Detection system and method for capacitively coupled electrophysiological detection with estimation of electrode-to-skin coupling - Patent Application 20070122999

Abstract

The sensing system and method uses a sensing electrode system for coupling to a body surface such that the sensing electrode system and the body (and the spacing between them) define a coupling capacitance. First and second sensing circuits have different transfer functions and generate first and second outputs, which are processed to determine the coupling capacitance. A monitored electrophysiological signal is also acquired by one or both of the sensing circuits. This allows the quality of electrode coupling to be determined in a simple and passive manner.

Description

[Technical Field]

[0001] The present invention relates to the detection of electrophysiological signals based on sensing electrodes capacitively coupled to the surface of the body being monitored, and in particular to the estimation of electrode-to-skin coupling in systems using such capacitive sensing electrodes. [Background technology]

[0002] Measurement of electrophysiological signals, such as ECG, EMG and EEG signals, is increasingly required in professional health monitoring and diagnostics, as well as in personal health products.

[0003] Conventionally, these signals are measured by electrodes attached to the skin via galvanic contacts, often using electrolytic gel. The main drawbacks of this measurement method are that it requires long preparation time, causes skin irritation during prolonged use, restricts the patient's freedom of movement, and is less comfortable for the patient, i.e., the patient is aware that they are being monitored.

[0004] Dry electrodes overcome some of these drawbacks because they do not require gel. However, this electrode type also requires galvanic contact with the skin. Furthermore, after applying these electrodes, it takes time for the electrode-skin interface to reach a stable equilibrium; for example, it typically takes 5-10 minutes for baseline fluctuations and noise levels to completely settle before reliable measurements can be performed. For spot-test-based applications, this is too long and therefore unacceptable.

[0005] To overcome the above-mentioned drawbacks, much research is currently being directed towards contactless (capacitive) measurement of electrophysiological signals. In this technique, a capacitor is effectively formed, with the human skin acting as one of the capacitor plates and the sensor electrode acting as the other. When capacitive detection is used, no galvanic contact to the skin is required (i.e., detection is contactless).

[0006] Capacitive electrophysiological sensors can be integrated into a wide range of everyday items such as office chairs, clothing, cars, and beds. Integrating sensors into clothing, for example, allows for long-term monitoring in a non-intrusive manner.

[0007] As with other types of electrophysiological measurement techniques, there is no galvanic contact in capacitive electrophysiological measurements, but it is important that the electrodes are well coupled to the body to ensure reliable monitoring. This means that the distance between the electrodes and the skin should be within a certain range (typically 1 cm). 2 electrode area), which means that the capacitive coupling should be large enough (typically greater than 1 pF). Summary of the Invention [Problem to be solved by the invention]

[0008] To ensure reliable measurements, it is desirable for the quality of the coupling to be communicated to the signal acquisition system, and therefore it is desirable for the measurement system to track the electrode-to-skin coupling.

[0009] A known technique for tracking the quality of coupling is based on injecting a current of known frequency (e.g., 1 kHz) into the human body through the electrode-to-skin interface. By determining the amplitude of the corresponding output signal when picked up by a capacitive sensor, an estimate of the electrode-to-skin coupling can be made. A drawback of this method is that safety issues can be a significant part of injecting current into the body, e.g., with regard to risks to the fetus in fetal monitoring applications. Even if the design is safe, it is complicated by additional requirements that must be addressed.

[0010] Despite the very attractive advantages of capacitive electrophysiological sensors, the problem of motion artifacts remains one of the major unsolved problems that hinder their reliable use in real-life applications. User movement induces changes in electrode-to-skin coupling, resulting in motion artifacts. This problem becomes more severe when electrostatic charges are trapped at the electrode-to-skin interface or in the case of triboelectric discharge.

[0011] Therefore, there is a need for improved systems and methods that can monitor the quality of the capacitive coupling of electrodes to a subject's body. [Means for solving the problem]

[0012] EP2783725A1 discloses a method and system for detecting a heartbeat or whether the electrodes are in good contact.

[0013] XU LIN et al.: "Motion-Artifact Reduction in Capacitive Heart-Rate Measurements by Adaptive Filtering" discloses an adaptive filtering method for motion artifact removal, in which a reference signal is extracted from power line interference.

[0014] XU LIN et al.: "Adaptive motion-artifact reduction in capacitive ECG measurements by using the power-line interference" discloses an adaptive motion-artifact reduction method in which a reference signal is extracted from the power-line interference.

