Electric heating – Microwave heating – Field modification
Reexamination Certificate
2001-03-02
2001-12-11
Leung, Philip H. (Department: 3742)
Electric heating
Microwave heating
Field modification
C219S732000, C219S759000, C219S762000, C219S694000, C333S228000
Reexamination Certificate
active
06329645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to sample processing in a microwave oven and, more particularly, is concerned with an apparatus for dampening standing wave pattern generation in a closed cavity of a microwave oven.
2. Description of the Prior Art
Automated mechanical and bench (hands-on) methods of sample processing are the standard practice today in research and clinical laboratories. Though relatively time-consuming, these methods are reliable in the sense that they provide reproducible results.
Over the last two decades there has been a growing interest in accelerating the steps required in processing of samples, such as tissue and other specimens, for research and clinical applications. Interest has focused on the use of microwave ovens which emit radiation at 2.45 GHz +/−50 MHz. The presence of microwave energy and its heating effects, produced via ionic conduction and dipole rotation, provide increased rates of heat diffusion which reduce overall processing times compared to mechanical or bench methods.
Uneven microwave induced specimen heating, however, is a problem. The closed cavity design of microwave ovens produces standing wave patterns which are characterized by regions of high to low electric field density. These regions cause uneven heating of samples during microwave exposure and are referred to as hot and cold spots. The non-uniform heating of samples placed at different locations in the microwave cavity affects run-to-run reproducibility.
To overcome problems with use of microwave ovens, users must be particularly mindful to keep processing conditions (e.g. sample container, fluid volume, container placement in microwave cavity, sample number, same microwave oven) the same for each run. Users typically take steps to identify hot and cold spots prior to actual sample processing by use of the conventional methods of recognition, such as thermographic paints, neon bulb arrays and liquid crystal sheets, in order to be able to select the correct container placement location. Also, users have recirculated a dielectric fluid, such as water, around a confined sample to help control rapid heating during microwave irradiation.
Dummy loads, usually a beaker filled with water primarily serving as a heat sink, are frequently used in the microwave cavity during sample processing. Also, it is known that the use of multiple water loads will produce relatively large areas of uniform energy for multiple sample processing. Kok et al. (Ref. 1) have disclosed that a flat layer of cold water in the microwave cavity is effective in reducing hot and cold spots. The dielectric properties of water, an absorptive material, are important when water is used as a static dummy load. It is known that as water heats its dissipation factor decreases and the penetration depth of microwave energy into the water increases. Giberson et al. (Refs. 2 & 3) have disclosed that the benefits of recirculation and cooling of water within the microwave cavity via the dummy or water load have been demonstrated during specimen processing. Also, Giberson et al. have disclosed that when the temperature of water can be held constant the microwave environment remains constant and relatively large areas of uniform heating can be created.
Although the potential benefits of water recirculation and cooling in microwave processing of samples are thus recognized and appreciated, there still exists an unfulfilled need for a device that will bring about the realization of these benefits in practice.
BACKGROUND REFERENCES
Ref. 1: Kok, L. P., Boon, M. E., Smid, H. M. 1993. The problem of hot spots in microwave equipment used for preparatory techniques—Theory and practice.
Scanning,
15:100-109.
Ref. 2: Giberson, R. T., Demaree, R. S. Jr. 1995. Microwave fixation: Understanding the variables to achieve rapid reproducible results.
Micros. Res. Tech.
32:246-254.
Ref. 3: Giberson, R. T., Demaree, R. S. Jr. 1999 Microwave processing techniques for electron microscopy: A four-hour protocol, In:
Methods in Molecular Biology.
N. Hajibagheri ed. Humana Press, Inc., Totowa, N.J., pp. 145-158.
SUMMARY OF THE INVENTION
The present invention provides an apparatus that satisfies the aforementioned unfulfilled need. As mentioned earlier, the closed cavity design of microwave ovens generates areas called hot and cold spots within the microwave cavity during periods of microwave irradiation at about 2.45 GHz. These areas have different energy densities and create regions having unequal heating properties. The apparatus of the present invention mitigates these areas of different energy densities and substantially minimizes these regions of unequal heating properties.
The apparatus of the present invention provides a unique dummy load which dampens the standing wave patterns generated by the closed cavity design of microwave ovens and, at the same time, provides a large sample processing area or surface. The apparatus minimizes the effects of standing wave patterns over the processing surface. The processing surface displays substantially uniform properties with respect to microwave sample heating when measured by thermographic paint, liquid crystal sheets, neon bulb arrays and experimental evaluation. As a result, the apparatus ensures that currently existing microwave ovens are now suitable for biomedical applications and research endeavors. The apparatus also ensures that microwave-assisted processing is now on a par with mechanical and bench methods on the basis of run-to-run reproducibility that is now, but was not previously, possible with currently existing microwave ovens.
Accordingly, the present invention is directed to an apparatus for dampening standing wave pattern generation in a closed cavity of a microwave oven. The apparatus includes a fluid table having an enclosure made of a microwave energy transparent material and means, such a generally flat top platform made of glass and held in place by the enclosure, for defining a processing surface for placement thereupon of samples to be processed. The apparatus also includes a quantity of dielectric fluid, such as water or fluid having dielectric properties similar to water, contained by the enclosure so as to provide a large flat surface of the dielectric fluid underneath the flat platform and thus below the processing surface. The apparatus further includes means for recirculating the dielectric fluid to and from the enclosure of the fluid table and for cooling the dielectric fluid to maintain the dielectric fluid within a given range of temperatures. The processing surface on the flat platform is used for placement of tissue samples, in containers, on slides or in a vacuum. The processing surface, the underlying dielectric fluid, and the control of the temperature of the dielectric fluid combine to provide uniform sample temperature control by mitigating energy density differences from standing wave patterns generated in the closed cavity of the microwave oven. The enclosure and dielectric fluid contained therein serve as a microwave energy sink that is maintained under relatively constant conditions and is of such a depth as to preclude the formation of standing wave patterns on the processing surface of the flat platform of the apparatus.
The apparatus of the present invention thus provides a processing surface available for use during microwave-assisted processing of samples for various biomedical, pharmaceutical, biological, industrial, agricultural or veterinary biomedical applications. More specifically, representative applications are processing of tissue specimens into paraffin or resins, special stain applications, epitope (antigen) retrieval, immunocytochemistry and decalcification.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.
REFERENCES:
pat
Giberson Richard Thorp
Hansen Paul Alex
Pella Ted
Thurmond S. K.
Flanagan John R.
Flanagan & Flanagan
Leung Philip H.
Ted Pella, Inc.
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