Background of the invention
[0001] The present invention relates to a microwave applicator, to a system of microwave
applicators and also to a method of using the applicator and the system in accordance
with the preambles of the independent claims.
[0002] Furthermore, the field of microwave applicators to which to present invention belongs
include those types having a load continuously transiting the heating chamber or chambers
of the system. The present invention is an improvement of heating systems consisting
of mainly multiple single mode applicator assemblies in which the load to be heated
has a constant cross section.
Description of the prior art
[0003] Many different kinds of microwave systems for loads fulfilling the above characteristics
exist. The simplest such applicator is a large multimode cavity, which may have holes
in its walls (then preferably with attached metal tubes confining the microwaves to
the cavity). For very small loads, the short circular single mode TM
010 cavity is well known, but has the drawback that it can only take loads up to about
10 mm in diameter under favourable conditions, at the common microwave frequency of
2450 MHz. Better efficiency may be obtained with a longer circular TM
01p applicator.
[0004] Only single mode systems are of concern in this context, so the question is what
significant other modes than the simplest TM mode (TM
01) may be useful and known. It is then of interest which mode types are created inside
a load which can for this purpose be of a circular cross section.
[0005] Using the load axis as reference, there are then transverse electric (TE) and transverse
magnetic (TM) modes. Any TE modes used for the excitation of the load field have inherently
a high impedance, and the typical loads of primary concern herein have a rather high
permittivity, mainly between 10 and 70, and will therefore have a low impedance. Furthermore,
the lossiness of dielectric loads is by an equivalent electrical conductivity, but
since TE modes lack an axial electric field component there is neither any efficient
coupling for small loads nor any possibility to avoid a minimum axial length of the
applicator of about half a free space wavelength. TE modes are thus inferior to TM
for the purpose here: namely allowing variations of the load permittivity, and using
an axially short applicator, while maintaining high microwave efficiency.
[0006] The lowest order TM mode in the load is of the TM
0 type. This has a rotationally symmetric field and provides maximum heating at the
load axis. The most advanced version is described in the patent DE-2345706, where
the load diameter is chosen so large that the heating intensity at the load periphery
is very low; the applicator is then of the TM
02 type. A drawback with that system is that the bound wave propagating at and in the
dielectric rod-shaped load is that a very large fraction of its field energy resides
inside the rod. This results in diffculties to confine the heating to only the load
part inside the applicator, which in turn makes it necessary to allow axial zones
outside the applicator with a length comparable to about twice the penetration depth,
for residual heating and leakage protection. Good external choking by wavetraps just
outside the applicator is not possible due to the substantial field confinement inside
the rod-shaped load. This is disadvantageous particularly when one or several axially
short applicators are used in order to achieve a high power in density in the load.
Another drawback is the need for such large applicator diameter that excitation of
the disturbing TM
1 mode is difficult to avoid.
[0007] The next higher order TM mode in the load is of the TM
1 type. The heating pattern in the cross section of a reasonably circular load has
then two diametrically located maxima, with a diametrical zone of zero heating at
±90°. A microwave heating applicator with this mode is described in for example the
patent US-5,834,744. The applicator disclosed in that patent is excited by two diametrical
slots fed by a common waveguide arranged in such a way that the TM
0 modes are suppressed. In order for this particular feed system to work, the applicator
is circular or polygonal, with the load located at the central axis, and the applicator
mode is characterised by being of the TM
120 type. Additionally, the applicator design is dedicated for functioning with a longest
possible axial length of the load of the order of one free space wavelength.
[0008] A waveguide mode transducer from rectangular TE
10 to TE
20 is described in for example the patent GB-1364734. The transducer system is used
to heat a wide and flat load moving past the end of the TE
20 waveguide. For that reason, stubs are placed in the waveguide to create mode impurities
which would result in a heating pattern caused by a combination of that by the TE
10 and TE
20 modes, in an added external cavity with at least two such applicators and equipped
with load rotation means.
One drawback with this known device is that the load needs to be wide and flat which
limits the possibilities to heat larger volumes and also limits the possibility to
control e.g. the heating rate.
[0009] The objects of the present invention are to achieve an applicator and a system of
applicators that enable heating of load having a large cross section, that make it
possible to more accurately control e.g. the heating rate and that better confine
the heating in the load.
Summary of the invention
[0010] The above-mentioned objects are achieved by an applicator, a system and also by a
method according to the independent claims.
Preferred embodiments are set forth in the dependent claims.
[0011] The system of microwave applicators according to the present invention consists mainly
of multiple air-filled single mode applicators in which the load to be heated has
a constant cross section.
[0012] A characteristic feature of the present invention is that the TM
1 type field in the load is created by using an applicator in which the basic second
order electrical mode, in the terminology of the theory for multipole fields, is created.
This is characterised by two maxima of the electrical field at opposite sides of the
axis of the load; in its pure form this occurs in a closed circular TE
110 or TE
120 cavity.
The simplest rectangular waveguide or resonator in which this electric mode exists
carries the TE
20 mode.
[0013] The microwave applicator is for applying microwave power to a load that preferably
has a constant cross section. The applicator is a mode transducer from rectangular
TE
10 at the generator end to TE
20 at the application end and the load is located approximately centred and near a shorting
wall of the latter section. In a system using at least two applicators the mutually
90° displaced applicators in multi-applicator stacked assemblies have two additional
functions: to confine the heating to take place mainly inside each applicator by choking
action, and to act as a filter which reduces the crosstalk between adjacent applicators.
The field in the load is of the cylindrical TM
1 type and the pattern is improved by adding for example tuning rods between the opposite
waveguide walls near the load.
