_Applied_  
_sciences_  
_Article_  
**Design of a Low-Power Radio Frequency Unit and Its Application for Bacterial Inactivation under Laboratory Conditions**  
**[PERSON] 1,2, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 2, [PERSON] 1, [PERSON] 1 and [PERSON] 1,*()**  
BioTeC+, Chemical and Biochemical Process Technology and Control, Department of Chemical Engineering, KU Leuven, Gebreoders de Smetsrait 1, 900 Ghent, Belgium; [EMAIL_ADDRESS] (D.S.K. ); [EMAIL_ADDRESS] (M.T. ); [EMAIL_ADDRESS] (P.C. ); [EMAIL_ADDRESS] (J.E. );  
[EMAIL_ADDRESS] (D.V. ); [EMAIL_ADDRESS] (S.A.)  
2 Research Center for Metallic Liquids Physics, Ural Federal University (UFLU), 19 Mira Street, 620002 Ekaterinburg, Russia; [EMAIL_ADDRESS]  
* Correspondence: [EMAIL_ADDRESS]  
Footnote 1: BioTeC+, Chemical and Biochemical Process Technology and Control, Department of Chemical Engineering, KU Leuven, Gebreoders de Smetsrait 1, 900 Ghent, Belgium; [EMAIL_ADDRESS] (D.S.K. ); [EMAIL_ADDRESS] (M.T. ); [EMAIL_ADDRESS] (P.C. ); [EMAIL_ADDRESS] (J.E. );  
[EMAIL_ADDRESS] (D.V. ); [EMAIL_ADDRESS] (S.A.)  
Footnote 2: Research Center for Metallic Liquids Physics, Ural Federal University (UFLU), 19 Mira Street, 620002 Ekaterinburg, Russia; [EMAIL_ADDRESS]  
Footnote 3: Correspondence: [EMAIL_ADDRESS]  
Footnote 4: We use the term “\(\times\)” to refer to the term “\(\times\)” to  
relevant for heating applications span from 1 to 300 MHz [7], only frequencies of 13.56, 27.12, and 40.68 MHz are designated for unlicensed use worldwide in industrial, scientific, and medical (ISM) applications [8]. When foods are exposed to RF radiation, dielectric heating is accomplished by a combination of (i) the dipolar rotation of free water and (ii) the depolarisation of solvated ions, with the latter being the dominant heating mechanism [7]. In comparison, microwave (MW) heating (i.e., frequencies of 300-300,000 MHz), which is the most well-known dielectric heating method, is mainly accomplished by the frictional heat generated from the dipolar rotation of free water molecules [7,9]. The main advantages of both dielectric heating methods (i.e., RF and MW) compared to conventional heating technologies are fast volumetric heating and high energy efficiencies [10]. In the food industry, there are three main reasons to select RF heating over MW heating, i.e., (i) larger penetration depths allowing the treatment of larger products, (ii) the possibility to effectively heat low-moisture foods, and (iii) the absence of power intensity interference due to the longer wavelengths [2,11]. Even though achieving homogeneous temperature distributions during RF heating processes remains challenging (i.e., especially concerning over-heating at the edge), the larger penetration depths of RF already result in more even heating than for MW processes [12,13]. Nowadays, there are two types of commercial RF equipment available for generating and transferring electromagnetic power: (i) the conventional free-running oscillator (FRO) and (ii) the 50 \(\Omega\) RF amplifier system. The FRO system consists of an RF generator (i.e., where the power is generated) and an RF applicator (i.e., where the material is placed and heated), which are both combined in one device. The applicator controls the power applied by the generator [14]. One of the main characteristics of this system is the variation of frequency during heating (typically, about 1-2 MHz above the standards). When the temperature rises, the dielectric properties of the product change and so does the capacitance of the oscillator, causing a shift in frequency [15]. The 50 \(\Omega\) RF equipment differs from the previous system in that the RF generator is separated from the RF applicator by a high-power coaxial cable [14]. This system uses a crystal oscillator to stabilise the frequency (e.g., 27.12 MHz) and to produce a weak signal. This signal is amplified and transmitted to the applicator. The generator is fixed at an output impedance of 50 \(\Omega\).