Hearing Aid Battery Technology
Technology Insights- Hearing Aid Battery Technology
In this article you will learn:
• The important role battery innovation plays in hearing aid development
• The advantages and patient benefits of Zinc-air batteries
• The battery characteristics required for a high-performance hearing aid
Modern hearing aids pose a unique challenge to engineers today. There is a constant drive to add new features while retaining a compact size, or even reducing it. This presents a challenging set of requirements to the battery being used, where low supply voltage is a necessity and low power consumption is critical.
A number of chemistries are used in batteries today for consumer products. The most widely used chemistry for hearing aid batteries is zinc-air. Zinc-air batteries are different from most other batteries in that they “breathe” oxygen from the air for use as the cathode reactant. The virtually limitless supply of air enables the zinc-air cell to offer many performance advantages when compared to other batteries.
Consumers often question why their watch battery lasts years and their hearing aid battery must be changed every 1-2 weeks. Although they both utilize low power semiconductors (1.5 volts), the level of sophistication in a hearing aid compared to a watch is dramatic. The integrated circuits used in hearing aids are highly sophisticated, using hardware platforms that are responsible for the customization of amplification and manipulation of sound. Hearing aid integrated circuits may also serve user interface and wireless communication functions. To power these devices, it is necessary to develop batteries that provide high-energy density, flat discharge characteristics, high current capability and are environmentally safe. Zinc-air is the ideal chemistry for this demanding environment.
The zinc-air battery was first discovered in the early 19th century but did not find its first commercial use until the 1930s. The world of zinc-air today includes a variety of button cell sizes used in hearing aids, including 10A, 312, 13 and 675. Each cell size provides the highest energy density for its size. The overall size also denotes the operating range, defined as milliamp hours.
Zinc-air exhibits a long shelf life; the rated storage life is more than three years. The cells are packaged with an adhesive tab or seal that inhibits gas and vapor transfer, resulting in the battery staying dormant until ready for use. The batteries are activated once the tab is removed, allowing oxygen from the air to enter the battery. Nominal voltage levels are attained immediately after the tab is removed. It is possible to prolong the life of the battery by re-covering the air holes with the tab after each use, but the benefits of this are dependent upon the environmental conditions.
Batteries play a crucial role in high-performance hearing aids. Zinc-air batteries have been widely used to deliver the high demand current requirements in hearing aids since the early 1980s. Because they provide up to three times the energy of other common batteries in a smaller size, zinc-air will continue to be the optimal choice for hearing aid makers. Future hearing aids will be developed using smaller integrated circuit geometry, solidifying the need for efficient low voltage, high-energy density batteries. Zinc-air is the ideal choice for today and the future.