**6. Conclusion and future outlook**

This chapter reviews the factors that affect wearable electrode performance, which are important to understand for the development of these electrodes. The mechanistic principle along with an electrical equivalent circuit for both wet and dry electrodes is discussed that explains the differences in the transduction mechanism of wet and dry electrodes. Various types of dry electrodes have been briefly covered to highlight the current state of art. Efforts made by researchers in developing different types of dry electrodes in a detailed manner can be found in the literature in recent review papers [55–58]. Several factors such as the electrode area, skin hydration, electrode material, and pressure that substantially impact the performance of the dry electrodes and their contribution to the individual parameters of the electrical model are discussed. This review suggests that higher relative permittivity of the electrode material's native electrode, an increase in electrode area, the application of pressure, and hydrated skin can help in achieving lower skin-electrode impedance. Thus, these factors can be used for the development of wearable biopotential electrodes, to improve high-quality biopotential signals. In addition to the consideration of the factors for the development of the electrodes, testing the wearable electrodes in a controlled way is crucial for evaluating their performance. Thus several research efforts to fabricate the skin phantoms simulating the electrical properties of the skin across a broad frequency range of 1 Hz–300 GHz are reviewed. Based on this review, phantoms simulating the electrical properties of the skin across their corresponding frequency range are shown in **Figure 7**. In addition to this, the skin phantom that is capable of simulating the electrical properties of stratum corneum in the frequency range crucial for biopotential signals (1 Hz–1000 Hz) along with the controlled hydration status is discussed, which can be used to model the interaction of dry electrodes.

#### **Figure 7.**

*Summary of the fabricated skin phantoms across the different frequency ranges. Numbers in square brackets show the reference numbers.*
