CA1044331A - Microwave thawing of frozen materials and applicators therefor - Google Patents
Microwave thawing of frozen materials and applicators thereforInfo
- Publication number
- CA1044331A CA1044331A CA231,622A CA231622A CA1044331A CA 1044331 A CA1044331 A CA 1044331A CA 231622 A CA231622 A CA 231622A CA 1044331 A CA1044331 A CA 1044331A
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- CA
- Canada
- Prior art keywords
- horn
- reflector
- power
- applicator
- extending
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/80—Apparatus for specific applications
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- Electromagnetism (AREA)
- Constitution Of High-Frequency Heating (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Microwave power is used for thawing and de-icing of permafrost and frozen soils and other materials and the present invention includes a novel microwave applicator consisting of an H-plane horn reflector terminated by a corrugated flange.
This flange is effective for reducing the microwave leakage level to a safe level so that the operator and other adjacent personnel are protected.
Microwave power is used for thawing and de-icing of permafrost and frozen soils and other materials and the present invention includes a novel microwave applicator consisting of an H-plane horn reflector terminated by a corrugated flange.
This flange is effective for reducing the microwave leakage level to a safe level so that the operator and other adjacent personnel are protected.
Description
BACKGROUND OF THE INVENTION
-1~ This invention relates to new and useful improvements in the use of microwaves and in the provision-of a novel micro-wave horn reflector or applicator.
One of the most severe obstacles that face the con-struction industry in cold climates is the long cold winter months. During these months the industry tends to slow down and concentrate on construction mainly above ground relying on sites excavated during the summer. The high cost of winter construction results in unemployment. Thus the design, test-ing and implementation of new techniques and equipment that permit all year round operation would naturally be of great interes~ ~o those involved in ~he construction industry in Car.ad~ and other similar locations of the world.
I~ is known that microwave power has already been employed in the construction industry for demolition of concrete .... . , . . ~ ~.. . . .
.
, : . :: .
. ;:~, ` -' 104433i .
and highway repair through heating of trapped moisture in the case of concrete and curing of polymer-concrete patches in the case of road and pavement repairs. The advantages of the micro- -wave technique in these applications have been the minimum dis-ruption of traffic or time to complete the construction due to the shorter time required relative to conventional techniques lusing fire or heavy mechanical equipment). Other advantages are the possible reduction in the cost and noise or pollution levels. However, one of the principal disadvantages of using microwave power for these applications is the leakage normally present which may be dange~ous not only to the operator but to others standing nearby.
~ ''' .
To date no serious effort has yet been made to aid the construction industry in the rapid thawing and de-icing of permafrost and frozen soils, de-icing of street intersections, sidewalks and airport runways, fast drying of conveyorized wet sand and other construction materials, noise-free demolition of concrete pipes, sewers, ~ridges, ~uildings, roads, rocks, de-icing of windows, windshields, aircraft wings or rapid curing of concrete and bricks and sensors for simultaneous monitoring of the curing process~
SUMMARY OF THE INVENTION
This invention comprises a microwave power alternative to he commonly used mechanical excavation technique for thawing ~`
of severely frozen soils during the winter and illustrates the - . . .. : . ~
~ 1~4433~
specific advantages in terms of reduction in constxuction time, cost, noise and environmental pollution which were verified in conjunction with construction industry personnel. One aspect of this invention is to provide a horn reflector for use with microwave energy comprising in combination a horn, a parabolic reflector operatively connected by one end thereof to said horn and a corrugated flange assembly connected to the other end of said parabolic reflector and extending upon each side thereof.
A further aspect of the invention is to provide a de- ~;
vice of the character herewithin described which is simple in construction, economical in operation and otherwise well suited to the purpose for which it is designed.
With the foregoing in view and other such advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, my inven-tion consists essentially in the arrangement and construction of parts all as hereinafter more particularly described, reference being had to the accompanying drawings in which:
DESCRIPTION OF THE DRAWINGS
Figure 1 is an isometric view of the horn reflector or applicator.
,, ,: , . ::
Figure 2 is a longitudinal section of Figure 1.
Figure 3 is a cross sectional view along the line 3-3 of Figure 2.
, i Figure 4 is a graph showing the power density level 5with and without the corrugated flange .
~ ~ ' Figure 5 is a schematic side elevation of the device set up for evaluating the performance of the applicator with clay samples.
,; ~.
''" '' In the drawings like characters of reference indicate corresponding parts in the different figures.
DETAI~ED DESCRIPTION
The first requirement of a microwave applicator for `
practical use in the construction industry is to possess a reasonably flat field distribution in the aperture with minimum 15power towards the edges of the radiator. The applicator con- -fi~uration must therefore allow for maximum and uniform power in the area of interest as well as minimum VSWR at the frequency of operation particularly since the applicator aperture is very closely separated from the ground surface. In order to meet this specification, a horn reflector type of radiator is used which is a combination of a sectoral electromagnetic horn and a re~lector which is a sector of a paraboloid of revolution.
Since the center of the wave guide is the focal point of the parabola and since this radiator is essentially an offset para-boloidal antenna, very little of the energy incident on the re-flector is reflected back into the feed to produce an impedance mismatch. Also, due to the shielding effect of the horn, the far side and back lobes are very small when radiating in free space. These desirable characteristics, together with high aperture efficiency, low side and back lobe levels, make the horn reflector quite attractive for this particular type of application.
