U.S. patent application number 11/722495 was filed with the patent office on 2011-10-13 for sensor system and methods for the capacitive measurement of electromagnetic signals having a biological origin.
This patent application is currently assigned to Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.. Invention is credited to Benjamin BLANKERTZ, Gabriel CURIO, Klaus-Robert MUELLER, Meinhard SCHILLING.
Application Number | 20110248729 11/722495 |
Document ID | / |
Family ID | 36202212 |
Filed Date | 2011-10-13 |
United States Patent
Application |
20110248729 |
Kind Code |
A2 |
MUELLER; Klaus-Robert ; et
al. |
October 13, 2011 |
SENSOR SYSTEM AND METHODS FOR THE CAPACITIVE MEASUREMENT OF
ELECTROMAGNETIC SIGNALS HAVING A BIOLOGICAL ORIGIN
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.
Inventors: |
MUELLER; Klaus-Robert;
(Berlin, DE) ; BLANKERTZ; Benjamin; (Berlin,
DE) ; CURIO; Gabriel; (Berlin, DE) ;
SCHILLING; Meinhard; (Wolfenbuettel, DE) |
Assignee: |
Fraunhofer-Gesellschaft zur
Foerderung der angewandten Forschung e.V.
Hansastrasse 27c
Muenchen
DE
D-80686
Technische Universitaet Braunschweig
Pockelstrasse 14
Braunschweig
DE
D-38106
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20100060300 A1 |
March 11, 2010 |
|
|
Family ID: |
36202212 |
Appl. No.: |
11/722495 |
Filed: |
December 23, 2005 |
PCT Filed: |
December 23, 2005 |
PCT NO: |
PCT/DE2005/002319 |
371 Date: |
November 24, 2009 |
Current U.S.
Class: |
324/686 |
Current CPC
Class: |
A61B 5/25 20210101; A61B
5/282 20210101; A61B 2562/182 20130101; A61B 5/291 20210101 |
Class at
Publication: |
324/686 |
International
Class: |
G01R 27/26 20060101
G01R027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2004 |
DE |
10 2004 063 249.9 |
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.
Description
[0001] The invention relates to a sensor system for the capacitive
measurement of electromagnetic signals having a biobiological
origin in accordance with the preamble of claim 1. The invention
further relates to two methods for the capacitive measurement of
electromagnetic signals having a biobiological origin, in
particular by using the inventive sensor system.
[0002] Such a sensor system for the capacitive measurement of
electromagnetic signals having a biobiological origin comprises 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. Such sensor systems are normally used in medical
technology, in particular in order to record signals having a
biobiological origin for electroencephalograms (EEGs) and
electrocardiograms (ECGs).
[0003] The capacitive measurement of the electromagnetic signals
having a biobiological origin exhibits a range of advantages over
the methods, known from the prior art, of using electrode devices
galvanically coupled to a measurement object. Particularly in the
case of the recording of an EEG, the frequently tiresome
preparatory work of clearing hair from the measurement areas on the
head of a test subject, and of reducing the electrical resistance
of the scalp in these areas, for example by using a peeling agent
in addition to the electrode gels required in any case, is
eliminated. In the case of a capacitive coupling between a
measurement area of the test subject and an electrode device, the
electrical resistance of the coupling region is no longer
relevant.
[0004] Capacitive sensor systems of the generic type are
respectively disclosed in US 2003/0036691 A1 and WO 03/048789
A2.
[0005] Since the measurement signals having a biobiological origin
that are to be determined are very small, the capacitive sensor
systems known from the prior art and intended for measuring
electromagnetic signals having a biobiological origin react
sensitively to external electromagnetic interference fields despite
the electrode shielding element that is present. Moreover, the
problem arises that electrode capacitance that is necessarily
formed by the arrangement of the sensor system at the measurement
object between the capacitive electrode device of the sensor system
and the measurement object, is changed by the movement of the
measurement object relative to the electrode device, such that the
electromagnetic signal detected by the electrode device has
movement artefacts superposed on it and undergoes interference.
[0006] It is therefore the object of the present invention to
provide an improved sensor system.
[0007] This object is achieved by means of a sensor system having
the features of claim 1.
[0008] It is provided according to the invention that 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 are designed in this case with different
compartments, the signal processing device being arranged in one
such compartment.
[0009] In this case, the feature of additional shielding means is
to be understood within the scope of the present invention such
that apart from the electrode shielding element additional
shielding means are provided that are arranged separately therefrom
in three dimensions. However, being separated in three dimensions
is not to be interpreted to the effect that the additional
shielding means are arranged without making mechanical and/or
electrical contact with the electrode shielding element. Thus, it
is by all means possible to provide an electrical contact between
the shielding means and the electrode shielding element, for
example for the purpose of ensuring an identical potential.
[0010] Apart from the electrode shielding element, the additional
shielding means preferably surround the signal processing device at
least partially. To this end, the additional shielding means can be
designed both in such a way that the signal processing device is
arranged in the region between the additional shielding means and
the electrode shielding element, and in such a way that the
additional shielding means at least partially surround both the
electrode shielding element and the signal processing device.
