Abstract:
A corrosion sensor is disclosed. The corrosion sensor has a retainer and a microcontroller retained by the retainer. A length of antenna wire arranged in a wound configuration is retained by the retainer and connected to the microcontroller. A corrosion sensitive element is conductively connected to the microcontroller. The microcontroller is programmed to receive a power signal from the antenna wire and test for corrosion of the corrosion sensitive element. The he microcontroller is also programmed to transmit a signal indicative of the test results via the antenna.

Description:
FIELD OF THE INVENTION 
       [0001]    This disclosure relates corrosion sensors in general and more particularly, but not by way of limitation, to wireless corrosion sensors, systems, and methods. 
       BACKGROUND OF THE INVENTION 
       [0002]    Almost every man made construction is subject to corrosive forces. Corrosion affects aircraft, trains, automobiles, pipelines, factories, and a host of other devices, buildings, structures, and apparatus. In the United States alone, costs associated with policing and repair of corrosion runs into the hundreds of billions of dollars. Industrial segments including transportation, utilities, production and manufacturing, governments, and other infrastructure have a need to detect corrosion prior to significant damage occurring to the structure of interest. 
         [0003]    Currently, it is not feasible to locate corrosion on reinforcing steel until corrosion has already developed and caused cracking of the surrounding concrete from the rust products. Once surface cracking of the concrete has occurred, an investigation into the deterioration is time-consuming and destructive to the element as cores are taken to investigate the surface of the reinforcing steel. This work requires lane closures, causes traffic delays, and involves elevated safety risks for maintenance crews and the traveling public. 
         [0004]    What is needed is a system and method for addressing the above and related concerns. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention of the present disclosure, in one aspect thererof, comprises corrosion sensor. The corrosion sensor has a retainer and a microcontroller retained by the retainer. A length of antenna wire arranged in a wound configuration is retained by the retainer and connected to the microcontroller. A corrosion sensitive element is conductively connected to the microcontroller. The microcontroller is programmed to receive a power signal from the antenna wire and test for corrosion of the corrosion sensitive element. The microcontroller is also programmed to transmit a signal indicative of the test results via the antenna. 
         [0006]    In some embodiments, the retainer is shaped substantially as a disc with an exterior track around a periphery of the disc retaining the antenna and an interior cavity near a center of the disc retaining the microcontroller. The antenna may be copper. The microcontroller may tests the corrosion sensitive element by testing continuity of the corrosion sensitive element. The microcontroller may communicates on a frequency of about 125 kHz. 
         [0007]    The corrosion sensor may have a plurality of corrosion sensitive elements conductively connected to the microcontroller. The plurality of corrosion sensitive elements may be utilized by the microcontroller to determine a degree of corrosion. The microcontroller may transmit identifying information, including location information. 
         [0008]    In some embodiments the corrosion sensor may include a support bracket for placing the retainer proximate a predetermined location on a test object. In other embodiments, the sensor may include concrete block attached to the retainer, and adapted to be enclosed within a concrete structure during assembly of the concrete structure. 
         [0009]    The invention of the present disclosure, in another aspect thereof; comprises a method of detecting corrosion of a metal support structure within a concrete structure. A non-conductive testing retainer having an outer periphery with a copper winding antenna is provided along with a programmable microcontroller retained by the testing retainer. The microcontroller is conductively attached to the antenna for receiving power and transmitting data. A test element is attached to the microcontroller. The testing retainer is placed into the concrete structure proximate a portion of the metal support structure. A power signal is provided to the microcontroller via the antenna. The test element is tested by the microcontroller, and the results are received wirelessly from the microcontroller via the antenna. 
         [0010]    In some embodiments, placing the testing retainer into the concrete structure proximate a portion of the metal support structure further occurs before the concrete is cured. A plurality of test elements may be connected to the microcontroller. In some cases a plurality of testing retainers may be placed on the metal support structure at known depths within the concrete structure to monitor for corrosion of the support structure at a plurality of locations and depths within the concrete structure. The testing retainer may be pre-assembled into a concrete block for handling when placing into the concrete structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic diagram of a wireless corrosion sensor according to aspects of the present disclosure. 
           [0012]      FIG. 2  is a perspective view of a wireless corrosion sensor according to aspects of the present disclosure. 
