US3472200A

US3472200A - Striping apparatus for highways

Info

Publication number: US3472200A
Application number: US367634A
Authority: US
Inventors: John E Gerling
Original assignee: Litton Industries Inc
Current assignee: Litton Industries Inc
Priority date: 1964-05-15
Filing date: 1964-05-15
Publication date: 1969-10-14
Anticipated expiration: 1986-10-14
Also published as: NO121458B; GB1110021A; GB1110022A

Description

J. E. GERLING Oct. 14, 1,969

. STRIPING APPARATUS FOR` HIGHWAYS Filed May 15, 1964 4 Sheets-Sheet 1.

NWN@

J. E. GERLING STRIPING APPARATUS FOR HIGHWAYS Oct. 14, 1969 4 Sheets-Sheet 2 Filed May 15, 1964 um ww NNN MNN. d u

Oct. 14, 1969 J. E. GERLING 3,472,200

STRIPING APPARATUS FOR HIGHWAYS Filed May l5, 1964 4 Sheets-Sheet 3 J /;ll/l///// /////////////////////////////l/ lll7 @ffy A l www ifa/weld Oct. 14, 1969 J. E. GERLING STRIPING APPARATUS FOR HIGHWAYS 4 Sheets-Sheet 4 Filed May 15, 1964 United States Patent O 3,472,200 STRIPING APARATUS F OR HIGHWAYS .lohn E. Geriing, Los Altos Hills, Calif., assigner to Litton Industries, Inc., Beverly Hills, Calif. Filed May 15, 1964, Ser. No. 367,634 lint. Cl. BSb 17/04; B056 5/02 US. Cl. 113-5 4 Claims ABSTRACT F THE DISCLQSURE This invention relates in one aspect to microwave heating or drying techniques and more particularly to apparatus for rapidly heating or drying thin films of fluid or paint materials; and in another aspect to the application of distinctive markings to highways or the like through the use of microwave energy.

In many processes the time required for heating films, Stich as paint or adhesives so they will dry, is excessive; the processes are therefore unduly costly. In the painting of traic lines on highways, for example, it usually takes at least a half-hour for the paint to dry. This prolonged drying time requires setting out of markers to keep traffic off the lines and requires the use of at least two crews, one of which sets out the trame markers and paints the lines, and the other crew picks up the traffic markers after the lines have dried. In addition to the expense of maintaining at least two crews for this job, many accidents are caused by the various factors which are necessarily present in the foregoing method.

A principal object of the present invention is to reduce the time required for the drying of paint or other liquid.

Another object of the invention is to put markings on roads, highways or the like in as short a time as possible.

In accordance with various aspects of the present invention, the problems relating to the single-step application of paint to the highway and its prompt drying are solved by the use of a combination of particular techniques. Generally, the present invention involves the application of microwave energy to paint or other similar material which requires drying; and it also encompasses the application of microwave energy to road markings and the like to fully set the markings in place as quickly as possible.

One aspect of the invention involves the use of a slowwave electromagnetic structure provided with one open side adapted for exposure to a film of paint or other iiuid which is to be dried. The slow-wave structure may be of the non-radiating type, such as a split or open sided, folded waveguide, and may be terminated in a dummy load or similar dissipative termination. In accordance with a preferred embodiment of the invention, several slow-wave structures are mounted on a vehicle so that the open side of the slow-wave structure is close to the pavement. Under these conditions, automatic regulation of power transfer is achieved. Thus, when the slow-wave structures are moving over a wet paint stripe, substantial power transfer will occur. However, if it is necessary to stop the vehicle or if the paint is not being applied to the road at the particular instant of time, energy will not be radiated from the slow-wave structures but will traverse them with little loss, and the microwave energy is dissipated in the dummy load.

