WO1990003714A1

WO1990003714A1 - Microwave-powered heating chamber

Info

Publication number: WO1990003714A1
Application number: PCT/GB1989/001148
Authority: WO
Inventors: David Harvey Briggs; Richard Ford Freeman
Original assignee: Core Consulting Group Limited
Priority date: 1988-09-28
Filing date: 1989-09-28
Publication date: 1990-04-05
Also published as: AU4413889A; GB8822703D0

Abstract

A microwave heating chamber has a support plate (12) for carrying foodstuffs (10) and a reflecting dome (18) located opposite a conical wave guide (16) to which microwave energy is supplied by a magnetron (14). An adjustable element or turning device may be provided in the wave guide to alter the pattern of energy, so that the foodstuff is more uniformly heated or so that some energy is diverted to a browning-aid adjacent the foodstuff.

Description

Title; Microwave-Powered Heating Chamber

Field of the Invention

This invention concerns chambers for heating foodstuffs, particularly frozen pre-cooked food, using microwave energy.

Background to the Invention

There is an increasing demand for fast food typically at railway stations, airports and garages. One of the more convenient ways of storing such pre-cooked foodstuffs is by deep freezing them after cooking; it is then only necessary to re-heat the foodstuff as quickly as possible to provide a hot meal or snack.

Microwave energy is most conveniently used for such re¬ heating and it is an object of the present invention to provide an improved form of heating chamber particularly adapted to the re-heating of pre-cooked foodstuffs.

Summary of the Invention

According to the broadest aspect of the present invention a chamber for heating foodstuffs includes a magnetron, a wave guide linking the magnetron to the chamber for projecting microwave energy thereinto, a curved or otherwise shaped microwave-reflecting surface located opposite the waveguide to reflect, focus or concentrate microwave energy incident thereon; and a support for the foodstuff located within the chamber, on which foodstuff can be located at or near the focal point of the reflecting surface i.e. at a point of maximum energy flux.

Where the foodstuff and platform are to be located between the open end of the waveguide and the reflecting surface, the foodstuff support is preferably formed from material which is substantially transparent to microwave radiation so that the latter can pass through the support.

The foodstuff will be, to a greater or lesser extent, also transparent to microwave energy. Consequently, radiation emanating from the wave guide in alignment with the foodstuff will partially heat the foodstuff and partially pass therethrough to be reflected from the reflecting surface and once again intercept the foodstuff and add to the heating thereof. This is especially true for frozen (i.e. ice-containing) products.

In conventional manner, means may be provided to time the period during which microwave energy is supplied to the chamber.

Conveniently, means may be provided within the wave guide to alter the direction in which the radiation emanates therefrom or alters the virtual point from which the radiation appears to come, so as to alter the position of the point in the chamber at which the radiation is generally brought to a focus or point of concentration. By moving the inserted element in the wave guide, so the position of focus or the' E-field shape and intensity can be varied so as to produce more uniform heating of the foodstuff, or to alter the shape of the concentrated field.

Where a browning-aid is located within the chamber, the adjustment of the focusing of the microwave energy may be used to divert some or all of the microwave energy from the foodstuff to the browning aid to thereby cause the latter to become heated to produce infra-red radiation in place of or in addition to the microwave radiation, for browning the foodstuff whilst it is being heated by microwave energy. This diversion may occur part-way through the heating process, in a progressed or programmed manner.

The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a schematic cross-section through a food heating chamber constructed as one embodiment of the invention.

Figure 2 shows one form of the variation in the intensity of the radiation across the line A-A of Figure 1.

Detailed Description of Drawings

Figure 1 shows a microwave heating chamber (E-field focussing or concentrating chamber) for heating pre-cooked foodstuffs of which an example is shown at 10. The latter is carried by a support plate of ceramic material 12 so as to be transparent to the microwave energy which emanates from a magnetron 14 which is located at the lower end of a conical wave guide 16 the upper end of which includes the circular plate 12 on which the foodstuff is located.

Above the plate 12 is located a hemispherical or similarly shaped dome 18 formed from, or at least coated on its inside surface with, a material which is highly reflective to microwave energy, so that radiation emanating from the magnetron 14 and reaching the reflecting surface of the dome 18 will be reflected back towards the foodstuff 10.

The distance of the dome 18 from the foodstuff and the radius of the hemispherical surface is selected so that in general any radiation incident on the concave surface of the hemisphere will be directed towards the central region of the plate 12 and thereby towards the foodstuff located thereon.

Although not shown, a browning-aid may be located within the chamber in the form of a plate, hemispherical shell or shaped lining which is an absorber of microwave energy, t convert the latter into infra-red radiation to irradiate the foodstuff and cause the surface to become crisped or brown. Movement of a deflector or tuning device (not shown) into and out of the path of the radiant microwave energy in the wave guide 16 can cause a change in the pattern of the energy incident on the reflecting surface 18 to thereby divert some or all of the radiant energy away from the foodstuff and onto the browning-aid when required.

The hemispherical dome may form a lid to a chamber, to which end the dome is hinged as at 20 so as to be capable of being lifted to reveal the interior of the chamber to allow foodstuff to be inserted or removed. Figure 2 shows how the intensity of the radiation varies along a diameter of the plate 12 between the points A-A of Figure 1. The corresponding points A-A are plotted on the graph of Figure 2 and the curve shows how there is zero radiation around the edge of the plate but that as you move towards the centre of the plate, so the intensity of the radiation increases quite dramatically as a result of the focusing effect of the dome 18. The highest intensity of the field strength is shown to occur at the centre of the plate denoted by chain dotted line 22 in Figure 2.

Other patterns of E-field intensity may be achieved by using shapes other than a hemisphere. The reflecting surface can be designed specifically to focus the Efield into the shape of a particular foodstuff, thereby perfectly matching the E-field to a particular foodstuff.

Claims

Claims ;

1. A microwave chamber for heating foodstuffs comprising a magnetron, a wave guide linking the magnetron to the chamber for projecting microwave energy thereinto, a curved or otherwise shaped microwave-reflecting surface located opposite the waveguide to reflect and concentrate microwave energy incident thereon; and a support for the foodstuff located within the chamber, on which foodstuff can be located at a point of maximum energy flux in the chamber.

2. A chamber according to "-claim 1 in which the foodstuff and support are located between the open end of the waveguide and the reflecting surface, and the foodstuff support is formed from material which is substantially transparent to microwave radiation so that the latter can pass through the support.

3. A chamber according to claim 1 or claim 2 further comprising means to time the period during which microwave energy is supplied to the chamber.

4. A chamber according to any one of claims 1 to 3 further comprising an adjustable element within the wave guid to alter the direction in which the radiation emanates therefrom or alters the virtual point from which the radiation appears to come, so as to alter the position of the point in the chamber at which the radiation is generally brought to a focus or concentrated.

5. A chamber according to claim 4 in which a browning-aid is located within the chamber, and in which the adjustment of the focusing of the microwave energy by the element is used to divert microwave energy from the foodstuff to the browning aid to thereby cause the latter to become heated to produce infra-red radiation in place of or in addition to the microwave radiation, for browning the foodstuff whilst it is being heated by microwave energy.

6. A microwave chamber substantially as herein described with reference to , and as shown in, the accompanying drawings.