Nick Hamilton EE April 2015 Abstract: When natural hearing is lost, cochlear implants provide an opportunity to restore hearing. These electronic devices are surgically implanted into a person’s cochlea and act as a replacement ear to bypass the damaged systems preventing normal hearing. The most significant part of these devices are the electrodes, which connect the electrical device to the biological system.

 Introduction to Cochlear Implants  Overview of How the Ear Functions  Design and Function of Cochlear Implants  Impact of Semiconductors  Pros and Cons  Comparison to Other Devices  Future of Cochlear Implants

Alessandro Volta first stimulated the ear in 1800 using electricity. The first implants did not exist until around The FDA allowed them to be implanted in adults in Since 2000, the implants are approved for infants over 12 months old. The sooner a cochlear implant can be used to restore hearing, the better chances of success. In some cases, the brain will not recognize the signals being sent. This often occurs if a person has been deaf for a very long time.

 Outer Ear ◦ Canal ◦ Drum  Middle Ear ◦ Malleus ◦ Incus ◦ Stapes These are the three smallest Bones in the human body.  Inner Ear ◦ Cochlea ◦ Auditory Nerve Sound enters the ear canal and contacts the ear drum. The vibrations are amplified by the malleus, incus, and stapes. This produces fluid waves in the cochlea. Tiny hairs in the cochlea transform these waves into signals sent to the brain. The deepest part of the cochlea responds to the lowest frequencies.

External Microphone Speech Processor Transmitter Internal Receiver Electrode Array

Converts sound to electrical signals that are sent to the speech processor. Good microphones have a broad range of frequency response, but are designed not to pick up lower frequencies. Sounds in this range include head movement and walking. A directional microphone will detect sound better in the direction it is facing. This can aid in picking up sound from conversations, especially in noisy environments. Piezoelectric microphones allow microphone size to be reduced while improving signal quality.

Software is capable of creating more frequencies than there are electrodes by stimulating two adjacent electrodes at once. This effectively enhances resolution. For example: An array with 16 electrodes has 15 possible pairs. This equates to 15 times the number of possible channels per pair. If 8 distinct channels can be created per pair, then 120 possible pitches may be generated. These in-between pitches are called virtual channels.

Information is sent through a radio frequency signal from the speech processor to the implanted component. A direct connection (wire) allows for superior transmission, but has a high chance of infection. This method is not used.

On the left are the connections for the implantable device. The electrode array and contacts are on the right side. The middle is a series of wave shaped wires surrounded by silicon. Overall length is 100 mm. The array is between 0.8 and 0.5 mm in diameter.

Inside the silicon casing are small wires. Each wire carries one channel of sound. The wires and contacts are 90% platinum and 10% iridium. These metals form a strong, conductive wire.

Cochlear implants are currently not intended to solve all degrees of hearing loss. They are best suited for those who have lost all or nearly all natural hearing. Current cochlear implants cannot fix hearing loss as a result of nerve damage. Implants can bypass damaged parts of the ear, except the nerve, and restore some hearing. The use of cochlear implants will cause a person to lose all natural hearing, if they have any left.

These implants are the only possibility for correcting complete loss of hearing in any person who does not have nerve damage. In any case where someone retains a measurable amount of hearing, other solutions are preferred, if possible. Some of these other options: Hearing Aids – Amplify sound in ranges where hearing loss exists Middle Ear Implants – Must rely on a fully functional cochlea. Replaces middle ear and also requires an external audio processor.

 Biologically Friendly Materials: ◦ Silicon: Used to encase the implant. ◦ Titanium: Used in the central part of the implant. ◦ Platinum: Used for the contacts. These materials are used because they do not react with anything inside the body. These materials also have excellent long-term stability. This means that they do not degrade or cause any issues after being implanted for a long period of time.

As the device feature size decreases in fabrication techniques, more features may become available to cochlear implants. The largest factor limiting the quality of these implants is the electrode array. The more channels possible, the better the frequency response and sound quality become. Fabrication may allow for smaller electrodes, meaning more of them can be used in an implant. Smaller device size also leads to smaller external components, providing more attractively sized external hardware with more capability. In order to carry more channels of sound, the amount of wires used to transmit into the cochlea must be increased.

 The final sound quality of a cochlear implant is comparable to that of an out-of-tune radio. Some describe it as sounding “robotic.”  Without context, it is difficult to understand some sounds generated by these implants. Speech recognition is possible.

Disadvantages: High cost: $40,000 - $100,000 Any natural hearing will be lost. Electromagnetic noise. Anti-theft sensors may detect implants. External components may be damaged by water. Physical contact may damage implant. Many diseases and infections Advantages: Hearing is recovered immediately after surgery. Speech recognition, possibly without lip-reading. Can detect a variety of sounds. Some people may enjoy music. Components are upgradeable. Increased independence.

There are no other devices that will resolve hearing loss at the range that cochlear implants are meant to. All other options provide superior sound quality and are preferred if at all possible. Other options are much cheaper than cochlear implants. Many do not require surgery. All solutions require a battery to power circuitry.

 Add additional sound channels  Water resistivity  Completely internalize components  Better frequency resolution (more channels)  Improved battery life  Lower manufacturing/medical cost

 How the Ear Functions  Hearing Loss and Cochlear Implants  Device Layout  Improvements

Information: hetics/CochlearImplants/ucm htm hetics/CochlearImplants/ucm htm /pages/microphone.html Pictures: and-channels/

 Sound travels into the ear, contacts the eardrum, and creates mechanical vibrations. These vibrations create waves in the cochlea that are detected by tiny hairs and transmitted through nerves as sound.  Cochlear implants directly stimulate the nerve cells in the cochlea.  Main components: Microphone, speech processor, transmitter, and electrode array.  Materials used are silicon, titanium, and platinum because they do not interfere or interact with the body when implanted.  The electrodes do not provide precise stimulation and do not allow for extremely high audio quality.