Abstract:
Various embodiments are described relating to devices and methods for detecting local human presence by olfactory reception of volatile organic compound (VOC) molecules dispersed in air. Such devices include a chamber inlet, a trap, a sensor and a communicator. The inlet receives the air that contains the VOC molecules, a trap for capturing the VOC molecules in the air. The sensor detects at least a threshold quantity of at least one of 3-hydroxy-3-methylhexanoic (3H3MH) acid and 3-methyl-2-hexanoic (3M2H) acid among the VOC molecules. The communicator provides notification of the threshold quantity. The methods include operations to receive the air, capture the molecules in the air, detect the 3H3MH and 3M2H acids, and signal notification of that detection.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to chemical detection of human presence. 
     BACKGROUND 
     Government and private officials often have responsibility for controlled areas subject to restrictive access to authorized persons. Such officials may employ various techniques to detect human presence. These tools generally depend on human activity to present a detectable signal. 
     Human activity may trigger a sensor based on various stimuli. For example, skeletal-muscular physical motion may form pressure gradients in the local environment, either the surrounding air or through the ground. For sufficiently intense pressure gradients, such motion may register motion or audio signals. Complimentarily, metabolic activity may yield a thermal contrast between the temperatures of a human body and the ambient surroundings. 
     SUMMARY 
     Various embodiments are described relating to devices and methods for detecting local human presence by the reception and detection of human-specific volatile organic compound (VOC) molecules dispersed in air. According to an example embodiment, such devices include a chamber inlet, a trap, a sensor and a communicator. The inlet receives the air that contains the human-specific VOC molecules, a trap for capturing the VOC molecules in the air. 
     The sensor detects at least a threshold quantity of at least one of 3-hydroxy-3-methylhexanoic (3H3MH) acid and 3-methyl-2-hexanoic (3M2H) acid among the VOC molecules. The communicator provides notification of the threshold quantity. The methods include operations to receive the air, capture the molecules in the air, detect the 3H3MH and 3M2H acids, and signal notification of that detection. 
     According to an example embodiment, the trap includes a sieve for capturing the VOC molecules from the air and a heater for releasing the captured VOC molecules from the sieve. In addition, the sensor comprises a chemical analyzer such as, for example, an ion-mobility spectroscope, a gas chromatograph, a gas chromatograph plus a mass spectroscope, and a flame ionization spectroscope. The corresponding exemplary method employs chemical detection of the 3H3MH and 3M2H acids. 
     According to another example embodiment, the trap comprises a filter that includes polyacrylamide fibers for capturing the VOC molecules from the air. In addition, the sensor comprises an electrode for responding to a physical property change in the polyacrylamide fibers. This physical property change, such as electrical characteristics, is caused by at least one of the 3H3MH and 3M2H acids in the captured VOC molecules. The corresponding exemplary method employs detection of characteristic changes in the filter&#39;s electrical properties. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which: 
         FIG. 1  is a diagram illustrating an olfactory detection system according to a chemical example embodiment; 
         FIG. 2  is a diagram illustrating an olfactory detection system according to an electrical example embodiment; 
         FIG. 3  is a flow diagram illustrating a logical sequence of operations for olfactory detection of human presence according to an example embodiment; and 
         FIG. 4  is a flow diagram illustrating a logical sequence of operations for olfactory detection of human presence according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Motion and thermal detectors require either physical or metabolic activity that cannot distinguish between human presence and non-human stimuli on a consistent or systematical basis. Consequently, sensor indication of movement or thermal contrast may result in false alarms that unproductively expend resources that operatives prefer to conserve. Thus, various exemplary embodiments describe techniques for exploiting human characteristics that exhibit unique and detectable manifestations. 
     Human skin, especially in axillary (i.e., armpit) regions, produces perspiration secretions whose molecules can be truncated by bacteria to produce hexanoic acids that represent volatile organic compound (VOC) molecules. These VOC molecules produce a recognizable odor and represent a uniquely human chemical signature, at least in detectable quantities. The odor produced by the VOC molecules can be sensed by olfactory receptors. The VOC molecules, as represented by hexanoic acids, include 3-hydroxy-3-methylhexanoic (3H3MH) acid and 3-methyl-2-hexanoic (3M2H) acid. After being captured, these VOC molecules can be heated to increase volatility for spectroscopic detection. 
       FIG. 1  is a diagram illustrating a VOC detection system  100  according to an example embodiment. The system  100  includes a pair of hollow chambers, represented by cylindrical tubes. The first chamber  110  is divided into an inlet portion  112  and a first filter portion  114  and a first convection portion  116 . The second chamber  120  is divided into a second convection portion  122 , a heater portion  124 , a second filter portion  126 , and an analysis portion  128 . 
     The system  100  further includes a communicator  130 . Upon detection of threshold-triggering quantities of 3H3MH and/or 3M2H acids, the communicator or signaler  130  transmits a wireless signal  132  to a remote receiver (not shown) for intrusion and/or threat assessment. 
     A person  140  within detection vicinity of the system  100  releases VOC molecules  142  into the ambient air  144 , A first fan  117  within the first convection portion  116  drives the air  144  into the chamber  110 . The molecules  142  in the air  144  enter the inlet portion  112  and pass into a sieve  115  disposed within the first filter portion  114  at a first position. The sieve  115  serves to capture or trap the molecules  142  by filtering the air  144  passing therethrough. 
