1 / 25

IIT Bombay

A High Sensitivity Bioimpedance Detector B. B.  Patil P. C.  Pandey V. K.  Pandey S. M. M. Naidu. National Conference on Virtual and Intelligent Instrumentation (NCVII -09), BITS Pilani, 13-14 Nov. 2009 ______________________________________________________________. IIT Bombay.

dylan-jimenez
Download Presentation

IIT Bombay

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A High Sensitivity Bioimpedance DetectorB. B. PatilP. C. PandeyV. K. PandeyS. M. M. Naidu National Conference on Virtual and Intelligent Instrumentation (NCVII -09), BITS Pilani, 13-14Nov. 2009 ______________________________________________________________ IIT Bombay

  2. Presentation Outline • Introduction • Bioimpedance Detector Circuit • Test Results • Conclusion

  3. Introduction • Bioimpedance Detector Circuit • Test Results • Conclusion

  4. Introduction (1/4) Sensing of the Variation in the Bioimpedance Noninvasive technique for monitoring ♦ changes in the fluid volume ♦ underlying physiological events Impedance Cardiography A noninvasive technique for monitoring stroke volume and obtaining diagnostic information on cardiovascular functioning by sensingthe variation in the thoracic impedance during the cardiac cycle. Sensing of the Thoracic ImpedanceA current ( 20 kHz – 1MHz, <5mA) passed through a pair of surface electrodes and the resulting amplitude modulated voltage sensed using the same or another pair of electrodes.

  5. Introduction (2/4) ICG Instrumentation

  6. Introduction (3/4) Bioimpedance Detection ♦ Detection of extremely low modulation index ( 0.2 – 2 %)♦ External noise suppression ♦ Carrier ripple rejectionAM Detector Ckts ♦Peak detector ♦Precision rectifier det. ♦ Synchronous det.♦ Slicing amplifier det. (Fourcin, 1979): high sensit., increased ripple♦ Synchronous S/H at carrier peak: very low ripple

  7. Introduction (4/4) Proposed Technique Features♦High sensitivity♦Carrier ripple suppression without filtering♦ Noise reductionRealization ♦ Slicing amplifier with sampling at the peaks of the sinusoidal excitation : high sensitivity, low ripple ♦ Summation of the signals obtained by sampling the +ve & -ve peaks : external noise reduction

  8. Introduction • Bioimpedance Detector Circuit • Test Results • Conclusion

  9. Bioimpedance Detector Ckt(1/6) Demodulation ♦ Two channels of slicing amplifier with synch. S/H at the +ve and –ve peaks of the excitation ♦ Addition of the two outputs: suppression of noise & low freq. drift Slicing Amplifier ♦ Realized using voltage clamp amplifier IC AD8037 (Greater of the V+ & VL inputs connected as the non-inverting input) ♦ Cktconfig. and resistors selection: ♦ V+ > VL: Output diff. i/p ♦ V+ < VL: Zero output Sample-and-hold (IC HA5351) Sampled near the excitation peak & held for ripple suppression

  10. Bioimpedance Detector Ckt(2/6) Demodulator using Slicing Amplifier & S/H IC3 : AD8037 voltage clamp amp., IC4: HA5351 S/H

  11. Bioimpedance Detector Ckt(3/6) Slicing Amplifier Waveforms Vo1: slicing amp o/p Vo2: S/H o/p

  12. Bioimpedance Detector Ckt(4/6) Bioimpedance Detector AM demod. of the sensed voltage using two channels of slicing amplifier with sync. S/H

  13. Bioimpedance Detector Ckt(5/6) Sinusoidal Excitation & S/H Pulse Generation Two direct digital synthesizer (DDS) chips (AD 9834) ♦DDS-1: Sinusoidal o/p for current excitation ♦ DDS-2: Square o/p with settable phase shift for S/H pulses Circuit Features Microcontroller based digital control of ♦ Excitation current level using a digital pot. ♦ Excitation frequency ♦ Slicing amplifier ref. level, using a digital pot. ♦ Phase shift between the two DDS outputs for precise alignment of hold edge of S/H pulses to the +ve and –ve peaks of the excitation

  14. Bioimpedance Detector Ckt(6/6) Detector Ckt Waveforms Vs: DDS-1 o/p (exc.) VΦ: DDS-2 o/p (phase shifted w.r.t. Vs) V3 & V4: slicing amp. Outputs V5 & V6: S/H outputs VSH1 & VSH2: sampling pulses

  15. Introduction • Bioimpedance Detector Circuit • Test Results • Conclusion

  16. Test results (1/5) Impedance Detector Performance Parameters ♦ Range of basal resistance ♦ Sensitivity (ΔVo / ΔR) ♦ Frequency response Thorax Simulator for Testing the Bioimpedance Detector ♦ Basal resistance (settable: 20  200 ) ♦ Periodic resistance variation (settable: 0.1  1.2 %) ♦ µC & digital pot.: settable ΔR, F, waveshape