[0011] The shielding means therefore shields the signal processing
device from the signal source and from the electrode device in such
a way that no parasitic galvanic, capacitive or inductive
influences react on the source or on the electrode device.
[0012] A compact sensor system is provided in this way that is
optimized with regard to shielding against external electromagnetic
fields. The sensor system can be designed to be particularly
compact by arranging the signal processing device adjacent to, that
is to say in a fashion neighboring the electrode shielding element.
The spatial proximity between the electrode device and signal
processing device is attended by a range of advantages that is
explained in yet more detail below.
[0013] For the purpose of the present invention, a signal
processing device is regarded as any system that varies the
incoming measurement signals, that is to say the system interacts
with the measurement signals in such a way that the measurement
signals have been varied upon passing through the system.
[0014] A preferred variant of the sensor system provides that the
additional shielding means at least partially surround the signal
processing device in such a way that the additional shielding means
shield the electrode device against electromagnetic interference
fields originating from the signal processing device.
[0015] Moreover, it is advantageous for the additional shielding
means to be designed in such a way that the electrode device and
the signal processing device are covered so as to define a solid
angle range from which originating electromagnetic signals can be
detected by means of the sensor system, without being substantially
influenced by the shielding means and/or the electrode shielding
element.
[0016] A further variant of the sensor system provides that the
distance between the electrode shielding element and the electrode
device and/or the geometry of the electrode shielding element and
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 between the electrode device and the electrode
shielding element that results therefrom is small enough to
minimize the coupling of noise signals of the signal processing
device into the electrode device. It is ensured in this way that
the signal path starting from the electrode device in the direction
of the signal processing device functions essentially as a "one way
street". The electrode device, which comprises at least one
electrode element, is decoupled as far as possible in this way from
the coupling of interference signals.
[0017] With regard to the geometry of the electrode device, it is,
furthermore, advantageous for this to be selected in such a way
that, together with a parasitic input impedance 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. This measure also
contributes to the aforementioned decoupling of the electrode
device from the signal processing device.
[0018] With regard to the geometry of the electrode device, it is
preferred for this to be selected in such a way that input noise
signals of the parasitic impedance of the signal processing device
lie with their upper cut-off frequency below the lower cut-off
frequency for the signals to be measured.
[0019] In one advantageous variant, the sensor system includes a
housing. This housing encloses the additional shielding means. That
is to say, the shielding means are designed as a component or
components of the housing. To this end, the components can be
designed in relation to the housing both as being of one piece and
in a modular fashion. The electrode device is preferably coupled to
the housing in such a way that the ohmic resistance between the
electrode device and the housing is so high that a signal recorded
capacitively by the electrode device is present at the input of the
signal processing device without corruption.
[0020] The capacitive electrode device is advantageously arranged
in the housing in such a way that there can be no occurrence of any
connections to electrical sources that entail the risk of
disruption of the electrode device or the signal processing device.
To this end, the sensor system includes, in particular, an
electrical insulator region for the electrical insulation of the
electrode device from a signal source. Said region is
advantageously designed 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.
Moreover, the insulator region has material properties such that
static charging of the insulator region by static environmental
charges is minimized.
[0021] The signal processing device of the sensor system preferably
includes an impedance converter as input stage. In one advantageous
variant, the signal processing device has a difference amplifier.
Particularly suitable in this case as difference signal is the
signal of an external reference electrode that is in contact with
the signal source.
[0022] A particularly preferred variant of the sensor system is
distinguished by an integrated analog-to-digital conversion of the
signals. To this end, the signal processing device comprises an
analog-to-digital converter and a digital signal processor. Such
processors are available at a satisfactory level of miniaturization
such that an appropriately compact sensor system can also be
provided with this functionality.
[0023] The input impedance of the signal processing device is
advantageously to be selected in such a way that, together with the
electrode capacitance of the electrode system, a highpass filter
with a cut-off frequency adapted to an electromagnetic, having a
biological origin, to be measured is formed. The electrode
capacitance of the electrode system can, in particular, be set via
the geometric parameters of the sensor system that have previously
been explained.
[0024] A highpass filter is preferably provided in the signal
processing device in such a way that a signal amplified in the
signal processing device passes through the highpass filter such
that DC voltage potentials are isolated from the dynamic
measurement signal.
[0025] A further variant of the sensor system provides that the
electrode device has a plurality of electrode elements for
detecting electromagnetic signals having a biobiological origin.
The plurality of the electrode elements acts in this case as a
plurality of capacitive electrodes. A corresponding signal
processing path is designed in the signal processing device for
each of these electrode elements. It is also conceivable to provide
a corresponding plurality of component signal processing
devices.
[0026] The sensor system preferably has an electrical line device
shielded to ground potential, for routing the measurement signal
away from the sensor system. Further variants of the sensor system
have means for line-conductive transmission and/or means for
lineless transmission of the measurement device signals from the
sensor system to a receiving spaced apart therefrom. Signals can be
transmitted optically and/or electrically both for the
line-conductive and for the lineless variants. For the optical
variant, the sensor system has an optoelectronic transducer that is
preferably of miniaturized design. Data can be transmitted both in
free beam fashion and via optical waveguides such as optical fibers
made from glasses or plastics.
