FEATURE
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The Emperor's new photonics clothes

Rachel Berkowitz discusses how wearable technologies for applications such as media, sports, logistics, and medicine are improving in terms of design and functionality

At some point in human history, ‘wearable technology’ meant wrapping yourself in the hide of the animal that you hunted with a hand-made spear. More recently, LED digital watches topped the 1970s charts for fashionable photonics. But now, wearable technology extends from head to toe, with glasses that project a smartphone screen in front of your eye; contact lenses poised to combine medical sensors with mobile virtual reality; and comfortable textiles integrated with LEDs and photonic sensors that monitor biological functions. 

Looking closer 

 

If the initial release of Google Glass left the scientific and non-scientific communities reeling in a fit of intrusiveness and bulky design, then a newly focused world of ‘smart’ eyewear should leave them excited about a sleek and useful product.  

In January 2015, Google halted sales of the Glass in its current form, with an aim to concentrate on developing and improving the product. Many industry commentators blamed this decision on a poor design and hefty price tag, which led to poor user adoption of the glasses.

Finland-based company Dispelix Oy describes smart eyewear as ‘the display challenge that everyone is trying to solve’. Their solution to developing a product is a near-to-the-eye, transparent display that looks like normal eyewear.

‘When Google withdrew their product, it shook up the market. People wanted to know if there would be another [form of] smart eyewear,’ said Antti Sunnari, CEO of Dispelix. Now, Dispelix is preparing to commercialise a new display, developed with VTT Technical Research Centre of Finland, which brings a virtual image equivalent to a 60-inch screen three metres in front of the eyes. ‘We’re working to combine three factors: image quality, thin lenses, and cost-effective optics manufacturing,’ Sunnari added.

To display a smartphone screen virtually, the first requirement is a battery to drive the electronics and illumination. Electronic switches from Android and iOS, which are found in many smartphones, control these components. The primary image source usually comprises a liquid crystal on silicon, from which the image is projected toward the coupling area with nanoscale diffractive patterns. This couples the light inside the eyewear. Then, total internal reflection out-couples the image towards the user’s eye.

‘There are a lot of different technologies [for communicating with the display], including eye tracking1, sensors, touch screen and voice. Nobody [yet] knows what the winner [will be],’ said Sunnari. Dispelix makes the optical components, but partner organisations design the electronics and integration into a product.

There is high demand among many industrial sectors for smart eyewear, as this makes it possible to display information easily for the worker. In warehouses – such as at that of international delivery company DHL – smart eyewear boosts efficiency, as workers can use both hands, have no need for barcode scanners or papers, and can follow mapped routes for locating packages.

In a world of increasingly complex machinery, customer service agents at Hewlett-Packard (HP) can view an image of, for example, a digital printing machine that a customer is struggling with, and help the client solve the problem. ‘That is something that many industries are looking for,’ Sunnari observed.

Moreover, in the field of sports, wristwatch electronics incorporated into a display on protective glasses would make it possible to monitor heartbeat, speed, and altitude without extra devices. And healthcare teams will be able to streamline workflows and access data intelligently delivered to smart glasses.

Lightweight and fashionable 

Consumers, particularly millennials, want devices with ever larger screens and rich, aggressive media, but that are also lightweight and fashionable. Steve Willey found an inherent conflict in the ability of virtual reality products to meet these goals. The conventional approach uses tiny flat-panel displays in the glasses aligned with optical components that focus the image, so that the wearer perceives they are viewing a normal television screen or small monitor. Willey proposed that removing the optical components from the glasses themselves might offer the answer.

‘As you move the optics closer to the eye, a smaller component will do the job of a larger one,’ noted Willey. His company, Seattle-based Innovega, has developed a technology to ‘float’ a one millimetre optic on the eye as part of a soft contact lens. This provides a focal plane at 15mm from the eye, which can be projected on an organic LED or liquid crystal micro-display panel integrated into any pair of glasses.

