Human Patch to Generate Electrical Energy Through Body Movements

Using the static electricity from human skin to generate enough energy for electronic devices which require little power – a group of researchers from National University of Singapore (NUS) presented this idea during the IEEE MEMS 2015 conference with a small, stamp-sized, flexible generator that can be strapped to the skin, which converts the friction it creates with the skin into electricity.  Such device can open the gates for wearable sensors that will utilize body movements to power itself, instead of using batteries.

For many years, there have been studies on how to harvest electricity from human body movement to power up mobile electronic devices and sensors such as the implants used in medicine as personal health tracker.  One common technology was the nanogenerator, where mechanical or thermal energy is used to produce electricity.  Studies on nanogenerators typically revolve on three methods: piezoelectricity, pyroelectricity, and triboelectricityPiezoelectricity is the energy accumulated from mechanical stress.  Temperature change, on the other hand, can also create electrical energy called pyroelectricity.  Lastly, triboelectricity is the type of energy produce by contact electrification.  It occurs when the layers of two different materials gain electrical charge through friction

A study about triboelectric effect took advantage of the static electricity induced by friction to generate electrical energy.  Since human skin is a natural triboelectric material, the National University of Singapore researchers were only required to develop the other half of the layer where the human skin will be put in contact.  They constructed a flexible rubber patch made from silicone and bonded it with gold film of 50 nm thickness.  The gold film served as the generator’s electrode, where the resulting electricity is accumulated.  Thousands of tiny pillar-like structures were attached beneath the silicone rubber layer to increase the surface area of the device that gets in contact with the skin.  This increases friction, which means generates more current.

Lokesh Dhakar, one of the researchers that presented this human patch nanogenerator, has described the skin as the most abundant surface on the human body and a natural choice for one of the triboelectric layers.  He further explained that skin as a triboelectric material has a high tendency to donate electrons or get positively charged, which is important in improving the performance of the device if the other triboelectric layer intentionally chosen as the one with a tendency to get negatively charged.

A simple finger-tap on the device has produced 90 V at 0.8 mW, generating enough power to light up 12 commercial LEDs.  The device was also tried by strapping it to a human forearm, where fist-clenching was able to create 7.3 V.  Moreover, with the device attached to the throat, speaking generated about 7.5 V.

Though Georgia Tech researchers had an earlier study on skin-based triboelectric effect generator, whose results were reported to generate as much as 1 kV in ACS NANO last 2013, this device has two main distinctions from the human patch presented by National University of Singapore: flexibility and wearability.  For one, Georgia Tech’s triboelectric effect generator is much larger than the human patch.  Moreover, the material used by Georgia Tech was not as flexible as the one used by the human patch.  Dhakar explained that their human patch was aimed to provide wearable options by means of a more flexible material for the nanogenerator.  They wanted their device to fit any possible shape of the human body, in any size required.

Strong increase in revenue for MEMS microphones

Novel method to produce green light LEDs using nanowires

A new report of HIS technology points out to a forecast of strong growth in global revenue for MEMS microphones from 2013 and 2014 from about $800 million to more than one billion dollars with a continued growth estimated to reach about $1.4 billion by 2017 with estimated shipments of more than 5 billion units, compared with the less than 2 billion shipped last year.

MEMS (micro-electro mechanical systems) microphones are technically analog-to-digital converter circuits that can be fabricated with traditional semiconductor fabrication processes and therefore at a reduced price and in large quantities.

Considering that the MEMS microphone industry is slightly more than a decade old, this exceptional growth can only be explained by the outstanding advantages that MEMS microphones have when compared to their conventional counterparts, the two most important being: limited dimensions and light weight.

Another factor that fostered the growth of MEMS microphones has without doubt been the massive adoption of smart phones and similar devices, most of them embedding one or more microphones with Apple and Samsung being the biggest customers for MEMS devices on the market.

Finally, being MEMS microphones produced, along with all other categories of micro-electro mechanical systems, using conventional semiconductor technology applied to high volume production, the price of a single device is extremely reduced when compared to conventional microphones as one single wafer can contain thousands or more of units.

Therefore, the very large part of the cost for producing a number of batches of MEMS microphones is required by the design, development and prototyping phase plus all the fixed costs required for production (mask costs, etc.)

Recent improvements in MEMS microphones come with a much better signal-to-noise ratio: best MEMS microphones have currently reached a value of 64 decibels. A high signal-to-noise ratio is very important, for example, in smartphones and tablets that have voice command functionality.

Another advantage of very-high-SNR microphones is enhanced support for voice commands like Apple Siri and Google Now.

Another example of device that uses high signal –to-noise ratio MEMS microphones is the Apple iPad, a device which embeds more than two microphones in a single tablet. Samsung is also working on and selling devices with multiple microphones per device. It is estimated that soon high-end devices may embed up to four microphones per single device, therefore increasing the usage of MEMS microphones all over the market.

It is now estimated that MEMS microphones make up almost the totality of all very high signal to noise ratio microphones sold today.

Other prominent applications for the device are in the hearing aid and in the automotive markets

Products like hearing aids require powerful MEMS microphones with high signal-to-noise ratios in order to guarantee the quality of the audio to be heard from the customer. Products like ReSound LinX, among others, are using multiple microphones per device in order to delive the best audio quality to the hearing aid user.

Another big market just ready to start a strong growth is the automotive market, with driverless automobile technology ready to pick up shortly.

Human support not limited to wheel driving has then to be complemented with voice command and therefore MEMS microphones are likely to find there a new, stimulating market.

If you are interested in MEMS design and development, please visit our MEMS design service page.

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