WO2023200377A1

WO2023200377A1 - Sensor for sensing electrical parameters of body surface layer

Info

Publication number: WO2023200377A1
Application number: PCT/RU2023/050091
Authority: WO
Inventors: Dmitriy Borisovich RYAVKIN
Original assignee: «Save Technology» Limited Liability Company («Save Technology» Llc)
Priority date: 2022-04-15
Filing date: 2023-04-14
Publication date: 2023-10-19

Abstract

Disclosed is a single-electrode sensor for sensing electrical activity of the body surface layer of the user, which comprises: a single electrode comprising a plurality of conductors and configured to be placed near the user's body on a distance providing capacitive and/or inductive electrode-body coupling; and an analysis unit configured to determine one or more electrical activity parameters of the body surface layer based on at least one of the following signals: electrode-body capacitor leakage current, electrode-body capacitor capacitance, electrode-body system inductance, signal generated by an external electromagnetic field and passing through said capacitor, and phase, frequency and/or amplitude modulation of said signal. The invention provides convenient recording of parameters indicative of psychophysiological parameters of the user, including at least one of degree of nervous tension, emotional state, pulse, and acceleration of a body part on or near which the sensor is arranged.

Description

SENSOR FOR SENSING ELECTRICAL PARAMETERS OF BODY SURFACE LAYER

FIELD OF THE INVENTION

The present application relates to devices for collecting, registering, and/or monitoring data indicative of psychophysiological parameters, including but not limited to the degree of nervous tension, pulse, acceleration of the body or parts thereof, based on the obtained electrical parameters on the surface layer of the body.

BACKGROUND OF THE INVENTION

Physical changes occurring in body tissues such as blood flow, sweating, lymph redistribution, changes in dielectric permittivity of biological tissues and liquids, changes in electrical conductivity of biological tissues and liquids, and the like lead to changes in electrical activity of the body. As the changes in electrical activity of the bodies of living warm-blooded organisms including humans can be caused by a number of biochemical, nervous and hormonal processes, the parameters of the body's electrical activity, including electrodermal activity parameters, can be used as signals indicative of various physiological and/or psychophysiological parameters of a person or an animal. The most widely used in the prior art electrodermal activity (EDA) parameters of living organisms are often of interest as being indicative of various states of said organisms. As used herein, the term "EDA" encompasses a number of parameters such as galvanic skin response (GSR), skin potential level (SPL), skin potential reaction (SPR), spontaneous skin potential reaction (SSPR), skin resistance level (SRL) or skin conductance level (SCL), skin resistance reaction (SRR) or skin conductance reaction (SCR), spontaneous skin resistance reaction (SSRR) or spontaneous skin conductance reaction (SSCR). Various EDA parameters can carry different information about the underlying processes.

For instance, the adrenaline stress hormone can cause vasoconstriction of the vessels of abdominal cavity, skin and mucous membranes, can lead to an increase in blood pressure and pulse, an increase in blood glucose level and an increase in tissue metabolism. High blood glucose level can lead to extra- and intracellular dehydration, destabilization of cell membranes and disruption of energy metabolism of skin cells, sebaceous glands and sweat glands. Therefore, physical properties of skin and subcutaneous layers change, which in turn can be observed when measuring EDA and other parameters of electrical activity of the body.

In order to assess the psychophysiological state of a living organism, the practice of registering the galvanic skin response (GSR) has been developed. A typical method of obtaining GSR data includes placing (at least two) electrodes on the skin with the obligatory provision of electrical contact between the electrode and the skin, and detecting signals indicating electrodermal activity such as conductivity, resistance or electrical potential of the skin. However, when using such electrodes, the placement of at least two electrodes is required. The relationship of the parameters measured using said method with the psychophysiological state correlates with varying sweating, and in order to obtain a more distinct measurement, it is preferable to place said at least two electrodes on certain parts of the body characterized by the presence of eccrine sweat glands. According to earlier studies, eccrine sweat glands are most sensitive to changes in the psychoneurological status, and the electrodermal activity of the skin and subcutaneous layers in the area of such glands is most indicative. Areas characterized by abundant presence of eccrine sweat glands include fingertips, palms, soles of feet, forehead and armpits, and the need to place several electrodes in said areas can be inconvenient, especially in the case of wearable devices.

