Research Paper
Volume : 3 | Issue : 11 | November 2014 • ISSN No 2277 - 8179
Engineering
Design and Construction of a Prototype
Hearing Aid With Cerumen Detection
Capability
KEYWORDS : Cerumen, Cerumen
detecting system, Hearing aids, Infrared
sensor, Receiver
Dr. Mohsen Ahmadi
Department of Biomedical Engineering, Faculty of Medicine, Shahid Beheshti University of
Medical Sciences, Tehran, Iranv Corresponding Author
Fatemeh Mirghaemi
Department of Biomedical Engineering, Faculty of Medicine, Shahid Beheshti University of
Medical Sciences, Tehran, Iran
ABSTRACT
Since the advent of ITE hearing instruments, the efficiency, reliability, performance, and life span of such devices
have been limited by cerumen build up within its key internal component, the receiver. Initially, cerumen accumulation physically blocks the receiver port, occluding the acoustic path and preventing sound waves from efficiently reaching the tympanic membrane. Eventually, the cerumen can penetrate into the receiver housing and damage the sensitive mechanical and electrical components located within the housing. The monetary and time costs associated with replacing failed hearing devices due to cerumen clogging and receiver
damage is significant. The management of cerumen continues to be a challenge for dispensing professionals, consumers, and the industry
alike. Historically, the quest for managing cerumen whether in the form of a wax guard, or collection device installed within the hearing aid
itself, or as a counter-top apparatus has yielded limited success and none of these systems have performed with optimum results. The aim
of this research work is to design and construct a prototype hearing aid with cerumen detecting system for hearing aids based on infrared
sensor. Our findings shows the system can detect cerumen efficiently, and can therefore resolve the key issue with hearing device failures
I: INTRODUCTION
One of the most common problems with hearing aids is their
ongoing exposure to moisture, wax and other foreign materials.
Even brief exposure to these harsh environments can degrade
and eventually interfere with proper hearing aid functionality.
The contaminations within the microphone and the receiver, result in high service costs, since the contaminated components
must be cleaned and in the worst case even exchanged. [1]
Hearing aids usually have a sound outlet port that is positioned
in the ear of the user to deliver sound. To prevent this port or
the connected tubing from being clogged by ear wax, it is common to use an ear wax guard in the port or tubing. It has been
suggested that a pin shaped, the ear wax guard is positioned
with the stem into the outlet port (U.S. Pat. No.6,795,562). Others have recommended that a hearing aid is disclosed having
a cover pivotally mounted in a recess of the tip portion of the
hearing aid to cover the outlet port located in the tip portion
(U.S. Pat. No. 6,105,713). In some design ideas, wax guards are
disclosed that allow complete removal and replacement without the necessity of performing custom trimming of an end
plate or tip portion of the hearing aid (U.S. Pat. No. 6,795,562
and 2004/0240694). The wax guards are provided with elevations
on the outer surface to keep them in position in the outlet port
by frictional fitting. In addition, the wax guard is adapted to facilitate cooperation with a removal tool (U.S. Pat. No. 6,795,562).
Figure 1, shows the wax guard of CIC hearing aids.
ent”). Although, the ‘500 patent also requires significant user intervention to clean the filter. [7]
However, in each of these devices the cerumen is simply collected and a user must still manually clear it from the device. [6]
II: MATERIALS AND METHODS:
The goal of this work was twofolds: 1) what can be used to effectively detect cerumen? and 2) would the utilization of infrared sensor be effective in detecting cerumen to prevent hearing
aid from cerumen-related breakdowns and loss of performance?
We hypothesized that cerumen can be detected by an infra red
sensor safely and reliably. To test the possibility of integrating an
infrared sensor inside the hearing aid device, a prototype hearing aid with an infrared sensor was designed and built to evaluate the concept. Figure 2, shows an overview of the system. An
AVR microcontroller (Atmega8) from Atmel corporation is used
for data conversion and processing.
SYSTEM DESIGN
A.Hardware
Audio amplification and cerumen detection were the main
features of the design. Audio signal from a microphone is captured, pre-amplified before being converted to a digital signal.
The Analog to Digital Converter (ADC) embedded within the
AVR microcontroller is used for this purpose. The signal is digitally filtered and converted back to analog form, using the Pulse
Width Modulated (PWM) option on the micro. However, the
signal is further filtered before driving the speaker.