[0015] EP2453792A1 discloses an apparatus and method for the capacitive measurement of electrophysiological signals in which movement artifacts are suppressed or reduced by providing a feedback mechanism.

[0016] The invention is defined by the claims.

[0017] According to an example according to one aspect of the invention, there is provided a detection system for detecting electrophysiological signals from a surface of a body, the system being configured, in use, to be coupled to a detection electrode system for coupling to the surface of the body, such that the detection electrode system and the body have a coupling capacitance (C e ) and the detection system a first detection circuit for detecting (receiving) a first signal at the surface from the detection electrode system and generating a first output based on a first transfer function; a second detection circuit for detecting (receiving) a second signal at the surface from the detection electrode system and for generating a second output based on a second transfer function different from the first transfer function; a processor adapted to determine a coupling capacitance from the first and second outputs.

[0018] Determining coupling capacitance allows electrode-to-body (eg, electrode-to-skin) coupling to be assessed without injecting current through the body.

[0019] This approach is based on an architecture in which an electrode system (either a single electrode or multiple closely spaced electrodes) is coupled to two different detection circuits with different topologies, each with a different transfer function. For example, there can be a parallel system of two detection circuits.

[0020] Each detection circuit provides an output signal based on the same electrophysiological signal (or signals that can be assumed to be the same based on physical proximity and temporal proximity of the measurements) and a corresponding transfer function. The first and second signals detected by the first and second detection circuits are therefore intended to represent the same physiological parameter of the body and have the same coupling capacitance. The transfer function is determined by the values ​​of the circuit components and is known. The coupling capacitance and the measured electrophysiological signal (such as voltage, current, or impedance) are unknown. The coupling capacitance can be analytically estimated from two transfer functions with two unknowns. Electrophysiology can be evaluated via detection electronics for detecting voltage, current, or impedance.

[0021] The two transfer functions are therefore orthogonal in the sense that two independent unknowns can be solved from the two functions.

[0022] In one embodiment, the system comprises a sensing electrode system for coupling to a surface of the body such that the sensing electrode system and the body define a coupling capacitance (Ce).

[0023] The signals detected by both sensors are electrophysiological signals such as voltage, current or impedance detectable at the skin.

[0024] The processor is preferably further adapted to process the first and second outputs to thereby determine a monitored electrophysiological signal at the surface, and thus the monitored electrophysiological signal is determined, and also a coupling capacitance indicative of coupling quality.

[0025] The processor is adapted to determine the electrophysiological signals monitored at the surface further taking into account the determined coupling capacitance, thereby providing body motion compensation, such that the coupling capacitance information is used to compensate for signal fluctuations caused by movement, which affects the coupling capacitance.

[0026] For example, in one set, the system further includes a switch system for coupling a selected one of the first and second detection circuits to the processor and a shared detection electrode, where one electrode is provided (for each pair of detection circuits) and each detection circuit is used in a time-shared manner. Thus, to generate two completely independent transfer functions, the amplifiers are alternately operated via a switch controlled by the processor.

[0027] For example, in another set, the detection electrode system comprises a first electrode connected to a first detection circuit and a second electrode connected to a second detection circuit, where separate detection channels are used simultaneously, provided the two electrodes are sufficiently close so that the coupling capacitance and the first and second signals are assumed to be the same.

[0028] The first and second detection circuits (for each detection electrode) each include, for example, a signal amplifier. In one example, the first detection circuit includes a voltage amplifier and the second detection circuit includes a charge amplifier. Different types of amplifiers, such as buffer amplifiers, provide suitable different transfer functions.

[0029] The electrophysiological signals include ECG signals, such as fetal ECG signals and maternal ECG signals. The system is, for example, part of a fetal monitoring system.

[0030] The electrophysiological signals include EMG signals. The system is, for example, part of a neuromuscular diagnostic system.

[0031] The system preferably further comprises an interface adapted to provide electrode contact quality information based on the coupling capacitance. This interface may be a user interface to inform the user that the measurement is unreliable and that the attachment of one or more capacitive electrodes needs to be improved. It may be an interface to another processing system to assist in the interpretation of the measured signal.

[0032] For example, the detection electrode system may comprise an array of electrodes, the processor being adapted to determine which electrodes of the array have adequate coupling to the body based on their respective coupling capacitances.

[0033] Thus, only electrodes that are properly bonded to the body are included, thereby eliminating poorly bonded electrodes from post-processing steps to provide a reliable measurement.

