CONFORMABLE MAGNETIC ARTICLES UNDERLAID BENEATH TRAFFIC-BEARING SURFACES

Abstract: A conformable magnetic article (300) for underlayment beneath a traffic-bearing surface which sends a magnetic signal to a sensor travelling over the traffic-bearing structure. The magnetic article comprises at least one conformable magnetic layer (2) comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through the traffic-bearing structure to a sensor.

Description: Conformable Magnetic Articles Underlaid Beneath Traffic-Bearing Surfaces 1. Field of the Invention The present invention relates to the field of magnetic articles, in particular, to articles which may be underlaid beneath a traffic-bearing surface such as a roadway, warehouse floor, and the like, to guide a vehicle or other mobile object thereon. 2. Background of the Invention Safer, more efficient and more accessible transit for citizens is a high priority for many governments. Public service workers, public transit vehicles and emergency vehicles must have the capability to move more rapidly and safely on roadways in a variety of weather conditions. Inclement weather and even blinding sunlight or oncoming traffic light present special problems both for existing travel systems and for guidance systems that offer lateral vehicle control. An unfortunate number of tragic accidents have occurred due to people driving under the influence of alcohol and over-the-counter medicines. Snowy conditions, fog, heavy rain, blowing dust and smoke are examples of challenges to vehicle drivers. Snowy weather presents particularly challenging driving conditions to snowplow drivers trying to clear lanes in blowing snow or when lane markers are obstructed by snow. Furthermore, reduced visibility brought by blowing snow has caused numerous tragic accidents when automobile drivers have rear-ended snowplows traveling slower than surrounding traffic. Winter weather will continue to challenge any intelligent transportation system (ITS) in which vehicles move at faster speeds and closer together on more crowded roadways. A magnetic, lateral guidance system addresses the special needs of drivers who cannot, for whatever reason, see the road. In addition to vehicles, other mobile objects such as farm animals, pets, fire fighters, visually impaired pedestrians, and the like may also benefit from control and/or guidance systems. Mobile robots equipped with magnetic sensors may be guided and/or controlled as they move on their path, for example, along an industrial assembly line. Perimeter and boundary awareness systems are needed in specific instances. Two examples include warnings of hazardous conditions in the environment and pet containment systems. Games frequently require defined boundaries, such as foul territory in baseball and out of bounds in soccer, and it is frequently desired that toys and sporting equipment emit audible signals when crossing a designated line. Several alternative methods for sensing the lateral position of a vehicle on a roadway are known. One option involves the use of visible signs or markings and optical sensors. However, a system which relies on optical sensors may have reliability problems. The signs or markings can be obscured by dirt, ice, or snow, and visibility can be impaired by fog, blowing snow, blowing dust, and the like. Furthermore, for night usage, a considerable amount of energy is expended, either to illuminate the signs or to emit a beam from the sensor. Another approach is the use of radar reflective markers with a radar ranging system on the vehicle. Both the markers and the radar detection systems are expensive in comparison with the magnetic system proposed herein. In addition, metallic radar reflective markers embedded in the roadway are likely to have durability and corrosion problems. A magnetic system offers several advantages: — it is not adversely affected by weather conditions; — it does not require expensive video or other radio frequency equipment; — the system's operating costs remain low since the marker is passive; no power is required to make a magnetic marker function; and the system's durability means that, once installed, a magnetic marker will likely last the life ofthe roadway (typical roadways have life spans of six to eight years) and may even be reprogrammed while still a part ofthe roadway. Known magnetic marking systems include using a series of magnetic "nails" embedded in the roadway. Because the field strength decreases as the cube ofthe distance from such a dipolar magnetic field source, the "nails" would have to be fairly closely spaced to produce a useful signal. Material costs would be high if the most powerful rare earth magnets were used to rnmimize the size and maximize the spacing. Boring holes in the roadway and using rigid nails may also lead to stress concentration and premature pavement failure, which may be exacerbated by corrosion of nails. The use of simple ferrous metal spikes would not provide the alternating signal desirable for effectively separating the position signal from noise. Another magnetic marking system employs a magnetic paint to produce magnetic stripes on the roadway. The paint stripe can be magnetized only after it had dried. With the typical thickness of paint layers, a sufficiently strong magnetic signal is difficult to obtain. However, if the thickness ofthe paint is built up to obtain a good magnetic signal, the paint durability would be poor. A specially designed magnetizing fixture would have to be driven along the strip. Because of limitations in the magnetic field produced by such a fixture, the coercivity ofthe magnetic material would likely be limited to about 1000 oersteds, making it susceptible to erasure, and anything other than a longitudinal magnetization pattern would be difficult to produce. Magnetic guidance systems ofthe prior art have been embedded within a roadway. One such system is disclosed in U.S. Patent No. 3,609,678. The polymer-based magnetic materials disclosed are resilient and flexible, such as nitrile and silicone rubber, and plasticized PVC. Resilient refers to recovering to substantially the original shape after removal of a deformation force. The '678 patent discloses, in one embodiment, a polymeric magnetic tape or sheet that is "either inserted edgewise in a narrow channel or slot or laid flat in a more shallow channel cut in the roadway." (col. 3, lines 4-6). This patent further states that magnets may also be embedded within the pavement ofthe roadway instead of in an open channel, (col. 3, lines 31-32). A flux sensor is mounted on a vehicle that travels over the roadway, and the sensor can generate an electric signal in response to the magnetic medium if the magnetic field is sufficiently strong to be sensed. The '678 patent discloses that the intensity ofthe magnetic field at the surface ofthe roadway should be at least 2 gauss, preferably at least 10 gauss, and more preferably at least 100 gauss, to provide a strong signal even when road conditions are less than optimal, (col. 4, line 75 through col. 5, line 6). Although it has its own utility, the system disclosed in the '678 patent may not be desirable because it relates specifically to embedding a magnetic medium in an existing road. That is, this patent discloses cutting a slot, hole, or other aperture in an existing road, inserting a magnet or plurality of magnets in a resilient material within the aperture, and then sealing the aperture to protect the magnets. Conventional conformable non-magnetic pavement marking sheet materials are known in the art and typically comprise a polymeric material, such as one that could be crosslinked to form an elastomer, but which is not crosslinked in the sheet material and thereby provides desired viscoelastic properties. Conformable refers to being capable of being deformed under a loading force and retaining a substantial part of that deformation after removal of a loading force. Illustrative examples of conformable non-magnetic pavement markings include U.S. Patent No. 4,490,432, U.S. Patent No. 5,316,406, U.S. Patent No. 4,069,281, and U.S. Patent No. 5, 194,113. None ofthe above disclosures describe the use of magnetic particles in a conformance layer or underlaying a conformable magnetic article beneath a traffic- bearing surface. 