However, more recent studies have shown that the occurrence of GSR is based not only on metabolic processes and sweat gland function, as secretory processes thereof are too inert compared to the speed of skin response. Studies of propagation rate of the skin response have shown that in the upper extremities said rate is 154.9 cm/sec, and 71.6 cm/sec in the lower extremities. Simultaneous studies of sweating, skin resistance and skin potential on the palms of 35 subjects in the process of solving mental arithmetics tasks (Andreassi, John L. Skin-Conductance and Reaction-Time in a Continuous Auditory Monitoring Task, The American Journal of Psychology, vol. 79, no. 3, University of Illinois Press, 1966, pp. 470-74) have shown that the change in skin resistance occurs 1.1 seconds earlier than sweating. It has also been found that the GSR "lag" time in a subject is basically constant.

The disadvantages of conventional GSR measurement using electrodes can further include possible electrode polarization and the skin becoming adjusted to constant current flow (in the case of using the method with application of external current or potential difference). Further, the possibility of skin reaction to the chemical composition of the electrode needs to be taken into account, further complicating manufacturing and use of devices for recording EDA.

It should also be noted that galvanic skin response does not cover the entire spectrum of electrodermal activity. Examples of improved devices are also known in the art.

For example, a different method of obtaining EDA data is known in the art, namely, using an optical sensor instead of electrodes with specific light wave recording ranges selected for said optical sensor. However, when using the prior art technical solution in practice in a wearable device, the informational value of the sensor can drop significantly due to environmental changes when the environment becomes less mild, e.g., during rainfall. Introduction of additional means of improving skin contact reduces mobility and ease of use of the device. Signal reliability can be affected by skin pigmentation, defects, tattoos and other obstacles for the optical signal.

On the other hand, W02020119245 discloses a wearable device for recognizing user’s emotions, the device comprising a GSR monitoring module. However, in the proposed device, GSR recording is carried out by measuring the electrical potential of the skin, which does not show peak values, the analysis of which could determine the nature of emotional manifestations. In other words, the means and methods used in W02020119245 to obtain data on electrical parameters of the skin are unable to provide a complete classification of emotions, which is especially important for non-neurotypical users, such as people with autism spectrum disorders, as well as for people with various psychological and mental considerations. For instance, the proposed device is unable to determine such emotional manifestations as hysteria, aggression and the like. In the prior art device, simultaneous use of three input data channels (pulse, ECG, GSR) is proposed, affecting device dimensions and energy consumption; the authors directly mention the latter issue in the context of preferred embodiments.

Among prior art wearable devices, EDA measurements using electrodes contacting the skin are also utilized: the use of various combinations of prior art methods for assessing human psychophysiological parameters, wherein the electrodes can be made from conductive polymers among others, and can further be woven into fabric as metal fibers, thus providing greater comfort in use of the respective devices. However, such devices have all the same disadvantages described above in the context of conventional EDA measurement devices. Additionally, when using spatially extended electrodes, it is impossible to ensure continuous contact with the skin required for such devices, thus leading to emergence of ambiguous signals which could indicate contact disruption or a change in (skin resistance) parameters.

It should further be noted that in the contact method of EDA recording, signal level further depends on the contact area of the electrodes with the surface. In other words, when using the conventional method, it is necessary to maintain continuously stable and identical contact area of the electrode with the skin. Thus, the use of prior art electrodermal activity sensors is associated with a number of issues which the present invention aims to solve.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a single-electrode sensor for sensing electrical activity of the body surface layer of a user is provided, the sensor comprising: a single electrode comprising a plurality of conductors and configured to be placed near the user’s body on a distance providing capacitive and/or inductive electrode-body coupling; an analysis unit configured to determine one or more electrical activity parameters of the body surface layer based on at least one of the following signals: electrode-body capacitor leakage current, electrode-body capacitor capacitance, electrode-body system inductance, filtering/modulation of signal generated by an external electromagnetic field and passing through said capacitor, and phase, frequency and/or amplitude modulations of said signal.

