1. ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA An energy efficient wearable tissue monitor ANNUS, Paul; MIN, Mart; PARVE, Toomas; LAND, Raul; HALDRE, Eero; KUUSIK, Alar; POOLA, Gustav

2. Why, what and how ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Need for monitoring of the tissue parameters after transplantation Two primary characteristics of tissue are considered for measurement:  Bioimpedance  Temperature Healing process is relatively slow Multiple simultaneous measurement points are needed Shortened pulse wave measurement of impedance and temperature is used Primary circuitry is preferably close to tissue sample RF link to data collecting and processing equipment - PC

3. In July of 1886 Oliver Heaviside introduced term "impedance" In 1893, Arthur Edwin Kennelly presented a paper on 'Impedance" to the American Institute of Electrical Engineers in which he discussed the first use of complex numbers as applied to Ohm's Law in alternating current circuit theory. Electrical impedance is a measure of opposition to a sinusoidal electric current. How to measure tissue parameters? Impedance Temperature ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA

4. Bioimpedance Essentials of the Electrical Bioimpedance EBI 3-element equivalent of the static EBI phasor diagram of the static EBI for two frequencies, low ω l and high ω h. r int C r ext ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA

5. Design choices ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Excitation waveform Analog versus Digital Current sources Multisensor or small single device Electrodes Current consumption Frequency range and Impedance range Speed User interface and representation of results

6. Sinusoidal signal(s) and square wave ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 4.0 -1.0 0.0 1.0 2.0 3.0 1000 0 1 10 100 0 0.01 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0.00 100001101001000 Frequency responses (kHz) of relative magnitude errors (a) and phase errors (b) caused by odd harmonics of the order of 3, 5, 7, 9, 11, and 13 in the case of using regular rectangular waveforms for both, excitation and reference signals when measuring 3-element bioimpedance equivalent with a pole at f1 = 160 kHz, and a zero at f2 = 2.5f1 in its frequency response. (Multi) Sinusoidal signal:  accurate measurements according to definition  not very easy to generate Square wave signal:  extremely easy to generate with almost any digital circuitry  large measurement errors due to higher harmonics

7. Shortened rectangular pulses The 1 st harmonic All the harmonics are coinciding Relative magnitude of harmonic t/T 18º 30º The 1 st harmonic Relative magnitude of harmonic The coinciding harmonics a is the constant amplitude value of the pulse signal, and β characterizes the shortening of pulses and is equal to the signal’s zero value interval within one half period β = 0 … pi / 2 a) square wave excitation and demodulation b) same with shortened pulses ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA

8. From almost analog… ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA VZVZ V ref,Re I exc V ref,Im V Re V Im t;  T exc 18  30  90  Analog synchronous detection waveforms for synchronous detection

9. … to mostly digital - ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA sampling and processing of the signal: (a)uniform sampling with 6°distance between samples (b)366° undersampling Digital multichannel solution

10. Device ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Block diagram of the measurement unit

11. Current sources I ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA

12. Current sources II ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA

13. Electrodes ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Needles from ordinary disposable hypodermic syringe ETHICON Surgical Stainless Steel Suture - Temporary Pacing Wire

14. Current consumption ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Design errors (LFO, SWPS) – 10 mA AD8251 – 4x5mA Oscillator (12 MHz) – 2 mA Microcontroller (AVR) – 10 mA Bluetooth – 15 mA Power supplies – 10 mA Average (Agilent 34410A) – 100 mA Device start | communication start | measure

15. User interface and some results ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA 270 ohms, all 4 channels 270 ohms parallel with 0,25 uF (2358 Hz)

16. Where to go from here ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA Final sensor unit to build, with:  Current source  Preamplifier  Integrated electrode temperature probe Search for new waveforms for measurement Compact and meaningful representation of measured parameters Search for even lower power solutions

17. Acknowledgements THANK YOU ! ICEBI ’07 ICEBI ’07 August 29th – September 2nd 2007 in GRAZ, AUSTRIA work was supported by grants no. 7212 and 7243 of Estonian Science Foundation, and by Enterprise Estonia through the Competence Centre ELIKO