Although the electric field will maintain its charac-teristic amplitude distribution of the TElo mode as it proceedsalong the H-plane sectoral horn of the applicator, a way must be found to control the side lobe levels excited by diffraction effects at the aperture as well as surface waves along the ground surface. This second requirement of minimum leakage into the surrounding area can be overcome by incorporating some fea-tures of the corrugated horn into the design of the applicator. ~;~
This horn has a property of concentrating energy in the main beam, while maintaining very low back lobe levels, high effi-iency, and almost monotonic amplitude distribution of the elec-tric field in the aperture. Its other useful properties include nearly axially symmetric radiation patterns for a square or con- -~ical shape, exceptionally low ~SWR and transmission losses.
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In order to combine the attractive properties of both types of structures (i.e. the horn reflector and the corrugated flang~ a horn reflector type of applicator coupled to a modified corrugated ~ is provided. The corrugations are placed on a 180 flange extension of the horn reflector. The corrugations are essentially metallic strips soldered to the flange which extended out at 90 to each of the parallel sides of the horn reflector. The spacing between each two strips is a A/4 slot , while the width of each strip is also A /4 in accordance with well kno~n theory. The material used is preferably copper sheets of 1/16" thickness while the feed waveguide section was the standard WR430 waveguide with appropriate co-ax to wave-guide adapter connection to the magnetron.
Proceeding therefore to describe the application in detail, reference should first be made to Figure 5 in which reference character 10 illustrates schematically a magnetron, connected to a tuning section 11 and having power meters 12 connected thereto by means of cables 13. r The applicator is collectively designated 14 and is shown in detail in Figures 1, 2 and 3. A rectangular cross section waveguide 15 is connected to the tuning section by means of flange 16 and terminates in the horn 17 which includes the upper outwardly fiared wall 18 and the lower wall 19 and it will be observed that the walls 18 and 19 extend at 120 from the transverse plane of the end of the waveguide as shown in :: . :- , . .. . . . .
Figure 2. However, t ~ angle can be varied depending upon design parameters.
A parabolic reflector 20 extends from the upper end 21 of the upper wall 18 of the horn and is provided with spaced and parallel side walls 22 which extend downwardly from the side edges 23 of the parabolic reflector and enclose same. The parabolic reflector terminates with a short vertical wall 24 and the wall 19 of the horn also terminates in a shoxt vertical wall 25 spaced and parallel to wall 24 with the lower edges lying in the same plane as clearly illustrated.
A corrugated flange assembly collectively designated 26 extends outwardly on each side of the assembly and includes substantially rectangular planar panels 27 secured to the side walls 22 of the parabolic reflector at a position spaced above the lower edges 28 of these side walls.
.'. ~ ', :
A plurality of spaced and parallel longitudinally extending strips 29 extend downwardly at right angles from the unaerside of the plates 27 and lie spaced and parallel with . .
th~ portions 30 of the side walls below the plates 27. These strips lie parallel to the longitudinal axis of the applicator. ~ , !.
.,, ~', '.
33~ ~
Low and high power performance tests have been carried out with this design as follows:
Low Power Performance Tests : - ,, In order to evaluate the performance of the applicator, a series of low power tests were carried out. The first of these tests was a measurement of the VSWR vs. frequency which was carried out using a network analyzer (Hewlett-Packard type HP8410S). The results for the frequency range 2410-2480MHz are given in the following Table 1.
FREQUENCY MHz VSWR
2410 3.95 2420 3.57 2430 3.01 2440 2.32 2450 1.88 `
2460 1.55 2470 1.25 2480 1.24 VSWR vs. frequency for the applicator Although the applicator performed satisfactorily at ~-2450 MHz, the best operating frequency was found to be 2480 MHz which was most probably due to deviations in production tolerances during rabrication. However, an operating frequency of between 2400 MHz and 2500 MHz is possible.
lU44331 In order to evaluate the radiation characteristics of the applicator, an x-y plot of the aperture field rather than the radiation pattern in the far zone was carried out using a suit-able generator. The detector was an open-ended WR430 waveguide operating at 2450 MHz and the probing was carried out at a distance of ~/2 from the aperture where the ground surface is approximately located in practice. A simple detection technique was adopted and the power density distribution was recorded in the trans-verse and longitudinal planes with the maximum power density at the mid-poi~t of the aperture set at a re~erence level o~ O dB.
The results are given in the following Tables 2 and 3. ;
x(inch) Power Density x(inch) Power Density Level Level O O
~S ~0-5 1.0 -0.4 -1.0 -0.8 ~
1.5 -2.4 -1.5 -2.8 ~ :
-1~ This invention relates to new and useful improvements in the use of microwaves and in the provision-of a novel micro-wave horn reflector or applicator.
One of the most severe obstacles that face the con-struction industry in cold climates is the long cold winter months. During these months the industry tends to slow down and concentrate on construction mainly above ground relying on sites excavated during the summer. The high cost of winter construction results in unemployment. Thus the design, test-ing and implementation of new techniques and equipment that permit all year round operation would naturally be of great interes~ ~o those involved in ~he construction industry in Car.ad~ and other similar locations of the world.
I~ is known that microwave power has already been employed in the construction industry for demolition of concrete .... . , . . ~ ~.. . . .
.
, : . :: .
. ;:~, ` -' 104433i .
and highway repair through heating of trapped moisture in the case of concrete and curing of polymer-concrete patches in the case of road and pavement repairs. The advantages of the micro- -wave technique in these applications have been the minimum dis-ruption of traffic or time to complete the construction due to the shorter time required relative to conventional techniques lusing fire or heavy mechanical equipment). Other advantages are the possible reduction in the cost and noise or pollution levels. However, one of the principal disadvantages of using microwave power for these applications is the leakage normally present which may be dange~ous not only to the operator but to others standing nearby.
~ ''' .
