Electrophysiological sensor and method of detecting electrophysiological signals

Abstract

This application discloses a wearable electrophysiological sensor comprising a flexible substrate and one or more dry electrodes for sensing electrophysiological signals. Each of the one or more electrodes are located on a skin facing surface of the flexible substrate. Each dry electrode has a non-solid pattern that is configured to flexibly accommodate contours of a patient's skin. In some examples, the electrophysiological sensor may be configured for use as an electrocardiogram (ECG) sensor. A method of use of the wearable sensor, a method of detecting electrophysiological signals and a method of manufacturing the wearable sensor are also disclosed.

Description

Electrophysiological sensor and method of detecting electrophysiological signalsTechnical Field

[0001] The present disclosure relates to wearable electrophysiological sensor, a method of using the wearable sensor, a method detecting electrophysiological signals and a method of manufacturing a wearable electrophysiological sensor. Certain examples relate to a wearable electrocardiogram (ECG) sensor.Background

[0002] Electrophysiological signals are electrical signals generated by biological cells and tissues. There is great interest in detecting and measuring electrophysiological signals from the human body, as they provide useful information about the subject and how well their body is functioning. Electrophysiological sensors have many uses, including monitoring patients, generating data for scientific research, checking a patient for any abnormalities or assessing the health of an individual.

[0003] Examples of electrophysiological signal measurements include, but are not limited to ECG (electrocardiogram), EMG (electromyogram), EEG (electroencephalogram), EOG (electrooculogram) and ECoG (electrocorticogram). ECG may be used for detection of cardiovascular issues and overall assessment of cardiac health. ECG measures the heart's electrical activity through repeated cardiac cycles by detecting differential voltages between electrodes placed at different locations on the skin. ECG can enable detection of cardiovascular issues and assessment of cardiac health. ECG (electrocardiogram) is particularly challenging as it requires accurate detection of very small differential voltages.

[0004] An ECG is typically performed in a hospital setting with the patient lying down. A number of leads are attached to electrodes placed at various locations on the patient’s body. The standard 12-lead ECG has 10 electrodes in total of which 6 are placed on the chest and 1 electrode is placed on each of the four limbs. While there areonly 10 electrodes in a 12-lead ECG, there are 12 leads, as some electrodes are attached to more than one lead.

[0005] In order to minimize skin-electrode impedance and produce a stronger signal, ECGs conventionally use wet electrodes. Wet electrodes use a conductive gel to contact the skin and improve electrical signal acquisition. Ag / AgCl electrodes are a commonly used wet electrode. Ag / AgCl electrodes comprise an Ag / AgCl electrode surrounded by a conductive gel. The gel is usually surrounded by an adhesive layer for attachment to the skin. These electrodes can be uncomfortable, dry out over time, and have been known to cause irritation and allergies in some patients. Furthermore, during prolonged or extended signal acquisition the electrode gels dry up and denature, causing loss of signal and further leading to a need to either replace the electrodes or continually add more electrode gel. Furthermore, the conventional electrophysiological sensors are bulky and have multiple cables that limit patient mobility.

[0006] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.Summary

[0007] A first aspect of the present disclosure provides a wearable electrophysiological sensor comprising: a flexible substrate; and one or more dry electrodes for sensing electrophysiological signals, each of the one or more dry electrodes being located on a skin facing surface of the flexible substrate; wherein each dry electrode is a planar electrode which comprises a number of electrode tracks arranged in a non-solid pattern connected together to form a labyrinth-like structure, the labyrinth-like structure being configured to flexibly accommodate contours of a patient’s skin while maintaining contact with the skin.

[0008] A second aspect of the present disclosure provides a wearable electrocardiogram (ECG) sensor for attachment to a patient’s skin, the wearable ECG sensor comprising: a flexible substrate having a first surface for attachment to the patient’s skin and a second surface opposite the first surface; one or more dry electrocardiogram (ECG) electrodes on the first surface of the flexible substrate; each dry ECG electrode comprising a non-solid pattern filling a respective two dimensional electrode area, wherein different sections of the non-solid pattern are movable relative to each other to accommodate contours of a surface of a patient’s skin, wherein the non-solid pattern comprises a plurality of electrode tracks which together form a plurality of concentric rings, each ring being connected to an adjacent ring.

[0009] In some examples the one or more dry electrodes may be formed from a conductive thin film layer having a thickness of 120nm to 5 microns. In some examples each electrode track may have a width of between 30 microns and 500 microns and gaps between adjacent electrode tracks are no more than 30 to 500 microns. In some examples, other than the outer perimeter, the electrode tracks are substantially uniform in width.

[0010] A third aspect of the present disclosure includes use of a wearable sensor according to the first or second aspect to sense electrophysiological signals, such as but not limited to electrocardiographic signals, at the skin of a patient.

[0011] A fourth aspect of the present disclosure provides a method of detecting electrophysiological signals comprising attaching a wearable sensor according to the first or second aspect to a patient’s neck or torso, and sending electrophysiological signals sensed by the one or more electrodes to a measurement device through a wired connection or wirelessly.

[0012] A fifth aspect of the present disclosure provides a method of manufacturing a wearable sensor according to the first or second aspect, the method comprising: providing a flexible substrate; and forming, on a surface of the flexible substrate, one ormore dry electrodes having a non- solid pattern that is configured to flex to accommodate contours of a surface of a patient’s skin.

[0013] Further aspects and features of the present disclosure are provided in the following description and the appended claims.Brief Description of Drawings

[0014] Examples of the present disclosure will now be described, by way of nonlimiting example only, with reference to the accompanying drawings, in which:

[0015] Fig. 1A shows a perspective view of a wearable electrophysiological sensor according to an example of the present disclosure;

[0016] Fig. IB shows a cross-sectional view of a wearable electrophysiological sensor according to an example of the present disclosure;

[0017] Figs. 2A to 2F show various, non-limiting, examples of electrode patterns which may be used in a wearable electrophysiological sensor according to the present disclosure;

[0018] Figs. 3 A to 4H show steps in a process of manufacturing a wearable electrophysiological sensor according to one example of the present disclosure;

[0019] Fig. 4 shows an example of a wearable electrophysiological sensor according to an example of the present disclosure;

[0020] Fig. 5 is a graph showing surface area vs resistance vs total track length for various designs of electrode according to the present disclosure;

[0021] Fig. 6A is a schematic representation of various sequences of depolarization and repolarization of the heart;

[0022] Fig. 6B shows tracings of the deflection waves corresponding to the depolarization and repolarization sequences of Fig. 6A;

[0023] Fig. 7(a) shows a subject in the lying down position;

[0024] Fig. 7(b) shows a subject with an electrophysiological sensor worn on the chest in the lying down position;

[0025] Fig. 7(c) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the lying down position;

[0026] Fig. 7(d) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the lying down position;

[0027] Fig. 7(e) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the lying down position;

[0028] Fig. 7(f) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the lying down position;

[0029] Fig. 8(a) shows a subject in the sitting position;

[0030] Fig. 8(b) shows a subject with an electrophysiological sensor worn on the chest in the sitting position;

[0031] Fig. 8(c) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the sitting position;

[0032] Fig. 8(d) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the sitting position;

[0033] Fig. 8(e) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the sitting position;

[0034] Fig. 8(f) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the sitting position;

[0035] Fig. 9(a) shows a subject in the standing position;

[0036] Fig. 9(b) shows a subject with an electrophysiological sensor worn on the chest in the standing position;

[0037] Fig. 9(c) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the standing position;

[0038] Fig. 9(d) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according toan example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the standing position;

[0039] Fig. 9(e) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the standing position;

[0040] Fig. 9(f) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the standing position;

[0041] Fig. 10(a) shows circular labyrinth pattern electrodes for an electrophysiological sensor;

[0042] Fig. 10(b) shows a subject with an electrophysiological sensor worn on the chest in the lying down position;

[0043] Fig. 10(c) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the lying down position;

[0044] Fig. 10(d) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the lying down position;

[0045] Fig. 10(e) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to anexample of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the lying down position;

[0046] Fig. 10(f) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the lying down position;

[0047] Fig. 11(a) shows circular labyrinth pattern electrodes for an electrophysiological sensor;

[0048] Fig. 11(b) shows a subject with an electrophysiological sensor worn on the chest in the sitting down position;

[0049] Fig. 11(c) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the sitting down position;

[0050] Fig. 11(d) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the sitting down position;

[0051] Fig. 11(e) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the sitting down position;

