Abstract:
A system and an apparatus for detecting explosive in real time is provided for. The apparatus involves a chamber in which items pass through or people walk through for detecting said explosive particles in real time. The explosive particles from either the people or items will be deposited into a cell by an influx of air flow from the chamber flowing to the cell. The cell includes a heating device and an optical scheme. The cell is heated to a predetermined temperature in which the explosive particles are divided into small molecular components that can be detected. The optical scheme detects the smaller molecules. The computer system controls the apparatus and analyzes the data gathered.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Technical Field  
           [0002]    The present invention relates to detecting a molecule present in the air. More specifically the invention relates to a laser device for detecting explosive particles. The device is controlled by a computer system.  
           [0003]    2. Description of the Related Art  
           [0004]    The colors of an object typically arise because materials selectively absorb light of certain frequency, while scattering or transmitting light of other frequencies. For example an object is red (wavelength range from 6300 and 6800 Å) if it absorbs all visible frequencies except those our eyes perceive to be “red.” Thus, we see the scattered wavelength range from 6300 and 6800 Å from that object.  
           [0005]    Similarly, molecules absorb at different frequencies. A predefined range of wavelength propagating through gas molecules are absorbed at the resonance frequencies of the atoms or molecules, so that one observes gaps in the wavelength distribution of the emerging wavelengths. Absorption lines of a molecule have its own intensity and spectral position. In detecting a molecule using laser technology, the laser radiates frequencies near the absorption line to amplify the sensitivity of the detection.  
           [0006]    Increasingly, more people are relying on airplanes as a mean for transportation to a distant destination. Airport personnel are vigilant about the security of the airport and the flight itself. Everyone and their carried on baggage must go through metal detectors before going to the departure gate and board on the airplane. The metal detector helps in finding guns and knives but it cannot detect explosives. The detection for explosives should not be intrusive and applies to everyone and their luggage when they decide to fly.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention provides a system and an apparatus for detecting explosive in real time. The apparatus involves a chamber in which items pass through or people walk through for detecting said explosive particles in real time. The explosive particles from either the people or items will be deposited into a cell by an influx of airflow from the chamber flowing to the cell. The cell includes a heating device and an optical scheme. The cell is heated to a predetermined temperature in which the explosive particles are divided into small molecular components that can be detected. The optical scheme detects the smaller molecules. The computer system controls the apparatus and analyzes the data gathered.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a block diagram of explosive particle detector according to an embodiment of the present invention.  
         [0009]    [0009]FIG. 2 is a block diagram of an optical scheme according to an embodiment of the present invention.  
         [0010]    [0010]FIG. 3 is a block diagram of a computer system according to an embodiment of the present invention.  
         [0011]    [0011]FIG. 4 is a block diagram of an particle detector controller in accordance with an embodiment of the present invention.  
         [0012]    [0012]FIG. 5 is a pictorial representation of particle detector in accordance with an embodiment of the present invention.  
         [0013]    [0013]FIG. 6 is a pictorial representation of interface module in accordance with an embodiment of the invention.  
         [0014]    [0014]FIG. 6( a ) is a DL current supply in accordance with an embodiment of the present invention.  
         [0015]    [0015]FIG. 6( b ) is a resistance-voltage transformer in accordance with an embodiment of the present invention.  
         [0016]    [0016]FIG. 6( c ) is a peltier supply in accordance with an embodiment of the present invention.  
         [0017]    [0017]FIG. 7 is a pictorial representation of a photodetector transformer/amplifier unit in accordance with an embodiment of the invention.  
         [0018]    [0018]FIG. 8 is a block diagram of software in accordance with an embodiment of the invention.  
         [0019]    [0019]FIG. 9 is a flowchart of signal processing in accordance with an embodiment of the invention.  
         [0020]    [0020]FIG. 10 is a flowchart for calculation of particle concentration in accordance with an embodiment of the present invention.  
         [0021]    [0021]FIG. 10 a  is an absorption profile.  
