Construction of Healthcare Network Based on

Proposed ECG and Physical-activity Sensor

Adopting Energy-harvesting Technologies

Makoto Kawashima, Taiki Nakamura, and Kaori Hata

Department of Computer Science, College of Engineering,

Chubu University,

Kasugai-City, Aichi, Japan

kawasima@cs.chubu.ac.jp +81-568519102

Abstract— Recently, ubiquitous vital signs sensing using

wireless medical sensors has become essential, not only for in-

hospital diagnosis but for healthcare at home.

In this work, the most advanced electrocardiography (ECG)

sensor is proposed. This sensor system makes it possible to

eliminate the use of both batteries and self-adhesive electrodes by

introducing energy harvesting technology and newly developed

unwoven fabric electrodes, respectively. By realizing smaller and

thinner implementation and easy handling, the complete sensors

may be easily mounted on underwear and allow long term

wearable usage for vital signs monitoring. The sensor has the

capability of transmitting ECG data to a cloud-based data

processing server set up in the Internet via a smartphone or other

ubiquitous tools.

This paper describes the configuration of the ECG sensor,

which adopts cutting edge technologies, and also the constitution

of the acquired ECG data transmitting and processing systems.

Keywords— healthcare network; electrocardiography (ECG)

sensor; energy-harvesting; Peltier device; cloud computer;

I. INTRODUCTION

The ECG sensor is one of the most widely applied devices for checking vital signs and health monitoring and serves a useful diagnostic purpose for the cardiovascular system.

The electrocardiograph isn't only applied for the detection of the state of activity or of diseases of the heart but for the detection of changes in the mental state of human beings. The application areas of ECG are expected to widen greatly in the future.

Recently the number of the medical doctors in Japan has been gradually reducing, so full time monitoring of patients is increasingly necessary, especially for those who are receiving medical treatment at home.

To conquer the problems described above, ECG sensors that can to worn on the human body on a full time basis should be available.

Aiming at a device which can be worn and allow monitoring full time, a newly developed ECG sensor is proposed in this work. Two newly proposed technologies are introduced to the sensor. The first is energy-harvesting technology which supplies sufficient electric power to the

sensor and the second is the adoption for the ECG electrode of a fabric which is modified to exhibit electric conductivity. These technologies basically make it possible for the ECG sensor to be worn full time. More specifically, the electric power is extracted from the temperature difference between the human body and the environment and fed to the ECG sensor by using Peltier energy harvesting devices, and for the ECG electrode the conductive unwoven fabric materials are attached to the underwear.

Since the size and the weight have already been made sufficiently small, the ECG sensor can be added to underwear and its full time use is becoming practicable.

In this paper, the configuration of the ECG sensor, which adopts cutting edge technologies, is described, along with experimental results of the trial-produced sensors, and also the composition of the systems for transmitting and processing the acquired ECG data, which also introduce robust and highly reliable cloud computing technologies [1][2].

II. BASIC CONFIGURATION OF HEALTHCARE NETWORK

First of all, the configuration of the healthcare network should be described, prior to looking at the details of the new vital signs sensor construction.

Fig. 1 shows the configuration of healthcare network introducing newly proposed vital signs sensor.

Fig. 1 Configuration of healthcare network introducing the proposed

vital signs sensors

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Both ECG and human movement signals detected by this vital signs sensor, which is mounted on the human body, are transmitted to a mobile terminal such as a smartphone by Bluetooth transmission. By using a smartphone as a gateway, the vital information is connected to the Internet through 3G or LTE networks and the information finally reaches the data processing server, which is based on a robust and highly reliable cloud computing system. The diagnostic or processed results of the vital signs data are delivered to a hospital, care-home or patients/family as needed for the situation. To deal appropriately with any abrupt change in the state, the healthcare network has to be working on a full-time basis, including the individual vital signs sensor and the data transferring network.

III. VITAL SENSOR POWER CONSUMPTION REDUCTION BY

QUASI-NORMALLY-OFF POWER CONTROL

For achieving full time basis monitoring of ECG, it is essential to give assurance not only about the supply of stable electric power to the sensor but also about the provision of an appropriate ECG sensing electrode which is not harmful to the human skin. Fig. 2 shows the proposed ECG and physical-activity sensor configuration for long term utilization in practical life.

