For the needs of bladder urinary volume noninvasive monitoring in clinical, we present a noninvasive bladder urinary volume monitoring system based on bio-impedance. The system uses a four-electrode structure,which is composed of a pair of excitation electrodes and a pair of measurement electrodes. The Direct Digital Frequency Synthesis (DDS) is applied to generate a 50 kHz sine current excitation source. The impedance information extracted from phase sensibility demodulation technology is transferred to a computer through Zigbee wireless technology for real-time monitoring. Two experiments are taken to verify the accuracy and feasibility of the system. The experiments results show that the system can accurately measure the corresponding electrical impedance change of the bladder. The system provides a new way to continuously and noninvasively monitor the bladder urinary volume of patients with bladder dysfunction.
 J. W. Warren, “Catheter-Associated Urinary Tract Infections,” Infectious Disease Clinics of North America, Vol. 11, No. 3, 1997, pp. 609-622. http://dx.doi.org/10.1016/S0891-5520(05)70376-7
 J. Y. Hwang, et al., “Novel Algorithm for Improving Accuracy of Ultrasound Measurement of Residual Urine Volume According to Bladder Shape,” Urology, Vol. 64, No. 5, 2004, pp. 887-891. http://dx.doi.org/10.1016/j.urology.2004.06.054
 Y. K. Huang, Y. H. Jing, Z. Zheng and Y. Ran, “Three Dimension Ultrasound Research Platform Based on Virtual Instrument and Clinical Application,” Journal of Electronic Measurement and Instrument, Vol. 22, No. Z1, 2008, p. S2.
 H. J. Niu, et al., “Design of an Ultrasound Bladder Volume Measurement and Alarm System,” 5th International Conference on Bioinformatics and Biomedical Engineering, Wuhan, 10-12 May 2011, pp. 1-4.
 M. A. Talibi, et al., “A Model for Studying the Electrical Stimulation of the Urinary Bladder of Dogs,” British Journal of Urology, Vol. 42, No. 1, 1970, pp. 56-65. http://dx.doi.org/10.1111/j.1464-410X.1970.tb11908.x
 F. M. Waltz, G. W. Timm and W. E. Bradley, “Bladder Volume Sensing by Resistance Measurement,” IEEE Transactions on Biomedical Engineering, Vol. 1, No. 1, 1971, pp. 42-46. http://dx.doi.org/10.1109/TBME.1971.4502788
 W. C. Liao and F. S. Jaw, “Noninvasive Electrical Impedance Analysis to Measure Human Urinary Bladder Volume,” Journal of Obstetrics and Gynaecology Research, Vol. 37, No. 8, 2011, pp. 1071-1075. http://dx.doi.org/10.1111/j.1447-0756.2010.01487.x
 K. S. Cole and R. H. Cole, “Dispersion and Absorption in Dielectrics I. Alternating Current Characteristics,” The Journal of Chemical Physics, Vol. 9, No. 4, 1941, pp. 341. http://dx.doi.org/10.1063/1.1750906
 Rigaud, B., et al., “In vitro Tissue Characterization and Modeling Using Electrical Impedance Measurements in the 100 Hz-10 MHz Frequency Range,” Physiological Measurement, Vol. 16, No. 3A, 1995, p. A15.