Patent Application: US-201414466362-A

Abstract:
active carbon filters and systems that are operative to detect active carbon filter degradations are provided . the active carbon filter can include a carbon filter comprising activated carbon and defining a filter surface ; a first piezoelectric wafer active sensor on the filter surface that is electrically isolated from the carbon filter ; and a second piezoelectric wafer active sensor on the filter surface that is electrically connected to the filter surface ; and an impedance monitoring device electrically connected to the first piezoelectric wafer active sensor and the second piezoelectric wafer active sensor . methods are also disclosed for determining if any degradation has occurred in an active carbon filter .

Description:
reference now will be made to the embodiments of the invention , one or more examples of which are set forth below . each example is provided by way of an explanation of the invention , not as a limitation of the invention . in fact , it will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the scope or spirit of the invention . for instance , features illustrated or described as one embodiment can be used on another embodiment to yield still a further embodiment . thus , it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents . it is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only , and is not intended as limiting the broader aspects of the present invention , which broader aspects are embodied exemplary constructions . in general , the present disclosure is directed to methods and systems for detecting the active carbon filter degradation of piezoelectric wafer active sensors ( pwas ), with combined use of electromechanical impedance spectroscopy ( emis ) and electrochemical impedance spectroscopy ( ecis ) methods . the combined use of electromechanical impedance spectroscopy ( emis ) and electrochemical impedance spectroscopy ( ecis ) with piezoelectric wafer active sensors ( pwas ) for degradation detection in active carbon filters can detect electrical and mechanical changes in active carbon filters , which can give a non - intrusive in - situ evaluation method to improve the safety of active carbon filter system . in certain embodiments , the presently disclosed methods can allow for degradation detection in active carbon filters based on the following fundamental objectives : in - situ monitoring , non - obstructive to carbon filter structure , ability to detect both electrical and mechanical changes associated with filter degradation , and / or ability to differentiate electrical and mechanical changes associated with filter degradation . in one particular embodiment , the presently disclosed method can use embedded pwas transducers to take emis and ecis measurement and evaluate chemical and mechanical degradations in active carbon filters . such an approach can allow for the determination of impregnant degradation , water condensation , contamination detection , carbon bed packing , settling and flow channeling , etc ., in an active carbon filter . however , the combination of emis and ecis methods can allow for these chemical and mechanical degradations can be differentiated . degradation detection and characterization is important to identify the cause of such degradation , and provide the filter user early warning for prevention actions . one major potential industrial application for such methods and systems is in active carbon air filtration devices . the emis method measures the coupled high - frequency sensor - structure dynamics in structural health monitoring and biomechanical research ( giurgiutiu 2008 , xu and giurgiutiu 2006 , giurgiutiu et al . 2004 ). the ecis method measures the dielectric properties of the media between two electrodes . when the carbon filter is contaminated ( e . g ., with chemical agent or water ) or integrity defects are formed , its mechanical properties ( e . g . density , stiffness , etc .) and electrical properties ( conductivity , resistance ) will change . the pwas sensor ( s ) inside the carbon filter will be able to detect the mechanical changes using emis method ; and the electrical changes using ecis method . because the ecis and emis approaches are different , the combination of these two methods will allow one to differentiate what aspects of filter degradation are monitored better by one method than by the other . pwas sensor can be configured to sense only mechanical changes , only electrical changes , or to sense both mechanical and electrical changes simultaneously . this approach can also differentiate the changes due to mechanical and electrochemical change . thus , in one embodiment , the presently disclosed methods and systems use pwas as ecis and emis sensors , which can be embedded in the active carbon granules or on the activated carbon filter , to detect electrical and mechanical changes associated with the degradation of active carbon filter . piezoelectric wafer active sensors ( pwas ) are inexpensive transducers that operate on the piezoelectric principle . pwas couple the electrical and mechanical effects through piezoelectric effects . pwas are the enabling technology for active structural health monitoring ( shm ) systems . for example , pwas are described in u . s . publication no . 2010 / 0132469 of giurgiutiu , et al . ; u . s . pat . no . 7 , 881 , 881 of giurgiutiu , et al . ; u . s . publication no . 2009 / 0188319 of giurgiutiu , et al . ; u . s . publication no . 2009 / 0048789 of yu , et al . ; u . s . publication no . 2008 / 0288184 of giurgiutiu , et al . ; u . s . pat . no . 6 , 996 , 480 of giurgiutiu , et al . ; and u . s . pat . no . 