automotive

Epic... Monitoring Driver Health

Plessey 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. Plessey is now producing a version that is ideal for certain types of contactless ECG measurement such as driver fatigue monitoring or seat occupancy.

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.

Information


 

Disruptive EPIC sensor with multiple proven applications

  • High sensitivity electric potential sensor that can be used in ether contact or non-contact mode
    • Contact mode: measures bio-electric signals like ECG, EMG, EOG and EEG
    • Non-contact mode: measures disruption in the electric field caused by human body movment enabling
      • Proximity sensing
      • Movement Sensing
      • Gesture recognition

Strong demand for products with major applications

  • Communications - smart-phones and tablets for ECG and proximity sensing
  • Consumer - remote sensing controllers for video games consoles
  • Automotive - alertness, occupancy and slow speed collision avoidance
  • Medical - ECG, tomography and "smart bed" applications

EPIC PCB hybrids and chips for all electric potential sensing applications

  • The integrated circuit provides a unique high impedance amplifier design
  • The PCB hybrid solution includes EPIC chip, tuning circuit and the sensor electrode

What Is EPIC?

EPIC is an acronym for "Electric Potential Integrated Circuit" but the term has become synonymous with the integrated circuit technology, the sensor itself, and, in a wider context, the physical principles of operation of the device within a system.

EPIC is a noncontact electrometer, meaning that there is no direct DC path from the outside world to the sensor input, a condition that is somewhat analogous to the gate electrode of an MOS transistor. The electrode is protected by a capping layer of dielectric material to ensure that the electrode is isolated from the body being measured. The device is AC coupled with a lower corner frequency (-3dB) of a few tens of MHz and an upper corner frequency above 200 MHz. This response is adjustable and can be tailored to suit a particular application. Such an electrometer cannot be DC coupled because the Earth's electric field close to the surface is ≈100-150 V/m.

In single-ended mode the device can be used to read electric potential; used in differential mode it can measure the local electric field; or it can be deployed in arrays to provide spatial potential mapping (locating a conducting or dielectric material placed within free space).

Figure 1 shows a basic block diagram of the EPIC sensor [1]. The size of the electrode is somewhat arbitrary and depends on the input capacitance required for a particular application. For bodies placed close to the electrode, the electrode's size is important and the device operation can be understood in terms of capacitive coupling. For devices that are several meters away, the coupling capacitance is defined only by the self-capacitance of the electrode and the device's response is largely a function of the input impedance as it interacts with the field. This is rather counterintuitive but is a function of the very small amount of energy that EPIC takes from the field in active mode.

Figure 1
Figure 1

The input resistance to the device can be boosted by using bootstrapping techniques while the input capacitance can be reduced using guarding techniques. The input capacitance can be driven as low as 10-17F with the input resistance being boosted to values up to around 1015Ω, thus keeping the interaction with the target field to an absolute minimum and ensuring that all currents are small displacement currents only.

A better understanding of the feedback mechanisms can be obtained by considering the input buffer of the amplifier and its associated impedances as shown in Figure 2. The resistors RG1 and RG2 are used to set the gain of the first stage, which is nominally unity. Cin and Rin represent the input capacitance and resistance native to the amplifier, respectively, and include any parasitic components due to layout or substrate issues. The capacitor Cext models the capacitive coupling to the measurement target.

Figure 2
Figure 2

For close coupling (Cext >> Cin) this is usually defined as

where:
a = the equivalent shared electrode/target area
d = the distance between target and sensor
ε0 = the permittivity of free space
εr = the relative permittivity of the dielectric in which the sensor is operating

For loose coupling (Cext << Cin) we have the limiting case (self-capacitance) shown as

Where r is the diameter of the sensor plate.

Analysis of the circuit shows us that we have a classic single-pole transfer function shown as

The Bode plot for this is shown in Figure 3.

Figure 3. Bode plot for the transfer function of Equation 3

The corner frequency (Fc1) can be expressed as

By applying the bootstrapping techniques mentioned earlier, we can control the values for Cin and Rin to give effective values, allowing us to control both the gain plateau and the corner frequency (Fc1 moves to Fc2). The response of the sensor can be further controlled by the design of subsequent stages and positive feedback loops. Thus we have a sensor that can be tailored to suit the particular application at hand.

Figure 4 shows a pair of Plessey EPIC sensors and the associated control box. The control box is an amplifier/filter combination and is used for demonstration purposes only. The electrodes shown here have been tailored for contact ECG measurement but can also be used for remote sensing and other applications.

Figure 4

Medical Applications

A great amount of interest has been generated within the medical community where the primary focus is on using EPIC for surface body electrode physiology applications such as electrocardiograph (ECG), electromyograph (EMG), electroencephalograph (EEG), and electrooculargraph (EOG).