[0027] It is advantageous to design the sensor system with a
reference electrode. This reference electrode can be arranged next
to the sensor system on a measurement object in such a way that the
reference electrode provides a reference potential for the sensor
system. The reference electrode is preferably designed in this case
as an ohmic electrode.
[0028] However, it is possible in principle that the reference
electrode is coupled to the measurement object in a resistive,
conductive or capacitive fashion.
[0029] In addition to the provision of a reference potential, the
reference electrode can also be 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. In this case,
the reference electrode fulfils a dual function, firstly that of
providing the reference potential and secondly as a source for an
alternating signal from which the movement signal can be derived
and it is thereby possible to compensate movement artefacts. One or
more reference electrodes can be used to feed in an alternating
signal. When use is made of a number of reference electrodes, it is
then possible to couple in alternating signals of different
frequency, it being possible to separately compensate the movement
artefacts of different electrode elements or electrode devices by
means of each individual alternating signal.
[0030] The sensor system described above can be integrated in a
multiplicity of measuring devices. By way of example, two that are
suitable for recording EEGs and ECGs, in particular, are to be
represented below.
[0031] One measuring device comprises a multiplicity of sensor
systems that are arranged in a helmet-like or cap-like carrier
device. This carrier device is designed in such a way that it can
be slipped at least partially over the head of a test subject. In
this case, it preferably has wearing properties for the test
subject that preclude the measurements from becoming unpleasant
over lengthy time intervals. That is to say, the weight, the uptake
of, or the transmissive properties for, body moisture etc. should
be optimized for wearing comfort with the aid of appropriate
materials. It is conceivable that such a measuring device in the
form of a previously explained cap is of great use, particularly
for EEG diagnostics in emergency medicine. It is likewise
conceivable that a person wearing such a cap interacts via his/her
brain activity with systems to be controlled. These systems to be
controlled can be computers, artificial limbs, robots or further
machines or complex systems to be monitored or to be controlled by
a human being. In this case, the cap would serve as interface
between man and machine.
[0032] In the leisure sector, it would be possible in this way to
control computer games entirely or partially. Thus, it would also
be conceivable to use an interposed computer for mental interaction
between a number of people.
[0033] A second measuring device comprises a multiplicity of sensor
systems, the sensor systems being arranged on a flexible carrier
device of two-dimensional design that can be fastened on the body
of a test subject. This measuring device is therefore suitable, in
particular, for recording ECGs. The statements previously made
apply correspondingly with regard to wearing comfort.
[0034] The electrode devices and/or the housing and/or the
additional shielding means and/or the electrode shielding elements
are preferably produced from suitable flexible plastic in order to
ensure that the measuring devices described previously have a
flexibility adapted to the individual shape of head and body.
[0035] A further aspect of the present invention consists in that
in the case of a capacitive measurement of electromagnetic signals
having a biobiological origin, the problem arises that even very
slight relative movements between the capacitive sensor system and
a signal source lead to clear inference signals. Thus, periodically
occurring mechanical pulse wave caused by the movement of the heart
of an organism is already sufficient to influence the measurement
signal. Moreover, clothing, hair etc. arranged between the sensor
system and signal source also necessarily lead to so-called
movement artefacts in the event of a movement of the signal
source.
[0036] In order further to optimize the capacitive sensor systems
known from the prior art, it is essential to minimize the influence
of the movement artefacts on the measurement signals. This aspect
of the invention is attained by means of the methods having the
method steps in accordance with claims 29 and 33.
[0037] When use is made of a sensor system described above or of a
measuring device described above, it is provided to arrange the
sensor system or the measuring device at a measurement object.
Thereafter, an electrical alternating signal is coupled into the
measurement object in order to use the temporal change in the
alternating signal detected via the electrode device 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. This determined electrode capacitance is
taken into account in a concluding step when evaluating the
measurement signals of the sensor system or of the measuring
device.
[0038] It is likewise conceivable that the alternating signal
coupled in can also be coupled out via a device other than the
sensor systems used, and can be evaluated in order to determine
electrode capacitance.
[0039] The coupling in is performed, for example, via a separate
electrode, arranged on the measurement object for this purpose.
This electrode can be designed both as an ohmic and as a capacitive
electrode. The frequency of the alternating signal coupled in is
usually removed by more than one order of magnitude from the
frequencies of the physiologically relevant measurement signals. It
is possible in a way that is technically known to undertake to
couple the alternating signal out by means of a lock-in amplifier
circuit.
[0040] 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 is preferably coupled into the
measurement object via the electrode device or via a reference
electrode cooperating externally with the sensor system or the
measuring device. The reference electrode fulfils a dual function
in this case.
