Contactless, Transformer-Based Measurement of the Resistivity of Materials
Patent Information:
1. Filing Country: USA
Application No: 09/907817
Filing Date: 19 July 2001
Patent No: 6639401
Issue Date: 28 October 2003
2. Filing Country: China
Application No: 02126224.1
Filing Date: 16 July 2002
Patent No: ZL02126224.1
Issue Date: 07 December 2005
Inventor 1: Mr. Wenlai, LI
Inventor 2: Prof. Zongjin, LI

Traditional methods for resistivity measurements of concrete have to use two plate electrodes at opposite sides of a prism specimen. The major drawback of such a method is that the electrodes can be easily detached from the specimen due to shrinkage of concrete. Thus the measurement of resistivity is not accurate and sometimes easily has an unacceptable error. To get accurate measurement of resistivity of cement-based materials, a new device is invented. The new device utilizes a toroidal current principle. The concrete to be measured is case into a ring shape specimen and acts as the secondary of a transformer. A formulae to provide accurate resistivity of concrete has been developed according to the relationship between the toroidal current, the toroidal voltage and the phase difference between them.
Potential Application   Advantage
- Electrical property measurement of cement-based and/or concrete-like materials
- Material properties monitoring during construction
  This new method is strict and sound in both theory and practice. It can provide the accurate measurement of electrical properties for materials, especially cement-based ones. The non-contact measurement without electrodes for electrical properties and the new formula to obtain resistivity are also new in this field.

The introduction of this invention solves the problem of inaccuracy measurement of electrical properties due to insecure electrode contacting and resistivity calculation in a toroidal current situation.
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Contact information :
Ms Shirley Woo
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HKUST R and D Corporation Ltd
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Technology Transfer Center
香港九龍清水灣 香港科技大學