Thoughts on energy harvesting for wearable equipment

Thoughts on energy harvesting for wearable equipment

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By eeNews Europe

Wearable applications including smart watches, sport watches, fitness bands and more are growing in popularity, and so, too, is the demand for intelligent sensors to use in them. If analyst predictions are correct, the market is going nowhere but up in the coming years.

So what are the keys to making wearables ubiquitous for daily life?

Significant features and functionality are a given, but equally critical is battery management. The more plentiful the features, the more power the wearable technology needs. Let’s face it, nobody will be happy with wearables with short battery lives.

Wearables manufacturers have several options for increasing battery life. The first involves reducing the power consumption of each individual block to a minimum. Another is using higher capacitance batteries – although in most cases this will also lead to larger battery size.

But there’s a great third option for extending battery life for wearables: energy harvesting. What if simply wearing the device could also extend its battery life? The concept isn’t new. One of the earliest examples of an energy harvesting application is the well-known self-winding watch, which was invented in 1770.

Today’s energy harvesting technologies have progressed significantly and the number of developments around energy harvesting is growing quickly in many different market segments:

A key unique selling proposition for watchmaker Citizen is micro energy harvesting with solar energy. Most of the company’s watches are powered by light that is harnessed on the dial. Seiko, one of the pioneers of digital watches, launched a solar-powered GPS watch last year. Earlier this year, Tissot introduced T-Touch Expert Solar, which includes various sensors and micro energy harvesting via solar power.

In the future it will be impossible to imagine many applications not using some form of energy harvesting technology. There are various applications in industry and in consumer markets where energy harvesting will be validated in the not-too-distant future:

Ultra low-power wireless systems (WSN)

Body Area Networks (to monitor vital signs/medical conditions)

Industrial monitoring

Intelligent thermostats

Smart textiles/garments

Independent of the energy source, all energy-harvesting applications have one common denominator: A dedicated part that transforms the energy from the source into electric power. To recover the energy for use in an application, a separate dedicated part must efficiently condition the power so it conforms to the requirements on the application side.

For the wearables market, no matter if using a solar cell or a thermoelectric generator, at the end, every wearable application needs a boost converter, which transmits the power from the low-input voltage side to the high-output voltage side (charging a battery or a supercap, for example). Depending on the application and the requirements, the boost converter must be designed and configured perfectly to use energy from the source part efficiently. Hence, using a standard converter, which should cover a wide area of end applications, will not lead us to a good result.


Instead, when harvesting energy for wearable applications, the converter must fulfill three major requirements:

It must be a very highly efficient booster.

Depending on the energy source and often on the end application’s associated space limitation, it has to be able to start up and work under very low-input voltage ranges.

It must be optimized perfectly to the used energy source part and its operating point. This is called “maximum power point tracking” and is defined as the capability to reach exactly this operating point, where the maximum power can be achieved from the energy source.

Due to these three important factors, for each type of wearable application and for every different kind of energy source a dedicated boost converter is required to achieve a highly efficient and satisfying system.

The wearables market and its growth will be exciting to watch. Manufacturers gearing up for a place at the table should be looking at the possibilities of energy harvesting. Keys to that will be creativity and a strong focus on IC solutions that address all three of the major criteria outlined above.

Thomas Kail joined AMS as an application engineer for standard products. More recently he has served as a product manager for power management products and his major task is defining the right products for the customers’ needs. This article first appeared on EE Times’ Planet Analog website.

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