To date no serious effort has yet been made to aid the construction industry in the rapid thawing and de-icing of permafrost and frozen soils, de-icing of street intersections, sidewalks and airport runways, fast drying of conveyorized wet sand and other construction materials, noise-free demolition of concrete pipes, sewers, ~ridges, ~uildings, roads, rocks, de-icing of windows, windshields, aircraft wings or rapid curing of concrete and bricks and sensors for simultaneous monitoring of the curing process~
SUMMARY OF THE INVENTION
This invention comprises a microwave power alternative to he commonly used mechanical excavation technique for thawing ~`
of severely frozen soils during the winter and illustrates the - . . .. : . ~
~ 1~4433~
specific advantages in terms of reduction in constxuction time, cost, noise and environmental pollution which were verified in conjunction with construction industry personnel. One aspect of this invention is to provide a horn reflector for use with microwave energy comprising in combination a horn, a parabolic reflector operatively connected by one end thereof to said horn and a corrugated flange assembly connected to the other end of said parabolic reflector and extending upon each side thereof.
A further aspect of the invention is to provide a de- ~;
vice of the character herewithin described which is simple in construction, economical in operation and otherwise well suited to the purpose for which it is designed.
With the foregoing in view and other such advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, my inven-tion consists essentially in the arrangement and construction of parts all as hereinafter more particularly described, reference being had to the accompanying drawings in which:
DESCRIPTION OF THE DRAWINGS
Figure 1 is an isometric view of the horn reflector or applicator.
,, ,: , . ::
Figure 2 is a longitudinal section of Figure 1.
Figure 3 is a cross sectional view along the line 3-3 of Figure 2.
, i Figure 4 is a graph showing the power density level 5with and without the corrugated flange .
~ ~ ' Figure 5 is a schematic side elevation of the device set up for evaluating the performance of the applicator with clay samples.
,; ~.
''" '' In the drawings like characters of reference indicate corresponding parts in the different figures.
DETAI~ED DESCRIPTION
The first requirement of a microwave applicator for `
practical use in the construction industry is to possess a reasonably flat field distribution in the aperture with minimum 15power towards the edges of the radiator. The applicator con- -fi~uration must therefore allow for maximum and uniform power in the area of interest as well as minimum VSWR at the frequency of operation particularly since the applicator aperture is very closely separated from the ground surface. In order to meet this specification, a horn reflector type of radiator is used which is a combination of a sectoral electromagnetic horn and a re~lector which is a sector of a paraboloid of revolution.
Since the center of the wave guide is the focal point of the parabola and since this radiator is essentially an offset para-boloidal antenna, very little of the energy incident on the re-flector is reflected back into the feed to produce an impedance mismatch. Also, due to the shielding effect of the horn, the far side and back lobes are very small when radiating in free space. These desirable characteristics, together with high aperture efficiency, low side and back lobe levels, make the horn reflector quite attractive for this particular type of application.
Although the electric field will maintain its charac-teristic amplitude distribution of the TElo mode as it proceedsalong the H-plane sectoral horn of the applicator, a way must be found to control the side lobe levels excited by diffraction effects at the aperture as well as surface waves along the ground surface. This second requirement of minimum leakage into the surrounding area can be overcome by incorporating some fea-tures of the corrugated horn into the design of the applicator. ~;~
This horn has a property of concentrating energy in the main beam, while maintaining very low back lobe levels, high effi-iency, and almost monotonic amplitude distribution of the elec-tric field in the aperture. Its other useful properties include nearly axially symmetric radiation patterns for a square or con- -~ical shape, exceptionally low ~SWR and transmission losses.
;;: ~ ' . ' ' .~
-5- ~
.. . .. ..
.: - . . ., , .. - .: . . : ,. . . . .
- ~ .. . . , "
l~'J ~ ~ 3 31 , .
In order to combine the attractive properties of both types of structures (i.e. the horn reflector and the corrugated flang~ a horn reflector type of applicator coupled to a modified corrugated ~ is provided. The corrugations are placed on a 180 flange extension of the horn reflector. The corrugations are essentially metallic strips soldered to the flange which extended out at 90 to each of the parallel sides of the horn reflector. The spacing between each two strips is a A/4 slot , while the width of each strip is also A /4 in accordance with well kno~n theory. The material used is preferably copper sheets of 1/16" thickness while the feed waveguide section was the standard WR430 waveguide with appropriate co-ax to wave-guide adapter connection to the magnetron.
Proceeding therefore to describe the application in detail, reference should first be made to Figure 5 in which reference character 10 illustrates schematically a magnetron, connected to a tuning section 11 and having power meters 12 connected thereto by means of cables 13. r The applicator is collectively designated 14 and is shown in detail in Figures 1, 2 and 3. A rectangular cross section waveguide 15 is connected to the tuning section by means of flange 16 and terminates in the horn 17 which includes the upper outwardly fiared wall 18 and the lower wall 19 and it will be observed that the walls 18 and 19 extend at 120 from the transverse plane of the end of the waveguide as shown in :: . :- , . .. . . . .
Figure 2. However, t ~ angle can be varied depending upon design parameters.
A parabolic reflector 20 extends from the upper end 21 of the upper wall 18 of the horn and is provided with spaced and parallel side walls 22 which extend downwardly from the side edges 23 of the parabolic reflector and enclose same. The parabolic reflector terminates with a short vertical wall 24 and the wall 19 of the horn also terminates in a shoxt vertical wall 25 spaced and parallel to wall 24 with the lower edges lying in the same plane as clearly illustrated.
A corrugated flange assembly collectively designated 26 extends outwardly on each side of the assembly and includes substantially rectangular planar panels 27 secured to the side walls 22 of the parabolic reflector at a position spaced above the lower edges 28 of these side walls.
.'. ~ ', :
A plurality of spaced and parallel longitudinally extending strips 29 extend downwardly at right angles from the unaerside of the plates 27 and lie spaced and parallel with . .
th~ portions 30 of the side walls below the plates 27. These strips lie parallel to the longitudinal axis of the applicator. ~ , !.
