GB2547902A

GB2547902A - ECG acquisition through a conductive material coating

Info

Publication number: GB2547902A
Application number: GB1603541.2A
Authority: GB
Inventors: Condon Adrian
Original assignee: B-Secur Ltd
Current assignee: B-Secur Ltd
Priority date: 2016-03-01
Filing date: 2016-03-01
Publication date: 2017-09-06
Also published as: GB201603541D0

Abstract

A user device 100 comprises a substrate 102, e.g. touchscreen display, with one or more electrodes 101 overlaid thereon. Each electrode 101 connects to an amplifier 108 for detecting an electrocardiogram (ECG) signal when touched. Preferably, electrodes 101 are transparent, e.g. Indium Tin Oxide (InSnO; ITO). Electrodes 101 may electrically interface with substrate 102. The set of electrodes may comprise parallel horizontal electrodes on top of orthogonal parallel vertical electrodes, both layers separated from each other by transparent insulating strips. A transparent printed circuit may be fabricated on the substrate to amplify and filter signals. The electrodes may also be provided on e.g. a steering wheel or a door handle. A method of use comprises displaying instructions to a user to touch a transparent dry set of electrodes 101 on a substrate 102 to obtain an ECG measurement. Instructions may comprise holding the touch for a period of time.

Description

ECG ACQUISITION THROUGH A CONDUCTIVE MATERIAL COATING Field of the Invention

This invention relates to electrocardiograph acquisition through a conductive material coating.

Background

As more and more electronic devices are used around the world, the more secure they have to be. User authentication is a process that verifies that a person in front of the device has rights (is authorized) to use the device’s resources. A standard approach to user authorization is password verification (and its derivatives, including two-factor authorization, one-use tokens, etc.). A good password should be long enough to provide general security from brute-force attacks and unique so if it is compromised (i.e. known to third parties) it cannot be used in other systems.

Unfortunately remembering a great number of long passwords can be hard for most people. Other ways of user authorization are required. One of the promising fields is biometrics-based authentication is a novel way of verifying a user’s identity using his or her natural characteristics. Most wide-spread methods include using information from fingerprints, iris or voice, as these are regarded unique to each user. Bioimpedance is also proposed for biometrics-based authentication, as described in W02001/20538, whereby different impedance measurements are made between different points on a user’s hand or body at different frequencies.

Heartbeat characteristics appear to be unique as well. Research effort is put into developing a system that can identify users using their heartbeat characteristics.

There are many ways to analyse one’s heartbeat, but the most practical approach is analysing the patterns gathered by Electrocardiograph, which records a heart’s electric potential changes in time. A longer recording of heartbeat activity is called an electrocardiogram or ECG and is recorded using one or more pairs of electrodes. Each pair measures the voltage between two points on the surface of the body. Changes in this voltage are strongly correlated with heart and muscle activity of the subject.

For a practical process, the system should be easy to use and be robust. In real life scenarios, the user cannot be expected to lie down and attach 12 electrodes to his or her body to provide a one-minute long ECG recording, just to authorize himself at an ATM (for example).

Summary of the Invention

In accordance with an aspect of the invention, a user device is provided for detecting an electrocardiograph signal when place in contact with skin. The user device comprises a substrate and at least one electrode, wherein the electrode is overlaid on the substrate and is connected to an amplifier.

The substrate may be a display substrate and the electrode may be transparent, e.g. made from Indium Tin-Oxide or other transparent conductive material. A viable electrocardiograph signal may be obtained by the user placing one or more fingers and/or thumbs on the surface of the display. In some embodiments the user places fmgers/thumbs at independent electrodes at any two independent points on the display.

The electrode(s) may be electrically interfaced with the substrate by means of connecting pins bonded by conductive glue, a heat-bonded connecting flexible connection or zebra or similar connectors interfaced to the substrate under pressure.

The electrodes may be made up of a series of parallel (e g. horizontal) electrodes on top of an orthogonal series of parallel (e g. vertical) electrodes separated from each other by a corresponding series of transparent insulating strips. These transparent insulating strips may be of sufficient width to completely insulate the top layer of vertical electrodes from the lower layer of horizontal electrodes. They may be made of polycarbonate, transparent plastics material or silicon-dioxide.

The substrate may additionally comprise a transparent printed circuit fabricated on it, with suitable electronic components bonded to transparent traces to provide functions of amplification and filtering locally and directly on the substrate.