         [0022]    [0022]FIG. 11 is a flowchart for DL temperature stabilization in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0023]    The description of the preferred embodiment of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention the practical application to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.  
         [0024]    With reference now to the figures and in particular with reference to FIG. 1, a pictorial representation of explosive particle detector  100  in accordance with an embodiment of the presentation of optical scheme is illustrated. Explosive particle detector  100  includes detection chamber  101 , cell  102 , and airflow  103 . Detection chamber  101  is an enclosed area in which items such as luggage and packages may pass through by entering the chamber for explosive detection in real time thereafter it exits the chamber. This could be achieved by putting the items on a conveyor belt capable of transferring the items from one place to other. If an item is detected to contain explosive, it is marked as such, removed from the chamber for further inspection and required to follow appropriate security measures. If an item does not contain explosive, it exits the chamber without being marked and continues its appropriate journey.  
         [0025]    The chamber  101  is connected to cell  102 . Cell  102  includes heater  110  and optical scheme  111 . Air flows from the chamber into the cell. Air flow  103  can be achieved by cell  102  having a vacuum mechanism to influx air into the cell  102  or air is blown from the chamber  101  into the cell  102  or a combination thereof. Because of the airflow, explosive particles, will be deposited in the cell  102  in which heater  110  and optical scheme  111  works together to detect the presence of explosive particle. Heater  110  heats up the cell to a temperature degree in which the explosive particles are divided into smaller molecular components.  
         [0026]    [0026]FIG. 2 shows a pictorial representation of optical scheme  200  in accordance with an embodiment of the present invention. This figure corresponds to optical scheme  111  of FIG. 1. Optical scheme  200  involves diode laser (“DL”)  201  assembled a thermistor  221 , a temperature sensitive resistor. Diode laser  201  radiating power is proportional to transformed DL current  216 . Diode laser  201  wavelength depends on the temperature of the diode laser  201 . Thermistor  221  sets and adjusts the temperature for diode laser  201  with the raw resistance voltage  212 . Other temperature stabilizing components can be substituted for thermistor  221 . Diode laser  201  and thermistor  221  are housed inside thermostatic enclosure  202 . Thermostatic enclosure  202  helps to keep the temperature of the assembly constant without the effect of the changing temperature of the outside environment. Outside of thermostatic enclosure  202 , the optical scheme further includes optical components for analytical optical scheme.  
         [0027]    In the analytical optical scheme, diode laser scanning radiation frequency  202  is channel into single mode fiber  203  of about two meters long. Single mode fiber  203  narrows the concentration of radiation in which the inhomogenity of DL radiation is 0.3%, thereby optical filters are not required. The output of the single mode fiber  203  is diverged at a 20° angle obeying the Gaussian law. Then the radiation is passed through objective  204  to be adjusted by refraction in order to fully illuminate the cube reflector  205 . Between objective  204  and reflector  205 , the radiation may have pass through an enclosure, for example, cell  102 . The absorption of the particle occurs for the first time. In a preferred embodiment of the present invention, particle molecules may be detected here. The reflected radiation fully illuminates spherical mirror  206  having a 6.5 cm diameter, which is positioned behind objective  204 . The optical path between reflector  205  and spherical mirror  206  undergoes a second absorption of the particle inside the enclosure. Because radiation passes through the enclosure twice, the absorption of the particle amplifies. Spherical mirror  206  focuses the absorbed radiation on the sensing area of analytical photodetector  207 . Then, photodetetor  207  generates raw analytical PD1 signal  214 .  
         [0028]    Those of ordinary skill in the art will appreciate that the detector is capable of detecting explosive and drug particles by the above optical scheme incorporating Tunable Diode Laser Spectroscopy or Fourier Transform Spectroscopy.  