.,, ~', '.
33~ ~
Low and high power performance tests have been carried out with this design as follows:
Low Power Performance Tests : - ,, In order to evaluate the performance of the applicator, a series of low power tests were carried out. The first of these tests was a measurement of the VSWR vs. frequency which was carried out using a network analyzer (Hewlett-Packard type HP8410S). The results for the frequency range 2410-2480MHz are given in the following Table 1.
FREQUENCY MHz VSWR
2410 3.95 2420 3.57 2430 3.01 2440 2.32 2450 1.88 `
2460 1.55 2470 1.25 2480 1.24 VSWR vs. frequency for the applicator Although the applicator performed satisfactorily at ~-2450 MHz, the best operating frequency was found to be 2480 MHz which was most probably due to deviations in production tolerances during rabrication. However, an operating frequency of between 2400 MHz and 2500 MHz is possible.
lU44331 In order to evaluate the radiation characteristics of the applicator, an x-y plot of the aperture field rather than the radiation pattern in the far zone was carried out using a suit-able generator. The detector was an open-ended WR430 waveguide operating at 2450 MHz and the probing was carried out at a distance of ~/2 from the aperture where the ground surface is approximately located in practice. A simple detection technique was adopted and the power density distribution was recorded in the trans-verse and longitudinal planes with the maximum power density at the mid-poi~t of the aperture set at a re~erence level o~ O dB.
The results are given in the following Tables 2 and 3. ;
x(inch) Power Density x(inch) Power Density Level Level O O
~S ~0-5 1.0 -0.4 -1.0 -0.8 ~
1.5 -2.4 -1.5 -2.8 ~ :
2,0 -4.8 -2.0 -7.1 2.5 -10.6 -2.5 -14.0 2a 3.0 -17.0 -3.0 -21
3.5 -23.0 -3.5 -24 . ~ : .
4.0 -27 -4.0 -26 4.5 -29 -4.5 -28
5.0 -35 -5.0 ~30 :
5.5 -40 -5.5 ~33
5.5 -40 -5.5 ~33
-6.0 -38 :~
Power density distribution in the transverse plane measured with respect to the mid-point of the aperture (x = 0).
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1~4433~
TABI,E 3 : .
y(inch) Power Density y(inch) Power Density Level Level 0 -0.8 1 -0.4 -1 -2 3 -0.8 -3 -6 -8.8 -5 -12 ;
Power density distribution in the transverse plane measured with respect to the mid-point of the aperture (x = 0).
_g_ . .
1~4433~
TABI,E 3 : .
y(inch) Power Density y(inch) Power Density Level Level 0 -0.8 1 -0.4 -1 -2 3 -0.8 -3 -6 -8.8 -5 -12 ;
7 -28 -7 -20
-8 -28 Power density distribution in the longitudinal plane measured with respect to the mid-point of the aperture (y ~ 0). -~
A graphical plot of the power density in the transverse direction is shown in Figure 2 where a comparison with theapplicator without the corrugated flange is also shown.
Although the corrugated flange introduces a consider-able improvement in the power density distribution (being relatively flat near the center and very low near the edges) as evident from Figure 2, it was found that the maximum power den-sity location is not at the bisector of the aperture. This is due to fabrication tolerances in part but~ainly due to the finite size of the probe aperture and the geometry of the applicator aperture which reflects different contributions of the edges.
' ''' , .
~04433~
~igh Power Performance Tests Since the applicator design appeared to be satisfactory at low power, various experiments were carried out to evaluate its performance at high power levels. The first test involved leakage measurements with the applicator connected to a Philips magnetron through the tuhin~ section and a transmission/
reflection power meter. The radiator was surrounded by absorbing material (styrofoam with carbon particles imbedded) and with the magnetron setting controlled through a variac. The maximum leakage level readings were recorded by a radiation monitor (Narda model B86~3) and the results are shown in Table 4.
Power input Maximum leakage -(Watts) level (mw/cm2) 100 discernable 200 discernable 400 0.43 500 0.96 -600 1.30 700 2.10 20 ~oo 3.40 900 6.30 1 000 ,' 1 0 No load leakage performance of the applicator.
Although the results recorded at no load seem unfavour-able, the maximum leakage level was found to be 4 mw/cm2 nearthe flange edges when the applicator was loaded with a clay ',': .
~ 4~3~ :
sample and properly matched at the input. Since the power at-tenuation through free space is proportional to the square of the inverse distance, it seemed that safe experiments could be performed with this applicator as designed.
The remaining experiments were done on dark clay soil samples of different sizes which represent soils most commonly found on construction sites. The temperature of each sample was assumed to be the ambient outdoor temperature at the time ~-of the experiment. The samples were all placed directly under ~ -the applicator at a separation distance of one inch and the measuring equipment (as illustrated schematically in Figure 3) was adjusted to affect minimum reflected power as recorded by the reflection meter. Each sample was irradiated at two minute intervals and penetration tests were performed using a sharp pointer (calibrated thin copper rod) at the end of each inter-val. Leakage power was constantly monitored from the sides of the applicator using a radiation monitor and the results are given in Table 5 as follows:
TAsLE 5 TEST #1 Sample size: 14"x14"x4"
Temperature: -10F. -Power Transmitted: 800 watts Irradiation Penetration Reflected Max. leakage Period (min.) Depth (inches) power (Watts) power (mw/cm2) 2 0.25 40 1.3 4 .25-.5 30 1.3 6 .75-1 20 1.3 8 1.25-1.5 20 1.3 1.5-1.75 20 1.3 12 1.75-2 20 1.3 14 2 20 1.3 16 2 20 1.3 .. , .. :
, ~
Thawing and leakage performance of the applicator.
