3-hydroxy-3-methylhexanoic acid and 3-methyl-2-hexanoic acid detection as identifiers to monitor human presence

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'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:

<figref idrefs="DRAWINGS">FIG. 1</figref> is a diagram illustrating an olfactory detection system according to a chemical example embodiment;

<figref idrefs="DRAWINGS">FIG. 2</figref> is a diagram illustrating an olfactory detection system according to an electrical example embodiment;

<figref idrefs="DRAWINGS">FIG. 3</figref> is a flow diagram illustrating a logical sequence of operations for olfactory detection of human presence according to an example embodiment; and

<figref idrefs="DRAWINGS">FIG. 4</figref> 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.

<figref idrefs="DRAWINGS">FIG. 1</figref> is a diagram illustrating a VOC detection system <b>100</b> according to an example embodiment. The system <b>100</b> includes a pair of hollow chambers, represented by cylindrical tubes. The first chamber <b>110</b> is divided into an inlet portion <b>112</b> and a first filter portion <b>114</b> and a first convection portion <b>116</b>. The second chamber <b>120</b> is divided into a second convection portion <b>122</b>, a heater portion <b>124</b>, a second filter portion <b>126</b>, and an analysis portion <b>128</b>.

The system <b>100</b> further includes a communicator <b>130</b>. Upon detection of threshold-triggering quantities of 3H3MH and/or 3M2H acids, the communicator or signaler <b>130</b> transmits a wireless signal <b>132</b> to a remote receiver (not shown) for intrusion and/or threat assessment.

A person <b>140</b> within detection vicinity of the system <b>100</b> releases VOC molecules <b>142</b> into the ambient air <b>144</b>, A first fan <b>117</b> within the first convection portion <b>116</b> drives the air <b>144</b> into the chamber <b>110</b>. The molecules <b>142</b> in the air <b>144</b> enter the inlet portion <b>112</b> and pass into a sieve <b>115</b> disposed within the first filter portion <b>114</b> at a first position. The sieve <b>115</b> serves to capture or trap the molecules <b>142</b> by filtering the air <b>144</b> passing therethrough.

In various exemplary embodiments, the sieve <b>115</b> is a polymeric filter that chemically binds to the molecules <b>142</b>, thereby capturing them in the sieve <b>115</b>. A transfer mechanism <b>118</b> (shown symbolically) may remove the sieve <b>115</b> from its first position in the first filter portion <b>114</b> to a second position in the second filter portion <b>126</b>. Alternatively, the sieve <b>115</b> may be transferred manually from its first to second filter positions.

The second convection portion <b>122</b> includes a second fan <b>123</b> with which to blow air <b>146</b> over the sieve <b>115</b> disposed at the second position. A heater <b>125</b> in the heater portion <b>124</b>, in cooperation with the second fan <b>123</b>, volatilizes and releases the trapped molecules <b>142</b> on the sieve <b>115</b> at the second position. The air <b>146</b> carries these molecules <b>142</b> by convection to the analysis portion <b>128</b>. The second fan <b>123</b> and the heater <b>125</b> may be disposed preferably upstream of the filter's second position.

The analysis portion <b>128</b> includes a chemical analyzer <b>129</b> to evaluate the molecules <b>142</b> for the presence of 3H3MH and/or 3M2H acids. Threshold detection determines human presence in the vicinity of the system <b>100</b>. In various exemplary embodiments, the chemical analyzer <b>129</b> 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.

<figref idrefs="DRAWINGS">FIG. 2</figref> is a diagram illustrating a VOC detection system <b>200</b> according to an example embodiment. The system <b>200</b> includes a hollow chamber <b>210</b>, represented by a cylindrical tube, divided into an inlet portion <b>212</b>, a filter portion <b>214</b>, a convection portion <b>216</b> and an outlet portion <b>218</b>.

