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Magnetic fields provide a new way to communicate 'wirelessly'

01 September 2015

UC San Diego engineers develop wireless communication technique that works by sending magnetic signals through the human body.

A prototype of the magnetic field human body communication system, developed in Mercier's Energy-Efficient Microsystems Lab at UC San Diego (photo:Jacobs School of Engineering, University of California San Diego)

The new technology, developed by Electrical engineers at the University of California, San Diego, could offer a lower power and more secure way to communicate information between wearable electronic devices, providing an improved alternative to existing wireless communication systems. The work was presented at the 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society in Milan, Italy.

While this work is still a proof-of-concept demonstration, researchers are looking to develop it into an ultra-low-power wireless system that can easily transmit information around the human body. An application of this technology would be a wireless sensor network for full-body health monitoring.

While Bluetooth technology uses electromagnetic radiation to transmit data, these radio signals do not easily pass through the human body and therefore require a power boost to help overcome this signal obstruction, or 'path loss'.

In this study, a technique called magnetic field human body communication uses the body as a vehicle to deliver magnetic energy between electronic devices. An advantage of this system is that magnetic fields are able to pass freely through biological tissues, so signals are communicated with much lower path losses and, potentially, much lower power consumption.

In their experiments, researchers demonstrated that the magnetic communication link works well on the body, but they did not test the technique's power consumption. Researchers showed that the path losses associated with magnetic field human body communication are upwards of ten million times lower than those associated with Bluetooth wireless.

The researchers also pointed out that this technique does not pose any serious health risks. Since this technique is intended for applications in ultra low power communication systems, the transmitting power of the magnetic signals sent through the body is expected to be many times lower than that of MRI scanners and wireless implant devices. Moreover, magnetic field human body communication could offer more security than Bluetooth networks.

The researchers have built a prototype to demonstrate the technique, consisting of copper wires insulated with PVC tubes. Atone end, the copper wires are connected to an external analyser and at the other wrapped in coils around three areas of the body: the head, arms and legs. These coils serve as sources for magnetic fields and are able to send magnetic signals from one part of the body to another using the body as a guide.

The mouth guard sensor offers an easy and reliable way to monitor uric acid levels in human saliva (photo: Jacobs School of Engineering, UC San Diego)

Researchers noted that a limitation of this technique is that magnetic fields require circular geometries in order to propagate through the human body. Devices like smart watches, headbands and belts will all work, but not a small patch that is applied to the chest to measure heart rate, for example.

Mouth guard sensor

Engineers at UC San Diego have also developed a mouth guard that can monitor health markers, such as lactate, cortisol and uric acid, in saliva and transmit the information wirelessly to a smart phone, laptop or tablet.

The technology, which is at a proof-of-concept stage, could be used to monitor patients continuously without invasive procedures, as well as to monitor athletes' performance or stress levels in soldiers and pilots. In this study, engineers focused on uric acid, which is a marker related to diabetes and to gout. Currently, the only way to monitor the levels of uric acid in a patient is to draw blood.

The team, led by nanoengineering professor Joseph Wang and electrical engineering professor Patrick Mercier (the latter responsible for the magnetic field human body communication technique) describes the mouth guard’s design and performance this month in the journal Biosensors and Bioelectronics.

"The ability to monitor continuously and non-invasively saliva biomarkers holds considerable promise for many biomedical and fitness applications," says Wang.

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