TEST #2 Sample size: 14"x14"x2 1/2"
Temperature: -10F.
Power Transmitted: 800 watts -.
Irradiation Penetration Reflected ~ax. leakage2 :
Period (min.) Depth (inches) power (watts) power (mw/cm ) 2 0.25 40 1.3 4 .25-.5 30 1.3 ~
6 .75-1 20 1.3 ~- ;
8 1.25-1.5 20n 1.3 1.5-1.75 20 1.3 12 2-2.25 20 1.3 14 2.5 20 1.3 ~ -.. - - :
Thawing and leakage performance of the applicator.
TEST #3 Sample size: 8"x14"x5"
. ,~ .. . .
Temperature: -10F.
Power Transmitted: 800 watts Irradiation Penetration Reflected Max. leakage2 Period (min.) Depth (inches) power (watts) power (mw/cm ) .'~' 2 0.25 40 1.3 4 .25-.5 30 1.3 6 .75-1 20 1.3 8 1.25-1.5 20 1.3 1.75-2 20 1.3 12 2-2.25 20 1.3 14 2.25 20 1.3 16 2.25 20 1.3 ...
`' :
:, . ' .
.~.
' '~' '. ', 1~44~31 ~::
Thawing and leakage performance of the applicator.
TEST #4 Sample size: 14"x14"x4" -Temperature: 15F.
Power Transmitted: 1000 watts Irradiation Penetration Reflected ~ax. Leakage2 Period (min.~ Depth (inches) power (watts) power (mw/cm ) 2 .5 20 3.4 4 .72-1.25 10 3.4 ~ -6 1.5-2 10 3.4 8 2.5-3 10 3.4 3.25-3.5 10 3.4 12 4 10 3.4 -Thawing and leakage performance of the applicator.
TEST #5 Sample size: 14"x7"x5" ~ -Temperature: 15F.
Power Transmitted: 1000 watts Irradiation Penetration Reflected Max. Leakage -Period (min.) Depth (inches) power (watts) power (mw/cm2) 2 .5 20 3.4 4 .75-1.25 10 3.4 6 1.5-2 10 3.4 ~`~
8 2.5-3 10 3.4 3.25-3.5 10 3.4 12 3.75 10 3.4 14 4 10 3.4 16 4.25 10 3.4 18 4.25 10 3.4 . .
~)4~331 Thawing and leakage performance of the applicator.
,.. .
TEST #6 Sample size: 14"x7"x5" - ~
Temperature: 20F. ~ -Power Transmitted: 1000 watts -Irradiation Penetration Reflected Max. Leakage2 Period (min.) Depth (inches) power (watts) power (mw/cm ) -~
2 .5 .5 20 3.4 . !
4 1-1.5 10 3.4 i 6 1.75-2.25 10 3.4 ;~
8 2.5-3 10 3.4 3.5-3.75 10 3.4 -12 4-4.5 10 3.4 ~, 14 5 10 3.4 Thawing and leakage performance of the applicator.
TEST #7 Sample size: same as in Test #5 Temperature: same as in Test #5 Power Input: variable Power Input Max. Leak~ge Power (watts) (mw/cm ) outside range of radiation monitor ~ -:.'. . :
Leakage performance of the loaded applicator at high power without the corrugated flange.
It should be noted that the first tests were per-formed at the same initial sample temperature and, since the ,: :.
''.: .~:
- 1 5 ~
.- . , sample was static, the thawing area was restricted to approx-imately 5" x 2.5" with the rest of the surface area remaining frozen. In fact it is evident from test number three that the effective area of thawing and penetration depth remained the ,;
S same as test numbers one and two indicating that the lateral ~ -size of the sample beyond the thawing area does not play an effective part in the static thawing process. The effect of the sample thickness also does not appear to play any part as evident from the results of tests number one and two. '~
It was also observed from tests 1 - 3 that there appears to be an acceleration effect for penetration depth ~' :
ranging between 0.25 and 1.75 inches. This was verified for thick samples where the penetration appeared to stop after about 2 to 2.5 inches. In all cases the moisture escaping from the -,-, samples was observed in terms of water droplets which condensed ~
on the face of the applicator. ~,-The results ~r tests 4 and 5 also indicate that the, lateral size of the sample does not have any effect on the depth of penetration and that, due to the higher initial sample tem-peratures, the thawing area was observed to be about 6 x 3 inches.
Examination of these results indicates that there isa period of accelerating action when microwave power is applied to frozen clay samples. However, with colder sample temperatures, , 31 `::
the thawing effect seems to stop at a certain penetration level.
This is most probably due to an equilibrium set up in the heat :
transfer process while most of the energy is used to drive out the moisture content of the sample. The loss of moisture can be observed as the water vapour rises above the surface of the sample under test and water droplets collect on the surface of the applicator. ~;
The tests also indicate that there is a roughly even distribution of power density in an area of approximately 5 x 2.5 inches which in fact is equivalent to the physical aperture of the horn reflector plus the first slot of the corrugated flange. The microwave power seems to concentrate in this region leaving the remainder of the sample ~most completely frozen from the surface down. This demonstrates one feature of the applicator when used in a static sense but is obviously of academic interest since applicators of this type would be mov- ~
ing over frozen ground in a practical construction application. ~ ~ -: .
, Although the flanged applicator presents a considerable improvement in lowering the leakage level relative to the un- `
flanged applicator, as evident from Table 2, it is believed that further reduction in the leakage power could be achieved by a more refined design of the slot dimensions and spacings as well as the flare angle of the flange.
~ ,',, .