3. Summary of the Invention The conformable magnetic articles ofthe present invention are underlaid beneath a traffic-bearing surface and are used as a part of an underlaid magnetic guidance system. The guidance system is defined herein as providing information to a vehicle driver or to another mobile object or system and/or controlling a vehicle or mobile object. The magnetic article may be either "retro-fitted" to the traffic- bearing structure, meaning that the article is underlaid beneath an existing traffic- bearing structure, or installed concurrently with the traffic-bearing surface. Thus, the magnetic article is much less susceptible to damage by vehicular traffic traveling over the magnetic article, and in particular cannot be damaged or peeled away from the surface by the blade of a snow plow. Often when a traffic-bearing structure is being resurfaced, the pavement markings already present on the surface are removed prior to resurfacing. The pavement markings are removed in order to prevent reflection cracking ofthe pavement around the buried shape ofthe marking beneath it. This cracking is likely caused by the mismatch of thermodynamic and mechanical properties between the traffic-bearing structure material and the buried pavement marking. Traffic driving over these traffic-bearing surfaces often accelerated this cracking. Surprisingly, the traffic-bearing structures exhibit no premature cracks or damage where the articles ofthe present invention are underlaid. The present invention provides a conformable magnetic article for underlayment beneath a traffic-bearing surface which sends a magnetic signal to a sensor traveling over the traffic-bearing structure. The magnetic article comprises at least one conformable magnetic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through the traffic-bearing structure to a sensor. The article ofthe present invention is substantially inelastic. The conformable magnetic articles ofthe invention preferably comprise a conformable magnetic layer containing permanently magnetizable particles such that the magnetic particles ofthe article can be oriented to produce a magnetic field that is detectable by a sensor mounted on a vehicle. Typical article width ranges from about 1 cm to 50 cm, preferably 5 to 20 cm, and typical article thickness ranges from about 0.1 cm to about 1 cm, preferably about 0.1 to 0.2 cm, although many other article shapes are possible such as a rope, a sheet, a perforated article, etc. The shape is dictated largely by the specific use ofthe article. The inventive articles may be magnetized in a single pattern, but are preferably magnetized in a pattern to produce a readily-detectable alternating magnetic signal on the sensor. However, to convey more detailed information, the inventive articles may be magnetized ("encoded" or "written") in more complicated patterns, as found in bar codes, credit card strips, or magnetic tape recordings. Another embodiment ofthe invention is a system for guiding vehicles or mobile objects traveling on a traffic-bearing structure, comprising: a) at least one conformable magnetic article for underlaying beneath a traffic-bearing surface to send a magnetic signal to a sensor traveling over the traffic-bearing surface. The magnetic article comprises at least one conformable magnetic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through a traffic-bearing structure; and b) a sensor for passing over a traffic-bearing surface. The sensor comprises a means for detecting the magnetic signal through the traffic-bearing structure. Another embodiment ofthe present invention is a system for guiding vehicles or mobile objectes traveling on a traffic-bearing structure, comprising: (a) a traffic-bearing structure comprising at least two layers of material; (b) a conformable magnetic article underlaid beneath the top surface of said traffic-bearing surface between two of said layers, said article adapted to send a magnetic signal to a sensor traveling over the traffic-bearing surface, said magnetic article comprising at least one conformable magnetic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through a traffic-bearing structure; and (c) a sensor for passing over the traffic-bearing surface, said sensor comprising means for detecting the magnetic signal through said traffic-bearing structure. The output ofthe sensor unit(s) would optionally be a lateral offset signal. The output ofthe sensor may be used to control a vehicle and/or provide infoπnation to a driver via a display unit. A method of providing a guidance system for a traffic-bearing structure is another aspect ofthe present invention. One particularly useful application ofthe invention is in conjunction with the magnetic guidance of a snow plow. It is important for a snow plow to be properly located on the traffic-bearing structure, so that inadvertent damage to curbs, roadside signs, mailboxes, and the like can be avoided. Because lane markers can be obscured by snow or ice on a road, a snow plow driver would benefit from having a magnetic guidance system ofthe type described, such that the snow plow remains on the traffic-bearing surface. The present invention may be particularly beneficial for guiding snow plows in white-out (intense, blowing snow) conditions when visual guidance is limited. Further, being underlaid, the articles ofthe present invention are less susceptible to damage from traffic or snow plows and less susceptible to vandalism. Other useful applications include an electronic "rumble strip" that would provide warning to a driver that the vehicle was approaching the edge of a traffic- bearing structure, or a school zone, bridge deck, curve in the traffic-bearing structure, or obscure traffic-bearing structure entrance or exit, and as a component of an automated highway system in which vehicles are automatically guided in assigned lanes. Further aspects and advantages ofthe invention will become apparent from the drawing figures, description of preferred embodiments, examples, and claims. 4. Brief Description of the Drawing FIGs. 1-5 are cross-sectional views (enlarged) of five different embodiments of conformable magnetic articles in accordance with the invention; FIG. 6 is a schematic diagram of an inventive control and/or guidance system in accordance with the invention; FIG. 7 is a schematic illustration of another embodiment ofthe present invention; and FIG. 8 is a graph showing representative data in connection with the embodiment of Figure 7. These figures, which are idealized and not to scale, are intended to be merely illustrative and non-limiting. 5. Detailed Description of Illustrative Embodiments The present invention provides for conformable magnetic articles underlaid beneath a roadway or other traffic bearing structure. Underlaid is defined herein as being completely surrounded by traffic-bearing structure material. Illustrative traffic-bearing structure materials include, but are not limited to, base layer materials, asphalt, gravel, concrete, cement, brick, wood, dirt, and clay. The general concept ofthe invention is illustrated in Figure 7. In Figure 7, a tape applicator 28 having pavement marking tape 30 ofthe invention applies a layer ofthe tape 32 to the traffic-bearing structure. Traffic-bearing structure material 33 is then laid over the pavement marking tape. The tape can then be detected by a sensor 34 on a vehicle 36 which drives over the traffic-bearing surface. The conformable magnetic article comprises a layer having a permanently magnetizable material in an organic binder. This layer is characterized by a high degree of conformance to the surrounding traffic-bearing structure material and high ratio of viscous damping to elasticity. Such a layer promotes and contributes to enhanced adhesion ofthe inventive article to the surrounding surfaces. The conformability ofthe article helps accommodate for the mismatch ofthe thermodynamic and mechanical properties between the traffic-bearing structure and the article. The conformable magnetic article ofthe present invention may be held in place by one or more optional fastening means. This optional fastening means, which may be a chemical adhesive (such as a pressure-sensitive, heat-sensitive adhesive, hot-melt thermoplastic, or contact adhesive) or a