[0052] Fig. 11(f) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to anexample of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the sitting down position;

[0053] Fig. 12(a) shows circular labyrinth pattern electrodes for an electrophysiological sensor;

[0054] Fig. 12(b) shows a subject with an electrophysiological sensor worn on the chest in the standing position;

[0055] Fig. 12(c) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the standing position;

[0056] Fig. 12(d) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the standing position;

[0057] Fig. 12(e) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the standing position;

[0058] Fig. 12(f) shows voltage against time for measurements from a wearable electrophysiological sensor having circular labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the standing position;

[0059] Fig. 13(a) shows square labyrinth pattern electrodes for an electrophysiological sensor;

[0060] Fig. 13(b) shows a subject with an electrophysiological sensor worn on the chest in the lying down position;

[0061] Fig. 13(c) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the lying down position;

[0062] Fig. 13(d) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the lying down position;

[0063] Fig. 13(e) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the lying down position;

[0064] Fig. 13(f) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the lying down position;

[0065] Fig. 14(a) shows square labyrinth pattern electrodes for an electrophysiological sensor;

[0066] Fig. 14(b) shows a subject with an electrophysiological sensor worn on the chest in the sitting position;

[0067] Fig. 14(c) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to anexample of the present disclosure taken under rest condition when worn on the chest for a subject in the sitting position;

[0068] Fig. 14(d) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the sitting position;

[0069] Fig. 14(e) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the sitting position;

[0070] Fig. 14(f) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the sitting position;

[0071] Fig. 15(a) shows square labyrinth pattern electrodes for an electrophysiological sensor;

[0072] Fig. 15(b) shows a subject with an electrophysiological sensor worn on the chest in the standing position;

[0073] Fig. 15(c) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the chest for a subject in the standing position;

[0074] Fig. 15(d) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to anexample of the present disclosure taken under physical stimuli condition when worn on the chest for a subject in the standing position;

[0075] Fig. 15(e) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the chest for a subject in the standing position;

[0076] Fig. 15(f) shows voltage against time for measurements from a wearable electrophysiological sensor having square labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the chest for a subject in the standing position;

[0077] Fig. 16(a) shows hexagonal labyrinth pattern electrodes for an electrophysiological sensor;

[0078] Fig. 16(b) shows a subject with an electrophysiological sensor worn on the neck in the lying down position;

[0079] Fig. 16(c) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the neck for a subject in the lying down position;

[0080] Fig. 16(d) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the neck for a subject in the lying down position;

[0081] Fig. 16(e) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according toan example of the present disclosure taken under mental stimuli condition when worn on the neck for a subject in the lying down position;

[0082] Fig. 16(f) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the neck for a subject in the lying down position;

[0083] Fig. 17(a) shows hexagonal labyrinth pattern electrodes for an electrophysiological sensor;

[0084] Fig. 17(b) shows a subject with an electrophysiological sensor worn on the neck in the sitting position;

[0085] Fig. 17(c) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the neck for a subject in the sitting position;

[0086] Fig. 17(d) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the neck for a subject in the sitting position;

[0087] Fig. 17(e) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the neck for a subject in the sitting position;

[0088] Fig. 17(f) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according toan example of the present disclosure taken under physical and mental stimuli condition when worn on the neck for a subject in the sitting position;

[0089] Fig. 18(a) shows hexagonal labyrinth pattern electrodes for an electrophysiological sensor;

[0090] Fig. 18(b) shows a subject with an electrophysiological sensor worn on the neck in the standing position;

[0091] Fig. 18(c) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under rest condition when worn on the neck for a subject in the standing position;

[0092] Fig. 18(d) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical stimuli condition when worn on the neck for a subject in the standing position;

[0093] Fig. 18(e) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under mental stimuli condition when worn on the neck for a subject in the standing position;

[0094] Fig. 18(f) shows voltage against time for measurements from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure taken under physical and mental stimuli condition when worn on the neck for a subject in the standing position;

[0095] Figs. 19(a) to 19(d) show the correlation of measurements taken from a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure with ideal 12-lead ECG parametersunder different stimuli; specifically Fig. 19(a) shows temporal parameters on the chest region, Fig. 19 (b) amplitude parameters on the chest region, Fig. 19 (c) shows temporal parameters on the neck region and Fig. 19 (d) shows amplitude parameters on the neck region.

[0096] Figures 20(a) to 20(d) show a comparison between amplitude parameters of wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure and a Welch Allyn device; specifically, Fig. 20(a) shows the comparison for a P-wave, Fig. 20 (b) for a R-wave, Fig. 20(c) for a T-Wave and Fig. 20(d) for a Q-wave.

[0097] Figures 21(a) to 21(d) show a comparison between temporal parameters of wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure and a Welch Allyn device; specifically, Fig. 21(a) shows the comparison for PR wave, Fig. 21(b) for a QT wave, Fig. 21(c) for a P-Wave intervals and Fig. 21(d) for ST wave.

[0098] Figures 22(a) to 23(d) show correlation between amplitude parameters of a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure with ideal 12-lead ECG parameters and a Welch Allyn device in the chest region under different stimuli; specifically, Fig. 22(a) shows for rest conditions, Fig.22(b) under mental stimuli, Fig. 22 (c) under physical stimuli and Fig. 22(d) under physical and mental stimuli;

[0099] Figures 22(e) to 22(h) show correlation between temporal parameters of a wearable electrophysiological sensor having hexagonal labyrinth pattern electrodes according to an example of the present disclosure with ideal 12-lead ECCG parameters and a Welch Allyn device in the chest region under different stimuli; specifically, Fig. 22(e) shows for rest conditions, Fig.22(f) under mental stimuli, Fig. 22 (g) under physical stimuli and Fig. 22(h) under physical and mental stimuli;

[0100] Figures 23A to 23C are schematic diagrams illustrating the difference between stretchability and flexibility;

[0101] Figures 24A to 24E are schematic diagrams illustrating examples of labyrinthlike structures and a Peano curve structure; and

[0102] Figures 24A to 24F are schematic diagrams illustrating examples of labyrinthlike structures.

[0103] Description of Embodiments

[0104] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The terms "includes" means includes but not limited to, the term "including" means including but not limited to. The term "based on" means based at least in part on. The term "number" means any natural number equal to or greater than one. The terms "a" and "an" are intended to denote at least one of a particular element.

[0105] A conventional ECG system comprises a plurality of wet electrodes placed on the patient’s limbs and chest, which are connected by a plurality of leads to an electronic data acquisition and processing device. The ECG is typically conducted in a controlled in-patient setting. The use of wet electrodes and a number of leads mean that the system is not suitable for long term monitoring or use by patients in daily settings, as it is easy to dislodge the electrodes and upset the ECG readings. Further, the conductive gel has a tendency to dry out and so is not suitable for prolonged use over hours or days.

[0106] Other electrophysiological signal measurements also use a number of wet electrodes placed on the patient’s skin and attached to leads. EMG (electromyogram) measure electrical activity of muscles, EEG (electroencephalogram) measures electricalactivity of the brain, EOG (electrooculogram) measures electrical activity associated with the eye, ECoG (electrocorticogram) measures electrical activity associated with the ear.

[0107] Dry electrodes do not use a conductive gel and may directly contact the skin. However, due to high skin-electrode impedance, dry electrodes tend to experience signal loss and vulnerable noise degradation. This makes it difficult to accurately measure small electrophysiological signals with dry electrodes. This problem is particularly pronounced when using dry electrodes for ECG, which is one of the most complex signals to acquire.

[0108] The present application proposes a wearable electrophysiological sensor comprising a flexible substrate and one or more dry electrodes for sensing electrophysiological signals. Each of the one or more dry electrodes is located on a skin facing surface of the flexible substrate and each dry electrode comprises a number of (i.e. one or more) electrode tracks arranged in a non-solid pattern that is configured to flexibly accommodate contours of a patient’s skin. A non-solid pattern means a pattern that comprises one or more empty spaces surrounded by one or more electrode tracks formed of conductive material. For example, each electrode may comprise a plurality of electrode tracks which are connected together, at least some of the plurality of electrode tracks being adjacent to each other and empty spaces between the adjacent electrode tracks.

[0109] As the sensor has a flexible substrate it may conform to the contours of the wearer’s skin. This enhances comfort and helps to maintain contact between the skin and electrodes. As the electrodes are dry electrodes no conductive gel is needed, so the electrode can be worn for longer and is more easily used outside a specialist medical or hospital setting. As the electrode has a non-solid pattern, the electrode is more flexible than a solid electrode and better able to adapt to the contours of the wearer’s skin and maintain contact in the absence of conductive gel.

