TDK Front Line

Vol. 6 Use of Wearable Biosensors for Progress of IoT Society

In the IoT society, about 50 billion devices are predicted to be connected via the Internet in 2020. Countless IoT devices equipped with sensors will be connected via wireless sensor networks (WSN), with the number of sensors expected to reach 1 trillion. TDK provides a wide and diverse range of high-performance sensors and software, and advanced sensor solutions combined with unique algorithms on global markets.
TDK's Silmee™ series consists of wearable biosensors for the IoT community that are friendly to both people and things. To transfer sensing data to dedicated clouds through smartphones and gateways, systems mainly based on wristband sensor-fusion devices that can handle various biological information including activity amount, conversation amount, sleep time, pulse, and skin temperature, and location information using beacons are developed. They can flexibly serve various purposes such as remote monitoring.

TDK Biosensor product line-up

Low power consumption allows continuous use for 10 days to 2 weeks per charge

The Wristband Biosensor Silmee™ W20/W22 is a multifunctional wearable device that integrates acceleration, pulse, skin temperature, and ultraviolet (UV) sensors with a microcomputer for processing signals, memories, chips for Bluetooth communication, etc.
The built-in acceleration sensor automatically estimates activity amounts, such as the number of steps, travel distance, and calorie consumption, as well as sleep time and sleep cycle information by differentiating activity and sleep states through unique algorithms.

Analog signals from different sensors are AD-converted and processed by digital signal processing by the microcomputer, stored in the memory, and sent to smartphones and gateways by Bluetooth.

Generally, the higher the sampling frequency of the acceleration sensor is set, the more information is collected. This facilitates activity analysis and reduces false detections but also increases the power consumption of the microcomputer and shortens battery capacity. Here, TDK has set the optimal sampling frequency by a detailed analysis of daily activities, and thereby reduced the operation time of the microcomputer while maintaining performance by adopting unique signal processing technology, significantly reducing power consumption. W20 can be used continuously for about two weeks and W22 for about 10 days per charge (the number of days is an approximation and varies according to the situation of use).

Equipped with LED and phototransistor pulse sensor

Pulse is measured by making use of the ability of hemoglobin in the blood to absorb light. The pulse sensor is located on the part of the device (back) that is in contact with the skin. The skin is irradiated with light from a green LED (wavelength: approx. 550 nm), which is a light emission source. The amount of light diffused and reflected from capillary vessels 1–2 mm below the surface of the skin is measured by the photodiode, which is the light receiving element. The amount of reflected light changes in correlation with the amount of blood in the capillary vessels under the skin. When the capillary vessels dilate with the beating of the heart, the amount of blood in the capillary vessels enlarges, which means that more light is absorbed by hemoglobin, resulting in less reflected light. On the other hand, when the capillary vessels contract, more light is reflected because there is less blood in the vessels. According to this principle (reflective photoelectric system), a person’s pulse can be measured in real time for 24 hours by wearing the wristband biosensor Silmee™ W20/W22.

The sensing data collected by the wristband biosensor can be automatically transferred to smartphones through the dedicated apps “Silmee Healthcare” or “Silmee Connect” for health management. With gateway device Silmee™ L10, data can be uploaded to the special TDK cloud directly without going through a smartphone.

Remote monitoring system at hospitals and nursing homes

The Silmee™ L10 gateway device can receive data from multiple wristband biosensors, allowing the operation of remote monitoring systems using wristband biosensors and gateways, and the system are utilized in the areas of medical and nursing care.

For example, if dementia inpatients wear a wristband biosensor (e.g., Silmee™ W20/W22) and Silmee™ L10 small gateways are installed in the hospital or anywhere on the premises, the biological and location information of the wearer can be remotely monitored through the cloud. Advantages of this system are that there is no need for large-scale construction, and gateways can be easily installed and moved. This not only improves the quality of medical and nursing care services, but also contributes to the workload reduction of staff. 

Silmee™ L20 is a mounting type gateway equipped with a human sensor, environment sensor, and acceleration sensor. They are installed in the ceilings of the rooms of the residents of nursing homes to chiefly monitor their movements on the bed. Gateways installed in multiple locations including corridors can alert staff members on their smartphones when the residents approach dangerous places such as staircases, thereby ensuring a safe environment for the residents through speedy response.

Biosensor Silmee™ is actively used in the areas related to distribution and logistics

Use of Silmee™ wearable biosensor is expanding from medical and nursing care areas to industrial fields such as distribution, logistics, and factories.
In the distribution industry, for example, the shortage of picking operators at warehouses is a grave problem. Not only that, human movement is complicated and differs from one individual and their habits to another, which are factors that cause waste. To increase the efficiency of picking work, a system exploring improvements has been developed where operators are asked to wear wristband biosensors, and data collected from the mounted acceleration sensors is used to estimate work contents (e.g., cart moving, walking, manual work, pausing) and identify problems, thereby significantly reducing inefficiencies. 

Promising mental health applications for problems such as sleep disorders and autonomic balance

Use of wearable biosensors for mental health applications is also coming, analyzing conditions such as autonomic balance and sleep disorders. For example, it has been pointed out that accidents involving drivers of long-distance buses are closely related to sleep disorders. However, it has been difficult to objectively track the depth, quality rhythm, etc. of sleep, resulting in the need for large complicated devices and hospitalization to examine sleep disorders.
Silmee™ Bar type Lite is a stick-on biosensor that can simultaneously measure multiple biological data including cardiac potential, pulse, amount of motion, posture, respiratory interval, and skin temperature. TDK has developed a unique algorithm capable of differentiating between sleep and wakefulness and determining autonomic balance and sleep stage from the biological data obtained by Silmee™ Bar type Lite. It is expected to help prevent accidents during long-distance bus drives, etc. by identifying conditions before work.

Also used for systems that “visualize” emotions such as joy and stress

The development of an emotion analysis system using wearable biosensors is also underway. This system collects and analyzes the wearer’s heartbeat data in real time to analyze emotions such as excitement/happiness, stress/irritation, depression/tiredness, and calm/relaxation and visualizes this information by displaying the wearers’ current emotions and daily emotion history in dedicated apps. It enables companies to track their employees' hidden emotional fatigue and psychological load and take appropriate measures promptly.
TDK's wristband biosensor is used for NEC Emotion Analysis Solution, jointly developed by NEC Corporation and Nagoya City University. 
TDK aims to become the world's number one provider of sensor solutions through different types of sensor fusion integrating multiple sensors with software and algorithms. To realize an IoT society that is friendly to both people and things, TDK will develop solutions applying Silmee™ biosensors in various fields.