mechanical fastener (such as a nail, rivet, screw, staple, tack, etc.) enhances attachment ofthe article to the surrounding surfaces. FIGs. 1-5 illustrate in cross-sectional views (enlarged) five noniimiting embodiments of conformable magnetic articles in accordance with the present invention. FIG. 1 illustrates conformable magnetic article 100, comprising a polymeric binder layer 4 having dispersed therein a plurality of magnetically orientable magnetic particles 6. The combination of organic binder 4 and magnetic particles 6 is referred to herein as magnetic layer 2. FIG. 2 represents the conformable magnetic article of FIG. 1 having an adhesive layer 8 with conformable magnetic article 200 having the same magnetic layer 2 as embodiment 100 in FIG. 1. Figures 3, 4, and 5 represent pavement marking tapes having irregular surfaces (i.e., the tapes comprise skid-resistant particles, microspheres, or both). Use of these tapes may be beneficial because of ease of manufacturing or to enhance adhesion to the surrounding surfaces. FIG. 3 represents an alternative magnetic pavement marking tape within the invention, again showing magnetic layer 2 comprising binder 4, magnetic particles 6, optional adhesive layer 8, and liner layer 10 temporarily adhered to adhesive layer 8. Embodiment 300 of FIG. 3 also illustrates a retroreflective and anti-skid layer comprised of a vinyl, epoxy, acidic olefin copolymer or polyurethane elastic support layer 12 which serves to adhere transparent microspheres 14 and irregularly shaped skid-resistant particles 16 to magnetic layer 2. These microsphere and skid-resistant particles may be placed on all sides of the article. In the illustrated embodiment 300, transparent microspheres 14 or other particles by providing a surface irregularity may prevent the article from sliding around within the traffic-bearing structure. Support layer 12 is less thick but generally less inelastic than magnetic layer 2. Thus, despite the inelastic deformable nature ofthe magnetic layer underlying the support layer and despite the very thin nature ofthe support layer, the support layer does not override the desired inelastic deformation properties of the magnetic layer that account for superior durability, and the support layer nevertheless supports the microspheres at the top ofthe article. In exemplary embodiments the thickness of magnetic layer 2 is at least about Vi millimeter, more preferably at least about 1 millimeter, but preferably less than 3 millimeters. When microspheres are pressed at normal room temperature into a sample of support layer 12 laid on a hard unyielding surface with a pressure that would embed microspheres into magnetic layer 2, the microspheres do not become embedded but remain on the surface of support layer 12 after the pressure has been released. In addition, support layer 12 has good adhesion to retroreflective elements or other particulate matter to be embedded in it, which assists in holding such particles against penetration into the magnetic layer, and possibly orienting magnetic particles 6 in an undesired direction. Vinyl-based polymers (polymers that include at least 50 weight percent polymerized vinyl monomer units) may be particularly useful materials for layer 12 because of their toughness and durability in a highway environment. Further, vinyl-based polymers tend to be abrasion resistant which may aid in securing the article within the traffic-bearing surface. Support layers based on vinyl polymers are typically plasticized to provide desired flexibility. Other support layer materials can be polyurethanes, acid containing olefin copolymers or other such materials known in the art. FIG. 4 illustrates an enlarged cross-sectional view of embodiment 400 of a conformable magnetic pavement-marking tape in accordance with the present invention. Embodiment 400 is essentially identical to that of embodiment 300 of FIG. 3 except that the adhesive layer 18 comprises a woven or nonwoven fibrous web 21 embedded in and impregnated by the adhesive layer. A stratum 20 ofthe adhesive layer illustrated in FIG. 4 is disposed between magnetic layer 2 and fibrous web 21, and another stratum 22 of adhesive is disposed on the side ofthe web opposite from magnetic layer 2 forming the exterior bottom surface ofthe inventive tape, although there is no requirement that any adhesive be between web 21 and magnetic layer 2. A liner material (not illustrated) may be included on adhesive layer 18 opposite magnetic layer 2. The fibrous web is preferably contained in the adhesive layer and is sufficiently porous and the fibers sufficiently separated so that the adhesive can saturate, i.e., surround individual fibers ofthe web. The fibrous web, if employed, may provide reinforcement or support for the conformance layer. Tape embodiment 400, with the fibrous web present, has a tensile strength of at least 0.5 kilogram per centimeter width, and preferably at least 1 kilogram per centimeter width. Despite good tensile strength, the residual force exhibited by all articles ofthe invention should be low so as to allow it to remain in good conformity to the irregularities ofthe traffic-bearing structure layers. This residual force is typically described as creep recovery in penetration mode, as further explained herein. Although the residual force properties just described characterize article embodiment 400, preferably the reinforcing web itself exhibits such properties independent ofthe other parts of article 400. In preparing articles ofthe invention which include a fibrous web in an adhesive layer, the fibrous web is typically impregnated with a liquid version ofthe adhesive (100% solids or less) for example by passing the web through knife coater. Sufficient adhesive may be applied to the reinforcing web in this manner so that it may be adhered to a magnetic layer; or the magnetic layer may be covered with a layer of adhesive prior to application ofthe impregnated web, and added adhesive can be applied to form the bottom portion ofthe adhesive layer. FIG. 5 illustrates an enlarged cross-sectional view of embodiment 600, which is an alternate magnetic marking embodiment ofthe invention. Skid particles are adhered only on the side surfaces and a portion ofthe top surface ofthe protuberances using an organic binder 26, such as a thermoplastic or thermosetting "particle-bond" material. One such binder is a vinyl-based thermoplastic resin including a pigment, as described in U.S. Patent No. 4, 117, 192. Other suitable particle-bond materials include two-part polyurethanes formed by reacting polycaprolactone diols and triols with derivatives of hexamethylene diisocyanate; epoxy based resins described in U.S. Patent Nos. 4,248,932; 3,436,359; and 3,580,887; blocked polyurethane compositions as described in U.S. Patent No. 4,530,859; and polyurethane compositions comprised of a moisture-activated curing agent (e.g., an oxazolidine ring) and a polyisocyanate prepolymer. Magnetic particles 6 are present in layer 2 as in the other embodiments ofthe invention. The protuberances are generally at least about one millimeter in height, with about one millimeter spacing. The conformable articles ofthe present invention may have non- conformable portions with or without magnetic particles. Binder Materials The articles ofthe invention have a plurality of magnetic particles in a binder which form a conformable magnetic layer. A sufficient amount of magnetic particles are present to provide a magnetic signal through the traffic-bearing structure to a sensor. Typically magnetic particles are non-spherical. In some organic binder embodiments, for example when the organic binder comprises non-crosslinked elastomeric precursors (see for example U.S. Patent No. 4,490,432), traditional rubber processing methods preferably are used to produce the conformable magnetic layer. Typically and preferably, compounding is performed in some type of heavy duty, batch or continuous, rubber kneading machine, such as a Banbury mixer or twin screw extruder. The conformable magnetic layer may be formed by calendering between heavy rolls and then slitting to the desired width, directly by extrusion through a die, or by a combination of such methods. If the extruded material is semi-liquid as it leaves the die, the desired magnetic