         [0029]    Referring now to FIG. 3, a block diagram of an explosive particle detector system is shown in accordance with a preferred embodiment of the present invention. Particle detector system  300  includes computer system  301 , optical scheme  302  (which corresponds to optical scheme  111  and  200 ), interface module  303 , photodetector transformer amplifier unit  304 , and software  305 . Software  305  initializes and synchronizes particle detector system  300 . It also provides for particle detector system signal processing and storing and analyzing data. Computer system  301  provides processing and control to particle detector system  300 . There are signals communicating between computer system  301  and optical scheme  302 . These signals must pass through interface module  303 .  
         [0030]    Referring now to FIG. 4, a block diagram of a computer system  301  is shown in accordance with a preferred embodiment of the present invention. Computer system  301  may employ a single microprocessor  401 , or in the alternative, multiple microprocessors on the system bus  402 . A storage device is connected to a memory bus  404 . An input/output (“I/O”) device may be integrated to the I/O bus  403  as depicted. A storage device includes memory devices such as hard disk drive  406 . I/O device includes a particle detector controller  405  for assisting in the control of a particle detector. Computer system  301  controls and communicates with the particle detector.  
         [0031]    Those of ordinary skill in the art will appreciate that the hardware depicted in FIG. 4 may comprise of multiple microprocessors, multiple storage devices, or multiple I/O devices. These devices may vary. For example, other peripheral devices, such as optical disk drives and the like, also may be used in addition to or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention.  
         [0032]    Referring now to FIG. 5, a block diagram of a particle detector controller  405  is illustrated. A multiplexor  510  allows successive connecting of inputs to analog to digital converter (“ADC”)  511  with set update rate, which value can&#39;t exceed a predetermined sampling frequency, 1.25 MHz. Next, dither  512  may be used for smoothing of bits in ADC  511  output signals. A timer controlled by software serves as clock cycle for particle detector controller  405 . It may include a frequency divider that allows for frequency adjustments of output signal generation and data acquisition. The timer controls a trigger. It serves as a signal to synchronize the signal generation and data acquisition. If this triggering synchronization switches at a common frequency, it creates an operational frequency for the particle detector controller  405 .  
         [0033]    With regards to controller&#39;s outputs, data are stored in buffer memory  513 . A predetermined pulsed signal for DL current pulse is stored in buffer memory  513  for DL current. The data stored in the buffer memory  513  flows to the first digital-to-analog converter (“DAC1”). DAC1 supplies continuous train of raw DL current  504 . Controller  405  is installed in the computer PCI bus  506  and connected with Interface module and photodetector transformer/amplifier unit. Data exchange between controller  405  and computer through reads and writes of controller&#39;s  405  buffer memories  513 . In a preferred embodiment of the present invention, controller  405  is configured from a standard multifunctional NI-DAQ board of the PCI-MIO-16E-1 produced by National Instruments, Inc.  
         [0034]    Referring now to FIG. 6, a pictorial representation of interface module  303  in accordance with an embodiment of the present invention is illustrated. Interface module  303  involves three analog units: DL current supply  610 , resistance—voltage transformer  620 , and peltier current supply  630 . Interface module  303  provides interface for three signals between the optical scheme  200  and particle detector controller  405 . In FIG. 6( a ), DL current supply amplifies  610  and transforms the pulse of raw DL current  617  into pulses of amplified DL current  618  feeding optical scheme. It includes three operational amplifiers,  611 - 613 . Resistance R 1   614  and capacitance C 1   615  define frequency bandwidth. Resistance R 2   616  defines the current/voltage transformation factor. The output operational amplifier A 2    613  and resistor R 2    616  are chosen thermo stable for preventing drift of output parameters.  
         [0035]    Two other units of interface module  303 , resistance—voltage transformer  620  is intended for stabilizing and adjusting the diode laser temperature. The temperature of thermistor having good thermal contact with diode laser in optical scheme  200  is measured in the Resistance/Voltage Transformer unit  620  as depicted in FIG. 6( b ). Resistance—voltage transformer unit  620  includes two operational amplifiers  621  and  622  and stable current supply  623 . Current supply  523  ensures that a current of 100 uA flows the thermistor R t    624 . Resistance—voltage transformer unit  620  transforms raw resistance—voltage signal  626  into a voltage value for transformed resistance—voltage signal  625 . Transformed resistance—voltage signal  625  transmits to Controller  405  as one of the inputs, which is later transformed into degree value in the device software.  
