Feature Story

Sensors for Wearable Technology - Enabling Product Differentiation

Sensors Insights by James Hayward, Guest Contributor

State Of The Art

It's no secret that wearable technology has garnered a lot of attention the past few years. The driving factor has been the adaption of technology that has been widely used in other consumer electronics areas into a form factor that can be worn on the body.

But to date, the extent of technologies that have been specifically developed for use in wearable device platforms remains limited. The majority of consumer wearable technology devices employ a 'components-in-a-box' approach, which makes use of commoditized components derived from the mobile phone, packaged in the form of a wearable product. Therefore, these simple devices, such as fitness bands, as we know them in 2015 have become commoditized rapidly, with options now produced in China for less than $5.

Infotainment devices are the most prone to this trend, as they will soon be moved to huge volume manufacturing in China, driving margins down quickly. However, with the advent of new types of sensors specifically designed and developed for use in wearable devices on the body, wearable technology will become part of our daily lives, disappearing into our clothing and presenting a huge commercial opportunity over the next decade.

Viewing only the commercially offered wearable products today provides a very narrow view of wearable technology products as a whole. In reality, there is a huge breadth of products that are emerging across very broad industry sectors.

Going Forward

In the medical space, there will be intelligent skin patches that will release drug molecules following the activation of chemical receptors, bionic suits that will augment human motion, and electronic components to aid and assist people with every kind of disability. In the infotainment space, smart glasses will provide augmented reality with intelligent responses to different stimuli. Immersive gaming solutions are already emerging with wearable devices to capture motion and enhance the user experience; and users will become increasingly connected, accessing senses beyond just sight and hearing to include remote touch responses.

Sensors

All of these advances will rely on sensors in some way. The main components of the majority of devices can be divided into the main categories of energy supply including both energy storage and also ambient energy harvesting, processors, sensor inputs, actuator outputs. and communication interfaces with other devices.

While generalizations are difficult with such a broad scope of devices, the majority of wearable tech devices today include at least an inertial measurement unit, consisting typically of a combination of a MEMS accelerometer and gyroscope, often alongside magnetometers and occasionally barometers, with the average number of sensors incorporated rising rapidly. The most widely used sensors are those that were directly adapted from existing billion-dollar sensor industries from devices like the mobile phone. However, as the market for wearable devices grows, the form factors that were suitable for other consumer electronics items will not be acceptable.

Sensors will need to achieve the same level of accuracy and reliability in smaller package sizes and with new form factors. They will also be combined in increasingly intelligent ways, to deduce the maximum amount of useful output from the data collected.

IMUs Dominate

Inertial measurement units (IMUs) are the most prominent sensor type driving the current hype around wearable technology. These are based on microelectromechanical (MEMS) accelerometers and gyroscopes. They enable devices to calculate data about how active someone is, including where they go, when they exercise and how well they sleep.

This data can all be collected from IMUs by using signal manipulation and data analysis algorithms to manage errors and other limitations from the individual sensors to output useful data. IMUs are readily available and very cheap. They can be purchased as individual units for individual experimentation and customization, or as complete multi-sensor packages with hardware (ASICs, etc.) and software drivers for ease of integration. They are also cheap, with accelerometers available for less than $1, and gyroscopes costing $2 to $3. These prices have been enabled by production of billions of sensors a year for consumer electronics and automotive industries.

Fitness and/or activity tracking devices based on these sensors have risen through the hype curve and now are dropping into disillusionment rapidly, with sales volumes that have not met expectations. Therefore, many companies are searching for additional sensing solutions that can add to IMU data used in sensor fusion. The hypothetical possibilities are clear, but the reality is that the quality of data is not sufficient for many applications, especially where medical and healthcare decisions rely on the data.

New Sensor Options Enable Greater Market Penetration

The majority of wearable devices are designed specifically to collect data about the body in order to improve quality of life. It is clear that if the quality of data is not sufficient, the device will not be useful and therefore will fail. However, there are other issues beyond quality of data that need to be taken into account.

If a wearable device is to be worn for a long period of time then it needs to be comfortable for the user. Lack of comfort will quickly negate the positives seen from useful data collection, resulting in failure. Also, even if the data is collected and used well, the gains to the user from the device need to be sufficient and obvious to the user or it won't be worn and will fail. The majority of devices tread these fine lines very closely, with most seeing some success in select communities but failing to reach large sales volumes.

The next generation of wearable sensors is beginning to emerge. It includes flexible stretch and pressure sensors for incorporation into clothing, skin patch sensors for measuring features such as chemical concentration and temperature, and finally new materials for dry electrodes enabling electrical measurement of the body in a comfortable, reliable way. The difference with these sensors is that they are being designed from scratch to suit the needs of wearable devices, with suitable form factors, material properties, power consumption and lifetimes.

Fig. 1: Relative Market Size in 2020 by Sensor Technology Type

Sensor Fusion

The data from individual sensors is useless without analysis and algorithms that are specifically designed for a specific output. The process of sensor fusion is the combination and analysis of data from more than one source to gain more useful information from the sensors. For example, sensor fusion logic can take raw data such as acceleration, rotation and position, and output useful information such as the direction of gravity, linear acceleration and device orientation.

Sensor fusion also allows data? Seems like there's a word missing here from different sensors to increase overall accuracy by tracking bias in other sensors. By combining data sources and adding additional assumptions and insight based on the system being measured, sensor outputs are converted into useful data that can be used in many applications.

Conclusion

The logic and software behind sensor data is enabling more and more applications derived from existing sensors. However, as the number of possible applications reaches saturation, continued growth will be dependent on the introduction of new hardware options to add data to the sensor fusion cloud.

The new sensors will compensate for the limitations in incumbent sensors, and add different, varied data points to enhance the overall insight that can be gained.

About the Author

James Hayward is a technology analyst at IDTechEx where he specializes in the markets and enabling technologies for wearable electronics. This includes authorship of several leading reports, including wearable sensors, haptics and materials. He graduated with First Class Honors from Imperial College London where he studied Chemistry with Medicinal Chemistry.

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