Preferably the display is a touch screen and the substrate is glass or transparent plastics material. There may also be a touch-sensitive layer, an LCD or other display layer and/or a backlight underlying the substrate.

An electrocardiograph measurement may be made by displaying instructions to a user to present a skin surface from which an electrocardiograph measurement can be taken, e.g. fmger(s)/thumb(s), to a transparent dry set of one or more electrodes on the surface of a substrate and receiving the electrocardiograph measurement from the electrode(s).

Optionally the user is prompted to present the skin surface in one or two particular areas of the substrate for a period of time. The user may also be prompted to remove the skin surface(s) at the end of the period of time.

The electrocardiograph signal may also be received from any conductive material with appropriate ancillary circuitry.

Preferred embodiments of the invention will now be described, by way of example only with reference to the drawings.

Brief Description of the Drawings

Fig. lisa diagram of a user device with individual electrodes.

Figs. 2 and 3 are examples of a user device with a top electrode and a case electrode.

Fig. 4a and 4b are diagrams of different embodiments of electrode configuration.

Figs. 5 and 6 are diagrams of different embodiments of multiple electrode configuration.

Figs. 7a and 7b are diagrams showing face-on and side on views of electrode connections Fig. 8 illustrates a single electrode configuration.

Detailed Description

Fig. 1 illustrates a display 100 comprising a transparent substrate 102, two electrodes 101a and 101b on the surface of the substrate, an optional capacitive or other touch sensitive input 103 and an LCD or other display 105 with backlight 107. The electrode(s) 101a and 101b are connected to respective inputs of an instrumentation amplifier 108. The amplifier 108 is connected to a processor 104 and (optionally) a ground connector 112. The processor has a bus 114 connecting to the display 100 to display instructions to the user.

The substrate 102 is preferably made of glass or transparent plastics material or transparent resin. The electrodes are transparent and are preferably made of Indium Tin Oxide but may be made of metal. In the case of metal (such as copper or gold), the electrodes are sufficiently thin to be transparent.

The amplifier 108 may be an instrumentation amplifier with a differential amplifier configuration. The instrumentation amplifier 108 gives good common-mode rejection, and has high input impedances. It preferably has separate input buffer amplifiers (not shown).

The electrodes 101a, 101b are preferably dry electrodes which eliminate the need for electrolytic gel used in conventional wet systems to penetrate hair, contact the skin and provide a clean conductive path.

In one example of operation, the display is held by a user and the user selects (using the capacitive touch sensitive input 103 or by other means) a process for which the processor 104 needs authentication or enrolment of an ECG. Alternatively, the display may be mounted (e g. in a cradle, e g. within a vehicle). As an alternative to user selection of the initial process, this may begin automatically or be initiated by other means.

In another example of operation, the user knows that the device is ECG enabled and knows what steps to follow. In this case there may not necessarily be a prompt for the user to place fingers and/or thumbs on the device. If there is difficulty in recording the ECG signal, then instruction messages may be displayed as described below.

The processor 104 optionally sends a message 114 to the display 100 to display instructions to the user on the display 100. These instructions (if used) preferably instruct the user to place a finger (or thumb) from each hand somewhere on the electrodes 101a & 101b and to hold them there firmly for a displayed length of time, preferably between one heartbeat (e.g. less than one second) or between 1 or 2 seconds and about 5 to 8 seconds (for authentication) but possibly up to 30 seconds or a minute and between about 30 seconds and 1 minute (for enrolment). Optionally, the processor 104 may instruct 114 the display 100 to display to the user when the time period has elapsed and/or when there has been a successful reading or when there has been an error and the user must repeat the process.

The electrodes 101 detect an ECG signal from the fmger(s) and/or thumb(s) of the user at a sampling rate of between 200Hz and 25kHz (preferably between 500Hz and 25KHz). The amplifier 108 amplifies the signal and the processor 104 processes it to create an ECG sample that can be enrolled or authenticated against other ECG samples. The ECG signal may be detected over a period of 2 seconds to 1 minute, depending on the mode of the processor 104 (enrolment, authentication etc.).

In addition to the two electrodes 101a, 101b, a reference electrode may also make contact with the user’s skin (e.g. via a case or backplate) and be tied at the mid-point of the instrumentation amplifier inputs. Additionally, there may also be a ground electrode in contact with the user’s skin to anchor the signal and prevent saturation of the amplifier 108. These additional electrodes are not shown.