     In various exemplary embodiments, the sieve  115  is a polymeric filter that chemically binds to the molecules  142 , thereby capturing them in the sieve  115 . A transfer mechanism  118  (shown symbolically) may remove the sieve  115  from its first position in the first filter portion  114  to a second position in the second filter portion  126 . Alternatively, the sieve  115  may be transferred manually from its first to second filter positions. 
     The second convection portion  122  includes a second fan  123  with which to blow air  146  over the sieve  115  disposed at the second position. A heater  125  in the heater portion  124 , in cooperation with the second fan  123 , volatilizes and releases the trapped molecules  142  on the sieve  115  at the second position. The air  146  carries these molecules  142  by convection to the analysis portion  128 . The second fan  123  and the heater  125  may be disposed preferably upstream of the filter&#39;s second position. 
     The analysis portion  128  includes a chemical analyzer  129  to evaluate the molecules  142  for the presence of 3H3MH and/or 3M2H acids. Threshold detection determines human presence in the vicinity of the system  100 . In various exemplary embodiments, the chemical analyzer  129  may be any of an ion-mobility spectroscope, a gas chromatograph, a gas chromatograph plus a mass spectroscope, or a flame ionization spectroscope. All of these analyzers are available as commercial off-the-shelf (COTS) devices. 
       FIG. 2  is a diagram illustrating a VOC detection system  200  according to an example embodiment. The system  200  includes a hollow chamber  210 , represented by a cylindrical tube, divided into an inlet portion  212 , a filter portion  214 , a convection portion  216  and an outlet portion  218 . 
     A person  140  within the detector&#39;s vicinity releases VOC molecules  142  into the ambient air  144 . A fan  217  within the convection portion  216  drives the air  144  with molecules  142  towards the chamber  210 . The molecules  142  in the air  144  enter the inlet portion  212  and pass through a filter  215  disposed within the filter portion  214 . 
     The filter  215  may include an electrode circuit  217  to sense changes in filter capacitance, conductance and/or light emission. Such physical characteristics are affected for detection by the electrode circuit  217  only when the filter  215  is saturated with 3H3MH and/or 3M2H acids, whereupon the communicator  130  transmits the wireless signal  132  to a remote receiver (not shown) for intrusion and/or threat assessment. The wireless signal  132  represents a radio signal within the electromagnetic spectrum, such as, but not limited to, radio, microwave and infrared frequencies. 
     In various exemplary embodiments, the filter  215  may include “memory” polymers, such as polyacrylamide. Such memory polymers can be produced via electrospinning techniques. By judiciously incorporating selected chemical additives or “dopants” to the polymer liquid prior to being electrospun, the filter  215  can respond to the binding of 3H3MH and/or 3M2H acids by changes in electrical conductance and/or electrical capacitance. 
     Dopants for enabling such property change detection by the electrode  217  include electrically conductive metal nanoparticles (particles whose diameter is less than 100 nanometers), such as gold, silver or copper, and/or electro-conductive polymers such as polyanilline. Alternatively, in response to binding with the molecules  142  the filter  215  can emit visible light  219  in response to the VOC binding. Dopants for enabling such light emission by the filter  215  include any semi-conducting material such as doped silicon. The light  219  may provide a visual indication of threshold quantities of the molecules  142  for further investigation. The light  219  may be transmitted to an eye-piece or through fiber optics to a remote monitoring station, or be used to trigger a radiofrequency signal by wireless transmission. 
     In various exemplary embodiments, the filter  215  may be exchanged with another filter, after the initially installed filter becomes saturated or to select an alternate particle size for transmission. The filter  215  may be connected to a tray or carrousel  220  having a series of filters  215 . The tray  220  may rotate about a carrousel center  222 , as shown, to exchange filters  215  mounted on spokes  224  and/or connected along a rim  226 . Alternatively, the tray  220  may translate as a conveyor belt  228  to exchange filters  215 . The filter  215  may be inserted through a slot  230  within the filter portion  214 . 
       FIG. 3  is a flow diagram illustrating an exemplarily process  300  of logical operations for olfactory detection of the VOC molecules  142  to indicate presence of the person  140 . The process begins with at step  310  and proceeds to blowing the air  144  towards a sieve at step  320 . The VOC molecules  142  in the air  144  adhere to the sieve  115  at step  330 . The heater  121  applied to the sieve  115  releases the molecules  142  at step  340 . 
     The chemical analyzer  129  receives and analyzes the molecules  142  at step  350  to determine at step  360  whether threshold quantities of 3H3MH and/or 3M2H acids are present. Upon such chemical detection, the communicator  130  transmits the signal  132  at step  370  to indicate presence of the person  140 . Otherwise, or at the conclusion of signal transmission, the process terminates at step  380 . 
       FIG. 4  is a flow diagram illustrating another exemplary process  400  of logical operations for olfactory detection of the VOC molecules  142  to indicate presence of the person  140 . The process begins with at step  410  and proceeds to blowing the air  144  towards a filter  215  at step  420 . The VOC molecules  142  in the air  144  adhere to the filter  215  at step  430 . The electrode circuit  217  connected to the filter  215  evaluates characteristic changes to electrical properties of the filter  215  at step  440  caused by saturation of the VOC molecules  142  to determine at step  450  whether threshold quantities of 3H3MH and/or 3M2H acids are present. 
     Upon such electrical detection, the communicator  130  transmits the signal  132  at step  460  to indicate presence of the person  140 . After reaching VOC molecular saturation, the filter  215  can changed at step  470 . In the absence of such detection at step  450 , or at the conclusion of signal transmission, the process terminates at step  480 . 
     While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.