Student Projects
Contact Information
Company: Institute for Reconstructive Sciences in Medicine
Participating University: University of Alberta
Team Members: Michael Emmelkamp, Craig Radke
Faculty Advisor: Dr. Bill Hodgetts
Engineering Advisors: Herman Lundgren, Dylan Scott
Email Address: emmelkam@ualberta.ca, caradke@ualberta.ca
Background
Some patients with hearing loss are unable to wear traditional air conduction hearing aids (ACHAs). For example, some are born without ear canals, while others may suffer from chronic ear disease, which precludes the use of a hearing aid in the ear canal. For these individuals, an implantable bone conduction amplification device (BCAD) is often the only solution. A great deal of benefit can be obtained with this solution; however, audiologists prescribing and fitting these devices often experience difficulty relating the mechanical vibrations of a BCAD to an individual's hearing loss in meaningful terms. In this paper, we propose an NI solution that allows for greater understanding of the vibrational properties of the human skull, as well as a clinical tool that can be used by audiologists to prescribe, fit and verify BCADs on individual patients.
Description
The purpose of this project was to design a test box that contains a system for configuring BCADs against audiometric targets, in order to fit them to individual patients in a clinical setting. Additionally, this system would allow for research into the acoustic/mechanical properties of the human skull - more specifically, the skull's mechanical point impedance. Similar test boxes for ACHAs exist and can be used for BCADs, but they display signal amplitudes in units that are only meaningful for ACHAs (sound pressure level). These test boxes require offline calculations in order to understand the metrics of interest to bone conduction hearing (force and acceleration).
Products
Labview 2010, Intel Pentium 4 processor, NI cDAQ-9172 chassis, two NI 9234 analog-to-digital input modules, one NI 9263 digital-to-analog output module.
The Challenge
The proposed software required several distinct modules, each of which would generate a different excitation signal and measure various response signals. For clinical purposes, the excitation signal would be sent to the BCAD, which would respond by transmitting a force to a skull simulator (accelerometer attached to a known mass). The signal from the accelerometer would simultaneously be read through one of the input modules, expressed in engineering units in terms of force, and analyzed by the module over the frequency band of human hearing (20 Hz – 20 kHz). The response signals would then be compared to audiometric targets in order to configure the BCAD for fitting.
For research purposes,the excitation signal would be directly transmitted to the BCAD attached to a human skull, and the responding force and acceleration signals (measured via sensors) would be recorded and combined in order to determine the mechanical point impedance of the skull.
The program required modules providing the following functionality:
- Calibration of different electromechanical transducers used for testing the acoustic properties of the skull.
- Generation of a swept sine signal (excitation) and analysis of the acceleration input (stimulus) and force output (response) from a transducer over the frequency domain.
- 3rd octave analysis of the BCAD’s response to a pink noise excitation/stimulus.
- 3rd octave analysis of the BCAD’s response to a speech excitation/stimulus (recorded signal or real speech).
- 3rd octave analysis of the BCAD’s response to a manually controlled pure tone excitation.
- Recording a response signal when a stimulus signal is detected.
The Solution
While this project’s development efforts are ongoing, two of the modules have been completed. Thus far, the team has completed modules for analyzing swept sine responses, as well as responses to signals from external sources.
The Swept Sine module is capable of generating an excitation voltage which is converted by the transducer into a mechanical signal that sweeps through the frequency range of human hearing. This signal is transmitted to an impedance head (transducer with sensors to measure acceleration and force) coupled to an abutment in the human skull. While the swept sine sound is being relayed to the impedance head, the module records data from both the accelerometer (stimulus) and the force meter (response). These data are then analyzed and the user is presented with graphs showing the force, acceleration, phase, and mechanical point impedance of the human skull in the frequency domain. This module has already been used clinically to determine the mechanical point impedance and force response functions of the skulls of a large group of BCAD patients.
The External Input module monitors an excitation voltage from an external source for the beginning of a signal. Once the start of the signal has been detected, the module records data from a force meter on an impedance head or a similar transducer connected to a BCAD and stores it for later analysis. The module also stops recording response data when the stimulus stops, and allows the user to start and stop recording. This module is useful in a clinical audiology setting, where there are several sound files for configuring hearing aids and where patient data may need to be retrieved on multiple occasions.
All of the existing modules as well as those that have yet to be developed are opened from a universal main menu that will allow the user to specify the types of transducers to be used, input and output channels, calibration settings, patient information and file paths.
Figure 1 - Front panel of the Swept Sine module.
Figure 2 - Front panel of the External Input module.
Figure 3 - Front panel of the Main Menu.
Figure 4 - Abutment and direct drive transducer with force meter attached to a human skull.
Figure 5 - Abutment to which BCAD or similar transducer is attached.
Figure 6 - Direct drive transducer: BCAD with a force-measuring (i.e., known mass) accelerometer attached.
Figure 7 - Assembly for the Swept Sine module, including NI cDAQ-9172 chassis with input and output modules.
