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Electric field sensor to monitor driver fatigue

Electric field sensor to monitor driver fatigue


EPIC sensor technology from Plessey Semiconductors enables development of reliable
detection systems that are capable of monitoring new parameters like driver fatigue

electric1.jpgPlessey Semiconductors’ award winning EPIC sensor technology has been creating considerable interest with car manufacturers as it can be used to provide low cost, reliable detection systems for several automotive applications. This has a lower gain and higher input impedance making it ideal for certain types of contactless ECG measurement such as driver fatigue monitoring or seat occupancy.

The EPIC sensor is a completely new area of sensor technology and works by measuring tiny changes in an electric field in a similar way to a magnetometer detecting changes in a magnetic field even at a distance and through clothing. There are several applications where EPIC can be used in cars. For example, driver monitoring for health and alertness by detecting heart rate and respiration or determining the occupancy of the car to adjust the ride, handling and air bag deployment depending on the size and location of occupants.

The EPIC sensor electrodes can be easily and discretely incorporated inside the seat backs to acquire the necessary biometric data. Mentions Derek Rye, Plessey Semiconductors’ Marketing Manager, “Regulations and economics are meaning that car designs are all becoming very similar so that manufacturers have to differentiate their products by the user features and comfort inside the car”. “We are only just starting to explore the new and exciting ways that these innovative sensors can be used to enhance and improve safety”, he adds.

electric2.jpgEPIC sensors are already in commercial production by Plessey Semiconductors. By adjusting the DSP and amplification circuitry, the sensors can be tuned for detection at a distance as required for these automotive applications. Volume production pricing for the PS25203 is in the region of $1-2. The PS25203 is supplied in a custom 4-pin PCB hybrid package measuring 10.5mm x 10.5mm x 3.45mm.

The EPIC sensor, which requires no physical or resistive contact to make measurements, will enable innovative new products to be made such as medical scanners that are simply held close to a patient’s chest to obtain a detailed ECG reading or safety and security devices that can ‘see’ through walls. The sensor can be integrated on a chip with other features such as data converters, digital signal processing and wireless communications capability.

The technology works at normal room temperatures and functions as an ultra-high, input impedance sensor that acts as a highly stable, extremely sensitive, contactless digital voltmeter to measure tiny changes in the electric field down to milliVolts. Most places on Earth have a vertical electric field of about 100 Volts per metre. The human body is mostly water and this interacts with the electric field. EPIC technology is so sensitive that it can detect these changes at a distance and even through a solid wall.

A new development from Aisin Seki Co., Japan, also works in the direction of preventing accidents caused by drowsiness during driving. The company has developed an eyelid monitor, which identifies symptoms in eyelid behaviour that indicate drowsiness in motorists. The new automated technology (Intelligent Transport System (ITS)) eliminates the fallibility of human judgement in gauging when drowsiness is becoming a driving hazard. While a number of physiological factors can indicate drowsiness monitoring eyelid movements is generally less restrictive for the driver.

electric3.jpgAisin’s eyelid monitor tracks a range of variables such as blink speed and frequency and average eyelid position. Trials of the new technology on motorists driving along a test track confirmed the reliability of using these measured parameters to rate the drowsiness level of the driver.

The company has also used its monitoring systems to identify other behavioural symptoms that indicate lapses in driving competency. Eye movement speed and fluctuations in the vergence angle – which indicates where the line of sight of right and left eye converge – are both linked with incidents of people deviating off lane and slow driver reaction times in driving simulations.

Drowsiness, a sign of fatigue, is a serious driving hazard worldwide and ranks as the number one cause of fatal car accidents in Japan. The drowsiness monitoring systems, soon to be available in Toyota cars, providing significant improvements to road safety, work. Drowsiness has also motivated a number of campaigns worldwide to encourage driver to take regular breaks and plan journeys responsibly.

The Aisin Seki technology works such by monitoring the eyelid movement as mentioned above. The monitoring equipment retrieves eyelid movement data from video frame images of the driver’s face recorded at 30 frames per second while driving. Eight quantities were recorded: average blinking intervals, average eyelid closure duration, maximum eyelid closure duration, blink frequency, average eyelid closure velocity, average eyelid opening velocity, average eyelid position, and integrated eyelid closure duration. These values were then used to identify five levels of drowsiness: 1, not drowsy; 2, a little drowsy; 3, drowsy; 4, considerably drowsy; and 5, very drowsy. Significant difference statistical analysis confirmed the reliability of the drowsiness monitoring system. A significant difference of 0.1 per cent was found for the recorded quantities. Aisin Seki has also identified the link between eye movement and lapses in motorist concentration during driving simulations. They used their specialised eye monitoring equipment to record the movements of left and right eye during driving. Slow fluctuation of the eyes and rapid fluctuation of the vergence angle, which measures the focal point of the line of sight of right and left eye, were both found to precede incidents when the car deviated from its lane or the driver’s reaction times were increased.

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