Because there are no bulky optics on the frames, the display screen can be brought into the field of view with very little motion, similar to the way a person wearing a hat would move their head slightly to improve their vision. Users can see media by merely dropping their chin half an inch.

Innovega’s ‘iOptik’ design comprises a passive contact lens with at least two components and no electronics inside the lens. The contact lens is 99 per cent the user’s normal prescription, and one per cent in the centre moulds the micro-lens for viewing media. Put on the glasses, and the micro-lens image projects onto the inside of the glasses and reflects back into the eyes, offering a 50° field of view. At the same time, light from the real world goes through the glasses to the user’s eyes, without interference from the tiny micro-components. The display can be controlled by touchpad, voice recognition, and – uniquely suited to the contact lens – eye tracking. ‘Now you have a situation where both your world and your media are in focus,’ said Willey. ‘You retain your regular [prescription] vision, but have a ‘magic’ decoder for anything by wearing the glasses.’

The basic technology is merely a screen. But adding a multitude of different sensors in the frame makes it a companion product for a smartphone, a tiny camera or accelerometer for sports, or an on-chip medical sensor component. ‘You can have a variety of glasses – ski goggles, sports glasses – depending on the application,’ added Wiley. ‘Our lens is passive, but you could place other sensors inside the lens. As much as our business enables big field-of-view glasses as a display or interface, it will extend into sensor-related applications.’

Innovega hopes to complete the FDA approval process and begin selling their product in late 2016.

Functional and flexible

Wearable tech goes further than what meets the eye, however. In August, President Obama announced a $171 million Manufacturing Innovation Institute to ‘secure US leadership in next-generation bendable and wearable electronic devices’. It will consist of a consortium of 162 companies, non-profit organisations, labs, and universities headquartered in San Jose, CA at the heart of Silicon Valley. Flexible electronics manufacturing has the ‘power to create sensors that can be lighter in weight, or conform to the curves of a human body, and stretch across the shape of an object or structure,’ according to a statement made by the White House.

On both sides of the Atlantic, wearable technologies are stretching to incorporate functional and fashionable photonics into thin-film materials that interface with tiny sensors and LEDs for media, sports, and healthcare applications.

In September, Electro Optics reported on a research collaboration between the Holst Centre, nanoelectronics research centre imec, and the Centre for Microsystems Technology (CMST) of Ghent University, Belgium; this resulted in the development of a stretchable and conformable thin-film transistor LED display that can be incorporated into clothing. Now, engineers who helped to develop the technology are working to improve reliability, resolution, and as well as applications that will provide the user with data.

‘Our technology is made in a way that we can integrate whatever sensor we want on the platform,’ said Frederick Bossuyt, team leader of CMST’s Stretchable Interconnects Department. Flexible islands of electronics are linked with stretchable metallic interconnects, and the entire system is then encapsulated into an elastic polymer. In one version – for large area, low cost applications – printed circuit board techniques are used to make the stretchable devices. In another version, miniaturised stretchable devices are constructed from layers of micron-thick polymer and metals with glued components. These stretchable devices are ideal to integrate into fabrics, combined with conductive yarns woven into a textile to allow communication and powering of these devices.

Bossuyt’s team collaborated with Philips Research to make a wearable device for treating repetitive strain injury with light therapy. The washable, breathable band can be wrapped around the wrist, with integrated blue LEDs. ‘Blue light applied on the skin frees nitric oxide molecules, which were being transported to the muscle leading to the pain. This small molecule has the effect that it relieves the pain,’ said Bossuyt. Challenges remain for making higher resolution displays and minimising the space between LEDs, while keeping the stretchability.

‘Now, we’re looking to smart garments that use integrated LEDs for visibility. We’ve also made a garment with solar cells to capture energy,’ added Bossuyt.

