Biomedical sensor

1. A biomedical sensor, comprising:

a printed bio-potential electrode on a substrate sheet configured to provide an electrical contact with a surface to be measured;

a bi-stable printed electronic ink indicator switchable from a first color to a second color to indicate a loose contact of a bio-potential electrode operation; and

a lead-off detector configured to detect a loose contact of the printed bio-potential electrode with the surface and to effect color switching of the bi-stable printed electronic ink indicator from the first color to the second color when a loose contact is detected.

2. The biomedical sensor according to claim 1 , wherein the bi-stable printed electronic ink indicator comprises a bi-stable electrochromic indicator or a bi-stable electrophoretic indicator.

3. The biomedical sensor according to claim 1 , wherein the bi-stable printed electronic ink indicator comprises an ink material having a predetermined decay time from the second color to the first color, and wherein a color change of the bi-stable printed electronic ink indicator is maintained by refreshing it with a voltage pulse at appropriate intervals.

4. The biomedical sensor according to claim 3 , wherein the second color corresponds to a basic state towards which the ink material of the bi-stable printed electronic ink indicator decays.

5. The biomedical sensor according to claim 1 , wherein the sensor has a hybrid structure.

6. The biomechanical sensor according to claim 5 , wherein the lead-off detector is a direct current lead-off detector, an alternating current lead-off detector, or a contact impedance meter, and wherein the lead-off detector is configured to perform an intermittent impedance measurement at a signal frequency band.

7. The biomedical sensor according to claim 5 , wherein the lead-off detector is a part of a biosignal preamplifier configured to both amplify the biosignal and detect a loose contact.

8. The biomedical sensor according to claim 7 , wherein the biosignal preamplifier comprises:

a differential amplifier stage comprising inputs connected to at least two electrodes, and an amplified biosignal output;

at least two resistors at the inputs of the differential amplifier stage configured to feed respective at least two DC currents to respective at least two electrodes;

a feedback amplifier loop with a high-pass filtering configured to remove a DC component from the amplified biosignal output and to feedback the amplified biosignal output;

wherein the feedback amplifier loop is configured to saturate due to a loose contact of one of the at least two electrodes and to cause pulling of the amplified biosignal output up to approximately a supply voltage, wherein the pulled up amplified biosignal output indicates a loose electrode.

9. The biomedical sensor according to claim 1 , further comprising at least one disposable printed battery.

10. The biomedical sensor according to claim 9 , wherein the at least one disposable printed battery is arranged in a hermetically sealed compartment on the substrate sheet.

11. The biomedical sensor according to claim 1 , further comprising at least one additional bi-stable printed electronic ink indicator configured to indicate a battery charge level, and an additional bi-stable printed electronic ink indicator configured to indicate a remaining or exceeded use time or storage time of the biomedical sensor.

12. The biomedical sensor according to claim 1 , wherein the biomedical sensor is a wireless biomedical sensor comprising an electronic circuit configured to wirelessly transmit biomedical measurement data.

13. The biomedical sensor according to claim 1 , wherein the biomedical sensor is a wireless biomedical sensor comprising an electronic circuit configured to store measurement data into local memory over a predefined period of time.