         [0036]    Referring now to FIG. 7, a pictorial representation of a photodetector transformer/amplifier unit  304  in accordance with an embodiment of the present invention is illustrated. Photodetector transformer/amplifier unit  304  transforms raw analytical PD1 signal  701  into differential amplified analytical PD1 signal  703 . Amplified analytical PD1 signal  703  is an input to Particle Detector Controller  405 . Base scheme of these transformer-amplifiers is shown at FIG. 7. The first stage of the scheme is typical transimpedance amplifier A 9  where R 9  and C 3  are feedback resistance and capacitance respectively. Amplifier frequency bandwidth is defined by capacitance C 3 , transfer factor at low frequencies is defined by resistance R 9 . Second stage of the scheme is voltage amplifiers A 10  and A 11  for generating differential outputs. Photodetector transformer/amplifier unit  304  is also battery-powered for providing high signal to noise ratio.  
         [0037]    Referring now to FIG. 8, a block diagram of software  305  in accordance with an embodiment of the present invention is illustrated. Software  801  initializes and synchronizes particle detector system  300 . It also provides for particle detector system computer program instruction for signal processing  802 , diode laser temperature stabilization  803 , calculation of particle concentration  804  and other operations are produced in the base part of the program  805 .  
         [0038]    Referring now to FIG. 9, a flowchart of signal processing  802  according to an embodiment of the present invention is illustrated. The software provides instructions for signal processing for generating the pattern of pulses of DL current (step  901 ). The pulse pattern period must in proportionate to the digital to analog converter update rate. The pattern is then stored in the particle detection controller&#39;s buffer memory (step  902 ). The software further provides instructions for applying the pattern to the particle detection controller&#39;s digital to analog converter (step  903 ). The DAC in the particle detector controller, transform the pulsed pattern into a continuous raw DL current.  
         [0039]    Referring now to FIG. 10, a flowchart for calculation of particle concentration  804  according to an embodiment of the present invention is illustrated. The process for calculating particle concentration starts with the receipt of sampled data from the analytical photodetector signal at beginning of the current pulse (step  1001 ).  
         [0040]    Three controller inputs (step  1002 ): (1) photodetector signal from analytical channel (step  1003 ), (2) photodetector signal from reference channel (step  1004 ), (3) signal proportional to thermistor resistance (step  1005 ), are used in the present invention. The signals are applied to the controller ADC successively, so sampling frequency of each input is three times lower than the controller update rate and equals 166.6 kHz. Pulse duration in photodetector signals includes 500 points, duration between adjacent pulses includes 100 points, and pulse repetition period includes 600 points. Modulation period in the signals is two times more than duration between adjacent points; so even points form one branch (low), odd points form another branch (high).  
         [0041]    The first channel contains sampled analytical PD1 signals made up of a train of pulses having 3.6 ms period (step  1003 ). The software separates the pulses for independent treatment of each pulse (step  1006 ) according to a period or cycle of a pulse. In step  1007 , the value of “zero signal” between two pulses is subtracted from each of the points respectively. “Zero signal” is PD signal when laser is switched off. This signal includes photodetector preamplifier output shift and value connected with illumination of photodetector by other light sources. The value of zero signal is averaged by 100 points between two adjacent pulses. Step  1007  lessens interference of photodetector illuminated by another sources (i.e. light illumination reflected by pieces of glass or car windows). The result from subtracting zero signal is saved as background pulse (step  1008 ). Next the process calculates the difference between the background pulse and the raw current (step  1009 ). The independent pulse is separated into two arrays: (a) an odd array for storing all the odd points and (b) an even array for storing all the even points. The logarithm of the ratio of respective even points over odd points (e.g. Ln(even/odd)) is calculated in step  1010 . The logarithm value is proportional to the difference of absorptions at the branches wavelength ranges and would lessen any low-frequency signal interference from mechanical vibration or interfering illumination. Steps  1013  through  1020  take the signal from the reference photodetector and perform the same steps that have been done on the analytical photodetector signal. That is, the signal is separated into independent pulses (step  1016 ), the zero signal is subtracted (step  1017 ), the results is saved a background pulse (step  1018 ), the difference between the background pulse and the raw current are calculated (step  1019 ) and the logarithm of the reference signal is calculated (step  1020 ). Finally, the calculated logarithms of both the analytical signal and the reference signal are used to calculate the correlation factor with reference function (step  1015 ). This ends the cycle.  