[0110] Compared to a ‘solid’ electrode having a continuous planar surface with no gaps, an electrode with a non-solid pattern may maintain contact with the skin over a larger area. While wet electrodes use a conductive gel to ensure electrical contact over a wide area, this is not possible for dry electrodes, and so the present application proposes providing an electrode with a number of electrode tracks arranged in a nonsolid pattern that is configured to flexibly accommodate contours of a patient’s skin.

[0111] One way of generating a non-solid pattern is to use a mathematical algorithm to generate a fractal pattern or space filling curve. A fractal pattern is a pattern with a structure that branches into smaller parts, which self -replicate at a smaller scale. A space filling curve is a curve comprising a plurality of repeating patterns which fill a 2- dimensional space. The pattern can then be applied to a thin film conductor by printing or etching etc.

[0112] Another way of generating a non-solid pattern is to use a mathematical algorithm to generate a labyrinth structure or labyrinth-like structure. A labyrinth is a structure comprising a set of connecting paths formed by gaps between walls (e.g. electrode tracks), which connecting paths lead to a central or inner point. A labyrinthlike structure means a pattern that has a number of connecting paths formed by gaps between electrode tracks. The term labyrinth-like structure thus includes labyrinth structures, but is broader as it does not require that the paths lead to a central point and includes patterns in which some or all of the paths are blocked by connections between adjacent tracks. The one or more electrode tracks which form the walls of the labyrinth are connected together so they are at the same electrical potential.

[0113] Another way of generating a non-solid pattern is to design an electrode comprising a plurality of electrode tracks which together form a plurality of concentric rings, each ring being connected to an adjacent ring. As each ring is connected to an adjacent ring, the rings are at the same electrical potential. Each ring may have a shape such as, but not limited to, a generally circular, oval, triangular, quadrilateral, square, hexagonal or other polygonal shape, or may be a loop shape which fully or partially encloses an inner ring (or loop) or central point of the electrode. Each ring may includeone or more breaks (thus forming a path connecting empty spaces on either side of the ring). The one or more breaks provide further flexibility.

[0114] It is possible to draw labyrinth, labyrinth-like or concentric ring structures manually. However, these patterns may be generated using an algorithm, which simplifies the design process and makes it possible to fill any specified two - dimensional area with the non- solid pattern. The labyrinth, labyrinth-like or concentric ring pattern can then be applied to a thin film conductor by printing or etching etc.

[0115] The inventors have found, unexpectedly, that the labyrinth-like and concentric ring structures provided a better performance compared to fractal and space filling curve structures. This is thought to be due, in part, to the high degree of flexibility realised by labyrinth-like and concentric ring structures, which enables them to better accommodate the contours of a patient’s skin. The labyrinth-like and concentric ring structures allow different parts of the electrode to flex in directions both parallel to and perpendicular to the plane of the electrode.

[0116] While fractal and space filling curve patterns provide a high degree of stretchability, they are not as good in terms of flexibility. The labyrinth-like and concentric ring structures exhibit a relatively higher degree of flexibility in terms of accommodating the contours of a patient’s skin. In terms of maintaining a large number of points of contact with the patient’s skin, flexibility is more important than stretchability.

[0117] Figures 23A to 23C are schematic diagrams which illustrate the difference between stretchability and flexibility. Figure 23A shows a planar electrode in an original non-deformed state. Figure 23B shows the planar electrode being stretched by application of forces in the plane of the electrode which elongate the electrode. Figure 23C shows a planar sensor being flexed by application of a bending force which bends the electrode. The bending forces includes a component perpendicular to the plane of the electrode.

[0118] Stretchability means the ability of a material to withstand stretching or elongation in a direction along a plane of the material, without permanent deformation or breaking such that it can return to the initial state once the force is removed. Stretchability may be measured by strain percentage. Flexibility means the ability of the material to bend when force is applied without breaking or permanently deforming. Flexibility may be measured by the achievable bend radius without breaking or permanently deforming. In some examples, the labyrinth-like and concentric ring structure electrodes of the present disclosure had a flexible bending radius of at least 4mm, meaning that they could be flexed around a cylinder having a diameter of at least 8mm. In some examples, an electrode having a labyrinth-like or concentric ring structure was tested and withstood 100 cycles of such flexing.

[0119] Figures 24A to 24D show some examples of labyrinth structures. Figure 24A shows an example of a hexagonal labyrinth structure, while Figures 24B, 24C and 24D show examples of circular, triangular and square labyrinth structures respectively.

[0120] A labyrinth structure may in some cases, including the examples shown in Figures 24A to 24D, comprise a plurality of concentric rings, with each ring being connected to an adjacent ring. The rings may have a polygonal (e.g. hexagonal, triangular, quadrilateral etc) shape, an oval or circular shape or a loop shape. Figure Figure 24A shows a structure with the first ring 501, second ring 502, third ring 503, fourth ring 504, fifth ring 505 and innermost ring 506. The innermost ring 506 in this example surrounds a central point of the electrode. The rings are connected together by cross portions of the pattern formed by portions joining adjacent electrode tracks.

[0121] This structure may allow different rings to move relative to each other in a plane perpendicular to the plane of the electrode and for different parts of a same ring to move relative to each other in a plane perpendicular to the plane of the electrode. At the same time the connections between the rings help to prevent large areas of the electrode moving out of contact with the patient’s skin. In contrast, a Peano curve structure, as shown in Figure 24E, comprises only a plurality of repeating patterns without an overarching structure and as such individual repeating pattern units such as601 or 602 in Figure 24E, or groups of repeating pattern units can independently stick and move out of contact with the skin leading to sub-optimal performance as a sensor.

[0122] Figures 25A to 25F show example variations of hexagonal labyrinth-like structures. The example shown in Figure 25A has three breaks or openings 711, 712, 713 in a first ring thereof, three breaks or openings 721, 722, 723 and 724 in a second ring thereof, two break or openings in the third ring and one break or opening in each of the fourth to sixth rings. The example shown in Figure 25B has two breaks 811, 812 in the first ring and two breaks in the second ring 821, 822. The greater the number of breaks the greater the flexibility of the electrode and the better able the electrode is to adapt to and maintain contact with contours of the skin. Figures 25D to 25F show more complicated hexagonal labyrinth-like structures with a greater number of breaks in the rings. Similar principes apply to labyrinth-like structures with other shapes of ring, including but not limited to triangular, quadrilateral and circular etc. In some examples the labyrinth-like pattern has at least one break in the outer two rings and in other examples at least three breaks in the outer two rings. In some examples the labyrinthlike pattern has at least one break in each ring and in other examples at least three breaks in each ring.

[0123] Figure 25C shows an example of a labyrinth-like structure which does not meet the strict mathematical formal of a labyrinth, as there is no clear path route from the centre to the exterior. The structure of Figure 25C is essentially the same as the labyrinth structure of Figure 25 A, except that additional parts 901, 902 and 903 have been added to block several of the paths. However, the general structure is derived from and similar to a labyrinth, so the structure is considered to be labyrinth-like and has the same advantages as described above.

[0124] In some examples, the present disclosure proposes a wearable electrophysiological sensor for attachment to a patient’s skin. The wearable sensor comprises a flexible substrate having a first surface for attachment to the patient’s skin and a second surface opposite the first surface. One or more dry electrodes are provided on the first surface of the flexible substrate. Each dry electrode comprises a non-solidpattern filling a respective two-dimensional electrode area, wherein different sections of the non- solid pattern are movable relative to each other to accommodate contours of a surface of a patient’s skin. The wearable electrophysiological sensor may be an electrocardiogram (ECG) sensor and the dry electrodes may be dry electrocardiogram (ECG) electrodes for use in conducting an ECG.

[0125] The sensors may be compact and lightweight so that they are easily wearable devices. They have many possible uses including, but not limited to monitoring athletic performance, ambulatory care, out-patient use, long-term monitoring of individuals at their home, work or in daily settings or for convenient use in hospitals in a bed-side setting. The potential for long term use in home care is particularly compelling as it reduces costs and may enable health issues to be spotted earlier, as well as for use in monitoring a patient after discharge from a hospital. In some examples, the sensor may have a wireless module for wirelessly transmitting data gathered by the sensor. In this way the need for leads is avoided and the wearer may remain mobile.

