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November 8, 2019
Nippon Telegraph and Telephone Corporation

Low-power and small wearable sensor for smart healthcare simultaneously measuring electrocardiac signal, acceleration, temperature and humidity inside garment

Nippon Telegraph and Telephone Corporation (Headquarters: Chiyoda Ward, Tokyo; President and CEO: Jun Sawada; hereinafter the "NTT") had developed the prototype wearable sensor that can collect and transmit not only biological information such as heart rate and electrocardiac characteristics, but also environmental information such as temperature and humidity inside a garment.

NTT had introduced 3 sensing functions (electrocardiac signal, acceleration, temperature, and humidity) to this wearable sensor and developed a multi-sensor data signal processing technology to enable smart healthcare applications such as the prevention of the heat stress on a human body. The features such as the long-operation time in low-power mode, the data collection without loss by memory and wireless functions, and the housing shape of the sensor based on ergonomics reduce the burden on its user and enable comfortable and easy acquisition of biological and personal-area environmental information in various scenes of a daily life.

NTT is also collaborating with specialized universities and institutions to verify the usefulness of the systems with wearable devices in the healthcare field, including rehabilitation supports and the prevention of the heat stress.

The results of this research and development are demonstrated on "NTT R&D Forum 2019*1" which is held from November 14 to 15, 2019. You can see them in the "Action for 2020 and beyond" display corner.

Background of development

To date, NTT has been evaluating the performances of athletes and monitoring the conditions of rehabilitation patients by capturing and analyzing electrocardiac signals and acceleration by using the wearable device attaching on the garments with the functional material "hitoe ®*2"sewn in the form of electrodes. In recent years, with concern over global warming, there has been a demand for technologies to visualize the heat stress on a human body. Utilizing the wearable device technologies cultivated through our researches and developments, we had started to develop the wearable sensor for simultaneously capturing biological and environmental data to understand the condition of the human body under hot environment.

Developed wearable sensor collecting biological and environmental information

The newly developed wearable sensor is mounted in the center of the front of an inner wear, acquiring the temperature and humidity inside an outer wear as well as acceleration and angular velocity of an upper body. The acquired data is transmitted to a smartphone or a IoT-gateway by the wireless module mounted on this wearable sensor, which enable to monitor the data in real time. Moreover, this wearable sensor calculates from the acquired data to several characteristics such as heart rate, RRI*3, number of steps, and tilt angle of upper body and then accumulates the data of the characteristics in a built-in memory. These advanced properties enable to continuously measure the data at off-line without wireless connection and also read out the characteristics data on batch process.

Key points on development

Conventionally, as the long-term measurement, analysis, and communication of multi-sensor data are simultaneously executed, the CPU load is high and thus power consumption increases, causing frequent charging by users or the implementation of a large-size battery due to short operating time. To overcome this issue, we developed the multi-sensor data signal processing technology which reduces the CPU load by activating the CPU process at only short time calculating the characteristics after buffering the multi-sensor data in the memory. As a result, continuous measurement for more than 100 hours is possible even with a small battery and the weight of the sensor is 12 g with plurality of sensors, a battery, transmitter module etc, being housed in a light-weight case. In addition, an ergonomically designed shape of a sensor enclosure makes it comfortable to keep on wearing this sensor by the elimination of hindering the body movements such as forward bending and crouch.

Figure 1. Main specifications of the prototype wearable sensor developed by NTT

Future Plans

With the aim of applying this technology to the prevention of the heat stress on human body, we will collect the data of the workers under the hot environments constructing network infrastructures for NTT services.

  • *1: URL of the NTT R&D Forum 2019 website
  • *2: hitoe ® is the functional material developed by Toray Industries, Inc. and NTT. By specially coating highly conductive resin on the nanofiber material, which is the most advanced fiber material, it is highly durable and can detect biological signals with high sensitivity despite being a non-metallic material. By attaching hitoe ® to the body surface, biological information such as heart rate, electrocardiographic waveform, and sleep data estimated from R wave intervals can be obtained. In addition, the use of nanofibers makes it possible to obtain vital signals by being closely attached to the human body, such as clothes and hats, because they are durable for home washing and also because their adhesiveness to the skin is enhanced, making it possible to perform highly sensitive measurements.
  • *3: RRI:R-R Interval, the interval between the R wave on the electrocardiographic waveform (ECG) and the next R wave.
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