Wearable Waveguides: Designing Metamaterials for Body-Area Networks

By Stephen Jorgenson-Murray

The body is a potential trove of data, but to make use of it that data needs to

first be captured and processed. The rise of Big Data and the Internet of Things has spurred wearable sensor technology in products like smartwatches, fitness trackers, vital signs monitors, and new medical products.

3M is a major multinational corporation that specializes in materials products ranging from adhesives and tapes to dental and health care. Jaewon Kim, Research Specialist at the 3M Corporate Research Lab and SIMULIA Champion is developing new technology to allow wearables to evolve to the next level.

For many applications across high-tech, health care, sports science and military industries, multiple sensors are needed across the body. Traditionally, these would be attached by wires, but as this limits the mobility and freedom of the wearer, they are increasingly being made wireless. This means that antennas and batteries have to be integrated into a small, lightweight package.

The human body has dielectric properties that differ significantly from those of free space, so antennas have to be designed with this in mind. The tissues of the body can absorb, refract and reflect radio waves, diminishing performance and leaving dead zones without signal. Developing antennas that direct power away from the body would improve off-body communication range and decrease power consumption – vital for improving the battery life of devices meant to be worn for extended periods.

To allow multiple sensors around the body to link up without wires, Kim helps develop new materials that act as waveguides, directing radio waves from one wearable device to another. These new materials direct the signals through the material over the skin, allowing multiple sensors to link to a central control device through a “body-area network” (BAN).

As well as improving energy efficiency and reception, the waveguiding material also gives designers, medics and users more freedom when deciding where to place the sensors. No wires are needed, and with no communication dead spots, the sensor can just be embedded in clothing or attached to the body wherever it is needed. The material directs waves away from the body, reducing human exposure and helping designers ensure they remain below regulated specific absorption rate (SAR) limits.

The product he works on are meta-materials – materials that bring together a composite of elements to achieve electromagnetic properties not found in nature. In this case, numerous small resonators made of a material with a high dielectric permittivity are embedded in a substrate material to form a “high dielectric resonator” (HDR) array. Kim’s goal is to find a resonator design that maximizes the power transfer.

Electromagnetic simulation in SIMULIA CST Studio Suite is a powerful tool for designing these resonators. A quick calculation of the properties of a single resonator with unit cell boundary conditions can be used to predict the behavior of a huge array of resonators very efficiently, allowing Kim to find a resonator geometry, spacing and material properties that offer the best transmission behavior in the required frequency band.

Once the initial resonator type is chosen, it is then integrated into the fabric. The 3D structure can be modeled in detail and bent around the body to simulate how it will work when worn.

Using simulation, Kim’s team was able to design an HDR waveguide that significantly improved transmission between wearable sensors. Measurements on a physical prototype agreed with the simulation and showed an improvement of 20 dB for the coupling between two antennas when using the HDR waveguide, as compared to free space. As a result of the work, the development process was significantly accelerated and 3M was able to use the modeling results to support their patent filings on this innovative new technology.

For more detail, please watch Kim’s presentation, entitled “EM Waveguiding through High Dielectric Resonator Metamaterial Array for Wireless Wearable Application,” here.