[0014] In cases where a high power density in the load is desired, the height of the applicator
is made low; if this height is less than a half free space wavelength there can then
be no mode with higher middle index than 0, i.e. the applicator fields are in principle
the same at all levels. By then using a TE
10 waveguide feed the advantages addressed in the present application is utilised, such
as stacking several applicators with a common load axis and then displacing adjacent
applicators by 90°, so that not only an improved overall heating pattern in a flowing
load is obtained, but also a choking action between adjacent applicators so that the
microwave propagation between them through the load is strongly reduced.
[0015] The present invention is not limited to using a TE
10 waveguide with approximately half the width of the TE
20 part of the applicator, as shown in Fig.1 - but also a generalised feed where a portion
includes a dielectric-filled waveguide carrying an equivalent mode to the rectangular
TE
10, which is also equivalent to the circular TE
11 mode.
[0016] The invention also includes applicators with larger heights, up to more than a full
free space wavelength. The uses of such applicators are typically not for continuously
flowing loads but instead for stationary liquid loads in a round cylindrical microwave
transparent container. Such loads may be stirred by additional mechanical means such
as a rotating beating device or a magnetic stirring system utilising small, magnetised
bodies in the liquid. The uneven heating pattern with two maxima in the circular cross
section is then overcome. In order for the axial evenness of the heating pattern to
be maintained, also under conditions where the filling height and dielectric properties
of the liquid vary, additional means are introduced according to the present invention.
Brief description of the drawings
[0017]
Figure 1 shows, in perspective, an applicator according to the invention, with a rod-shaped
load extending through it.
Figure 2 shows, in perspective, a system consisting of a second applicator placed
directly on a first applicator, with a rod-shaped load extending through both applicators.
Figure 3 shows the heating pattern in the central horizontal plane of an applicator
according to Figure 1, as a thermal plot obtained by microwave modelling.
Figure 4 shows the load heating pattern in a vertical plane containing the load axis
and the angular location of the heating maxima of a lower applicator with a very small
height, with only the lower applicator energised, in a system consisting of two equal
90° displaced applicators according to Figure 2, as a thermal plot obtained by microwave
modelling.
Figure 5 shows an alternative embodiment of the applicator where the part with the
load has been made significantly axially smaller than the generator feed TE10 end.
Figure 6 shows a further alternative embodiment of the applicator in a system where
the load is a square cross section load.
Figure 7 shows an example of heating pattern in the central cross section plane of
an applicator according to the present invention.
Figure 8 shows a cross-sectional view of an alternative embodiment of the applicator
where the part with the load has been made significantly axially larger than the generator
feed TE10 end.
Figure 9 shows a view from above schematically illustrating the embodiment shown in
figure 8
Figure 10 shows a cross-sectional view of a sixth embodiment of the present invention.
Figure 11 shows a view from above schematically illustrating the embodiment shown
in figure 10.
Detailed description of the invention
[0018] The desired excitation type is the circular TM
1 field in a load, which is considered to have a small diameter for the purpose of
this reasoning. In a circularly cylindrical cavity with a centred axial load and where
the feed is ignored for the moment, the mode is then TM
110. The simplest rectangular mode type in an empty waveguide that can excite the same
load field type is the TE
20 waveguide mode. The field along the centreline of propagation is then only magnetic,
in the direction of propagation along the waveguide.
Even if, in principle, waveguides and cavities of any shape allowing the load to be
excited by this field type are within the scope if the invention, certain excitation
methods and means as well as constraints in mechanical design result in practical
limitations. Hence, the applicators according to the invention have single feeds at
the periphery of the waveguide-like structure, which has zero index in the axial (height)
direction of the load. The simplest such structure is thus a rectangular TE
201 cavity, but the feedings according to the invention and the fact that there is a
net power propagation from the feeding towards the load will result in the last index
being somewhat undefined, and in any case this distance to be more than half a guide
wavelength in that direction.
Hence, a first example of the simplest applicator cross section perpendicular to the
load axis is a rectangular box supporting a field which can best be described as rectangular
TE
202. For improving the mode purity, and compensating against the field modifications
caused by the feed, a part of the rectangular shaped applicator wall opposing and
across from the feeding has a triangular cut. This is schematically illustrated in
figure 1.
[0019] Referring now to the figures, and most particularly to figure 1, the first embodiment
of the present invention relates to a rectangular TE
10/TE
20 mode applicator (or transducer) 1 with the generator 2 connected at the TE
10 section. The TE
20 section being closed by a shorting metal wall 3, and a cylindrical load 4 is located
approximately at the centreline of the TE
20 section. A tuning means 5 (here in the form of a rod) extends the whole way between
the top and bottom surfaces in the TE
20 section.
The applicator is air-filled and made up from metal walls according to well-established
manufacturing technique for microwave applicators.
In the case of a pure TE
20 mode, the load location at the centreline provides the desired cylindrical TM
1 field in the load. The rod 5 (preferably made from a metal) may then not be needed
to obtain a symmetrical heating pattern in the load. However, it is of interest to
provide a compact design, so in particular the TE
20 section is quite short. The rod is then very convenient for adjusting the heating
pattern; in addition, the rod 5 may also act to stabilise the heating pattern under
conditions of different permittivity and dimensional changes of the load, as well
as for improving the impedance matching.
The location of the load axis in relation to the shorting wall 3 should in accordance
to the first order theory be a quarter mode wavelength away. However, it is normally
determined by experiment or by microwave modelling. Since the applicator is primarily
intended for loads having a radius exceeding half a wavelength in the load substance,
there may be considerable deviations from this first order theory, resulting in the
optimum position of the load being closer to the shorting wall. Experiment or microwave
modelling is also used for the determination of the diameter and location of the rod
5.
