TMS Coil Acoustic Noise Reduction via Node Mounting
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Solution Overview
Problem
Transcranial magnetic stimulation (TMS) coils produce loud acoustic noise due to high currents, posing risks to hearing and causing unwanted neural activation, with existing mitigation methods like hearing protection and noise cancellation being insufficient to reduce sound levels effectively.
Innovation Solution
A double-containment coil design with an air gap and sound-absorbing materials, where the winding block is mounted at acoustic nodes to minimize vibrations and sound transmission, and an outer casing with optimized thickness and sound-absorbing panels to reduce acoustic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high current is pulsed through the TMS coil to produce peak magnetic field on the order of 1 T, then the magnetic stimulation strength is improved, but the acoustic noise level increases with peak sound pressure level exceeding 130 dB(Z)
Solution Approach 1:
The coil assembly is segmented into multiple functional components: the coil winding, rigid support structure, acoustic damping material, and outer casing. Each segment serves a specific function in either generating the magnetic field or managing the acoustic noise, allowing the system to achieve both high stimulation strength and noise reduction
Solution Approach 2:
Acoustic damping material is introduced as an intermediary substance between the coil assembly and the external environment. This material absorbs and dissipates the mechanical vibrations and acoustic noise generated by the high current pulse, preventing them from propagating outward while allowing the magnetic field to function effectively
2Object-generated harmful factors
If the coil is enclosed in an outer casing to contain acoustic noise, then the sound transmission is reduced, but the electric field output may be affected
Solution Approach 1:
The outer casing is designed with non-uniform thickness to optimize both acoustic containment and electric field output. The casing thickness is minimized in regions where electric field output is critical to maintain stimulation effectiveness, while being maximized in regions where acoustic noise containment is the primary concern. This localized variation in thickness allows the system to balance both requirements
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 design significantly reduces peak sound pressure levels and continuous sound levels during TMS, maintaining high stimulation strength and energy efficiency, thereby mitigating hearing risks and unwanted neural activation.
Implementation Method 1
an electromagnet coil placed on the subject's scalp is pulsed to create a rapidly changing magnetic field (B-field) which induces an electric field (E-field) in the vicinity of the coil
Implementation Method 2
The high current and magnetic field produce a mechanical vibration of the coil, which manifests itself in a loud, impulsive sound
Implementation Method 3
The rest of the winding block is isolated from the casing by an air gap, and the sound is absorbed by polyester fiber panels within the casing
Data Source
AI summary
Methods and systems for magnetic stimulation. In some examples, a coil assembly for magnetic stimulation includes a rigid block and a coil potted in the winding block. The coil assembly includes a casing enclosing the winding block. The winding block is mounted to the casing at one or more acoustic nodes of the winding block that are subject to a minimum vibration during a magnetic stimulation pulse, e.g., a transcranial magnetic stimulation pulse.