[0041] The influence of the movement artefacts on a sensor system
for measuring electromagnetic signals having a biobiological origin
can therefore be minimized in entirely general fashion by means of
a method having the following steps. Firstly, a capacitive sensor
system suitable for measuring electromagnetic signals having a
biobiological origin is arranged on a measurement object. An
electrical alternating signal is then coupled into the measurement
object, the alternating signal coupled in is then evaluated in
order to determine the electrode capacitance of the sensor system,
and then the electrode capacitance determined is finally taken into
account when evaluating the measurement signals.
[0042] One of the previously named methods can preferably be
carried out in such a way that a line-frequency interference signal
is used as electrical alternating signal. The 50 or 60 Hz signal of
the power supply is present in any case and would not firstly need
to be generated by means of a device provided specifically
therefor.
[0043] It is advantageous in this case to use the method to take
account of the relative temporal change in the electrode
capacitance of the electrode device of the sensor system or of the
measuring device, and to derive the movement of the electrode
device relative to the measurement object from the relative
temporal change in the electrode capacitance. The movement thus
determined can then be used to determine the movement artefacts
superposed on the electromagnetic signals having a biological
origin, and to compensate them.
[0044] A further method making use of a previously described sensor
system and/or of a previously described measuring device provides
the following steps. Firstly, the sensor system or the measuring
device is arranged on a measurement object. Subsequently, the
position parameters of the position of the sensor system or of the
sensor systems are determined relative to the measurement object
during the measurement, and the determined position parameters are
taken into account for the purpose of compensating movement
artefacts in the measurement signal.
[0045] All the sensor systems are provided with position measuring
systems in order to determine the required position parameters.
These position measuring systems determine the required relative
position via a suitable measurement method. Suitable, in
particular, to this end are optical, acoustic and piezoelectric
devices and methods using these devices.
[0046] It is preferred to use robust methods of digital signal
processing in order to process the electromagnetic signals that can
then be measured with the aid of the electrode device. In
particular, the data are filtered, both spatially and in the
frequency domain. In this case, all the filters can also be adapted
to the instantaneous signal characteristic during the measurement,
if appropriate in real time. Furthermore, use is made, in
particular, of univariate denoising methods that are based on the
decomposition of the signals into arbitrary--including
overdetermined or underdetermined--base systems such as, for
example, wavelets, sinusoidal functions etc. Univariate denoising
means that a measurement signal of the sensor system per se is
denoised in a fashion isolated from the other, parallel measurement
signals of the sensor system.
[0047] In particular, it is also possible to use techniques for
describing signal dynamics (for example, autoregressive
coefficients, nonlinear dynamic parameter extraction methods), or
for describing synchronicity, in order to extract suitable signal
features.
[0048] Furthermore, use is also made of multivariate methods for
denoising. In this case, a number of measurement signals of the
sensor system are denoised in a common process. These processes are
based on a spatial projection of the measured data, for example
with the aid of main component analysis, independent component
analysis, projection pursuit techniques, sparse decomposition
techniques or Bayesian subspace regularization techniques.
[0049] Use is made, furthermore, of projection techniques that take
account of the geometry of the sensor system, in particular of the
electrode device and of the shielding means and/or of the electrode
shielding element such as, for example, beam-forming techniques,
and laplace filters.
[0050] It is also possible to use variants of the said spatial
projection methods that adapt to changes in the signal
characteristics, so-called nonstationarities, if appropriate in
real time. Nonstationarities are understood very generally as
changes in the environmental conditions, for example, the addition
or omission of noise sources, relative movements between sensor
system and measurement object, variation in the physiological state
of the measurement object etc.
[0051] Before beginning the actual measurement, it is optional to
carry out a calibration measurement in the case of which signals
are measured under specific conditions. This permits the use of
monitored processing methods such as, for example, the common
spatial patterns technique for spatial projection.
[0052] The calibration data are also used in order to carry out a
model selection (determination of the best suited method and of the
values of the settable parameters).
[0053] On the basis of these preprocessed, denoised data, use is
made of suitable adaptive techniques for classification and
regression that, as appropriate, adapt in real time to a possibly
nonstationary signal characteristic. Examples of such methods are
linear/nonlinear discriminance analysis, (kernel) Fisher
discriminants, kernel-based learning methods (for example support
vector machines, linear programming machines etc.) boosting,
decision trees and neural networks.
[0054] Such techniques for classification and regression can be
used, for example, to distinguish different (brain) states on the
basis of the measured and preprocessed measurement signals, and
thus to transmit information.
[0055] It is also possible to predict states.
[0056] Further properties and advantages of the invention are
explained in connection with the following drawings. In the
drawings:
[0057] FIG. 1a shows a schematic cross section of a first exemplary
embodiment of the sensor system according to the invention;
[0058] FIG. 1b shows a schematic cross section of a second
embodiment of the sensor system according to the invention;
[0059] FIG. 2 shows a schematic equivalent circuit diagram of the
sensor system according to the invention;
[0060] FIGS. 3a-3c show three variants relating to the multipartite
configuration of the electrode device of the sensor system;
[0061] FIG. 4 shows a schematic equivalent circuit diagram of an
embodiment of a compensation circuit for compensating static
charges on the electrode device;
[0062] FIG. 5 shows a schematic of the arrangement of the electrode
device at a distance from the measurement object;
[0063] FIG. 6 shows a graph of the frequency spectrum of an
alternating signal modulated by a movement of the electrode
device;
[0064] FIG. 7 shows a graph of an alternating signal modulated by a
movement of the electrode device, and of the movement signal
calculated from the modulated alternating signal;
[0065] FIG. 8 shows a flowchart of a method relating to the method
for minimizing the influence of movement artefacts by using a
sensor system; and
[0066] FIG. 9 shows a flowchart of a second method relating to the
method for minimizing the influence of movement artefacts by using
a sensor system.