It will therefore be appreciated that an improved horn reflector antenna has been provided which, by incorporating a corrugated flange, makes the antenna suitable for effective and safe thawing of frozen soils. Further analysis and experiment-ation to improve the design of the flange taking the dielectricproperties of the soil and the separation distance from the appli-cator into account is undoubtedly necessary particularly if micro-wave power is combined with other forms of energy (e.g. hot air) and power switching and profiling is employed.
It is believed that this applicator will have various other applications for outdoor heating with microwave power, For example, one such application could be the de-icing of street pavements or airport runways and the like, on which the formation of ice creates a considerahle hazard to both pedestrians and vehi-cles and aircraft in severe winter months. Since ice is a low loss material compared with the concrete pavement, the impinging microwave power on the ice surface would in this case be mainly dissipated in the concrete. This would heat up the upper surface of the concrete resulting in a thin layer of melted water at the concrete-ice interface. Once this occurred, there would be an accelerating effect of melting due to the relatively much higher loss property of water, thus allowlng easy scraping of the ice us-ing mechanical means. Also of importance is the use of the device for noise free microwave demolition of concrete pipes, sewers, bridges, building9, roads, sidewalks and the breaking of rocks.
; . ~ , - 1~3~331 The device is well suited for use in microwave de-icing of windows, windshields and aircraft wings.
Anot~er use of the device enables microwaves to be used for rapid c~ring of concrete and bricks and sensors for simultane-ous monitoring of the curing process.
Finally, the data indicates that tne application of micro-wave power for thawing of soil is favourable and can be used for further applications in the constr~ction industry, The accelerated ~-rate of thawing by the present applicator not only proves to be safe, but also provides a great saving of time particularly when dealing with frozen soils in foundations and ditches excavated across major roads for construction and maintenance in the winter -time, ~
. ,.', .........
Since various modifications can be made in my invention as hereinabove described, and many apparently widely different em-bodiments of same made within the spirit and scope of the claims `^
without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.
~". .
~19-- . ~. . .
A graphical plot of the power density in the transverse direction is shown in Figure 2 where a comparison with theapplicator without the corrugated flange is also shown.
Although the corrugated flange introduces a consider-able improvement in the power density distribution (being relatively flat near the center and very low near the edges) as evident from Figure 2, it was found that the maximum power den-sity location is not at the bisector of the aperture. This is due to fabrication tolerances in part but~ainly due to the finite size of the probe aperture and the geometry of the applicator aperture which reflects different contributions of the edges.
' ''' , .
~04433~
~igh Power Performance Tests Since the applicator design appeared to be satisfactory at low power, various experiments were carried out to evaluate its performance at high power levels. The first test involved leakage measurements with the applicator connected to a Philips magnetron through the tuhin~ section and a transmission/
reflection power meter. The radiator was surrounded by absorbing material (styrofoam with carbon particles imbedded) and with the magnetron setting controlled through a variac. The maximum leakage level readings were recorded by a radiation monitor (Narda model B86~3) and the results are shown in Table 4.
Power input Maximum leakage -(Watts) level (mw/cm2) 100 discernable 200 discernable 400 0.43 500 0.96 -600 1.30 700 2.10 20 ~oo 3.40 900 6.30 1 000 ,' 1 0 No load leakage performance of the applicator.
Although the results recorded at no load seem unfavour-able, the maximum leakage level was found to be 4 mw/cm2 nearthe flange edges when the applicator was loaded with a clay ',': .
~ 4~3~ :
sample and properly matched at the input. Since the power at-tenuation through free space is proportional to the square of the inverse distance, it seemed that safe experiments could be performed with this applicator as designed.
The remaining experiments were done on dark clay soil samples of different sizes which represent soils most commonly found on construction sites. The temperature of each sample was assumed to be the ambient outdoor temperature at the time ~-of the experiment. The samples were all placed directly under ~ -the applicator at a separation distance of one inch and the measuring equipment (as illustrated schematically in Figure 3) was adjusted to affect minimum reflected power as recorded by the reflection meter. Each sample was irradiated at two minute intervals and penetration tests were performed using a sharp pointer (calibrated thin copper rod) at the end of each inter-val. Leakage power was constantly monitored from the sides of the applicator using a radiation monitor and the results are given in Table 5 as follows:
TAsLE 5 TEST #1 Sample size: 14"x14"x4"
Temperature: -10F. -Power Transmitted: 800 watts Irradiation Penetration Reflected Max. leakage Period (min.) Depth (inches) power (Watts) power (mw/cm2) 2 0.25 40 1.3 4 .25-.5 30 1.3 6 .75-1 20 1.3 8 1.25-1.5 20 1.3 1.5-1.75 20 1.3 12 1.75-2 20 1.3 14 2 20 1.3 16 2 20 1.3 .. , .. :
, ~
Thawing and leakage performance of the applicator.
TEST #2 Sample size: 14"x14"x2 1/2"
Temperature: -10F.
Power Transmitted: 800 watts -.
Irradiation Penetration Reflected ~ax. leakage2 :
Period (min.) Depth (inches) power (watts) power (mw/cm ) 2 0.25 40 1.3 4 .25-.5 30 1.3 ~
6 .75-1 20 1.3 ~- ;
8 1.25-1.5 20n 1.3 1.5-1.75 20 1.3 12 2-2.25 20 1.3 14 2.5 20 1.3 ~ -.. - - :
Thawing and leakage performance of the applicator.
TEST #3 Sample size: 8"x14"x5"
. ,~ .. . .
Temperature: -10F.
Power Transmitted: 800 watts Irradiation Penetration Reflected Max. leakage2 Period (min.) Depth (inches) power (watts) power (mw/cm ) .'~' 2 0.25 40 1.3 4 .25-.5 30 1.3 6 .75-1 20 1.3 8 1.25-1.5 20 1.3 1.75-2 20 1.3 12 2-2.25 20 1.3 14 2.25 20 1.3 16 2.25 20 1.3 ...
