Bone Conduction Microphone Flexible Wall Impedance Matching
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Solution Overview
Problem
State-of-the-art acoustic devices using bone conduction microphones struggle with low consonant/vowel/consonant recognition rates due to deformation of sound vibrational waves during transmission from vocal cords to the transducer, resulting in poor signal quality.
Innovation Solution
The acoustic device features a support wall with a hardness of 45-85 Shore A and a thickness of 0.4-0.6 mm, made of synthetic rubber, which is designed to match the mechanical impedance of the cheek, along with an accelerometer transducer and acoustic decoupling means to improve signal transmission and reduce high-frequency vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid housing is used for the transducer, then the transducer is well protected, but the mechanical impedance mismatch deforms the vibrational waves and reduces signal quality
Solution Approach 1:
The housing uses a flexible membrane made of elastomeric material (silicone rubber or thermoplastic elastomer) with specific hardness (40-80 Shore A) and thickness (0.3-0.8 mm) to match the mechanical impedance of the cheek. This flexible membrane allows efficient transmission of mechanical vibrations from the cheek to the transducer while maintaining protection, resolving the contradiction between rigid protection and signal quality.
Solution Approach 2:
The patent specifies precise parameter ranges for the housing material: hardness between 40-80 Shore A (preferably 50-70 Shore A) and thickness between 0.3-0.8 mm (preferably 0.4-0.6 mm). These parameter optimizations ensure the housing's mechanical impedance matches the cheek, enabling efficient vibration transmission while providing adequate protection.
2Manufacturing precision
If the housing wall is too thin, then the mechanical impedance matches the cheek better, but the transducer protection is insufficient
Solution Approach 1:
The flexible membrane housing with thickness of 0.3-0.8 mm provides both adequate protection and good mechanical impedance matching. The flexibility of the elastomeric material compensates for the thin wall thickness, allowing efficient vibration transmission while maintaining protective function.
Solution Approach 2:
The housing uses composite elastomeric materials (silicone rubber or thermoplastic elastomer) that combine flexibility, durability, and appropriate mechanical impedance. These composite materials achieve both protection and impedance matching simultaneously, resolving the contradiction between wall thickness and protection.
3Stability of the object's composition
If high-frequency vibrations are transmitted to the acoustic module, then the connection is stable, but parasitic noise is amplified
Solution Approach 1:
The patent introduces acoustic decoupling means that selectively filter out high-frequency parasitic vibrations while allowing stable mechanical connection. The decoupling mechanism extracts harmful high-frequency components from the vibration signal, maintaining connection stability while reducing parasitic noise amplification.
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
This configuration enhances the quality of sound signal reception and transmission, significantly increasing the consonant/vowel/consonant recognition rate and reducing parasitic noise, while ensuring compatibility with protective helmets and various headgear.
Implementation Method 1
the transducer with bone mechanical excitation arranged in the housing, said transducer being able to receive by bone conduction a sound signal coming from the vocal cords
Implementation Method 2
the wall in contact with the transducer of the microphone has a hardness of between 45 and 85 shores A and a thickness of between 0.4 and 0.6 mm
Implementation Method 3
the spacing between the edges, outside and facing each other, of the two connecting arms is progressively increasing from the microphone towards the acoustic module, in order to allow attenuation of the mechanical sound waves
Data Source
Figure 1
Figure 2~4
Figure 5~6
AI summary
The invention relates to an acoustic device (2) including a contact acoustic microphone (4), and an arch (10) for maintaining the microphone (4) against a side flange of the skull, said microphone (4) including a housing (16) and a transducer for mechanically energizing bone and arranged in the housing (16), said transducer being capable of receiving a sound signal from the vocal cords by bone conduction, and said housing (16) including a wall (20) bearing on an area of the cheek. The acoustic device (2) is characterized in that the wall (20) is in the form of a skin in contact with the transducer of the microphone (4), and in that the wall (20) has a Shore A hardness of between 45 and 85 and a thickness of between 0.4 and 0.6 mm.