orientation ofthe magnetic particles may be produced by exposure to a permanent magnet or electromagnet at the exit ofthe die. Mechanical working, such as that which occurs during extrusion or calendering, and/or externally applied fields will promote orientation. Orientation enables one to obtain desired magnetic performance. Other methods of preparation and orientation will be apparent to one skilled in the art. "Elastomer precursor" is used herein to describe a polymer which can be crosslinked, vulcanized, or cured to form an elastomer. An "elastomer" is a material that can be stretched, to at least about twice its original dimensions without rupture and upon release ofthe stretching force rapidly returns to substantially its original dimensions. Illustrative examples of useful elastomer precursors include acrylonitrile-butadiene polymers, neoprene, polyacrylates, natural rubber, and styrene-butadiene polymers. Extender resins, preferably halogenated polymers such as chlorinated paraffins, but also hydrocarbon resins, polystyrenes or polycyclodienes, are preferably included with the non-crosslinked elastomer precursor ingredients, and are miscible with, or form a single phase with, the elastomer precursor ingredients. The extender resins preferably account for at least 20 weight ofthe organic components in a conformable layer when using this binder. Useful thermoplastic reinforcing polymers are known in the pavement marking art (e.g., polyolefins, vinyl copolymers, polyethers, polyacrylates, styrene- acrylonitrile copolymers, polyesters, polyurethanes and cellulose derivatives). In other embodiments ofthe invention, the conformance layer has two primary components: a ductile thermoplastic polymer and a nonreinforcing magnetic mineral particulate. Preferably, the thermoplastic polymer is a polyolefin. These binders are described generally in U.S. Patent No. 5,194,113. Another embodiment ofthe present invention may utilize a conformability layer comprising microporous thermoplastic polymer. Non-magnetic fillers and extenders may be used as desired. Conformability Tests The desired conformance properties of a material can be indicated by a penetration creep-recovery test (see generally U.S. Patent No. 5, 127,973). In this test, which is based on isothermal thermomechanical analysis, a probe is placed in contact with a sample ofthe material to be tested, a load placed on the probe, and penetration of the probe into the sample monitored. After a time, the load is removed from the probe and the probe position monitored as the sample is allowed to recover. Testing is typically carried out in a helium atmosphere using a thermomechanical analyzer module controlled by a temperature programmer, such as a Perkin Elmer TMS-1 thermomechanical analyzer controlled by a Perkin Elmer DSC-2 temperature programmer. The flat-point penetration probe assembly is used, with the probe tip diameter specified (typically 1 millimeter with the Perkin Elmer equipment). Samples ofthe materials to be tested have a thickness of approximately 0.8 millimeter and an area of approximately 3 -millimeter-by-3 -millimeter. The sample is transfened to a small aluminum pan and placed on the sample platform ofthe thermomechanical analyzer. A load of one gram is placed on the probe and the probe released and allowed to fall onto the sample. After about 3 to 5 seconds of contact with the sample, the one gram load is removed and the sample allowed to relax. This results in the probe tip resting on the sample in a zero-loading condition. The temperature control chamber ofthe thermomechanical analyzer is raised to surround the sample platform and bring the sample to thermal equilibrium at the desired temperature of the test (generally about room temperature or up to 30°C). The sample is allowed to equilibrate at the test temperature for approximately five minutes with the probe still in contact with the sample surface in a zero-loading condition. Data acquisition ofthe probe position is then begun with the probe still under a load of zero to establish the zero-load baseline. After a short time, approximately 20 seconds, a mass of 20 grams is placed on the probe and the probe deflection monitored as it penetrates into the sample. The load is allowed to remain on the sample for two minutes, after which the 20-gram mass is removed from the probe to again attain a zero-load condition for the recovery step ofthe test. Sample recovery is monitored for at least two more minutes. The amount of penetration two minutes after the load was applied and the percentage of recovery two minutes after the load is removed are measured from creep-recovery data traces obtained in the experiment. When performing the above test, a probe having a diameter of 1 millimeter generally penetrates at least 0.05 millimeter, and preferably penetrates at least 0.08 millimeter into useful conformance layers. The top layer in some embodiments of the invention undergoes a penetration of less than 0.05 millimeter in the described test. To minimize the elastic recovery which would loosen sheet material from the surrounding surfaces ofthe traffic-bearing surface, the conformable layer should recover after removal ofthe load no more than 65 percent ofthe distance to which the probe has penetrated, and preferably no more than 50 percent ofthe penetrated distance. Consistent with the properties of conformability discussed above, the conformable layer is preferably a stretchable or flowable material. For example, the conformable layer is preferably capable of being stretched at least 50 percent before break at a strain rate of 0.05 second '1 for a 1 cm wide sample. Another test which may be used to indicate conformability is inelastic deformation. For example, articles having a layer characterized by exhibiting, when tested using standard tensile strength testing apparatus, at least 25% inelastic deformation (ID) after being stretched once to 115% ofthe original sample length have sufficient conformance. In a broader sense, one may use a layer characterized by at least 25% (ID) after being stretched to 115% of its original length in sheet construction, although the whole article may exhibit less ID. See for example U.S. Patent Number 5,082,715. Inelastic deformation may be tested using the following method. A test strip (standard strip size for tensile strength testing) is pulled in a tensile strength apparatus (at, for example, a rate of 300%/minute), until it has stretched some predetermined amount, e.g., 15%. The deformation is reversed, causing a decrease in tensile stress to zero. On repeated tensile deformation, no force is observed until the sample is again taut. The strain at which force is first observed on a second pull is a measure of how much ofthe first deformation was permanent. This strain divided by the first (e.g., 15%) deformation is defined as the inelastic deformation QD). A perfectly elastic material or rubber would have a 0% ID. Conformable materials useful in the present invention combine low stress of deformation and ID greater than 25%, preferably greater than 35%, more preferably greater than 50%. As a more simple test, and with experience, one skilled in the pavement marking art can generally determine if a particular sample of a conformance layer material will exhibit the desired creep recovery and inelasticity characteristics by simply handling the sample and probing it with a finger. Such "hand" characteristics are often employed in day-to-day testing. Magnetic Particles The most likely choice of magnetic material is a composite of particles of a permanent magnetic material dispersed in a matrix of an organic binder. Many types of magnetic particles capable of being remanently magnetized are known to those familiar with the magnetic materials art. The major axis length of such particles (defined as the maximum length in any direction) suitable for use in this invention ranges from about 1 millimeter down to about 10 nanometers. The preferred range is from about 200 micrometers down to about 0.1 micrometer. The saturation magnetization ofthe magnetic particles can range from about 10 to about 250 emu/g (electromagnetic units/gram), and is preferably greater than 50 emu/g. The coercivity of such particles can range from about 100 to about 20,000 