[0020] The second preferred embodiment of the present invention as shown in figure 2 relates
to a system comprising two applicators 1,1' where the applicators have a common load
axis, and that the applicators being rotated by approximately 90° around the load
axis in relation to each other. It is naturally possible to arrange additional applicators
where each applicator being rotated approximately 90° around the load axis with regard
to an adjacent applicator.
[0021] As seen in Figure 3, the heating pattern has two diametrical maxima (each maximum
is indicated by a "+"), one on each side of the TE
20 waveguide centreline 6; its angular variation can be described by a cos
2 function, according to known mode theory. By the 90° displacement, a second applicator
will give a sin
2 variation, so that the summed angular variation will be 1, i.e. not vary at all.
[0022] According to a first aspect of the second embodiment of the invention the energy
coupling between adjacent 90° displaced applicators by the load field may be made
very small, so that the so-called crosstalk between such applicators will be very
small, even if the associated generators are simultaneously excited.
[0023] According to a second aspect of the second embodiment the applicator 1 is designed
so that it also works as a choke for the propagating fields from a first applicator
through the load to a second applicator. An example of this is shown in Figure 4,
where only the lower applicator 1 is energised, and there is a second applicator 1'just
above but none below the first applicator. Actually, this feature is closely related
to the first aspect of the second embodiment mentioned above. For efficient choking
to be possible, it is necessary that a significant part of the microwave energy is
bound to the load 4 is outside it. This may be the case for the TM
1 mode type, but is not for the TM
0 type mode. In figure 4 the heating pattern is schematically illustrated in the same
way as in figure 3.
For the optimisation of choking, it is firstly to be considered that what needs to
be choked in the second, "passive" applicator is a 90° rotated load field from that
produced by this second applicator. Hence, the mode type to be choked is TE
10.
The choking action is to be of the source (meaning excited load in this case) firstly
being mismatched by the shorting wall 3, secondly by a field mismatch to this TE
10 mode in the TE
20 section, and thirdly another field mismatching when the TE
10 mode in it encounters the transducer section to the TE
10 section. The third phenomenon has typically the strongest effect, and the procedure
for choking optimisation is then by variation of the length of the TE
20 section, which is arbitrary with regard to the proper function of the applicator
in heating mode, since the transition section as such is matched for that primary
power flow.
The second parameter, for fine-tuning of the two functions of the applicator, is to
vary the location of the load axis in relation to the shorting wall 3, in combination
with the use of one or several metal rods 5. Rather than performing this co-optimisation
of heating and choking functions by hardware experiments, microwave modelling may
be employed and will also allow studies of the various field patterns and intensities
to assist in the work.
[0024] A third embodiment of the present invention relates to the design and use of multiple,
low and closely stacked applicators to achieve high power densities in elongated or
moving loads. The TE
20 mode can in theory exist in a waveguide with arbitrarily small height, but there
are of course practical limitations by the fact that the waveguide (integrated) impedance
is proportional to its height, requiring a very large transformation ratio from the
typically standard height of between a quarter and a half free space wavelength at
magnetron generator transition to the TE
10 portion.
There are, however, generally no problems when the height is changed in one short
step 7 as shown in figure 5, by a factor of up to 3. This is then normally in the
TE
20 section as shown in the same figure. The step can also be used to improve the choking
function, as described for the overall length of the TE
20 section for the second embodiment of the present invention.
[0025] An important aspect of the present invention in conjunction with the use of very
low applicator heights is that the load location is where the electrical field of
the TE
20 mode (there is in essence only a vertical such field) is minimum. Hence, the risk
of arcing when high power is used is very much less than with rectangular TE
10 applicators (or, equivalently, cylindrical TM
0n0 applicators).
By the combined use of multiple 90° displaced applicators with mutual choking function,
extremely high heating intensities can quite easily be achieved also with typical
magnetron powers, without any risk of arcing.
[0026] As an example when using 2450 MHz, a TE
20 section height of 12 mm with a load diameter of 30 mm and 3 kW microwave generators
in a 6-applicator system (plus two non-energised end-choking applicators) will result
in 18 kW over a total length of 8 × 14 mm = 112 mm, i.e. 80 mL. With a specific heat
capacity of the load of half of that of water, the heating rate then becomes over
100 K/ second. Such heating rates may be desirable in pharmaceutical
microwave chemistry applications, where polar liquids with reactants are very rapidly
heated under high pressure to over 200°C. Of course, larger systems using the other
common microwave heating frequency band using a frequency around 915 MHz can achieve
the same heating rate with commercially available magnetrons of 30 kW and higher.
Such applications may include very rapid expansion causing cell wall rupturing in
some types of hardwood, where a slower heating rate would result in energy waste by
loss of pressure by diffusion thus requiring prolonged heating time; or malfunction
of the process by rupturing not occurring at all.
[0027] An example of the choking function also confining the heating pattern to only the
energised applicator is shown in Figure 4 where an upper and a lower applicator are
indicated.
The two stacked waveguide applicators (as illustrated in figure 2) are 25 mm high
(b dimension) and the TE
10 and TE
20 sections are 86 and 172 mm wide (α dimension), respectively. The load diameter is
40 mm, its permittivity is 25-j6, the load is contained in a 5 mm material thickness
glass tube with permittivity 4 and the operating frequency is 2450 MHz. The distance
from the TE
20 shorting wall to the centrally located load axis is 28 mm; the metal rod has a diameter
of 17 mm and is located 10 mm to the left (in the direction of the TE
10 H knee inner corner) and 80 mm from the TE
20 shorting wall. There is a protective metal tube below and above the load, outside
the applicators (indicated as 4 in figure 2). Only the lower applicator is energised.
With a mode transducer optimised triangular cut in the outer H knee corner of 29 mm
at the TE
10 side and 86 mm at the TE
20 side (as indicated in for example Figure 1) and an optimised distance between the
TE
20 shorting wall to the opposite side wall of 210 mm, the transmission factor between
the two TE
10 ports of the applicators becomes 0,03 (which is the same as -30 dB crosstalk power).
