Measurement System for Mechatronic Property ofBiological Electrolyte Solution
with Micro-Vibrating Electrode
Takayuki Sekiyama, Shigehiro Hashimoto, Yusuke Morita, Tomohiro Sahara,Yuta Morioka, Teruyuki Yamanari, Kenichi Yamasaki, Hideo Kondo, Aki Nakajima
Biomedical Engineering, Dept. of Electronics, Information, and Communication Engineering,Osaka Institute of Technology, Osaka, 535-8585, Japan
hasimoto@elc.oit.ac.jp
andHajime Otani, Hiroji Imamura
Dept. of Thoracic and Cardiovascular Surgery, Kansai Medical University
Moriguchi, JapanABSTRACT
A new methodology to measure mechatronic propertyof biological electrolyte solution has been proposed,and measurement system has been designed with amicro-vibrating electrode. The signal was picked up
with the designed system as a function of viscosity ofthe sodium chloride aqueous solution including
dextran. The output signal depends on viscosity athigher frequency (>100 Hz), and on frequency at
higher viscosity (>0.01 Pa s). The experimental data
show that the designed system is effective to measuremechatronic property of biological electrolytes.
Keywords: Bio-measurement, Mechatronic property,
Biological electrolyte solution, Micro-vibratingelectrode, Viscosity, Frequency

1. INTRODUCTION
A biological body includes various electrolytes. Somestudies tried to analyze the structure of organs withmeasurement of local electric impedance [1-6]. To
avoid the change of structure by movement of ionswith a direct current, an alternating current is applied
to measure electric impedance of electrolyte solutions.
In the previous study, a new methodology to measure
local electric impedance has been proposed, andmeasurement system has been designed with amicro-vibrating electrode [7,8]. In the present study,
a new methodology to measure mechatronic propertyof biological electrolyte solution has been proposed,
and measurement system has been designed with amicro-vibrating electrode.

2. METHODS
Measurement of local electric impedance
The impedance between two electrodes soaked in anelectrolyte solution varies with the distance between
them. When the distance oscillates sinusoidally witha mechanically vibrating electrode, the impedance
oscillates, too. The oscillation corresponds to thevariation of impedance of the local space, where theelectrode is vibrating (Fig. 1). The amplified variation
was analyzed with spectrum and the amplitude at thecorresponding frequency was measured.
Theequations to calculate local impedance from the output
signal are described in the previous study [7].

Fig. 1: One electrode is fixed at point A andthe other electrode is vibrating between B andC.

ElectrodeThe electrode was made of a glass micro-capillary
filled with a potassium chloride aqueous solution (3mol/L). A platinum wire was inserted in the center ofthe capillary. The diameter of the tip of the capillary
is 0.04 mm. One of the electrodes was vibrated with apiezoelectric actuator (Fig. 2).
Measurement system
The measurement system consists of an oscillator, anamplifier, a spectrum analyzer, a phase-contrast
optical microscope, a charge-coupled device camera, arecorder, and a monitor.
Electrolyte solution
The manufactured system was applied to measureelectrolytes solution.
The saline solution wassubstituted for biological electrolyte solution. The
sodium chloride aqueous solution of 0.9 percent
concentration was modified with dextran (<35percent) to make variation in viscosity (0.001-0.6 Pas).
To evaluate the effect of viscosity independently ofimpedance of electrolyte solution, two kinds ofsolution were prepared. One is solution with dextran:
viscosity of 0.28 Pa s and sodium chloride
concentration of 3 percent. The other is sodium
chloride aqueous solution, which has same impedanceas the dextran solution with stationary electrodes.
The performance has been tested at 25 degrees
centigrade.

Fig. 2b: Vibrating electrode (upper) andstationary electrode (lower). Distance
between two electrodes is 0.15 mm, andthe amplitude of vibration is 0.02 mm.

3. RESULTS
Figure 3 exemplifies power spectra of the output
voltage, when the electrode is vibrating at 150 Hz and
the input voltage oscillates at 450 Hz. The spectrum
at 60 Hz is the signal, which comes from electric
power line. The local impedance was calculated fromthe spectrum at the frequency of vibration of theelectrode.
The experimental data show that impedance increases
with viscosity of sodium chloride aqueous solution(Fig. 4).
Figure 5 shows that local impedance with the vibrating
electrode increases with frequency of the vibrating
electrode. The tendency is remarkable in the sodiumchloride aqueous solution including dextran of higher
viscosity (>0.01 Pa s). Figure 6 shows that the local
impedance with the vibrating electrode increases withviscosity of the solution. The tendency is remarkablewith the vibrating electrode at higher frequency (>100Hz).
Figure 7 shows experimental results, when total
impedance of the circuit through solution including
dextran was adjusted to that through saline solution
with additional sodium chloride (0.26 mega-ohm).

Fig. 2a: Vibrating electrode (upper) andstationary electrode (lower). Distance
between two electrodes is 0.05 mm, andthe amplitude of vibration is 0.02 mm.

Amplitude of vibration of the electrode was kept

constant, which was confirmed with the optical
microscope.
Impedance, kilo-ohm

025dB

2080 Hz15150 Hz

10200 Hz250 Hz

50-80

00200

400
Frequency, Hz

0.2

0.4

0.6

Viscosity, Pa s

Fig. 6: Local impedance with vibrating
electrode as a function of viscosity.

