People have been interested in better hearing for a very long time. As soon as there was aging, there was hearing loss. As soon as there were diseases to challenge the ears, and auditory function, there was hearing loss. The first power to help hearing was provided by an involuntary hand, cupped and raised to the side of the head. It was a simple attempt to capture more sound and bring it to the ear. We've come a long way since those humble beginnings!
We're in the age of silicon, and electrons, plastics, and precious metals. Now the power to hear is provided by an astonishing, sophisticated hearing instrument, and a carefully designed energy source, the zinc-air battery.
What makes all of this possible? A small, portable source of electricity, the hearing aid battery, often called a zinc air cell. Almost every hearing instrument uses a small zinc air button cell battery. It is the needs of the hearing impaired that guide the design and testing of zinc air cells. The zinc air cell is a tiny device that converts chemical energy into electrical energy. The voltage of the cell is characteristic of the anode material, zinc metal, and the cathode material, oxygen. The source of the oxygen is air. An electrolyte, which is conductive, and full of useful hydroxyl ions (-OH), permits the electrons to flow in an outside circuit as long as there is zinc metal left inside the cell. When all of the zinc has been discharged, zinc oxide is left, and the cell is done.
The zinc air battery is different from any other battery system because it contains only one of the electrode materials, the zinc. The other electrode carries only a small amount of oxygen, and when that is used, it looks for more from the outside air. That's why there are air holes on the bottom of the cell. They allow air to enter the cell as it is being used. The tab that is placed over the vent holes blocks air from entering and moisture from either entering or leaving, during the time that battery is in storage before the user needs it.
The zinc air battery could even be thought of as being half a battery and a half fuel cell. In a traditional battery all of the materials needed to make electricity are contained inside, including the source of the oxygen. In the case of a fuel cell, the reacting materials are brought together in the fuel cell only when electricity is needed. In the zinc air cell, the zinc and the electrolyte are added during manufacturing, but only the sophisticated air electrode is present. The air comes in later, entering the cell when it is needed. There's no air tank strapped on the side, it doesn't take up any extra room. That puts a lot of energy into a small, powerful package. You get electrons on demand and the power to hear.
Making a zinc air cell involves many different metals, plastics, and other materials. Each one must be carefully assembled because the materials in a battery always want to react with each other. They would, except that we keep them separated, so the only time they react is when an external circuit, such as a hearing aid, calls for the electrons to actually flow.
What materials find their way into a zinc air cell? Besides the zinc, there are parts made of nickel, iron, copper, chromium, manganese, carbon, nylon, PTFE, polypropylene, polyester, polyvinyl, potassium hydroxide, and high purity water. In order to put the most electrical energy into the small space available, parts are kept thin, and many parts perform several functions at once.
How has the demand on batteries changed?
The new technologies that drive the hearing industry are primarily the result of the digital revolution in electronics. Starting with computers, digital signal processing has now become a recognized means of analyzing an incoming sound, and almost instantly sending a customized signal to be amplified, to the output stage of the hearing instrument. This increases the power requirements of the whole instrument, and for the battery there is another demand. DSP circuitry will not function correctly if the voltage drops below a critical level, usually 1.05 to 1.1V.
The hearing aid wearer often wants a discrete, unobtrusive, and maybe even an invisible fitting. We all hear it, all the time....The smaller, the better, right?
The desire to make it smaller places an extra demand on the battery, because high performance instruments need to work very well, using the smallest battery possible. Adding features adds greater load on the battery and in so doing, the result is the user may be disappointed with short battery life.
In fact, this is the most common complaint battery companies receive from hearing aid battery customers. The hearing healthcare professional may need to adjust the users expectations, especially if the new aid that they are receiving is one of the new, smaller digital devices, if it serves a profound hearing loss, and especially if it is going down in battery size. Settings and features increase the power requirements. The formula is pretty straight forward:
BATTERY CAPACITY / DEVICE CURRENT = SERVICE LIFE.