           [0013]      FIG. 3  is a side view of a wireless corrosion sensor clamped to structural rebar according to aspects of the present disclosure. 
           [0014]      FIG. 4  is a perspective view of a corrosion sensitive concrete block according to aspects of the present disclosure. 
           [0015]      FIG. 5  is a side view of a bridge structure containing a plurality of embedded wireless corrosion sensors according to aspects of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    Early detection of corrosion of steel reinforcement in concrete, through the use of sensors described herein, may help to preserve structural integrity of concrete structures. Such structures may include bridges and roadways but may also include occupied structures such as buildings and stadium. The sensors described herein may reduce the risk of substantial section loss or fatigue failure that is initiated by corrosion damage. Until now, it has not been feasible to locate corrosion on reinforcing steel until corrosion was already developed and caused cracking of the surrounding concrete from the rust products. Once surface cracking of the concrete has occurred, an investigation into the deterioration is time-consuming and destructive to the element as cores are taken to investigate the surface of the reinforcing steel. In the case of highways and bridges, this work requires lane closures, causes traffic delays, and involves elevated safety risks for maintenance crews and the traveling public. Thus, embedded wireless monitoring as described herein will increase the safety of the workers and reduce delays, as well as provide the owner with crucial information about the health of the structure. This information may be used to intelligently schedule maintenance to optimize resources or to modify the current uses of the structure to prolong its life. In one example, it is estimated that the use of the presently disclosed sensors will allow the engineers to employ “best maintenance practices” that are estimated to save 46 percent of the annual corrosion cost of a black steel rebar bridge deck, or $2,000 per bridge per year. 
         [0017]    Referring now to  FIG. 1 , a schematic diagram of a wireless corrosion sensor is shown. The sensor  100  is passive in that it does not contain a power source and may remain inactive until energized by radiofrequency, magnetic, microwave, or other wireless energy fields. In the present embodiment, the sensor  100  is based upon radio frequency identification (RFID) technology. In the present embodiment, the sensor  100  is based upon a microcontroller  102  that is programmed to operate in accordance with known RFID protocols such that commercially available RFID readers can be utilized. In the present embodiment, an 8-bit PIC Microcontroller such as the pic12F683 from Microchip Technology, Inc. is used. However, other ultra low powered microcontrollers capable of being powered by RF energy could be utilized. In other embodiments, the sensor  100  may be based on known and commercially available RFID tag circuits suitably modified to meet the demands of the user. In U.S. Pat. No. 7,675,295 (hereby incorporated by reference) it was shown how an off-the-shelf commercial RFID tag could be modified to monitor for corrosion. The present disclosure describes, among other things, how commercial RFID protocols can be implemented in a sensor that monitors for corrosion of a metallic structure that may be deeply embedded within concrete and other building materials. 
         [0018]    In order to successfully operate with commercial RFID tag readers, the sensor  100  must communicate with an RFID tag reader using a protocol that is known to the reader. However, this communication must take place through layers of concrete and other building materials. Furthermore, if the sensor  100  is to be passive and avoid the need for a battery or other power source that would be subject to failure, the sensor  100  must be powered by energy received from the reader itself. 
         [0019]    An RFID reader or scanner will transmit microwave, magnetic, or radiofrequency energy to the sensor  100 . Some RFID systems rely upon load modulation or reflected power/backscatter technology. One standard that can be used for RFID is the ISO/IEC 18000 RFID Air Interface Standard. However, other suitable protocols may be implemented or developed for use with the sensors of the present disclosure. 
         [0020]    Although the sensor  100  the present disclosure may be able to operate with RFID systems of almost any frequency, the intended use of the sensor  100 , being buried within a concrete structure, may dictate that the most useful frequencies are along the order of kilohertz rather than in the megahertz bands. In one embodiment, the frequency will be about 125 KHz. At this frequency, the supplied energy may come from magnetic induction in the near field range. The 125 KHz frequency is virtually transparent to soil, concrete, paper, water, conductive liquids and slurries. 
         [0021]    Sensors of the present disclosure that operate at low frequencies in the near field will rely on an alternating current in a scanner coil (not shown) to induce a current in an antenna coil  104 . This current may be used to power the microcontroller  102 . When the sensor  100  has been powered, information contained within the sensor  100  may be sent back to the scanner by load modulation. In load modulation, the loading of the sensor&#39;s coil is changed in a pattern over time that affects the current being drawn by the scanner coil. In order to recover the information or identity transmitted by the sensor  100 , the scanner decodes the change in current as a varying potential developed across a series of internal resistors (not shown). 