1. DESIGN OF THE SENSOR SYSTEM
[0067] FIG. 1a shows a cross sectional illustration of a first
embodiment of the sensor system according to the invention. This
illustration is purely schematic and not true to scale. The
electrode device 10 is arranged on an insulator element 12 of a
dimensional design that acts as an insulator region. The electrode
device 10 is surrounded essentially completely by an electrode
shielding element 20 on the side of the insulator element 12 facing
the electrode device 10. This electrode shielding element 20 is
likewise fitted on the insulator element 12 and galvanically
decoupled from the electrode device 10 by the insulator element
12.
[0068] The electrode shielding element 20 has an opening for
leading through a signal line 4 emerging from the electrode device
10. This signal line 4 leads to a signal processing device 30
arranged outside the electrode shielding element 20. Both the
signal processing device 30 and the electrode shielding element 20
are surrounded by additional shielding means 21 on the side of the
insulator element 12 facing the electrode device 10. The additional
shielding means 21 have a leadthrough for an electrical line device
40, screened to frame potential, for routing the measurement signal
away from the sensor system.
[0069] The line device 40 shown can also be designed optically in
the form of a light guide. In such a case, the signal processing
device 30 includes a suitable electrooptic transducer. The light
guide could then be designed both as an optical fiber and in
optically integrated fashion. The use of a light guide as line
device 40 would have the advantage that said light guide would
require no shielding against external electromagnetic fields.
[0070] The insulator element 12 ensures, firstly, a galvanic
decoupling of the electrode device 10. Secondly, it likewise serves
the purpose of galvanic decoupling between the electrode shielding
element 20 and the additional shielding means 21. In FIG. 1a, the
electrode shielding element 20 is designed in cross section as two
L-shaped limbs arranged lying opposite one another. Of course, a
multiplicity of other geometric configurations for example with
cambered sections of the electrode shielding element 20, are
possible. It is especially important that the electrode shielding
element 20 surrounds the electrode device 10 in such a way as to
define a solid angle coming from which electromagnetic fields reach
the electrode device 10 without experiencing attenuation caused by
the electrode shielding element 20 in so doing.
[0071] The preceding statements are valid mutatis mutandis with
regard to the spatial configuration of the additional shielding
means 21. As illustrated in FIG. 1b, it is possible to design the
additional shielding means 21 with different compartments. In one
such compartment, it is then possible to arrange the signal
processing device 30 in such a way that the additional shielding
means 21 also shield the electrode device 10 together with the
electrode shielding element 20 against the signal processing device
30. The interference of electromagnetic fields generated in the
signal processing device 30 is minimized in this way.
[0072] The existence of a multiplicity of geometric configurations
both of the electrode shielding elements 20 and of the additional
shielding means 21 is clear. This is associated, in particular,
with the spatial configuration of the signal processing device 30.
The signal processing device 30 does not imply that the latter must
undertake the entire extent of the processing of the measurement
signals. The signal processing can also run only partially in the
illustrated signal processing device 30. Further signal processing
devices arranged removed from the sensor system can be connected
downstream of the illustrated signal processing device 30.
[0073] It is likewise valid with regard to the additional shielding
means 21 that the latter need not necessarily be designed in one
piece. A hybrid design comprising individual shielding elements is
also possible. The passage openings for the signal lines 4 can
likewise be of variable design in order to fulfil different
requirements placed on shielding between signal processing device
30 and the electrode device 10.
[0074] Furthermore, the signal processing device 30 illustrated as
a unitary component in FIGS. 1a and 1b can be constructed from a
plurality of spatially separate subelements. Individual ones of
these subelements, or all of them can be surrounded by the
additional shielding means 21 in different or the same
compartments.
[0075] FIG. 2 shows a schematic equivalent circuit diagram of the
sensor system according to the invention. The electrode device 10
has an electrode capacitance C with respect to a measurement object
Q that acts as a source of electromagnetic signals having a
biobiological origin.
[0076] An electric field, and the electrical potential of the
source Q resulting therefrom, influences charge the capacitive
electrode device 10 in accordance with the capacitance C thereof.
This charge, which is itself also time-dependent given a
time-dependent source Q, reaches an operational amplifier, acting
as an impedance converter 31, of the signal processing device 30.
