Catwalk goes techno

The latest from the world of wearable electronics.

At the hospital

People in the very near future will have a whole range of small devices incorporated into their clothing or stuck to their bodies as clever sticking plasters.

Much of the research into wearable electronics is focused on medical applications. Small sensors, incorporated into patients' clothing, could monitor their health while they go about their day-to-day lives. These devices could measure heart rate, temperature, blood pressure or brain activity.

At this year's CeBIT electronics show in Hannover, researchers at Fraunhofer-Gesellschaft demonstrated a 'digital assistant' to help asthma sufferers. The assistant includes respiration sensors that are based on conductive strips integrated into the patient's t-shirt. The conductors expand and emit small electrical signals as the patient breathes.

Fraunhofer researchers have also demonstrated a 'mobile health assistant' for cardiovascular patients based on a highly-flexible dry electrode that can be woven into the elastic fibres of a sensor shirt.

Smartex, a small Italian research unit founded by textile companies, is also interested in integrating sensors into clothing. According to Rita Paradiso, R&D director of Smartex, incorporating sensors into the textile material offers major benefits over conventional methods. "For clinical monitoring, you usually need to locate the sensor in a fixed position, so it must be done by experts in hospital rather than by the patients themselves," she points out. In contrast, if the sensors were already in the correct position in an item of clothing, then the patient would simply need to get dressed.

Smartex has already devised a prototype of its sensor shirt, which it calls 'Wealthy'. Paradiso said that the company's clothes are not significantly heavier than normal and that the only noticeable addition is a small electronics box similar in size to a mobile phone.

Small devices incorporated into clothing could also deliver treatment. Smartex is currently researching ways for clothing to apply electrical stimulation to treat patients with tremors.

The company is also looking at incorporating its technology into bed sheets that would generate data about a patient's movements when they are asleep. Movement sensors in sheets and clothing would be useful to physiotherapists to monitor whether their patients are doing their exercises correctly and what impact their normal movements have on their bodies.

"What really excites me is the possibility of getting information in real life and correlating it with physiology, for example, breathing and ECG readings to monitor stress," says Paradiso.

At the gym

An obvious extension of this idea is to use such devices to monitor performance and health of people during exercise.

Smartex has teamed up with WearTech in Spain to develop systems to help people when they exercise at home or in the gym. These systems will be based on a shirt, top or bra that will send data about the user's health and performance to their mobile phone.

Beyond health and wellbeing applications, companies are also looking at incorporating lifestyle devices, such as music players and computers, into clothing. The defence industry is interested in wearable electronics to conceal communication devices in a soldier's clothing.

With so many potential applications and gadgets, a key challenge is to develop ways for them to communicate with each other. Using radio waves and personal devices that communicate radio signals is already very popular. However, the antennas on mobile phones are designed to communicate away from the body while medical sensors and other devices on the body need to communicate around it. This means that antenna designs have to be rethought so that they radiate around the body while not protruding too far out.

William Scanlon and colleagues at Queens University Belfast are addressing this with a new patch antenna design that radiates more efficiently out of its side than previous patch antennas. It also exploits the creeping wave effect to transmit signals around the body.

Another issue that makes radio communication around the body tricky is that human bodies are good absorbers of radio waves. For health and safety, as well as performance, these need to be kept to a minimum, which raises challenges: shorter wavelength radiation is absorbed more than longer but antenna size is related to the above. This means that longer wavelengths require bigger antennas - an obvious disadvantage for devices that are intended to be discretely concealed in their users' clothing.

In textiles

There are further challenges in incorporating electronics into clothing. Firstly, there is the choice of fibre. Paradiso of Smartex pointed out that metal yarns and fibres have often been used in the textile industry and bring good conducting properties.

What's more, modern knitting technologies enable a multilayer structure to be produced so that the textile is electrically insulated, except where it needs to conduct electrical signals. The company has also been researching the best types of yarn for piezoresistivity, a property where the resistivity of a material changes when mechanical stress is applied. Such properties are required for sensors that detect changes with breathing or other movements.

Some of the biggest challenges in making clever clothing, however, come from the other fibres rather than the ones with special electrical properties. Elastic fibres are necessary in body sensors so that the clothes can make good contact with the body. However, the elastic fails over time in just the same way that elasticated underwear becomes looser, especially when the washing temperature is too high.

There are a range of options for embedding antennas into clothing. Scanlon believes that incorporating them as printed circuit boards is a good approach and that these could perhaps be made flexible. He says that fabric antennas can present problems with robustness.

"Incorporation into clothes is not as straightforward as you might think," observes Yang Hao of Queen Mary College, University of London. "You need low-permittivity materials if you are using them for the antenna substrate. These are good because they are low-loss, but bad because they make the antenna large." He adds that flexible metallic materials such as copper mesh or rubber, coated with conductive particles, are very good for incorporating antennas into clothes. Such fabric antennas can be sewn or ironed onto clothing or printed directly onto the fabric.

However, Hao agrees with Scanlon that there are challenges with this approach. "Because the substrate is so flexible, there can be bending issues," he says. "Antenna performance can also be affected if the clothes get wet."

Another option is the approach taken by John Batchelor at the University of Kent. He has developed a circular antenna that looks just like the button on a pair of jeans. This is designed to communicate in two modes: around the body and away from the body to another device.

Power challenges

Power also presents challenges to anyone designing wearable devices as the power sources have to be carried by the users or incorporated into the clothing. Batteries are the traditional approach but there is plenty of research into lighter and better ways to power them.

Nanotechnology researchers at Georgia Institute of Technology in the USA, for example, recently reported a way of generating electricity from people's movements using nanowires grown on the fibres of their clothes. Their approach uses the piezoelectric effect, where electricity is generated when certain materials are exposed to mechanical stress. The researchers anticipate that it could eventually help people power devices such as iPods as well as medical sensors.

The swish of fabric as a model shows off a new dress on the catwalk creates a powerful impression on fashion connoisseurs. But that walk could be more powerful than simply giving birth to a new clothing trend. As the model struts in front of photographers, her dress could be providing the power for biological sensors or a wide range of other portable electronic devices.

When batteries are not included

Another approach, intended for monitoring brain waves, was recently demonstrated by IMEC in Belgium. Researchers there have developed a battery-free electroencephalography (EEG) system that is powered by body heat and ambient light. The hybrid power supply combines a thermoelectric generator that uses the heat from a person's temples and silicon photovoltaic cells. It can provide an average power of more than 1MW indoors, which is sufficient to power the EEG system.

The idea of incorporating energy harvesting into textiles is also being explored by Sheila Kennedy at Massachusetts Institute of Technology. In a recent project, she made curtains based on solar textiles. These curtains harvest energy from the Sun and in her demonstration were used to power the solid-state lighting in a house.

When cost is an issue

Cost is another important factor for wearable devices. In particular, the goal for many medical applications is for the sensors to be disposable. For Scanlon at Queens University Belfast, improvements in antenna efficiency can help bring down the costs. "Our antenna is about eight times as efficient as a typical medical antenna across the link from one side of the body to the other. That efficiency could allow you to turn down the power or to use cheaper - even disposable - transceivers," he says.

Despite all the great advances in wearable electronics, there are still some issues to be resolved. Security issues have been considered extensively for mobile telecoms, but it is not yet known whether others might be able to tap into the wealth of personal information being gathered and communicated around our bodies via our clothes.

The creators of science fiction films always recognise that the clothes of the future will be different from today's fashions. In the real future, however, changes in clothing style are likely to be far more than just a sign of changing tastes. What might those metallic jump suits really be telling the world about you?

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