[0034] The invention provides a method for detecting electrophysiological signals from a body surface, comprising: detecting (receiving) a first signal at the surface from a sensing electrode system coupled to the surface of the body such that the sensing electrode system and the body define a coupling capacitance, and generating a first output based on a first transfer function; detecting (receiving) a second signal at the surface from the detection electrode system and generating a second output based on a second transfer function different from the first transfer function; and determining a coupling capacitance from the first and second outputs.

[0035] The method further includes determining an electrophysiological signal from the first and / or second output.

[0036] In one embodiment, the method further comprises coupling the sensing electrode system to a surface of the body such that the sensing electrode system and the body define a coupling capacitance (Ce).

[0037] The method further comprises determining an electrophysiological signal at the surface further taking into account the determined coupling capacitance, thereby providing body motion compensation.

[0038] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0039] For a better understanding of the invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief explanation of the drawings]

[0040] [Figure 1] 1 illustrates a detection system for detecting electrophysiological signals from the body of a subject. [Figure 2] SUMMARY OF THE INVENTION A method for detecting electrophysiological signals from a body surface is presented. [Figure 3] 2 illustrates an example of a switching signal used to control the circuit of FIG. 1. [Figure 4] 3 shows an enlarged region of FIG. 3 to illustrate that overlap between the two signals is avoided. [Figure 5] The upper plot shows the simulation output, which is the raw output and the lower plot after filtering with a high-pass filter. [Figure 6] 1 shows an example of an output signal during measurement from a prototype system. DETAILED DESCRIPTION OF THE INVENTION

[0041] The invention will now be described with reference to the drawings.

[0042] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are schematic only and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to indicate the same or similar parts.

[0043] The invention provides a detection system and method that uses a detection electrode system for coupling to a body surface such that the detection electrode system and the body (and the spacing between them) define a coupling capacitance. The detection system has first and second detection circuits that have different transfer functions and generate first and second outputs. These outputs are processed to determine the coupling capacitance, allowing the quality of electrode coupling to be determined in a simple and passive manner. The monitored electrophysiological signal is also acquired by one or both of the detection circuits.

[0044] The body may be, for example, the body of a subject, and the surface may be the skin. This particular use of the invention is described in the detailed example below.

[0045] 1 shows a detection system 10 for detecting electrophysiological signals from a surface 16 (i.e., skin) of a subject's body 12. In use, the detection system is arranged to be coupled to a detection electrode system 14 and is provided for capacitive coupling to the surface 16 without galvanic contact, such that the detection electrode system 14, the body 12, and the gap therebetween form a coupling capacitance C e In one embodiment, the system comprises a detection electrode system 14.

[0046] Typically, there is mechanical contact between the sensing electrode system and the surface 16, but no galvanic contact. For example, the sensing electrode system may be tightly coupled to the body, with clothing in between. The capacitance is formed by the surface and the electrode system and the gap between them. This gap may be a layer of material that acts as a dielectric or a gap.

[0047] A physical capacitor also exists between the surface and the detection electronics, thereby realizing two capacitors in series (physical capacitor and gap). Thus, although there is a galvanic contact to the surface through one plate of the physical capacitor, there is no DC signal sent to the detection electronics; capacitive signal detection is again used.

[0048] The first sensing circuit 20 is positioned to receive or sense a first electrophysiological signal in the body via the sensing electrode system 14 and provides a first output V based on a first transfer function. OUT_VA A second sensing circuit 22 is arranged to receive or sense a second electrophysiological signal in the body via the same sensing electrode system and produces a second output V based on a second transfer function different from the first transfer function. OUT_CA These first and second electrophysiological signals result from the same physiological process and therefore represent the same physiological parameter being monitored.

[0049] In the examples described below, the first and second electrophysiological signals are described as voltages, but detection may instead be based on current or impedance measurements.

[0050] The processor 30 processes the first and second outputs to thereby determine the coupling capacitance C e The processor 30 determines the monitored electrophysiological signal V bio The monitored electrophysiological signal is determined from only one of the detection circuits (i.e., a preferred one of the detection circuits, the other detection circuit being provided for the purpose of enabling determination of coupling capacitance). Alternatively, the monitored electrophysiological signal is derived from both the first and second outputs. The determined coupling capacitance is also taken into account when deriving the physiological parameter of interest from the first and / or second outputs.

[0051] In this example, the first detection circuit 20 is a voltage amplifier having at its input a parallel bias resistor R i and input capacitance C i The amplifier is realized by an operational amplifier with a closed negative feedback path.