This impedance converter 31 has an input impedance Zi. All the
resistive, capacitive and inductive external contributions of the
environment, and the internal input impedance of the impedance
converter 31 are combined in this input impedance Zi. The external
part of the impedance Zi is intended to have as small as possible a
capacitive and inductive and as high as possible a resistive
fraction. The impedance converter 31 converts its input signal to
such a small output impedance that conventional circuits 32 can
subsequently be used for the further signal processing. The output
signal of the impedance converter 31 constitutes the potential for
the electrode shielding element 20. This potential is denoted as
guard potential in the case of commercially available guard
electrode systems.
[0077] During the recording of the charge signal via the capacitor
C, parasitic signals occur that can be coupled in via a parasitic
shielding capacitor Cg acting between electrode device 10 and
electrode shielding element 20, via a parasitic first shielding
capacitor Cs1 acting between electrode shielding element 20 and the
shielding means 21, and via a parasitic second shielding capacitor
Cs2 acting between electrode device 10 and the shielding means
21.
[0078] It is therefore advantageous to set the previously described
parasitic capacitors Cg, Cs1 and Cs2 by an appropriate adaptation
of geometric parameters such as, in particular, the tolerances and
the surface contour of the electrode shielding element and of the
shielding means, the respective spacing between electrode device
10, electrode shielding element 20 and shielding means 21.
Furthermore, the parasitic capacitor Cg can be influenced via the
dielectric properties of the medium 11 arranged between electrode
device 10 and electrode shielding element 20. A corresponding
statement is, of course, also valid for the parasitic capacitors
Cs1 and Cs2.
[0079] As an alternative to feeding the processed signal back to
the electrode device 10 via the compensation impedance Ck, the
processed signal can be combined together with the output line of
the impedance converter 31 in order to generate the potential for
the electrode shielding element (guard potential) from a suitable
logic operation. The parameters of the signal processing determine
which type of signal logic operation (for example subtraction,
addition etc.) is suitable for generating the guard potential. The
dynamics range of the sensor system can also be increased in the
way illustrated above.
[0080] Different variants of the design of the electrode device 10
are illustrated in FIGS. 3a to 3c. Each of the three variants shown
comprises a plurality of electrode elements 100.
[0081] Four electrode elements are illustrated in FIG. 3a in the
topology of symmetrically arranged quadrant elements. FIG. 3b shows
a structure, interlocking in a finger-like fashion, of two
comb-like electrode elements 100. In FIG. 3c, the electrode device
10 is designed in the form of five electrode elements 100 arranged
as concentrically arranged rings of different diameter.
[0082] In the case of the multipartite design shown for the
electrode device 10, there is a respective need for a corresponding
plurality of signal lines and signal processing paths in order to
ensure parallel signal processing in the signal processing
device.
2. COMPENSATION OF STATIC CHARGES ON THE ELECTRODE DEVICE
[0083] The effect of external charges in the environment of the
sensor system and of the electrode device 10 of the sensor system
is to generate on the electrode device 10 or the individual
electrode elements 100 of the electrode device 10 static charges
that collect there and lead to static charging of the electrode
device 10. Such static charging of the electrode device 10 or of
the electrode elements 100 of the electrode device 10 greatly
impairs the dynamic range of the sensor system for receiving the
electromagnetic signals from the measurement object Q, and reduces
the signal-to-noise ratio of the sensor system that can be
achieved.
[0084] The detection of electromagnetic signals from the
measurement object Q is attended by charge transfers on the
electrode device 10. If an electromagnetic signal to be detected
passes from the measurement object Q to the electrode device 10,
the electromagnetic signal effects a charge transfer on the
electrode device 10, induces a current and therefore a signal that
is processed in the signal processing device 30. If, however,
static charges are present on the electrode device 10 as a
consequence of external charges in the environment of the sensor
system, this has the effect that the dynamic range of the electrode
device 10 is reduced for the electromagnetic signal from the
measurement object Q that is actually to be detected and, in
addition, interference signals are more strongly superposed on the
electromagnetic signal.
[0085] In addition, the static charge located on the electrode
device 10 exerts a substantial influence on the interference of the
electromagnetic signal to be received from the measurement object
Q, owing to movement artefacts caused by the movement of the
electrode device 10 relative to the measurement object Q. The
change in the signal received by the electrode device 10 as a
function of the distance of the electrode device 10 from the
measurement object Q can be described by the following equation:
.differential. U .differential. d = l C .times. .differential. Q
.differential. d - Q C 2 .times. .differential. C .differential. d
( 1 ) ##EQU1##
[0086] In equation (1), the first term represents the change in the
voltage U of the electrode device 10 with the spacing d between the
electrode device 10 and the Measurement object Q, the second term
represents the change in the charge Q with the spacing d and the
third term represents the change in the electrode capacitance C
with the spacing d. In the case of a signal U detected by the
electrode device 10 and not interfered with by movement artefacts,
the second and third term of equation (1) must vanish, that is to
say make no contribution, and so the signal U is independent of the
change in the electrode capacitance C relative to the distance d
between the electrode device 10 and the measurement object Q. As
may be seen from equation (1) the third term is proportional to the
charge Q collected on the electrode device 10. The suppression of
the charge Q collected on the electrode device 10 is therefore
attended by the reduction of movement artefacts interfering with
the received signal.
