Principle Investigator: Prof. Alexander Mamishev
Graduate Students: Xiaobei Li, Kishore Sundara Rajan
Active industrial collaborators: Kraft, Metso Automation , Procter & Gamble
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The project explores the possibility of using fringing electric field sensors to measure moisture content in organic materials. |
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By integrating moisture sensors in the production line, feedback control of the product's moisture content can be achieved. |
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Samples we are currently working with include cookies and paper pulp. |
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Transformation from parallel plate capacitor to coplanar electrodes with fringing electric field lines penetrating into the dielectric |
Multi-wavelength Fringing Electric Sensor
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Offers non-destructive, one-side access. |
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Penetration depth are proportional to the distance between driving and sensing electrodes. |
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By varying excitation patterns, multiple penetration depth are acheivable. |
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nFringing electric fields can detect various characteristics of a sample. |
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Most samples vary in multiple ways – all of which affect the output signal. |
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In the case of this project, we are trying to measure the moisture concentration within the samples. |
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The challenge is to decouple the information and remove the effect of other characteristics to determine the functional dependence of moisture on the electrical measurements. |
Three-wavelength fringing electric field sensor.
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Copper electrodes on flexible hydrophobic substrate |
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Three sensor head with different wavelengths (distance between fingers) mounted on the same substrate. |
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Varying penetration depths at different locations of the sample are acheivable. |
Three-channel parallel plate sensor
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Driving plane on top and three sensing plate at the bottom. |
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Signals sent to measurement circuit through shielded coaxial wires. |
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Designed specially for measuring radial diffusion of moisture out of a regular-sized cookie. |
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The signal generator sends out a sinusoidal frequency sweep signal (usually from 10Hz to 100 kHz) to drive the sensor array. |
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Measurements from the sensing electrodes get sent to the measuring circuit (sensor interface). |
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All measurements get collected by the computer through the DAQ board. |
Milestones
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nFind dependence of electrical measurements (transimpedance) on the moisture level of cookies. |
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Compensate for disturbance factors, e.g. geometric shape, density, porosity of the cookie, and environment temperature and humidity. |
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Determine analytical function between transimpedance and moisture by curve fitting the compensated data. |
Current Experimental Procedure
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Sensor array driven by a 6V sinusoidal frequency sweep from 10 Hz to 100 kHz. |
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Start with an original cookie from the store, gradually add water to the center of the cookie. |
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Measurements from all 3 sensor heads collected simultaneously. |
Capacitance measurements against moisture levels of a cookies.
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A general trend exists in the above plot. |
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For all frequencies, capacitance increases with increasing moisture level. |
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A near-linear dependence is demonstrated. |
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By curve fitting, the functional dependence of capacitance on moisture can be determined. |
Capacitance measurements against moisture content of paper pulp.
Note that the percentages shown in the above plot are those for the paper content (not water content) in the paper pulp.