[0028] In a fourth embodiment of the present invention additional metal rods 8 are used
as shown in Figure 6, with loads of such cross sectional size or shape that some deviations
from the sin
2 angular variation occurs. Such variations are primarily caused by internal resonance
effects in the load, or by non-resonant edge diffraction if the load has axial edges.
The method for determining the locations and sizes of these rods is again primarily
by microwave modelling. It is then generally preferred to arrange four rods in a square
pattern if the load cross section is also square (as in figure 6), to maintain the
capability for choking by adjacent applicators. The rod pattern can then be varied
by both side length and angular position in relation to the TE
20 waveguide axis direction.
An example of heating pattern in the central cross section plane of a 100 × 100 mm
square, long load with permittivity 30-j3 at 915 MHz in an applicator with 60 mm height
and 500 mm TE
20 section width is shown in Figure 7. The heating pattern is illustrated by using "++"
for the warmest part, "+" for the next warmest parts and so on to the coldest part
that is indicated with a "-". In this case there are no rods or other devices, and
the load axis is 126 mm from the shorting wall and displaced by 18 mm from the applicator
centreline. It is seen that the heating pattern becomes quite even with two, and even
more so with four 90° displaced applicators.
[0029] According to a fifth embodiment of the present invention the applicator is substantially
thicker at least in the part of the TE
20 mode section where the load is arranged than in the TE
10 mode section, in a direction perpendicular to the major wave propagation. This fifth
embodiment is illustrated in figures 8 and 9.
Thus, the present invention also includes applicators with larger heights, up to more
than a full free space wavelength.
Even if it may be possible to successfully just increase the applicator height (7'
in figure 8) by making either a step or a slope 7 as shown in figure 5 (but now to
a larger instead of a smaller height) to fit a load higher than about a half free
space wavelength, and then obtain a reasonably even heating in the axial direction,
typical variations in load permittivity and load filling height will almost inevitably
result in heating concentrations at either load end.
[0030] A refinement of this embodiment of the invention is to then use metal plates parallell
to the broad sides (floor and ceiling) of the applicator. One metal plate 8 is seen
in figures 8 and 9. These plates may be in continuous galvanic contact with the side
(vertical) applicator walls, but that is not necessary for proper function. A plate
acts as a mode filter, prohibiting propagation of other than TE
20p modes, provided the (vertical) distance between any plate(s) and the applicator floor
or ceiling does not exceed about a half free space wavelength. Several plates may
thus be used.
An extension of this embodiment is to firstly employ an upwards slope 7' from a part
of the applicator near or in its feed by a TE
10 waveguide, or near the dielectric rod feed, being the transducer means according
to the sixth embodiment described below, and secondly use a metal plate which extends
to a position rather close to the slope. This is illustrated in figure 8 where the
metal plate 8 extends close to the waveguide slope 7' and the opposite applicator
side wall in one cross section, and from the side wall of the TE
10 waveguide almost all the way to the load in the perpendicular cross section.
Figure 9 schematically illustrates the fifth embodiment from above where is shown
the TE
20 mode section 12 provided with a metal plate 8, a load 4 and a tuning means 5.
It is also possible to use plates, which are bent up-, or downwards in the feed region,
to achieve the same goal which is to split the incoming power in a controlled way,
to achieve an improved heating evenness in the axial direction of the load.
By using one or two metal plates as just described, it is possible to use applicator
and load heights up to and exceeding a free space wavelength of the microwaves, while
maintaining a reasonably even heating in the axial direction, for limited intervals
of liquid column height but for wide variations of the dielectric properties of is
as a load.
[0031] According to a sixth embodiment of the present invention a generalised transducer
means is arranged between the waveguide transition between the TE
10 mode section and TE
20 mode section. This generalised transducer means will be described with references
to figures 10 and 11. The transducer means is applicable to all embodiments of the
present invention described herein.
[0032] Figure 10 shows a cross-sectional view of the sixth embodiment of the present invention
and figure 11 shows a view from above schematically illustrating the same embodiment.
Figure 10 a schematic illustration showing the TE
10 mode section 14, a transducer means 10 and the TE
20 mode section 12. The same features are shown in figure 11 that in addition show the
load 4 and the tuning means 5.
The transducer means 10 includes a dielectric-filled waveguide carrying the same mode
as the rectangular TE
10, which is equivalent to the circular TE
11 mode.
There is often a need for separating the generator and applicator parts of the system,
so that for example noxious gases or load spillage cannot escape out from the applicator
towards the generator and other ancillary equipment. There may also be a need to heat
the liquid load to temperatures above its boiling temperature under atmospheric pressure.
Such pressurised windows are just variable thickness, microwave transparent plates
under mechanical pressure between two TE
10 waveguide flanges. The impedance mismatching due to the plate is commonly so small
(since the plate is relatively thin) that compensation is made by simple discrete
components such as metal posts in the waveguide. For thicker windows, the fact that
a half wavelength thick plate (of the window material) may minimise reflections may
be employed. Conical tapering into both the mating waveguides using low permittivity
plastic material bodies is another possibility.
According to this sixth embodiment of the present invention a mode transition between
the TE
10 airfilled waveguide and a circular TE
11 or rectangular TE
10 mode in the form of the transducer means 10 being a dielectric filled metal tube
or bore. Such a transducer means is fed from a symmetrically located hole in the shorted
end of the TE
10 waveguide and is impedance matched without any additional means. The length of the
dielectric-filled waveguide portion can therefore be arbitrarily long. This design
is inherently different to prior art windows by the intermediate dielectric-filled
waveguide section being impedance matched to the airfilled waveguide.