A person <b>140</b> within the detector's vicinity releases VOC molecules <b>142</b> into the ambient air <b>144</b>. A fan <b>217</b> within the convection portion <b>216</b> drives the air <b>144</b> with molecules <b>142</b> towards the chamber <b>210</b>. The molecules <b>142</b> in the air <b>144</b> enter the inlet portion <b>212</b> and pass through a filter <b>215</b> disposed within the filter portion <b>214</b>.

The filter <b>215</b> may include an electrode circuit <b>217</b> to sense changes in filter capacitance, conductance and/or light emission. Such physical characteristics are affected for detection by the electrode circuit <b>217</b> only when the filter <b>215</b> is saturated with 3H3MH and/or 3M2H acids, whereupon the communicator <b>130</b> transmits the wireless signal <b>132</b> to a remote receiver (not shown) for intrusion and/or threat assessment. The wireless signal <b>132</b> 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 <b>215</b> 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 <b>215</b> 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 <b>217</b> 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 <b>142</b> the filter <b>215</b> can emit visible light <b>219</b> in response to the VOC binding. Dopants for enabling such light emission by the filter <b>215</b> include any semi-conducting material such as doped silicon. The light <b>219</b> may provide a visual indication of threshold quantities of the molecules <b>142</b> for further investigation. The light <b>219</b> 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 <b>215</b> may be exchanged with another filter, after the initially installed filter becomes saturated or to select an alternate particle size for transmission. The filter <b>215</b> may be connected to a tray or carrousel <b>220</b> having a series of filters <b>215</b>. The tray <b>220</b> may rotate about a carrousel center <b>222</b>, as shown, to exchange filters <b>215</b> mounted on spokes <b>224</b> and/or connected along a rim <b>226</b>. Alternatively, the tray <b>220</b> may translate as a conveyor belt <b>228</b> to exchange filters <b>215</b>. The filter <b>215</b> may be inserted through a slot <b>230</b> within the filter portion <b>214</b>.

<figref idrefs="DRAWINGS">FIG. 3</figref> is a flow diagram illustrating an exemplarily process <b>300</b> of logical operations for olfactory detection of the VOC molecules <b>142</b> to indicate presence of the person <b>140</b>. The process begins with at step <b>310</b> and proceeds to blowing the air <b>144</b> towards a sieve at step <b>320</b>. The VOC molecules <b>142</b> in the air <b>144</b> adhere to the sieve <b>115</b> at step <b>330</b>. The heater <b>121</b> applied to the sieve <b>115</b> releases the molecules <b>142</b> at step <b>340</b>.

The chemical analyzer <b>129</b> receives and analyzes the molecules <b>142</b> at step <b>350</b> to determine at step <b>360</b> whether threshold quantities of 3H3MH and/or 3M2H acids are present. Upon such chemical detection, the communicator <b>130</b> transmits the signal <b>132</b> at step <b>370</b> to indicate presence of the person <b>140</b>. Otherwise, or at the conclusion of signal transmission, the process terminates at step <b>380</b>.

<figref idrefs="DRAWINGS">FIG. 4</figref> is a flow diagram illustrating another exemplary process <b>400</b> of logical operations for olfactory detection of the VOC molecules <b>142</b> to indicate presence of the person <b>140</b>. The process begins with at step <b>410</b> and proceeds to blowing the air <b>144</b> towards a filter <b>215</b> at step <b>420</b>. The VOC molecules <b>142</b> in the air <b>144</b> adhere to the filter <b>215</b> at step <b>430</b>. The electrode circuit <b>217</b> connected to the filter <b>215</b> evaluates characteristic changes to electrical properties of the filter <b>215</b> at step <b>440</b> caused by saturation of the VOC molecules <b>142</b> to determine at step <b>450</b> whether threshold quantities of 3H3MH and/or 3M2H acids are present.

Upon such electrical detection, the communicator <b>130</b> transmits the signal <b>132</b> at step <b>460</b> to indicate presence of the person <b>140</b>. After reaching VOC molecular saturation, the filter <b>215</b> can changed at step <b>470</b>. In the absence of such detection at step <b>450</b>, or at the conclusion of signal transmission, the process terminates at step <b>480</b>.

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.