ISFET Ion Sensor Voltage Control for Stable pH Measurement
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Solution Overview
Problem
Current methods for continuously measuring ion concentration, such as those using litmus paper, glass electrodes, and ISFETs, face challenges with clogging and temporal fluctuations, making it difficult to obtain stable signals over long periods, especially in agricultural applications like soil pH measurement.
Innovation Solution
An ion concentration measuring device with a power supply control unit that manages the voltage between a measurement target and a measurement ion-sensitive membrane, ensuring the polarity of the membrane voltage matches non-measurement ions and reducing the voltage difference to prevent infiltration, thereby stabilizing the signal over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a glass electrode with liquid dropping portion is used to ensure electrical connection, then electrical connection is improved, but the liquid dropping portion is easily clogged
Solution Approach 1:
The patent extracts and eliminates the liquid dropping portion from the electrode structure. By using a solid contact electrode that directly contacts the measurement target without requiring liquid droplets, the invention removes the component that is prone to clogging while maintaining electrical connection functionality.
Solution Approach 2:
The patent introduces a different intermediary mechanism - a solid contact interface with controlled electrical properties - to achieve electrical connection without using liquid droplets. This intermediary layer enables charge transfer while being resistant to clogging from fine particles in the measurement target.
2Measurement precision
If ISFET is used for measurement, then measurement capability is improved, but temporal property fluctuation (drift) occurs in the output
Solution Approach 1:
The patent changes the electrical parameters (voltage levels) applied to the ISFET structure. By controlling the voltage between the measurement target and the ion-sensitive membrane, and adjusting the membrane voltage polarity to match non-measurement ions, the invention suppresses drift while preserving measurement capability.
Solution Approach 2:
The patent applies preliminary control actions by setting specific voltage conditions before measurement begins. The power supply control unit pre-establishes voltage relationships that prevent non-measurement ions from interfering with the measurement, thereby preventing drift before it occurs.
3Duration of action of stationary object
If continuous measurement is performed over long period, then measurement duration is improved, but signal stability deteriorates due to drift
Solution Approach 1:
The patent maintains continuous useful action by implementing ongoing voltage control through the power supply control unit. The system continuously adjusts and maintains optimal voltage relationships between measurement components, ensuring stable operation over extended periods without signal drift.
Solution Approach 2:
The patent incorporates feedback control through the power supply control unit, which monitors and adjusts voltage levels to maintain stable measurement conditions. This feedback mechanism compensates for environmental changes and maintains signal stability throughout continuous operation.
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
The device enables continuous and stable ion concentration measurement over long periods by suppressing drift caused by non-measurement ions, ensuring accurate and reliable data collection.
Implementation Method 1
a measurement ion sensitive membrane selectively trapping the measurement ions to generate a voltage corresponding to the number of trapped measurement ions
Implementation Method 2
the power supply control unit controls the measurement target power supply and the measurement membrane power supply, and thus, the polarity of the measurement membrane voltage with respect to the measurement target voltage can be identical to the polarity of the non-measurement ions
Implementation Method 3
According to such a relationship between the measurement target voltage and the measurement membrane voltage, the non-measurement ions are not attracted to the measurement ion sensitive membrane
Data Source
AI summary
A pH sensor obtains the concentration of measurement ions by being provided in a measurement target containing the measurement ions and non-measurement ions. The pH sensor includes: a measurement target power supply that controls a measurement target voltage of the measurement target; a measurement ISFET that includes a measurement ion sensitive membrane selectively trapping the measurement ions to generate a pH-dependent voltage corresponding to the number of trapped measurement ions; a measurement membrane power supply that controls a membrane control voltage of the measurement ion sensitive membrane; and a power supply control unit that controls the size of a voltage to be output from each of the measurement target power supply and the measurement membrane power supply.