In accordance with a collateral feature of the invention, the slow-wave structure may be arranged to provide "ice substantially constant energy transfer along its length by increasing the coupling between the slow-wave structure and the paint at points farther from the source of microwave energy. This can be accomplished by tilting the slowwave structure with respect to the road, or by changing the electrical characteristics of the structure along its length, for example.

In accordance with another aspect of the invention, the present drying or coating process is carried out with particular types of paint or other liquids. Specifically, it has been determined that many of the usual types of paints do not absorb microwave energy, but that high coupling of microwave energy to fluid films is achieved when bi-polar paint vehicles are employed. Furthermore, this coupling is enhanced when the conductivity of the fluid is selected and designed to have a realtively high value, above five millimhos per centimeter, for example.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which an illustrative system embodying the principles of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

In the drawings:

FIG. 1 is a View of a slow electromagnetic wave structure 12 of the non-radiating type which may be employed to dry films of liquids in accordance with one aspect of the invention;

FIG. 2 is a partial cross-sectional View taken along lines 2-2 of FIG. l; and FIG. 2A is a partial view of a modied form of the structure of FIG. 2;

FIG. 3 is a cross-sectional view through the coupling to the slow-wave structure, taken along lines 3 3 of FIG. 2;

FIGS. 4 and 5 are side and top views, respectively, of mobile painting units carrying the slow-wave structures of FIGS. 1 through 3 and other related painting and auxiliary equipment;

FIGS. 6 and 7 are detailed views of the supporting arrangements for the slow-wave structures, in the mobile units of FIGS. 4 and 5;

FIG. 8 is a View of a portion of FIG. 4, showing the slow-wave structure tilted with respect to the paint stripe, to obtain more uniform heating of the paint stripe;

FIGS. 9 and l() show alternative arrangements for obtaining uniform microwave radiation intensity from a slow-wave structure; and

FIG. 11 is a chart indicating the variation in microwave energy absorption with solutions of different conductivity.

Referring more particularly to the drawings, the slowwave structure of FIG. 1 is made up essentially of a folded waveguide path in which electromagnetic waves are forced to transit the structure many times as a result of the vanes 14 which extend between the

conductive side walls

16 and 18. Thus, input electromagnetic waves are applied to the structure through the coaxial connector 20 to the input coupling vane 22. The microwaves follow the path indicated by arrows 24 and eventually reach the output coaxial lead 26, which is connected to the output coupling vane 28.

FIGS. 2 .and 3 indicate the nature of the slow-wave structure of FIG. 1 in greater detail. Initially, it is noted that the showing of FIG. 2 differs from that of FIG. 1 in that the lower ends of the Vanes 14 are provided with enlarged portions 32, and an insulating cover plate 34 has been added to the open side of the split folded waveguide structure. The bracket 36 is employed to support the slow-wave structure. The slow-wave structure is conductively bounded at its upper surface by the conductive plate 38. Above the plate 38 is a plenum chamber 39, which may be supplied with air under pressure through tube 40. The air may be directed through openings 41 in plate 38 and openings 41 in cover plate 34 to assist in driving o volatile gases and vapors released upon application of the microwave energy.

FIG. 3 is taken along lines 3-3 of FIG. 2 and shows the input coupling vane 22 in greater detail. The conductive rod 42 is an extension of the inner conductor of the coaxial line 20 and connects it to the end of the vane 22.

In addition to the components shown in FIGS. l and 2, a road 44 and a paint stripe 46 on the road are shown in FIG. 3. To reduce any possible radiation danger to minimal levels, conductive wire cloth shields 48 and 50 are secured to the two

side walls

16 and 18 of the slowwave structures 12. In many cases, the radiation levels are suliciently low that these shields are unnecessary.