For ECG signal sensing, the conductive unwoven fabric electrode is newly introduced in this work. After sensing by this fabric electrode, the acquired ECG signal is amplified by the high CMRR instrumentation amplifier. After A/D conversion, the digitized ECG data is sent to the smartphone by Bluetooth wireless transmission. The ECG data is routed to the

cloud based processing server via the smartphone which acts as a gateway to the Internet.

For all of the blocks in the sensor circuit, precise power control is performed so that circuits are “off” when not required and as a result, the power consumption of a sensor can be reduced to around one to tenth of the specification described in the Mixed-signal CPU datasheet.[3]

Furthermore, energy harvesting technologies are introduced to provide long-term and stable electric power for the sensor. In this work, Peltier devices are applied as practical energy harvesting components.

Table 1 shows the fundamental specification of proposed vital signs sensor.

Photos of an experimental production of the ECG and physical-activity sensor are shown in Fig. 3.

The sensor consists of a Mixed-signal CPU, 3-axis accelerometer and Bluetooth transceiver, and all of the circuits are mounted on a 40 x 50 mm2 thin PCB. For the power supply of this previous version of the experimental ECG sensor, a coin cell (CR2032) was mounted, as shown in Fig. 3

Fig. 4 shows the remarkable reduction in sensor power consumption by introducing the “normally off” computing scheme.

Power feeding control is managed by the timing of the ECG signal sensing sequence, specifically switching on, or to standby mode, of the analog amplifier, CPU (for noise suppressing), A/D conversion and communication module. For almost all of the sampling period, most of the circuit modules in the sensor can remain in standby mode, so reducing the total power consumption enormously.

Fig. 2 Proposed ECG and physical-activity sensor configuration for

long term use in practical life

TABLE I. FUNDAMENTAL SPECIFICATION OF ADVANCED

VITAL SIGNS SENSOR

Fig. 3 Photo of experimental ECG and physical-activity sensor

Fig. 4 Remarkable reduction of sensor power consumption by

introducing normally-off computing scheme

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Fig. 5 shows the displayed ECG waveform on smartphone by using experimentally made ECG sensor described above (Fig. 3). Generally, the smartphone is used as a gateway to Internet, but assured the monitoring capability of the ECG waveform for the experimental ECG sensor.

IV. POWERFEEDING TO VITAL SENSOR BY INTRODUCING

ENERGY-HARVESTING TECHNOLOGIES

In the past few years, there have been many proposals for getting energy efficiently from the environment, such as the proposition of an energy-efficient ASIC development for wireless body sensor realization [4][5]. A summary of energy-harvesting technologies is shown in Fig. 6. There are many energy sources around us, such as light power, electromagnetic wave energy and even the temperature of the human body, that are able to be converted to electric power. To provide an effective realization for this concept, the technologies of ultra-small-voltage step-up circuitry combined with Peltier devices are proposed in this work. The experimentally constructed energy harvesting circuitry is shown in Fig. 7. Although the output voltage obtained from the Peltier device is only several tens of millivolts, this can be boosted up to 2 to 5 volts by laboratory-made charge pump type ultra-small-voltage step-up circuitry. In this circuit, an electric double layer capacitor works effectively especially for Bluetooth data transceiver.

Fig. 8 shows the relationship between the output voltage and the temperature difference between the two sides of the Peltier device. As shown in Fig. 8, assuming that a consumed current of 600μA is needed to operate the ECG sensor (the actual working current of the experimental sensor), a

temperature difference of 8 is required.

Fig. 9 depicts the characteristics of the feeding voltage when actually connected the ECG sensor. This characteristic shows that the output voltage remains stable after a certain elapsed time because of an equal balance between the charging and discharging (power consumed by the sensor) of the electric double layer capacitor. Fig. 9 also shows that the appropriate capacitance value should be chosen for charge pump capacitor.

Fig. 6 Energy harvesting technologies

Fig. 7 Ultra-small-voltage step-up circuitry for energy harvesting

Fig. 8 Basic characteristics of ultra-low-voltage step-up circuitry

and Peltier device

Fig. 5 Observed ECG waveform displayed on smartphone

Fig. 9 Power supply characteristics of energy harvesting

circuitry for vital sensor feeding

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V. NEWLY DEVELOPED UNWOVEN FABRIC ELEGTRODE FOR

ECG SIGNAL SENSING

A conductive unwoven fabric electrode has been developed for ECG sensing. A photo of the experimentally made conductive fabric electrode and a factory made ECG electrode are shown in Fig. 10. The main specifications of those electrodes are compared in Table 2. As shown in both the figure and the table, although the conductive area of each of them is not very different, the resistance value is ten times lower for the fabric electrode. This lower resistance value makes it possible to lower the ECG measurement system’s impedance, and this seems to be an advantageous for the S/N characteristic of the ECG sensing system. Fig. 11 clearly shows the difference between the two types of ECG electrode. From the observed ECG waveforms, the laboratory made electrode can measure the ECG signal with a rather higher S/N ratio compared to the factory made one. In the case of advanced sensing or estimation of heart activities, this seems to be a great advantage because the sensing frequency range is also wider in the case of using unwoven fabric electrodes.