A preferred design of the transducer means is shown in figure 10, where a rectangular
TE
10 waveguide 14 has a lower height (commonly labelled
b dimension) than the other similar waveguide 12. A circularly cylindrical ceramic
body 10 protrudes certain but different distances into the waveguide ends, and is
surrounded by metal between the waveguides. There are no additional matching components.
This type of matched transducer means requires certain dielectric data and diameters
of the body, in relation to the rectangular waveguide dimensions and operating frequencies,
in order for a sufficiently broadband impedance matching to be achieved. As a first
example, with the standard WG340 (43×86 mm) waveguide in the 2450 MHz ISM band, an
alumina rod with permittivity 9 must be about 29 mm in diameter and protrude about
25,5 mm into the waveguide. As a second example, with a 60×86 mm waveguide and a rod
with permittivity 6,8, its diameter must be about 38 mm and the protrusion must be
about 28 mm.
Establishing optimum dimensions for waveguides and rods with other data can be made
by experiment or numerical microwave modelling, using the start data above. This also
applies when the rod has a square or rectangular cross section.
If one of the waveguides is subjected to pressure, for example by the applicator being
a direct continuation of the waveguide 12, the protruding part of the rod 10 can be
made slightly wider than the rest, so that the rod cannot slide away. The protrusion
length of the wider part must than be made somewhat shorter. Other deviations from
the cylindrical shape can also be employed for the purpose, and are all within the
scope of the invention as defined by the appended claims.
When using a rod feed of the type just described, it is not necessary to feed the
applicator via a TE
10 waveguide. Instead, the rod may be protruding directly into the TE
20p applicator. This is shown in figure 11 where the applicator 12 with a load 4 and
a tuning means 5 is disclosed.
[0033] According to an additional improvement of the present invention in particular with
regard to the insensitivity to liquid column height variations is to employ rod-shaped
dielectric bodies with rather high permittivity, parallell to the metal rod 5. The
rods must then have a permittivity comparable with that of the liquid load, and also
a comparable cross section area. As an example, two rods with permittivity 20 and
diameter 30 mm are located close to the load, on each side of the TE
20 centreline. The sensitivity to liquid column height variations, as well as to load
permittivity variations, is then reduced. Also the impedance matching variations for
variations of these load parameters is reduced.
[0034] A typical applicator for 2450 MHz will have horizontal dimensions about 170 × 210
mm, plus the prolongation by a TE
10 feed waveguide. With a diameter of the load container of about 55 mm, the filling
factor (load volume divided by applicator volume) becomes quite small. There may be
instances when it is desirable to reduce the applicator dimensions. This can then
be made by three methods:
1.Folding down or up the outer parts of the TE20 part (i.e parallel to the power flow direction) so that an inverted U shape is created.
The applicator feed is then from below or above. However, this method is not efficient
if the waveguide applicator height is large.
2.Inserting metal ridges in the TE20 part, in the same way as in standard ridged waveguides. This means that two ridges,
ending on each side of the load, are introduced.
3.Inserting partial dielectric filling in the TE20 part. As an example, using PTFE with about 50 % filling factor, the 170×210 mm dimensions
can be reduced to about 125×155 mm.
[0035] As a further alternative, in particular with regard to the above-mentioned second
method related to the ridged waveguide, the waveguide (the TE
20 mode section) is filled (or partly filled) with a dielectric material, e.g. PTFE
or a ceramic material. This is mainly in order to decrease the size of the TE
20 mode section.
[0036] The present invention also relates to the use of the applicator, the system or the
method for performing organic chemical synthesis reactions, and also for very rapid
heating of wood, for cell wall disruption or similar.
[0037] Within the scope of the invention as it is defined by the appended claims also the
following exemplary structural alternatives are included:
- The metal rods must not go the whole way between the major planes of the waveguides
- Instead of using rods, metal plates may be used.
- The metal plates may be replaced by dielectric inserts or tubing, for example alumina
ceramic.
- In order to achieve an improved heating at the load axis, the load may be displaced
somewhat from the position which gives a symmetrical heating pattern.
- The load may be in a microwave transparent tube or holder.
- The load may be short and entirely located inside a single applicator.
- The TE10 section may be bent and extended so that there is sufficient space for the generators
also when multiple, low stacked applicators are used
- Systems may be designed for any microwave frequency, depending on the load dimensions,
dielectric properties and required capacity of the system. For reasons of availability
of generators, and since the systems are primarily foreseen for high power density
applications, the standard frequencies about 2450 and 915 MHz are preferred.
1. A microwave applicator for heating loads being a waveguide transition between the
rectangular TE10 and TE20 modes comprising a TE10 mode section and a TE20 mode section, characterized in that said TE20 mode section is such that it is adapted to receive the load (4) inside said TE20 mode section and such that the load is adapted to be located with its major axis
perpendicular to the major propagation direction of the TE20 mode, close to a shorting wall (3) of said TE20 mode section and also close to the centreline of said propagation direction.
2. Microwave applicator according to claim 1, characterized in that the microwave energy is applied to the applicator via a feeding means arranged at
the TE10 mode section.
3. Microwave applicator according to claim 1, characterized in that a dielectric transducer means (10) is arranged between the TE10 mode section (14) and TE20 mode section (12).
4. Microwave applicator according to claim 3, characterized in that said dielectric transducer means includes a tube filled with a dielectric material.
5. Microwave applicator according to claim 1, characterized in that the applicator is substantially thinner at least in the part of the TE20 mode section where the load is arranged than in the TE10 mode section, in a direction perpendicular to the major wave propagation.
6. Microwave applicator according to claim 1, characterized in that the applicator is substantially thicker at least in the part of the TE20 mode section where the load is arranged than in the TE10 mode section, in a direction perpendicular to the major wave propagation.
