Surface electromyography (sEMG) electrode coating technology: precision coating solution for gold, silver, and platinum

1、 Introduction: Technological evolution of sEMG electrodes and the value of coating

Surface Electromyography (sEMG), as a non-invasive method for detecting muscle electrical activity, is playing an increasingly important role in fields such as rehabilitation medicine, sports science, human-computer interaction, and neuroengineering. With the rapid development of wearable medical devices and flexible electronic technology, the performance requirements for sEMG acquisition electrodes are constantly increasing - not only good conductivity and signal fidelity are needed, but also flexibility, biocompatibility, and long-term comfort of the electrodes are required.

Electrode coating technology, as a key link in improving the performance of flexible electrodes, directly determines the conductivity, contact impedance, signal-to-noise ratio, and service life of the electrodes. In recent years, significant progress has been made in the innovation of coating materials and processes for flexible sEMG electrodes, providing solid technical support for high-performance non-invasive electromyography signal acquisition.

2、 Core technical requirements for sEMG electrode coating

The coating layer of flexible sEMG electrodes must meet the following core requirements:

• Low contact impedance.The impedance of the electrode skin interface is a key parameter that affects signal quality. Low impedance means higher signal transmission efficiency and better signal-to-noise ratio. Research has shown that through reasonable selection of coating materials and process optimization, interface impedance can be effectively reduced.
• High conductivity and stability.The coating layer needs to have excellent conductivity and maintain stable electrical performance under mechanical deformation conditions such as repeated bending and stretching.
• Good biocompatibility.As a device that comes into direct contact with the skin, the coating material needs to be non-toxic, non irritating, and meet the biological safety requirements for long-term wear.
• Flexibility and adhesion.The coating layer needs to be firmly combined with the flexible substrate, and should not fall off or crack in dynamic usage scenarios such as bending and twisting.

3、 Advanced Institute Technology: A professional manufacturer of flexible substrate coating

Advanced Institute (Shenzhen) Technology Co., Ltd. was established in 2016 and is located in Bao'an District, Shenzhen, Guangdong Province. It is a national high-tech enterprise specializing in shielding materials, insulation materials, thermal conductivity materials, and precious metal coatings. The company has its own registered trademark "Research Platinum" and has production bases in Shenzhen and Dongguan. It has passed ISO9001 quality management system certification and its products comply with GJB 773A aerospace standards and RoHS environmental requirements.

In the field of coating technology, the company has independently built magnetron sputtering and vacuum evaporation production lines, using roll to roll continuous production technology, which can continuously deposit metal layers on the surface of flexible polymer films. Suitable substrates include various flexible materials such as FEP, PI, PET, LCP, PPS, PEN, PP, etc., and can be plated with metals including gold, silver, copper, aluminum, tin, nickel, titanium, platinum, etc. Relying on advanced physical vapor deposition (PVD) technology, the company has achieved nanometer level precise control of metal thin films on the substrate surface, with thickness ranging from a few nanometers to several hundred nanometers, ensuring extremely high uniformity and density.

4、 Core coating process

• Plasma pretreatment activation.In response to the problem of insufficient bonding strength between metal and polymer substrates, Advanced Institute Technology has developed a plasma pretreatment process, which effectively improves the bonding strength between the substrate and the metal layer by bombarding the substrate surface with plasma.
• Magnetron sputtering and vacuum evaporation.The company uses composite processes such as magnetron sputtering and vacuum evaporation to deposit metal coatings on flexible polymer film substrates such as PI (polyimide), PET, FEP, etc. The metal coating achieves stress transition from the substrate to the metal layer through gradient coating design, effectively avoiding interface delamination caused by modulus differences.
• Cyanide free gold plating and pulse electroplating.In the gold plating process, the company adopts cyanide free gold plating technology, which has significant advantages in reducing environmental pollution and improving operational safety. Simultaneously introducing pulse electroplating technology, by precisely controlling the switching time and frequency of the current, the porosity in the coating is effectively reduced, and the density and uniformity of the coating are improved.