[0126] Fig. 1A shows an example of a wearable electrophysiological sensor 100 according to the present disclosure. Fig. IB shows a portion of the same wearable sensor 100 in cross-section. The wearable sensor 100 comprises a flexible substrate 110 and one or more dry electrodes 120 for sensing electrophysiological signals. The electrodes 120 are located on a skin facing surface 112 of the flexible substrate. Each electrode comprises one or more electrode tracks 122 arranged in a non- solid pattern 200 that is configured to flexibly accommodate contours of a patient’s skin.

[0127] The dry electrodes may be planar electrodes, which have a substantially planar surface when not in use before being applied to the patient’s skin. That is the electrodes are not needle electrodes which have multiple pointed ends contacting the skin, but rather a planar electrode having a flexible surface, which adapts to the contours of the patient’s skin. The electrodes may be direct contact electrodes which make direct contact between the conductive material of the electrode and the surface of the skin, rather than indirect contact or capacitive electrodes which provide an insulating layer between the conductive material of the electrode and the skin.

[0128] The flexible substrate 110 may have two surfaces. The first surface may be the skin facing surface 112 for attachment to the patient’s skin. The second surface 114 may be opposite the first surface. Each electrode 120 may comprise a non-solid pattern 200 filling a respective two-dimensional electrode area and different sections of the non-solid pattern may be movable relative to each other to accommodate contours of a surface of a patient’s skin. Figs. 2a to 2f show non-limiting examples of non-solid patterns 200 which may be used.

[0129] While the examples in Figs 1A and 2A-2F show three electrodes on the surface of the flexible substrate, in other examples there could be one electrode, two electrodes or more than three electrodes. Many applications need at least two electrodes in order to measure a potential difference or differential voltage between two electrodes. Where there are three or more electrodes, then in some examples the electrodes may be substantially equidistant from each other. In this context equidistant is measured from the perimeter or outermost edge of the electrodes, e.g. in the case of three electrodes, the shortest distance from the perimeter of a first electrode and the perimeter of a second electrode is substantially equal to the shortest distance from the perimeter of the first electrode and the perimeter of a third electrode, and substantially equal to the shortest distance from the perimeter of the second electrode and the perimeter of the third electrode. This arrangement of equidistant electrodes mounted on a flexible substrate makes it possible for the sensor to cover the Einthoven’s triangle for ECG sensing with the correct electrode spacing between the 3rdand 4thintercostal spaces.

[0130] The design of the individual electrodes plays a key role in the performance of the sensor. By using dense geometrical patterns, it is possible to increase the area of contact between the skin surface and the electrode, while still maintaining the advantages of a non-solid electrode pattern. As can be seen in Figs. 2A to 2F the patterns may be made relatively dense with a large portion of the electrode area occupied by conductive electrode tracks. Figs 2B and 2F show fractal or space filling curve patterns, while Figs 2A and 2C to 2E show labyrinth-like patterns.

[0131] The non-solid electrode patterns comprise one or more empty spaces 124 surrounded by one or more electrode tracks 122 formed of conductive material. For example, the non-solid electrode pattern may comprise a plurality of electrode tracks which are connected together. As the plurality of electrode tracks 122 are connected together they are at the same electrical potential and form a single electrode.

[0132] In order to achieve a high density, at least some of the plurality of electrode tracks may be adjacent to each other, with empty spaces between the adjacent electrode tracks. For instance, the electrode may comprise a plurality of substantially parallel electrode tracks, or tracks with substantially parallel portions, and gaps between the parallel electrode tracks or parallel track portions. The plurality of electrode tracks are connected together, for instance by connecting sections of the electrode, so that the various tracks form a single electrode.

[0133] In some examples, for each electrode, the empty spaces take up no more than 75% of a surface area occupied by the electrode. In this way the electrode is flexible due to the empty spaces or gaps, but has a large area of contact with the skin. Having a large area of contact reduces impedance. In some examples the electrode tracks take up between 20% and 75% of the surface area occupied by the electrode (with the remainder being empty spaces between the electrode tracks). It was found that this range of occupancy or density of the electrode tracks provided a good balance between a large contact area on one hand and allowing greater flexibility and adaptability to contours of the patient skin on the other hand. Electrodes with a higher density in which over 75% of the surface area was occupied by the electrode tracks was found to result in a poorer performance in practice due to difficulty in such electrodes adapting to the contours of the patient skin.

[0134] In some examples, each of the one or more electrodes has an electrical resistance of less than 3 Ohms. In terms of electrical impedance, each electrode may have an electrical impedance of less than 10 kOhms for electrical current having a frequency between 0.1 and 10 KHz. Reduced electrical resistance and impedanceallows for more sensitive and accurate measurement of smaller signals. This is helpful in applications such as ECG which measure very small electrical signals.

[0135] In Figures 2B and 2F the electrode comprises one or more electrode tracks which together form a fractal-like structure or a space-filling curve structure comprising a plurality of repeating patterns. Fig. 2B shows an example of an electrode pattern in the shape of a Peano curve, which is an example of a two-dimensional space filling curve. While in mathematical terms, a space filling curve reaches every point in a two-dimensional unit space, in the present disclosure the term is used more generally to mean a curve comprising a plurality of repeating patterns to fill a large portion, e.g. more than 70 percent of a two-dimensional space with points on the curve. Fig. 2F shows a Hilbert curve which is an example of a fractal like structure. In the present application the term fractal does not necessarily require strict compliance with the mathematical definition of a fractal, but rather refers to a pattern which has a structure that branches into smaller parts, which self-replicate at a smaller scale.

[0136] The inventors have found that an electrode comprising a plurality of electrode tracks which are connected together to form labyrinth-like structure works well and is able to adapt to contours of the patient’s skin while maintaining a high degree of contact with the skin. Examples of such patterns are shown in Fig. 2A which shows a triangular labyrinth, Fig. 2C which shows a circular labyrinth, Fig. 2D which shows a hexagonal labyrinth and Fig. 2E which shows a square labyrinth. A labyrinth is a set of connecting paths formed by gaps between electrode tracks, which lead to a central or inner point. In the context of the present disclosure, labyrinth-like means that the electrode has a number of connecting paths formed by gaps between electrode tracks. However, it is not required that the paths lead to a central point and some or all of the paths may be blocked by connections between adjacent tracks.

[0137] In some examples, the electrode comprises a plurality of electrode tracks which together form a plurality of concentric rings, each ring being connected to an adjacent ring. Each ring may have a shape such as, but not limited to, a generally circular, triangular, quadrilateral, hexagonal or polygonal shape or the ring may have aloop shape which fully or partially encloses an inner ring or central point of the electrode. Similar to a labyrinth, the overarching structure of the concentric rings provides flexibility and the ability to adapt to the contours of the patient’s skin while maintaining a large number of points of contact with the patient’s skin.

[0138] In some examples, the one or more dry electrodes are formed from a conductive thin film layer having a thickness of 120nm to 5 microns. The use of a thin film layer facilitates mass production, as the electrode patterns can be applied using printing, lithography, etching and other such techniques. In addition the properties of electrodes formed by a thin film conductor or layer are well understood and easy to model as the material may be homogeneous. This is in contrast to nano-wire deposition of electrode tracks which is difficult to scale and also difficult to model and provide predictable electrical properties due to anisotropic properties, quantum confinement effects and high aspect ratio of the nano-wires.

[0139] In some examples each electrode track has a width of between 30 microns and 500 microns and gaps between adjacent electrode tracks are no more than 30 to 500 microns. These are small enough to cover the two dimensional electrode area at a relatively high density, but large enough to avoid the quantum confinement effects and high aspect ratio and other issues associated with very thin electrode tracks.

[0140] In some examples, the electrode tracks are substantially uniform in width, except for the outer perimeter which may have one or more portions with larger width. This is in contrast to a structure which has solid electrode contacts (e.g. solid discs of metal) connected by meander line tracks; in such structures the majority of the skin contact area is through the solid electrode contacts, rather than the connecting meander tracks which makes the structure less resilient to contours in the skin as if one or more solid electrode contacts loses contact with the skin performance of the electrode is significantly affected. In contrast where the electrode tracks are substantially uniform, the contact points are very well distributed and the performance is not significantly impacted if a small area of the electrode loses contact with the skin, to not units can help to ensure that the majority of the tracks come into contact with the skin. In someexamples the electrode has no solid portions having a greater width than the electrode tracks and / or no solid portions having a greater width than 500 microns.

