SENSOR SYSTEM AND METHODS FOR THE CAPACITIVE MEASUREMENT OF ELECTROMAGNETIC SIGNALS HAVING A BIOLOGICAL ORIGIN

• US 20110248729A2
• Filed: 12/23/2005
• Published: 10/13/2011
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: Charite-Universitatsmedizin Berlin, Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., Fraunhofer-Gesellschaft ZUR Forderung Der Angewandten Forschung EV, Leica Geosystems Company Limited (Melker Schörling Tjänste AB), Technische Universitã¤T Braunschweig, Technische Universitat Munchen
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., Technische Universitã¤T Braunschweig
• Inventors: BLANKERTZ, Benjamin, MUELLER, Klaus-Robert, CURIO, Gabriel, SCHILLING, Meinhard
• Granted Patent: US 8,193,821 B2
• Time in Patent Office: Days
• US Class Current: 324/686
• CPC Class Codes: A61B 2562/182 Electrical shielding, e.g. using a Faraday cage
• CPC Class Codes: A61B 5/25 Bioelectric electrodes therefor
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/291 for electroencephalography [EEG]

Abstract

The invention relates to a sensor system and several method for the capacitive measurement of electromagnetic signals having a biological origin. Such a sensor system comprises a capacitive electrode device (10), an electrode shielding element (20) which surrounds the electrode device (10) at least in part in order to shield the same (10) from interfering external electromagnetic fields, and a signal processing device (30) for processing electromagnetic signals that can be detected by means of the electrode device (10). According to the invention, additional shielding means (21) three-dimensionally surround the electrode device (10) and the electrode shielding element (20) at least in part in order to block out interfering external electromagnetic fields. The changes in the electrode capacity of the capacitive sensor system are determined with the aid of several methods which particularly use the inventive sensor system in order to take said changes into account when the test signals are evaluated.

Claims

1. A sensor system for the capacitive measurement of electromagnetic signals having a biobiological origin, comprising

a capacitive electrode device (10)

an electrode shielding element (20), at least partially surrounding the electrode device (10) for shielding the electrode device (10) against external electromagnetic interference fields, and

a signal processing device (30) for processing electromagnetic signals that can be detected by means of the electrode device (10)

characterized in that additional shielding means (21) for shielding out external electromagnetic interference fields at least partially surround the electrode device (10) and the electrode shielding element (20) in three dimensions, the additional shielding means (21) being designed with different compartments, and the signal processing device (30) being arranged in one such compartment.

2. The sensor system as claimed in claim 1, characterized in that the shielding means (21) surround the signal processing device (30) at least partially.

3. The sensor system as claimed in claim 1 or 2, characterized in that the signal processing device (30) is arranged adjacent to the electrode shielding element (20).

4. The sensor system as claimed in one of claims 1 to 3, characterized in that the shielding means (21) surround the signal processing device (30) at least partially in such a way that the shielding means (21) also act as an electromagnetic shield between the signal processing device (30) and electrode device (10).

5. The sensor system as claimed in one of claims 1 to 4, characterized in that the shielding means (21) cover the electrode device (10) and the signal processing device (30) in such a way as to define a solid angle range from which originating electromagnetic signals can preferably be detected by means of the sensor system.

6. The sensor system as claimed in one of claims 1 to 5, characterized in that the distance between the electrode shielding element (30) and the electrode device (10) and/or the geometry of the electrode shielding element (20) and of the electrode device (10) and/or the dielectric properties of a filling in material (11) arranged between the electrode shielding element (20) and the electrode device (10) are selected in such a way that the shielding capacitance (Cg) resulting therefrom is sufficiently small to minimize the coupling of noise signals of the signal processing device (30) into the electrode device (10).

7. The sensor system as claimed in one of claims 1 to 6, characterized in that the geometry of the electrode device (10) is selected in such a way that, together with a parasitic leakage resistance of the signal processing device (30), the electrode capacitance (C) of the electrode device (10) forms a highpass filter with a cut-off frequency adapted to an electromagnetic signal, having a biobiological origin, to be measured relative to a measurement object.

8. The sensor system as claimed in claim 7, characterized in that the geometry of the electrode device (10) is selected in such a way that noise signals of the parasitic input resistance of the signal processing device (30) lie with their upper cut-off frequency below the lower cut-off frequency for the signals to be measured.

9. The sensor system as claimed in one of claims 1 to 8, characterized in that the sensor system has a housing enclosing the shielding means (21) the electrode device (10) being arranged in the housing in such a way that the ohmic resistance between the electrode device (10) and the housing is so high that a capacitively recorded signal is present at the input of the signal processing device (30) without corruption.

10. The sensor system as claimed in one of claims 1 to 9, characterized in that the sensor system has an electrical insulator region (12) for the electrical insulation of the electrode device (10) in such a way that both the electrode shielding element (20) and the shielding means (21) are galvanically isolated from a signal source during measurement of said signal source.

11. The sensor system as claimed in claim 8, characterized in that the insulator region (12) has material properties such that static charging of the insulator region (12) by static environmental charges is minimized.

12. The sensor system as claimed in one of the preceding claims, characterized in that the signal processing device (30) has an input stage (31) designed as impedance converter.

13. The sensor system as claimed in one of the preceding claims, characterized in that the signal processing device (30) has a difference amplifier, it being possible to process the signal of an external reference electrode as difference signal.

14. The sensor system as claimed in one of the preceding claims, characterized in that the signal processing device (30) comprises an analog-digital converter and a digital signal processor.