7. Microwave applicator according to claim 6, characterized in that at least one metal plate (8) is arranged in said TE20 mode section in order to act as a mode filter.
8. Microwave applicator according to any of claims 1-7, characterized in that at least one tuning means (5) is arranged extending through the applicator and being
located close to the load so as to provide an essentially symmetrical cylindrical
TM1 type mode pattern in the load.
9. Microwave applicator according to claim 8, characterized in that said tuning means is made from metal.
10. Microwave applicator according to claim 8, characterized in that said tuning means is made from a dielectric material, e.g. alumina.
11. Microwave applicator according to any of claims 8-10, characterized in that two or four tuning means (8) are arranged diametrically pairwise surrounding the
load.
12. Microwave applicator according to any of claims 8-11, characterized in that said tuning means is rod-shaped.
13. Microwave applicator according to any preceding claim, characterized in that the load has a cross section that is essentially circular.
14. Microwave applicator according to any preceding claim, characterized in that said TE20 mode section is at least partly filled with a dielectric material, e.g. PTFE or a
ceramic material.
15. A system consisting of at least two microwave applicators according to any of claims
1-14, characterized in that the applicators have a common load axis, and that adjacent applicators being rotated
by approximately 90° around said load axis.
16. System according to claim 15, characterized in that at least one of the applicators being energised, and that adjacent energised or non-energised
applicators act as chokes for adjacent energised applicators.
17. A method for designing an applicator according to any of claims 1-14 or a system according
to any of claims 15 or 16,
characterized in that the method comprises:
- using an essentially complete mode transducing function between rectangular TE10 and TE20 of the 90° H knee type,
- shorting the TE20 end and locating the load with its major axis perpendicularly to the major propagation
direction of the TE20 mode, close to a shorting wall of said section and close to the centreline of said
propagation direction,
- introducing a tuning means between opposite major walls of the waveguide near the
load,
- establishing a TM1 type field in the load by performing experiments or microwave modelling using the
diameter and positions of the tuning means as variables.
18. A method according to claim 17 when dependent on claims 15 or 16,
characterized in that the method further comprises:
- changing the length of the TE20 section by experiment or microwave modelling, until the crosstalk between the applicators
becomes minimal.
19. A method according to claim 17,
characterized in that the method further comprises:
- changing the thickness of the TE20 section by experiment or microwave modelling.
20. A method according to any of claims 17 or 19,
characterized in that the method further comprises:
- adding a second, 90° displaced but otherwise identical applicator, so that the load
axis becomes common.
21. A method according to any of claims 17-20,
characterized in that the method further comprises:
- adapting the applicator for a load having a non-circular cross section by using
two or four tuning means that at least diametrically pair wise surrounding the load,
and by
- varying the positions of these tuning means by experiment or microwave modelling
until an acceptably even integrated heating has been achieved.
22. Use of an applicator, a system or a method according to any preceding claim for performing
organic chemical synthesis reactions.
23. Use of an applicator, a system or a method according to any of claims 1-21 for very
rapid heating of wood, for cell wall disruption or similar.
1. Applicateur de micro-ondes pour chauffer des charges fonctionnant par une transition
de guide d'ondes entre les modes rectangulaires TE10 et TE20 comprenant un élément de mode TE10 et un élément de mode TE20, caractérisé en ce que ledit élément de mode TE20 est tel qu'il est adapté pour recevoir la charge (4) à l'intérieur dudit élément
de mode TE20 et tel que la charge est adaptée pour être placée avec son axe principal perpendiculaire
à la direction principale de propagation du mode TE20, près d'une paroi de mise en court-circuit (3) dudit élément de mode TE20 et également à proximité de la ligne centrale de ladite direction de propagation.
2. Applicateur de micro-ondes selon la revendication 1, caractérisé en ce que l'énergie de micro-ondes est appliquée à l'applicateur par l'intermédiaire de moyens
d'alimentation disposés au niveau de l'élément de mode TE10.
3. Applicateur de micro-ondes selon la revendication 1, caractérisé en ce que des moyens de capteur diélectrique (10) sont disposés entre l'élément de mode TE10 et l'élément de mode TE20 (12).
4. Applicateur de micro-ondes selon la revendication 3, caractérisé en ce que lesdits moyens de capteur diélectrique comportent un tube rempli d'un matériau diélectrique.
5. Applicateur de micro-ondes selon la revendication 1, caractérisé en ce que l'applicateur est essentiellement plus mince au moins dans la partie de l'élément
de mode TE20 dans laquelle la charge est disposée, que dans l'élément de mode TE10, dans une direction perpendiculaire à la propagation principale des ondes.
6. Applicateur de micro-ondes selon la revendication 1 caractérisé en ce que l'applicateur est essentiellement plus épais au moins dans la partie de l'élément
de mode TE20 dans laquelle la charge est disposée que dans l'élément de mode TE10, dans une direction perpendiculaire à la propagation principale des ondes.
7. Applicateur de micro-ondes selon la revendication 6, caractérisé en ce qu'au moins une plaque métallique (8) est disposée dans ledit élément de mode TE20 afin d'agir comme un filtre de mode.
8. Applicateur de micro-ondes selon l'une quelconque des revendications 1 à 7, caractérisé en ce qu'au moins un moyen de réglage (5) est disposé de façon à s'étendre à travers l'applicateur
et est placé à proximité de la charge de façon à fournir dans la charge une configuration
de mode de type essentiellement TM1 cylindrique symétrique.
9. Applicateur de micro-ondes selon la revendication 8, caractérisé en ce que lesdits moyens de réglage sont faits de métal.
10. Applicateur de micro-ondes selon la revendication 8, caractérisé en ce que lesdits moyens de réglage sont constitués d'un matériau diélectrique, par exemple
de l'alumine.
