Solving Smart Apparel Design Challenges with Printed Flexible Sensor Technology

From fitness trackers and smartwatches to virtual and augmented reality (VR/AR) headsets, wearables are now permeating the daily lives of consumers around the world. People have come to rely on wearable devices to monitor their health and well-being, keep them connected to the outside world, and provide endless opportunities for engagement. Analysts predict the wearable technology market will reach US$51.60 billion by 2022, driven by these consumer preferences for sophisticated gadgets, the growing incorporation of next-generation displays in wearable devices and their intersection with the growing popularity of the Internet of Things (IoT). ) and other connected devices.[1]

As the enabling technologies of flexible and printed electronics continue to improve, the field of wearables is already moving beyond rigid devices to encompass a host of textile-based smart wearables, ties, eyewear, headgear and shoes. This article will focus on the challenges associated with designing smart clothing and how flexible printed sensor technology can provide solutions.

What is driving the smart clothing market?

Smart wearables are a rapidly emerging market for fitness and rehabilitation applications, both clinically and personally. Medical applications are a good starting point for smart wearables, as they have the potential to reduce medical costs and allow clinicians to collect patient data outside of medical facilities. It also allows patients’ rehabilitation progress to be tracked more accurately; for example, tracking improvements in range of motion or gait over longer periods of time and in real-world scenarios. However, due to stricter approval processes, the time to market for medical apps is likely to be longer than for consumer apps. For this reason, industry growth is expected to be faster in the consumer space.

For sports enthusiasts, the smart workout gear offers the ability to track their own biometric data, including health and fitness indicators such as heart rate, calories burned, stress level and production of energy.[2] For example, fashion apparel designer Ralph Lauren and performance wear brands like Hexoskin, Athos, and Physiclo first showcased their smart workout gear at New York Fashion Week in 2015.

Figure 1 There are many points where technology can be integrated into clothing to monitor performance and biometrics.

For these businesses, tracking biometrics is just the start. The next steps will be to incorporate technology that stimulates muscles and increases the effectiveness of a workout. The idea is that the clothes will be seen not only as tracking devices, but also as essential pieces of fitness equipment.[3]

Existing technological approaches

The integration of sensors and their complementary electronic components into smart sports equipment has been going on since 2002, when miniaturized electronic devices began to replace the probes, electrodes and masks worn by athletes in training laboratories.[4] These approaches relied on silicon-based sensors, microcontrollers (MCUs), Bluetooth transceivers, and available standard batteries. Miniaturization was a key goal of these devices, which were sewn into small pockets of fabric as unobtrusively as possible. In some cases, however, these early efforts made clothing bulky and uncomfortable, and hampered performance. Additionally, designers were limited in sensor placement, which reduced the ability to capture important metrics from multiple data points.

More recently, flexible and printed sensor technologies have been implemented as a solution. Sensoria‘s smart socks, for example, use chemically treated textile patches as variable resistors and weave a flexible, silver-based conductive thread that connects each sock to a magnetic Bluetooth anklet, which then transmits data to a smartphone app. . These approaches are still quite expensive and very complex to design. In 2015, two pairs of socks and an anklet sold for $200.

The printed detection solution

As printed and flexible sensor technology becomes more advanced and readily available, it opens the way to solving many design challenges that cannot be solved by incumbent technologies. Unlike rigid wearables, designing smart wearables requires considerable customization. Working with silicon-based technology is an expensive and time-consuming undertaking. Delivering a new product can take six to nine months, with development costs running into millions of dollars. Alternatively, implementing a new design using printed/flexible electronics may take only a few weeks and cost several thousand dollars. Flexible, printed sensors therefore lend themselves well to high-volume manufacturing, thanks to short time-to-market and lower-cost materials.

Flexibility of the sensing device is critical to acquiring accurate data in rehabilitation applications as well as performance training. Sensors must be able to maintain a signal, even when bent at the most extreme angles. This is not possible with rigid silicon-based sensors.

Sensor washability and durability are also important factors in smart wear applications. If they cannot be washed, they must be replaceable. As such, new printed sensor solutions should be inexpensive and easily replaced.

Power consumption is another design challenge, as carrying a battery adds wearer discomfort. Printed sensors use less than 1% of the system’s power budget, 99.9% of which is allocated to microcontrollers and associated wireless devices.

Finally, data acquisition from the sensor must be considered. Rather than relying on just a few data points, printed sensors allow small-scale networks located throughout the garment to obtain many data points in a small footprint.

The Science Behind Printed Sensors

Printed sensor technology requires a mastery of materials science, in addition to the development of electronics. The materials themselves must be sensitive to different stimuli, and the ability to isolate one stimulus from another is essential. Understanding the materials science behind the sensors is therefore integral to the success of this technology.

Figure 2 Materials scientists at Brewer Science have worked closely with apparel and electronics designers to develop a family of flexible printed sensors that address the unique challenges of smart apparel design.

For example, flexible sensors can use materials such as conductive carbon junctions to sense external stimuli while maintaining a thin form factor that is conformable, flexible, and durable. Additionally, printed sensors made from these materials exhibit high sensitivity and can be easily transformed into arrays.

Motion monitoring is another strength of printed sensors. Their flexible form factor enables the measurement of bi-directional flexural strength data with a wide range of motion, ±100 degree linearity, and constant signal amplitude.

Printed humidity sensors, when made with the right materials, can track variations in humidity with pinpoint accuracy.

Design Considerations for Printed Sensors

The most challenging aspect of implementing printed sensor technology in smart wearables is integrating the sensor with non-printed electronic components, such as a microcontroller, Bluetooth device, and power source. Although these devices could eventually be printed, they do not lend themselves to the format and that would require years of expensive development.

When implementing printed sensors in a smart wearable design, fast and accurate analog-to-digital conversion is crucial to both save energy and obtain the most useful data. Selecting analog embedded microcontrollers or standalone analog devices with a low signal-to-noise ratio is another important consideration to ensure accurate data collection.

picture 3
Brewer Science Humidity Sensor Dimensions in Millimeters

The speed of sensor response to stimulus is also an important issue in controlling power consumption. A traditional silicon-based temperature sensor can take up to five seconds to respond to a change, causing the MCU to wake up more often for comparative readings. Printed sensors can provide instantaneous response to temperature changes, allowing better control of the MCU’s sampling rate and enabling it to spend more time in battery-efficient sleep mode.

From the perspective of the clothing designer, one of the biggest hurdles to overcome in designing smart clothing is the lack of technical knowledge to integrate sensors and electronics. To optimally support them in achieving their design goals, partners should provide apparel companies with technical know-how that encompasses not only the finished printed sensor and its integration with system electronics, but also an understanding of the best materials to be used in this sensor.

Additionally, pairing garment designers with these partners from the earliest design stages is critical to ensure design feasibility and allow time for the necessary customization of the printed sensor. This expertise and early collaboration, coupled with the inherent low cost and speed of customizing printed sensor form factors for mass production, are critical to successfully bringing smart wearables to the mass market.

The references

  1. Wearable tech market worth $51.60 billion by 2022», Markets and market studies
  2. Mr. Schlossberg, “The Next Big Sportswear Trend Isn’t About Style At All», September 11, 2015, BusinessInsider
  3. L. Dishman, “Here’s Why You’ll Soon Be Wearing “Smart” Workout Clothes” September 11, 2015, Fortune
  4. Mr. Reisch, “With the help of electronics, fitness clothing is getting smarter” December 7, 2015,
  5. Mr. Reisch, ditto

Robert (Chris) Cox is the Director of R&D for New Business Development at Brewer Science.

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