Electrodes are used in many technologies, fundamentally acting as transducers that convert the body’s ionic currents into electronically processable signals and vice versa. In medical diagnostics, they are inseparable from procedures like electrocardiograms (ECGs), electroencephalograms (EEGs), and electromyograms (EMGs), enabling the detection and analysis of electrical activity in the heart, brain and muscles, respectively.
Ongoing advancements in materials science and nanotechnology are driving the development of more biocompatible, sensitive and minimally invasive electrodes, expanding their applications and improving patient outcomes.
All electrodes work on the same principle: they facilitate the flow of electrical current between the body and an electronic device. The key difference lies in how they achieve this connection. A good electrode needs to make consistent, reliable contact with the skin (or other tissue) while minimizing interference and maximizing signal quality.
Before discussing the different types of electrodes, it’s essential to acknowledge the work of Hans Berger, who is credited with the discovery of the electroencephalogram (EEG) in the 1920s. His pursuit of understanding the brain’s electrical activity led him to develop the first EEG machine, a device that could record these minute electrical signals. Berger’s early electrodes were typically made of silver and required a conductive paste to ensure good contact with the scalp. His pioneering work laid the foundation for all subsequent EEG research and clinical applications, demonstrating the immense potential of measuring the activity of the brain. While modern electrode technology has advanced significantly since Berger’s time, his initial designs and techniques were crucial for establishing the field of electroencephalography.
Nowadays, there are different types of electrodes available made of various materials, whose features can heavily impact the signal, the current and the comfort of the user. In this article, we will discuss dry, wet and soft electrodes, exploring their pros and cons.
Comparison of dry electrodes
In this section, we will discuss dry electrodes that are designed to establish an electrical connection without the use of conductive gels or liquids. These electrodes offer the advantage of rapid setup and increased user comfort, eliminating the disorganization associated with traditional wet electrodes. The following comparison outlines the key characteristics of dry electrodes, highlighting their potential benefits alongside the challenges that must be considered for optimal performance.
| PROS | CONS |
| Dry electrodes can significantly decrease the time required for setup of the electrodes compared to wet electrodes. This is a major advantage for practical applications as it can help perform the tests faster and more efficiently. | Nevertheless, signal discrepancies can occur, thus dry electrodes can show lower signal correlation. |
| Eliminates the discomfort caused by abrasive gel application, drying gel and scalp irritation that comes with wet electrodes. Also, wet electrodes can be messy due to gel or saline, meaning that dry electrodes are more practical and hygienic. | Hair length and type can greatly influence the contact and performance of the electrodes. It may also affect signal quality. In addition, the skin of the scalp has to be clean for good contact, also, long-term use can prove to be uncomfortable or irritating. |
| Dry electrodes provide better signal quality which guarantees continuous and uninterrupted recording of the brain data. | Dry electrodes tend to have higher impedance than wet electrodes, which may make them more susceptible to motion artifacts. |
Comparison of wet electrodes
Wet electrodes, employing conductive gels or saline solutions, have established themselves as a traditional and reliable method in electrophysiological recording. Their longstanding use has helped to accumulate a large amount of data and established benchmarks, but they are not without their limitations. The following comparison outlines the core advantages and disadvantages of wet electrodes.
| PROS | CONS |
| The use of gel or saline solution in wet electrodes generally provides good conductivity between the electrode and the scalp, leading to a strong signal. | One of the biggest disadvantages is that the gel or saline used in wet electrodes tends to dry out over time. This changes the impedance characteristics of the electrodes and can affect the signal quality, making them unsuitable for long-term recordings and experiments. |
| Wet EEG electrodes have been used for decades and are a well-known and tested technology, thus, they can be seen as reliable. There is a large amount of research and clinical experience supporting their use. Therefore, they are trusted by different researchers. | Wet electrodes require more preparation time due to the application of gel or saline. This process can also be quite messy and inconvenient for both of the parties of the recording; it also makes the hair and scalp wet and sticky. |
| Wet electrodes often prove to be a cost-effective solution, as they are inexpensive to produce, especially if advanced systems aren’t required. | The values of the recording obtained with wet electrodes tend to change more than with dry electrodes. This can be attributed to the changing electrical properties of the wet electrode as the solution dries. This can make it difficult to maintain stable recordings. |
Comparison of soft electrodes
Soft electrodes represent a significant advancement in electrode technology, designed to enhance user comfort and biocompatibility, particularly for long-term monitoring and wearable applications. However, as a relatively new technology, they present their own advantages and challenges, which will be highlighted in the following section.
| PROS | CONS |
| Soft electrodes conform to the skin better, making them more comfortable for extended use compared to rigid electrodes. Their flexibility allows them to move with the body, which reduces discomfort. | Soft electrodes can be expensive. Materials like gold nanoparticles and advanced conductive polymers increase manufacturing costs. High-end manufacturing processes, such as laser patterning and nanomaterial deposition, add to the expense. |
| Wet electrodes often cause skin irritation due to the gel and adhesives used. Soft electrodes, made from biocompatible materials like graphene, carbon nanotubes and conductive polymers, minimize skin reactions. | Despite improved adhesion techniques, soft electrodes may still struggle to maintain strong contact. Factors like sweat, body oils and skin elasticity can reduce adhesion, requiring reapplication. |
| Soft electrodes can be integrated with flexible circuits and wireless systems, which enhances real-time health monitoring capabilities in healthcare. | Soft electrodes are still seen as experimental in many areas and widespread validation is still ongoing. Their performance can vary depending on material composition, manufacturing techniques and application conditions. |
Conclusion
The choice between dry, wet and soft electrodes depends heavily on the specific application, user needs and desired outcomes. As research progresses, we can expect to see further improvements in signal quality, user comfort and application versatility. The right electrode choice will continue to be a balance between practicality, technological capabilities and the specific demands of each case, whether we are talking about medical diagnostics or brain-computer interfaces.
Sources/ References
Afif, N. F., Pratama, S. H., Haryanto, F., Khotimah, S. N., & Suprijadi, N. (2020). Comparison of wet and dry EEG electrodes based on brain signals characterization in temporal and anterior frontal areas using audio stimulation. Journal of Physics Conference Series, 1505(1), 012069. https://doi.org/10.1088/1742-6596/1505/1/012069
Borck, C. (2018). Brainwaves: A Cultural History of Electroencephalography.
Di Flumeri, G., Aricò, P., Borghini, G., Sciaraffa, N., Di Florio, A., & Babiloni, F. (2019). The Dry Revolution: Evaluation of three different EEG dry electrode types in terms of signal spectral features, mental states classification and usability. Sensors, 19(6), 1365. https://doi.org/10.3390/s19061365
Kim, H., Kim, E., Choi, C., & Yeo, W. (2022). Advances in soft and dry electrodes for wearable health monitoring devices. Micromachines, 13(4), 629. https://doi.org/10.3390/mi13040629Ltd, O. (n.d.). What are Electrodes? Ossila. https://www.ossila.com/pages/electrodes