The permittivity (dielectric properties) of a material is one of the factors that determine how the material interacts with an electromagnetic field. The knowledge of the permittivity of materials and its frequency and temperature dependence is important in various areas of science and engineering in both basic and applied research. It has always been an important quantity to electrical engineers and physicists involved in the design and application of circuit components. Over the past several decades the knowledge of permittivity has become an important property to scientists and engineers involved in the design of stealth vehicles. These applications are most often associated with the defense industry. For the typical electrical engineer permittivity is a number that is needed to apply Maxwell’s equations. Besides discussing the various techniques that can be used to measure permittivity, one of the purposes of the course is to explain why a material has a particular permittivity. The short answer is that a material has a particular permittivity because of its molecular structure. Another purpose is show how permittivity can be related to other physical material properties.
The knowledge of permittivity has become increasingly important to additional scientific disciplines. Agricultural engineers, biological engineers, biomedical engineers, chemists and food scientists have found applications for the knowledge of a materials permittivity. The most obvious application of this knowledge is in microwave and RF heating of food products. Here the knowledge of permittivity is important in determining how long a food item needs to be exposed to the RF or microwave energy for proper cooking. For prepackaged food items, the knowledge of the permittivity of the packaging materials is also important. The electromagnetic interaction with the packaging material also determines the cooking time. Besides these obvious applications there are also numerous not-so-obvious applications. Permittivity can often be related to a physical parameter of interest. This is because a change in the molecular structure or composition of a material results in a change in its permittivity. It has been reported that material properties such as moisture content, fruit ripeness, bacterial content, mechanical stress, tissue health and other seemingly unrelated parameters are related to the permittivity of the material. Many key parameters of colloids such as structure, consistency and concentration are directly related to permittivity. Yeast concentration in a fermentation process, bacterial count in milk, and the detection and monitoring of microorganisms are a few examples on which research has been reported. Diseased tissue has a different permittivity from healthy tissue. Accurate measurements of these properties can provide scientists and engineers with valuable information that allows them to properly use the material in its intended application or to monitor a process for improved quality control.
Tutorial outline: The following topics will be included in the proposed tutorial.
- Definition of Electromagnetic Materials Properties and their relationship to molecular structure and composition.
- Maxwell’s equations
- Non-magnetic materials
- Applications where the knowledge of permittivity is useful
- Electrical Engineering
- Chemical processes
- Measurement instrument
- Vector network analyzer
- Instrument calibration
- An overview of permittivity measurement techniques
- Transmission line techniques
- Resonant cavity techniques
- Open-ended coaxial line techniques
- Open-ended waveguide techniques
- Free-space techniques
- Measurement demonstration
- Transmission line techniques
- Free-space techniques
Dr. Bartley received a BS and MS in Electrical Engineering from Old Dominion University in 1973 and 1976. He received his Ph.D. from the University of Georgia in 2005. He is a Senior member of IEEE. He was a lecturer in the I&M Society Distinguished Lecturer Program. He reviews papers for the society. His work experience includes positions at several US Naval facilities. His duties included writing software for computer aided test systems. These systems included avionics, mines, guided bombs and missiles. He was a microwave systems engineer and district manager at the Hewlett Packard Company, HP, in the 1980’s (the instrument portion of HP split off to become part of Agilent Technologies and is now Keysight Technologies). He developed the materials measurement software that was marketed as HP/Agilent/Keysight 85070, 85071 and N1500. He has taught at the Southern Polytechnic State University, Old Dominion University and the University of Georgia. In 1997, he was named ASAE teacher of the year at the University of Georgia. While at Georgia he worked with the Agricultural Research Service of the USDA. This work involved measuring the permittivity of agricultural products. These measurements can be correlated to moisture content, fruit ripeness and product quality. He has had numerous technical papers published on the measurement and application of the electromagnetic property of materials. His current interests include developing measurement techniques for low-loss materials and measurements techniques in the Terahertz frequency range. He also has an interest in using electromagnetic property measurements as a sensor for agricultural, pharmaceutical, medical, biological and chemical processes.