Figure 1: Wax guard of CIC hearing aids
A lot of ideas regarding cerumen filter for hearing aids discloses
a “Cerumen Barrier for a Custom”, in the ear type hearing instrument. They do provide some level of protection against cerumen to the internal components of the hearing device. (U.S. Pat.
No. 5,401,920, entitled “Cerumen Filter For Hearing Aids” (“the
‘920 patent”), U.S. Pat. No. 5,327,500, entitled “Cerumen Barrier
for Custom in the Ear Type Hearing Instruments” (“the ‘500 pat244
IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH
Figure 2: Block Diagram of the system
The system is powered by an Alkaline 9 volts DC battery which
is regulated to 5 volts where needed. An infrared (IR) light emitting diode (LED) is used as a cerumen sensor. The output of the
sensor is amplified before connected to a i/o pin of the micro.
Figure 3, shows the prototype hearing aid system with the infrared sensor incorporated.
Research Paper
Volume : 3 | Issue : 11 | November 2014 • ISSN No 2277 - 8179
III: EVALUATION OF SYSTEM PERFORMANCE
To test the efficiency and performance of our prototype, a series
of experiments were performed with the goal of detecting cerumen. The hearing aid system was placed in an environment
similar to ear canal in terms of light and sound presence. In a
series of experiments, natural cerumen from patients was used
to evaluate the functionality, sensitivity and reliability of the
sensor. The quantity of cerumen was reduced from 15 to 1 mg
in steps of 2. The experiment was repeated with dark color cerumen as well as transparent. The cerumen was placed anywhere
between the emitter and receiver of the sensor in a random
manner. By adjusting the sensitivity of the sensor’s preamplifier,
tiny quantity of cerumen could be detected every time, reliably.
Figure 3: Hearing aid prototype system
SYSTEM DESIGN
B. Software
Figure 4, shows the flow sequence of events within the micro.
The hearing aid starts working when the switch is pressed. It
converts the pre-amplified microphone output into digital format. The signal is then digitally filtered and converted into
analog form using PWM technique embedded within the micro.
The analog signal then drives the speaker. The micro also monitors the input from the photo diode. As the voltage level reaches
the threshold, the signal is read off and activates a buzzer indicating the presence of cerumen or any other contaminants.
DISCUSSIONS
The evaluation tests of the prototype system have shown the
correct interaction of system’s hardware and micro’s software.
The overall resolution and accuracy of the system meets the design criteria and compares quite well with similar commercial
systems currently on the market. More improvement in sound
quality may be achieved by using a specific audio amplifier instead of a general amplifier. Different signal processing algorithms like echo cancellation, feedback compensation, noise
reduction, adaptive filtering, better directionality etc. can be implemented to make hearing aid work better.
The functionalities built within this system are quite adequate
for effective cerumen detection for hearing aids.
CONCLUSIONS
The current design of our prototype was used to verify and
evaluate a conceptual technique that can be considered for cerumen detection within a hearing aid device. We have shown
in this research work that a simple infrared sensor integrated
within a hearing aid device can indeed detect cerumen and wax
contaminant reliably. Using surface mount technology in hearing aid construction can incorporate this idea quite easily and
resolve the key issue with hearing device failure, wax accumulation of the diaphragm and blockage to the internal receiver port.
We suggest that it can perhaps be an essential addition to every
dispensing practice.
ACKNOWLEDGMENTS/DISCLOUSURES
The authors declare no competing financial interests. This paper
is a part of a Msc. thesis in Biomedical engineering by Miss Fatemeh Mirghaemi. We also acknowledge our gratitude to all those
involved in the project at Biomedical Engineering Department,
Shahid Beheshti University of Medical Sciences.
Figure 4: An overview of the code driving the micro
REFERENCE
[1] Agnew J. Toward a better understanding of cerumen. Hearing Review. 1994;1(4):16-20. | [2] A.Rogalski and K.Chrzanowski, Infrared detection
and devices, Opto-electronics review 10(2), (2002). | [3] Ballachanda B. The Human Ear Canal. San Diego: Singular Publishing Group;1995. | [4]
F.Mirghaemi, "Current Trends In Hearing Aid Technology", Alborz, Tehran, 2013. | [5] Hain TC. Earwax. Available at: www. dizzinessandbalance.com/disorders/ hearing/wax2.html.
Accessed: April 9, 2007. | [6] Kochkin S. MarkeTrak VII: Customer satisfaction with hearing instruments in the digital age. Hear J. 2005; 58(9):30-43. | [7] www.freepatentsonline.com |
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