Principle Investigator: Prof. Alexander Mamishev
Graduate Students: Xiaobei Li, Kishore Sundara Rajan
Active industrial collaborators: Kraft, Metso Automation , Procter & Gamble
The project explores the possibility of using fringing electric field sensors to measure moisture content in organic materials.
By integrating moisture sensors in the production line, feedback control of the product's moisture content can be achieved.
Samples we are currently working with include cookies and paper pulp.
Transformation from parallel plate capacitor to coplanar electrodes with fringing electric field lines penetrating into the dielectric
Multi-wavelength Fringing Electric Sensor
|Offers non-destructive, one-side access.|
|Penetration depth are proportional to the distance between driving and sensing electrodes.|
|By varying excitation patterns, multiple penetration depth are acheivable.|
|nFringing electric fields can detect various characteristics of a sample.|
|Most samples vary in multiple ways – all of which affect the output signal.|
In the case of this project, we are trying to measure the moisture concentration within the samples.
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.
|Copper electrodes on flexible hydrophobic substrate|
|Three sensor head with different wavelengths (distance between fingers) mounted on the same substrate.|
|Varying penetration depths at different locations of the sample are acheivable.|
Three-channel parallel plate sensor
Driving plane on top and three sensing plate at the bottom.
Signals sent to measurement circuit through shielded coaxial wires.
Designed specially for measuring radial diffusion of moisture out of a regular-sized cookie.
|The signal generator sends out a sinusoidal frequency sweep signal (usually from 10Hz to 100 kHz) to drive the sensor array.|
|Measurements from the sensing electrodes get sent to the measuring circuit (sensor interface).|
|All measurements get collected by the computer through the DAQ board.|
|nFind dependence of electrical measurements (transimpedance) on the moisture level of cookies.|
|Compensate for disturbance factors, e.g. geometric shape, density, porosity of the cookie, and environment temperature and humidity.|
|Determine analytical function between transimpedance and moisture by curve fitting the compensated data.|
Current Experimental Procedure
|Sensor array driven by a 6V sinusoidal frequency sweep from 10 Hz to 100 kHz.|
|Start with an original cookie from the store, gradually add water to the center of the cookie.|
|Measurements from all 3 sensor heads collected simultaneously.|
Capacitance measurements against moisture levels of a cookies.
|A general trend exists in the above plot.|
|For all frequencies, capacitance increases with increasing moisture level.|
|A near-linear dependence is demonstrated.|
|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.