## 1 Introduction  
High intensity pulsed electric fields (PEF) can trigger increased permeability of biological cells to exogenous molecules to which the cells were initially impermeable [1]. PEF polarizes the cell membrane, which causes reorientation of lipids and formation of pores [2; 3], thus increasing molecular transport across the cell membrane [4; 5]. In case of reversible electroporation (depends on pulse parameters), the cell membrane is then resealed [6]. As a result, there is a variety of electroporation applications, which include cancer treatment [7], gene delivery [8], food processing [9], biorefinery [10] and many other [11; 12]. In each case, various PEF parameters are required, which establishes a challenge in generator design in terms of universality. The straightforward distribution of applications in the pulse amplitude-duration space is summarized in Figure 1[13; 14; 15; 16; 17; 18; 19]. It can be seen that the majority of applications lie in the micro-millisecond range. Indeed, the range of longer but lower amplitude pulses dominated the field for decades, however, in the recent years the number of works focusing shorter (nanosecond) pulses increased significantly. The reason lies in the limitations of conventional microsecond range methodologies such as bioimpedance-dependent field distribution [20], Joule heating [21], muscle contractions [22], electrical breakdown [23] and oxidative stress [24]. Nanosecond pulses cannot solve all the problems completely, however, in many cases the negative factors are diminished. However, state-of-art pulsed power electronics are required for generators to form pulses up to tens of kV and hundreds of amperes in the nanosecond range. Therefore, the price and engineering complexity of such generators is high, nevertheless, the trends in applications of nanosecond PEF make it viable (Figure 2). As it can be seen in Figure 2, there is a definitive rise in publications in the last decade, which partially is a consequence of better availability of pulse forming switches on the market. Development of laboratory grade generators for electroporation has intensified with the development of better semiconductors (i.e., silicon-carbide technology) [25]. Nevertheless, the number of papers focusing nanosecond pulse generators for electroporation is still low. A similar trend is observed in the frontier of short microsecond or sub-microsecond pulses using high frequency bursts (Figure 3), which possibly is a natural transition step from long micro-millisecond to the nanosecond range. For the optimal effectiveness of the treatment many electroporation parameters must be adjusted, i.e., the pulse amplitude and duration, repetition frequency, waveform and number of pulses. As a result, universality of electroporators is important when a study of new phenomena and biological effects of PEF are established. Figure 1: Generalized representation of pulse parameters for different electroporation applications. Figure 2: The trends in the number of publications on the topics of nanosecond electroporation according to Clarivate Analytics Web of Science (25 May 2020). There is high diversity of techniques used for the development of the PEF generators for electroporation applications. Some are well commercialized and a first comprehensive list of commercially available electroporators has been collected in 2004 [26], which was later updated in 2010 [15], 2017 [27] and 2019 [28]. It can be seen, that commercial approach had followed the most common demands of electroporation application. As a result, most of the commercial electroporators were developed with the pulse amplitude up to few kV and duration from tens of \(\upmu\)s to seconds. In comparison, the selection of commercial high-voltage nanosecond pulsed electric field (nsPEF) electroporators is significantly lower [27; 28]. Additionally, it is common, that the commercial devices have a limited range of available pulse durations and repetition frequencies, thus the device applicability is non-flexible.