Measurement of Moisture Distribution in Organic Materials

Principle Investigator: Prof. Alexander Mamishev

Graduate Students: Xiaobei Li, Kishore Sundara Rajan

Active industrial collaborators: Kraft, Metso Automation , Procter & Gamble

Table of Contents

  1. What is the goal of the project?
  2. What is a fringing electric sensor?
  3. What can a fringing field sensor measure ?
  4. What do the actual sensors look like?
  5. How is the measurement system set up?
  6. How do we go about measuring moisture in cookies?
  7. What are the recent experimental results?

What is the goal of this project?


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.

What is a fringing electric sensor?




   Transformation from parallel plate capacitor to coplanar electrodes with fringing electric field lines penetrating into the dielectric

Multi-wavelength Fringing Electric Sensor

bullet Offers non-destructive, one-side access.
bullet Penetration depth are proportional to the distance between driving and sensing electrodes.
bullet By varying excitation patterns, multiple penetration depth are acheivable.

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What can a fringing field sensor measure?

bullet nFringing electric fields can detect various characteristics of a sample.

bullet 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.

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What do the sensors look like?

Three-wavelength fringing electric field sensor.


bullet Copper electrodes on flexible hydrophobic substrate
bullet Three sensor head with different wavelengths (distance between fingers) mounted on the same substrate.
bullet 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. 

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How is the measurement system set up?

bullet The signal generator sends out a sinusoidal frequency sweep signal (usually from 10Hz to 100 kHz) to drive the sensor array.
bullet Measurements from the sensing electrodes get sent to the measuring circuit (sensor interface).
bullet All measurements get collected by the computer through the DAQ board.

Measurement circuit based on voltage divider.        Picture of a cookie on the sensor assembly.
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How do we go about measuring moisture in cookies?


bullet nFind dependence of electrical measurements (transimpedance) on the moisture level of cookies.
bullet Compensate for disturbance factors, e.g. geometric shape, density, porosity of the cookie, and environment temperature and humidity.
bullet Determine analytical function between transimpedance and moisture by curve fitting the compensated data.

Current Experimental Procedure

bullet Sensor array driven by a 6V sinusoidal frequency sweep from 10 Hz to 100 kHz.
bullet Start with an original cookie from the store, gradually add water to the center of the cookie.
bullet Measurements from all 3 sensor heads collected simultaneously.
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What are the recent experimental results?

 Capacitance measurements against moisture levels of a cookies.

bullet A general trend exists in the above plot.
bullet For all frequencies, capacitance increases with increasing moisture level.
bullet A near-linear dependence is demonstrated.
bullet 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.

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Xiaobei Li  Graduate Student, EE, University of Washington.
Copyright 2002  [SEAL]. All rights reserved.
Revised: 12/03/02.