A capacitively-coupled ECG electrode (CC-ECG) has been proposed [6], and it seems a combination of unwoven electrode and a CC-ECG will be more convenient for the patients.

VI. CONSTRUCTION OF HEALTHCARE NETWORK BASED ON

PROPOSED ECG SIGNAL SENSORS

The proposed ECG sensor will in practice only be effective if introduced to real medical systems that have certain size of network scale and number of users. The configuration of the healthcare network has also been researched in parallel with the high level of sensor development described in the previous section. Fig. 12 illustrates the applied virtualization of the healthcare server to provide better performance and robustness, and this virtualization is an important functionality for constructing a cloud computer system.

Fig. 13 shows the cloud computing-based architecture of the data processing server for the healthcare network. The virtual middle layer provides the robustness and expandability of the server construction. At first the actual ECG signal processing application is constructed by using LabVIEW, which is suitable for measuring system development since it allows easy upgrading of the functionality and performance increases for the future. However, it is obviously difficult to achieve sufficient scalability for the required increase in customer numbers with LabVIEW, so the application software will be rebuilt using C++ or Java language after performance evaluation of the LabVIEW version of the prototype system.

Factory made ECG electrode (right) Experimentally made fabric electrode (left)

Fig. 10 Photo of experimental conductive fabric electrode and

factory made ECG electrode

Fig. 11 Observed ECG waveforms using using experimentally made

fabric electrode and factory made ECG electrode

Fig. 12 Applied virtualization of cloud computing components

Fig. 13 Architecture of developed cloud-based computer for

healthcare network

TABLE II. COMPARISON OF TWO TYPES OF ECG ELECTRODES

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VII. CONCLUSIONS

With the aim of allowing full time utilization of the vital

signs sensors, a new type of sensor has been proposed,

introducing two cutting edge technologies. One of the

outstanding technologies is energy harvesting and the other is

the adoption of unwoven fabric electrode for ECG sensing.

In this work the configurations and characteristics of

these two technologies have been researched and

experimentally clarified. Energy harvesting technology using a

Peltier device generates electric power of approximately

1.8mW, which has been proved to be sufficient for the

laboratory made ECG sensor to be completely powered,

including the Bluetooth transceiver. Newly developed

unwoven conductive fabric electrodes are applied as the new

type of ECG electrodes to realize a wearable vital sensor. The

resistance value of the fabric electrode is very low and this

leads to an increase in S/N ratio of the measured ECG

waveform. By adopting these two technologies, a wearable

vital sensor has come into view.

As the advanced ECG sensors are only practicable when

introduced into the real medical systems, a healthcare network

has also been developed by introducing cloud computer.

We are planning to develop the practical system’s

implementation and operation, to improve the usability of the

whole system based on the proposed cutting edge vital signs

sensors.

REFERENCES

[1] Toshinori KAGAWA et al: Advanced exercise control using miniature ECG and 3D acceleration sensors, D&D forum, IEEE GLOBECOM, December 2008

[2] Taiki NAKAMURA et al: The proposed configuration of advanced ECG sensor and construction of healthcare network, Technical Committee on Medical Information & Communicarion Technology (MICT), MICT2013.5, May 2013.

[3] http://www.ti.com/lit/ds/slas508i/slas508i.pdf [4] Xiaoyu Zhang et.al: An energy-efficient ASIC for wireless body sensor

networks in medical applications, Vol. 4, No. 1, IEEE Transactions on Biomedical Circuits and Systems, Feb. 2010, pp. 11-18.

[5] Carlos F. Garcia-Hernandez et.al.: Wireless sensor networks and applications: a survey, Vol. 7, No. 3 International Jornal of Computer Science and Network Security. March 2007, pp. 264-273.

[6] Ebrahim Nemati et.al: A wireless wearble ECG sensor for long-term applications, Vol. 50, IEEE Communication Magazine, Jan. 2012, pp. 36-43.

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