MICROWAVE-POWERED HEATING CHAMBER

COMPARTIMENT DE CHAUFFAGE MICRO-ONDES

English Abstract

ABSTRACT
A microwave-powered heating chamber has a ceramic support
(12) for foodstuff (10), and a curved surface (20) of microwave
absorbing material disposed opposite a waveguide (16) which is
connected to a microwave energy source, such as a magnetron (14).
A reflecting shield may be temporarily positioned over the curved
surface (20) to enable the foodstuff to be microwave-heated,
after which the shield is removable to allow browning to occur.

Claims

WO 90/03716 PCT/GB89/01150




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Claims

1. A microwave chamber for heating foodstuffs comprising
a source of microwave energy for projecting microwave
energy into the chamber via a waveguide, a curved surface
of microwave absorbing material located opposite the
waveguide to convert microwave energy incident thereon
into infra-red radiation, and to direct or focus the
infra-red radiation generally towards the centre of the
chamber wherein is located a support by means of which the
foodstuff can be located at or near the focal point of the
curved surface.

2. A chamber according to claim 1 in which the foodstuff
support is located between the open end of the waveguide
and the absorbing surface and is formed form 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 preceding claim in
which means is provided within the source of microwave
energy to alter the direction in which the radiation
enters the chamber or to alter 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


WO90/03716 PCT/GB89/01150



radiation is generally brought to a focus or
concentrated.

5. A chamber according to claim 4 in which said means
comprises an element inserted in the waveguide, so the
position of focus or concentration can be varied to
produce more uniform heating of the foodstuff.

6. A chamber according to any one of the preceeding claims
in which moving or fixed elements, as appropriate are
employed to match more closely the concentration of the E-
field to each of several different food products.

7. A chamber according to any one preceding claim and
further comprising a microwave-absorbing browning aid
located within the chamber; a removable shield of
microwave reflecting material positionable over the
surface of the absorbing material until such time as the
microwave heating has raised the temperature of the
foodstuff sufficiently, after which the shield is
removable to allow browning to occur.

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

Description

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WO90/03716 PCT/GB89/01150




Tit~e: 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 i8 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 and 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 which
require to be browned during the heating process.

Summary of the Invention

According to the present invention a chamber for heating
foodstuffs which includes a sourc~ ~f microwave energy for
projecting microwave energy into the chamber, a curve~
microwave absorbing sur~ace is located opposite the

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W O 90/03il6 PC~r/G B89/0115



waveguide to convert microwave energy incident thereon
into infra-red radiation, and to direct or focus the
infra-red radiation generally towards the centre of the
chamber wherein is located a support by means of which the
foo'dstuff can be located at or near the focal point of the
curved surface.

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.

Where the support is an absorber of infra-red radiation,
the support will be heated and assist in browning the
underside of the foodætuff.

~he foodstuff will be, to a greater or lesser extent, also
transparent to microwave energy and consequently radiation
emanating from the source in alignment with the foodstuff
will partially heat the foodstuff and partially pass
therethrough to be absorbed by the absorbing surface and
once again intercept the foodstuff - this time as infra-
red radiation.

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

Means may be provided within the source of microwave
energy to alter the ~irection in which the radiation
enters the chamber or to alter the virtual point from
which the radiation appears to come, so as to alter the
position of the point in the cha~ber at which the

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Wo90/037i6 PCT/GB89/01150



radiation is generally brought to a focus or
concentration. In one aspect, this is achieved by moving
an inserted element in the wave guide, so the position of
focus can be varied to produce more uniform heating of the
foodstuff.

In another embodiment, moving or fixed elements, as
appropriate may be used to match more closely the
concentration of the E field to each of several different
food products.

Where a microwave-absorbing browning aid is located wi~hl.
the chamber in accordance with the invention, a removable
shield of microwave reflecting material may be located
over t~e surface of the absorbing material until such time
as the microwave heating has raised the temperature of the
foodstuff sufficiently, after which the shield is removed,
to allow browning to occur.

The invention will now be described by way of example with
reference to the accompanying drawing in which the single
Figure is a schematic cross-section through a food heating
chamber constructed as one embodiment of the invention.

Detailed description of the Drawing




The drawing shows a microwave heating chamber for heating
pre-cooked foodstuffs, of which an example is shown at lO.
The latter is carried by a support plate of ceramic
~aterial 12 so as to be transparent to the microwave
ene~gy which emanates from a magnetron 14 which is locate~
at the lower end of a wave guide 16 the upper end of which
includes the circular plate 12 on which the ~oodstuff is
locateA.



~- .

2 ~ 3

WO90/03716 PCT/GB89/01150



Above the plate 12 is located a hemispherical ~omed or
similarly shaped clos~re member or lid 18 which carries a
similarly shaped microwave absorbing member 20, which on
being heated by incident microwave energy emits infra-red
radiation as at 22 in a direction towards the foodstuff
10 .

The distance of the member 20 from the foodstuff and the
radius of the hemispherical surface of the member 20 is
selected so that in general any infra-red radiation
emanating therefrom will be focussed towards the central
region of the plate 12, and thereby towards the foodstuff
10 located thereon.

The hemispherical dome 18 forms a lid to the chamber, to
which end the dome is hinged as at 24 so as to be capable
of being lifted to reveal the interior of the chamber to
allow foodstuff to be inserted or removed.

The member 20 may be removable so as to be capable of
being inserted after a preliminary heating process.

Alternatively, not shown, a shield of microwave reflecting
material may be located in front of the member 18 until
browning is required.

Representative Drawing