Self-Calibrating Ion Meter Using Dual ISFETs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ion meter systems, such as ISFET devices, require frequent recalibration due to changes in resistive properties over time, making them impractical for long-term ion concentration measurements.
Innovation Solution
The use of two ISFET devices with different gate surface areas allows for self-calibration by comparing the electric activity across their gates, eliminating the need for recalibration before each use and enabling extended period measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single ISFET device is used for ion concentration measurement, then the device structure is simple, but the device requires frequent recalibration due to changes in resistive properties over time
Solution Approach 1:
The system is divided into two ISFET devices with different gate surface areas. The first ISFET serves as the measurement sensor while the second ISFET serves as a calibration reference. This segmentation allows the measurement function and calibration function to be separated, enabling automatic calibration without requiring external calibration substances or complex recalibration procedures.
Solution Approach 2:
The system performs self-calibration by using the ratio of responses between the two ISFET devices with different gate areas. Since both devices are subject to the same environmental conditions and aging effects, the ratio method automatically compensates for drift in resistive properties, eliminating the need for external calibration substances or manual recalibration by the user.
2Ease of operation
If multiple identical ISFET transistors are used for self-calibration, then calibration can be performed without external substances, but not all transistors are completely identical and they cannot all change in resistive properties in the same manner over time
Solution Approach 1:
Instead of using identical ISFET transistors, the invention uses two ISFETs with deliberately different gate surface areas. This parameter difference creates a predictable relationship between the two devices' responses to pH changes. By measuring the ratio of their responses and using the known area ratio, the system can accurately determine pH while compensating for individual device variations and aging effects.
3Ease of operation
If ISFET devices are used without calibration, then the operation is simple, but the measurements become inaccurate after a week's time
Solution Approach 1:
The system continuously performs calibration measurements by repeatedly measuring the responses of both ISFET devices and calculating the pH based on their ratio. This continuous calibration process ensures that the measurement remains accurate throughout extended periods of use, eliminating the need for periodic manual recalibration while maintaining measurement precision.
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 allows for stable and accurate ion concentration measurements over time without the need for frequent recalibration, improving the reliability and usability of ion meter systems.
Implementation Method 1
use ion-sensitive field effect transistor (ISFET) devices to measure the concentration of ions in a solution
Data Source
AI summary
An ion meter is calibrated by providing two ISFETS with different areas, where the two gate areas are used to calibrate the two ISFETS with respect to one another. The use of two ISFET gates that can be calibrated with respect to one another eliminates the need for an ion meter to be recalibrated before every use, and allows the ion meter to measure the concentration in the solution over an extended period of time.