The slow-wave structure of FIG. 1 is somewhat unusual in that it is of the non-radiating type. Thus, the eld intensity drops otf rapidly with increasing distances from the open side of the slow-wave structure and, in the absence of microwave absorbing material close to the open surface, little or no energy is lost in transmission through -the slow-wave structure 12. In operation, therefore, one or `more of the slow-wave structures are inserted between a microwave source and a dissipative termination. When the units are rolled over wet paint of the proper type, the microwave energy is absorbed by the paint and dries it. However, after the paint is dry, or in the absence of paint, there is no danger of microwave radiation into the open air. Instead, substantially all of the microwave energy is transmitted from the input coaxial lead 20 to the output 26 and is then coupled to the dissipative termination. Through this technique, automatic regulation of power ow is achieved and there is full coupling to dry the paint when it is required `and no radiation when there is no useful work -to be done.

With regard to particular features of the invention, the lower insulating plate 34 is provided to keep the slowwave structure clean and to direct air flow onto paint at high velocity. The plate 34 may be made of a low dielectric constant material, such as polypropylene. The lower ends of the vanes 14 may either be straight as shown in FIG. l or may be enlarged or tapered as shown in FIGS. 2 and 2A. The broader ends of the slow-wave structure serve to increase the electromagnetic field gradient across the gap and increase the intensity of the electromagnetic eld at particular points an inch or two away from the slow-wave structure. On the other hand, the integrated value of microwave energy will be increased somewhat by the tapered vanes shown in FIG. 2A. For most applications, however, the simpler structure of FIG. l may be used.

FIG. 4 is a schematic showing of a mobile paint application vehicle. The vehicle is about twenty feet long and would normally be less than a foot or a foot and a half in height. As shown in FIG. 4, the vehicle moves from right to left. Toward the rear of the vehicle, a number of slow-wave structures 12A through 12F are mounted. These units are constructed as shown in FIGS. 1 through 3 of the present drawings. At the front of the paint vehicle or train is an infrared preheater unit 54. This unit may be disconnected or merely turned off when the painting apparatus is employed with dry pavement. The second articulated frame unit 56 of the vehicle carries a paint gun 58 and a reflecting bead dispenser 60. `Each of the next three articulated

frame units

62, 64, and 66 carries two of the slow-wave structures 12.

In operation, the damp highway surface is initially dried by the infrared preheating unit 54. In passing, it may be noted that the unit 54 may be powered by a propane cylinder or may be electrically energized. Commercially available propane heaters employing ceramic heating elements are to be preferred. Following the initial pavement drying step, paint from gun 58 is applied onto the surface of the pavement. While the paint is still wet, reflecting beads are dropped into its surface from the bead dispenser unit 60. Microwave energy is then applied to the paint stripe on the pavement by the six trailing slow-wave structures 12A through 12F.

It is contemplated that the mobile painting unit shown in FIG. 4 may be drawn by a larger vehicle or may be secured to a trailer. Mounted on the trailer will be such heavy and bulky units as the paint cans, the radio frequency sources, the dummy loads or termination for the microwave energy, and compressed air and propane when these are employed. A typical block diagram for the microwave circuit is shown in FIG. 5. In FIG. 5 there are two sources of microwave energy 72 `and 74. Similarly, two microwave dummy loads or

terminations

76 and 78 are provided. Microwave energy from the source 72 is transmitted through the coaxial lead 8l) through slowwave structure 12C and the two additional slow-

Wave structures

12B and 12A. Any residual microwave energy which has not been absorbed by the paint stripe is coupled to the termination or dummy load 76 by the coaxial line 82. Similarly, the three slow-

wave structures

12D, 12E, and 12F are connected in series between the microwave source 74 and the dummy load 78.