11. Applicateur de micro-ondes selon l'une quelconque des revendications 8 à 10, caractérisé en ce que deux ou quatre moyens de réglage (8) sont disposés par paire diamétralement autour
de la charge.
12. Applicateur de micro-ondes selon l'une quelconque des revendications 8 à 11, caractérisé en ce que lesdits moyens de réglage sont configurés en forme de tige.
13. Applicateur de micro-ondes selon l'une quelconque des revendications précédentes,
caractérisé en ce que la charge présente une section transversale qui est essentiellement circulaire.
14. Applicateur de micro-ondes selon l'une quelconque des revendications précédentes,
caractérisé en ce que ledit élément de mode TE20 est au moins partiellement rempli d'un matériau diélectrique, par exemple de PTFE
ou d'un matériau céramique.
15. Système constitué d'au moins deux applicateurs de micro-ondes selon l'une quelconque
des revendications 1 à 14, caractérisé en ce que les applicateurs possèdent un axe de charge commun, et en ce que les applicateurs adjacents effectuent une rotation de 90° environ autour dudit axe
de charge.
16. Système selon la revendication 15, caractérisé en ce que au moins l'un des applicateurs est excité, et en ce que les applicateurs adjacents excités ou non excités agissent comme des pièges pour
des applicateurs adjacents excités.
17. Procédé pour concevoir un applicateur selon l'une quelconque des revendications 1
à 14 ou un système selon l'une quelconque des revendications 15 ou 16,
caractérisé en ce que le procédé consiste à :
- utiliser une fonction de conversion de mode essentiellement complète entre un mode
rectangulaire TE10 et un mode TE20 de type H coudé à 90°,
- mettre en court circuit l'extrémité de TE20 et placer la charge avec son grand axe perpendiculaire à la direction principale
de propagation du mode TE20, à proximité d'une paroi de court-circuit dudit élément et près de la ligne centrale
de ladite direction de propagation,
- introduire des moyens de réglage entre des parois principales opposées du guide
d'onde près de la charge,
- établir un champ de type TM1 dans la charge en exécutant des expériences ou en modélisant des micro-ondes en utilisant
comme variables le diamètre et des positions des moyens de réglage.
18. Procédé selon la revendication 17 lorsqu'elle dépend des revendications 15 ou 16,
caractérisé en ce que le procédé consiste, de plus, à :
- changer la longueur de l'élément TE20 par expérimentation ou modélisation de micro-ondes jusqu'à ce que le couplage parasite
entre les applicateurs devienne minimal.
19. Procédé selon la revendication 17,
caractérisé en ce que le procédé consiste, de plus, à :
- modifier l'épaisseur de l'élément TE20 par expérimentation ou modélisation des micro-ondes.
20. Procédé selon l'une quelconque des revendications 17 ou 19,
caractérisé en ce que le procédé consiste de plus à :
- ajouter un second applicateur déplacé de 90° mais par ailleurs identique, de façon
que l'axe de charge soit commun.
21. Procédé selon l'une quelconque des revendications 17 à 20,
caractérisé en ce que le procédé consiste, de plus, à :
- adapter l'applicateur destiné à une charge présentant une section transversale non
circulaire en utilisant deux ou quatre moyens de réglage qui entourent la charge au
moins diamétralement par paire, et
- modifier les positions de ces moyens de réglage expérimentalement ou par modélisation
de micro-ondes jusqu'à ce qu'un chauffage régulier intégré de façon acceptable ait
été obtenu.
22. Utilisation d'un applicateur, d'un système ou d'un procédé selon l'une quelconque
des revendications précédentes pour exécuter des réactions de synthèse en chimie organique.
23. Utilisation d'un applicateur, d'un système ou d'un procédé selon l'une quelconque
des revendications 1 à 21 pour un chauffage très rapide de bois, pour une désorganisation
de paroi de cellule ou similaire.
1. Mikrowellenapplikator für ein Einleiten von Lasten, welcher ein Wellenleiterübergang
zwischen dem Rechteck-TE10 und -TE20-Modus ist, enthaltend einen TE10-Modus-Abschnitt und einen TE20-Modus-Abschnitt, dadurch gekennzeichnet, dass der TE20-Modus-Abschnitt derart angepasst ist, dass er die Last (4) in dem TE20-Modus-Abschnitt aufnehmen kann, und dass die Last so angepasst ist, dass sie mit
ihrer Hauptachse senkrecht zu der Hauptausbreitungsrichtung des TE20-Modus in der Nähe einer Kurzschlusswand (3) des TE20-Modus-Abschnitts und auch in der Nähe der Mittellinie der genannten Ausbreitungsrichtung
angeordnet ist.
2. Mikrowellenapplikator nach Anspruch 1, dadurch gekennzeichnet, dass die Mikrowellenenergie über eine Zuführeinrichtung, welche an dem TE10-Modus-Abschnitt angeordnet ist, dem Applikator zugeführt wird.
3. Mikrowellenapplikator nach Anspruch 1, dadurch gekennzeichnet, dass eine dielektrische Wandlereinrichtung (10) zwischen dem TE10-Modus-Abschnitt (14) und dem TE20-Modus-Abschnitt (12) liegt.
4. Mikrowellenapplikator nach Anspruch 3, dadurch gekennzeichnet, dass die dielektrischen Wandlereinrichtung ein mit dielektrischem Material gefülltes Rohr
enthält.
5. Mikrowellenapplikator nach Anspruch 1, dadurch gekennzeichnet, dass der Applikator mindestens in dem Teil des TE20-Modus-Abschnittes, in welchem die Last angeordnet ist, in einer Richtung senkrecht
zu der Hauptwellenausbreitungsrichtung wesentlich dünner ist als in dem TE10-Modus-Abschnitt.
