Carbon Nanotube Sensor to Stop Drunk Drivers Revealed, 1,000 Times More Sensitive Than Conventional Sensors

Delphi Technologies, Inc. (Troy, MI) engineers have developed a passive chemical vapor sensor that can determine if a driver is too drunk to drive without a person doing anything other than getting in the car.  The sensor passively measures ethanol vapor with high sensitivity and chemical specificity to 0.1 to 10 parts per million in the air of the car's cabin. The sensor could also transmit a message to a computer in the car to automatically increase the distance between the car and other cars on the road if the driver is a bit tipsy or send a warning message to police.  The sensors can be placed in multiple locations in the car. 

In an aspect, ethanol vapor in a vehicle cabin is measured, and sufficient sensitivity is provided to passively detect a motor vehicle driver that exceeds a legal limit of blood alcohol concentration (BAC), for use with vehicle safety systems. The sensor can be situated in an inconspicuous vehicle cabin location and operate independently without requiring active involvement by a driver. A vapor concentrator is utilized to amplify a sampled vapor concentration to a detectible level for use with an infrared (IR) detector. In comparison to conventional chemical sensors, the sensitivity of detection of ethanol vapor is increased by a factor of about 1,000. Further, a single channel of infrared detection is utilized avoiding spurious infrared absorption and making the chemical vapor sensor less costly to implement say inventors David K. Lambert, Larry M. Oberdier and Christopher M. Thrush in  U.S. Patent 7,700,044.

The vapor adsorber material is one of carbon, carbon molecular sieves, activated carbon, carbon nanotubes, porous organic polymer, inorganic materials having a high surface area and zeolite. 

               

Intoxicated drivers are a major cause of traffic accident fatalities in the United States. A recent NHTSA report showed that 40% of the total accident fatalities in the U.S. in the year 2003 were alcohol related. More specifically, In 2003, 12,373 motor vehicle occupants were killed in crashes that involved a blood alcohol concentration (BAC) of 0.08% or higher. This equates to over 33% of the 37,132 U.S. motor vehicle fatalities in 2003. In addition to the societal impact, the cost of such crashes in the U.S. is about $40 billion per year. It is well established that the rate of fatal traffic accidents per mile traveled is related to a driver's (BAC) and that there is a correlation between impairment in driving skills and the driver's BAC. The definition of drunk driving in the U.S. involves a BAC level of either 0.08% or 0.10%, depending on the particular state law. Moreover, the states of the U.S. that currently have a 0.10% BAC limit have passed laws lowering the BAC limit to 0.08%, to take effect soon. Various approaches to combat drunk driving have been utilized. The following existing approaches require active involvement of a vehicle driver.

Ethanol concentration in human breath is a good indication of BAC. Inside the human lung, there is a chemical equilibrium between the concentration of ethanol in the air and the concentration of ethanol in an individual's blood. An approach to combat drunk driving, which utilizes this notion of ethanol concentration in human breath, uses an electrochemical sensor to measure ethanol concentration in air. For law enforcement purposes, an electrochemical sensor is built into an object such as a clipboard or flashlight that a police officer can, under certain circumstances, justifiably insert into a vehicle. However, currently available electrochemical sensors have a limited lifetime and typically must be replaced after about three years. To be used as an on-board component of the safety system, an ethanol sensor must have a lifetime of at least ten to fifteen years. 

The ethanol sensitivity needed to passively detect a driver at the threshold of intoxication is additionally determined by the present invention. CO2 that is naturally present in human breath is used as a tracer to determine sensor measurement requirements (sensitivity required) for passive detection of ethanol in a vehicle cabin. This avoids the use of intoxicated human subjects. Ethanol and CO2 do not separate significantly as exhaled breath drifts from a driver's mouth to a location where air is sampled by the passive sensor. The transport of both ethanol vapor and CO2 from a driver's mouth to the sensor is dominated by convection, which is the same for both ethanol and CO2. The concentration of ethanol vapor in breath is proportional to BAC, and is 210 ppm when BAC is 0.08%. The concentration of CO2 in exhaled breath is approximately 36000 ppm (as compared to 370 ppm in ambient air). Like ethanol, CO2 in exhaled breath comes from exchange with blood in the alveolar sacs in the lung. Based on CO2 measurements with a test subject, the breath alcohol concentration at the sensor is at least 0.5 ppm for any HVAC setting (with the windows closed) at 5 minutes after a driver with BAC of 0.08 is seated in the vehicle. Some drivers breathe only half as much air as the test subject, so the ethanol sensor requires sensitivity to 0.2 ppm ethanol in air. Therefore, the sensor must be capable of measuring ethanol concentration in the range of 0.2 ppm to 10 ppm ethanol in air by volume.

The safety consequences of drunk driving result from impaired driving skills and extra risk taking. One approach is to give an impaired driver more time to react. The present invention provides for automatic compensation by a safety system for the slowed reaction time of a drunk driver. For example, if a predetermined concentration of ethanol is exceeded, as measured by the chemical sensor (i.e., an IR sensor), an appropriate safety system response can be carried out by an engine microcontroller. The safety system can impose restrictive requirements and limitations including requiring or increasing a minimum headway distance behind a preceding vehicle, as well as constrain vehicle performance.

Additionally, the safety system can transmit to police, through a wireless transmitter, a message that indicates a measured ethanol concentration or that the ethanol concentration in the vehicle cabin or the vehicle driver's BAC exceeds a preset level. Further, in an embodiment, in the case of a traffic accident, the safety system can alert an EMS responder, or police, that ethanol is detected. Additionally, if a predetermined level of ethanol vapor or BAC is detected, then the safety system can transmit the measured value to a flight recorder for eventual downloading by a third party.

The ethanol detection can be employed prior to vehicle startup, and can be performed repetitively during vehicle operation. Repetitive sensing enables the present invention to monitor a driver for previously consumed alcohol that will cause the ethanol concentration in the driver's breath to increase over time, perhaps above the legal limit. 

An additional approach to combat drunk driving uses a heated film of metal oxide that changes electrical resistance in response to ethanol concentration. Such sensors are used in commercially available "breath interlocks," sometimes mandated following a drunk driving conviction, which requires the driver to breathe into a tube to check for excess breath alcohol before the vehicle will start. However, such sensors do not have sufficient sensitivity for passive detection of a drunk driver in regard to measuring ethanol vapor in the air of a vehicle cabin. The breath sample blown into a tube is undiluted so the detection level needed is only about 210 ppm ethanol. Also, the minimum ethanol concentration that can be reliably detected with a metal oxide film is typically in the range of 10 to 50 ppm. A further disadvantage is that the response to ethanol concentration is non-linear as a function of ethanol concentration.

A further approach to combat drunk driving uses an electrochemical sensor that is pressed against an individual's skin to determine alcohol intoxication through remote detection of ethanol that evaporates from the driver's skin. This approach is an active system since contact with the driver's skin is required. The lifetime of this sensor has not been demonstrated.