[0087] In order to compensate the collection of static charges on
the electrode device 10, a feedback is arranged in the sensor
system between the output of the signal processing device 30 and
the electrode device 10. In the case of the equivalent circuit
diagram, as seen in FIG. 2, of the sensor system, a compensation
impedance that is designed as a capacitor Ck is provided for this
purpose. This compensation impedance acts between the electrode
device 10 and the signal output of the signal processing device.
This compensation impedance Ck, can, as illustrated in FIG. 2, be
capacitive, but also resistive or inductive. The dynamic range of
the sensor system can be enlarged by the provision of the
compensation impedance Ck.
[0088] FIG. 4 illustrates a further embodiment of a compensation
circuit using a compensation impedance Ck. The compensation circuit
illustrated has an electrode device 10, an impedance converter 31
and a circuit 32 that serves for feeding the signal from the output
of the signal processing device 30 back to the electrode device 10
via the compensation impedance Ck. The circuit 31 comprises two
stages, of which the first stage, comprising the resistors R1, R2,
R3 and Rt, the capacitors C1, Ct and the operation amplifier O1,
constitutes a second order lowpass filter, and the second stage,
comprising resistors R4, R5, R6, R7, capacitor C2 and the operation
amplifier O2, constitutes a control circuit for feeding the signal
back to the electrode device 10. A signal detected by the electrode
device 10 is then led via the impedance converter 31 to the lowpass
arrangement, filtered by the lowpass arrangement and fed back to
the electrode device 10 via the control circuit and the
compensation impedance formed by the capacitor Ck.
[0089] The effect of the compensation impedance Ck is that charge
can be exchanged between the electrode device 10 and the output of
the signal processing device 30. In this case, a lowpass-filtered
output signal of opposite sign can be fed back to the electrode
device 10 via the compensation impedance Ck, such that it is
precisely the charge quantity opposite to the charge quantity
collected on the electrode device 10 that is coupled into the
electrode device 10. In this case, the cut-off frequency of the
lowpass arrangement can be selected to be so small that the
lowpass-filtered signal is essentially static in nature, and so it
is also only the low frequency, essentially static components of
the output signal that are fed back to the electrode device 10.
Consequently, only the low frequency charge components of the
electrode device 10 are compensated, these being (quasi) static in
nature, that is to say only the substantially static charges that
have collected on the electrode device 10. The cut-off frequency of
the lowpass arrangement can in this case sensibly be of the order
of magnitude of 200 mHz, and thus much below the frequency range of
the electromagnetic signals to be detected from a measurement
object Q.
[0090] A most far reaching complete suppression of the static
charging of the electrode device 10 can be achieved by means of the
compensation impedance Ck illustrated in FIG. 2 and in FIG. 4. It
is thereby possible to improve the dynamic range of the electrode
device 10, and to enlarge the achievable signal-to-noise ratio of
the sensor system.
3. METHOD FOR CORRECTING MOVEMENT ARTEFACTS BY MEANS OF THE SENSOR
SYSTEM
[0091] According to the invention, a method is provided by means of
which it is possible to minimize the influence of movement
artefacts on a measured electromagnetic signal from a measurement
object Q as effected by a relative movement of the capacitive
electrode device 10 with reference to the measurement object Q. In
the case of the method according to the invention, it is provided
in this case that a sensor system with an electrode device 10, or a
measuring device having a multiplicity of sensor systems and
electrode devices 10, is/are fitted on a measurement object Q, an
electrical alternating signal is coupled into the measurement
object via the electrode device 10, the alternating signal coupled
in is evaluated, and the temporal change in the electrode
capacitance C of the electrode device 10 of the sensor system is
thereby determined. The determination of the electrode capacitance
C is performed separately in this case for each electrode device 10
of each sensor system such that the movement of each electrode
device 10 can be compensated separately.
[0092] The compensation is performed by taking account of the
temporal change in the electrode capacitance and evaluating the
measurement signals of each sensor system, and the movement
artefacts caused by movement are thereby removed from the
measurement signal by calculation.
[0093] A schematic sketch of the arrangement of an electrode device
10 on a measurement object Q is illustrated in FIG. 5. Here, the
electrode device 10 lies at a distance d(t) from the measurement
object Q, the distance d(t) being temporally variable, and
therefore the capacitance C, formed by the electrode device 10 with
the measurement object Q, is also temporally variable.
[0094] In order to determine the movement artefacts, a temporally
variable alternating signal a(t) is applied to the electrode device
10, and the response signal b(t) of the alternating signal (a(t) is
measured. The alternating signal a(t) is in this case a carrier
signal at a specific frequency, for example 300 Hz, while the
response signal b(t) corresponds to the modulation of the
alternating signal a(t) by the movement of the electrode device 10
relative to the measurement object Q. The movement of the electrode
device 10 relative to the measurement object Q is correlated in
this case with the temporal change in the electrode capacitance C,
such that the information relating to the temporal change in the
electrode capacitance C is contained in the response signal b(t)
formed by the modulated alternating signal a(t).
