## 1 Introduction  
A layer of an organism called biofilm rapidly covers any surface submerged in the sea. They work as a foundation for biofouling growth. Biofouling is the accumulation of microorganisms, plant algae, or small marine animals that are not wanted on marine structure surfaces. Marine biofouling can be divided into two phases or types; micro and macro biofouling. Microfouling refers to biofilm formed on a material surface due to bacterial activity. Macrofouling refers to the adherence of organisms such as oysters, barnacles, soft corals, and seaweed to produce a fouling community (Figure 1a). It is estimated that 5.7 billion US dollars are spent by governments every year to remove biofouling. Biofouling occurs mainly in the shipping and offshore industry [1]. Traditional techniques to prevent fouling build-up include coating the offshore structure with Teflon and alloys [2; 3; 4], nanocomposites, plastics, fiber-reinforced polymers, and alloys. However, using chemicals or changing the water pH is not feasible due to environmental concerns. Therefore, water jets are predominately used in the marketplace for biofouling removal. However, as shown in Figure 1b, using such a technique is costly and requires a marine vessel. Furthermore, biofouling removal through a high-pressure water jet cleaning method might damage the coating and add chemicals to the water [5; 6]. Exposing the structure to the magnetic and electric field can also remove biofouling [7; 8]. In addition, removing biofouling through cavitation generated by ultrasonic waves has been studied by several researchers [9; 10]. Cavitation can be defined as small vapor-filledbubbles or voids due to the reduction in the static pressure of the fluid below the liquid's vapor pressure [11]. Two types of cavitation exist, inertial cavitation and non-inertial cavitation. Inertial cavitation is when a liquid bubble quickly collapses, producing a shock wave [12; 13]. It occurs in nature in the strikes of mantis and pistol shrimps and the vascular tissues of plants. Non-inertial cavitation, on the other hand, is the process in which a bubble is forced to oscillate due to some form of input, such as an acoustic field. This type of cavitation is often employed in ultrasonic cleaning baths [14; 15]. Inertial cavities collapse and generate shock waves when they enter higher-pressure regions or are exposed to pressure waves [16]. The shock waves are very strong, close to the imploding bubble but attenuate rapidly compared with a typical acoustic wave in the fluid. It is mainly the shock wave energy that removes biofouling from the marine structure [17]. The attenuation value from the shock wave is estimated by the inverse square of the distance until the wave becomes so weak that it follows the underwater acoustic law [18]. Due to such a quick reduction in the shock wave amplitude, [PERSON] et al. [19] recommended using an array of transducers for biofouling removal. When microbubbles are exposed to even low-intensity ultra-sonification, a shock wave, and water jet can be produced. Such a phenomenon was used by [PERSON] et al. [20] for biofouling removal. Therefore, to detach biofouling from marine structures, it is crucial to understand the interaction between the microbubbles and ultrasound waves. High-power ultrasound transducers can be optimized to produce high amplitude vibration for different applications [21], namely in welding [22; 23; 24], sonochemistry [25], cutting [26], cleaning of different food fouling materials [27], and biofouling removal [17]. A detailed review of power ultrasound's application has been studied by several researchers. For example, see [28; 29]. Moreover, the generation of cavitation by these transducers is exploited in different applications [30]. The threshold for producing cavitation in the water is investigated by several researchers based on broadband noise level [31; 32] and other techniques, which are well explained in reference work [33]. [PERSON] et al.