Norton-Equivalent Circuit Compensation for OAE Measurement Errors
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Solution Overview
Problem
Existing methods for measuring otoacoustic emissions (OAEs) are hindered by variations in ear probe placement and middle ear acoustics, leading to inconsistent results due to standing waves and the non-uniform nature of the ear canal, making it difficult to accurately reproduce OAE responses over time.
Innovation Solution
A device and method that characterize the middle ear as a Norton-equivalent circuit to determine a compensated pressure level (Pnpl) by accounting for ear canal acoustics and middle ear effects, using calibration stimuli to measure reflectance and propagation coefficients, which reduces sensitivity to ear canal length errors and provides a more accurate and reproducible OAE measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the ear probe is placed manually in the ear canal for OAE measurement, then the measurement can be performed, but the OAE response varies significantly due to variations in placement and standing waves in the non-uniform ear canal
Solution Approach 1:
The patent applies parameter changes by transforming the measured acoustic pressure into a compensated pressure level that corrects for ear canal acoustics. The compensation involves calculating correction factors based on ear canal length, reflectance, and propagation characteristics, thereby normalizing the OAE measurement across different placement conditions and ear canal geometries.
Solution Approach 2:
The patent introduces an intermediary compensation model that acts as a mediator between the raw measurement and the true OAE response. This model uses耳 canal characteristics (length, reflectance, propagation coefficient) as intermediary parameters to translate the measured pressure into a standardized compensated pressure level that is independent of placement variations.
2Measurement precision
If the Thévenin-equivalent circuit approach is used to characterize the middle ear, then the middle ear influence can be removed, but the method is extremely sensitive to accurately estimating the ear canal length which is ill-defined
Solution Approach 1:
The patent changes the approach from Thévenin-equivalent (pressure source) to Norton-equivalent (flow source) circuit representation. This parameter change fundamentally alters the sensitivity characteristics, making the compensation less sensitive to ear canal length estimation errors while maintaining the ability to characterize middle ear acoustics.
Solution Approach 2:
The patent inverts the conventional approach by using a flow source representation instead of a pressure source representation. This inversion transforms the problem from one where pressure compensation is highly sensitive to length errors into one where flow-based compensation is more robust to such errors.
3Measurement precision
If the emitted pressure level calculation is used to compensate for ear canal acoustics, then standing wave effects can be reduced, but the approach still requires accurate knowledge of ear canal length and uniform geometry
Solution Approach 1:
The patent changes the compensation methodology by using Norton-equivalent circuit parameters (flow source, conductance) instead of the traditional emitted pressure level approach. This parameter transformation reduces the dependency on precise ear canal length and uniform geometry assumptions, thereby simplifying the practical implementation while maintaining compensation effectiveness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The compensated pressure level (Pnpl) is less sensitive to small length errors and ear probe insertion variations, allowing for more reliable monitoring of OAE responses over time and improved assessment of cochlear health across multiple frequencies.
Implementation Method 1
One or more of the speakers emit acoustic stimuli, the level of which are adjusted using the microphone. The microphone further measures the OAE response from the cochlea that is emitted into the ear canal through the middle ear.
Implementation Method 2
standing waves between the tympanic membrane, where an OAE enters the ear canal, and the ear probe influence the OAE response
Implementation Method 3
standing waves between the tympanic membrane, where an OAE enters the ear canal, and the ear probe influence the OAE response, resulting in amplification of the OAE response near resonance frequencies
Data Source
AI summary
Disclosed herein are embodiments of a device for measuring otoacoustic emissions (OAE) of a test subject. The device includes a stimulus generator configured to generate at least one acoustic stimulus, an ear probe, where the ear probe includes an output unit for emitting said at least one acoustic stimulus into an ear canal of the test subject, and an input unit for measuring an acoustic emission (Pspl) from the ear of the test subject. The device can further include an analysis unit configured to receive said measured acoustic emission (Pspl) and to determine a compensated pressure level (Pnpl) of said measured acoustic emission (Pspl), where the determination of the compensated pressure level is based on characterizing the middle ear of the test subject as a Norton-equivalent circuit. The present application further relates to a method of measuring otoacoustic emissions (OAE) of a test subject and to a computer program.