The user may hold the display in one hand and place one finger (or thumb) from the other hand on the display 100. An embodiment for this purpose is shown in Fig. 2. In this embodiment, there is a single electrode 101 in a sheet on the screen surface, on which one finger (or thumb) is placed by the user. The second electrode connection is provided by the user holding the case 202 of the display 100. This aspect may also optionally have the reference and ground electrodes described above. The screen may have electrodes as shown in Fig. 3. In this figure, there is a central electrode 410 and a peripheral electrode 408. The latter is connected to the case 202. Alternatively, the region 408 is devoid of any surface electrode and acts as a buffer region around electrode 410.

Fig. 4a shows an arrangement suitable for the embodiment of Fig. 1. There are two areas 412, 414, connected to the two inputs of the amplifier 108. Separate messages (e.g. “place finger here”) or images (e.g. images of fingerprints) may be displayed in the different areas of the display to direct the user to put one finger (or thumb) in one area and another finger (or thumb) in the other area.

Fig. 4b shows a grid of alternate electrodes 101, 101’ and 113, 113’ being connected to opposite inputs of the amplifier 108. The size of each electrode is preferably of the order of the size of a finger, for example between 0.5cm^ and lOcm^ (e.g. of linear dimension from 0.8cm to 3cm). This embodiment works with two fingers (and/or thumbs), on electrodes 101, 113 of opposite sets (connected to opposite inputs of the amplifier 108). The electrodes may be substantially smaller (e.g. between 9 and 900 per cm^).

Fig. 4b shows just four from such an array by way of example (e.g. on a display the size of a credit card). It shows spacing between the electrodes of a size similar in dimension to the size of each electrode, but the spacing may be smaller. For a larger display, there may be many electrodes 101, 10Γ and 113, 113’ in each set, alternating in rows and columns in an array (e.g. along each row and along each column.

There may be an area around the edge of the display that contains no electrodes. This is to prevent the fingers of the hand that holds the display from touching the electrodes unintentionally as they curl around the edge.

Fig. 5 shows a variation in which the two or more electrodes 101 etc. may be positioned on top of an insulating substrate 506, which itself is positioned on top of traces for the electrodes 101 that connect the electrodes to individual amplifiers 508, each electrode having its own trace (not shown) and its own amplifier. Connections between the electrodes 101 and their respective traces are by means of conducting ‘via’ holes through the insulating substrate 506. The rows and columns of the electrodes are completely insulated from each other by the insulating substrate 506, preventing the electrodes from short circuiting. This embodiment allows the whole surface of the substrate to read the user’s ECG and also enables the position of the finger placed on the device to be located. The resolution of this location may be very high, hypothetically comparable to that of a TFT dot matrix LCD and limited only by the trace width.

In the embodiment of Fig. 6, two sets of electrodes 601 and 602 are arranged as diagonal strips. The strips on one diagonal are separated by those on the other diagonal by a layer of insulation. Both sets of strips are exposed to the surface. Each strip has its own amplifier 608, 609. Two fingers placed side by side (in either the x or y direction) will not touch the same strip electrode 101. This embodiment allows the whole surface of the substrate 102 to read the user’s ECG. It is (optionally) possible to locate the position of the user’s fingers from the point where the finger intercepts the strips.

The above embodiments may be used individually or in combination with one another.

Additionally, the above embodiments may also detect fingerprints when the electrodes are very small (e.g. of a size similar to that of a display pixel). In operation, the electrodes may scan the finger by sequentially enabling of their respective amplifiers. By so scanning, the electrodes are able to detect the presence of a ‘ridge’ of the fingerprint by the contact point and a ‘gully’ or edge of the finger by the lack of contacts. The ECG recording may be taken sequentially or at the same time by enabling the one or more electrodes 101 that have contact with the user’s skin for a sufficient period of time.

The circuit may be a transparent printed circuit on the substrate 102 with suitable electronic components such as amplifiers and/or filters bonded to the transparent traces to provide the functions of amplification and filtering locally and directly on the substrate 102.

The processer 104 may utilise the ECG data to authorise users for biometric security, using algorithms that previously relied on wet electrode systems, such as is described in ECG Based Recognition Using Second Order Statistics by F. Agrafioti.

In wet electrode systems, a gel serves as a buffer to ‘fill-in’ gaps formed between the sensor and skin during application and user movement. The gel is not needed in the present case. Moreover, only a short amount of contact time is needed between the electrode and the skin, provided the instructions displayed to the user are (i) to avoid movement during this time period and (ii) to press firmly on the display.

