Abstract:
Materials display innate resistance, capacitance, and inductance (RCL) properties and can therefore be distinguished in accordance with these properties. A high voltage is applied across a material, and a waveform is obtained whose rise time, frequency content, duration, and fall time represent the RCL properties of the material. The high voltage can be applied by passing air containing the material through a pair of screens held at a potential difference or by gluing a sample of the material to two rods held at a potential difference. The voltage may or may not be enough to cause the material to arc.

Description:
GOVERNMENT INTEREST 
     The invention described herein may be manufactured, used and licensed by or for the U.S. Government. 
     FIELD OF THE INVENTION 
     The present invention is directed to a device and method for inspection and detection of a fiber material by applying a high voltage to the material and observing its high-voltage waveform. 
     DESCRIPTION OF RELATED ART 
     There is a need in the art to detect low impedance fiber in extremely low concentrations. Current detectors, such as the ETI high-voltage plate, detect only the presence of low impedance fibers and provide no further differentiation or other information. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a device and method for discerning material type or measuring differences in material quality caused by differences in crystalline structure. 
     It is another object of the invention to provide such a device and method for detection and quality control. 
     To achieve these and other objects, the present invention is directed to a device for taking data representative of a material for analysis of the material, the device comprising: a voltage supply for supplying a voltage; testing means for receiving the material and for applying the voltage across the material to obtain a resulting waveform; and detecting means for detecting the resulting waveform to produce an output representing the resulting waveform. 
     The present invention is further directed to a method of taking data representative of a material for analysis of the material, the method comprising: (a) applying the voltage across the material to obtain a resulting waveform; and (b) detecting the resulting waveform to produce an output representing the resulting waveform. 
     The invention employs the principle that all solids, at least in theory, display innate resistance, capacitance, and inductance (RCL) properties. More specifically, all material can be analyzed in terms of an equivalent circuit having resistive, capacitive, and inductive elements. A crystalline material should have such elements in series. The equivalent circuits, and thus the materials themselves, display responses having distinctive patterns when energized with high voltage. 
     Thus, when a material is activated with sufficient voltage, distinct wave forms should appear. The differential patterns should be discernible by rise time, frequency content, duration, and fall time. 
     The invention allows detection of fiber in extremely low concentrations. It also allows detection and differentiation of any material of sufficient conductivity to initiate an arc. 
     The invention allows inspection analysis of known materials for density and crystalline structure and also allows detection of material types in an unknown environment. Minor differences in crystalline structure within material types will affect the equivalent circuits and will thus be measurable. Hardness, crystalline structure, and thickness can be discerned. 
     The invention can be used in a production environment to monitor material quality. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will be set forth in detail with reference to the drawings, in which: 
     FIG. 1 shows a block diagram of one setup according to the preferred embodiment; 
     FIG. 2 shows one of the screens used in the setup of FIG. 1; 
     FIG. 3 shows a flow chart of operational steps in carrying out the preferred embodiment; 
     FIG. 4 shows a modified version of the setup of FIG. 1; 
     FIG. 5 shows a block diagram of the high-voltage supply used in the setup of FIG. 4; 
     FIG. 6 shows a flow chart of the operational steps of FIG. 3 modified for the setup of FIG. 4; and 
     FIGS. 7-12 show experimental results. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows one setup according to a preferred embodiment of the present invention. As shown in FIG. 1, setup  101  includes high-voltage (HV) supply  103 , which can be a high-voltage capacitor, to supply high voltage to the material to be tested. Testing area  105  includes two screens  107 ,  109  of brass or the like, which are mounted in parallel on air-flow tube  111  of an insulating material such as that sold under the trade name PLEXIGLAS so as to have a separation of ⅛ to 1 inch, typically ⅜ inch. This separation defines cavity  113  between screens  107  and  109 . Each of screens  107  and  109  has the appearance shown in FIG.  2 . Muffin fan or other blowing device  115  drives air or another fluid containing the material to be tested at a rate of about 7 m/sec to move in the direction indicated by arrow A. Alternatively, testing area  105  could be oriented so that the material to be tested could fall through screens  107  and  109 . Oscilloscope  117 , resistor  119  (such as a 1 Ω or 10 Ω resistor, although any suitable value can be used), and grounding connection  121  form discharge detection circuit  123 . Grounding connection  121  grounds one terminal of HV supply  103  and one terminal of oscilloscope  117  and also grounds screen  109  through resistor  119 . With the connection shown in FIG. 1, oscilloscope  117  measures the voltage drop across resistor  119 . 
     Screen  107  is connected to one terminal of HV supply  103 , while screen  109  is grounded through resistor  119  of discharge detection circuit  123 , so that screens  107  and  109  are at voltages of V a  and V b , respectively. These voltages can be selected as needed; a voltage difference V a −V b  between 1,800 and 7,000 V is generally used, while a voltage difference of 4,000 V or more is required to fire an arc if the material being tested is human hair. 