[0141] In some examples, each of the one or more electrodes may have a thickness between 50nm and 500nm. In some examples, each of the one or more electrodes has a thickness between 50nm and 200nm. This makes the electrode more flexible and able to adapt to the contours of the patient’s skin. Thickness is the dimension from indicated by t in Fig. 1A and represents the distance between the skin facing surface of the flexible substrate and the skin facing surface of the top of the electrode.

[0142] In some examples each electrode comprises one or more electrode tracks and each electrode track has a width of between 30 microns and 500 microns, preferably between 50 microns and 450 microns. In some examples, each electrode comprises one or more electrode tracks and wherein adjacent electrode tracks are separated by gaps of between 50 microns and 700 microns, preferably between 140 microns and 650 microns. In some examples each electrode track may have a width of between 30 microns and 500 microns and gaps between adjacent electrode tracks are no more than 30 to 500 microns. The width of the electrode track is the dimension indicated by w in Fig. 1 A. Having narrow electrode tracks helps to provide a dense structure, which is flexible to adapt to contours of the patient’s skin, but also has a large number of points of contact due to the large number of electrode tracks which may be fitted into the electrode area.

[0143] In some examples, each electrode comprises one or more electrode tracks and wherein for each electrode the total length of the one or more electrode tracks is at least 600 mm, preferably at least 1000 mm. The length of an electrode track refers to the length to which the track extends in the plane of electrode along its longest dimension and the total length refers to the sum of the length of all of the electrode tracks.

[0144] As the pattern may be very dense, the total path length may be comparatively large compared to the surface area of the electrode as a whole. In this context the surface area of the electrode as a whole refers to the total area covered by the electrodeincluding both the tracks and the empty space or gaps between the tracks, i.e. it refers to the two-dimensional footprint of the electrode.

[0145] The total length of the one or more electrode tracks, or total path length, refers to the total length of all of the electrode tracks of the electrode.

[0146] The surface area or footprint of the electrode is distinct from the contact area of the electrode. The contact area of the electrode refers to the total area occupied by electrode tracks, but not the gaps. In designs in which each electrode track has the same width, the contact area may be equal to the total length of all the electrode tracks multiplied by the electrode track width. In some examples each electrode occupies a two-dimensional surface area of between 50 square millimeters and 500 square millimeters.

[0147] In some examples, for each electrode, a ratio of the total length of the one or more electrode tracks (in mm) to the surface area (mm2) of the electrode is at least 3, preferably at least 4 and in some examples between 4 and 10. This provides a relatively dense electrode pattern which reduces the impedance.

[0148] In some examples, the wearable sensor is configured to detect electrical signals having a voltage as low as 0.05mV. Due to the low impedance and high density of the electrode pattern, at least some of the above described structures of dry electrode are capable of detecting electrical signals having a voltage of this low level. This makes the sensor suitable for use in applications, such as ECG, which require detection of small electrophysiological signals.

[0149] The one or more electrodes are formed of an electrically conductive material. In some examples the material is or comprises a metal, including halides, alloys and composites thereof. In some examples, the one or more electrodes comprises or consists of a metal, metal halide, metal composite, or a conductive polymer. Preferably, the material is biologically inert so that it does not chemically react with the biological tissue of the subject during use. In some preferred embodiments, the electrodecomprises or consists of one or more metals selected from Au, Ag, Cu, Sn, Pt, Ti and alloys thereof. Other examples of possible metal-based electrodes include, but are not limited to, Au, Ag, Ag / AgCl, Ti, Sn, Pt, Cu, brass and stainless steel. In one example, the one or more electrodes comprise or consist of a noble metal (e.g. the electrode is Ag, Ag / AgCl, Au, Pt, Pd etc.). In another embodiment, the one or more electrodes comprise or consist of a Group 11 metal (e.g. the electrode is Cu, Ag, Ag, Ag / AgCl etc.). Metal-based electrodes tend to have good electrical conductivity as well as being long lasting and resistant to degradation. The electrode may be formed of a biologically inert metal, so that it does not chemically react with the biological tissue of the subject during use. In some examples, the electrode may be formed of a conductive polymer, which may be a biologically inert conductive polymer.

[0150] The flexible substrate is often a thin film made of a flexible material. In some examples, the flexible substrate comprises a polymer or elastomer, which may be a thin film. Examples of suitable polymer or elastomers include, but are not limited to, polyimide (PI), polyethylene terephthalate (PET) and polydimethylsiloxane (PDMS). Preferably, the polymer or elastomer is bioinert or biocompatible.

[0151] In some examples, the one or more electrodes are either physically or chemically deposited, including electro-deposition, machined, assembled, printed or photo-lithographically formed on the flexible substrate.

[0152] According to examples of the present disclosure, a method of manufacturing a wearable sensor may comprise providing a flexible substrate and forming, on a surface of the flexible substrate, one or more dry electrodes having a non-solid pattern that is configured to flex to accommodate contours of a surface of a patient’s skin. The method may be used to make any of the wearable sensors described above and may incorporate any of the features described above. For instance, the flexible substrate may be a thin polymer film and the one or more dry electrodes may be formed of a biologically inert metal-based material. In some examples the one or more dry electrodes are formed by depositing a conductive (e.g. metal) layer on the substrate and photo-lithographically etching the conductive layer to form the one or more electrodes.

[0153] Figs. 3A to 3H shows one example method of manufacturing a wearable electrophysiological sensor according to the present application. Photo-lithography is able to produce very fine and dense patterns. However, depending on the design and density of the electrodes, in some implementations other techniques could be used such as electro-deposition or printing etc.

[0154] Fig. 3 A shows a first step in which a first substrate, for instance a wafer which may be a silicon wafer, is provided. Fig. 3B shows a subsequent step in which a flexible substrate, such as polymer substrate is deposited on the first substrate. Fig. 3C shows a further step in which a photo-resist layer is deposited on the flexible substrate. For instance the photo-resist layer may be deposited by spin-coating. Figs. 3D and 3E show further processes in which the photo resist layer is photographically etched. For instance, the layer may be exposed to ultraviolet light through a maskless or masked aligner for forming the desired pattern of electrode as shown in Fig. 3D and the photoresist layer may be developed, as shown in Fig. 3E, using a photoresist developer to dissolve or remove portions of the photoresist layer which were not exposed to the ultraviolet light. Then as shown in Fig. 3F the conductive material (e.g. metal) for the electrodes may be deposited. In some examples gold may be used as the conductive material. Subsequently, as shown in Fig 3F, the photoresist is removed leaving conductive material forming one or more electrodes having the desired pattem(s) on the surface of the flexible substrate. Then, as shown in Fig. 3G, the first substrate may be removed or peeled off from the flexible substrate to leave a flexible substrate with a number of patterned electrodes on the upper surface.

[0155] Fig. 4. shows a schematic exploded diagram showing components of a wearable electrophysiological sensor according to the present disclosure which further includes a wireless module. In the example of Fig. 4, the wearable sensor 400 comprises a flexible substrate 110, which may for instance be formed of polymide, having a first (skin facing) surface 112 and a second (non-skin facing) surface 114. There are one or more electrodes 120 having a non-solid pattern on the first surface as previously described. In addition, there is a wireless module 410, for instance but not limited to a Bluetooth, cellular communications or wifi module, mounted on the secondsurface of the flexible substrate 110. The wireless module 410 is electrically connected to the one or more electrodes 120 and arranged to wirelessly communicate information based on the sensed electrophysiological signals to an external apparatus, such as a mobile device, computer, access point, the cloud or a server etc.

[0156] The wearable sensor 400 further comprises a second flexible layer 420 for positioning over the flexible layer 110 to attach the flexible layer to the skin 1 of a user. For instance, the second flexible layer may be an Allevyn® (trademark) dressing.

[0157] A wearable sensor as described in any of the above examples may be used to sense electrophysiological signals detectable at the skin of a patient. For instance, a wearable sensor with two or more non-solid patterned electrodes as described above, may be used to detect a voltage differential between two of the electrodes. The wearable sensor may be used to sense electrocardiographic signals at the skin of a patient or other electrophysiological signals, such as but not limited to EMG (electromyogram), EEG (electroencephalogram), EOG (electrooculogram) or ECoG (electrocorticogram) .