         [0042]    DL temperature variations directly affect the DL radiation wavelength variation. The stabilization of DL temperature ensures that DL will operate in the stable range near the maximum particle absorption band at 1.39268 um. FIG. 10 a  illustrates an absorption profile.  
         [0043]    Referring now to FIG. 11, a flowchart for DL temperature stabilization  803  according to an embodiment of the present invention is illustrated. Initially, the diode laser&#39;s temperature is set with the help of the thermistor (step  1101 ). First the process receives the transformed resistance/voltage signal (step  1102 ) from thermistor. With a predetermined load thermistor calibration function, the thermistor&#39;s actual temperature can be calculated (step  1103 ). Then with a set predetermined laser temperature and thermistor&#39;s actual temperature, the process calculates the temperature difference (step  1104 ). Next, the process calculates the PID (Proportion, Integral, Derivative) value (step  1105 ) in order to determine the pump current (step  1106 ). Initially, the diode laser and thermistor should have the same temperature until the diode laser generates more heat in which the temperature of the two components differs. As a result, thermistor&#39;s temperature is stabilized and not the diode laser. After the initial setting of the temperature, the process switches to line stabilization position (step  1110 ) for stabilizing DL temperature. The absorption line position within a recorded pulse is an unbiased criterion of DL true temperature. First, it receives the sampled data from amplified reference PD2 signal (step  1111 ). Each pulse is separated from the other (step  1112 ) for subtraction from zero signal (step  1113 ). The process repeats step  1113  one hundred times (100×) for one-hundred pulse period before it takes the average value (step  1114 ). Next, with a preferred predetermined laser temperature and the calculated average value, the temperature difference is calculated (step  1115 ). Then the PID value must be calculated (step  1116 ) before the determination of pump current (step  1117 ). The difference between current absorption line position and predetermined one come to the input of PID (Proportion, Integral, Derivative) program module. Value from output of this module is applied to DAC 2 for feeding Peltier element. This value at n step of the program cycle (V n ) is calculated in conformity with formula:  
         
       V 
       n 
       =a*P 
       n 
       +b*I 
       n 
       +c*D 
       n  
     
         [0044]    where P n  is the difference (see above) at n step of the program cycle,  
           I   n     =       ∑   0   n                     P   i         ,                         
  D   n   =P   n   −P   n−1 , a, b, c-factors.  
         [0045]    Because Pump current is not constant and must be determined, Pump current is tunable and directly stabilizes DL temperature. The determined Pump current is applied DAC2 on the controller in which the Pump current is made continuous before channeling to the interface module. DL temperature variations directly affect the DL radiation wavelength variation. The stabilization of DL temperature ensures that DL will operate in the stable range near the maximum particle absorption band.  
         [0046]    Although preferred embodiments of the present invention have been described in the foregoing Detailed Description and illustrated in the accompanying drawings for particle detection, it will be understood that the invention is not limited to the embodiments disclosed, but is capable detecting other gas molecules which may require numerous rearrangements, modifications, and substitutions of steps without departing from the spirit of the invention. For example, each gas molecule having distinct absorption band would require a diode laser radiating at or near that band, the photodetector functions at the distinct absorption band, the predetermined DL current may differ in the sampled points and duration, the reference cell may differ in content. Accordingly, the present invention is intended to encompass such rearrangements, modifications, and substitutions of steps as fall within the scope of the appended claims.