6. Mikrowellenapplikator nach Anspruch 1, dadurch gekennzeichnet, dass der Applikator mindestens in dem Teil des TE20-Modus-Abschnittes, in welchem die Last angeordnet ist, in einer Richtung senkrecht
zu der Hauptwellenausbreitungsrichtung wesentlich dicker ist als in dem TE10-Modus-Abschnitt.
7. Mikrowellenapplikator nach Anspruch 6, dadurch gekennzeichnet, dass mindestens eine Metallplatte (8) in dem TE20-Modus-Abschnitt angeordnet ist, um als Modusfilter zu wirken.
8. Mikrowellenapplikator nach einem der Ansprüche 1-7, dadurch gekennzeichnet, dass mindestens eine einzige Abstimmeinrichtung (5) so angeordnet ist, dass sie sich durch
den Applikator hindurch erstreckt und sich in der Nähe der Last befindet, um ein im
Wesentlichen symmetrisches zylindrisches Modusmuster vom TM1-Typ in der Last vorzusehen.
9. Mikrowellenapplikator nach Anspruch 8, dadurch gekennzeichnet, dass die Abstimmeinrichtung aus Metall hergestellt ist.
10. Mikrowellenapplikator nach Anspruch 8, dadurch gekennzeichnet, dass die Abstimmeinrichtung aus einem dielektrischen Metall, z. B. Aluminium, hergestellt
ist.
11. Mikrowellenapplikator nach einem der Ansprüche 8 - 10, dadurch gekennzeichnet, dass zwei von vier Abstimmeinrichtungen (8) paarweise diametral die Last umgebend angeordnet
sind.
12. Mikrowellenapplikator nach einem der Ansprüche 8-11, dadurch gekennzeichnet, dass die Abstimmeinrichtung stabförmig ist.
13. Mikrowellenapplikator nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Last einen Querschnitt hat, welcher im Wesentlichen kreisförmig ist.
14. Mikrowellenapplikator nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass der TE20-Modus-Abschnitt mindestens teilweise mit einem dielektrischen Material gefüllt ist,
z. B. PTFE oder einem keramischen Material.
15. System bestehend aus mindestens zwei Mikrowellenapplikatoren nach einem der Ansprüche
1-14, dadurch gekennzeichnet, dass die Applikatoren eine gemeinsame Lastachse haben, und dass benachbarte Applikatoren
um ungefähr 90° um die Lastachse gedreht sind.
16. System nach Anspruch 15, dadurch gekennzeichnet, dass mindestens einer der Applikatoren mit Energie versorgt ist, und dass benachbarte
mit Energie versorgte oder nicht mit Energie versorgte Applikatoren als Drossel für
benachbarte mit energie versorgte Applikatoren dienen.
17. Verfahren zum Entwerfen eines Applikators nach einem der Ansprüche 1
- 14 oder eines Systems nach einem der Ansprüche 15 oder 16, dadurch gekennzeichnet, dass das Verfahren folgende Schritte enthält:
- Verwenden einer im Wesentlichen vollständigen Modus-Wandler-Funktion zwischen Rechteck-TE10- und TE20 des 90° H Knie-Typs
- Kurzschließen des TE20-Endes und Anordnen der Last mit ihrer Hauptachse senkrecht zu der Hauptausbreitungsrichtung
des TE20-Modus nahe einer Kurzschlusswand des Abschnitts und nahe der Mittellinie der Ausbreitungsrichtung,
- Einführen einer Abstimmeinrichtung zwischen einander gegenüberliegenden Hauptwänden
des Wellenleiters nahe der Last,
- Einrichten eines TM1-Typ-Feldes in der Last mittels Durchführen von Experimenten oder Mikrowellen-Modellieren
unter Verwendung von Durchmesser und Stellungen der Abstimmeinrichtung als Variable.
18. Verfahren nach Anspruch 17, wenn dieser von Anspruch 15 oder 16 abhängt,
dadurch gekennzeichnet, dass das Verfahren weiterhin enthält:
- Ändern der Länge des TE20-Abschnittes durch Experiment oder Mikrowelle-Modellieren, bis die Kreuzkopplung zwischen
den Applikatoren minimal wird.
19. Verfahren nach Anspruch 17,
dadurch gekennzeichnet,dass das Verfahren weiterhin enthält:
- Ändern der Dicke des TE20-Abschnitts durch Experiment oder Mikrowellen-Modellieren.
20. Verfahren nach einem der Ansprüche 17 oder 19,
dadurch gekennzeichnet, dass das Verfahren weiterhin enthält:
- Hinzufügen eines zweiten, um 90° versetzten, jedoch ansonsten identischen Appliaktors,
so dass die Lastachse eine gemeinsame wird.
21. Verfahren nach einem der Ansprüche 17 - 20,
dadurch gekennzeichnet, dass das Verfahren weiterhin enthält:
- Anpassen des Applikators an eine Last mit einem nicht-kreisförmigen Querschnitt
durch Verwenden von zwei oder vier Abstimmeinrichtungen, welche mindestens diametral
paarweise die Last umgeben, und durch
- Verändern der Stellungen dieser Abstimmeinrichtungen durch Experiment oder Mikrowellen-Modellieren,
bis eine akzeptabel gleichmäßige, integrierte Erhitzung erreicht worden ist.
22. Verwendung eines Applikators, eines Systems oder eines Verfahrens nach einem der vorherigen
Ansprüche zum Durchführen von organisch chemischen Synthesereaktionen.
23. Verwendung eines Applikators, eines Systems oder eines Verfahrens nach einem der Ansprüche
1-21 für sehr schnelles Erhitzen von Holz, für Zellwandunterbrechung oder dergleichen.