Dry electrode solution

Category: Brain-computer interface

Time：2024-12-21

With the rapid development of brain science, artificial intelligence, chips, algorithms, and other technologies, non-invasive Brain-Computer Interface (BCI) technology has made significant progress in recent years. Due to its advantages of real-time interaction and high accuracy, it has shown unique application value in various fields, such as medical rehabilitation, sleep monitoring, driving, brain-controlled typing, and more.

Non-invasive Brain-Computer Interface electrodes are generally divided into two main categories: wet electrodes and dry electrodes. Traditional wet electrode technology requires the use of a syringe with a needle to inject gel onto the subject in order to reduce the contact impedance between the electrode and the scalp. The wearing process is cumbersome, requiring a significant amount of time, and as the conductive paste evaporates, the signal quality is affected, preventing long-term stable data collection.

Dry electrode technology, on the other hand, does not rely on conductive paste, is easy to use, and supports prolonged data collection. Common dry electrodes include skin patch electrodes, microneedle electrodes, and metal column-type dry electrodes. Although innovations in materials and processes have significantly improved the performance of skin patch dry electrodes and microneedle electrodes, they still face limitations in application scenarios due to interference from hair. Metal column-type dry electrodes, while durable, can be uncomfortable, causing pressure and pain during use. To ensure both comfort and stable contact, they often require complex mechanical designs, such as helmets or spring clips.

Greentek’s dry electrodes aim to improve wearing comfort. The electrodes are made from soft, conductive elastomer materials, which deform under pressure, reducing the sense of pressure on the scalp. The claw-shaped contact area at the front is modified with silver/silver chloride (Ag/AgCl) material, which retains the natural low polarization and low noise characteristics of silver chloride, maximizing the signal-to-noise ratio of the recorded EEG signal. Additionally, the electrodes feature three different claw lengths, allowing them to better penetrate through hair and conform to different head shapes.

Figure 1: Electrode potential difference of a pair of dry electrodes in an electrolyte.

Figure 2: AC impedance spectrum of a pair of dry electrode gels in an electrolyte (10mV disturbance, 1-10k Hz bandwidth).

Table 3: Dry Electrode Specifications

Testing results show that when used with a Brain Product amplifier (V-amp 16-channel), the dry electrode meets the functional requirements for EEG signal collection. The dry electrodes, combined with a blue triangular cap, maintain an electrode-scalp impedance greater than 100 kΩ, and the collected EEG signals are stable with good signal quality. Characteristic waveforms can be observed in both blink and eye-closure states. The electrodes offer good comfort, and the flexible material has moderate hardness, providing a comfortable fit with no significant discomfort even after one hour of use.

It is worth noting that while dry electrodes can collect EEG signals within a certain range, due to the direct contact between the electronic conductor and the skin (without a conductive paste or saline plasma interface), the contact impedance is still much higher compared to wet electrodes. This high impedance can lead to greater noise in EEG collection and lower signal quality. To overcome the high noise and signal interference during the dry electrode collection process, active electrode technology or algorithms are often used to compensate.

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Semi-dry EEG electrode solution