oersteds, more preferably ranging from about 200 to about 5000 oersteds. Particles with coercivities less than about 200 oersteds are too easily accidentally demagnetized, while particles with coercivities greater than 5000 oersteds require relatively expensive equipment to magnetize fully. The article ofthe present invention may comprise sections of alternating polarity along the length ofthe article. One class of high-performance permanent magnet particles are the rare earth-metal alloy type materials. Examples ofthe incorporation of such particles into a polymeric binder include U.S. Patent No. 4,497,722, which describes the use of samarium-cobalt alloy particles, and European Patent Application No. 260,870, which describes the use of neodymium-iron-boron alloy particles. Such particles are not the most preferred for this application, because the alloys are relatively costly; the alloys may experience excessive corrosion under conditions of prolonged outdoor exposure; and the coercivity of such alloys is typically greater than 5000 oersteds. Many other types of metal or metal-alloy permanent magnet particles could be used, but are not the most preferred. They include Alnico (aluminum-nickel- cobalt-iron alloy), iron, iron-carbon, iron-cobalt, iron-cobalt-chromium, iron-cobalt- molybdenum, iron-cobalt-vanadium, copper-nickel-iron, manganese-bismuth, manganese-aluminum, and cobalt-platinum alloys. The most preferred magnetic materials are ofthe class of stable magnetic oxide materials known as the magnetic ferrites. One particularly preferred material is the hexagonal phase ofthe magnetoplumbite structure commonly known as barium hexaferrite, which is generally produced as flat hexagonal platelets. Strontium and lead can substitute in part or completely for the barium, and many other elements can partially substitute for the iron. Thus strontium hexaferrite is also a preferred material. Another class of preferred materials is the cubic ferrites, which are sometimes produced as cubic particles, but more often as elongated needle-like, or acicular, particles. Examples include magnetite (Fe^), magnemite or gamma ferric oxide (gamma-Fe O 3 ), intermediates of these two compounds, and cobalt-substituted modifications ofthe two compounds or of their intermediates. All of these magnetic ferrites are produced in large quantities at relatively low cost and are stable under conditions of prolonged outdoor exposure. Their coercivities fall in the most preferred range of 200 to 5000 oersteds. Chromium dioxide is another alternate material which may be useful as a magnetic particle in the invention due to its low Curie temperature, which facilitates thermoremanent magnetization methods. The magnetic particles are generally dispersed in the polymeric matrix at a high loading. The magnetic particles constitute at least 1 volume percent ofthe magnetic layer, while it is difficult to include particles in an amount constituting more than about 75 volume percent ofthe material. Preferably, the conformable magnetic article has a binder comprising at least 30 volume percent of magnetic particles. A preferred loading range would be about 30 to 60 volume percent, more preferably from about 45 to about 55 volume percent. To obtain the highest remanent magnetization, the particles preferably are substantially domain-size, anisotropic particles, and there preferably is substantially parallel alignment of prefeπed magnetic axes of a sufficient number ofthe particles so as to make the magnet material itself anisotropic. Ferrites, especially barium, lead, and strontium ferrites, generally in a roughly plate-like form having preferred magnetic axes peφendicular to the general planes ofthe plates, are preferred as the particulate materials. However, other materials having permanent magnetic properties, such as iron oxide particles or such as particles of manganese-bismuth or iron protected against oxidation, can also be used. As is known in the art and referred to above, the orientation ofthe magnetic particles may be optimized by physically orienting (e.g. calendering) the particles. For an exemplary magnetic article having a width of approximately 10 cm, and an average magnetic thickness layer of about 0.1 cm, the magnetic field is about 10 gauss at the surface ofthe article, 5 gauss at a distance of about 5 cm, 2 gauss at a distance of about 10 cm, and 1 gauss at a distance of about 15 cm. Thus, if the tape were underlaid about 10 cm beneath a traffic-bearing surface, the magnetic field strength at the traffic-bearing surface would be approximately 2 gauss, which is believed to be sufficient to be detected by a sensor. Of course, stronger or weaker magnetic fields may also be produced by the magnetic article, depending on the materials and processes used to make the article. The magnetic article may also be provided with protuberances or other topographical features that aid in preventing the article from shifting within the traffic-bearing structure after it has been underlaid. In yet another embodiment of an underlaid magnetic article, the article includes a longitudinally extending tape or strip, in which a multitude of perforations have been formed along the length ofthe tape. The perforations could allow flow ofthe traffic-bearing structure material through the strip, providing even greater mechanical anchorage within the traffic- bearing structure itself. In this way, the possibility of flexure and cracking in the traffic-bearing structure may be reduced. Installation Methods The magnetic articles ofthe present invention may be underlaid beneath an existing traffic-bearing surface or within a new traffic-bearing surface. The conformability feature ofthe inventive magnetic article is particularly useful when the article is retrofitted to a traffic-bearing structure. In such applications, a portion of an existing traffic-bearing structure is typically ground or cut away, and the debris removed. The exposed seαion ofthe traffic-bearing structure often is not smooth, and thus the conformability ofthe magnetic article of the present invention enables the article to bond more securely to the bottom surface ofthe exposed section. The exposed section may then be potted, or filled, with a patching material, and the magnetic article is thus underlaid beneath the traffic-bearing surface. Inelasticity is an important feature because traffic-bearing structure, and particularly asphalt cement concrete (commonly known as blacktop, or asphalt), transmit forces applied by vehicles to any object embedded in the traffic-bearing structure. If an embedded article is elastic relative to the traffic- bearing structure material, the traffic-bearing structure may flex and bounce back toward an applied force, and ultimately crack or break apart, which is manifestly undesirable. Thus, an irreversibly deformable magnetic article is desirable in the context of this and other embodiments. A preferred method of underlaying the article, however, is in conjunction with new traffic-bearing structure construction. Traffic-bearing structures are typically constructed by laying several courses or layers of materials atop each other. For example, a typical asphalt road construction typically includes a crushed rock undercourse on top of which three or four layers of various grades of asphalt may be applied. The asphalt layers may be on the order of about 2 to 20 cm thick, and thus the finished traffic-bearing structure is a composite, or laminate, comprising the various layers. In the preferred embodiment ofthe method of underlaying a magnetic article beneath a traffic-bearing structure, the magnetic article is applied in a continuous strip in a desired location on the penultimate layer ofthe traffic-bearing structure, such that the final layer ofthe traffic-bearing surface covers both the penultimate layer and the magnetic article. Thus, the magnetic article is underlaid beneath the traffic-bearing surface and protected from vehicular traffic, and yet is sufficiently close to the finished surface ofthe traffic-bearing surface to permit detection ofthe magnetic signals by a sensor mounted on a vehicle. Although it is prefeπed to underlay the magnetic article beneath only one layer of a multi-layer traffic-bearing structure, the article may be underlaid at any