The EPIC sensor can be used, for example, as a replacement technology for traditional wet-electrode ECG pads, because it requires neither gels nor other contact-enhancing substances. When the EPIC sensor is placed on (or in close proximity to) the patient, an ECG signal can be recovered. The sensor is capable of both simple 'monitoring' ECG as well as making more exacting clinical diagnostic measurements. In the latter application it can be used as a replacement for the traditional twelve-lead ECG, in which electrodes are placed on the limbs and torso (each pair of electrodes is called a lead and each lead measures the electrical activity of the heart from a slightly different perspective) to achieve a clearer picture of how the patient's heart is working. An array of EPIC sensors placed on the chest can be used to recreate the lead required with resolution as good as or better than that achieved using traditional systems. Figure 5 shows a comparison between the results using EPIC and using traditional wet electrodes for leads II and aVL [2]. These two leads are important in the diagnosis of conditions such as coronary artery occlusion.

Figure 5. ECG readouts showing the results using EPIC (top) vs. traditional wet electrode ECG (bottom)

The sensor can also be used for recovering other physiological signals such as those caused by the electrical activity of the eye muscles as one looks left, right, up, or down. These signals have unique signatures; an EOG can be used to track the position of the eyes and therefore produce targeting information for military and gaming applications, for example. Perhaps the most exciting application in the medical field is that of electroencephalography (EEG) where the electrical activity of the brain is recorded. Application of the EPIC sensor to this field is still in its infancy but the potential ability to record identifiable signals against known thought patterns opens up possibilities that currently only exist in science fiction.

Other Applications

Security

Because of EPIC's mode of operation, it can be used to detect any disturbance in the local electric field at distances of up to several tens of meters. The human body, because it acts as a large container of conducting/polarizable material, causes a large perturbation in the electric field and so presents an easily detectable target for the sensor. Sitting a few meters away from the sensor, one has only to raise the sole of one's foot to create a strong signal. Arrays of sensors can be used to provide spatial resolution and therefore the location of a target. Such arrays can also distinguish between humans and quadrupeds because the time signature of the response is a direct function of cadence. Such a system of sensors could perhaps be used for border security in remote areas.

Man-machine interface

The ability of EPIC to resolve signals unique to various muscles or groups of muscles presents opportunities for improved man-machine interaction. For example, a quadriplegic who currently depends on either a unicorn stick or a suck/blow tube to issue commands to equipment within his or her local environment could achieve a faster and more efficient interaction using EPIC for eye tracking and detection of activity in any muscle groups still under voluntary control. Alternatively, because EPIC can assign a unique signature to the use of certain muscle groups, it opens up many possibilities for interfacing with and controlling prosthetic limbs.

Microscopy

EPIC is also a useful tool in the microscopic domain. Small sensors scanning a microchip, for example, can show areas of high or low potential, allowing the user to map the current distribution within metal tracks and other circuit elements. Faults in dielectric materials can also be detected either by passive means (by detecting piezoelectric effects) or by identifying leakage paths in an active circuit.

Recently a ≈6 µm sensor has been used to reveal a human fingerprint left on an insulating PTFE material (Figure 6) and to characterize its decay over time [3]. The advantage to the forensic scientist of being able to date a fingerprint is obvious. The technique is nondestructive and leaves no chemical residue, which means that DNA samples can be taken at a later date.

Figure 6

Conclusions

The release of EPIC technology into the wider commercial environment has been talked about as being disruptive. The technology is certainly novel in its operation and opens up a wide range of fields in which EPIC may be applied to provide solutions to diverse engineering problems. In this article we have only touched on a small subset of these. Other potential applications could include building and vehicle health, communications, and seismology. The future for EPIC is an exciting and challenging one. It is my opinion that in years to come, the introduction of this technology will be seen as marking a milestone in sensor technology development.

References

[1] Private communication from Professor Robert Prance, University of Sussex, U.K.

[2] C. J. Harland, N. S. Peters, et al., "A compact electric potential sensor array for the acquisition and reconstruction of 7-lead ecg without electrical charge contact with the skin," Physiol. Meas. 26 (2005) 939–950, doi:10.1088/0967-3334/26/6/005

[3] P. Watson, R. J. Prance, and S. T. Beardsmore-Rust, "Latent electrostatic fingerprints and their decay: towards a forensic timeline," submitted to Nature.

This page contains summary information and documented details for the currently developed end applications.

See the end of this page for links to detailed application notes.

ECG using wrist-mounted EPIC sensors

  • Sensors mounted in a wrist watch, one sensor in permanent contact with the wrist.
  • Touch the sensor display ECG in elf-contained unit.
  • Output to watch display, or by Bluetooth to external device.
  • Aimed primarily at sports-watch type applications with sample already built.

ECG sensor in a SmartPhone

  • Sensors mounted in Smart Phone case.
  • Touches sensors to display ECG on the Phone which is linked by Bluetooth.
  • Self-contained ECG measurement add-on, no bigger than a phone case.

