Electrodes for wearables

Electrodes used in consumer electronics are mostly used for measuring Heart Rate (HR), electrocardiogram (ECG), stress (Heart Rate Variability or HRV), muscle activity (EMG), brain activity (EEG), and muscle stimulation (EMS).

Best known to the general public are electrodes used in sports and medical products to measure heart-rate and ECG, respectively. The difference between the two is HR is looking at the contractions’ peak-to-peak signal (‘beats per minute’). The ECG looks at the full image or time line of the heart signal.

Electrodes commonly used for medical ECG or HR measurement are single use adhesive patches. They are uncomfortable to use, as they are ‘glued’ to the skin. The glue also includes a gel, needed for the electronic connection. This is also why these electrodes are often referred to as ‘wet-electrodes’.

In sports, graphite based electrodes are used, which are not sticky and do not make use of a conductive gel. These are therefore referred to as ‘dry-electrodes’.

Read more background information in our blog post about electrodes for wearables.

Interested in learning more about electrodes for wearables?

What are ‘dry’-electrodes and why are they interesting? Dry electrodes, as mentioned before, are named like that because they don’t need (additional) gels or fluids to make them work (make proper contact with the skin). They can even (almost) feel like textile and comfortable to the skin.  Next to that, this also often implies they can be reused, making them more suitable for longer and more frequent usage, even daily and at home.

But, of course there is a catch. Using non-adhesive electrodes, can have a negative influence on the signal quality. This happens because the electrode can slightly move across the skin, which leads to ‘noise’ or ‘movement artifacts’, which create a less easy to read signal.

Next to electrodes, you could also use a photoplethysmogram (PPG) sensor to measure heart rate. A PPG sensor can also measure blood oxygen (also referred to as ‘blood oxygen saturation’ and ‘SpO2’), stress (HRV), blood pressure and more.

PPG sensors are those red and green LED lights on the back of your smart watch, or those little plastic devices you get clamped on your finger when hospitalised. The big advantage if these sensors over electrodes is that they are simple, small, reliable and inexpensive. And, they can be worn away from the chest area, like on the wrist or even the ear.

Want to discuss which technology is right for your wearable development?

Over the last few years, several companies and research institutes have focused their R&D efforts on overcoming the problems of noise artefacts, skin impedance (connectivity), comfort, and washability.

A handful of them have succeeded in developing easy-to-integrate, high quality signal, comfortable, and sometimes even washable electrodes! Of course, each of them have their own advantages and disadvantages, depending on how you want to use them and for what use case.