7 , 174 , 255 of giurgiutiu , et al ., all of which are incorporated by reference herein for the entirety of their disclosures . the emis method measures the dynamic mechanical spectrum of a structure directly with an electric instrument , i . e ., an impedance measurement device . miniaturized impedance measurement approach has been developed in the recent years ( xu and giurgiutiu 2006 ), which significantly reduce the complexity , cost and energy requirement for such device , and make impedance spectroscopy devices portable . the emis method has been used extensively in structural health monitoring ( shm ) applications ( giurgiutiu , 2008 ) and biomechanical research ( giurgiutiu et al . 2004 ). the result of applying the electromechanical impedance method is to generate the dynamic spectrum of the mechanical response of the structure . by observing modifications in the dynamic spectrum , one can infer that mechanical changes have taken place in the investigated structure . the electrochemical impedance spectroscopy measures the electrochemical spectrum of the material and , when the spectrum changes , it infers that changes have taken place at the material level . the emis and ecis method have similarities , in principal because they both measure impedance and both deal with spectral analysis . however , there are several major differences between emis and ecis , as follows : 1 . emis is a high - frequency method because it measures in the high khz and mhz frequency range ; in contrast , ecis is a relatively low frequency method because it typically measures in the low khz range 2 . emis uses piezoelectric pwas transducers to couple the electrical and mechanical energies ; in contrast , ecis uses simple electrode probes inserted ( or intimately connected to ) the material it is apparent that emis is a structural - level method whereas ecis is a material - level method . therefore , the use of these methods in combination is likely to expand the investigative options by offering multi - scale opportunities ( structural scale and material scale ). because the ecis and emis approaches are different , the combination of these two methods will allow one to differentiate what aspects of filter degradation are monitored better by one method than by the other . in this new approach , pwas sensors will be used as both emis and ecis sensors . for emis measurement , the pwas will be insulated from the carbon granules with a non - conductive coating . in this configuration , only mechanical changes will be detected . for ecis measurement , non - insulated pwas will be used , the measurement will be conducted at low frequency range ( several hz to several khz range ), well below the electromechanical resonance . in this configuration , the two electrodes on the pwas sensors will be used for ecis measurement . with measurement data from both ecis and emis methods , one can differentiate the changes due to mechanical and electrochemical change . fig1 shows a schematic of an exemplary embodiment according to the present invention . specifically , fig1 shows an in - situ degradation detection in active carbon with pwas , where the pwas sizes are exaggerated , and not to scale and can be less than 10 mm in diameter in most embodiments . the pwas transducer ( s ) are inserted into or onto the filter during the filter manufacturing process . an impedance monitoring device can be connected to the transducer ( s ) through connector ( s ) on the filter . the monitoring device incorporates a impedance measurement circuit and a signal processor . the impedance measurement circuit is configured to measure the ecis and emis spectrum and also to detect the surrounding temperature and humidity for measurement calibration . when the filter is manufactured , a baseline impedance measurement can be taken ; with both ecis and emis being stored to non - volatile memory onboard the monitoring device . at desired interval , the monitoring device can measure the ecis and emis spectrum and compare with the baseline impedance data . a damage index can be generated to give a numerical indicator for the severity of the degradation of the active carbon filter . the signal processor is configured to control the measurement activities and perform measurement data evaluations . when the measurement data is available , the signal processor can evaluate the degradation status and use light and sound indicator ( s ) to inform and warn the filter user . this method can , in certain embodiments , encompass the following innovative concepts : monitoring active carbon filter degradation with embedded pwas transducers ; use as a qa / qc instrument for determining proper sealing pressure of the gasket of colpro filters ; use of pwas emis to detect mechanical changes associated with active carbon filter degradation ; use of pwas as ecis sensor , and / or the combined use of emis and ecis method to differentiate mechanical and electrical changes associated with active carbon filter degradation . the major potential industrial application of the presently disclosed methods and systems is in active carbon air filtration devices . with the inexpensive and non - intrusive pwas transducers , a simple solution is provided for monitoring active carbon filters for detecting degradations during operation , which can be adopted by industrial and military applications , federal and industrial laboratories , original equipment manufactures , and / or operators of military and related industrials that are required to assure the safety of active carbon filter users . two groups of tests were conducted to demonstrate the capability of pwas in detecting electrochemical and mechanical changes in active carbon granules : ( a ) pwas for humidity level detection , and ( b ) pwas for pressure detection . the test results show that using emis - ecis method , pwas are able to detect and differentiate electrical and mechanical changes associated with filter degradation , such as water condensation and integrity defect formation ; hence can assist carbon filter residual life prediction . the results are presented hereafter . in humidity level detection tests , non - insulated pwas was embedded into carbon granules , very small amount ( 2 . 