According to one of the embodiments, the analysis unit is configured to analyze signals obtained using the electrode to obtain psychophysiological parameters of the user, including at least one of the degree of nervous tension, emotional state, pulse, and acceleration of the body part on or near which the sensor is arranged.

According to one of the embodiments, the analysis unit is configured to analyze signals obtained using the electrode and to output a signal indicative of critical/hazardous conditions, and/or when the obtained signal does not correspond to specified physiological parameters of the body.

According to one of the embodiments, the analysis unit configured to analyze the signals obtained using the electrode, providing data on the dynamics of user’s sleep parameters.

According to one of the embodiments, the analysis unit is configured to analyze the signals obtained using the electrode and the signals from an external temperature sensor and to output a warning signal when the combination of sensor signals is indicative of user’s hypothermia.

According to one of the embodiments, the analysis unit is configured to analyze the signals obtained using the electrode and to generate a warning signal when the analysis indicates that the user’s concentration is reduced.

According to one of the embodiments, the single-electrode electrical activity sensor comprises a frequency-determining signal generator. According to one of the embodiments, the analysis unit is configured to analyze the skin and subcutaneous layers electrodermal activity parameters obtained using the electrode and to output a signal indicative of acceleration of the body or parts thereof.

According to one of the embodiments, in the disclosed single-electrode electrical activity sensor of the body surface layer, the capacitive/inductive electrode-body coupling coefficient is at least 0.1.

Other aspects of the disclosure will be apparent from the following detailed description, the accompanying figures and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows an example of an electrode consisting of a group of conductive elements.

Fig. 2 depicts a schematic of an electrode in the form of a flat inductance coil according to one embodiment of the present invention.

Fig. 3 depicts a schematic of an electrode obtaining a capacitance signal according to one embodiment of the present invention.

Fig. 4 depicts a schematic of a sensor according to one embodiment configured for direct measurement of electrode-body capacitor leakage current.

Fig. 5 depicts a schematic of a sensor according to one embodiment configured for measurement of electrode-body capacitor capacitance.

Fig. 6 depicts a schematic of a sensor according to one embodiment configured for measurement of electrode-body capacitor leakage current by measuring load voltage drop.

Fig. 7 depicts a schematic of a sensor according to one embodiment configured for measurement of current capacitance of the disclosed electrode-body capacitor.

Fig. 8 illustrates an embodiment of the present invention based on analysis of filtering/modulation of a natural external electromagnetic field by the user’s body.

Fig. 9 illustrates an embodiment of the present invention based on analysis of filtering/modulation of an artificial electromagnetic field by the user’s body.

Fig. 10 illustrates an embodiment of the present invention based on analysis of modulation of an external electromagnetic field passing through user’s body to obtain abrupt movement data.

Fig. 11 shows an example of a signal indicating relative vessel filling.

Fig. 12 illustrates changes in sensor signal with increasing user’s concentration. DETAILED DESCRIPTION OF THE INVENTION

It should be noted that the term "user" refers herein to a person or a warm-blooded animal, and the term "electrode" refers to a single element or a set of elements functioning as an electrode and forming a single informative signal. For example, the electrode can be formed by a strand of conductors (11) connected in a single point with electrode elements (12) formed at the ends thereof, or can have a different shape distributed in space (e.g., as seen in Fig. 1). When a body reacts to a stimulus, a number of changes occur in the body of the subject, said changes further observable in the skin, e.g. a change in lymphatic flow direction, a change in capillary lumens, or sweating. According to various previous studies, electrical activity of the body surface layers depends on the degree of novelty of the stimulus, the type of the human nervous system, the functional state of the person, the neuro-emotional state, the level of stress, any irritation, the general condition of the central nervous system and its various parts, various pathologies, age, individual and sex differences, the magnitude of the stimulus (there is a direct relationship between the magnitude of the stimulus and skin response amplitude), etc.

But either way, changes in the psychophysiological state of the user lead to changes in physical characteristics of the skin and subcutaneous layers, which in turn affect conductivity of the skin and subcutaneous layers. The operational principle of the present invention is based on the use of an electrode-body system for recording physical characteristics of the skin and subcutaneous layers, the dynamics thereof being informative in relation to various psychophysiological parameters of the user.