[0052] The second detection circuit 22 is a current amplifier. It is connected to a parallel bias resistor R fand capacitance C f This is realized by an operational amplifier having a negative feedback path with

[0053] Capacitance C i and C f involves the parasitic effects of the amplifier.

[0054] Therefore, a front-end amplifier architecture is used, with two amplifiers per sensing electrode.

[0055] The transfer function of the voltage amplifier 20 is:

number

[0056] This

number

[0057] The transfer function of the charge amplifier is:

number

[0058] This

number

[0059] In the example shown, the two detection circuits are alternately activated via switches S1-S4 controlled via processor 30 to generate two completely independent transfer functions. Voltage amplifier 20 has switch S1 at the input and switch S2 at the output. These switches are controlled by a switching signal SW VA The charge amplifier 20 also has a switch S3 at the input and a switch S4 at the output. These switches are controlled via a switching signal SW CA It is controlled via

[0060] Thus, the processor 30 is adapted to switch from one scheme for acquiring signals using a first detection circuit to another scheme using a second detection circuit, which is performed during the determination of coupling capacitance and during electrophysiological signal acquisition as described above, where detection uses one or both of the detection circuits as described above.

[0061] To ensure accuracy of the measurements, the switching scheme should be such that the characteristics of the electrophysiological signal being measured (in terms of rate and duration) can be assumed to be constant.

[0062] Each amplifier generates the same electrophysiological signal (V bio ) and the corresponding transfer function (T VA and T CA ) based on the output signal (V OUT_VA and V OUT_CA ) is provided.

[0063] The output signal of the voltage amplifier is therefore:

number

[0064] The charge amplifier output signal is:

number

[0065] In Equation 3 and Equation 4, C i and C f is a circuit value that is known by design or can be estimated by a calibration procedure. Such calibration can be an integral part of the electronics circuit and can be performed whenever needed, for example, when temperature changes i and C f This can be done based on temperature changes, which can cause drift in the

[0066] In the calibration procedure, C i and C f can be estimated by Equations 3 and 4, respectively. In this case, V bio is temporarily set to a known AC signal generated by the circuit itself. In order to have an accurate estimation, the frequency of the generated signal should be within the band of the electrophysiological signal of interest, e.g., 100 Hz for ECG signals.

[0067] C e For,real (e.g., on-chip, off-the-shelf) capacitors are used for such,calibration (with typical values ​​in the range: 1-100 pF).

[0068] By substitution, Equation 3 and Equation 4 can be combined to derive Equation 5 to estimate the electrode-skin capacitive coupling.

number

[0069] It is beneficial to switch between detection circuits with a higher frequency to improve accuracy. Higher frequency switching reduces the skin-electrode capacitance C e This allows faster changes in the signal to be detected. This also ensures that the two amplification means minimize electrophysiological signal changes. However, there is also an upper limit to the switching frequency, since if the frequency is too high, the measurement results will be degraded by the finite speed of the detection circuit, switches, and communication interface. Therefore, as will be apparent to those skilled in the art, there is a range of suitable switching frequencies.

[0070] The estimated value of the coupling capacitance can be used to control the switching of the amplifier and to determine the availability of the acquired signal.

[0071] 2 shows a corresponding method for detecting signals from a body surface. The method includes, in step 40, coupling a detection electrode system to the body surface, such that the detection electrode system and the body (and the spacing therebetween) form a coupling capacitance (C e ) is specified.

[0072] In step 42, a first signal in the body is sensed via a sensing electrode system and a first output is generated based on a first transfer function (voltage amplifier).

[0073] In step 44, a second signal in the body is detected via the detection electrode system and a second output is generated based on a second transfer function (charge amplifier).

[0074] In step 46, a coupling capacitance C is connected from the first and second outputs. e is determined.

[0075] In step 48, an electrophysiological signal (V bio ) is determined.

[0076] To prevent overloads or short circuits, the timing of the switching signals is chosen so that there is no overlap in the "on" periods of the switches.

[0077] Figure 3 shows the switching signal SW VA and SW CA Figure 4 shows an enlarged region to illustrate that overlap between the two signals is avoided.

[0078] Proof of principle of the inventive approach has been demonstrated first by simulation and second by laboratory measurements of a constructed prototype, the results of which are presented below.

[0079] simulation The circuit in Figure 1 was simulated. As an example, values ​​were calculated for two calibration points: C e= 20pF and C e = 100pF is selected and a simulation is run to determine the unknown parameter C i and C f is determined according to Equation 3 and Equation 4, so that: C i =1.1pF C f =5.5pF

[0080] Unknown electrode capacitor C e To estimate , the combined amplifiers are switched as explained above.

