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Signals in Bioimpedance Measurement: different waveforms for different tasks

ICEBI ’07 August 29 th – September 2 nd 2007 in GRAZ, AUSTRIA. TUT. Signals in Bioimpedance Measurement: different waveforms for different tasks. by Mart Min, Paul Annus, and Raul Land T allinn U niversity of T echnology, Tallinn, Estonia and

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Signals in Bioimpedance Measurement: different waveforms for different tasks

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  1. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA TUT Signals in Bioimpedance Measurement:different waveforms for different tasks by Mart Min, Paul Annus, and Raul Land Tallinn University of Technology, Tallinn, Estonia and Uwe Pliquett, Thomas Nacke, and Andreas Barthel, Institute of Bioprocessing and Analytical Measurement Techniques, Heilbad Heiligenstadt, Germany

  2. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 2 TUT I. Introduction • Fast frequency domain analysis of bioimpedance is required in: a) high throuput microfluidic devices, and b) real-time cardiac monitors and pacemakers. • Joint time-frequency analysisis needed, becausethe spectra are time dependent (time-frequency-intensity diagrams for Re and Im). Questions: 1) what kind of waveforms are suitable for excitation when the fast broadband analysis is required? 2) what kind of methods could be used for processing the responses to such excitations ? The presentation answers the first question, and discusses the second one as well.

  3. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 3 TUT 1.1. Focus:identifyingappropriate excitation waveforms for the fast time dependent spectral analysis a) b) c) d)

  4. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 4 TUT 2.1. Rectangular pulses II. Waveforms for excitation signals 1 0.707 2T 2/ of max value 1/T 2/T

  5. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 5 1.0 real sinc, limited to 6 periods real sinc, windowed by Hanning 6 periods = 12T 0 time 2T TUT 2.2. Sincfunctionssinc(ωt) = sin(ωt)/(ωt) Amplitude

  6. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 6 ideal sinc, unlimited duration real sinc, limited duration real sinc, windowedby Hanning TUT 2.3. Spectral density of sinc functions 1.0 6 periods = 12T 0 Spectral densitylinearscale 2T 1.0 0.5 0 0 1/2T lin f Spectral density, log-logscale 0 dB log f -6dB -40dB/dec 1/2T

  7. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 7 TUT 2.4. Sinc & haversincpulses sinc(x) = sin(x)/x 1.0 0.707 haversinc(x) = sin2(x)/ x time 2T 1/2T lin f

  8. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 8 TUT 2.5. Asinc (fs) modulation (AM) of sine wave carrier (fc) sinc(2pfs)٠sin(2pfc) time Rectangle BW=1/T Blackman-Harris fc- fs fc fc+ fs lin f

  9. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 9 TUT 2.6. ComparisonofGaussian&sincpulses Gaussian G(t) = A0exp(-0.5(t/s)2) TG max sin(ωt)/(ωt) 0.5max sinc(ωt) = 0 2T time max 0.5max 0 1/2T lin f 1/TG

  10. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 10 TUT 2.7. Comparison ofGaussian derivative&haversinc pulses Gaussian derivativedG(t)/dt Haversinc sin2(x) / x Haversinc 1/2T 1/T

  11. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 11 TUT 2.8. Using of chirp excitation Tpulse= 100ms = tobs amplitude time Responsefrom atransplanted muscle lin magn linear response 0 0 1MHz lin f BW = 10kHzto 1MHz log f log response 10kHz = 1/100ms 1MHz

  12. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 12 TUT III. Provisional experimentations 3.1. A microfluidic device and measurement set-up

  13. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 13 TUT T = 2us T = 25ns 3.2. Spectroscopy in microfluidic device: Gaussian excitation Magnitude in ohms Frequency in Hz Phase in degrees Frequency in Hz

  14. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 14 TUT 10us 100us 3.3. Spectroscopy in microfluidic device: Chirp excitation Magnitude in ohms Frequency in Hz Phase in degrees Frequency in Hz

  15. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 15 TUT V. Summary • Broadband excitation and the fast spectral analysis areadvantageous, when the lowered signal-to-noise ratio is acceptable; • Up to three decades of frequency range is feasible; • The chirp pulse is favoured because it features the highest flexibility; • The derivative of Gauss function and the haversinc function canbe also used, butonly a decade wide frequency band is covered. • Elaborating of the most suitable algorithms for processing the broadband responses is the next step of our studies; • The future task is to find reasonable combinations of both: a) rational excitation waveforms, and b) specific methods for processing of responses, for getting the best measurement results.

  16. ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 16 TUT Acknowledgements • The work was supported by • - the European Community (FP6, Marie Curie Fellowship, Transfer of Knowledge, project 29857 InFluEMP),and • Estonian Science Foundation(grants no. 7212, 7243), and • Enterprise Estonia through the Competence Centre ELIKO Thank you !

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