Fig. 7 shows how the two or more electrodes 101 may, in one embodiment, be connected to the edge of the substrate 102, and hence the circuit detailed in Fig. 6. The electrodes 101 are connected by means of one or more tabs 704 extending to the edge of the substrate and one or more clips 702 attaching the tabs 704 there. Preferably the clips 702 have a flat (front) side and a spring (read) side.

Any of the two or more electrodes 101 may be electrically interfaced by being glued (by conductive glue) to connecting pins bonded to the substrate 102. The electrode(s) 101 may alternatively be interfaced by a heat-bonded connecting flexible connection or by zebra connectors interfaced to the substrate 102 under pressure.

Fig. 8 shows an embodiment with just one electrode. A ground contact 812 may connect to the outside of the device, or to a cradle (for example in a car) or may provide an earth connection in some other way.

Instead of an electrode coating a display substrate, the electrode coating could alternatively coat any apparatus that requires access or identification of a user. For example, a car (the coating positioned on the handle of the door or other surface or on the steering wheel or dashboard), a door, a non-conductive back or cover of a phone, or an apparatus that logs user usage of equipment. The electrode coating preferably has ancillary circuitry integrated with it.

Any of the above embodiments may occur as described or in combination with one or more other embodiments.

Claims

1. A user device (100), comprising: a substrate (102); and at least one electrode (101), wherein the at least one the electrode (101) is overlaid on the substrate (102) and is connected to an amplifier (108) for detecting an electrocardiograph signal when placed in contact with skin.

2. The user device of claim 1, wherein the substrate (102) is a display substrate and the electrode (101) is transparent.

3. The user device of claim 1, comprising a set of discrete transparent electrodes (101).

4. The user device of any one of claims 1 to 3, wherein the or each electrode (101) is made from Indium Tin-Oxide or other transparent conductive material.

5. The user device of any one of claims 1 to 4, wherein the electrode(s) (101) is/are electrically interfaced by means of connecting pins bonded to the substrate (102) by conductive glue.

6. The user device of any one of claims 1 to 4, wherein the electrode(s) (101) is/are electrically interfaced by a heat-bonded connecting flexible connection.

7. The user device of any one of claims 1 to 4, wherein the electrode(s) (101) is/are electrically interfaced by zebra connectors interfaced to the substrate (102) under pressure.

8. The user device of any one of claims 1 to 7, comprising a series of parallel horizontal electrodes on top of an orthogonal series of parallel vertical electrodes separated from each other by a corresponding series of transparent insulating strips.

9. The user device of claim 8, wherein the transparent insulating strips are of sufficient width to completely insulate the top layer of vertical electrodes from the base layer of horizontal electrodes.

10. The user device of claim 8, wherein the transparent insulating strips are polycarbonate, transparent plastics material or silicon-dioxide.

11. The user device of any one of the preceding claims, wherein one or more of a user’s fingers and/or thumbs may be placed on any two independent points on the surface of the display and meet with independent electrodes from which a viable electrocardiograph signal may be obtained.

12. The user device of any one of the preceding claims, wherein the substrate (102) additionally comprises a transparent printed circuit fabricated on said substrate (102) with suitable electronic components (108, 402, 404) bonded to transparent traces to provide functions of amplification and filtering locally and directly on the substrate (102).

13. The user device (100) of any one of the preceding claims, wherein the display is a touch screen.

14. The user device (100) of any one of the preceding claims, wherein the substrate is glass or transparent plastics material.

15. The user device (100) of any one of the preceding claims, further comprising, underlying the substrate, one or more of: a. a touch-sensitive layer b. an LCD or other display layer c. a backlight.

16. A method of recording an electrocardiograph measurement comprising: displaying instmctions to a user to present a skin surface from which an electrocardiograph measurement can be taken to a transparent dry set of one or more electrodes (101) on the surface of a substrate (102); and receiving the electrocardiograph measurement from the electrode(s).

17. The method of claim 11, wherein the user is prompted to present the skin surface in a particular area (304) of the substrate (102).

18. The method of claim 11, wherein the user is prompted to present the skin surface at two areas on the substrate (102).

19. The method of claim 11, wherein the user is prompted to present the or each skin surface for a period of time and is prompted to remove the skin surface(s) at the end of the period of time.

20. A display substantially as herein before described with reference to any one of the accompanying figures.

21. A display substantially as herein before described with reference to the examples as described in the description.