         [0022]    The boundary of the near field and far field is governed by the frequency of the alternating current used to energize the coils of the scanner. The boundary is approximately limited to a distance of C/2.pi.f, where C equals the speed of light and f equals the frequency. Depending upon the location of the sensor  100  and/or the test object, relatively larger scanners and/or sensors  100  may be utilized to increase the effective communication distance. 
         [0023]    Rather than the usual flat or square antenna utilized by many commercial RFID tags, the sensor  100  employs a coiled copper antenna  104 . The coiled copper antenna  104  allows for sufficient power to be received by the antenna  104  even when operating buried in several inches of concrete or other building materials. Moreover, the coiled copper antenna  104  also allows for sufficient data transfer back through the concrete to the RFID reader via load modulation or other methods. A relatively low Q coil may be required to function properly with certain RFID readers. In one embodiment a 30 mm coil diameter will be used. It is also understood that copper is used as an example here but an appropriate antenna could be constructed from other metals or conductors. 
         [0024]    A corrosion sensitive element  106  may be connected across one or more leads of the microcontroller  102 . In one embodiment, the microcontroller will test the continuity or resistance of the corrosion sensitive element to determine whether or not corrosion is resistant. If the resistance of the element  106  is infinite (or very large) it may be corroded to a significant degree. The microprocessor&#39;s  102  programming may be relatively simple in that it&#39;s only task upon being powered by the antenna coil  104  is to test the continuity of the element  106  and report this status back via RFID protocol. However, other information could also be provided back to the reader including an identification number, and installation date, or even a location. In a structure with a plurality of embedded sensors  100 , being able to determine the location of the reporting sensor could be useful. Additionally, the microcontroller programming may provide for anti-collision schemes or other methods to allow for reliable communication from more than one sensor  100  in range of a single RFID reader. 
         [0025]    The material comprising the test link or corrosion sensitive element  106  may vary according to the underlying material of the test object. For example, if a sensor is employed to detect corrosion on rebar structures within a concrete bridge, the link  106  may comprise a medium carbon wire. In some cases, it may be desirable to detect corrosion long before the test structure becomes corroded, or to refrain from reporting minor amounts of corrosion while monitoring for catastrophic corrosion. In such case, the link material  106  could be selected have a corrosion sensitivity that is greater or less, respectively, than the underlying structure. The thickness of the link  106  can also be varied in order to detect corrosion at a threshold level. In other embodiments, multiple link  106  of varying thicknesses could be used that would allow the microprocessor  102  to determine not only presence of corrosion, but a relative degree of corrosion. This could then be reported back to the RFID reader. 
         [0026]    Referring now to  FIG. 2 , a perspective view of a wireless corrosion sensor according to aspects of the present disclosure is shown. In the present embodiment, the sensor  100  has been packaged into a component suitable for embedding within a concrete structure in a location where corrosion detection is needed. A retainer  200  is provided that defines a hole or depression  202  into which the microprocessor  102  and possibly the corrosion sensitive link  106  may be placed. A track  204  may be defined around a peripheral edge of the retainer  200  for retaining the antenna coil  104 . In the present embodiment, the retainer  200  is substantially disk shaped and defines a cavity  202  near the center thereof. However, the retainer  200  need not necessarily be configured in this way. For example, the microprocessor  102  and corrosion sensitive element  106  could be surface-mounted on an outside of the retainer  200 . Similarly, the antenna coil  104  need not necessarily be placed in a peripheral track  204 . However, the present embodiment does present a compact and durable method of retaining all of the required elements of the sensor  100 . 
         [0027]    In some embodiments, the retainer  200  will be comprised of Delrin®. However, in other embodiments, other plastics or nonconductive materials could be utilized. Following assembly of the sensor  100 , the unit may be coated with a sealant while leaving the corrosion sensitive element  106  exposed in order to detect corrosion. In such an embodiment, the microprocessor  102  and the antenna coil  104  would remain operational long after the corrosion sensitive link  106  were severely corroded or even gone. In some embodiments, the sensor  100  may be coated, at least in part, with a flexible plastic in order to eliminate stress points within the concrete structure that may result from the presence of the sensor  100 . 
