Sensor system and methods for the capacitive measurement of electromagnetic signals having a biological origin

• US 8,193,821 B2
• Filed: 12/23/2005
• Issued: 06/05/2012
• Est. Priority Date: 12/23/2004
• Status: Active Grant

• Current Assignee: Charite-Universitatsmedizin Berlin, Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V., Leica Geosystems Pty Ltd (Hexagon 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, Curio, Gabriel, Schilling, Meinhard, Mueller, Klaus-Robert
• Primary Examiner(s): Patel, Paresh
• Application Number:
  US11/722,495
• Publication Number:
  US 20100060300A1
• Time in Patent Office: 2,356 Days
• Field of Search: None
• 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 method for minimizing the influence of movement artefacts to measure electromagnetic signals having a biobiological origin, comprising the following steps:

fitting a sensor system or a measuring device on a measurement object,

coupling an electrical alternating signal into the measurement object,

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

taking account of the determined electrode capacitance of the electrode devices when evaluating the measurement signals of the sensor system or of the measuring device, wherein the relative temporal change in the electrode capacitance of the electrode device of the sensor system or of the measuring device is taken into account, a movement signal of the electrode device relative to the measurement object is derived from the relative temporal change in the electrode capacitance, and the interfering movement artefacts superposed on the electromagnetic signals having a biobiological origin are compensated by means of the determined movement signal.

2. The method as claimed in claim 1, in which the electrical alternating signal for determining the electrode capacitance of the electrode device of the sensor system, or for determining the electrode capacitance of the electrode devices of the measuring device are coupled into the measurement object via the electrode device or via an external reference electrode cooperating with the sensor system or the measuring device.

3. The method as claimed in claim 1, wherein a line frequency interference signal is used as electrical alternating signal.

4. The method according to claim 1, using a sensor system for the capacitive measurement of electromagnetic signals having a biobiological origin, the sensor system comprising:

a capacitive electrode device,

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

a signal processing device for processing electromagnetic signals that can be detected by means of the electrode device,

wherein additional shielding means for shielding out external electromagnetic interference fields at least partially surround the electrode device and the electrode shielding element in three dimensions, the additional shielding means being designed with different compartments, and the signal processing device being arranged in one such compartment.

5. The method of claim 4, wherein the shielding means surround the signal processing device at least partially.

6. The method of claim 4, wherein the signal processing device is arranged adjacent to the electrode shielding element.

7. The method of claim 4, wherein the shielding means surround the signal processing device at least partially in such a way that the shielding means also act as an electromagnetic shield between the signal processing device and electrode device.

8. The method of claim 4, wherein the shielding means cover the electrode device and the signal processing device 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.

9. The method of claim 4, wherein the distance between the electrode shielding element and the electrode device and/or the geometry of the electrode shielding element and of the electrode device and/or the dielectric properties of a filling in material arranged between the electrode shielding element and the electrode device are selected in such a way that the shielding capacitance resulting therefrom is sufficiently small to minimize the coupling of noise signals of the signal processing device into the electrode device.

10. The method of claim 4, wherein the geometry of the electrode device is selected in such a way that, together with a parasitic leakage resistance of the signal processing device, the electrode capacitance of the electrode device 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.

11. The method of claim 10, wherein the geometry of the electrode device is selected in such a way that noise signals of the parasitic input resistance of the signal processing device lie with their upper cut-off frequency below the lower cut-off frequency for the signals to be measured.

12. The method of claim 11, wherein the insulator region has material properties such that static charging of the insulator region by static environmental charges is minimized.

13. The method of claim 4, wherein the sensor system has a housing enclosing the shielding means, the electrode device being arranged in the housing in such a way that the ohmic resistance between the electrode device and the housing is so high that a capacitively recorded signal is present at the input of the signal processing device without corruption.

14. The method of claim 4, wherein the sensor system has an electrical insulator region for the electrical insulation of the electrode device in such a way that both the electrode shielding element and the shielding means are galvanically isolated from a signal source during measurement of said signal source.

15. The method of claim 4, wherein the signal processing device has an input stage designed as impedance converter.

16. The method of claim 4, wherein the signal processing device has a difference amplifier, it being possible to process the signal of an external reference electrode as difference signal.

17. The method of claim 4, wherein the signal processing device comprises an analog-digital converter and a digital signal processor.

18. The method of claim 4, wherein the signal processing device is shielded from a signal source and from the electrode device by the shielding means such that no parasitic galvanic, capacitive or inductive influences react on the signal source or on the electrode device.

19. The method of claim 4, wherein a feedback of processed signals to the electrode device is provided via a compensation impedance implemented in a capacitive, resistive or inductive fashion.

20. The method of claim 4, wherein the input impedance of the signal processing device is selected in such a way that, together with the electrode capacitance 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.

21. The method of claim 4, wherein a signal amplified by the signal processing device passes through a highpass filter in order to isolate DC voltage potentials from the dynamic measurement signal.

22. The method of claim 4, wherein the electrode device has a plurality of electrode elements 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.

23. The method of claim 4, wherein an electrical line device is shielded to ground potential, for routing the measurement signal away from the sensor system.

24. The method of claim 4, wherein 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.

25. The method of claim 4, wherein the measuring device having has a multiplicity of sensor systems in accordance with claim 4, 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.

26. The method of claim 4, wherein the measuring device has a multiplicity of sensor systems in accordance with claim 4, 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.

27. The method of claim 4, wherein the sensor system cooperates with a reference electrode that can be fastened next to the sensor system on a measurement object, and provides a reference potential for the sensor system.

28. The method of claim 27, wherein the reference electrode is coupled to the measurement object in a resistive, conductive or capacitive fashion.

29. The method of claim 27, wherein the reference electrode is used for coupling in an alternating signal by means of which a movement signal can be derived and it is therefore possible to compensate movement artefacts in the electromagnetic signal having a biobiological origin.

30. The method of claim 27, wherein one or more reference electrodes are used.

31. The method of claim 30, wherein a number of reference electrodes are used for coupling in alternating signals of different frequency, it being possible to compensate the movement artefacts of different electrode elements or electrode devices by means of each individual alternating signal.