In the most general embodiment of the present invention, the device comprises a single electrode of a free shape configured to be placed on or near the user’s body with conductivity provided over the electrode, and an analysis unit configured to determine an electrical activity parameter of the body surface layer based on signals obtained using said electrode. Unlike some of the prior art electrodermal activity sensors, the present invention does not require galvanic coupling, thus eliminating the need for direct contact with the skin of the user, while the sensor placement on or near the body can be arbitrary and is not limited to the areas with the highest concentration of eccrine sweat glands.

According to some embodiments of the present invention, the sensor components are arranged in a housing. The electrode is placed in the housing, e.g., according to one embodiment, on the bottom of the housing from the side that is supposed to face the skin of the user. According to one embodiment, the electrode is placed in a dielectric housing so that when the electrode is placed on or near the user’s body, a dielectric layer is arranged between the electrode and the body. According to other embodiments, the electrode may be formed without any additional layers or elements arranged between the electrode and the body in use of the sensor.

The distance between the electrode and the surface of the user’s body is selected such as to ensure capacitive and/or inductive coupling of the electrode and the body. As said distance is affected by weight/size of the body and electrode dimensions, shape and structure, the distance can be different in particular cases. Practically, the capacitive/inductive coupling coefficient how much the changes in the body affect the sensor, in other words, the coefficient is related to sensitivity of the sensor. In general, it can be said that the further from the body the sensor electrode is located, with all other factors being equal, the smaller/worse the signal is; and the smaller the sensor electrode is in size, with all other factors being equal, the smaller/worse the signal is. However, in particular cases, a relatively remote placement of the electrode with respect to the body is possible, which, in combination with other features of the invention, is able to provide sufficient sensitivity of the sensor and a high coupling coefficient. An example of such implementation can be a sensor wherein the electrode has a larger area and/or length, or use of the sensor on a body part having a larger area with which the electrode interacts electrically. For instance, a mat under a body, a sensor on a seat and the like.

According to one embodiment, the electrode is placed near the user’s body to provide a coupling coefficient of the electrode and the body of at least 0.1; in this case, the sensor is formed by a body accessory, e.g., in the form of a bracelet on the arm or a necklace.

Hereinafter, the term "coupling coefficient" denotes the coefficient characterizing the capacitive coupling or inductive coupling (depending on the type of signal being sensed) observed between the electrode and the body.

In general, the electrode is placed such that the signal from the sensor (frequency, amplitude, pulse ratio, etc.) clearly indicates the registering of data correlated with the current state of the user depending on the intended usage. For some embodiments described herein, when the coupling coefficient of less than 0.1, it is difficult to isolate a useful signal from noise without further improvements to the signal recording and processing means.

Among the embodiments, it is worth mentioning those wherein the sensor is arranged at arm's length. For instance, according to one of such embodiments, the electrode can be a plate or a conductor of a size comparable to the body. Changes in the body of the user which is moving or located near the electrode are registered by the sensor.

Due to the fact that the upper keratinized layer of the user's skin is also a dielectric

(according to some embodiments, the electrode is coated with a dielectric layer), and a medium with greater conductivity is located under said layer, an electrode-body capacitor system is formed, with one plate thereof formed by the electrode, and the other formed by the human body. The capacitance of the capacitor and the leakage current depend on dielectric permittivity of the skin and the electrical properties of conductive layers of the body/surface (practically forming the second capacitor plate). The sensor detects a signal passing through the "capacitor" which, according to some embodiments, is subsequently processed by a controller. Thus, the operational principle is based on a change in physical properties of the capacitor formed by the sensor electrode and the body, and the signal from the electrode indicates:

- changes in the charge on the body and, accordingly, on the electrode;

- leakage current through the formed capacitor.

