Multi-Electrode Impedance Measurement Using Orthogonal Frequencies
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Solution Overview
Problem
Existing medical devices with multiple electrodes face challenges in determining contact status with tissue while maintaining safe current limits, as increasing the number of electrodes reduces the magnitude of drive current required to avoid exceeding auxiliary current thresholds, leading to signal-to-noise ratio issues and crosstalk between channels.
Innovation Solution
The system generates multiple drive signals with unique frequencies, allowing for increased drive current magnitudes and the number of electrodes while maintaining safe current levels by using orthogonal frequencies and synchronous demodulation to minimize crosstalk and maximize signal-to-noise ratios, enabling accurate impedance measurement across multiple electrode pairs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple electrodes are used to improve contact status determination, then measurement precision is improved, but device complexity increases and current management becomes more difficult
Solution Approach 1:
The patent segments the measurement process by assigning unique identification frequencies to different electrodes. Each electrode is characterized by a specific frequency signature, allowing the system to independently measure impedance at multiple electrodes simultaneously without requiring complex switching or multiplexing circuitry. This frequency-based segmentation simplifies the overall system architecture while enabling precise contact status determination across multiple electrodes.
Solution Approach 2:
The patent changes the frequency parameter of drive signals to differentiate between multiple electrodes. By modulating each electrode's drive signal at a unique frequency, the system can distinguish and measure impedance at each electrode independently. This parameter-based differentiation allows simultaneous multi-electrode measurement without increasing hardware complexity, as the same physical circuitry can process multiple frequency components.
2Measurement precision
If drive current magnitude is increased to improve signal-to-noise ratio, then measurement precision is improved, but safety constraints are violated due to excessive auxiliary current
Solution Approach 1:
The patent employs periodic modulation of drive signals at unique frequencies for different electrodes. By using frequency-modulated periodic signals rather than continuous DC current, the system achieves several benefits: (1) the time-averaged auxiliary current is reduced compared to continuous DC, (2) the periodic nature enables synchronous demodulation to extract impedance information, and (3) different frequencies allow simultaneous multi-electrode operation within safety limits.
Solution Approach 2:
The patent changes the frequency parameter of drive signals to enable simultaneous operation at multiple electrodes within safe current limits. By distributing the total current across multiple frequency channels, each electrode receives adequate current for accurate measurement while the sum of all currents remains below safety thresholds. This frequency-domain multiplexing allows the system to achieve high signal-to-noise ratios without violating auxiliary current constraints.
3Productivity
If multiple drive signals are applied simultaneously to increase number of electrodes interrogated, then productivity is improved, but crosstalk between channels increases
Solution Approach 1:
The patent segments the frequency spectrum into distinct channels, with each electrode assigned a unique frequency. This frequency segmentation creates orthogonal measurement channels that minimize mutual interference. By separating the measurement space into frequency domains rather than using spatial or temporal multiplexing, the system achieves high productivity with minimal crosstalk, as each frequency component can be independently extracted through synchronous detection.
Solution Approach 2:
The patent applies preliminary frequency modulation to each drive signal before application to the electrodes. By pre-assigning unique frequencies to each electrode's drive signal, the system establishes orthogonal channels in advance. This preliminary frequency assignment enables the measurement circuitry to selectively respond to each frequency component, effectively preventing crosstalk before it can occur during the measurement process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases the number of electrodes that can be interrogated and the magnitude of drive current applied while keeping the sum current below safe thresholds, enhancing the accuracy and reliability of contact status determination without overwhelming noise.
Implementation Method 1
measuring impedances between individual pairs of electrodes of the connected medical device
Implementation Method 2
A demodulator is configured simultaneously demodulate the response signal(s) for each unique modulation frequency
Data Source
AI summary
The present disclosure is directed to measuring impedance across a plurality of electrode pairs. The disclosed systems and methods may simultaneously provide drive signals between electrode pairs and then sense the voltage signals that develop at the electrodes. Digital signal processing may be used to synchronously demodulate the voltage signal at each electrode to determine impedances at the electrodes. Each electrode pair may be driven at a unique frequency to allow for significantly increasing a number of electrode pairs and/or increasing drive current magnitudes. Synchronous demodulation allows the unique frequencies to be detected independent of each other while minimizing crosstalk. Typically, the drive frequencies are made orthogonal by setting the drive frequencies at harmonics of a common base frequency and measuring a response over an integer number of cycles. In an embodiment, quadrature demodulation may occur providing a real component for resistive impedance and an imaginary component for reactive impedance.