Fig. 3: Power spectra of the output voltage:
vibration of electrode, 150 Hz: oscillation ofinput voltage, 450 Hz.

600

Impedance. ohm

Impedace, kilo-ohm

1500100050002000000.2

0.40.61002003000.8Frequency, Hz

Viscocity, Pa s

Fig. 4: Impedance with stationary
electrodes as a function of viscosity.

Fig. 7: Impedance with vibrating
electrode as a function of frequency:
0.001 Pa s, circle; 0.28 Pa s, triangle.
4. DISCUSSION AND CONCLUSION

25

Impedance, kilo-ohm

4000 . 0 0 ‚ PP as

2015100.010 Pas

50.11 Pa s

00.58 Pa s
0100

200300Frequency, Hz

Fig. 5: Local impedance with vibrating
electrode as a function of frequency.

An electrode should be minimized to measure localimpedance.
The minimized electrode has highimpedance, which varies with its morphology. A
measurement system with vibrating electrode has been
proposed in the previous study to pick up a signal
independently of impedance of electrodes [7].
The previous study shows that impedance calculated
from the output signal increases with the decrease in
the concentration of sodium chloride in the solution.
Impedance also increases with the amplitude ofvibration of the electrode. The previous results also
show that impedance depends on the variation ofelectrolytes and that the ratio of impedance between
the potassium chloride (0.1 percent) and sodium
chloride (0.1 percent) is similar to the value calculated
from electric conductivity of chronological scientifictables [8].

The vibrating movement of the electrode mightchange the electrical property of an electrolytesolution. The effect of the vibration was evaluatedwith experiments, in which the output signals werecompared at various frequencies of the electrode andat various viscosity of the electrolyte solution.
At lower vibrating frequencies (<100 Hz) of theelectrode, both the frequency and viscosity do notaffect output electrical signals.
At lower viscosity (<0.01 Pa s) of the electrolyte
solution, both the frequency and viscosity do notaffect output electrical signals of the present system.
On the other hand, the output electrical signal depends
on viscosity at higher vibrating frequencies (>100 Hz).
The output signal also depends on frequency at higherviscosity (>0.01 Pa s). The calculated impedance
increases with frequency and with viscosity. Thissystem can be applied to measure local viscosity of anelectrolyte solution.
Impedance of an electrolyte solution depends onmobility of ion in the solution. The mobility depends
on viscosity of the solution. The stirring withvibrating electrode might affect the mobility.
The experimental data show that the designed systemis effective to measure mechatronic property of
biological electrolytes.

5. ACKNOWLEDGMENT
This work was supported in part by a Grant-in-Aid for
Scientific Research from the Japanese Ministry ofEducation, Culture, Sports, Science and Technology.

6. REFERENCES[1] S. Hashimoto, N. Nagano, Y. Murashige, S.
Yamauchi, “Measurement of cell distribution inorgans with lissajous of impedance”, Proceedingsof the 5th World Multiconference on Systemics,
Cybernetics and Informatics, Vol. 10, 2001, pp.
443-447.
[2] Y. Wang, D.R. Haynor, Y. Kim, “A finite-element
study of the measured impedance change inimpedance cardiography”, IEEE Transactions on
Biomedical Engineering, Vol. 48, No. 12, 2001, pp.
1390-1401.
[3] C. Grosse, M. Tirado, “Improved calibration ofimpedance analyzers for measurement on highlyconductive liquids”, IEEE Transactions on
Instrumentation and Measurement, Vol. 50, No. 5,2001, pp. 1329-1333.
[4] J.D. Weiland, D.J. Anderson, “Chronic neuralstimulation with thin-film, iridium, oxide
electrodes”, IEEE Transactions on Biomedical
Engineering, Vol. 47, No. 7, 2000, pp. 911-918.
[5] J.Z. Tsai, H. Cao, “Dependence of apparent
resistance of four-electrode probes on insertiondepth”, IEEE Transactions on Biomedical
Engineering, Vol. 47, No. 1, 2000, pp. 41-47.
[6] J.Z. Tsai, J.A. Will, S.H.-V. Stelle, H. Cao, S.
Tungjitkusolmun, Y.B. Choy, D. Haemmerich, V.R.
Vorperian, J.G. Webster, “In-vivo measurement ofswine myocardial resistivity”, IEEE Transactions
on Biomedical Engineering, Vol. 49, No. 5, 2002,
pp. 472-483.
[7] S. Yamauchi, S. Hashimoto, Y. Murashige, H. Oku,
M. Sakai, T. Sahara, H. Otani, H. Imamura,“Measurement system for local electric impedanceof gel with vibrating electrode”. Proceedings of the
6th World Multiconference on Systemics,
Cybernetics and Informatics, Vol. 13, 2002, pp.
314-319.

[8] T. Sekiyama, S. Hashimoto, S. Yamauchi, Y.
Morita, D. Kozaki, T. Sahara, Y. Wu, H. Otani, H.
Imamura, “Measurement system for local electric
impedance of biological electrolyte solution withmicro-vibrating electrode”, Proc. World Congress
on Medical Physics and Biomedical Engineering,
CD-ROM, 2003.