5、 SEMG electrode coating scheme

（1） Gold Plated Electrode - Optimal Selection for Low Impedance and High Signal to Noise Ratio

Gold has become one of the preferred materials for flexible sEMG electrode coating due to its excellent conductivity, chemical stability, and biocompatibility. Research has shown that electrodes plated with gold (approximately 2 μ m thickness) on polyimide (PI) flexible substrates have lower impedance and can obtain stable baseline and good sEMG signals.

• Low contact impedance.The electrode with gold plating on the surface has lower impedance, which can obtain stable baseline and good sEMG signal. The study also shows that nano gold electroplating can achieve acceptable signal enhancement while reducing noise.
• Excellent biocompatibility.The chemical inertness of gold endows gold-plated electrodes with excellent corrosion resistance, making them suitable for long-term skin contact and even implantation scenarios.
• Flexible substrate adaptation.Using flexible materials such as PI (thickness 50 μ m) as carriers, it has high mechanical flexibility and is suitable for wearable device applications.

（2） Silver plated/silver chloride electrode - standard protocol for clinical sEMG

Silver/silver chloride (Ag/AgCl) is the most common material system in biopotential electrodes and dominates clinical sEMG records. It is usually achieved by electrochemically depositing a thin layer of silver chloride on a silver electrode.

• Mature material system.Ag/AgCl electrode is a standard configuration for clinical sEMG recording, with mature technology and reliable performance.
• Balancing performance and cost.Silver plated electrodes have both performance and cost advantages.
• Flexible craftsmanship.It can be achieved through various process routes such as electrochemical chlorination and nano silver wire composite.

（3） Platinum plated electrode - guarantee of high precision and long-term application

Platinum plated electrodes exhibit excellent performance in high-precision signal acquisition and long-term application scenarios due to their low resistivity characteristics.

• Extremely low electrical resistivity.The sintered resistivity of the platinum electrode slurry developed by the company is as low as 1.65 μ Ω· cm, and the square resistance is as low as 20 ± 5m Ω/□, ensuring high sensitivity and fast response of the electrode.
• Long term stability.The chemical inertness of platinum ensures stable performance of the electrode during long-term use.
• Suitable for high-frequency signal acquisition.Platinum plated electrodes have become an ideal choice for monitoring precise signals such as high-frequency EEG, effectively capturing transient electrical activity.

6、 Typical application scenarios

• Wearable sEMG devices.Flexible gold/silver plated electrodes are combined with flexible substrates such as PI and PET to adapt to wearable forms such as wristbands and patches, achieving long-term and comfortable electromyographic signal monitoring.
• High density electrode array.Gold plated circular electrodes are arranged at a spacing of 3-5mm for multi-channel sEMG signal acquisition, which can finely capture spatial distribution information of muscle activity.
• Dry electrode sEMG system.The dry electrode without conductive gel is prepared by the coating technology to avoid the drying of gel and skin irritation of the traditional wet electrode. The titanium thin film dry electrode prepared by magnetron sputtering has been proven to be suitable for sEMG recording.
• Medical grade and research grade sEMG.Gold/platinum plated electrodes are suitable for professional scenarios such as clinical diagnosis, rehabilitation assessment, sports science, and human-computer interaction due to their low impedance and high signal-to-noise ratio.

7、 Conclusion

The performance of surface electromyography electrodes largely depends on the selection of coating materials and processes. Advanced Institute (Shenzhen) Technology Co., Ltd. relies on its independent process platform of roll to roll magnetron sputtering and vacuum evaporation to provide multiple options for gold plating, silver plating, platinum plating, etc. for flexible sEMG electrodes. It supports various flexible substrates such as PI, PET, FEP, etc., and the coating thickness can be precisely controlled at the nanometer level.

The company adheres to the full package service concept of "material process application solutions" and is committed to providing high-performance electrode coating solutions for wearable medical, human-computer interaction, neural engineering and other fields, helping to continuously improve electromyographic signal acquisition technology.

*The data in this article is sourced from publicly available information on advanced technology and industry literature, and is provided for reference only. The product parameters are subject to the actual customized specifications.