depth within the traffic-bearing structure, under any number of layers ofthe traffic- bearing structure, subject only to the ability of a sensor to receive a magnetic signal from the article. The magnetic article may also be underlaid beneath a traffic-bearing surface by providing a base (herein defined as any components the traffic-bearing structure below the traffic-bearing surface layer) for the traffic-bearing structure, positioning the article at a location on or above a portion ofthe base, and then applying a paving material such as Portland cement concrete (commonly known as concrete) over the article and the base. Thus, the article is suspended within the traffic- bearing structure, rather than lying completely under it, although the latter is also possible. The magnetic article may also underlie a gravel road, either by plowing a trench in an existing gravel road and placing the article under the finished surface of the traffic-bearing structure, or by installing the article on the undercourse of a new gravel road prior to the application ofthe final layer(s) of that traffic-bearing structure. In another embodiment, paver bricks may be used as the traffic-bearing structure material and be laid over the prepared baselayer . The continuous magnetic article ofthe present invention may be applied to the traffic-bearing structure either manually, or by a machine. The machine may travel ahead of a paving machine, or may be mounted at the leading end ofthe paving machine, such that the continuous magnetic article is applied to the traffic- bearing structure at some time prior to the application ofthe final layer or layers of the traffic-bearing structure. The magnetic articles ofthe present invention may be installed as part of a traffic-bearing structure using any one of a variety of apparatus, such as human pushable dispensers, "behind a truck" types of dispensers, and "built into a truck" types of dispensers. For example, U.S. Patent No. 4,030,958 discloses a suitable behind a truck type dispenser for applying the articles ofthe invention in the form of adhesive-backed tapes to a surface and U.S. Patent No. 4,623,280 discloses a manual-tape applicator. Following application ofthe conformable magnetic article to the desired surface, a further layer ofthe traffic-bearing structure material is applied to underlay the article beneath the top surface ofthe traffic-bearing structure. The conformable magnetic articles ofthe present invention may be underlaid at various depths. Other means may be used to install the articles ofthe invention, such as simple manual application or the previously mentioned mechanical fasteners. Guidance Systems The invention also provides a system for guiding vehicles or mobile objects traveling on a roadway, through a warehouse, and the like. The primary components ofthe systems ofthe invention are the conformable magnetic articles underlaid beneath a traffic-bearing surface ofthe invention, and a system to detect the magnetic field from the article. A typical sensor system includes a sensor device and a guidance device. A typical lateral position indicator system ofthe invention suitable for use in guiding a human operated vehicle is illustrated in FIG. 6. The inventive magnetic article also is unpowered, meaning that it does not require an outside power source either to send or receive a signal. In this regard, the present invention is distinguishable from powered embedded articles such as those that are typically used to determine whether a vehicle on a roadway is stopped at an intersection, such as at a red light. Embedded sensors of this type are further distinguishable from the present invention in that the former requires electrical power, whereas the latter is an unpowered magnetic field source. The unpowered magnetic article ofthe present invention also requires less installation time and less maintenance, costs nothing to operate, and may be used in remote locations where a power supply is not readily available. Thus, the unpowered magnetic article of this invention provides several advantages over conventional embedded powered articles. Sensors A number of sensors and transducers are available to convert the magnetic signal from the articles ofthe invention into an electrical signal suitable for further processing. Illustrative examples of such sensors include flux-gate magnetometers, Hall effeα sensors, and solid-state magnetoresistive (MR) sensors. A potential problem exists in distinguishing the guidance signal from magnetic "noise" produced by steel reinforcing bars, other vehicles, and the like. If the inventive article is magnetized in a regular alternating pattern or in some "unique" pattern, the magnetic signal will then be periodic with a frequency proportional to the vehicle's speed. Modern signal processing techniques can then be used to extract the signal at a known frequency from the noise. The sensor is mounted in a position suitable for measuring the fields produced by the underlaid tape ofthe present invention. Magnetic sensors attached to the vehicle may determine the field in one, two, or all three directions. The signal from one sensor or a mathematical combination of two or three field components may be used to compute a signal that can be related to lateral distance of a vehicle from the inventive articles. By magnetizing the strip in a more complicated pattern, additional information can be encoded. For example, information about the direction and radius of an upcoming curve in the road or about the slope of an approaching upgrade or downgrade could be used for feed-forward control ofthe lateral position and speed ofthe vehicle. As part of a vehicle navigation system, location codes could be given. Indicating Means Illustrative examples of indicating means include at least one horn, gauge, whistle, eleαrical stimulation, LCD, CRT, light, combination of these, and the like. One or more indicating means may be desired in a particular situation. Guidance Means An eleαronic control means may be used as a guidance means in the present invention. 7. Examples The articles and systems ofthe invention are further explained with relation to the following examples, wherein all parts and percentages are by weight, unless otherwise specified. Table of Components The following materials were used in the examples. Component Description Available From ParacrilW ft F medium acrylonitrile content Uniroyal Chemical Co., nitrile rubber Akron, Ohio Chlorez™ 700S solid chlorinated paraffin Dover Chemical Corp., Dover, Ohio Paroil 140 LV a liquid chlorinated paraffin Dover Chemical Corp., Dover, Ohio Stearic Acid process aid Humko Chemical Division of Witco Chemical Corp., Memphis, Tennessee Vanstay™ SC "chelating agent" type R.T. Vanderbilt Company, Inc. stabilizer Norwalk, Connecticut Santowhite™ Crystals antioxidant Monsanto Chemical Co., St. Louis, Missouri PE Minifiber 13038F high density polyethylene Mini Fibers, Inc., fiber Johnson City, Tennessee PET 6-3025 fibers 1/4" x 3d. polyester fiber Mini Fibers, Inc., Johnson City, Tennessee Barium hexaferrite magnetic pigment Arnold Engineering Co., Norfolk, Nebraska P-235 Methyl isobutyl ketone solvent Eastman Chemical Co., Kingsport, Tennessee Zinc 2-ethylhexanoate (Hexogen Zinc Octoate) AKZO Chemie America, catalyst New Brunswick, NJ Stan-Tone™ 10 EPX03 white pigment dispersion in Harwick Chemical Corp., diglycidyl ether of Akron, Ohio bisphenol A epoxy resin Stan-Tone™ 25 EPX01 red pigment dispersion in Harwick Chemical Corp., diglycidyl ether of Akron, Ohio bisphenol A epoxy resin Stan-Tone™ 90 EPX04 black pigment dispersion in Harwick Chemical Corp., diglycidyl ether of Akron, Ohio bisphenol A epoxy resin Example 1. A conformable magnetic article ofthe invention was made by compounding the following in a Banbury-type internal mixer to thoroughly mix the ingredients. Material Snec. Grav. Parts Paracril B 0.98 100.0 Chlorez 700S 1.66 70.0 Paroil 140 LV 1.16 5.0 Stearic Acid 0.84 0.5 Vanstay SC 0.89 0.5 Santowhite Crystals 1.07 1.0 PE Minifiber 0.94 20.0 PET fiber 1.38 10.0 Barium hexaferrite P-235 5.3 950.0 Total Weight 1157 When the temperature ofthe mix reached 146°C the mix was dropped from the mixer onto a two roll rubber mill. The material was sheeted off the rubber mill and fed through a two-roll