As a conductor, the electrode also has an inductance which, among other factors, depends on the presence and the properties (magnetic permeability and conductivity) of the material/substance within/near the conductor. In this case, the inductance as one of the parameters of the electrical activity of the body surface layer will be affected by the properties of skin and subcutaneous layers, e.g. by blood, lymph and other electrically conductive components. Accordingly, the signal from the sensor will change with the change in inductance. According to some embodiments of the present invention, the electrode is configured such that a change in inductance has a stronger effect on signal dynamics than a change in capacitance; e.g. according to some embodiments, the electrode can have an elongated shape, e.g. formed by a flat inductance coil as shown in Fig. 2, or a serpentine electrode. On the other side, the electrode can be arranged such that the change in capacitance is the most indicative, such as the electrode (1) formed by a plate of an arbitrary shape shown in Fig. 3. As will be shown further in the exemplary embodiments, depending on the parameters for which the sensor signal is to be indicative, it is possible to use a capacitive and an inductive signal separately, and a combination thereof.

By means of the disclosed single-electrode sensor, it is possible to clearly observe the response of the autonomic nervous system to stimuli, as well as a general picture of electrical activity of the user’s body.

According to various embodiments, the sensor is an electrode with electronic or hole conductivity (a semiconductor) that has free shape, is a wire/cord/chain (closed or open), is placed on body surface or implanted therein, or placed in/on clothes, shoes (or elements thereof) of a human or animal. In various embodiments, the sensor is designed as a piece of wearable electronics, jewelry and other accessories. Thus, according to one embodiment, the disclosed sensor or a set of sensors is designed as a mat to be placed under user’s body. The mat allows monitoring the physiological state and outputs signals in critical/hazardous conditions. For instance, the mat can be placed in the crib of an infant, in particular for prevention of sudden infant death syndrome (SIDS) and prevention of pathological conditions. This application does not require wearing any devices on the body, thus being comfortable and convenient in use. According to some embodiments, the sensor comprises an analysis unit which in the present embodiment is configured to analyze electrodermal activity parameters of the skin and subcutaneous layers obtained using the electrode and to output a signal indicative of critical/hazardous conditions when detecting signals characteristic of SIDS precursors (when used with children), and/or when the obtained signal does not correspond to specified ranges of the physiological parameters of the body.

The change in sensor signal can also indicate phases and the course of sleep. According to one embodiment of the present invention, the sensor functions to monitor user’s sleep parameters. According to some embodiments, the sensor comprises the analysis unit which in the described embodiment is configured to analyze electrical activity parameters of the body surface layer obtained using the electrode, thus providing data on the dynamics of user’s sleep parameters. According to some embodiments, the analysis unit is configured to analyze the level of tonic electrodermal resistance as an indicator of the functional state of the central nervous system. It is known that in a relaxed state, e.g. during sleep, skin resistance increases, while decreasing in a highly aroused state. Physical parameters change rapidly in response to the development of a state of nervous tension, e.g. with the development of anxiety or increasing mental activity. The sensor can further be used in conjunction with an alarm application to select the optimal alarm time taking into account sleep parameters observed using the sensor, to automatically correct the alarm time taking into account the sensor signals, to provide recommendations regarding the time for falling asleep if the proposed time shift is acceptable, and to record sleep structure and characteristics for subsequent analysis by a specialist. This implementation of the sensor does not require wearing any devices on the body, such as fitness bracelets, smart watches and the like, thus positively affecting sleep comfort and operational reliability of the device.

The disclosed sensor can also be formed by an accessory or a built-in element for shoes and/or clothes, providing the possibility of monitoring user’s parameters. According to some embodiments, the use of the data from the disclosed sensor in conjunction with a temperature sensor allows assessing the combination of concurrent signals indicating the temperature and emotional state and providing signals warning about dangerous cooling of a limb and/or about dangerous condition of the body. According to some embodiments, the sensor comprises the analysis unit which, in the described embodiment, is configured to analyze electrical activity parameters of the skin and subcutaneous layers and temperature sensor signals, and to output a warning signal when the combination of sensor signals indicates user’s hypothermia. This implementation can be particularly relevant for people with disabilities, impaired sensitivity and/or consciousness, for young children, athletes, workers, astronauts and tourists in extreme conditions. The use of only temperature sensors for these purposes indicates only local (comparable to the size of the temperature sensor) temperature changes which can also be attributed to physiological characteristics of the body or skin defects which are not cause for concern, while the use in conjunction with the disclosed sensor provides a more complete picture due to a more comprehensive assessment of a user’s condition. It is appreciated that the electrode in the sensor can have any spatial structure and area. In this embodiment, the combination of conductive elements forming the electrode provides information not only about local temperature changes but also about the unconscious reaction of the body manifested in EDA changes and changes in blood flow in the skin and subcutaneous layers. These changes affect physical parameters of the electrode-body capacitor as some blood components (in particular, blood plasma) have a relatively high electrical conductivity.

