## 1 Introduction  
The human vestibular system is essential for maintaining stable gaze and posture, as well as contributing to motion perception and spatial orientation [1]. It consists of three semicircular canals (SCCs), horizontal, anterior, and posterior, and two otolith organs, which detect rotation and acceleration [2, 3]. Several researchers have studied methods for vestibular stimulation, such as galvanic [4], caloric [5], and magnetic stimulation [6, 7], and these studies have been shown to effectively activate the vestibular system. However, these methods are limited by spatial and temporal resolution [8]: galvanic vestibular stimulation (GVS) lacks spatial resolution, as it activates adjacent SCCs and otoliths simultaneously; caloric vestibular stimulation (CVS) exhibits limited temporal resolution due to its gradual onset; and magnetic vestibular stimulation (MVS) faces challenges in providing a clear event onset. Furthermore, the mechanisms underlying these methods are not fully understood [7, 9, 10], particularly regarding their interactions with the vestibular system to evoke specific neural responses, and they may also induce non-specific or unintended neural responses. As a result, new approaches are needed to address these limitations.  
This study focuses on the SCC, which is responsible for detecting rotational movement [3, 11], and proposes a novel method of vestibular stimulation using continuous low-intensity focused ultrasound (LIFU) to modulate the flow of endolymph [12]. By precisely controlling fluid motion within the SCC, this approach offers a new way of inducingrotational sensations, distinct from existing technologies. Acoustic streaming, induced by high-frequency sound waves, is a biocompatible method that is well suited for human application [13; 14; 15]. LIFU has shown significant potential in neural stimulation and has been successfully applied in areas such as brain stimulation [16; 17] and drug delivery [18]. This study expands on these possibilities and investigates LIFU's potential in the vestibular system as part of a pilot study.  
A 3D finite element model was constructed to simulate how LIFU affects the flow of endolymph within the SCC, and thermal effects were evaluated to ensure that temperature increases remained within safe limits. Additionally, fluid-structure interaction (FSI) was used to quantify the effects of LIFU on endolymph flow and cupula displacement [19]. This cupula displacement was then compared with the rotation-induced cupula displacement to evaluate the biomechanical effects of LIFU on the SCC. The method for this comparative analysis is described in the Methods section. The results demonstrated that LIFU can precisely control the flow of endolymph, with cupula displacements exceeding 1 \(\upmu\)m. Additionally, simulations showed that the temperature increase remained below 1 \({}^{\circ}\)C during 1 second of exposure, ensuring thermal safety [20; 21]. Additionally, adjustments to the focal point of the ultrasound transducer showed effective control over fluid flow and cupula displacement, and thereby confirmed LIFU's effectiveness in vestibular stimulation. This suggests that LIFU allows for more precise control compared to existing vestibular stimulation methods, and it opens new possibilities for the treatment of vestibular disorders.