calender to yield a sheet of material having a thickness of approximately 1.4 mm. The sheet of material was embossed according to the process described in U.S. Patent No. 5,227,221 (col. 2, lines 47-65) to provide a conformable magnetic sheet having a plurality of protrusions projecting from one of its major surfaces. The embossed sheet had a thickness of about 0.5 mm in the valleys between the protrusions, and a thickness of about 1.6 mm at the protrusions. A discontinuous layer of liquid particle bond material was applied to the top and sides ofthe protrusions ofthe embossed sheet using the process described in U.S. Patent No. 5,227,221. The particle bond material was the same as the polyurethane bead bond of U.S. Patent No. 5,227,221 (col. 4, hnes 20-39), with the exception that the pigment dispersion was made with the following composition: Particle Bond Pigment Dispersion Ineredient % fbv weiehti methyl isobutyl ketone 7.04 zinc 2-ethylhexanoate 3.52 Stan-Tone 10 EPX03 41.55 Stan-Tone 25 EPX01 3.52 Stan-Tone 90 EPX04 44.37 The surface ofthe particle bond material coated protrusions was sprinkled with durable black spheroidal anti-skid particles ofthe type available from Carbo Ceramics of New Iberia, Louisiana, under the designations CARBOLITE and CARBOPROP. The particles were applied so as to partially embed them in the liquid particle bond material. The liquid particle bond material was solidified as described in U.S. Patent No. 5,227,221 by passing the sheet through an oven at a temperature of about 175°C for approximately 10 minutes of residence time. A layer of rubber resin pressure sensitive adhesive with a thickness of about 125 micrometers was laminated to the bottom side ofthe sheet. The sheet had a hand charaαeristic of conformable pavement marking tapes and quite similar to those of STAMARK™ 380 Series pavement marking tape and STAMARK™ 385 Series Non-Refleαive Joint Cover Tape available from Minnesota Mining and Manufacturing Co. (3M) of St. Paul, Minnesota. The sheet was visually similar to STAMARK™ 385 except that the non-particle coated regions between the projections were dark purplish-brown in color instead of black. Example 2. This sample was prepared as disclosed in Example 1, except that the coating of a particle bond material and anti-skid particles were omitted. The sample had a hand charaαeristic similar to Example 1. The sample was suitable for being underlaid beneath a layer of paving material. Example 3. This example was prepared in the same manner as was Example 2, except that the calendered shea material was not embossed. The sample had a hand charaαeristic similar to conformable sheet materials disclosed in U.S. Patent No. 4,490,432. The sample was suitable for being underlaid beneath a layer of paving material. Example 4. The sheet material of Example 1 was magnetized by passing the sheet between the magnetic poles of a permanent magnet assembly. The magnetizing field was about 10,000 gauss (1 tesla), and the resulting permanent magnetization of the she material was about 120 eleαromagnetic units per cubic centimeter (120 kilo-amperes per meter). Example 5. The she material of Example 1 was magnetized by passing a web ofthe sheet between the magnetic poles of an eleαromagnet assembly. The magnetizing field was about 10,000 gauss (1 tesla). The resulting permanent magnetization of the she material was about 120 eleαromagnetic units per cubic centimeter (120 kilo-amperes per meter). A length encoder measured the length of web passing between the poles ofthe eleαromagnet. After a fixed length of tape web, typically between 0.9 and 3.0 meters, had passed between the poles, the direction of cuπent flow was automatically reversed, thus reversing the direction of magnetization of the tape. The magnetic field ofthe sheet of this Example was measured near the top surface ofthe sheet as shown in the following Table. Distance above sheet (cm) Magnαic field strength ( gauss) 0 (surface measurement) 10 5 5 10 2 15 1 Example 6. A magnetic sheet material could be made following the steps used to produce the article of Example 1, with the additional step of punching an aπay of holes completely through the sheet. The holes should be large enough, preferably on the order of 5 mm or more, or more preferably 8 mm or more, in diameter so as to allow flow of roadway paving material through the sheet to contaα and bond with the underlying roadway base. The article could be magnetized following processes such as those used in Examples 4 and 5. Example 7. A layer of asphalt paving compound was applied to the gravel undercourse of a roadbed and tamped. A roll of sheet material prepared in accordance with Example 6 was applied to the top surface ofthe layer of asphalt while the asphalt was still hot (about 65 to 95°C and tamped into place by having a person walk on the sheet. The sheet measured 10.2 cm in width and 55 m in length. The sheet had a magnetization pattern of alternating north and south poles direαed upward with a field direαion change every 2.13 m. A layer of asphalt concrete cement paving material was paved over the magnetic strip and underlying base to yield an underlaid conformable magnetic article ofthe invention. The layer of asphalt was about 4 cm thick, and the temperature ofthe apphed material was about 120°C. The magnetic field emanating from the strip was deteαable through the layer of asphalt by means of a simple compass or pivoted bar magnet, as well as by various types of magnetomαers. The nα magnetic field strength, coπeαed for the earth's field, above the centeriine ofthe strip was 6 gauss (600 microtesla), as determined with a Model 4048 hand-held digital gauss/tesla meter, available from F.W. Bell, Inc. of Orlando, Florida. Example 8. The magnetic strip of Example 7 was installed beneath pavement with a longitudinal orientation ofthe strip running in a generally east/west direction and north/south direαion. The magnetic field ofthe underlaid magnetic strip was measured at a height of 30.5 cm above the pavement surface at a range of lateral distances of from 4 cm to 1.2 m while traveling along the length ofthe underlaid strip. The speed of travel was approximately 1.07 m/s in the easterly direαion. The ambient air temperature was approximately 24°C and the pavement surface temperature was approximately 35°C. A graph of representative data from measurements made in each ofthe X, Y, and Z direαions while traveling at a lateral distance of 0.6 m south ofthe strip is shown in Figure 8. The X direαion is the direction of travel (east). The Y direction is transverse to the strip (north). The Z direction is vertical elevation (upward). Amplitudes of magnetic field strength were estimated from the data for each of several runs at lateral distances of from 4 cm to 1.2 m by measuring the peak to peak amplitude ofthe waveform and dividing by two to account for pole reversal for each direαion X, Y, and Z for measurement runs made at each distance. The data are shown in the following table. Lateral Distance from Center of Strip Magnetic Field 0.04 m 0.6 m 0.9 m 1.2 m Strength X direction 180 milligauss 27 milligauss 11 milligauss 4.5 milligauss Y direction 50 milligauss 38 milligauss 14 milligauss 6 milligauss Z direction 215 milligauss 12 milligauss 9 milligauss 6.5 milligauss Other magnetic field strength readings were taken using a gauss mαer over the period of one year. Results as well as visual observations are set forth below. August 17. 1995 Readings were taken using a F.W. Bell gauss meter model 4048 before the final 4 cm topcoat of asphalt was laid. The readings were taken about 2.5 cm above the surface, centered over the tape, away from the field transitions, and normal to the tape or peφendicular to the field. The surface temperature was about 95°C. The average reading was 7 gauss (±10 percent). August 18. 1995 After laying the final topcoat, readings were taken about 2.5 cm above the pavement surface. The surface temperature was about 20°C. Readings were taken from both the east-west and the north-south strips. The average reading was 3.2 gauss (±10 percent). Visual observations: nothing out ofthe ordinary. August 30. 1995 The surface temperature was about 20°C. Readings were taken from both the east- west and the north-south strips. The average reading was 3.8 gauss. Visual observations: no noticeable defeαs in the surface where the tape was underlaid. September 16. 