Getting a Tattoo to Send a Signal

On-skin electronic devices are an emerging technology that holds great promise in various fields. These devices are designed to be seamlessly integrated onto the surface of the skin, offering a wide range of applications and advantages over traditional hardware platforms. By harnessing the flexibility and stretchability of thin films and other advanced materials, on-skin electronics enable comfortable, non-invasive, and unobtrusive monitoring and interaction with the human body.

One of the primary uses of on-skin electronic devices is in the field of healthcare and medical monitoring. These devices can be utilized to measure vital signs such as heart rate, body temperature, blood pressure, and oxygen levels, providing real-time data for healthcare professionals. Beyond healthcare, these devices have applications in various other domains. They can be employed in sports and fitness to track performance metrics like motion, muscle activity, and hydration levels. Additionally, they have potential uses in augmented reality and virtual reality applications, enabling the creation of interactive experiences by incorporating sensors and actuators directly onto the skin.

But as might be expected, for these devices to be unobtrusive, the choice of possible components that they can include is quite limited. One area that on-skin devices have really struggled to perform adequately is in wireless communication. This traditionally requires hardware like a transceiver, amplifiers, analog to digital converters, and batteries. And all of that hardware makes for a lot of bulk, which is obtrusive for the wearer, and also limits where the device can be placed on the body to locations like the wrist where it will be less of a burden.

Future wearable devices may be able to be a lot more compact and comfortable thanks to the work of a pair of researchers at Yeditepe University and Istanbul Technical University in Turkey. They have developed what they call a nano-tattoo that can be sprayed anywhere onto the body (or other surfaces, for that matter). Once in place, this nano-tattoo can passively send data to an external device without wires or an onboard power source.

The tattoos are composed of two different inks layered on top of one another. One is made up of a zinc oxide that has nanowires embedded within it. On top of that is a graphene aerogel conductive ink. By including a small amount of aerogel in the bottom layer as well, the two inks are able to strongly adhere to each other. These inks are both painted onto the surface of the skin using needles.

The unique composition of the nano-tattoo allows it to generate electricity via a piezoelectric effect as the tattoo changes shape while the wearer moves normally. Then by utilizing backscattering communication principles, an external device like a smartphone can reflect signals off the tattoo to receive data, with the help of a broadband modem.

These signals allow the tattoo and the smartphone to establish a link, after which the phone can continuously monitor radio frequency signals being emitted by the tattoo. These signals are interpreted with the help of an artificial intelligence algorithm.

This innovation solves a problem that has long persisted in on-skin wearable devices — how to seamlessly retrieve data from the device under real-world conditions. The team believes that their device will enable all sorts of new use cases for wearable devices. They are presently working on a wearable electroencephalogram based on their technology, however, the requirement for motion to generate electricity could be a problem for such an application. No need to worry about that though — another technique is in the works that will do the job using sweat or saliva.