Control circuitry may be provided for sensing any departure from optimum energy absorption conditions. Arrangements may also be provided for changing one or more of the conditions in `accordance with the sensed departures from optimum. Thus, for example, temperature sensing circuits 83 may be associated with the dummy loads 76 and 78. Signals developed by the temperature sensing circuitry, which may include a bolometer and an amplifier, for specific example, are connected to control the microwave sources 72 and 74, `as indicated in FIG. 5. When the microwave dummy loads become overloaded, the microwave power sources may be turned off or reduced in their power output levels. Other control arrangements which may be provided include a directional coupler in the output leads from the power sources to pick up a small fraction of the retlected energy from the d slow-wave structures 12. When substantial reflection occurs, for example when the apparatus crosses a manhole cover, the output power level of the microwave source may be reduced. Finally, the distance of the slow-wave structure from the material being dried, may be controlled to insure optimum energy absorption by the material which is being heated or dried. In the case of industrial process, a heat sensing element may be located immediately below the material being processed, and the distance between the slow-wave structure and the material may be varied to maintain a predetermined temperature, and avoid overheating or undercuring with variations in the ambient temperature or other condi` tions. In the case of the painting apparatus of FIG. 5, the height above the road may be adjusted in accordance with energy sensing device at the input or output of the slow-wave structures, or in response to changes in speed of the vehicle, which could result in overheating of the painted stripe.

In FIG. 5 it may be noted that the slow-wave struc` tures 12A through 12F are mounted at a significant angle with respect to the direction of movement of the vehicle. This `angle is selected in order to achieve uniform irradiation and heating of the paint stripe by the electromagnetic ield pattern. With reference to the cross-sectional view of FIG. 3 of the drawings, the fringing field from the slow-wave structure is not uniform across the width of the slow-wave structure; instead, it rises to broad maximum points near each side of the structure and drops to a fairly uniform moderate level in the central area of the structure. If the slow-wave structures 12A through 12F of FIG. 5 were aligned with the vehicle, some areas of the paint stripe would be more strongly irradiated and would dry faster than other areas of the paint stripe. With the angular orientation such -as shown in FIG. 5, however, the entire width of the paint stripe is heated to the same extent.

FIG. 6 and 7 are detail views showing the mounting of slow-wave structures 12 to the supporting plates, such as plate 62. To permit both vertical and angular adjustment of the slow-wave structures 12 with respect to their supporting frames, a bolt 102 is secured through the slot 104 in the mounting plate 62 land'through a hole 106 in the flange 36 at the end of the slow-wave structure 12. The height of each end of the slow-wave structure 12 may be adjusted by rotation of the nuts S by which the bolt 102 is secured to plate 62.

FIG. 8 shows an yarrangement in which the

bolts

102 and 102 are secured to plate 62 so the slow-wave structure 12B has one end located further from the paint stripe 110 which is to be dried than its other end. In FIG. 8 the microwave energy is applied to slow-wave structure 12B through the coaxial cable 112. It leaves the slow-wave structure by way lof cable 114. In the course of traversing the llength of the slow-wave structure, a substantial portion of the energy is -absorbed by paint stripe 110. Accordingly, less energy remains for drying the paint at the output end of the slow-wave structure. To compensate for this reduction in microwave energy level, the slow-wave structure 12B has its righthand end (as shown in FIG. 8) mounted closer to the roadway and the paint stripe than" the left-hand end of the slow-wave structure. By thus increasing the coupling between the slow-wave lstructure and the paint stripe to be dried, the reduction in energy toward the output from the slow-wave structure is counteracted.

While the eifect discussed above in connection with FIG. 8 is not of paramount importance in -a system as shown in FIG. 5 where several micro-wave sources are employed, and where they direct microwave energy across the area to be irradiated in opposite directions, in smaller installations where a single slow-wave structure is used, the effect may be critical. Without some technique, such as that shown in FIG. 8 for evenly distributing the impinging microwave energy unto the irradiated surface, some areas could be heated too rapidly and could even be charred while other areas could remain undried for lack of sufficiently intense irradiation.

The diagram of FIG. 9 shows a folded waveguide or slow-wave structure 122 and a surface 124 requiring microwave irradiation. By Way of example the surface 124 may be a strip of flexible material having a surfacecoating of paint or other material which is to be dried or otherwise processed. Microwave energy is applied to the slow-wave structure 122 at the coaxial input lead 126 and is coupled from the output end of the folded w-aveguide 122 to the dummy load 128 by coaxial conductor 130.