[0081] FIG. 5 shows the simulation output, where the upper plot is the raw output, while the lower plot is after filtering with a high-pass filter (cutoff at 3 Hz) to remove the DC component.

[0082] The filtered plot shows a voltage amplifier output amplitude of 3.05 mV. However, the designed voltage amplifier has a built-in gain of 2, so after correcting for this gain, the actual voltage amplifier output amplitude is: V OUT_VA =1.525mV

[0083] The plot also shows the current amplifier output amplitude: V OUT_CA =14.37mV

[0084] According to Equation 5, the electrode-skin capacitive coupling can be estimated as follows:

number

[0085] In this simulation, C e The true value of was 50 pF. Therefore, the deviation from the estimated value was 0.7 pF, which is mostly due to rounding error.

[0086] The table below shows the e Results for other values ​​of (true vs. predicted) are shown.

[0087] [Table 1]

[0088] Laboratory measurements A prototype of the front-end amplifier architecture was designed and fabricated as an ASIC and integrated into a capacitive sensing system. Various capacitors (with different values) were soldered to the input of the amplifier and connected to an ECG signal generator.

[0089] The true values ​​of these capacitors were measured by a capacitance meter with an accuracy of 0.1 pF.

[0090] First, the known capacitor C e =1.6pF and C e = 104.2pF is used as the calibration point, which is C i =7.26pF and C f =7.71pF. Next, a series of "unknown" coupling capacitors were tested.

[0091] Figure 6 shows an example of the output signal during measurement. Again, the raw signal is shown on top and the filtered signal on the bottom.

[0092] The table below shows that the estimated values ​​are again close to the actual values ​​of the coupling capacitors.

[0093] [Table 2]

[0094] The above example is based on a voltage amplifier and a current amplifier. However, any two detection circuits can be used as long as the electrophysiological signal and the coupling capacitance provide two independent equations that can be solved for separately.

[0095] The detection circuit is another kind of amplifier (or even a non-amplifier circuit) with a different transfer function.

[0096] The above example is based on one electrode. However, there may be electrode systems with two (or more) separate electrodes with two separate (and different) amplifiers. One electrode is connected to a first type of detection circuit, and the other electrode is connected to a second type of detection circuit. As long as the electrodes are spaced closely enough, the electrophysiological signal V bio Correlation is C e (and can be assumed to be the same for the two electrodes). The advantage is that measurements can be made using both transfer functions simultaneously, without the need for a switch system and corresponding controls.

[0097] If the coupling impedance is complex (i.e., a combination of resistance and capacitance rather than just capacitance), three measurement systems with three different transfer functions are used to resolve the real and virtual impedances and the electrophysiological signal.

[0098] The invention relates to all applications where electrophysiological signals (e.g. ECG, EMG) are measured. Exemplary applications are contactless fetal and neonatal monitoring.

[0099] The invention is also applicable to other contactless sensing applications not necessarily related to electrophysiological signals, and therefore applies more generally to contactless capacitive sensing of signals on any surface.

[0100] Two particularly relevant examples of applications that can significantly benefit from capacitive electrophysiological measurements are described below.

[0101] A first example is neonatal monitoring in neonatal intensive care units. New monitoring technologies in neonatal care have improved survival rates for premature newborns, but the damage caused by the invasive aspects of such technologies can affect the newborn's development. The thin skin of premature babies is easily damaged by adhesive electrodes. Capacitive electrodes offer an attractive option for widespread monitoring of neonatal ECGs and can be embedded into support systems or even clothing worn by the newborn. This increases comfort, aids in better recovery, and avoids the scars caused by adhesive electrodes.

[0102] See, for example, Atallah, L. et al., Unobtrusive ECG monitoring in the NICU using a capacitive sensing array, Physiol. Meas. 35, 895-913 (2014).

