Electro-physiological measurement with reduced motion artifacts

• US 9,603,542 B2
• Filed: 07/06/2010
• Issued: 03/28/2017
• Est. Priority Date: 07/13/2009
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Veen, Jeroen, Meftah, Mohammed, Lambert, Nicolaas, De Boer, Bart Michiel, Feddes, Bastiaan, Gourmelon, Lena, Rietman, Ronald, Husen, Sri Andari
• Primary Examiner(s): Cohen, Lee S
• Assistant Examiner(s): Cardinal, Erin M
• Application Number:
  US13/383,302
• Publication Number:
  US 20120116198A1
• Time in Patent Office: 2,457 Days
• Field of Search: 600/372, 600/382, 600/509, 600544-545
• US Class Current: 1/1
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/302 for capacitive or ionised electrodes, e.g. metal-oxide-semiconductor field-effect transistors [MOSFET]
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths

Abstract

An apparatus and method (4,5,6,7,2) for capacitive measurement of electrophysiological signals (1) suppresses or reduces motion artifacts by providing a feedback mechanism. An average voltage between a capacitive sensor electrode (1) and the body (3) is controlled so as to reduce or minimize motion-induced signals.

Claims

1. An apparatus configured to measure at least one electrophysiological signal of a body, comprising:

at least one capacitive sensor electrode;

a vibrator configured to vibrate the at least one capacitive sensor electrode, or a support or casing supporting or housing the at least one capacitive sensor electrode, and

a feedback loop coupled to the vibrator to generate a feedback signal to control an average voltage between the at least one capacitive sensor electrode and the body for reducing or minimizing the average voltage.

2. The apparatus according to claim 1, wherein the frequency of the vibration is outside of a bioelectric frequency band of the electrophysiological signal to be measured.

3. An apparatus configured to measure at least one electrophysiological signal of a body, comprising:

at least one capacitive sensor electrode which generates a sensor output signal which includes an additive mixture of the at least one electrophysiological signal and motion induced signals;

a circuit configured to control an average voltage between the at least one capacitive sensor electrode and the body, the circuit including;

a processing circuit configured to estimate a power or an entropy of the sensor output signal of the at least one capacitive sensor electrode,

a feedback subcircuit configured to generate a feedback signal based on the average voltage, and

a control subcircuit configured to bring the average voltage to a defined value;

wherein the processing circuit is configured to estimate the average voltage and iteratively adjust the estimated average voltage based on a slope of a change in the estimated power or entropy relative to a change in the average voltage and wherein a convergence speed to the estimated average voltage is slower than an oscillation rate of the electrophysiological signal.

4. An apparatus configured to measure at least one electrophysiological signal V_bio of a body comprising:

at least one capacitive sensor electrode which has a measurement capacitance and outputs a measurement signal including the at least one electrophysiological signal V_bio and a motion component;

a reference electrode configured to output a reference signal V_ref;

a buffer amplifier configured to receive the at least one electrophysiological signal V_bio and output an output voltage V_o;

a subtraction circuit configured to subtractively combine the output voltage V_o and the reference signal V_ref;

an integrator configured to integrate the subtractively combined output voltage V_o and the reference signal V_ref and derive an equalizing feedback signal V_f;

a capacitive network connected between the at least one capacitive sensor and the buffer amplifier; and

an equalizing circuit configured to feedback the equalizing feedback signal V_f to the capacitive network for equalizing a transfer function V_o/V_bio to adaptively control the transfer function V_o/V_bio, such that the equalizing feedback signal V_f brings a gain of the buffer amplifier to unity.

5. The apparatus according to claim 4, further comprising:

means configured for modulating the reference signal V_ref to a value above a maximum expected frequency of the electrophysiological signal of interest, and

means configured for demodulating the subtractively combined output voltage V_o and reference signal V_ref to generate a demodulated subtractively combined output voltage V_o and reference signal V_ref for integration by the integrator to generate the equalizing feedback signal V_f.

6. An apparatus configured to measure at least one electrophysiological signal of a body, comprising:

at least one capacitive sensor electrode;

at least one reference electrode arranged to be close to or in galvanic contact with the body, wherein the at least one reference electrode is connected to a voltage source, a current source or a reference potential; and

a circuit configured to actively control an average voltage between the at least one capacitive sensor electrode and the body by reducing or minimizing an electric field between the at least one capacitive sensor electrode and the body to reduce or minimize motion-induced signals caused by the electric field and variations in a distance between the at least one capacitive sensor electrode and the body, wherein the circuit includes;

an oscillator configured to generate an oscillating signal with a higher frequency than a frequency of the electrophysiological signal;

a modulator configured to modulate one of a signal from the capacitive sensor or a reference signal indicative of motion induced components with the oscillating signal;

an amplifier configured to amplify the electrophysiological signal;

a demodulator configured to demodulate the amplified electrophysiological signal with the oscillating signal; and

an integrator configured to integrate the demodulated amplified electrophysiological signal to generate a feedback signal to control the average voltage.

7. The apparatus according to claim 6, wherein the at least one sensor electrode includes at least two sensor electrodes coupled to inputs of a differential amplifier.

8. The apparatus according to claim 6, wherein the at least one sensor electrode includes at least two sensor electrodes configured to measure essentially the same electrophysiological signal and adapted to be arranged at different distances to the body and/or supplied with different average voltages, a feedback signal being generated based on output signals of the sensor electrodes so as to bring the average voltage to a defined value.

9. The apparatus according to claim 8, wherein the at least one sensor electrode includes at least three sensor electrodes, the at least three sensor electrodes being arranged:

in a triangular fashion, or

in concentric circles, or

in the form of small segments, the segments of all electrodes being distributed in an interspersed manner, or

in segments arranged as a ring or a matrix.

10. The apparatus according to claim 6, further including at least one buffer amplifier configured to convert an output signal of the at least one capacitive sensor electrode, applied to an input of the buffer amplifier, into an output signal while keeping the average voltage on the at least one capacitive sensor electrode at a level defined by a signal applied to a further input of the buffer amplifier.