Measurement of Mechatronic Property of Biological Gel
with Micro-Vibrating Electrode
Takatsugu Furukawa, Shigehiro Hashimoto, Yusuke Morita, Koichi Imoto,Tomohiro Sahara, Kenichi Yamasaki, Hideo Kondo, Wataru Ikeda, Masahiko Yoshiura
Biomedical Engineering, Osaka Institute of Technology, Osaka, 535-8585, Japan
hasimoto@elc.oit.ac.jp
andHajime Otani, Hiroji Imamura, Toshiji Iwasaka
Cardiovascular Center, Kansai Medical University, Moriguchi, Japan
ABSTRUCTA new methodology to measure local
mechatronic property of biological gel has been
proposed, and measurement system has beendesigned with a micro-vibrating electrode.
The designed system consists of two electrodes,
where one of the electrodes vibrates withpiezoelectric actuator.
The component ofvariation at impedance between two electrodes
with vibration of electrode is analyzed at thecorresponding spectrum.
The system wasapplied to measurement of impedance in saline
solution and potassium chloride aqueoussolution. The experimental results show thatthe component increases with amplitude ofvibration of the electrode and with theimpedance of solution.
Keywords: Bio-measurement, Mechatronic
property, Biological gel, Micro-vibrating
electrode, Frequency, Electric impedanceof structure by movement of ions with a direct
current, an alternating current is applied tomeasure electric impedance of electrolyte
solutions.
In the present study, a new
methodology to measure local mechatronic
property has been proposed, and measurement
systemhas
beendesignedwitha
micro-vibrating electrode.
2. METHODS
Measurement principle
The impedance between two electrodes soaked
in an electrolyte solution varies with thedistance between them (Fig. 1). When thedistance oscillates sinusoidally with amechanicallyvibratingelectrode,
theimpedance oscillates, too.

ABC

1. INTRODUCTIONX

A biological body includes various electrolytes.
Several studies had been tried to estimate
structures of the human body with electric
impedance. Some studies tried to analyze thestructure of organs with measurement of local
electric impedance [1-5]. To avoid the changedx

Fig. 1: One electrode is fixed at point A and theother electrode is vibrating between B and C.

The oscillation corresponds to the variation ofimpedance of the local space, where theelectrode is mechanically vibrating (Fig. 2).
The variation was analyzed with spectrum andthe amplitude at the corresponding frequency
was measured [6].

Rx

1 MΩ
3 MΩ
5 MΩ
8 MΩ

I2

10 MΩ

Electrodes
The electrode was made of a glass
micro-capillary filled with a potassium chloride
aqueous solution (3 mol/L). A platinum wire
was inserted in the center of the capillary.
The diameter of the tip of the capillary is 0.01mm (Fig. 3).
One of the electrodes wasvibrated with a piezoelectric actuator.

I1CZ-Measurement object
VinVoutR+OP ampCLPF

Fig. 4: Measurement circuit diagram. To cut
high-frequency component, Low Pass Filter (LPF)
is applied.

Minimum amplitude

Maximum amplitude

Vdx

Microscope
Piezoelectric actuator

Micro-motion stage

Fig. 2: An output electric alternating voltage
signal (Vout in Fig. 4) oscillates with time. Vdx
corresponds to impedance of the local space,
where the electrode is mechanically vibrating.

Fig.5: Microscope.

Electrode vibration signal
Piezoelectric controller

10 μm
Fig.3: Electrodes. The upper electrode is vibrating.

Oscillator
Input signal

Piezoelectric actuator

Oscillator
Objective lens

Output signal
Amplification circuit
Electrode graphics

Digital oscilloscope

PCFig. 6: Measurement system

Experiments
The manufactured system was applied tomeasure electrolytes: a sodium chloride
aqueous solution, a potassium chloride aqueous
solution, and an egg. Variations were made inconcentration (weight percentage of 0.1-9.0) of
the sodium chloride aqueous solution.
Insodium chloride aqueous solution of 0.5 percent,variations were made on amplitude of vibrationof the electrode. In the test with an egg, one
electrode was stuck into yolk and the other wasset in the surrounding solution, while theimpedance of surroundings was varied withpotassium chloride.
The performance wastested at 25 degrees centigrade.

increases with the increase in the amplitude ofvibration of the electrode to 0.023 mm (Table 1).
The local impedance is proportional to output
signal spectrum, which corresponds to themechanically vibrating frequency of theelectrode [6].