In any photonics-based wearable, the main challenge is the battery, particularly because lighting applications have high power consumption. The wristband uses a mobile phone lithium-polymer battery, which is still relatively large and bulky. But thin-film solar cells integrated into the fabric itself, as with the Holst Centre’s ‘solar shirt’, make device charging a possibility, as well as storing electricity for later use.

Band aid-like optics 

 

The new world of printed and flexible electronics has opened the market for analysing an increasing array of medical functions. 

Detailed monitoring of sensitive information allows for early-warning of signs of trouble, and thus preventive measures to be taken against a range of skin and blood diseases. If it’s easy to use, and cheap to the point of being disposable, so much the better.

Last year, engineers at UC Berkeley developed a band-aid-like pulse oximeter for measuring pulse rate and blood oxygen levels2. Current wearable devices can be comparatively large and cumbersome. Rather than silicon, the Berkeley team used organic optoelectric sensors on a flexible plastic substrate to make a disposable device that performed just as well as conventional models. Now, they are developing a second-generation optical sensor that will allow placement beyond the conventional fingertips or earlobes, for integration with patches on the wrist or chest.

A standard pulse oximeter sends red and infrared light through a fingertip or earlobe, and a sensor on the other side detects how much light is transmitted. Bright, oxygen-rich blood absorbs more infrared light, while darker, oxygen-poor blood absorbs more red. Comparing the transmitted wavelengths reveals how much oxygen is in the blood. The Berkeley sensors use red and green organic LEDs (OLEDs) and compare wavelengths transmitted to an organic photodiode (OPD).

In the second-generation reflection mode, OLEDs and OPDs are placed on the same side of the tissue, and reflected light is used for data on oxygenation. ‘The big plus for these devices is that we can fabricate them on flexible substrates. If you use a flexible OPD bent around your finger, the conformal interface to the skin reduces background noise, essentially increasing the signal-to-noise ratio,’ explained Yasser Khan who, along with Claire Lochner and Adrien Pierre, formed the team that conducted the study in Ana Claudia Arias’ lab.

A positive response from the medical community has brought offers of clinical trials to the project. ‘The idea that these sensors are flexible, and can be used in places other than the finger or the earlobe, has been a key point for this positive response,’ said Khan.

From the fabrication and assembly point of view, the photonic sensor array is challenging. But from the measurement side, it offers a simple, easy-to-use, non-contact technique, as opposed to the complex contact-based technique of conventional electrode arrays.

Indeed, flexible electronics labs are not focused on organic photonics alone: complementary to the exciting potential of light-based wearables are other electronic sensors engineered to a flexible, wearable substrate. Arias’ lab has also developed a ‘smart bandage’ that detects pressure ulcers, or bedsores, before damage reaches the skin’s surface, using a 3D-printed array of electrodes on a thin film3.

The technique – in which a current is run between the electrodes and electrical impedance measured as a function of frequency to create a map of tissue damage – could have applications for the monitoring of other conditions such as subcutaneous damage, or bone healing.

‘There are challenges with optimising the process for printing the electrodes, and with the materials for the flexible substrate,’ said Michel Maharbiz, UC Berkeley associate professor of electrical engineering and computer sciences and head of the smart-bandage project. ‘The key is that we are at this really nice convergence of electronics becoming smaller and low power, and a massive information infrastructure.’

This convergence is prompting people to try new applications for all sorts of parameters. Much of the work to build very small sensors is driven by clinically important applications. ‘We’re experiencing a revolution in wearables, with interest in understanding how this could be brought to bear in clinic,’ added Maharbiz.

Today’s wearable technologies are yesterday’s science fiction and fairy tales. And the scientists and engineers who are weaving these magnificent fabrics offer new designs encompassing media, sports, and medical applications, well worthy of public awe. 

References

 

1www.tobii.com

2www.nature.com/ncomms/2014/141210/ncomms6745/abs/ncomms6745.html

3www.nature.com/ncomms/2015/150317/ncomms7575/full/ncomms7575.html