[0158] The wearable sensor may, for example, be attached to a patient’s neck or torso. The wearable sensor may send electrophysiological signals sensed by the one or more electrodes to a measurement device through a wired connection or wirelessly. In some examples a plurality of wearable sensors as described above may be attached to different locations on the patient’s body (e.g. limbs, chest, back, back of neck, head, etc) in order to measure signals at different locations or differentials between signals at a variety of locations. As the wearable sensor may be secured by an adhesive dressing or second flexible layer, it is easily attachable to different parts of the body.

[0159] EXAMPLES

[0160] Electrodes were fabricated according to each of the electrode patterns shown in Figs. 2A to 2F using gold as the electrode material. The electrodes had a thickness of 150 nm. Table 1 below shows the design parameters of each electrode pattern. In Table1, the term “footprint” refers to the combined surface area of all the electrodes in the sensor (which the example of the sensor of Fig. 3 is three electrodes). The term “surface area” refers to the surface area of a single individual electrode, while the total length of electrode tracks refers to the total length of the tracks for a single individual electrode. The electrode distance refers to the distance between the outer edge of perimeter of adjacent electrodes, while the electrode thickness and resistance refer to the thickness and resistance of a single individual electrode.Table 1: Electrode design parameters

[0161] Figure 5 shows the surface area compared to resistance and total length of the one or more electrodes tracks (“total path length”) for each electrode design.

[0162] Three equidistant electrodes of each type were formed on a substrate and the resulting sensor tested.

[0163] ECG signal acquisition under different postures and stimuli

[0164] Measurements were taken by placing the electrodes in the posterior of the neck and the anterior of the chest (4thintercostal space) regions. Similar studies werecarried out at the posterior of the neck, as this could be used to give information on the events of heart arrhythmias and palpitations occurring which can be caused by underlying stress, exercises, medication or due to an underlying medical condition. There is increased neural activity at the neck region and electrodes that interface at this region directly have an additional benefit from having large total path lengths for a given area- this in turn helps to have better conformability and more areal coverage. The ECG signals were acquired from the subject using different positions that include sitting, standing, and lying for different stimuli: complete rest, mental stimuli (MS), physical stimuli (PS), mental + physical stimuli (PS+MS). For each specific electrode configuration, total of 12 measurements (which is a combination of varying body positions and stimuli) were obtained to perform the extensive studies. Among the designs studied, the hexagonal labyrinth, square labyrinth and Hilbert curve designs were found suitable for ECG signal acquisition at both regions categorically as shown in Table 2 below, with the hexagonal labyrinth being the best candidate- due to its relatively better conformability and its ability to establish intimate contact on both the anterior of the chest and posterior of the neck region. The Peano curve design was found not to be suitable for neck region and only suitable in some, but not all situations, for the chest region. As will be discussed later, while the Hilbert curve could be used for both the chest and neck region, the very high density of the electrode pattern in the Hilbert curve design (over 85% occupancy of the space by electrode tracks) was one factor which resulted in poorer performance in practice.Table 2 | Suitability of electrodes across different regions of placement in different positions under varying stimuli.

[0165] Suitability of ECG electrodes for chest and neck regions

[0166] Table 2 gives the comprehensive list of each electrode and its suitability in different regions of placement across all positions and stimuli. Upon evaluation, the hexagonal labyrinth-based design was found to be the best performing overall for both the chest and neck regions across all the different stimuli. The suitability of the electrodes was evaluated based on the following criteria: (i) how well the electrodes conform to the region of placement, (ii) ability to acquire ECG signals with minimal data loss and minimal noise, (iii) ability to acquire ECG signals on both the anterior of chest and posterior of neck regions, (iv) ability to acquire ECG signals under different stimuli.

[0167] The hexagonal labyrinth-based design was found to have the best response among the investigated designs, matching the performance of commercially available portable ECG monitor when attached to the chest area across the 4thintercostal space. This was evaluated based on how well the electrodes were able to conform to the skin of the subject and with good quality ECG signal acquisition. Hexagonal labyrinth geometry was found to offer one of the least resistances with a large total length of electrode tracks, while having a relatively smaller surface area as seen from Figure 5 and Table 1, with the ability to have more point of contact with increased arealcoverage on the site of inspection. The hexagonal labyrinth design-based electrode design was also found to have one of the least resistances of 0.295 Q among all the electrode designs. Measurements were taken by placing the ECG electrodes on the regions of study- posterior of the neck, and anterior of the chest along the 4thintercostal plane and enclosing it with commercial Allevyn® bandage. This particular dressing was used owing to its antimicrobial effects and its ability to offer additional conformability of the ECG sensor along the curvature of the skin. The non-sticky yet adhesive nature of this dressing helps in enhanced locking of the ECG device in place. Figure 4 shows the schematic of how the ECG electrodes were sandwiched between the epidermis of the skin (target region) and the Allevyn® bandage.

[0168] Tracing ECG waves

[0169] A typical functioning of the heart involving sequences of depolarization and repolarization and tracing the deflections of these waves as shown in Figure 6. The mechanism and the sequence are as follows: (i) the first step in this mechanism is the initiation of atrial depolarization by the SA node which causes the P wave, (ii) This is followed by the completion of the atrial depolarization, wherein the impulse is delayed at the AV node constituting the P-R interval, (iii) Ventricular depolarization begins at the apex, causing the QRS complex (atrial repolarization occurs), (iv) following this, ventricular depolarization is complete, yielding the S-T interval, (v) then ventricular repolarization begins at the apex, causing the T wave (vi) finally followed by the completion of the ventricular repolarization.

[0170] From the perspective of a 3 -lead wearable ECG sensor which is applicable to the present device, it is possible to look at key cardiac parameters that is indicative of cardiac activity and events. These include the following (a) flatline ECG which can be asystole (characterized by absence of pulse and electrical activity) and pulseless electrical activity (PEA), where there is electrical activity of the heart, but the pulse is absent. Asystole is a serious medical emergency and needs to be immediately intervened by cardiopulmonary resuscitation (CPR), (b) absence of P-wave which could indicate sinus dysfunction or the presence of fibrillation or flutter waves, (c)heart rate variability (HRV) from R-R wave data, and other ventricular activity abnormalities such as (d) prolonged QT wave intervals, (e) indication of ST wave elevation / depression and (f) T-wave depression.

[0171] ECG acquisition on the anterior of chest region

[0172] Figure 7 shows ECG response of the hexagonal labyrinth design-based sensor placed on the anterior region of the chest along the 4thintercostal space to the right of the sternum in the lying posture under the following stimuli- rest, mental stress, physical stress, and physical + mental stress. Figures 8 and 9 show the ECG response of the hexagonal labyrinth design-based sensor for the same testing conditions under the sitting and standing postures respectively. The sensor was able to obtain high quality signals in all these different postures under different stimuli. Figures 10-12 show the ECG response of the circular labyrinth design-based sensor in the lying, sitting and standing postures under different stimuli, while Figures 13-15 show the ECG response of the square labyrinth design-based sensor in the lying, sitting and standing postures under different stimuli. The sensors were able to obtain high quality signals in these postures and stimuli also, although the circular labyrinth design was found less suitable for the lying down posture than the other designs tested.

[0173] Temporal parameters - Chest region

[0174] ECG signal interpretation is a structured assessment of the waves and intervals present / absent in the acquired ECG signal. The ECG signal essentially consists of the temporal parameters along the x-axis and the amplitude parameters along the y-axis. Some of the key temporal parameters are the PR, QT, ST waves and the P-wave interval.

[0175] The PR segment serves as the isoelectric line (baseline) of the ECG curve, and it reflects the slow impulse conduction through the atrioventricular node. Further, the amplitude of any wave is measured by using the PR segment as the baseline. Table 3 shows the time parameters measured from the ECG signals under the lying down posture. Normally the PR interval ranges between 0.12-0.22 s. We found the PR segment to be around 0.17-0.21 s when obtained from the hexagonal labyrinth electrodes. QT duration is measured from the onset of the QRS complex, and the QT interval increases when heart rate slows and decreases when the heart rate increases. QT duration is then used to find the corrected QT duration (QTC) which is given by QTc = • Interpretation of the ST segment helps in understanding andstudying possibilities of myocardial ischemia. ST segment analysis helps in studying the possible presence of heart failure, ischemic ST depressions and supraventricular tachycardias. ST interval normally lies between 0.05-0.15 s. ST segment values ranged from 0.05-0.14 s when tested using the hexagonal labyrinth electrodes.

