Research On The Digitized Measurement Platform Of Electrical Bioimpedance

The tissues and organs of human body have unique electrical characters, such as impedance, admittance and permittivity. The characters will vary with changes of physiological and pathological conditions during the process of metabolism. Electrical bioimpedance technology is a noninvasive detecting technique, which can extract biomedical information though the electrical properties of tissues and organs. It has many advantages, as noninvasive, inexpensive, safe and informative, but the greatest is extractions the functional or prospective information. So this technology is widely used in function evaluation of circulation system, early detection and diagnosis of cancer, gastric motility measurement, body composition determination and electrical impedance tomography.Based on the progress and theories of electrical bioimpedance technology, a research of digitized biological impedance measurement platform has been carried out based on FPGA, in order to meet the requirements of multi-frequency and complex impedance measurement. The main works and results are as follows:1. The digitized, multi-frequency and complex impedance measurement system is designed through analyzing the technological developments. Then the framework and functions of each module are devised after study the development and design methods of digital systems based on FPGA.2. Based on FPGA and DDS technology, the digital signal generator is designed and can provide multi-frequency excitation signals in the range of6.1KHz-390.6KHz. It adopts an improved Howland circuit to build constant current excitation source by THS4021device. The output impedance of the source is stability, it can maintain200K Ω in the range of6.1KHz-97.7KHz, and to170KΩ when the frequency is390.6KHz.3. In order to achieve complex impedance measurement. Demodulation and communication module are completed by FPGA according to the digital quadrate demodulation technology. Both the real and the virtual information of the measured impedance can be extracted, acquired and transferred.4. Measurements about resistor, capacitor, and three component models have been performed firstly to verify the validity of this platform. Then the flume around with16electrodes and filled with salt solution was used as the measuring field, through the imaging experiments by the mode of adjacent current incentives-adjacent voltage, it provides a foundation for the construction of EIT system.Finally, the summaries are presented, and some suggestions for improving the research platform are provided.