15. The sensor system as claimed in one of the preceding claims, characterized in that the signal processing device (30) is shielded from a signal source and from the electrode device (10) by the shielding means (21) such that no parasitic galvanic, capacitive or inductive influences react on the signal source or on the electrode device (10).

16. The sensor system as claimed in one of the preceding claims, characterized in that a feedback of processed signals to the electrode device (10) is provided via a compensation impedance (Ck) implemented in a capacitive, resistive or inductive fashion.

17. The sensor system as claimed in one of the preceding claims, characterized in that the input impedance of the signal processing device (30) is selected in such a way that, together with the electrode capacitance (C) of the sensor system, a highpass filter with a cut-off frequency adapted to an electromagnetic signal, having a biobiological origin, to be measured is formed.

18. The sensor system as claimed in one of the preceding claims, characterized in that a signal amplified by the signal processing device (30) passes through a highpass filter in order to isolate DC voltage potentials from the dynamic measurement signal.

19. The sensor system as claimed in one of the preceding claims, characterized in that the electrode device (10) has a plurality of electrode elements (100) for detecting electromagnetic signals having a biobiological origin, the signal processing device being designed as a corresponding plurality of parallel connected component signal processing devices.

20. The sensor system as claimed in one of the preceding claims, characterized by an electrical line device (40) shielded to ground potential, for routing the measurement signal away from the sensor system.

21. The sensor system as claimed in one of the preceding claims, characterized in that the sensor system has means for line-conductive transmission and/or means for lineless transmission of the measurement signals from the sensor system to a receiving device spaced apart therefrom.

22. The sensor system as claimed in one of the preceding claims, characterized in that the sensor system cooperates with a reference electrode that can be fastened next to the sensor system on a measurement object (Q), and provides a reference potential for the sensor system.

23. The sensor system as claimed in claim 22, characterized in that the reference electrode is coupled to the measurement object (Q) in a resistive, conductive or capacitive fashion.

24. The sensor system as claimed in one of claims 22 or 23, characterized in that the reference electrode is used for coupling in an alternating signal (a(t)) by means of which a movement signal (B(t)) can be derived and it is therefore possible to compensate movement artefacts in the electromagnetic signal having a biobiological origin.

25. The sensor system as claimed in one of claims 22 to 24, characterized in that one or more reference electrodes are used.

26. The sensor system as claimed in claim 25, characterized in that a number of reference electrodes are used for coupling in alternating signals (a(t)) of different frequency, it being possible to compensate the movement artefacts of different electrode elements (100) or electrode devices (10) by means of each individual alternating signal (a(t)).

27. A measuring device having a multiplicity of sensor systems in accordance with one of claims 1 to 26, in which the sensor systems are arranged in a helmet-like or cap-like carrier device that can be at least partially slipped over the head of a test subject.

28. The measuring device having a multiplicity of sensor systems in accordance with one of claims 1 to 26, in which the sensor systems are arranged on a flexible carrier device of two-dimensional design that can be fastened on the body of a test subject.

29. A method for minimizing the influence of movement artefacts by using a sensor system as claimed in one of claims 1 to 26, or using a measuring device as claimed in one of claims 27 or 28, in order to measure electromagnetic signals having a biobiological origin, comprising the following steps:

fitting the sensor system or the measuring device on a measurement object (Q)

coupling an electrical alternating signal (a(t)) into the measurement object (Q)

evaluating the coupled in alternating signal in order to determine the electrode capacitance (C) of the electrode device (10) of the sensor system, or the electrode capacitance (C) of the electrode devices (10) of the measuring device, and

taking account of the determined electrode capacitance (C) of the electrode devices (10) when evaluating the measurement signals of the sensor system or of the measuring device.

30. The method as claimed in claim 29, in which the electrical alternating signal for determining the electrode capacitance (C) of the electrode device (10) of the sensor system, or for determining the electrode capacitance (C) of the electrode devices (10) of the measuring device are coupled into the measurement object via the electrode device (10) or via an external reference electrode cooperating with the sensor system or the measuring device.

31. The method as claimed in one of claims 29 to 30, characterized in that a line frequency interference signal is used as electrical alternating signal.

32. The method as claimed in one of claims 29 to 31, characterized in that the relative temporal change in the electrode capacitance (C) of the electrode device (10) of the sensor system or of the measuring device is taken into account, a movement signal (B(t)) of the electrode device (10) relative to the measurement object is derived from the relative temporal change in the electrode capacitance (C), and the interfering movement artefacts superposed on the electromagnetic signals having a biobiological origin are compensated by means of the determined movement signal (B(t)).

33. A method for minimizing the influence of movement artefacts by using a sensor system as claimed in one of claims 1 to 26, or by using a measuring device as claimed in claim 27 or 28 in order to measure electromagnetic signals having a biobiological origin, comprising the following steps:

fitting the sensor system or the measuring device on a measurement object (Q), the sensor system or the measuring device being provided with a position measuring system,

determining position parameters of the position of the sensor system or of the sensor systems relative to the measurement object (Q) by means of the position measuring system during the measurement and,

taking account of the determined position parameters in order to compensate movement artefacts in the measurement signal.

34. The method as claimed in one of claims 29 to 33, characterized in that the measurement signals are filtered for denoising purposes by means of digital filters, the digital filters being adapted to the instantaneous signal characteristic.

35. The method as claimed in claim 34, characterized in that use is made in addition of univariate or multivariate denoising methods that decompose the measurement signals into base systems.