         [0028]    Referring now to  FIG. 3 , a side view of a wireless corrosion sensor  100  clamped to a segment of structural rebar  302  according to aspects of the present disclosure is shown. In many cases, it may be desirable to retain a corrosion sensor  100  securely in a known location along the structure being monitored. In the present embodiment, a retaining element  300  is provided that retains the corrosion sensor  100  in a relative position on a segment of rebar  302 . In the present embodiment, legs  304  and  306  connect on substantially opposite sides of the sensor  100  to clamps  308 ,  310 , respectively. In some embodiments, the retaining element  300  may be plastic or another suitably resilient material. 
         [0029]    Referring now to  FIG. 4 , a perspective view of a corrosion sensitive concrete block according to aspects of the present disclosure is shown. Here, the concrete block provides a depression or cutout  402 . The sensor  100  is suspended on arms  403  within the cutout  402 . Forming the block  400  in this matter will allow the sensor  100  to be in direct contact with the concrete of the monitored structure. This will allow for more accurate assessment of corrosion as the concrete of the structure may have different properties (e.g., pH, permeability, mix ingredients) than that of the block  400 . Channels or recesses  404  may be provided for fitting the block  400  onto structural rebar  302  or other structural material. Clamps (not shown) may also be provided to assist in retention of the block  400  on the monitored structure. 
         [0030]    A number of blocks  400  may be embedded throughout a concrete structure when it is being assembled. The block  400  provides on way that the sensor  100  may be transported and handled with less fear of damage. In some embodiments, the sensor  100  may be entirely buried within the block. In another embodiment, the retainer  300  of  FIG. 3  will be buried within a concrete block, possibly with clamps  308 ,  310  exposed for attachment to the structure. The concrete block  400  may be labeled with an assembly date or a location indicator which may also be programmed into the sensor  100 , as previously described. 
         [0031]    Referring now to  FIG. 5 , a side view of a bridge structure containing a plurality of embedded wireless corrosion sensors according to aspects of the present disclosure is shown. The bridge structure  500  is only one non-limiting example of the manner in which the passive wireless corrosion sensors of the present disclosure may be utilized. In the present example, the bridge structure  500  defines a road surface  501  and pillars  502 ,  504 . A concrete railing  506  is also provided and the entire concrete structure may be framed from within by a steel framework  510 . 
         [0032]    It can be seen in  FIG. 5  that wireless corrosion sensors, as described herein, may be placed throughout the structure  500  in order to detect corrosion and levels of corrosion wirelessly and non-destructively. For example, multiple wireless corrosion sensors may be placed beneath the road surface  501  in order to inform when corrosion of the steel structure  510  beneath the road surface  501  is occurring. In this way, the remaining life span of the road surface  501  can be determined in a non-destructive way. In some embodiments, a plurality of wireless corrosion sensors  400  may be arranged in a stack  514 . The corrosion sensors within the stack  514  may be placed at varying depths such that the precise location of corrosion of the steel structure  510  underlying the road surface  501  can be determined. Similarly, sensors may be placed within the pillars  502 ,  504 . In this way, the internal corrosion level of the structure support members can be determined. In some cases, for example, only the surface of the road  501  may have a significant degree of corrosion while the pillars  502 ,  504  may be essentially sound. A determination of this may mean that the entire structure need not necessarily be disassembled and repaired. 
         [0033]    It is understood that, within a single structure such as bridge structure  500 , multiple versions of the wireless corrosion sensors of the present disclosure may be utilized. For example, a sensor  100  may simply be embedded within the concrete, or it may be attached to a retaining member  300 , or it may be previously embedded in a concrete block  400 , which is then constructed into the structure  500 . The location and configuration of the sensor  100  may be determined based upon the needs of the user. For example, in some structures, only corrosion of critical locations such as a high stress area  512  may be monitored. 
         [0034]    In some embodiments, to determine the state of corrosion within the structure  500 , a technician may traverse the bulk of the structure using a hand-held RFID reader. As the reader is placed in the vicinity of each of the wireless corrosion sensors, the sensors may report their identification, location, n and/or state of corrosion within their area. In other embodiments, large readers may be constructed in order to speed up such a process. For example, a large truck-mounted reader may be capable of quickly scanning the entire road surface  501  in a relatively short amount of time. 
         [0035]    Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.