Single arm ECG measurement using EPIC

  • Sports armband giving continual ECG monitoring in a self-contained unit with Bluetooth output
  • Aimed primarily at longer-term health monitoring. Demo capabilities available.

Non-contact ECG measurement using EPIC

  • Non-contact ECG measurement through clothing allowing sensor to be mounted in seats, mattresses, clothing etc.
  • Driven Right Leg circuit coupled onto body enables ECG signal to be extracted from noise without skin contact.
  • Primary applications are medical and automotive.

Movement and gesture applications of EPIC sensors

  • Determining position of a hand or body by measuring signals from pairs of sensors.
  • Hand position sensing enables gesture recognition and device control.
  • Body position within a room enables automatic switching, security surveillance, assisted healthcare etc.

ECG Measurement for hand rail scales

  • Two sensors mounted into handrail of weighing scales providing a one-stop health monitoring system.
  • Optional additional sensors may be incorporated under feet.
  • Aimed at medical and well-being market
  • Plessey has a Application Support Centre to assist you with your application questions. Our experts will provide you with accurate and prompt responses to your design-in and development needs.
  • To contact our experienced application engineers, please either
  • Please provide a detailed description of your request. If you have an application problem, please describe it as fully as possible.
  • EPIC Overview

    This video shows the general capabilities of the multi award winning EPIC sensor. As application examples, this video will trigger your imagination into the world of opportunities that the EPIC sensor will give.

  • Movement and gesture applications of EPIC sensors

    This video demonstrates how EPIC can be used to determine the position of a hand or body by measuring signals from a pair of sensors. It shows how hand position sensing enables gesture recognition and therefore device control.

    This simple demonstration shows how the application can be extended to cover body position within a room to enable automatic switching, security surveillance or assisted healthcare.

  • Driven Right Leg circuit

    This video is a practical demonstration of the automotive application for non-contact ECG measurements, through clothing in the difficult environment of a car.

EPIC datasheets are available for the EPIC product family, defined as:

EPIC Chip

  • Plessey's unique high impedance amplifier design for electric potential sensing applications (PS25151/2/3)

EPIC Sensor

  • PS25201 EPIC PCB hybrid sensor, optimised for contact ECG
  • PS25401 EPIC PCB hybrid sensor, optimised for movement
  • Includes EPIC chip, R&C tuning discretes and an anodized Titanium electrode for the PS25201

ECG Reference Board / Demo

  • EPIC sensor with on board charge pump
  • Available in single and dual formats (PS25012A/B PS25014A/B)

Demonstration kit

  • EPIC sensors in can or board form.
  • Supply and basic filtering interface box for PC or scope.
  • Labview™ acquisition and display software.

Test and Demonstration Kits

EPIC sensors are available in can or board form
Included in the demo kits are: -

  • Supply and basic filtering interface box for PC or scope
  • Labview™ acquisition and display software
  • Installation (291484) & user (291187) guides.
Please contact Plessey to order your demo kit
  • Make your request via "Ask a Question"
  • Contact your local sales representative (Contact Us / Sales Offices)
  • Plessey has a Technical Support Centre to assist you with your technical questions about our products and applications. Our experts will provide you with accurate and prompt responses to your design-in and development needs.
  • To contact our experienced application engineers, please either
  • Please provide a detailed description of your request. If you have a technical problem, please describe your application as fully as possible.
Plessey are developing an online technical support desk to further enhance our customer experience and to speed the resolution process. Details will be posted on the home page when available.
What is the gain of the EPIC sensor?
What supply voltage do I need?
What is the current drain per sensor?
What is the output voltage?
What is the output resistance of the sensor?
Why is the sensor output only showing mains frequency signals?
Is the EPIC sensor directional?
Can EPIC sensors detect stationary fields or stationary objects perturbing that field?
Can EPIC be used for gesture recognition?
Can moving targets be tracked in 2D using "real time" algorithms?
Can adults be distinguished from children?
What is the "range" of the EPIC sensor for motion sensing?
Can the EPIC sensor "see" through walls?
Are the sensors affected by RF signals, such as those from mobile phones?

Test and Demonstration Kits

EPIC sensors are available in can or board form
Included in the demo kits are: -
  • Supply and basic filtering interface box for PC or scope
  • Labview™ acquisition and display software
  • Installation (291484) & user (291187) guides.
Please contact Plessey to order your demo kit
  • Plessey has a Technical Support Centre to assist you with your technical questions about our products and applications. Our experts will provide you with accurate and prompt responses to your design-in and development needs.
  • To contact our experienced application engineers, please either
  • Please provide a detailed description of your request. If you have a technical problem, please describe your application as fully as possible.
Plessey are developing an online technical support desk to further enhance our customer experience and to speed the resolution process. Details will be posted on the home page when available.