Magnet-less Voice Coil Actuator Using Pot Core Electromagnet
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Solution Overview
Problem
Conventional loudspeakers rely on expensive and heavy permanent magnets, which are inefficient and costly, especially in applications where weight reduction is crucial, and they suffer from low-frequency range distortion and high costs due to the use of rare earth elements like Neodymium.
Innovation Solution
A magnet-less electromagnetic voice coil actuator using a low-cost iron electromagnet structure with a pot core magnet made from Soft Magnetic Composites (SMC) material, driven by separate amplified signals from the audio input, providing efficient magnet circuitry with minimal stray field loss and linear actuation force, and employing PWM Class-D amplifiers for efficient energy recirculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If permanent magnets (NdFeB) are used in conventional loudspeakers, then magnetic field strength is achieved, but weight and cost increase significantly
Solution Approach 1:
The patent removes the permanent magnet from the speaker system entirely, extracting the heavy and costly rare earth element while maintaining the magnetic field generation capability through an alternative electromagnet design. This extraction directly addresses the weight and cost problems associated with NdFeB magnets.
Solution Approach 2:
The patent replaces expensive permanent magnets with a cost-effective electromagnet structure using iron and copper components. While the electromagnet requires continuous power, the material costs are significantly lower, making it economically viable for consumer applications.
2Force
If permanent magnets are used in conventional loudspeakers, then magnetic field strength is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive permanent magnets with a cost-effective electromagnet structure using iron and copper components. While the electromagnet requires continuous power, the material costs are significantly lower, making it economically viable for consumer applications.
3Force
If permanent magnets are used in conventional loudspeakers, then magnetic field strength is achieved, but low-frequency range distortion occurs
Solution Approach 1:
The patent transitions from a static permanent magnet field to a dynamic electromagnet field that can be actively controlled and adjusted in real-time. This dynamic control allows the magnetic field strength to be optimized for different frequency ranges, particularly improving low-frequency response and reducing distortion through active field modulation.
4Force
If electromagnets with internal power sources are used, then magnetic field generation is achieved, but weight and complexity increase
Solution Approach 1:
The patent integrates the electromagnet's power supply directly into the speaker's existing electrical system, allowing the same power amplifier that drives the voice coil to also power the field coil. This multi-functional use of the power system eliminates the need for separate power sources, reducing overall system complexity.
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 solution results in a lightweight, efficient, and cost-effective loudspeaker system with improved frequency response and reduced distortion, capable of handling low-frequency ranges and high-resolution audio, while eliminating the need for rare earth magnets.
Implementation Method 1
the induced magnetic field interacts with the magnetic field of the permanent magnet to alternately attract and repel the voice coil
Implementation Method 2
a field coil constructed of copper wire
Data Source
AI summary
A magnet-less electromagnetic voice coil actuator comprises a pot core magnet structure having a magnetic flux conductive core, a field coil within the pot core magnet structure for generating magnetic field through the magnetic flux conductive core and across an air gap, a voice coil wound on a voice coil former forming an under-hung voice coil design within the air gap and an electronic signal processor configured to split an audio input signal into a positive definite field coil signal and a bipolar voice coil signal. The voice coil and the field coil are each driven by an amplified signal derived from the audio input signal to create an actuation force. The bipolar voice coil signal is adjusted so that the product of the bandwidth limited positive definite field coil current and the bipolar voice coil current, hence the actuation force, is a linear function of the bipolar audio input current.