1.8
1.6
1.4
Output signal

Measurement system
The measurement system consists of anoscillator, an amplifier (Fig. 4), a spectrumanalyzer, a phase-contrast optical microscope(Fig. 5), a charge-coupled device camera, arecorder, and a monitor (Fig. 6).

100 Hz1.2200 Hz

1300 Hz0.8400 Hz

0.6

500Hz

0.4
0.2
00246810Concentration of NaCl (%)

Fig. 7: Relation between output signal andconcentration of NaCl.

3. RESULTS AND DISCUSSION
Figure 7 shows relation between the output
voltage signal and concentration of sodium
chloride aqueous solution, when the frequencyof the input signal was varied between 100 and500 Hz.
The output voltage signal isstandardized with that of 0.1 percent, so thatthe value is unity at 0.1 percent NaCl in Fig. 7.
The output voltage signal without the amplifier
was directly measured at the output resistancewithout vibration of the electrode in Fig. 7.
Impedance is inversely proportional to theelectric current, which is proportional to theoutput voltage signal. The experimental data
show that impedance of the sodium chloride
aqueous solution between two electrodes
decreases with increase in the concentration ofsodium chloride in the solution from 0.1 to 9.0percent, and that impedance does not vary withfrequency between 100 and 500 Hz.
Figure 8 exemplifies spectra of the output
signal, when the amplitude of vibration (150Hz) of the electrode is 0.023 mm. The spectra
at 60 Hz and 100 Hz correspond to frequency ofthe electric power source and the input signal,respectively.
The experimental data showthat power spectrum at 150 Hz of output signal(dBV)-20-100
50
100
150200 (Hz)Fig. 8: Out put voltage (top) and its spectrum(bottom).

Table 1: Spectrum for each amplitude ofmechanical vibration of electrode.
Amplitude
mm0Spectrum –96

0.006 0.014

0.020

0.023

–95–87–87–90Output voltage tracing for the sodium chloride
aqueous solution of 0.1 percent is exemplified
in Fig. 9, where the electrode is vibrating at
100 Hz. Figure 10 shows spectra of the output
voltage signal. The spectra at 60 Hz and 150
Hz correspond to frequency of the electric
power source and the input signal, respectively.
The experimental data show that power
spectrum at 100 Hz of output signal varies withthe electrolyte.
Fig. 9: Output voltage tracing. 10 ms/div for timescale.

Fig. 10: Spectra of output voltage. 50 Hz/div for theaxis of abscissas.

Table 2 shows experimental data for electric
conductivity of two kinds of electrolyte solution.
Conductivity is the inverse number ofimpedance. The results show that impedance
depends on the variation of electrolytes andthat the ratio of impedance between thepotassium chloride (0.1 percent) and sodium
chloride (0.1 percent) aqueous solutions is 0.80,
which can be approximated to 0.83 calculated
from electric conductivity of chronologicalscientific tables.
The experiment with an egg shows that theimpedance is independently measured of thatof the surroundings when the electrode stuck
into the yolk is vibrating, while the impedanceof the surrounding solution varies with theconcentration of electrolyte.
The output
signal, however, depends on the concentrationof electrolyte in the surrounding solution, whenthe electrode is not vibrating.
The results show that the local impedance atthe vibrating electrode governs the output
signal of the measurement system.

Table 2: Electric conductivity of aqueoussolution.

D (dBV) Vout (mV)κ (Ω-1m-1×10-3)

KCl

–70.0

0.95

2.02

NaCl

–70.0

0.85

1.62

Several designs had been tried to analyze
biological impedance. Spectra are applied toanalysis of impedance [1]. Viscosity gives
effects on output signals of a vibrating sensor[3]. In the previous study, the signal was also
picked up as a function of viscosity, when theelectrode was vibrated in the sodium chloride
aqueous solution including dextran.
Theoutput signal depends on viscosity at higher
frequency (>100 Hz), and on frequency at
higher viscosity (>0.01 Pa s) [7].

4. CONCLUSION
The experimental data show that the designed
system is effective to measure local
mechatronic property of biological gel.
5. ACKNOWLEDGMENT
This work was supported in part by aGrant-in-Aid for Scientific Research andAcademic Frontier from the Japanese Ministryof Education, Culture, Sports, Science andTechnology.
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