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Engineers Try to Solve Cochlear Implant Problem on Plastic Slides

Washington University in St. Louis, News & Information, May 4, 2006 – By Alison Drain

Static electricity buildup from sliding down a plastic slide -- instant summertime fun for the hearing set – can temporarily silence the world to children wearing cochlear implants.

Robert Morley, D.Sc., associate professor of electrical engineering at Washington University in St. Louis, Missouri, and his colleague Ed Richter, have tested static electricity buildup on sliding children to quantify the sparks. Thanks to some publicity and increased awareness, their research has inspired the St. Louis County Parks and Recreation Department to consider the problem, and an anti-static coating company to try to solve it.

Cochlear implants, often referred to as bionic ears, help provide a sense of sound to a profoundly deaf or severely hard-of-hearing person. The costly surgical procedure invites a doctor to wind an array of up to 22 electrodes through a diseased cochlea, the part of the inner ear that sends electrical impulses to the brain. An externally-worn speech processor filters sound, selecting and prioritizing tonal frequencies specifically for its wearer, and sends it to a magnetic transmitter behind the external ear. The
internal device, then, perceives the processed sounds after the transmitters ends
them by electromagnetic induction. The catch? Once the device is implanted in the cochlea, the patient submits to total hearing loss when their unit is switched off or malfunctioning.

The speech processors aren’t zap-proof. Their smarts can scramble if a wearer removes her sweater too fast or slides down a high-voltage-generating plastic slide. When a child discharges the electricity by touching something -- like a fellow slider -- the processor temporarily loses function. Restoring hearing requires an inconvenient visit to an audiologist to have the unit reprogrammed.

“The kids who have cochlear implants are told that if they want to go to the playground and go down the plastic slides like the other kids, they have to take off their speech processors,” Morley explained. “So then, of course, they are at a disadvantage on the playground because they can’t hear.”

Morley, who learned static electricity testing as a graduate student while running companies from his basement, developed a plan to test slides in humid St. Louis and in much drier Tucson, Arizona. He set out to quantify static buildup on different clothing materials, with different kids and slide techniques, on slides with different manufacturers and in different climates. His project was sponsored by the U.S. Government Access Board.

“So we bought some clothes, we got some measurement equipment to measure static electricity, and we used a laptop that we had,” Morley said. “This was a very low budget -- $25,000 -- which, for Washington University research, is a drop in the bucket.”

Low-budget doesn’t have to mean low-impact. Morley and Richter sent two daughters apiece to do some work on local playgrounds and procured some interesting results. The girls slid for science, testing variable clothing and St. Louis slides; their dads measured voltages the girls discharged upon landing. Richter’s brother performed the same tests in Tucson, where dry air encourages static electricity buildup.

Parents can’t take steps to remediate the problem, Morley found. He found no correlation between voltage and polyester, cotton, or nylon. Different children and different slide techniques gave the same results.

Morley explained his plotted data: “One thing of interest here is, out in Tucson, at low humidity, we see some final voltages for slides at one park.  On the same day, Richter’s brother got really high voltages at another park.” All plastic slides are not created equal. Humidity, a known static electricity deterrent, remains the most important factor in voltage buildup. But Morley and Richter found that a manufacturer’s materials choices
could affect the amount of static electricity on sliders in arid climates by a factor of three.

As a result of this research, people began to acknowledge the problem. One St. Louis County Parks and Recreation employee probed Morley for his slide replacement project at Faust Park. One local company, which manufactures anti-static coating for fighter jets, contacted Morley after hearing about the issue. The company thinks its coating could be applied as a durable, inexpensive polymer that could withstand wear over a plastic slide’s lifetime.

“That would be the best outcome of this project -- that we solve the problem instead of just quantify it,” Morley said.

St. Louis is home to four deaf schools including Washington University’s Central Institute for the Deaf, which draws students from as far away as Hawaii, Mauritius, and Pakistan. Nearly 100,000 people worldwide have restored functional hearing because of their cochlear implants. About half of those people are children.

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