# Four-Dimensional Adjustable Electroencephalography Cap for Solid–Gel Electrode

## TL;DR

A new 4D adjustable EEG cap improves fit and performance for a wide range of head shapes, enhancing accuracy and comfort in brain activity measurements.

## Contribution

A four-dimensional adjustable EEG cap that adapts to diverse head shapes, improving signal quality and usability.

## Key findings

- The 4D cap adapts to various head shapes more quickly than commercial caps.
- It reduces impedance and improves signal-to-noise ratio and measurement accuracy.
- The cap offers better comfort and performance in brain-computer interface applications.

## Abstract

Currently, the electroencephalogram (EEG) cap is limited to a finite number of sizes based on head circumference, lacking the mechanical flexibility to accommodate the full range of skull dimensions. This reliance on head circumference data alone often results in a poor fit between the EEG cap and the user’s head shape. To address these limitations, we have developed a four-dimensional (4D) adjustable EEG cap. This cap features an adjustable mechanism that covers the entire cranial area in four dimensions, allowing it to fit the head shapes of nearly all adults. The system is compatible with 64 channels or lower electrode counts. We conducted a study with numerous volunteers to compare the performance characteristics of the 4D caps with the commercial (COML) caps in terms of contact pressure, preparation time, wearing impedance, and performance in brain–computer interface (BCI) applications. The 4D cap demonstrated the ability to adapt to various head shapes more quickly, reduce impedance during testing, and enhance measurement accuracy, signal-to-noise ratio (SNR), and comfort. These improvements suggest its potential for broader application in both laboratory settings and daily life.