Apparatus for electrodermal activity measurement with current compensation
Inventors
TOGNETTI, SIMONE • CENCI, IVAN • RESNATI, DANIELE • GARBARINO, MAURIZIO • LAI, MATTEO
Assignees
Publication Number
US-10506944-B2
Publication Date
2019-12-17
Expiration Date
2034-03-17
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Abstract
An apparatus for measuring electrodermal activity can include a first electrode in contact with a first portion and a second electrode in contact with a second portion of a stratum corneum, and in electronic communication with the second electrode through the stratum corneum. A processing module is electrically coupled to the first electrode and the second electrode and is operable to (a) bias the first electrode at a first voltage V+ and the second electrode at a second voltage V− (b) measure a current flowing between the first electrode and the second electrode, the current corresponding to the conductance of the stratum corneum, (c) subtract a compensation current from the measured current (d) measure a resulting current producing an amplified output voltage (e) measure a conductance of the stratum corneum, and (f) adjust at least one of the first voltage, the second voltage and the compensation current to desaturate the output voltage.
Core Innovation
The invention provides an apparatus and method for measuring electrodermal activity by using a pair of electrodes in contact with separate portions of the stratum corneum of skin. The apparatus includes a processing module operable to bias the electrodes at defined voltages, measure the current flowing through the skin (corresponding to skin conductance), and apply a compensation current to reliably measure both tonic and phasic levels of electrodermal activity. The processing module adjusts at least one of the electrode voltages or the compensation current to desaturate the output voltage, ensuring accurate conductance measurement over a wide range.
The problem addressed is that conventional electrodermal activity sensors suffer from limitations including narrow measurement ranges due to saturation of output signals, inability to accurately resolve both tonic (slow-changing) and phasic (rapid-changing) conductance levels, and electrode electrolysis leading to sensor degradation and skin irritation. Existing DC-based sensors are affected by electrolysis, while AC-based sensors do not resolve phasic conductance well. Furthermore, known systems lack compensation mechanisms to dynamically adjust measurement parameters to maintain signal fidelity across varying conductance ranges.
Claims Coverage
The patent claims define multiple inventive features centered on an apparatus and method for measuring skin conductance with compensation to prevent signal saturation and improve measurement fidelity.
Adaptive compensation current adjustment
The processor biases first and second electrodes at specified voltages and measures the current flowing between them which corresponds to skin conductance. It subtracts a compensation current from this measured current and amplifies the result to produce an output voltage. The processor dynamically adjusts the compensation voltage generated by a digital-to-analog converter to modify the compensation current, preventing saturation of the output voltage.
Bidirectional adjustment of compensation based on output voltage
The processor further executes instructions to decrease the compensation current if the output voltage falls below a predetermined minimum value, thereby maintaining output voltage within an operable range.
Output voltage indicating phasic conductance
The system output voltage is indicative of the phasic value of electrodermal activity, isolating rapid conductance changes associated with environmental or cognitive stimuli.
Electrode polarity reversal to reduce electrolysis
The processor reverses the polarity of at least one electrode after a predetermined period of time to reduce electrode electrolysis and prolong sensor durability.
Applicability to any skin portion and conductance resolution
The apparatus measures conductance of the stratum corneum of any skin portion and is configured to calculate tonic level conductance in the range of 0.05 μS to 50 μS, with resolution of 0.0001 μS.
Wearable form factor integration
The apparatus can be integrated into wearable forms including wrist bands, head bands, arm bands, foot bands, ankle bands, and rings, housing the processor and electrodes.
Inclusion of additional physiological sensors
The apparatus can further include sensors for heart beat, accelerometer, temperature, blood oxygen, and glucose, and a communications module to transmit multiple physiological data types to external devices via wired or wireless interfaces.
Quasilinear relationship for compensation current
The compensation current subtracted from the measured skin current is a quasilinear function of the compensation voltage generated by the digital-to-analog converter.
The claims collectively cover an apparatus and method employing electrode biasing, compensation current adjustment via DAC to prevent output saturation, signaling phasic electrodermal activity, electrode polarity reversal to reduce electrolysis, applicability to various skin areas with precise conductance resolution, wearable integration, additional physiological sensors, and compensation current as a quasilinear function of compensation voltage.
Stated Advantages
Capability to measure electrodermal activity across a wide conductance range covering the entire expected tonic level range.
High resolution measurement of phasic level conductances.
Reduction in electrode electrolysis, increasing durability and reducing skin irritation.
Real-time electrodermal activity measurement facilitated by integration in wearable devices like wrist bands.
Documented Applications
Wearable devices such as wrist bands, head bands, arm bands, foot bands, ankle bands, and rings for continuous monitoring of electrodermal activity.
Measurement of skin conductance of various portions of the user's skin, including wrist and finger.
Integration with additional physiological sensors including heart beat sensors (e.g., photoplethysmography), accelerometers, temperature sensors, blood oxygen sensors, and glucose sensors for comprehensive physiological monitoring.
Use in determination of human well-being through heart rate variability analysis using heart beat sensor data processed by the device or external systems.
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