# A Novel Piezoelectric Ceramic Actuator with Scissoring Composite Vibration for Medical Applications
## 1 Introduction  
Piezoelectric ceramic actuators or vibrators, in general, and actuators with hybrid modes, in particular, are being widely utilized in a variety of fields, including ultrasonic motors [1; 2], wire drawing [3], mental forming [4] and medical devices [5; 6; 7], due to their compact size, high power, small weight, fast response time and high precision accuracy [8; 9; 10]. In the past years, several research groups aimed to design different piezoelectric actuators with longitudinal-bending type [11; 12; 13] and longitudinal-torsional type [14; 15] composite vibrations, indicating the widespread demand and utilization of composite actuators. Recently, piezoelectric actuators, with actuating compositemovement and small size, have garnered significant research attention for medical applications, such as cataract emulsifier, ultrasonic scalpel and mechanical thrombectomy [16; 17; 18; 19].  
In general, two approaches are commonly adopted to achieve the composite vibration mode; mode coupling and mode conversion. The vibrations in different directions, originating from two or more discrete sets of piezoelectric elements, are combined in mode coupling [20]. Moreover, the piezoelectric elements polarized or poled in different directions separately generate longitudinal, tangential or torsional vibrations, which are subsequently combined at the output port of the actuator. However, the independent driving frequencies of the piezoelectric elements need to match with each other to ensure the resonance of the actuator at the same frequency, which requires complex geometrical design and electrical excitation to maintain frequency matching. On the other hand, the mode conversion requires only one set of the piezoelectric elements and a vibration converter between the piezoelectric element and front working horn of the actuator [21]. The desired composite vibrations can be easily achieved by changing the propagation path of vibration wave through structural modifications. In general, the linear piezoelectric actuator with the longitudinal-bending mode is an excellent choice to achieve compact-sized devices [22]. In most of the previous designs, the effective output vibrations are rendered by the tip vibrations, which are attained by complete or partial excitation of the actuator, resulting in extra vibration along other parts of the actuator. However, the narrow spaces applications, such as minimally invasive surgery, do not allow unnecessary bending vibrations along the actuator apart from the effective tip bending vibration. For instance, the extra transverse vibration at the phaco needle in cataract phaco emulsification surgery causes corneal burns due to the vibrational friction between the needle and cornea. However, the effective needle tip vibration is allowed in the narrow eye chamber [23]. Moreover, for obtaining effective transverse stirring vibration in narrow blood vessel for clot dissolution, the deflection of actuator (micro-stirrer) on other part should be restricted carefully in order to avoid vibrational bruise between the actuator and vascular wall due to many curves and turns of the vessel shapes [18]. Therefore, we aimed to design a novel and miniaturized actuator to convert longitudinal vibration into bending vibration only at the actuator tip for medical applications.  
Herein, we propose a novel compact-size actuator, which can generate scissoring composite vibrations at the distal tip of the actuator by only one axially poled piezoceramic stack. The as-designed actuator acts like a scissor and effectively degenerates longitudinal vibration from the piezoelectric stack into a double-opposite bending vibration only at the actuator tip. For the first time, the design principle and theoretical analysis of the actuator are described in detail. Moreover, the design effectiveness of the proposed composite actuator is verified by finite element modeling (FEM). Finally, a prototype of the as-designed actuator is manufactured and the working performance is assessed by laser vibrometer test.