Displays that move with you
Most wearable screens today are small, rigid panels in a case on the wrist or in a headset. Research and concept work goes further: bendable panels that wrap around a limb, light-emitting fibers woven into fabric, and ultra-thin films that rest on the skin like a temporary tattoo. These are described here as ideas and experiments. Which of them reach everyday life is unknown.
Each pushes the same question: what happens to a display when it is no longer a rigid object that you look at, but a thing that touches, stretches and moves with a body?
Forms being explored
Curved or bendable wrist displays. A flexible panel can follow the shape of a forearm. This depends on flexible substrates and on stacks that tolerate repeated bending.
Textile displays. Light-emitting fibers or small emitters attached to fabric aim to make garments that glow or show patterns. The basic challenge is that fabric flexes, stretches, gets pulled and, importantly, gets washed.
Stretchable displays. Bendable is different from stretchable. A bent sheet can keep its length, but a stretched one must change it. Designs use wavy or serpentine conductors, or small rigid islands connected by flexible links, so that the material can extend without breaking its circuits.
Skin-mounted films. Extremely thin layers might be placed directly on the skin and hold simple indicators such as lights or color changes. These are generally not high-resolution video screens.
Smart eyewear and headsets. Display glasses and contact-lens concepts bring the screen to the eye. The optics for those are discussed under augmented reality and microdisplays, and they raise their own issues of power and heat near the face.
Comfort puzzles
A wearable display touches or sits near skin for long periods, so comfort is not optional.
- Weight and bulk. Items that feel fine for a minute can be tiring for hours.
- Breathability. A sealed, waterproof film can trap sweat and heat on the skin.
- Heat. Power used by a display becomes heat, and the same display heat considerations that affect a desk monitor become more noticeable when the device is against the body. Surface temperatures need to stay comfortable and safe, and standards for this are set by regulators and differ by place.
- Edges and materials. Parts that touch skin must not irritate it. Some people react to certain materials, and anyone with skin concerns should seek professional guidance.
- Fit. Bodies differ in size and shape, and a display that suits one may not suit another.
Durability puzzles
Everyday wear is rough.
- Repeated flexing. Joints and fabric bend thousands of times in ordinary use, causing fatigue like that found in folding panels.
- Moisture. Sweat, rain and washing expose electronics to water and salts. Some light-emitting layers are sensitive to moisture and oxygen, so protective barriers matter, but they must also be flexible.
- Impact and abrasion. Knocks, rubbing and pulling can scratch or crack a layer, as with cracked screens on phones.
- Cleaning. A garment may be washed in agitated, soapy water, which is far harsher than the gentle screen cleaning advised for ordinary panels. Many experimental textile prototypes avoid or minimize washing, and how to handle it for real products is an unresolved point.
- Connections. Wires, contacts and joins are frequent failure points where a rigid part meets a flexible one.
Power
Wearables cannot carry a large battery comfortably. Options include small batteries, wireless charging and energy harvesting from motion, light or heat. Harvesting typically yields very little power, so the display must be modest in its demands. That favors approaches with low consumption, such as e-paper displays, which hold an image without power, or displays that are only on briefly. Even for ordinary watches, always-on displays illustrate the trade-off between convenience and battery life, and the same trade-off applies here with tighter limits.
Input and feedback
Body-worn displays rarely work alone. They may include touchscreens or touch-sensitive fabric for input, and haptic feedback to give information through vibration when looking at a screen is inconvenient. Tiny, stretchable sensors that follow skin movement are an active research area, but they are separate from the display problem.
Privacy, safety and sense
A screen on the body can be seen by others, so what it shows has social and privacy implications. Anything intended for health or safety use should be treated carefully, because such products are subject to rules and testing that differ from place to place, and a general article cannot say what is appropriate. Eye comfort matters too for head-worn designs, where a poorly set focus distance or flicker can bother some wearers.
What is still unresolved
- Whether stretchable and washable displays can last for years.
- How to supply enough power in a light, comfortable package.
- Which uses are better served by a simple indicator light than by a full display.
- How to make them affordable and repairable.
A reasonable view is that simple, rugged wearable indicators are more plausible than detailed skin-like video, but this is a judgment about difficulty, not a prediction.