August 12, 2013
Ready and ABLE to Protect Soldiers' Hearing
One Saturday last summer, Dan Simon finished an article about the problem of hearing damage in warfighters and went outside to mow his lawn with the story still on his mind. As he placed his finger over the hole in the mower’s primer bulb, he experienced an “aha” moment, as he thought: “Maybe a little check valve is the answer to solving the problem of ear protection for soldiers.”
Less than a year later, Simon, an engineer in the Asymmetric Operations Department, teamed up with other APL scientists and engineers on an inexpensive prototype earpiece designed to prevent catastrophic hearing damage after sudden explosive blasts, and together they earned the first-ever Ignition Grant Prize for Innovation for their work. Hearing loss is the leading disability of veterans returning from war zones, according to the Department of Veterans Affairs.
The low-cost device—called the “Anti-BLast Earplug” (ABLE)—includes a modified check valve that is normally open to allow soldiers to hear what is going on around them. In the event of a nearby explosion, it quickly closes to protect warfighters’ hearing by blocking the blast wave from the ear.
“We knew we needed to keep our solution simple and practical,” says Simon. “We want the technology to provide adequate protection, but we also want to remove barriers that would prevent soldiers from using it regularly. The ABLE prototype is comfortable, doesn’t interfere with ordinary hearing, and is inexpensive, so soldiers don’t need to worry about losing or damaging it.”
Engineers from multiple departments across APL (including biomedical and materials fabrication groups) collaborated to develop the ABLE prototype, which is a modified commercial earplug that behaves like a normally open poppet valve. A poppet valve contains a moveable structure (a plug or “poppet”) that can block fluid or other elements from flowing through it. Automobile engines use poppet valves to control airflow in and out of the cylinders.
ABLE’s passageway remains open under normal conditions. During an explosion, the pressure imbalance caused by the blast wave displaces the poppet, which moves to form a barrier to the wave and reduce the peak pressure reached in the ear cavity. Blast waves move faster than the speed of sound—making a fast-reacting poppet valve critical to the device’s effectiveness. The poppet also needed to be strong enough to withstand the extremely destructive shock front at the leading edge of the blast.
The APL team tested a number of materials to develop a device that would react effectively when a blast occurs. Ian Wing, a biomedical engineer in the Research and Exploratory Development Department (REDD), verified the materials in a series of blast tube tests. To optimize some of the prototype materials, Simon also sought the expertise of Paul Biermann in REDD’s Engineered Materials Fabrication Group.
“There are multiple materials and many ways to solve this problem,” Biermann says. “We focused on finding an inexpensive material to keep the overall concept as simple as possible.” He considered the heat of the human body, the moisture and salinity of the environment, as well as the storage aspects of the material in which he chose to encase the poppet—a tiny lightweight ball that Simon had selected from a local hobby store.
“It is important not to forget that sometimes industry might already have part of the solution we are looking for,” Biermann adds.
So far, the ABLE prototype has demonstrated that it can be worn without significantly attenuating soft sounds. It can also dramatically reduce pressure levels experienced after blast impacts, and it is able to be implemented at low cost. “We are confident that ABLE can reduce catastrophic hearing loss for soldiers in the field and are eager to work with a government sponsor to further optimize the design, ensure that it delivers meaningful injury protection, and bring it to the warfighter,” says Simon.