[0103] A second example is pregnancy (fetal and maternal) monitoring. Traditional noninvasive fetal monitoring systems use Doppler ultrasound devices to measure fetal cardiac activity. Contractions are typically monitored using strain-gauge-based pressure sensors. These systems are quite bulky, limit the pregnant woman's mobility, and require skilled personnel for accurate application and operation. This means they can only be used in clinical settings such as hospitals. Over the years, numerous studies have been published on the beneficial effects of walking during pregnancy. For example, walking and an upright position during the first stage of labor shortens the length of labor. Cable-free fetal monitoring systems exist that solve the problem of the mother being "cabled" to her bedside. Furthermore, wearable fetal monitoring solutions in the form of patches have also been developed based on electrophysiological measurements. Fetal and maternal heart rates are derived from ECG measurements using wet electrodes attached to the pregnant woman's abdomen. The same electrodes are used to derive uterine contractions from EMG measurements. These new wearable monitoring solutions further enhance patient mobility and comfort. Because the measurement patches are very lightweight, easy to apply, and do not require repositioning of the electrodes during operation, unfortunately, these electrophysiological patches are not yet optimal for home monitoring. This is mainly due to challenges related to ease of use (e.g., abrasion of the skin with sandpaper, precise positioning of the patch), comfort (e.g., adhesive gel electrodes irritate the skin), and measurement reliability (in contrast to a hospital environment, the home is an uncontrolled environment, i.e., lacking contextual information).

[0104] For fetal monitoring applications, capacitive electrophysiological sensors have the potential to be a comfortable alternative because they do not require skin preparation or direct skin contact. Capacitive electrophysiological sensors can be incorporated into wearable patches or easily embedded in pregnancy belts / pants, allowing measurements through thin, electrically insulating layers (e.g., textiles). Ultimately, this enables solutions that can monitor at-risk pregnant women in the home environment, close to their families, further reducing hospital workload and healthcare costs. The feasibility of extracting fetal and maternal ECGs (and heart rates) using capacitive electrophysiological sensors has been demonstrated, for example, in E. Rendon-Morales, R.J. Prance, and R. Aviles-Espinosa, "Non-invasive recordings of fetal electrocardiogram during pregnancy using electric potential sensors," American Institute of Physics, October 12, 2018.

[0105] As described above, the system utilizes a processor to perform data processing. The processor can be implemented in many ways, including software and / or hardware, to perform the various functions required. The processor typically uses one or more microprocessors that are programmed using software (e.g., microcode) to perform the required functions. The processor is implemented as a combination of dedicated hardware to perform some functions and one or more programmed microprocessors and associated circuitry to perform other functions.

[0106] Examples of circuitry used in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0107] In various implementations, a processor is associated with one or more storage media, such as volatile and non-volatile computer memory, including RAM, PROM, EPROM, and EEPROM. The storage media are encoded with one or more programs that, when executed in the one or more processors and / or controllers, perform the desired functions. The various storage media are either fixed within the processor or controller or portable such that the one or more programs stored thereon can be loaded into the processor.

[0108] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the singular does not exclude a plurality.

[0109] A single processor or other unit may fulfill the functions of several items recited in the claims.

[0110] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0111] It should be noted that when the term "adapted to" is used in the claims or description, it is intended to be equivalent to the term "configured to."

[0112] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. A detection system for detecting electrophysiological signals from a surface of a body, the detection system being coupled, in use, to a detection electrode system for coupling to the surface of the body, whereby the detection electrode system and the body define a coupling capacitance, the detection system comprising: a first detection circuit that detects a first signal at the surface via the detection electrode system and generates a first output based on a first transfer function; a second detection circuit that detects a second signal at the surface via the detection electrode system and generates a second output based on a second transfer function different from the first transfer function; a processor for determining the coupling capacitance from the first output and the second output; A detection system wherein the first detection circuit comprises a voltage amplifier and the second detection circuit comprises a charge amplifier.

2. The detection system of claim 1 , wherein the processor further processes the first output and / or the second output to determine the electrophysiological signal at the surface.

3. The detection system of claim 2 , wherein the processor determines the electrophysiological signal at the surface further taking into account the determined coupling capacitance, thereby providing body motion compensation.

4. 4. The detection system of claim 1, further comprising a switch system for coupling a selected one of the first and second detection circuits to the processor and a shared detection electrode.

5. 4. The detection system of claim 1, further comprising a detection electrode system, the detection electrode system comprising a first electrode connected to the first detection circuit and a second electrode connected to the second detection circuit.

6. The detection system of claim 1 , wherein the signal comprises an ECG signal.

7. The detection system of claim 6 , wherein the signals include a fetal ECG signal and a maternal ECG signal.

8. The detection system of claim 1 , wherein the signal comprises an EMG signal.

9. The detection system of claim 1 , further comprising an interface for providing electrode contact quality information based on the coupling capacitance.

10. 10. The detection system of claim 5, wherein the detection electrode system comprises an array of electrodes, and the processor determines which electrodes of the array have adequate coupling to the body based on their respective coupling capacitances.

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