In FIG. 9 the spacing of the material from the slowwave structure 122 is carefully matched to the characteristics of electromagnetic field extension from the open surface of the slow-wave structure and the rate of energy absorption of the work material to provide uniform irradiation of strip 124 as it passes over the waveguide structure 122. i

FIG. l0 shows, diagrammatically, a slow-wave structure 142 having an input end 144 and an output end 146. At the input end 144, the vanes forming the folded wave guide path are spaced close together so that the electromagnetic field does not extend far beyond the surface of the slow-wave structure. At the output end 146 of the slow-wave structure 142, however, the vanes are spaced relatively far apart to increase the fringing eld, and thus its intensity at any give distance from the waveguide. With this arrangement, the amount of energy coupled to a work surface located a constant distance from the slow- EXAMPLE I Weight C omponent Source grams) WO-l Vinyl Chloride Goodyear Chemical 55. 0

Division. M-70 LoW Viscosity Vinyl ...do 45. 0

Chloride.

Di-iso' ecyl Phthalate Monsanto 45. 0 G-62 Epoxy Rohm and Haas 5.0

6V6 A Stabilizer.. Ferro Chemical Corp.

R-900 TiO2 Du Pont Barytes #22 (Barium Sulfate) C. K. Williams Products Ethylene Glycol Mono Kessler Chemical Company.

Laurate 400. Di-isobutyl Ketone Union Carbide 30.

EXAMPLE II Weight Component Source (grams) XYHL Vinyl Butyral Union Carbide Bakelite 50.0

Division.

Denatured Alcohol (Bellsol) Commercial Solvents 170.0 W te 5.0 50.0 Bks 2710 Phenol do 200.0 3530-55 Urea. Formaldehide Reichbold Chemical 10S. 0

50.0 100.0 Mineral Pigments 40. 0 Castor Oil AA Baker Castor Oil Co 10.0

Both of the paint formulations set forth above show good drying properties in the presence of microwave energy. Specifically, with relatively low intensity microwave elds from a structure such as that shown in FIGS. 1 through 3, drying was obtained with both of these formulations in between iive and ten seconds.

FIG. l1 is a chart showing relative temperature rise plotted against conductivity for three different microwave frequencies. Plot 152 represents data taken at a frequency of 915 mc.; plot 154 was taken at 2,450 mc.; and plot 156 was obtained at 5,800 mc. These frequencies are the standard Government-approved frequencies available for microwave heating purposes. It may be noted that the relative increase in temperature rise achieved at 915 mc. is much greater than that obtained at higher frequencies. However, in view of the fact that the absolute increase in temperature for distilled water is greater at higher frequencies, the absolute increase in temperature for the lower frequency at high conductivities is not as great as might appear at first glance, from the characteristic of FIG. 11.

With reference to FIG. 11, it may be noted that the

plots

152, 154 and 156 start increasing at conductivities of about 1 or 2 millimhos per centimeter. At conductivities above 5 millimhos per centimeter, the energy absorption is significantly increased, particularly at the 915 megacycle region of principal interest.

For many applications, it is particularly useful to use a relatively low frequency. Such a low frequency permits the use of a large slow-wave structure to provide wide area irradiation and a fringing electromagnetic eld which extends a significant distance from the slow-Wave structure. When the lower frequency of 915 mc. is employed to achieve these desirable results, the effect of conductivity becomes more important as indicated by FIG. l1, as the drying time may be reduced by an order of magnitude if higher conductivities are employed.

While the characteristics of FIG. 11 were obtained with water and table salt solutions at G-watt power levels and an irradiation time of 60 seconds, the results are not limited to these parameters. They have been corroborated by experiments with other solutions in which the conductivity has been selectively Varied, and -by tests with paints of different conductivities.