5 % v / v ) of water were then incrementally added to the carbon bed ; emis measurement was taken at each level . fig2 ( a ) shows the emis signals at different water level . considering the conductivity of water may influence the impedance measurement , we have also tested with kerosene which is non - conductive . same procedure was taken on kerosene test , and the data are plotted in fig2 ( b ). to identify the underlying electrical change due to liquid loading level , pwas admittance was calculated from the impedance data , and plotted in fig2 ( c ) and ( d ). admittance is the inverse of the impedance . the real part of admittance is the conductance , which measures the conductivity of the material . for data analysis , three different frequencies were taken to quantify the change pattern in impedance data , shown in fig3 ( a ). impedance amplitude at these frequencies was plotted against the water loading level , as shown in fig3 ( b ). from the plot we have identified that emis data kept at low level before it reaches 12 . 5 % water loading level ; then emis data went up almost linearly with the water loading level . the same approach was taken on the kerosene test data , and the plots are shown in fig3 ( c ) and ( d ). it can be seen that with kerosene , the threshold of impedance change changed to 5 % volume level , and reaches a plateau at 12 . 5 % volume level . the admittance data plots show similar pattern . for data analysis , two non - resonances frequencies were selected , and the admittances were compared at different liquid loading levels , as shown in fig4 . in water test data plots , fig4 ( a ) and ( b ), the admittance kept at low level at below 12 . 5 % v / v water loading , and then increased almost linearly with the water loading level . in kerosene test data plots , fig4 ( c ) and ( d ), the admittance followed a similar pattern , the admittance was low for kerosene loading level below 5 %, and increase almost linearly between 5 % and 15 %, at kerosene level about 17 . 5 %, the admittance reaches a plateau and increase slowly . ecis measurements were also done for the water loading test . as shown in fig5 ( a ), the impedance nyquist plot shows a pattern of lowering signals with increased water loading . fig5 ( b ) shows the real part of the same group of data plotted against frequency indicating that the impedance decreases with increased water level . in summary , pwas embedded in an activated carbon bed can sense the presence of water ( or other liquid agent ) in the carbon bed . in a certain range the emis impedance and admittance change linearly with water level . the threshold and plateau demonstrated pwas has its sensitivity limit , and saturation levels . these tests demonstrated that pwas can be used to detect humidity level in the carbon granules through measuring the impedance and admittance . in the pressure test , increasing pressure was applied to the carbon bed in 0 . 9 kpa increment steps ; emis measurements were taken at each step . some of the experimental data are shown in the figures . it can be seen that the resonance peaks of impedance curve were reduced greatly when pressure increased . then , at higher pressure , the peaks went below normal impedance level ; seem like “ negative ” peaks . finally , at 18 kpa , the non - peak impedance level increased and got flatter , and almost displayed constant level over the observed frequency range . in order to understand these significant changes , a tentative simplified model was created for the pwas - carbon bed system , as shown in fig7 . mechanically , the carbon bed was considered as a complex spring - damper system supporting the pwas ( fig7 a ). electrically , the resistance of carbon granule was modeled as a variable resistor . it was connected in parallel with the pwas transducer &# 39 ; s capacitance . when pressure is increased , the spring - damper becomes stiffer , and carbon resistance decreases . the model was used with increasing pressure levels . fig8 shows comparison of experimental data and modeling results for increasing pressure levels . similar pattern of behaviors is observed between experimental data and model . from experimental data and analytical modeling , we noticed that at high pressure level , the dominant component is the carbon filter granule resistance . when more pressure is applied , the carbon granules contact resistance will decrease . when the pressure goes beyond a certain threshold , the resistance will not increase significantly . since the pwas has two conductive electrodes , it can sense not only the mechanical change , but also the electrical ( conductivity ) changes . pwas was also tested as a pure mechanical change detector . insulated pwas were manufactured using polyurethane coating and used in a repeated pressure test . the emis impedance curves for insulated pwas are shown in fig9 . as different from the bare pwas ( fig6 ), the insulated pwas only show minor changes as pressure increased . however , when the peak amplitude and frequency are plotted against applied pressure , a clear pattern appears , as shown in the figures . the peak amplitude decreases and frequency increases with added pressure . this matches our previous knowledge about pwas behavior when the support stiffness changes . these and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art , without departing from the spirit and scope of the present invention , which is more particularly set forth in the appended claims . in addition , it should be understood the aspects of the various embodiments may be interchanged both in whole or in part . furthermore , those of ordinary skill in the art will appreciate that the foregoing description is by way of example only , and is not intended to limit the invention so further described in the appended claims . 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