[0095] In the arrangement illustrated in FIG. 5, the response
signal b(t) corresponds to the amplitude modulation of the
alternating signal a(t) as caused by the electrode capacitance C
changing with the distance. However, it is also possible to
conceive arrangements in which the alternating signal a(t) is
modulated in frequency or phase by the changing electrode
capacitance C, or by other known modulation methods, it being
possible to this end to make use of known circuits in which the
electrode capacitance C functions in each case as a modulating
component.
[0096] It is also possible, as an alternative to feeding the
alternating signal a(t) directly via the electrode device 10, to
couple the alternating signal a(t) into the measurement object Q
via a separate reference electrode, that is arranged at another
site on the measurement object Q, and to detect via each electrode
device 10 arranged on the measurement object Q a response signal
b(t) that then corresponds to the modulated component of the
alternating signal a(t) and contains for the respective electrode
device 10 the information relating to the temporal change in the
respective electrode capacitance C. This enables a simplification
of the design of the sensor system, since in this case it is
necessary only to receive signals via each electrode device 10,
whereas an alternating signal a(t) is coupled in via a separate
reference electrode. A feed path for feeding the alternating signal
a(t) into each electrode device 10 is superfluous in this case, and
so, as illustrated in FIG. 2, the sensor system need only have a
receiving path, that is to say means 30, 31, 32 for receiving a
signal. Such an electrode arrangement can, for example, be designed
as illustrated in FIGS. 3a to c, in which case one of the electrode
elements 100 would then serve as reference electrode, and the other
electrode elements 100 as receiving electrodes.
[0097] The reference electrode can generally be fitted on the
measurement object Q in resistive, inductive or capacitive fashion,
in order to feed an alternating signal a(t) into the measurement
object Q. It is also conceivable to use a number of reference
electrodes that feed in alternating signals of different frequency,
an electrode device 10 respectively receiving an alternating signal
a(t) at a frequency from which it is then possible to draw
conclusions relating to the movement of the respective electrode
device 10 relative to the measurement object Q.
[0098] FIG. 6 illustrates an example of a response signal b(t)
received by an electrode device 10. Shown here is the frequency
spectrum of the response signal b(t) which corresponds to the
Fourier transformed F{b(t)} of the response signal b(t). In the
case illustrated in FIG. 6, an alternating signal a(t) is coupled
in via a reference electrode that is fitted on the measurement
object Q in a resistive fashion, the electrode device 10 executing
a movement at a frequency of 10 Hz relative to the measurement
object Q. Correspondingly, the response signal b(t) illustrated in
FIG. 6 has two sidebands around the frequency of the alternating
signal a(t) of 300 Hz, specifically at 290 Hz and at 310 Hz, that
are generated by the modulation of the alternating signal a(t)
owing to the movement of the electrode device 10 relative to the
measurement object Q.
[0099] FIG. 7 shows a measured response signal b(t) (bottom in FIG.
7) and a movement signal B(t) (top in FIG. 7) that is calculated
from the response signal b(t) and is correlated with the temporal
change in the electrode capacitance C, and therefore contains the
information relating to the temporal change in the electrode device
10 relative to the measurement object Q. The movement signal B(t)
is derived here from the response signal b(t) by subjecting the
response signal b(t) to highpass filtering, and the components of
the electromagnetic signal having a biobiological origin that is to
be detected from the measurement object Q, which lie in a frequency
range below the frequency of the alternating signal a(t), in this
case 300 Hz, are suppressed. Subsequently, the highpass filtered
response signal b(t) is demodulated, and so the component of the
original alternating signal a(t) is removed from the response
signal b(t) by calculation and the movement signal B(t) is thereby
determined. Since the movement signal B(t) is correlated with the
temporal change in the electrode capacitance C, and thus contains
the information relating to the relative temporal change in the
electrode capacitance C as a function of the movement of the
electrode device 10 relative to the measurement object Q, the
movement signal B(t) can be further processed and can be used with
the aid of known signal processing algorithms to compensate the
movement artefacts in the detected electromagnetic measurement
signal having a biobiological origin. The compensation of the
movement artefacts can be carried out in this case either in a post
processing step downstream of the actual measurement, or else run
in real time, given a correspondingly more powerful signal
processing device 30, during the measurement for the purpose of
direct compensation of the movement artefacts.
[0100] FIG. 8 shows the fundamental sequence of the method for
minimizing the influence of movement artefacts by using the sensor
system according to the invention, in the case of which the change
in the electrode capacitance C of the electrode device 10 is taken
into account when evaluating the measurement signals of the sensor
system or of the measuring device.
[0101] The fundamental sequence of a further method for minimizing
the influence of movement artefacts is illustrated in FIG. 9. In
this method, the sensor system or the measuring device is firstly
arranged on a measurement object, the sensor system or the
measuring device being provided with a position measuring system
for determining the position of the sensor system or measuring
device. Subsequently, the position parameters of the position of
the sensor system or the sensor systems are determined relative to
the measurement object during the measurement, and the determined
position parameters are taken into account to compensate movement
artefacts in the measurement signal.
* * * * *