most residential ovens.
The mode pattern in the oven cavity, as well as the energy distribution in the cavity changes as the mode stirrer 12 rotates. Having two mode stirrers on opposite walls of the oven, rotating in opposite directions minimizes the amount of cross talk between the two magnetrons 14. This is due to the fact that the two mode stirrers 12 will seldom be in phase with each other.
Although the present invention has been described with reference to certain preferred embodiments thereof, other versions are readily apparent to those of ordinary skill in the preferred embodiments contained herein.
This application claims benefit of U.S. Provisional Application Ser. No. 61/753021, filed Jan. 16, 2013, pursuant to 35 USC §119(e),
Number | Date | Country | |
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61753021 | Jan 2013 | US |