1996 The surface temperature was about 20°C. Readings were taken from both the east-west and the north-south strips. The average reading was 3.8 gauss. Visual observations: cracked asphalt, but not along the surface where the tape was underlaid; in one instance, the asphalt cracked peφendicular to the direαion in which the tape was underlaid beneath the surface. Example 9. The sheet material of Example 4 was underlaid within a traffic-bearing surface of a road in June 1996. The tape was laid over the 3rd layer of asphalt (surface temperature 111°F (44°C)) using a MHT A-1 Manual Highway Tape Applicator available from 3M. Then, three single passes were made with a RTC-2 Roller-Tamper Cart with a 200 lb. (90.8 kg) weight (available from 3M) to tamp the tape into place. Then a tack layer of oil was apphed and allowed to "dry". Then a final layer of asphalt (about 4 cm tbick)was placed over the tape. Each tape was 0.75 miles (1.2 km). A reading was taken using a gauss mαer at approximately 2.5 cm above the top layer of asphalt and measured 2.9 gauss at a surface temperature of about 95°C. Approximately three months later, no damage to the road was apparent. Various modifications and alterations will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims: What is claimed is: 1. A conformable magnetic article for underlayment beneath a traffic- bearing surface to send a magnetic signal to a sensor traveling over the traffic- bearing suiface, said magnetic article comprising at least one conformable magnαic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through a traffic-bearing structure to a sensor. 2. The magnαic article of claim 1, wherein said conformable layer has an original sample length and is charaαerized by exhibiting, when tested before adhering it to a substrate surface at least 25 percent inelastic deformation after being stretched one to 115 percent ofthe original sample length. 3. The magnetic article of claim 1, wherein said article is substantially inelastic. 4. The magnetic article of claim 1, wherein said article is perforated along its length. 5. The magnetic article of claim 1, wherein said article comprises seαions of alternating polarity along the length ofthe article. 6. The magnetic article of claim 1, wherein said magnetic article further comprises a layer of pressure-sensitive adhesive applied to a major surface ofthe article. 7. A system for guiding vehicles or mobile objects traveling on a traffic-bearing structure, comprising: (a) at least one conformable magnetic article for underlaying beneath a traffic-bearing surface to send a magnetic signal to a sensor traveling over the traffic-bearing surface, said magnetic article comprising at least one conformable magnetic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through a traffic-bearing structure; and (b) a sensor for passing over the traffic-bearing surface, said sensor comprising means for deteαing the magnetic signal through the traffic-bearing structure. 8. The system of claim 7, wherein said conformable layer has an original sample length and is characterized by exhibiting, when tested before adhering it to a substrate suiface at least 25 percent inelastic deformation after being stretched one to 115 percent ofthe original sample length. 9. The system of claim 7, wherein said magnetic article is substantially inelastic. 10. The system of claim 7, wherein said magnetic article is perforated along its length. 11. The system of claim 7, wherein said magnetic article comprises seαions of alternating polarity along its length. 12. The system of claim 7, wherein said sensor is mounted on a vehicle adapted to travel over the traffic-bearing surface. 13. The method of claim 7, wherein said magnetic article further comprises a layer of pressure sensitive adhesive apphed to a major surface ofthe article. 14. A system for guiding vehicles or mobile objeαs traveling on a traffic-bearing structure, comprising: (a) a traffic-bearing structure comprising at least two layers of material; (b) a conformable magnαic article underlaid beneath the top surface of said traffic-bearing structure between two of said layers, said article adapted to send a magnetic signal to a sensor traveling over the traffic-bearing surface, said magnαic article comprising at least one conformable magnetic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through a traffic-bearing structure; and (c) a sensor for passing over the traffic-bearing surface, said sensor comprising means for deteαing the magnetic signal through said traffic-bearing structure. 15. The system of claim 14, wherein said conformable layer has an original sample length and is charaαerized by exhibiting, when tested before adhering it to a substrate surface at least 25 percent inelastic deformation after being stretched one to 115 percent ofthe original sample length. 16. The system of claim 14, wherein said magnαic article is substantially inelastic. 17. The system of claim 14, wherein said magnetic article is perforated along its length. 18. The system of claim 14, wherein said magnαic article comprises seαions of alternating polarity along its length. 19. The system of claim 14, wherein said sensor is mounted on a vehicle adapted to travel over said traffic-bearing surface. 20. The system of claim 14, wherein said traffic-bearing structure comprises asphalt cement concrete, and wherein said two layers are the outermost two layer of said traffic-bearing structure. 21. The system of claim 14, wherein said magnαic article further comprises a layer of pressure sensitive adhesive apphed to a major surface ofthe article. 22. A method of providing a guidance system for an existing traffic- bearing structure, comprising the steps of: (a) removing an amount of material from the traffic-bearing structure to provide a depression; (b) placing within the depression a conformable magnetic article adapted to send a magnetic signal to a sensor traveling over the traffic-bearing surface, said magnetic article comprising at least one conformable magnαic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnetic signal through a traffic-bearing structure; and (c) placing a sufficient amount of a material within the depression to completely underlay the magnetic article within the material. 23. The method of claim 22, wherein said magnetic article further comprises a layer of pressure sensitive adhesive apphed to a major surface ofthe article. 24. The method of claim 22, wherein said magnetic article is affixed within the depression by at least one mechanical fastener prior to step (c). 25. A method of providing a guidance system for a traffic-bearing structure, comprising the steps of: (a) providing a traffic-bearing struαure base; (b) providing a conformable magnetic article adapted to send a magnetic signal to a sensor traveling over the traffic-bearing surface, said magnetic article comprising at least one conformable magnetic layer comprising a binder and a sufficient amount of magnetic particles dispersed within the binder to provide a magnαic signal through a traffic-bearing structure; (c) positioning the magnetic article at a location on or above a portion ofthe traffic-bearing structure base; and (d) applying a traffic-bearing structure material over the magnetic article and over the traffic-bearing structure base. 26. The method of claim 25, wherein the traffic-bearing structure materials are seleαed from the group consisting of asphalt cement concrete, Portland cement, and gravel. 27. The system of claim 25, wherein said magnetic article further comprises a layer of pressure sensitive adhesive apphed to a major surface ofthe article. 28. The method of claim 25, wherein said magnetic article is affixed to the traffic-bearing structure by at least one mechanical fastener prior to step (d).

Inventors: CLARK GARY W, DAHLIN THOMAS J, FAYLING RICHARD E, GONZALEZ BERNARD A, HOPSTOCK DAVID M, JACOBS GREGORY F, KEECH RICHARD L, CLARK, GARY, W., DAHLIN, THOMAS, J., FAYLING, RICHARD, E., GONZALEZ, BERNARD, A., HOPSTOCK, DAVID, M., JACOBS, GREGORY, F., KEECH, RICHARD, L.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1996
Main classification: E01F9
IPC codes: B32B5, E01F9, E01F11, G05D1