The hearing healthcare professional can help the hearing aid wearer appreciate battery use in several ways. One way is to help the wearer recognize that even moderate changes in life style can affect the rate of battery use in the aid. If they find that they are changing batteries more frequently, it may be that they have taken up some new activity, such as mall walking, where there is significantly more background sound being amplified. The battery is powering the aid all the time, even when the wearer is ignoring the sound that is being amplified!
As younger people start to wear hearing aids, they will take them into more athletic and more environmentally challenging situations. Wearing hearing aids during a vigorous workout may be fine, but it exposes the hearing aids, and the battery, to that dangerous chemical, sweat! Once sweat gets inside the hearing aid, sweat can cause corrosion, damaging the contacts, and other tiny circuit components. Sweat will also react across the narrow gap between the can and the top of the battery, producing a corrosion product that looks rusty. The cell has not leaked, but it is wet, and looks terrible. The chloride ions from the sweat are very destructive to the metal part in the hearing aid, and the fact that they are in a circuit, with an electrical current flowing accelerates the corrosive effect. Hearing aid users should be counseled to keep sweat out of their instrument.
Remove the battery, and dry it off before re-inserting it into the face-plate, or battery door. Users may want to try a drier (''dry aid kit'') for their hearing aid, although it really isn't necessary to put the battery in the drier. If the user feels the battery needs to be protected, the tab can be replaced. Under most conditions that extra effort isn't necessary. Re-tabbing is definitely advised if the battery is not going to be used for an extended period of time, such as a delay of a week or more.
Battery Clubs are a good way to build your business. They help maintain contact with your clients and patients, especially those who are heavy battery users. Coupons and special offers encourage clients and patients to keep your practice at the top of their minds when they think of their battery needs. Battery clubs help the hearing healthcare professional get to know the normal pattern of battery use for their clients and patients, and that helps determine when a change has occurred, which might indicate the need for an office visit. Has their hearing loss changed? Has the instrument been damaged? Is the person wearing the aid much less, or much more?
The good news for your clients is the fact that zinc air batteries give them the power to hear. The good news for you is the fact that zinc air batteries are a great way to maintain a year round dialogue with your clients concerning their hearing health, and they also represent a profitable part of your practice.
For more information on hearing aid batteries:
Hearing Aid Batteries: Marketing Hints
Tom Begley, Director of Sales, and Jennifer Clark, Associate Marketing Manager, Rayovac, Madison, Wisconsin
Listen Up! A Consumer's Guide to a Successful Hearing Aid Experience
Tina M. Prout, MS, CCC-A, doctoral student at The University of Memphis
The Power to Hear is Powered by Batteries
Rod McKenzie, Principal Technical Officer, Rayovac Zinc Air Batteries
Hearing Aids: Reasonable Expectations for the Consumer
Rose L. Allen, Ph.D., CCC-SLP/A, Assistant Professor of Audiology, East Carolina University, Dept. of Communication Sciences & Disorders
Battery Life: Technical Issues and Answers
Denis Carpenter, Zinc Air Technical Manager, Rayovac, Madison, Wisconsin.
Interview with Tom Begley, Director of Sales, Rayovac
Dry aid kits and hearing aid batteries
Denis Carpenter , Rayovac Corporation, Zinc Aid Technical Manager
Extending Hearing Aid Battery Life
Denis Carpenter , Rayovac Corporation, Zinc Aid Technical Manager
Hearing Aid Battery Testers
Denis Carpenter, Rayovac Zinc Air Technical Manager
Efficacy of Using Drying Kits with Batteries
Randy Rea Ph.D. , Director, Zinc-air Technology, Rayovac Technology Center
**********************************************************
Click here to visit the Rayovac website.
Batteries are the Sound Choice for Better Hearing
September 29, 2003
Share:
This article is sponsored by Rayovac.
