###### Abstract
There are many commonly applied hardware-based methods for minimizing the interferences inherent in biopotential signal recordings, such as twisting input leads together to reduce the area of the loop formed by the wires [19], or making the acquisition devices dependent on batteries (direct current) for their power supply [20]. Adopting a high common-mode rejection ratio amplifier, a driven-right-leg circuit, active electrodes, and isolation can further suppress interferences [21, 22, 23]. The conventional hardware-based methods are limited since they can only reduce the extraneous interferences to a certain extent. Furthermore, [PERSON] et al. proposed an interference model that considers interference directly coupled to the measuring electrodes and adds an internal interference arising from the amplifier's power supply [19]. Their study suggested that internal interference from the power supply can affect any measuring instrument with either differential or single-ended input. While the model mainly focused on the case of using analog amplifiers powered by power line transformers, battery-supplied biopotential recording systems did not suffer from such problems with power-supply interference. In addition, shielded technology is also one of the commonly used hardware methods to suppress power line interference. The most popular shielded technology is the use of a small coax cable, where the outer layer is connected to a certain type of driven signal to prevent the inner wire signal from being contaminated by extraneous interferences. [PERSON] showed that unshielded electrodes account for most power line interference, and electrode shielding, together with driven-right-leg, is quite effective in reducing that interference [24]. [PERSON] et al. proposed a method that utilized a faraday shield in which the subjects were required to be in a faraday metal cage to eliminate 50 Hz power line interference in an ECG signal, whereby the whole size of the cage must be significantly smaller than the wavelength of the noises [25]. [PERSON] et al. developed a flexible active electrode that contained a shielding metal plate with guarding feedback to protect the ECG signals from extraneous noises [26]. [PERSON] et al. used a shielding layer on printed circuit board and implemented a non-contact sensor to record clear EEG and ECG signals [27]. With so many shielded technologies coexisting, it is necessary to compare the performance of different shielding methods so that a general guideline can be established when selecting shielded technologies; it would be best to propose an improved method that could be used reliably to achieve effective biopotential acquisition in clinical or academic practices. On the other hand, various software-based filtering techniques have also been utilized to minimize the power line noise/interference inherent in biopotential signal recordings [28]. The most common approach is to use a digital notch filter at the power line frequency (50 Hz/60 Hz), which could be easily implemented with low computational cost [29; 30]. However, there are often cases when the power line interference contains not only the 50 Hz/60 Hz component but also multiple harmonic components, as well as other interferences caused by the instability of the power supply system [31; 32; 33]. Hence, filter banks with notch frequencies located at the fundamental and harmonic components of power line interference were also employed [34]. However, such filter banks would cause information loss of target signals since the frequency range largely overlaps for the biopotential signals and power line interference [35]. Hence, a number of improved filtering techniques have been proposed over the years to minimize interferences in biopotential recordings [36; 37; 38; 39; 40]. For instance, [PERSON] et al. used an adaptive power line interference filter to estimate the fundamental frequency and harmonics of power line interference, and the estimated interference was subtracted from the noise-affected biosignal [22]. [PERSON] et al.