[0176] Amplitude parameters - Chest regionThe amplitude parameters are tabulated in Table 4 for the lying down posture measured using the various electrode designs. The key amplitude parameters are the P, R, Q and T-waves. The R-wave should ideally be around 0.2 mV, and we obtained 0.22-0.23 mV for R-wave duration using the hexagonal labyrinth design. The amplitude response for the P-wave should be within 0.25 mV, and we obtained a P-wave response of 0.1 mV from our hexagonal labyrinth design. R-wave should be within 1.6 mV, and we obtained a value of 0.5 mV for the measured R-wave. Q-wave measured was 0.5 mV is about 40% of the R-wave. T-wave which should be between 0.1-0.5 mV was measured to be 0.08 mV. The slight deviations are as would be expected in an ambulatory ECG measurement. It is noted that the Hilbert curve electrode performed poorly for Q waves compared to the labyrinth designs. This is thought to be in part due to the high density of the design and poor ability to adapt to the contours of the skin while maintaining adequate contact with the skin compared to the labyrinth-like structures.Table 4 | Amplitude parameters of the various electrode designs: anterior of chest.

[0177] Numbers in parenthesis alongside Q wave values are amplitude percentage with reference to the R wave.

[0178] ECG acquisition on the posterior of neck region

[0179] Further measurements were taken by attaching the hexagonal labyrinth designbased sensor on the posterior of the neck region in the lying posture under the following stimuli- rest, mental stress, physical stress, and physical + mental stress as seen in Figure 16. Figures 17 and 18 show the same under the sitting and standing postures respectively. The sensor was able to obtain good quality signals in all these different postures under different stimuli as seen in Table 3 and Table 4, and was able to differentiate between the subject being in complete rest and under duress.

[0180] Temporal Parameters - Neck region

[0181] Table 5 shows the time parameters measured from the ECG signals under the lying down posture. Normally the PR interval ranges between 0.12-0.22 s. We found the PR segment to be around 0.17-0.21 s when obtained from the hexagonal labyrinth electrodes. ST interval normally lies between 0.05-0.15 s. ST segment values ranged from 0.09-0.14 s when tested using the hexagonal labyrinth designs. Normal QT wave interval is between 0.34-0.44 s, and we found our device to exhibit QT values between 0.38-0.41 s. P-wave interval is ideally 0.11 s, and we found the P-wave to lie between 0.10-0.12 s.Table 5 | Temporal parameters of the various electrode designs: posterior of neck.

[0182] Amplitude parameters - Neck region

[0183] The amplitude parameters are tabulated in Table 6 for the lying down posture measured using the various electrode designs. The key amplitude parameters are the P, R, Q and T-waves. The R-wave should ideally be less than 0.2 mV. We obtained 0.22- 2.25 mV for the R-wave duration using the hexagonal labyrinth electrode. Typically, the amplitude response for the P-wave should be within 0.25 mV. We measured a P- wave response between 0.06-0.24 mV from our hexagonal labyrinth design. R-wave should be within 1.6 mV, and we obtained a valued of 1.25 mV for the R-wave measured. Q-wave is about 25% of the R-wave, and we obtained a value of 0.5 mV for the Q-wave which is 22% of the measured R-wave. T-wave which should be between 0.1-0.5 mV was measured to be 0.08 mV. The slight deviations are as would be expected on an ambulatory ECG measurement, and close correlation metrics can hence be established for neck region accordingly.Table 6 | Amplitude parameters of the various electrode designs- posterior of neck.

[0184] Numbers in parenthesis alongside Q wave values are amplitude percentage with reference to the R wave. Again, it is noted that the Hibert curve electrode performed poorly for Q waves compared to the labyrinth designs.

[0185] Comparison with ideal (standard) 12-lead ECG monitor

[0186] Following this we have compared and correlated the nature of response obtained from both regions to ideal 12-lead ECG response under lying conditions (matching standard posture of ideal 12-lead ECG sensing) across different stimuli. As in the case of a typical ambulatory measurement, the response parameters are usually corrected with a certain factor to be correlated with typical 12-lead ECG measurements. Figures 19a- 19d show the temporal and the amplitude parameters of the hexagonal labyrinth design-based sensor and the ideal 12-lead ECG response. As shown in Figure 19a, for the chest region, the temporal parameters (PR, QT, ST waves, and P-wave interval) are closely correlated. Figure 19c shows the temporal parameters obtainedfrom the neck region, and they were found to be closely correlated as well, with deviations when stimuli are applied, for both positions. The amplitude parameters for the hexagonal labyrinth design-based sensor for the chest and neck regions are shown in Figures 19b and 19d. It can be seen that the P, Q and T wave parameters are closely correlated, and the differential R-wave parameter is held as the device specific variation and correlated with standard ECG measurements. We can also obtain a clear demarcation between the state of the subject- whether the subject is under rest or under a certain duress. These device specific responses can be taken into consideration during the development phase of an ECG sensor incorporating the specific electrode configuration. Obtaining more dataset across different categories of subjects (number, age, body composition, health conditions) can further give us a comprehensive understanding and correlation metrics to calibrate and associate with this device specific ECG measurements.

[0187] Comparison with commercial portable 12-lead ECG monitor: Welch Allyn®

[0188] Readings from a sensor according to present disclosure with dense non-solid pattern electrodes were compared with readings from a 12-lead configuration Welch Allyn ECG device. Figure 20 shows the obtained amplitude parameters from the sensor with hexagonal labyrinth electrodes according to the present disclosure compared with ECG sensing response acquired from a commercially available Welch Allyn Wireless 12-electrode configuration ECG device for the lying down position under different stimuli. Figure 21 shows the obtained temporal parameters from the sensor with hexagonal labyrinth electrodes according to the present disclosure compared with ECG sensing response acquired from a commercially available Welch Allyn Wireless 12- electrode configuration ECG device for the lying down position under different stimuli.

[0189] Comparisons of the hexagonal labyrinth design-based sensor with the Welch Allyn monitor were made and their correlation are shown in Figure 22. The correlation in the amplitude parameters can be seen in Fig. 22 (a-d). Being ambulatory device, the devices each exhibit a characteristic device specific slight variation in measurement. This can be used in calibration of the device to match with expected ideal 12-lead ECGresponse. When a stimulus is applied as shown in Fig. 22 (b-d), as expected, there is a significant change in the amplitude response, indicating the subject is under duress. The temporal response parameters across the devices and their correlation are shown in Fig. 22 (e-h). As seen in Figure 22e, under the rest condition, the PR, QT and ST waves, and P-wave interval seem to be closely correlated.

[0190] Under different applied stimuli, as seen in Fig. 22 (f-h), the as-developed hexagonal labyrinth design-based ECG sensor was found to be more closely correlated to ideally expected ECG values. The Welch Allyn® device also exhibited closely corelated values for almost all temporal parameters, except for the P-wave interval. These slight deviations can be associated with the inherent electronic system design and the ambulatory device-dependent acquisition.

[0191] In terms of signal acquisition, the as-fabricated ECG sensor was found to be capable of performing in the capacity of a potential wearable ECG sensor patch. It was also found that the margin of deviation in the temporal and amplitude parameters between the herewith reported hexagonal labyrinth design-based ECG sensor and the commercially available portable Welch Allyn ECG device can be associated to the fact that the wired 12-electrode Welch Allyn monitor has complex electronics and amplification circuitry that is able to compensate for signal gain and signal-to-noise ratio (SNR). The reported sensor is proposed to be a simpler 3-electrode type, lightweight ECG patch that is compact and offers portable and wireless ECG sensing capabilities. The Welch Allyn device is comparatively clunky and weighs 200 grams. The entire electrode patch weighs 5 grams and together packed with the Allevyn® dressing and battery has a net weight of 12 grams, with a compact footprint of 6.5 cm (length) x 6.5 cm (width) x 1.2 cm (height). Further, the Welch Allyn device makes use of thick paste of silver / silver chloride (Ag / AgCl) material (wet electrode gel), whereas our device is based entirely on dry electrodes incorporating gold (Au) thin films with thickness of 150 nm which is less than the diameter of human hair strand, and no electrode gel playing a role in ECG signal acquisition.

[0192] A fully functional, compact, wearable ECG sensor incorporating thin films of dry electrodes, that is capable of continuous monitoring of cardiac activity was also prototyped. Bluetooth wireless measurements were done using a custom designed Bluetooth module. Surface mounted devices (SMDs) were used to design the BLE module. Dialog Semiconductor GmbH DA 14531MOD-OOFO 1002 was the BLE 5.1 SMD component of choice, capable of operating at a frequency of 2.4 GHz to 2.4835 GHz at an output of 2.2 dBm and sensitivity of -93 dBm. The BLE module was powered by a 3.3 V coin battery. The BLE signal communication range was —40 m.

