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Project ID: 2005KS40B

Title: A Real-Time Permittivity Sensor for Simultaneous Measurement of Multiple Water-Quality Parameters

Project Type: Research

Start Date: 03/01/2006

End Date: 02/28/2007

Congressional District: 2

Focus Category: Water Quality

Keywords: water quality, permittivity, dielectric constant, conductivity, sensor, frequency-response method

Principal Investigators: Zhang, Naiqian; Barnes, Philip; Kluitenberg, Gerard; Ziegler, Andre

Federal Funds: $23,000

Non-Federal Matching Funds: $48,276

Abstract: This is the continuation of an existing KWRI project. The main objective of the proposed work is to develop a novel, frequency-response-based permittivity sensor to detect and measure the concentrations of several types of pollutants in surface and ground water that are crucial to water quality.

Since the beginning of the project in March 2003, we have designed and fabricated the sensor and associated signal conditioning, processing, and control circuit. For the sensor, we used a cascaded-electrode structure to enlarge the capacitive effect. The hardware included a signal generator board, a gain and phase detector board, and a microcontroller to control the boards.

Laboratory tests were conducted to observe the frequency response (gain and phase) of different types of waters, including lake, stream, tap, and distilled waters, and air. Significant differences were observed in both gain and phase responses. For waters, the differences were found mainly in frequencies below 35 MHz. However, between two different types of dielectric materials, such as water and air, the differences can be seen throughout the 200 Hz-120 MHz frequency range tested. This gives a clear indication that the sensor is capable of detecting differences in dielectric properties.

Water samples with different combinations of soil sediment and salt (KCI) concentration levels were tested using a circulation system that provided uniform sediment concentrations. The sensor accurately measured KCI concentrations at each sediment concentration level. For sediment concentration measurement, the sensor only gave accurate measurement in water without added KCI and with KCI concentration of higher than 5.000 mg/L. For simultaneously measurement, the R-square values reached 0.86 and 0.87 for KCI and sediment, respectively.

During the second year, a systematic experiment will be conducted in laboratory to test the sensor with different types and amounts of sediments nutrients, and pesticides. First, these parameters will be measured separately to study effects of different pollutants on the conductive and capacitive behaviors. Combinations of the parameters will then be measured simultaneously using prediction models established based on the frequency-response data. Various pattern-recognition methods, including statistical multivariate analyses and neural networks, will be used to establish the prediction models.

Field tests will then be conducted at existing USGS real-time continuous stream and lake monitoring installations with the cooperation of USGS water quality specialists.

Based on experiences obtained from the laboratory and field tests, the sensor?s structure will be further improved to enhance the portability and ease-of-use. The hardware will be modified to reduce the effect of parasitic impedance that may affect the high-frequency performance of the sensor. Different options for data storage and transmission will be studied. One of them will be real-time, wireless transmission to the Internet through a commercial wireless-phone system.

Progress/Completion Report, PDF

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