     The operation of setup  1  will now be explained with reference to the block diagram of FIG.  1  and the flow chart of FIG.  3 . The operation starts in step  301 . In step  303 , the medium flow is started, e.g., by turning on fan  115 , so that the fluid containing the medium to be tested flows through testing area  105 . In this way, at least some of the fibers, such as fiber F shown in FIG. 1, can contact both screens  107  and  109  simultaneously. In step  305 , the high voltage is applied from HV supply  103  to screens  107  and  109 , e.g., by discharging a capacitor. Thus, the HV is applied instantaneously across the ends of fiber F, so as possibly to cause the fiber to arc; the voltage needed to cause the arc depends on the material. Although FIG. 3 shows step  303  to precede step  305 , the order of step  303  and step  305  may be reversed. In step  307 , the response is watched on oscilloscope  117 , which can have capabilities such as printing the response or storing it on disk. In step  309 , the response is analyzed, e.g., by comparing it with archived or calculated responses. The frequency content and duration of a discharge from the material manifested in the response are dependent on the material. The initial effects are believed to be skin effects as the electrons rush across the surface of fiber F from one screen to the other. Suitable software can be written for the analysis. In step  311 , the operation ends. 
     Tests verified that the resultant waveforms were different for the various materials tested, i.e., graphite, coated graphite, human hair, stainless steel, and spider silk. All displayed significant differences in waveform characteristics. Since these materials are non-polar in nature, no polarization effect was either expected or observed. The voltages used in step  305  ranged from 1,800 V to 7,000 V; the coated graphite and the human hair did not arc at less than 4,000 V. 
     There is the concern that in setup  101  of FIG. 1, the resultant waveform is heavily influenced by the RCL of setup  101  itself. Moreover, the orientation of the fiber may give false results. To overcome these concerns and generally to provide a cleaner, more efficient and more tractable way to gather data, a modified setup was developed, which will now be explained with reference to FIG.  4 . In FIG. 4, elements which are the same as those in FIG. 1 are represented by the same element numbers, while elements which are modified from those in FIG. 1 are represented by element numbers increased by 300. 
     FIG. 4 shows modified setup  401 , which uses discharge detection circuit  123  in combination with a more robust HV supply  403  and testing area  405  improved for individual mounting of fibers. HV supply  403  uses a slapper switch and will be described in detail below. Testing area  405  uses brass rods  407 ,  409 , or other suitable mounting elements formed out of any suitable material, to which fiber F is secured with silver paint  425 , which has a drying time of approximately two hours. Any other suitable manner of securing fiber F to rods  407 ,  409  can be used. Multiple pairs of brass rods  407 ,  409  can be provided to form multiple testing jigs within testing area  405  so that multiple fibers can be mounted at a time; setups such as setup  401  have been built with up to five such pairs of rods. More than the two pairs of brass rods  407 ,  409  shown in FIG. 4 may be employed. Microscope  427 , such as a binocular microscope, can be used to mount and inspect the fibers. 
     HV supply  403  is of the “slapper switch” type and provides a high-voltage pulse from a predetermined capacitance and switch-on time. HV supply  403  is designed for testing and evaluation of bridgewire detonators. 
     As shown in FIG. 5, HV supply  403  includes the following components. Low-impedance shunt  501  allows analysis of the voltage supplied and includes monitoring point  503  to allow monitoring of the HV supply by any suitable monitoring equipment. The voltage is stored in high-capacitance capacitor  505 , whose capacitance is selected to provide the desired voltage to setup  401 . Capacitor  505  is discharged by a fast-acting switch such as vacuum switch  507  under control of a low-voltage firing input received through input lead  509 . 
     FIG. 6 shows a series of operational steps for using setup  401 . This series of operational steps is the same as in FIG. 3, except that step  303  is replaced with step  603  of attaching fiber F to rods  407  and  409 . 
     EXAMPLES 
     Experimental results from setup  401  will now be described with reference to FIGS. 7-12. In these figures, the x axis represents time in seconds, while the y axis represents voltage in kV. 
     FIG. 7 shows experimental results obtained with 8-micron graphite. The curve has regions  701  and  702 . Region  701  corresponds to the application of ˜2,000 V to provide a “ramp-up” in voltage. This region contains the spectral information characteristic of the material. Region  702  shows a voltage arc associated with vaporization of the material. 
     The remaining results show corresponding regions, except that when arcing does not occur, neither does the region corresponding to region  702 . 
     FIG. 8 shows results for 4-micron graphite. FIG. 9 shows curves for three samples of 4-micron stainless steel when placed in three respective different positions  1 ,  2  and  5 , i.e., between different brass rods  407 ,  409  of the device setup  401  having five pairs of rods  407 ,  409  in the setup. Positions  3  and  4  are not shown because the samples fractured in handling. FIG. 10 shows results for human hair, which acts as a high-impedance circuit. Arcing did not occur in this sample. FIG. 11 shows results for 12-micron stainless steel, while FIG. 12 shows results for 4-micron stainless steel. 
     While two variations of a preferred embodiment of the invention have been described in detail, those skilled in the art who have reviewed this disclosure will readily appreciate that other embodiments can be described within the scope of the invention. For example, modifications disclosed together can be used separately, while modifications disclosed separately can be combined. Also, any conventional analytical hardware, software, or techniques can be incorporated into setups according to the invention. Any disclosed process can be automated. The data collected can be combined with electron microscope pictures, manufacturing information, low-voltage measurements, or any other information useful in analysis of the material.