In yet another embodiment, the sensor provides monitoring of mental concentration and performance ability of the user. According to one embodiment, the sensor comprises an analysis unit configured to analyze electrodermal activity parameters of the skin and subcutaneous layers obtained using the electrode and to output a signal indicating concentration and performance ability of the user. According to some embodiments, the analysis unit is further configured to generate a warning signal in the event of the analysis showing a high likelihood of the user currently having reduced concentration. The tests conducted by the applicant with participation of users having different levels of concentration have shown that when the user is concentrated, the sensor signal is more monotonous and less susceptible to external influences (e.g., it correlates less with user’s movements or pain experienced by the user). Fig. 12 shows an example of a signal, the amplitude and level of which are limited in a narrower range when the tested user is focused on performing a task.

According to one embodiment, concentration/focus on the task is characterized by a relative level of sensor signal of 40-50%. When a person is focused working at a computer or performs tasks related to fine motor skills and small spatial movements, movements and external influences (noise) do not substantially affect the level of the observed signal. Whereas during concentrated work the signal had a level of about of 50% on the said scale, a decline in user’s energy level caused its drop to 10-20%. High performance ability, or the so-called alert state, when the user is simultaneously calm and ready for immediate action, was characterized by a signal level of about 90-100%. In accordance with these patterns, an algorithm for interpreting the change in signal level can be developed.

According to a similar embodiment, signal analysis includes measuring sensor signal level, evaluating a relative level thereof, generating an output signal containing extreme values, and subsequent interpretation thereof according to a set algorithm.

In contrast to other devices used for monitoring concentration and performance ability, the disclosed invention does not require a significant reorganization of the user’s workplace (e.g., installing cameras) and is undemanding in terms of electrical contact (as in the case of analyzing the parameters sensed by a conventional GSR sensor) or close contact between the sensor and the skin (e.g., as in the case of an optical pulse sensor). The disclosed sensor in this embodiment is convenient for monitoring the condition of drivers, operators, pilots and persons of other professions requiring concentration and emotional stability, as it can easily be integrated into a steering wheel, rudder, protective equipment (helmets, etc.), furniture (a chair, mat, etc.) and other items.

Due to the fact that the present invention provides, in particular, monitoring of changes in skin conductivity, it can also be used for searching for local anomalies in skin conductivity.

In some embodiments, the electrode (with electronic or hole conductivity) is coated with a layer of dielectric, ion-selective or other metamaterial, or a combination of such layers, adapted for a particular application. In various embodiments, an ion-selective electrode is used, for example, providing additional possibilities for sensing certain ions (e.g., Ca, K, Na, Cl ions) in sweat and/or on the skin, which are also among the physiological parameters of the body that are being determined.

According to one embodiment shown in Fig. 4, the device is configured for direct measurement of electrode-body capacitor leakage current by measuring load voltage drop. The signal is subsequently analyzed by the analysis unit which in some embodiments also comprises a communication module. In particular, according to the embodiment shown in Fig. 4, the analysis unit comprises a measurement and processing module (3), which in this embodiment is represented by a microcontroller, and a communication module (4) represented by a Bluetooth module. A dielectric layer (13) is arranged between a user’s body and the electrode (1).

Figure 5 shows another embodiment of the present invention, which is based on a capacitance measurement of the electrode-body capacitor. The electrode is connected to a circuit of a frequency-determining signal generator (2). The change in capacitance and the electromagnetic waves passing through the capacitor modulate the frequency, phase, relative pulse duration and amplitude of the output generator signal. The signal is then analyzed by the analysis unit. According to a particular embodiment shown in Fig. 5, the analysis unit comprises a microcontroller (3) and a Bluetooth module (4). According to one embodiment, signal analysis includes measuring amplitudefrequency response, relative pulse duration and phase of the signal, conducting pre-processing to separate information components of the signal, conducting pre-segmentation for each information component, analyzing the obtained segments and interpreting segment-by-segment and in combination, according to a set algorithm.

