Planar Motor for Bone Conduction Audio
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Solution Overview
Problem
Traditional headphones and speakers propagate sound waves through air, lacking privacy and efficiency in reproducing a wide spectrum of audible frequencies, and past pistonic acoustic systems have insufficient magnetic induction and voice coil length to effectively drive a user's pinna for audio transmission.
Innovation Solution
A high-efficiency motor with a rigid structure, such as a printed circuit board, positioned between magnets, where traces act as a moveable coil, increasing magnetic B-field and conductor length, allowing for a motor that can drive a user's pinna to reproduce a wide spectrum of frequencies while fitting into a small form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a traditional voice coil and diaphragm configuration is used, then the structure is simple and easy to manufacture, but the magnetic induction (B) and conductor length (L) are insufficient to provide high mechanical output power for driving a user's pinna
Solution Approach 1:
The patent transitions from a traditional cylindrical voice coil to a planar pancake coil configuration, changing the spatial dimension of the conductor arrangement. This allows the coil to be positioned flat between magnet faces, maximizing the magnetic field interaction area and increasing the effective conductor length within the magnetic field, thereby improving mechanical output power without proportionally increasing overall device volume
Solution Approach 2:
The patent employs a flexible printed circuit board (FPC) instead of a rigid coil former, allowing the motor structure to accommodate dynamic movements when driving the user's pinna. The FPC can bend and flex during operation, enabling the motor to adapt to the dynamic requirements of bone conduction while maintaining electrical connectivity throughout the range of motion
2Length of stationary object
If the magnets are placed farther apart to accommodate a traditional thick voice coil, then the coil can be longer, but the magnetic B-field strength decreases, reducing motor efficiency
Solution Approach 1:
The patent uses a planar pancake coil layout where the conductor winds in a flat plane between the magnet faces rather than forming a cylindrical shape. This dimensional change allows the coil to achieve significant length within a compact thickness, enabling strong magnetic coupling between closely-spaced magnets while maintaining adequate conductor length for efficient power conversion
3Ease of operation
If air-borne sound transmission is used, then the audio can be heard by others, but privacy is lost and efficiency in reproducing a wide spectrum of frequencies is reduced
Solution Approach 1:
The patent replaces the traditional acoustic radiation mechanism (pushing air to create sound waves) with a direct mechanical vibration mechanism. The motor drives the user's pinna or skull bones directly through bone conduction, substituting air-borne acoustic transmission with solid-mechanics-based vibration transmission, thereby improving both privacy and frequency reproduction efficiency
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 motor provides increased mechanical output power with reduced electrical input, enabling efficient audio reproduction directly to the user's pinna, enhancing privacy by avoiding air-borne sound transmission and achieving a wide frequency range.
Implementation Method 1
When the electrical audio signal is applied to the coil, the coil moves back and forth. The diaphragm is connected to the coil and, as such, moves with the coil.
Data Source
AI summary
The disclosed high-efficiency motor may include the following: at least two magnets, a rigid structure arranged between the at least two magnets, where the rigid structure has traces configured to act as a moveable coil, and at least two couplings that respectively link the magnets to the rigid structure in a flexible manner. An electrical input signal applied to the moveable coil may cause motive force to be applied the rigid structure according to the input signal, so that the rigid structure moves orthogonally relative to the magnets as driven by the input signal. In this manner, the high-efficiency motor may be incorporated into a system that may reproduce a full-range audio signal. Various other methods, systems, and computer-readable media are also disclosed.