Wednesday, February 22, 2012

#MEDICAL: "Magnetic Sensors Empower Drive-by-Tongue"

Electrical engineers have redefined the level of fine control afforded to drive-by-tongue systems used by spinal cord injury patients to control their wheelchairs.

Reduced size magnetic sensors are embedded in a dental retainer worn in the mouth (right) to recognize seven different tongue movements (left).

Tiny micro-electro-mechanical system (MEMS) sensor chips, a minuscule wireless transmitter, and an encircling power-beaming battery pack enough smarts into a centimeter sized Tongue Drive System for patients suffering spinal cord injuries to maneuver a wheel chair and operate a computer with their tongue. The Tongue Drive System was demonstrated at this week's IEEE International Solid-State Circuits Conference in San Francisco.

Four magnetic sensor chips recently enabled this downsized Tongue Drive System to fit onto a dental retainer, which held the device immobile against the roof of the mouth, making its use invisible to outside observers. Previous models used a headset to hold the magnetic sensor circuitry. That eliminated the need for a wireless connection, but made it more difficult for patients to operate--especially when the headset got knocked askew.

"Moving the sensors inside the mouth [gives] the Tongue Drive System increased mechanical stability and comfort, making is nearly unnoticeable, " said professor Maysam Ghovanloo, at the Georgia Institute of Technology.

A permanent magnet, on a tongue stud, is used to activate the magnetic sensors on the Tongue Drive System. The system sends a wireless command to a nearby Apple iPod, which in turn sends a control signal to the wheelchair. When not driving, the Tongue Drive System also gives drivers access to text messaging, the Internet, and iOS apps.

The software running on an iPod controls the movements of a cursor on its screen or substitutes for the joystick function in a conventional powered wheelchair. An additional app allows the patient to craft their own custom commands to perform repetitive tasks.

The circuitry for the Tongue Drive System is completely encased in water resistance vacuum-molded high-impact dental acrylic, making it extremely durable, impervious to moisture, and completely isolated from its environment. In order to charge the lithium-ion battery pack on the Tongue Drive System, an embedded antenna loop around the outside of the dental retainer receives a 13.56 MHz radio beam. The induction coil drives an energy harvesting circuit that charges the battery wirelessly at night in a charging dock on the wheelchair.

Clinical trials at the Atlanta-based Shepherd Center and the Rehabilitation Institute (Chicago) were conducted recently involving 11 patients suffering spinal cord injuries. Each received a tongue piercing to install the tongue stud containing a permanent tiny magnet embedded in the upper ball. Patients performed 12 test sessions--two per week over a six-week period--to troubleshoot the Tongue Drive System.

Funding was provided by the National Institute of Health (NIH), the National Science Foundation (NSF), and the Christopher and Dana Reeve Foundation.