LOW INVASIVE MEASUREMENT OF ELECTROCARDIOGRAM
FOR NEWBORNS AND INFANTS
Yoichi Furusawa1 , Akinori Ueno 1 , Hiroshi Hoshino 1 , Sachiyo Kataoka2 , Hiroko Mitani3 , Yoji Ishiyama 3
1Tokyo Denki University, School of Science and Engineering, JAPAN2
Aprica Kassai Incorporated, JAPAN
3
Kyorin University, School of Health Sciences, JAPAN

Abstract-In the present study, it is investigated whether
capacitive electrode can detect electrocardiogram (ECG) at acondition where some cloth is interpolated between theelectrode and body surface of an adult subject. The result
showed that constructed devices could measure ECG whensilk of 247µm thickness was mediated. Though there is room
to improve measurement devices or signal processing forpractical use, feasibility of capacitive electrode for low
invasive measurement of ECG for newborns and infants isindicated.
Keywords - ECG, Capacitive Electrode, Barium Titanate

I. INTRODUCTION
Cause of death in newborns and infants are mostly
cardiovascular disease, respiratory disease or sudden infant
death syndrome (SIDS) in Japan. For the purpose ofdiagnosis, medical treatment, or medical research of thesediseases, electrocardiogram (ECG) is measured
continuously from the newborns and infants whennecessary. Metal electrodes are conventionally used andattached to the body surface with conducting paste oradhesive gel for detecting ECG. However adhesion ofthese paste and gel is so tight for newborns and infants thatthe skin is seriously damaged and, in some cases, theelectrodes peel off the skin in detaching the electrodes
from the body surface. In other case, metal electrode oftencases allergic reaction on the skin where the electrode isattached. So it is desired to develop low invasive methodfor detecting ECG from newborns and infants.
In the present study, we investigated whether or not
capacitive electrode can detect ECG at a condition wherethin cloth is interpolated between the electrode and thebody surface.

III. M EASUREMENT SYSTEM
We constructed ECG measurement system (see in Fig.2).
The system consists of 5 electronic circuits of impedance
converter, instrumentation amplifier, high pass filter, lowpass filter, and notch filter. The capacitive electrodes areconnected to the impedance converter circuit and placed
indirectly on the back of an adult subject at a condition
where thin silk is interpolated between the electrode andthe body surface. The subject was instructed to lie insupine position. The output signal of the system wasdigitized at 250Hz by A/D converter and stored in PC.
IV. RESULTS
A. Fundamental measurement of the capacitive electrode
Cross-sectional images of the barium titanate in thecapacitive electrode and the interpolated silk are obtainedby scanning electron spectroscopy. As can be seen in Fig.3,
thickness of both materials was 247µm and 240µm
respectively.
Impedance
ConverterInstrumentation
AmplifierHigh P ass
FilterLow Pass
Filter

Notch
Filter

Fig.2 Block diagram of the system for ECG measurement

II. CAPACITIVE ELECTRODE
Capacitive electrode can detect alternating bioelectric
signal as a capacitor by inserting impedance converter
circuit posterior to the electrode. Since a small area of thebody surface can be regarded as a conductive material inmeasuring bioelectric signal, one of the parallel plates of
the capacitor may be substituted by the body surface. Thus,
capacitive electrode can be constructed from a insulator
mounted on a conducting plate. In this study, barium
titanate is used as an insulator and silver is employed as aconducting plate, as can be seen in Fig.1.
Insulator

BaTiO3(a) Barium titanate in the capacitive electrode

Lead Wire

Silver(b) Silk mediated between the electrode and the skinFig.1 Fabrication of a capacitive electrodeFig.3 Cross-sectional images of the barium titanate in the capacitiveelectrode and the interpolated silk between the electrode and thebody surface, which is observed by scanning electron microscope

0-7803-7944-6/03/$17.00©2003 IEEE.

300.04
Capacitance [pF]

0.03
0.02
Voltage[V]ε2 / ε0 = 2345678910250.01
0-0.01-0.02

2015105-0.03-0.04
30323436

3840

200

300

Time[sec]

Fig.4 A record of ECG by the capacitive electrode with interpolation ofthe silk between the electrode and the body surface of the subject

400500Thickness of the cloth[µm]

100

e2

Cloth

247 [µm]

Impedance [GΩ]BaTiO3700

Fig.6 Thickness-capacitance characteristic of the capacitive electrodeε 2 /ε 0 = 2Silver
e1600

345678910101d [mm]0.10Body surface
Fig.5 A model of the capacitive electrode interpolated by cloth102030405060Frequency [Hz]Fig.7 Frequency -impedance characteristic of the capacitive electrodeB. ECG measurement by the capacitive electrodeoccasion) of the capacitive electrode is derived by dividing
reciprocal of the C by angular frequency ω = 2π f , so that

Result of ECG measurement by the capacitive electrodeis shown in Fig. 5. Despite the interpolation of the silk
between the electrode and the body surface, periodic Rwave potentials could be successfully detected. However,when thicker cloth such as cotton was interpolated, noeffective signal could be observed. Furthermore,
fluctuating base line was noticed and S/N ratio wasinsufficient for practical use. Thus, there are still somerooms to improve measurement devices or signal
processing.

1
1.06 × 10 −10 × d + 2. 47 × 10− 4 × ε 2(2)=2π fC
3.35 × 10−11 × f × ε 2
If the thickness of the silk ( 2.40 × 10 −4 m) is substituted
for d, impedance of the capacitive electrode is regarded asa function of f and ε 2 . As can be seen in Fig.7, impedanceof the capacitive electrode including interpolated silk is
assumed to of the order of 1012 Ω at a frequency of 10 Hz.
Consequently, input impedance of the impedance
converter circuit should be equal to or more than 1012 Ω inorder to detect stable ECG.
Z=V. DISUCUSSION
Capacitance of the capacitive electrode includinginterpolated cloth can be estimated using a capacitor modelin Fig.5 and Eq.(1). Since insulation between two parallelconducting materials has 2 layers of barium titanate andthe cloth, capacitance of the electrode can be calculated asa capacitance of series-connected capacitor, so that

ε1 × ε 2 × S(1)
ε1 × d × 10− 3 + ε 2 × 2. 47 × 10− 4
where ε 1 and ε 2 are dielectric constants of the barium
C=titanate and the cloth, S is area of the electrode face, and dis thickness of the cloth.
Substituting 1.06 × 10 −7 F/m for ε 1 and 5.03 × 10 − 5 m2for S, the capacitance C can be treated as a function of ε 2and d. Then Fig.6 is calculated according to this function.
The simulated data shows that capacitance of thecapacitive electrode are significantly small of the order of
10-12 F. Also capacitive reactance (impedance on thisVI. CONCLUSION
We experimentally observed that the capacitiveelectrode could detect ECG even when thin silk wasinterpolated between the electrode and the body surface ofthe subject. Though there is room to improve measurement
devices or signal processing for practical use, the result
implies that capacitive electrode is feasible for lowinvasive measurement of ECG for newborns and infants.
REFERENCES[1] M. Matsuo, M. Esashi and K. Iijima, “Capacitive Electrode for
Biomedical Use (2)”, Medical Electronics and Bioengineering, pp. 19, 1973
[2] Y. Okazaki, M. Fukasawa and J. Nakazoe, “Measurement ofBioelectric Signals by the New Capacitive Electrode using
Semiconductor”, Proceedings of 2000 Electronics, Information andSystems Society Conference of IEEJ, pp. 165-170, 2000