With regard to the type of electromagnetic structure which may be employed, satisfactory results have been achieved 'with simple radiating structures, such as horns or the like. In accordance with one aspect of the present invention, however, it has been determined that opensided nonradiating slow-wave structures having a fringing field which extends significantly from the slow-wave structure may advantageously be employed. As discussed above, such structures transfer power to lossy material within the fringing field, but do not radiate any substantial amounts of power if no lossy material is present.

It is recognized that closed microwave irradiation structures, such as ovens, have been employed heretofore for irradiation purposes, Similiarly, radiating slow-wave structures with shields to confine and direct microwave energy into an object to be irradiated are known in the art. The preferred slow-wave structures of the present invention, however, distinguish from these known microwave heating devices by the use of nonradiating structures which are open on one side and which have a fringing field which does not radiate except when there is lossy material in immediate proximity to the slow-Wave structure. To indicate the properties of the slow-wave structure disclosed herein, the device of FIGS. 1 through 3 has a width of approximately 3.7 inches and a depth of approximately 3.4 inches and is approximately 22 inches long. The foregoing gures relate to inside dimensions. In the absence of lossy material within two or three inches from the open face of the slow-wave structure, the total loss through the device is less than 0.25 decibel, when the device is energized at the 915 megacycles per second frequency. The loss through the slowwave structure increases up to nearly 100 percent when a sheet of lossy material, such as a plastic loaded with carbon or other lossy particles, is placed directly over the open surface of the slow-wave structure. In one test, substantially 100 percent loss was obtained using a lossy sheet having a thickness of 0.032 inch, of a material known as Synthane. When a 6-inch circle of filter paper 0.007 inch thick, soaked with denatured alcohol was placed on the plastic cover over the open side of the slow-wave structure, the loss was approximately 60 percent. When the strip of Synthane was moved back to a distance of approximately one inch from the surface of the slow-wave structure, the loss dropped to approximately 64 percent energy absorption. It appears that the energy absorption drops off in accordance with a relatively high power, such as the cube, of the distance between the lossy lm and the surface of the slow-wave structure.

With regard to the frequency range in which the present devices are operative, it has been noted above that the lower microwave frequencies are preferred for applications such as the drying of paint on streets because the slow-wave structure must be given road clearance of an inch or so, and the fringing field extends further from the larger types of slow-wave structure which are characteristically employed at the lower microwave frequencies. In manufacturing processes, where smaller areas are to be dried, closer approaches are permitted; a conveyor belt could be moved past a slow-wave structure within a fraction of an inch of the open side of the slowwave structure. Under these conditions7 higher microwave frequencies may be used. With regard to a lower frequency limit, slow-wave microwave structures become exceedingly large at frequencies below 200 or 300 megacycles; accordingly, slow-wave structures would not normally be employed to implement the invention at frequencies below this range.

In the present specification and claims, the term liquid is employed in a broad sense to encompass solutions, suspensions, pastes, and other similar materials which change properties with microwave irradiation. It is further noted that the liquid films or layers may be on the surface of or impregnated into solid or porous material.

It is to be understood that the above-described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements Within the scope of the invention may be devised by those skilled in the art. Thus, by way of example and not of limitation, other forms of open nonradiating slow-wave structures with fringing fields may be employed, other types of materials, such as adhesives, plastics, or plastic powder, may be dried, melted and/or cured, or irradiated, instead of paint, and the moist films or material requiring irradiation may be moved past the slow-wave structure rather than vice versa.

