For some deaf children, a plastic slide is a more formidable foe than the school wedgie-giver. Static electricity buildup from sliding down a plastic slide — instant summertime fun for those with normal hearing — can temporarily silence the world to cochlear implantees.
Robert E. Morley, D.Sc., associate professor of electrical engineering at Washington University in St. Louis, and his colleague Ed Richter, research associate in electrical engineering, 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 transmitter sends 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.”
Testing humid St. Louis, dry Tucson
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 a much drier Tucson. 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, his Washington University colleague, 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 on an insulated pad.
Richter’s brother performed the same tests in Tucson, where dry air encourages static electricity buildup.
What they found was that parents can’t take steps to remediate the problem. They found no correlation between voltage and polyester, cotton or nylon. Different children and different slide techniques gave the same results.
Referring to his plotted data, Morley said, “One thing of interest here is, out in Tucson, at low humidity, Ed’s brother measured voltages at two different parks on the same day with the same humidity and the voltages at one park were three times higher than at the other park.” All plastic slides are not created equal, the researchers concluded.
Humidity, a known static electricity deterrent, remains the most important factor in voltage buildup. However, Morley and Richter found that the materials a slide manufacturer selects 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 a slide replacement project at Faust Park. One local company, which manufactures anti-static coating for fighter jets, contacted Morley after hearing the issue. The company thinks their 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 schools for the deaf and hearing-impaired, including the Central Institute for the Deaf at Washington University Medical Center. CID 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 them are children.