`' :
:, . ' .
.~.
' '~' '. ', 1~44~31 ~::
Thawing and leakage performance of the applicator.
TEST #4 Sample size: 14"x14"x4" -Temperature: 15F.
Power Transmitted: 1000 watts Irradiation Penetration Reflected ~ax. Leakage2 Period (min.~ Depth (inches) power (watts) power (mw/cm ) 2 .5 20 3.4 4 .72-1.25 10 3.4 ~ -6 1.5-2 10 3.4 8 2.5-3 10 3.4 3.25-3.5 10 3.4 12 4 10 3.4 -Thawing and leakage performance of the applicator.
TEST #5 Sample size: 14"x7"x5" ~ -Temperature: 15F.
Power Transmitted: 1000 watts Irradiation Penetration Reflected Max. Leakage -Period (min.) Depth (inches) power (watts) power (mw/cm2) 2 .5 20 3.4 4 .75-1.25 10 3.4 6 1.5-2 10 3.4 ~`~
8 2.5-3 10 3.4 3.25-3.5 10 3.4 12 3.75 10 3.4 14 4 10 3.4 16 4.25 10 3.4 18 4.25 10 3.4 . .
~)4~331 Thawing and leakage performance of the applicator.
,.. .
TEST #6 Sample size: 14"x7"x5" - ~
Temperature: 20F. ~ -Power Transmitted: 1000 watts -Irradiation Penetration Reflected Max. Leakage2 Period (min.) Depth (inches) power (watts) power (mw/cm ) -~
2 .5 .5 20 3.4 . !
4 1-1.5 10 3.4 i 6 1.75-2.25 10 3.4 ;~
8 2.5-3 10 3.4 3.5-3.75 10 3.4 -12 4-4.5 10 3.4 ~, 14 5 10 3.4 Thawing and leakage performance of the applicator.
TEST #7 Sample size: same as in Test #5 Temperature: same as in Test #5 Power Input: variable Power Input Max. Leak~ge Power (watts) (mw/cm ) outside range of radiation monitor ~ -:.'. . :
Leakage performance of the loaded applicator at high power without the corrugated flange.
It should be noted that the first tests were per-formed at the same initial sample temperature and, since the ,: :.
''.: .~:
- 1 5 ~
.- . , sample was static, the thawing area was restricted to approx-imately 5" x 2.5" with the rest of the surface area remaining frozen. In fact it is evident from test number three that the effective area of thawing and penetration depth remained the ,;
S same as test numbers one and two indicating that the lateral ~ -size of the sample beyond the thawing area does not play an effective part in the static thawing process. The effect of the sample thickness also does not appear to play any part as evident from the results of tests number one and two. '~
It was also observed from tests 1 - 3 that there appears to be an acceleration effect for penetration depth ~' :
ranging between 0.25 and 1.75 inches. This was verified for thick samples where the penetration appeared to stop after about 2 to 2.5 inches. In all cases the moisture escaping from the -,-, samples was observed in terms of water droplets which condensed ~
on the face of the applicator. ~,-The results ~r tests 4 and 5 also indicate that the, lateral size of the sample does not have any effect on the depth of penetration and that, due to the higher initial sample tem-peratures, the thawing area was observed to be about 6 x 3 inches.
Examination of these results indicates that there isa period of accelerating action when microwave power is applied to frozen clay samples. However, with colder sample temperatures, , 31 `::
the thawing effect seems to stop at a certain penetration level.
This is most probably due to an equilibrium set up in the heat :
transfer process while most of the energy is used to drive out the moisture content of the sample. The loss of moisture can be observed as the water vapour rises above the surface of the sample under test and water droplets collect on the surface of the applicator. ~;
The tests also indicate that there is a roughly even distribution of power density in an area of approximately 5 x 2.5 inches which in fact is equivalent to the physical aperture of the horn reflector plus the first slot of the corrugated flange. The microwave power seems to concentrate in this region leaving the remainder of the sample ~most completely frozen from the surface down. This demonstrates one feature of the applicator when used in a static sense but is obviously of academic interest since applicators of this type would be mov- ~
ing over frozen ground in a practical construction application. ~ ~ -: .
, Although the flanged applicator presents a considerable improvement in lowering the leakage level relative to the un- `
flanged applicator, as evident from Table 2, it is believed that further reduction in the leakage power could be achieved by a more refined design of the slot dimensions and spacings as well as the flare angle of the flange.
~ ,',, .
It will therefore be appreciated that an improved horn reflector antenna has been provided which, by incorporating a corrugated flange, makes the antenna suitable for effective and safe thawing of frozen soils. Further analysis and experiment-ation to improve the design of the flange taking the dielectricproperties of the soil and the separation distance from the appli-cator into account is undoubtedly necessary particularly if micro-wave power is combined with other forms of energy (e.g. hot air) and power switching and profiling is employed.
It is believed that this applicator will have various other applications for outdoor heating with microwave power, For example, one such application could be the de-icing of street pavements or airport runways and the like, on which the formation of ice creates a considerahle hazard to both pedestrians and vehi-cles and aircraft in severe winter months. Since ice is a low loss material compared with the concrete pavement, the impinging microwave power on the ice surface would in this case be mainly dissipated in the concrete. This would heat up the upper surface of the concrete resulting in a thin layer of melted water at the concrete-ice interface. Once this occurred, there would be an accelerating effect of melting due to the relatively much higher loss property of water, thus allowlng easy scraping of the ice us-ing mechanical means. Also of importance is the use of the device for noise free microwave demolition of concrete pipes, sewers, bridges, building9, roads, sidewalks and the breaking of rocks.