According to yet another embodiment of the present invention, the sensor directly measures leakage current of the “electrode(l)-body” capacitor by measuring voltage drop (V1-V2) on the load R (Fig. 6).

Another embodiment is based on indirect measurement of current capacitance of the “electrode-body” capacitor described above. The capacitance is connected to the circuit of the master frequency generator (2) (Fig. 7). The change in capacitance directly affects frequency, phase, pulse rate and amplitude of the output signal (5) of the master frequency generator. The external electromagnetic waves that have passed through the capacitor have additionally modulated phase and amplitude and are then analyzed. The signal contains several components and carries information about relative changes in the skin, subcutaneous layers and body surface layer, as well as spatial movement of the body or parts thereof. In particular, signal level indicates a change in permittivity and electrical properties of the electrically conductive layers of the body/surface (practically forming the second plate of the capacitor) or conductivity thereof. The electrode is connected to a circuit of master frequency generator, and the resulting electrode-body currents affect the parameters of generator signal. The signal from the generator is processed and analyzed in the analysis unit.

Yet another embodiment of the present invention is based on the analysis of properties (amplitude, phase, frequency, pulse rate) of the natural (external) and/or artificial electromagnetic field having passed through the body and/or surface layers (Figs. 8, 9). Acceleration of the body or parts thereof in the natural (external) and/or artificial electromagnetic field causes a change/modulates the signal passing through the body, affecting its frequency, phase, amplitude, and the level of the signal from the electrode; during abrupt movements, the signal changes noticeably (Fig. 10). According to yet another embodiment of the present invention, the sensor comprises the analysis unit configured to analyze electrodermal activity parameters of the skin and subcutaneous layers obtained using the electrode and to output a signal indicative of acceleration of the body or parts thereof. Application of the invention according to these embodiments enables tracking rhythmic and abrupt movements without need for an accelerometer.

Since changes in the active and reactive resistance of the skin and subcutaneous layers are caused by the dynamics therein (including fluid dynamics), it is clear that pulsations of blood in the capillaries also affect these changes. These changes are tracked visually in people with exposed parts of the skin. Accordingly, pursuant to yet another one embodiment of the present invention, the sensor comprises the analysis unit configured to analyze electrodermal activity parameters of the skin and subcutaneous layers obtained using the electrode and to output a signal indicating at least one of the following: heart rate and/or heart rate variability. According to one of similar embodiments of the present invention, the sensor comprises the analysis unit configured to analyze electrodermal activity parameters of the skin and subcutaneous layers obtained using the electrode and to output a signal indicating the relative filling of the vessels (in particular, based on signal level of the associated oscillations). Figure 11 shows an example of such signal: the upper graph shows a signal from the sensor after pre-processing, and the lower signal corresponds to an optical pulse sensor used as a reference.

According to the most general embodiment, the analysis is configured to determine one or more electrical activity parameters of the body surface layer based on leakage current of the electrode-body capacitor and/or capacitance of the electrode-body capacitor. As mentioned above, leakage current and capacitance depend on the properties of the dielectric separating the plates of such capacitor (electrode-body capacitor); the body surface layer where blood and lymph flow, sweat is released, and cells continuously absorb and release, functions as said dielectric. Since a change in the state of the body (the release of hormones, among other things) affects blood flow, the lumen of blood vessels, the work of cells, the secretory function of the skin and other physiological processes, both leakage current and capacitance of the electrode-body capacitor also change, which is registered by the disclosed sensor.

