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Hearing aids get makeover with wireless

Posted: 01 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:hearing aids? wireless makeover? Bluetooth?

Thanks to the rise of wireless technology, the Rodney Dangerfield of the gadget world is about to get a makeover. The humble hearing aid, long shunned by engineers as a technological dinosaur, is going stereo and getting linked to cellphones and MP3 players, moves that could turn this badge of old age into a gizmo with the cachet of a Bluetooth ear clip.

The transition will be no flash dance. Hearing aids have frustratingly restrictive size and power requirements that make most wireless technologies non-starters, and public perceptions are slow to change. Indeed, only one in five people with significant hearing loss in the United States and Europe actually uses a hearing aid, in part because the devices are perceived as granny accessories. What's more, the regulatory environment is somewhat confusing and is currently more focused on problems of wireless interference than on interoperability.

In fact, the two worlds are so far apart that an IEEE group recently completed a 113-page report on the pitfalls of mixing wireless technology and health care.

"We wanted to bring attention to the complexity of the issues," said Joe Morrissey, a senior researcher at Motorola Labs and chairman of the RF wireless group within the IEEE 11073 group on medical communications standards. "There is an influx of wireless in all areas of health care, and none of the technologies were developed with medical systems in mind."

For instance, the IEEE report notes that most of the QoS approaches used by wireless networks are focused on delivering voice and video traffic. They do not mention medical alertssmall but significant bursts of data that need to be received instantly.

Nevertheless, a number of companies are reporting some progress on addressing the challenges in adapting wireless technologies for hearing aids. A Danish company launched in April what it claimed was the first hearing aid to sport integrated wireless.

Stereo effects
The Epoq hearing aid from William Demant Holdings, which rolled out at a conference of audiologists in the U.S., uses a proprietary magnetic-coupling technology to provide links between two hearing aids so users can get stereo effects to better locate the source of voices. "That's very important when you have a lot of background noise, which is a big problem for hearing aid users," said Jes Olsen, director of business and product development for the company.

As many as 80 percent of hearing aid users in the U.S. wear devices in both ears. The figure drops to 60 percent in Europe and just 12 percent in the rest of the world.

Part of the new offering is the optional Epoq Streamer. The size of an iPod Nano, the Streamer has a Bluetooth radio that can link to a suitably equipped cellphone or MP3 player. It streams the music or voice call back to the hearing aid over the company's wireless link.

The proprietary magnetic-coupling approach uses a 3.84MHz frequency to send up to 120Kbps of data over a 1-2m link. It consumes 300W in receive mode and 300-600W in transmit mode. A typical hearing aid has a total power budget of about 1mW, Olsen said.

The wireless link is implemented in 1mm? of the hearing aid's ASIC. It requires just two external capacitors and a 4mm3 antenna, and adds about 15 percent more cost to a hearing aid, which typically sells for $1,500 to $3,000.

"I am sure all our competitors are working on something like this that they may roll out later this year or early next year," said Olsen.

Olsen thinks the Apple iPhone "could be the ideal companion for this product," because it is expected to include the Advanced Audio Distribution Protocol to stream music efficiently over Bluetooth.

In the future, the product could be used to link to media on a DTV or PC. It has been tested with as many as 100 people using the devices in a single room without experiencing interference, thanks to the short range of the link, Olsen said.

Market driver
Market watchers project that even the smaller, "thin tube" behind-the-ear hearing aids coming out now, in increasingly fashionable styles, will help grow the market starting this year. By 2010, the thinner-tube models could add 3.3 million units in sales, accounting for 30 percent growth.

Engineers at William Demant considered but rejected 900MHz and 2.4GHz wireless links because their parts were too large and power-hungry. Some hearing aid makers use a form of FM relay to link the devices to cellphones or radios, but that approach requires bulky clip-ons that can cost more than the hearing aid itself.

The FM method is also insecure, since it uses an open broadcast mode. By contrast, the Epoq systems use Bluetooth pairing, which requires a user to press and hold a setup button on the Streamer, then set up a secure link from the Bluetooth phone or music player.

The Epoq technology is roughly similar to the magnetic- or capacitive-coupling approaches used in implantable devices such as pacemakers. Many of the implantable devices are moving to a 400MHz Medical Implant Communications Service (MICS) standard defined by IEEE 11073, but Olsen said his company was not aware of that standard.

There's little hope of integrating Bluetooth directly into hearing aids because the link typically requires 50mW, or 50 times the total power budget of a hearing aid. Wibree, the low-power version of Bluetooth developed by Nokia, is also a nonstarter because it lacks an audio-streaming capability, said Marc Niklaus, product manager for hearing aid DSPs at AMI Semiconductor Inc.

AMI in April rolled out Ezairo, an integrated 24bit DSP for hearing aids. Part of the rationale for the new device was to provide processing headroom beyond AMI's current 16bit chips to handle applications, such as wireless, that are expected to be integrated in hearing aids starting in 2008. Niklaus said he expects many hearing aid makers will build in RF components for the MICS standard next year. AMI expects to provide its own software for handling wireless baseband processing on Ezairo in 2008.

Besides stereo sound and cellphone links, the wireless technology, when used with a DSP, will let audiologists do the fine-tuning hearing aids need by using a simple PC program while their patients are wearing the devices, Niklaus said.

- Rick Merritt
EE Times

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