; . ~ , - 1~3~331 The device is well suited for use in microwave de-icing of windows, windshields and aircraft wings.
Anot~er use of the device enables microwaves to be used for rapid c~ring of concrete and bricks and sensors for simultane-ous monitoring of the curing process.
Finally, the data indicates that tne application of micro-wave power for thawing of soil is favourable and can be used for further applications in the constr~ction industry, The accelerated ~-rate of thawing by the present applicator not only proves to be safe, but also provides a great saving of time particularly when dealing with frozen soils in foundations and ditches excavated across major roads for construction and maintenance in the winter -time, ~
. ,.', .........
Since various modifications can be made in my invention as hereinabove described, and many apparently widely different em-bodiments of same made within the spirit and scope of the claims `^
without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.
~". .
~19-- . ~. . .
Claims
WHAT I CLAIM AS MY INVENTION IS:
(1) A horn reflector for use with microwave energy comprising in combination a horn, a parabolic reflector opera-tively connected by one end thereof to said horn and a corru-gated flange assembly connected to the other end of said para-bolic reflector and extending upon each side thereof.
(2) The horn reflector according to Claim 1 in which said parabolic reflector includes an arcuately curved reflector wall extending from the upper side of said horn and spaced and parallel vertical side plates extending downwardly from the side edges of said reflector wall.
(3) The horn reflector according to Claim 1 in which said corrugated flange assembly includes a planar panel secured adjacent the lower end of said parabolic reflector and extending outwardly upon each side thereof and a plurality of spaced and parallel vertically situated plates secured to the underside of said panels and extending downwardly therefrom.
(4) The horn reflector according to Claim 2 in which said corrugated flange assembly includes a planar panel secured adjacent the lower end of said parabolic reflector and extending outwardly upon each side thereof and a plurality of spaced and parallel vertically situated plates secured to the underside of said panels and extending downwardly therefrom.
(5) The horn reflector according to Claim 4 in which said planar panels are secured to the side plates of said reflec-tor at a position spaced upwardly from the lower edges of side plates, the lower edges of said side plates and the lower edges of said spaced and parallel vertically situated plates lying in the same plane and extending parallel to the longitudinally axis of said horn reflector.
(1) A horn reflector for use with microwave energy comprising in combination a horn, a parabolic reflector opera-tively connected by one end thereof to said horn and a corru-gated flange assembly connected to the other end of said para-bolic reflector and extending upon each side thereof.
(2) The horn reflector according to Claim 1 in which said parabolic reflector includes an arcuately curved reflector wall extending from the upper side of said horn and spaced and parallel vertical side plates extending downwardly from the side edges of said reflector wall.
(3) The horn reflector according to Claim 1 in which said corrugated flange assembly includes a planar panel secured adjacent the lower end of said parabolic reflector and extending outwardly upon each side thereof and a plurality of spaced and parallel vertically situated plates secured to the underside of said panels and extending downwardly therefrom.
(4) The horn reflector according to Claim 2 in which said corrugated flange assembly includes a planar panel secured adjacent the lower end of said parabolic reflector and extending outwardly upon each side thereof and a plurality of spaced and parallel vertically situated plates secured to the underside of said panels and extending downwardly therefrom.
(5) The horn reflector according to Claim 4 in which said planar panels are secured to the side plates of said reflec-tor at a position spaced upwardly from the lower edges of side plates, the lower edges of said side plates and the lower edges of said spaced and parallel vertically situated plates lying in the same plane and extending parallel to the longitudinally axis of said horn reflector.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA231,622A CA1044331A (en) | 1975-07-16 | 1975-07-16 | Microwave thawing of frozen materials and applicators therefor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA231,622A CA1044331A (en) | 1975-07-16 | 1975-07-16 | Microwave thawing of frozen materials and applicators therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1044331A true CA1044331A (en) | 1978-12-12 |
Family
ID=4103622
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA231,622A Expired CA1044331A (en) | 1975-07-16 | 1975-07-16 | Microwave thawing of frozen materials and applicators therefor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1044331A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1984003021A1 (en) * | 1983-01-25 | 1984-08-02 | Deryck Brandon | Apparatus and method for heating, thawing and/or demoisturizing materials and/or objects |
| US4571473A (en) * | 1983-06-14 | 1986-02-18 | Canadian Patents & Development Limited-Societe Canadienne Des Brevets Et D'exploitation Limitee | Microwave applicator for frozen ground |
| US4590348A (en) * | 1983-07-20 | 1986-05-20 | Canadian Patents And Development Limited | System for heating materials with electromagnetic waves |
| WO1995003884A1 (en) * | 1993-08-02 | 1995-02-09 | Scetauroute Nord | Method and device for varying the entropy of a polar molecular system |
-
1975
- 1975-07-16 CA CA231,622A patent/CA1044331A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1984003021A1 (en) * | 1983-01-25 | 1984-08-02 | Deryck Brandon | Apparatus and method for heating, thawing and/or demoisturizing materials and/or objects |
| US4571473A (en) * | 1983-06-14 | 1986-02-18 | Canadian Patents & Development Limited-Societe Canadienne Des Brevets Et D'exploitation Limitee | Microwave applicator for frozen ground |
| US4590348A (en) * | 1983-07-20 | 1986-05-20 | Canadian Patents And Development Limited | System for heating materials with electromagnetic waves |
| WO1995003884A1 (en) * | 1993-08-02 | 1995-02-09 | Scetauroute Nord | Method and device for varying the entropy of a polar molecular system |
| FR2708481A1 (en) * | 1993-08-02 | 1995-02-10 | Chapuis Philippe | Method and device for modifying the entropy of a polar molecular system. |
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