What is claimed is:

1. In an apparatus for painting stripes on highways,

the combination comprising:

paint having a conductivity of at least 5 millimhos per centimeter;

infrared heating means for drying the highway prior to paint application;

paint applicator means vfor applying said paint to a highway;

a slow-wave structure in the form of a split folded waveguide having one side open, means for blowing air out the open side of said structure, and flexible conductive means extending from said structure around its open side to reduce undesired microwave energy radiation;

a source of microwave energy coupled to one end of said slow-wave structure;

a dummy load connected to the other end of said slowwave structure;

wheeled vehicular means `for supporting said infrared heating means, said paint applicator and said slowwave structure for the successive transit of said infrared heating means, said paint applicator, and said slow-wave structure over highway areas to paint said areas, said slow-wave structure being supported with the open side facing the highway and at angles both with the plane of the highway and the direction of travel of the slow-wave structure;

means for sensing departures from optimum energy absorption conditions in said apparatus; and

means for changing microwave energy levels in the apparatus in response to indications from said sensing means.

2. In an apparatus for painting stripes of paint on highways, the combination comprising:

infrared heating means for drying the highway prior to paint application;

paint applicator means for applying said paint to a highway;

a slow-wave structure -in the form of a split folded waveguide having one side open, means for blowing air out the open side of said structure, and flexible conductive means extending from said structure around its open side to reduce undesired microwave energy radiation;

a source of microwave energy coupled to one end of said slow-wave structure;

a dummy load connected to the other end of said slowwave structure; and

wheeled vehicular means for supporting said infrared heating means, said paint applicator and said slowwave structure for the successive transit of said infrared heating means, said paint applicator7 and said slow-wave structure over highway areas to paint 9 10 said areas, said slow-wave structure being supported a dummy load connected to the other end of said slowwith the open side facing the highway and at angles wave structure; both with the plane of the highway and the direction Wheeled vehicular means for supporting said paint apof travel of the slow-wave structure. plicator and said slow-wave structure for the succes- 3. yIn an apparatus for painting stripes of paint on sive transit of said paint applicator and said slowhighways, the combination comprising: wave structure over highway areas to paint said infrared heating means for drying the highway prior areas, said slow-Wave structure being supported with to paint application; the open side facing the highway and at angles `both paint applicator means for applying said paint to a with the plane of the highway and the direction of highway; 10 travel of the slow-wave structure; a waveguide structure having one side open, and means means for sensing departures from optimum energy for blowing air out the open side of said structure; absorption conditions in said apparatus; and a source of microwave energy coupled to one end of means for changing microwave energy levels in the said waveguide structure; apparatus in response to indications for said sending a dummy load connected to the other end of said means,

waveguide structure; and References Cited Wheeled vehicular means for supporting said infrared UNITED STATES PATENTS heatlng means, sald palnt applicator and sald waveguide structure for the successive transit of said 2,560,903 7/ 1951 Stiefel 219-1055 infrared heating means, said paint applicator, and 2,940,105 6/ 1960 WoellWarth 94-44X said waveguide structure over highway areas to paint 2,942,142 6/ 1960 Dench S33-31 X said areas, said waveguide structure being supported 3,018,704 1/ 1962 Searlght 94--44 with the open side facing the highway and at angles 3,056,877 10/ 1962 Schrnldt et al. 219-1055 X both with the plane of the highway and the direction 3,182,165 5/ 1965 Van Der Helm 2l9-10.55 of travel of the slow-wave structure. 2,676,416 lf/1954*l CalOSl et al. 2l9-10.61X 4. In an apparatus for painting stripes of paint on 2,868,939 1/ 1959 Pound 219-10.55 highways, the combination comprising: 3,058,840 10/ 1962 Kerr et al 118-620 X paint applicator means for applying said paint to a 3,216,849 11/ 1965 Jacobs 117-9331 highway; a slow-wave structure Iin the form of a split folded PC REIGN PATENTS waveguide having one side open, means for blowing 718,511 11/1954 Great Brltam.

air out the open side of said structure, and flexible a :u conductive means extending from said structure WALTER A' SCHEEL l Hmmy Exmunel around its open side to reduce undesired microwave JOHN P. MClNTOSl-l, Assistant Examiner energy radiation; a source of microwave energy coupled to one end of U.S. C1. X.R.

said slow-wave structure; 11S-6 3, 305, 64?