IEEE Consumer Electronics Magazine - October 2016 - 40

Noise

Eardrum

Ear Canal

DSP
Reference
Microphone
Noise

Ear Canal
Noise
Leakage

DSP
Reference
Microphone

Eardrum

Loudspeaker
(a)

(b)

Figure 8. An illustration of the noise effect in different types of
hearing aids: (a) closed fit and (b) open fit.

Error
Microphone
Secondary
Loudspeaker
Figure 9. An experimental setup of an audio-integrated ANC for
an open-fit hearing aid.

Figure 10. An audio-integrated ANC system for an infant incubator.

function of digital hearing aids, and interferes with speech.
To solve the noise leakage problem, audio-integrated ANC
techniques can allow ANC and speech functions to work
simultaneously [24]-[27].
For simplicity of development, we use an earphone as a hearing aid in the lab. An additional error microphone is installed on
40 IEEE Consumer Electronics Magazine

OCTOBER 2016

the earphone close to the eardrum (Figure 9). The secondary loudspeaker is shared with the existing loudspeaker of the earphone.
To perform both the ANC function and the hearing aid functions,
the audio-integrated feedback ANC algorithm is required.

anC inFant inCubatorS
Every year, about 15 million babies are born preterm (before
37 completed weeks of gestation), and this number is rising
[28]. The use of infant incubators in neonatal intensive care
units (NICUs) significantly helps such premature and medically challenged infants. The infant incubator is an enclosure with
sections that are transparent for viewing the baby within. Some
sensors and devices are placed inside the incubator for monitoring the baby's vital statistics and for controlling the temperature, humidity, supplementary oxygen, and other parameters.
High levels of noise from these internal devices, from
medical equipment outside the incubator and human activities inside the NICU, can result in numerous adverse health
effects for an infant, including sleep disturbance and other
forms of stress. The internal ear structures of a baby may not
yet be fully developed, so an infant can develop significant
long-term hearing loss.
Passive noise reduction is not effective for low-frequency
noise. Furthermore, most passive techniques either take up limited incubator space or block the view of an infant to caregivers, or
both. These difficulties motivated the development of ANC systems to cancel low-frequency noise inside incubators [29]-[32].
The goal of applying ANC is to establish a quiet zone around
the infant's ear inside the incubator. Therefore, two secondary
loudspeakers are installed inside the incubator along with two
error microphones, as shown in Figure 10. A challenging problem for an incubator ANC is that noise comes from multiple
noise sources inside and outside the incubator.
In addition to noise cancellation, therapeutic functions are
essential for enhancing treatment and optimizing premature
infants' physical and neurological development. A parent's voice
has been shown to enhance vocalization in premature infants
[33]. Music and sound therapy, such as womb sounds that provide infants with the ambience of the mother's womb, have also
been shown to benefit infants in such ways as weight gain,
reduced observed stress behaviors, shorter term of hospitalization, and increased oxygen saturation levels for short periods of
time [34]. Therefore, the incubator ANC also can apply audio
integration techniques to allow the secondary loudspeakers to
play the sound without interfering with the ANC function.
Besides, crying detection or other sound monitoring can be
added, since the error microphones are available for use.

anC HelmetS
Motorcycle noise levels on an open road are in the range of
78-90 dBA at 30 mi/h to 116 dBA at 120 mi/h, depending on
the type of helmet, motorcycle, and road condition [35].
According to the WHO report, continuous exposure to noise
levels of 95 dBA for more than 47 min may result in various
hearing impairments, such as hearing loss, tinnitus, or acoustic
shock, and may even lead to accidents [36].

Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - October 2016