  17. Test results (2/5) Thorax Simulator Ckt I1 & I2: current injection E1 & E2: voltage sensing ♦ Variation in the thorax impedance ♦ DM & CM voltages (ECG) ♦ Sync. output

  18. Test results (3/5) Microcontroller and Power Supply Ckt of the Thorax Simulator

  19. Test results (4/5) Testing Using the Thorax Simulator ♦ Excitation: 1 mA rms, 100 kHz ♦ Thorax Simulator F: 1 - 250 Hz Ro = 196  ΔR / Ro = 0.1 to 1.2%

  20. (a) (b) (c) (d) Vo Vo Vo Vo Test results (5/5) Sync. & Det. Output Waveforms F = 8 Hz, Ro = 196 . Resistance variation ΔR / Ro: • 1.2 % sinusoidal • 0.6 % sinusoidal • 1.2 % square • 0.6 % square • Time scale: 40 ms/div, Ch1: 5 V/div, Ch2: 500 mV/div.

  21. Introduction • Bioimpedance Detector Circuit • Test Results • Conclusion

  22. Conclusion (1/1) A bioimpedance detector for ICG instrumentation ♦ Slicing amplifier for AM demod. with mod. index < 2% ♦ Sync. sampling for ripple rejection without lowpass filtering the output ♦ Digital control of ▫ Exc. parameters (Frequency, current level) ▫ Demod. parameters (Slicing amp. ref., Φ-shift for sync. S/H) Ckt operation verified using a thorax simulator for detecting ΔR / Rowell below 2%, sinusoidal & square wave variations with freq. of 1 - 250 Hz.

  23. THANK YOU

  24. B. B. Patil, P. C. Pandey, V. K. Pandey, and S. M. M. Naidu, “A high sensitivity bioimpedance detector”, Proc. National Conference on Virtual and Intelligent Instrumentation (NCVII-09), BITS Pilani, 13-14Nov. 2009.Abstract: A bioimpedance detector is developed as part of instrumentation for impedance cardiography. It uses slicing amplifier for increasing the sensitivity for the impedance variation and synchronous sampling for a ripple-free output. The circuit provides digital control of excitation current and frequency used for the measurement. Its operation has been verified using a thorax simulator for detecting the impedance variations well below 2%. Prof. P. C. Pandey Address: EE Dept. / IIT Bombay / Powai Mumbai 400 076 / India / E-mail: pcpandey [at] iitb.ac.in

  25. References • J. Nyboer, Electrical Impedance Plethysmography. 2nd ed., Springfield, Massachusetts: Charles C. Thomas, 1970. • L. E. Baker, "Principles of impedance technique", IEEE Eng. Med. Biol. Mag., vol. 8,pp. 11 - 15, 1989. • M. Min, T. Parve, A. Ronk, P. Annus, and T. Paavle, "Synchronous sampling and demodulation in an instrument for multifrequency bioimpedance measurement", IEEE Trans. Inst. Measurements, vol. 56, pp. 1365 - 1372, 2007. • W. G. Kubicek, F. J. Kottke, and M. U. Ramos, "The Minnesota impedance cardiograph – theory and applications", Biomed. Eng., vol. 9, pp. 410 - 416, 1974. • M. Qu, Y. Zhang, J. G. Webster, and W. J. Tompkins, "Motion artifact from spot and band electrodes during impedance cardiography", IEEE Trans. Biomed. Eng., vol. 33, pp. 1029 - 1036, 1986. • J. Fortin, W. Habenbacher, and A. Heller, "Non-invasive beat-to-beat cardiac output monitoring by an improved method of transthoracic bioimpedance measurement", Comp. Bio. Med.,vol. 36, pp. 1185 - 1203, 2006. • J. N. Sarvaiya, P. C. Pandey, and V. K. Pandey, “An impedance detector for glottography”, IETE J. Research, vol 55, no. 3, pp 100-105, 2009. • A. J. Fourcin, "Apparatus for speech pattern derivation", U. S. Patent No. 4,139,732, Feb. 13, 1979. • B. B. Patil, "Instrumentation for impedance cardiography", M.Tech. Dissertation, Biomedical Engineering, Indian Institute of Technology Bombay, 2009. • V. K. Pandey, P. C. Pandey, and J. N. Sarvaiya, "Impedance simulator for testing of instruments for bioimpedance sensing", IETE J. Research, vol. 54, no. 3, pp. 203 - 207, 2008. • B. B. Patil, V. K. Pandey, and P. C. Pandey, "A microcontroller based thorax simulator for testing and calibration of impedance cardiographs", in Proc. Int. Symp. Emerging Areas in Biotechnology & Bioengineering (ISEABB), Mumbai, India, 2009, pp. 122-125.

More Related