## 1 Introduction  
In recent years, there has been a revival of interest in raw materials with strong antioxidant properties due to their health potential. Plants that were used in folk medicine are experiencing a renaissance, and rowan is an example of one. Currently, about 250 species of rowan are known [1]. In Poland, five species grow wild, including _Sorbus aucuparia_ (_S. aucuparia_), commonly known as rowan [2]. The chemical composition of rowan fruits (genus _Sorbus_ L.) includes sugars, organic acids, phenolic acids, flavonoid compounds, anthocyanins, tannins, cyanogenic glycosides, vitamins, and bioelements [3; 4; 5].  
Due to their rich chemical composition, fruits and other organs of rowan have numerous therapeutic effects: antioxidant, antidiabetic, antihyperlipidemic, anti-inflammatory, antibacterial, anticancer, antiviral, antifungal, vasoprotective, neuroprotective, cardioprotective, and hepatoprotective [6; 7; 8; 9]. In unconventional medicine, rowan fruits are used in the treatment of diabetes, metabolic disorders, kidney stones, arthritis, rheumatism,gastritis, duodenal and small intestine catarrhs, irritable bowel syndrome, and diseases of the liver and gallbladder [10] as a laxative and a detoxifying agent [11].  
The choice of the extraction technique plays a crucial role in obtaining bioactive compounds from plant matter. Currently, different techniques are used, such as Soxhlet extraction, maceration, supercritical fluid extraction, microwave-assisted extraction, pressure-solved solvent extraction, extraction assisted by a pulsed electric field [12,13], and UAE. In contrast to other methods, UAE offers several benefits: a short extraction time, minimal solvent usage and low-cost equipment. The mechanism principle behind the enhanced extraction process facilitated by ultrasound involves the disruption of plant cells, and releasing their contents into the solvent [14]. Process conditions should be selected in such a way as to avoid thermal and chemical degradation as well as biochemical changes in phenolic compounds. The effectiveness of the extraction process is influenced by many factors, including time, power, type and amount of solvent, pH, temperature, the degree of material fragmentation, and the operating mode of the ultrasonic processor (continuous or pulsed) [15].  
The process of acoustic energy transmission to the extracted sample depends greatly on the type of ultrasonic system used. The shape of the reaction vessel is critical during utilising an ultrasonic bath. An important factor here is, in particular, the lack of homogeneity of the sound pressure in the entire volume of the sample due to the point arrangement of the emitters in the ultrasonic bath [16]. Progress in the construction of acoustic generators has allowed the use of transducers immersed directly in the solution, a so-called probe system. This technique allows a higher energy to be transferred to the solvent, but this system also has a sharp decrease in ultrasound intensity in both the longitudinal and transverse directions. Some authors have tried to optimise the extraction efficiency by changing the immersion of the ultrasonic probe in extraction flasks. [PERSON] et al. [17] observed a substantial decrease in the extraction yield of \(\beta\)-carotene from citrus peels as the liquid height increased. [PERSON] et al. [18] investigated how the size and diameter of the extraction vessel impact the amount of mangiferin extracted from _Mangiferinatica_ leaves. Their findings demonstrated that as the extraction vessel's diameter grows, the yield of mangiferin increases until reaching a certain threshold, after which it stabilises.  
The current state of knowledge prompts us to assume that the shape of the extraction vessels may have a significant impact on the extraction efficiency. Therefore, the aim of the study was to analyse the impact of the dimensions of the extraction vessels on the efficiency of extraction of rowan fruits assisted by a pulsed ultrasonic field.