In situations requiring more selective registration of changes specifically in the conductive elements/body surface structures, it is convenient to base measurements on the inductance signal of the electrode-body system. According to the most simple embodiments preferable for use in this case, the electrode is an elongated conductor or a strand of conductors. The sensor registers changes in the current flowing through the electrode:

where P_si is total magnetic flux, I is current strength in the circuit, and L is inductance. The current in the electrode depends on the magnetic flux and the inductance of the conductor as such. The electrode is arranged on the surface of the body or near it, and said surface (as does the entire body) consists of conductors (lymph, blood and other electrolytes). Since the magnetic field of the electrode partially permeates the structures of body surface, this magnetic field is being "closed" by the conductive structures of the body, which affects the current in the conductor when changes occur in said conductive structures of the body. For instance, the disclosed sensor can be used to observe and record the dynamics of such processes as blood pulsation, interstitial fluid flow (including edema), and deeper changes in the form of muscle contraction.

In case it is required to register spatial movement of the body or parts thereof and the flows of conductive substances in the body surface layer, it is preferable to register a signal generated by an external electromagnetic field and passing through said “electrode-body" capacitor, phase modulation, frequency and/or amplitude of said signal. In this case, the analysis unit analyzes the signal received by the passive electrode. As mentioned above, in this embodiment, it is possible to use both a certain background electromagnetic radiation and the radiation from a separate electromagnetic wave generator. Signal amplitude is affected by a change in dielectric permittivity of the skin and the electrical properties of the electrically conductive layers of the body/surface, in the result of which the capacitance of the “electrode-body” capacitor changes, the reactance of the “electrode-body” capacitor changes and the signal level changes. Among other factors, this type of signal is informative in relation to mental concentration of the user. Among other factors, the amplitude of this signal is affected by the relative abrupt spatial movement of the body or parts thereof (arm swings, leg swings, standing up/sitting down, contractions of individual muscles). Signal level in this case indicates the total voltage/excitation. To record blood pulsation in this embodiment, it is preferable to use an additional electromagnetic wave generator.

The disclosed and mentioned embodiments of the disclosed sensor can be combined to provide combined acquisition of data regarding psychophysiological parameters of the user, including emotional state, concentration, stress level, changes in chemical processes in the body, heart rate and heart rate dynamics, hypothermia, rhythmic movements, and sudden accelerations. One of ordinary skill in the art will also appreciate that the analysis unit according to this embodiment is configured to analyze the received signals to produce a number of warning signals indicating hazardous or peak values of aforementioned parameters.

Claims

1. A single-electrode sensor for sensing electrical activity of body surface layer of a user, the sensor comprising: a single electrode comprising a plurality of conductors and configured to be placed near the user’s body on a distance providing capacitive and/or inductive electrode-body coupling; an analysis unit configured to determine one or more electrical activity parameters of the body surface layer based on at least one of the following signals: “electrode-body” capacitor leakage current, “electrode-body” capacitor capacitance, “electrode-body” system inductance, filtering/modulation of signal generated by an external electromagnetic field and passing through said capacitor, and phase, frequency and/or amplitude modulations of said signal.

2. The single-electrode electrical activity sensor according to claim 1, wherein the analysis unit is configured to analyze signals obtained using the electrode to obtain psychophysiological parameters of the user, including at least one of the degree of nervous tension, emotional state, pulse, and acceleration of the body part on or near which the sensor is arranged.

3. The single-electrode electrical activity sensor according to any one of claims 1-2, wherein the analysis unit is configured to analyze the signals obtained using the electrode, providing data on the dynamics of the user’s sleep parameters.

4. The single-electrode electrodermal activity sensor according to any one of claims 1-3, wherein the analysis unit is configured to analyze the signals obtained using the electrode and the signals from an external temperature sensor and to output a warning signal when the combination of said sensors’ signals indicates user’s hypothermia.

5. The single-electrode electrical activity sensor according to any one of claims 1-4, wherein the analysis unit is configured to analyze the signals obtained using the electrode and to generate a warning signal when the analysis indicates that the user’s concentration is reduced.

6. The single-electrode electrical activity sensor according to any one of claims 1-5, further comprising a master frequency signal generator.

7. The single-electrode electrical activity sensor according to any one of claims 1 -6, wherein the analysis unit is configured to analyze the skin and subcutaneous layers electrodermal activity parameters obtained using the electrode and to output a signal indicative of acceleration of the body or parts thereof.

8. The single-electrode electrical activity sensor according to any one of claims 1-7, wherein the capacitive/inductive coupling coefficient of the electrode and the user’s body is at least 0.1.