[0193] A wireless device has the advantage of having the capability to attach the as- developed ECG device on both the anterior of the chest and the posterior of the neck region has huge implications in monitoring athletic performance, in neonatal care, rehabilitation, aged care sectors, patient transport, cardiac monitoring of patients with pacemaker, and patients with dementia, where continuous and uninterrupted acquisition of ECG is paramount while ensuring that the device is not easily prone to user impediment. This as-developed 3-electrode, wireless ECG device has the ability of providing key cardiac information and could be used as a screening device in POC settings. The use of dry electrodes with dense non-solid patterns on a flexible substrate, as disclosed herein, makes such wireless sensors possible, which would be difficult or impossible using conventional 12-lead ECG devices with wet electrodes.

[0194] Skin comfort of the wearable 3 -lead ECG sensor

[0195] A water-proof sensor as disclosed herein was worn by a user for a period of 7 days to check for biocompatibility. By the end of the 7 days, no skin irritation, rashes, or allergies were noticed. This makes this sensor suitable for long-term PoC applications which can remain unaffected when the user showers, sweats and during the day-to-day routine of a user.

[0196] Conclusions

[0197] As disclosed herein, a compact, waterproof, comfortable 3-electrode based wearable ECG sensor that uses dry electrodes was tested for continuous monitoring of cardiac parameters. It could be used for observing abnormalities and palpitations and was capable of differentiating between user’s condition of rest / unrest. Various designs were tested and found to be suitable, with the hexagonal labyrinth design-based electrode design found to give particularly good performance amount the tight-space designs evaluated. The dry patterned electrodes disclosed herein are able to establish more contact points on the surface of the skin, providing better signal acquisition while at the same time minimising material consumption.

[0198] A 3-electrode type compact, wearable ECG sensor using these electrode designs was compared with a commercially available Welch Allyn 12-lead ECG monitor and was found to operate on par with it. The sensor’s light weight, compactness, wireless measurement capabilities, ability to acquire ECG signals from both the chest and the neck area while being able to differentiate between rest and duress measurements under varying stimuli, and its capability to offer high quality ECG sensing within a 3-electrode configuration system show great promise for future applications in wearable ECG sensing particularly in ambulatory care and PoC applications wherein measurements can be made using the device standalone or embedded within wearable fabrics.

[0199] In some examples, photolithography techniques were employed in the fabrication of thin film sensor electrodes. In some examples a AZ5214E photoresist was used in the lithography process. The photoresist was spin-coated onto polyimide films at a speed of 3000 rpm, an acceleration of 1000 rpm / s for a duration of 30s. This was further soft baked at 95 °C for 90 s. Gold (Au) was the electrode material of choice. 30 nm of chromium (Cr) as an adhesion layer and 150 nm of Au was deposited using e-beam deposition. Allevyn® Ag Gentle Border, which is a silicone gel adhesive based antimicrobial hydro -cellular bandage was used as the dressing layer.

[0200] All of the features of the various example apparatus disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all ofthe blocks of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or blocks are mutually exclusive.

[0201] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A wearable electrophysiological sensor comprising: a flexible substrate; and one or more dry electrodes for sensing electrophysiological signals, each of the one or more dry electrodes being located on a skin facing surface of the flexible substrate; wherein each dry electrode is a planar electrode which comprises a number of electrode tracks arranged in a non-solid pattern connected together to form a labyrinthlike structure, the labyrinth-like structure being configured to flexibly accommodate contours of a patient’s skin while maintaining contact with the skin.

2. A wearable electrocardiogram (ECG) sensor for attachment to a patient’s skin, the wearable ECG sensor comprising: a flexible substrate having a first surface for attachment to the patient’s skin and a second surface opposite the first surface; one or more dry electrocardiogram (ECG) electrodes on the first surface of the flexible substrate; each dry ECG electrode comprising a non-solid pattern filling a respective two dimensional electrode area, wherein different sections of the non-solid pattern are movable relative to each other to accommodate contours of a surface of a patient’s skin; wherein the non-solid pattern comprises a plurality of electrode tracks which together form a plurality of concentric rings, each ring being connected to an adjacent ring.

3. The wearable sensor of claim 1 or claim 2 wherein the one or more dry electrodes are formed from a conductive thin film layer having a thickness of 120nm to 5 microns.

4. The wearable sensor of any one of the above claims wherein each electrode track has a width of between 30 microns and 500 microns and gaps between adjacent electrode tracks are no more than 30 to 500 microns.

5. The wearable sensor of any one of the above claims wherein other than an outer perimeter of the electrode, the electrode tracks are substantially uniform in width.

6. The wearable sensor of any one of the above claims wherein for each electrode, the electrode tracks take up between 20% and 75% of the surface area occupied by the electrode.

7. The wearable sensor of any one of the above claims wherein each electrode comprises one or more electrode tracks having a width of between 30 microns and 500 microns, preferably between 50 microns and 450 microns, and wherein adjacent electrode tracks are separated by gaps of between 50 microns and 700 microns, preferably between 140 microns and 650 microns.

8. The wearable sensor of any one of the above claims wherein each electrode comprises one or more electrode tracks and wherein for each electrode the total length of the one or more electrode tracks is at least 600 mm, preferably at least 1000 mm.

9. The wearable sensor of claim 10 wherein each electrode has a surface area and wherein for each electrode, a ratio of the total length of the one or more electrode tracks to the surface area of the electrode is at least 3, preferably at least 4 and in some examples between 4 and 10.

10. The wearable sensor of any one of the above claims wherein each electrode occupies a 2 dimensional area of between 50 square millimeters and 500 square millimeters.

11. The wearable sensor of any one of the above claims wherein each of the one or more electrodes has an electrical impedance of less than 10 kOhms for electrical current having a frequency between 0.1 and 10 KHz.

12. The wearable sensor of any one of the above claims wherein each electrode has a pattern selected from the group comprising: a triangular labyrinth, a circular labyrinth, a hexagonal labyrinth, and a square labyrinth.

13. The wearable sensor of any one of the above claims wherein the one or more electrodes comprise a metal, metal alloy, metal halide, metal composite, or a conductive polymer.

14. The wearable sensor of any one of the above claims wherein the flexible substrate comprises a polymer or elastomer, which may be a thin film.

15. The wearable sensor of any one of the above claims wherein the one or more electrodes are either physically or chemically deposited, printed or photo- lithographically formed on the flexible substrate.

16. The wearable sensor of any one of the above claims comprising two or more, preferably three or more electrodes on the surface of the flexible substrate.

17. The wearable sensor of any one of the above claims, wherein the wearable sensor is configured to detect electrical signals having a voltage as low as 0.05 mV.

18. The wearable sensor of any one of the above claims further comprising a wireless module on a second (non-skin facing) surface of the flexible substrate, the wireless module being electrically connected to the one or more electrodes and arranged to wirelessly communicate information based on the sensed electrophysiological signals to an external apparatus.

19. The wearable sensor of any of the above claims further comprising a second flexible layer for positioning over the flexible layer to attach the flexible layer to the skin of a user.

20. Use of a wearable sensor according to any one of the above claims to sense electrophysiological signals at the skin of a patient.

21. Use of a wearable sensor according to any one of claims 1-19 to sense electrocardiographic signals at the skin of a patient.

22. A method of detecting electrophysiological signals comprising attaching a wearable sensor according to any one of claims 1-19 to a patient’s neck or torso, and sending electrophysiological signals sensed by the one or more electrodes to a measurement device through a wired connection or wirelessly.

23. The method of sensing electrophysiological claim 22 comprising attaching a plurality of wearable sensors according to claims 1-19 to different locations on the patient’s body.

24. A method of manufacturing a wearable sensor according to any one of claims 1- 19, the method comprising: providing a flexible substrate; and forming, on a surface of the flexible substrate, one or more dry electrodes having a non-solid pattern that is configured to flex to accommodate contours of a surface of a patient’s skin.

25. The method of claim 24 wherein the flexible substrate is a thin polymer film and the one or more dry electrodes are formed of a biologically inert metal.

26. The method of claim 24 or claim 25 wherein the one or more dry electrodes are formed by depositing a metal layer and photo-lithographically etching the metal layer to form the one or more electrodes.

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