# Analysis and Experimental Research of a Multilayer Linear Piezoelectric Actuator
## 1 Introduction  
Ultrasonic piezoelectric actuators (UPAs) are a modern type of micro-actuator which are based on the inverse piezoelectric effect of piezoelectric ceramics and the displacement amplification effect of mechanical resonance [1; 2; 3; 4]. They have been widely used for precise positioning and for their excellent properties such as high energy density, short response time, self-lock at power-off state and high displacement resolution [5; 6; 7]. Due to these merits, this kind of actuator has attracted many researchers' attention, and in recent years, various kinds of piezoelectric ceramic actuators have been proposed, some of which have already obtained commercial success such as the Physik Instrumente (PI) GmbH & Co.KG (Dorfen, Germany) and Nano-motion Company (Goa, India). Ultrasonic linear piezoelectric actuators (ULPAs) [8] working under the composite vibration modes of a piezoelectric ceramic block, such as the first longitudinal and second bending vibration modes, are a research hotspot and many new structures have been proposed [3; 9; 10]. The structures can be classified into two categories, one of which is the piezoelectric ceramic chip attached to metal as a driving element [7; 11], and the other is a single piezoelectric ceramic as a driving element [6; 12]. The former can be designed into more types of structures since the metal base can be easily manufactured into different shapes and is less likely to fracture. Researchers such as [PERSON] et al. [13], [PERSON] et al. [14] and [PERSON] et al. [15] have done valuable works in this category. However, since the chips attached to metal are usually thin, energy poured into the driving elements is limited, thus reducing the energy density of the driving element. Meanwhile, thepiezoelectric ceramic chip is usually bonded with metal through an adhesive to form a driving element, and adhesive precision and adhesive thickness will both influence the driving modes of the actuator, thus degrading its performance. The latter kind, the single piezoelectric ceramic type, with a more simple structure and thick piezo-block, can partially solve the shortage of the former kind, but it needs a very large voltage to drive effectively, 200 V/mm as a typical value, which significantly complicates the circuit and is not conducive to miniaturization and integration of the whole system. [PERSON] et al. [16] proposed a piezoelectric linear motor using a multilayer piezoelectric ceramic block and with frictional material plates at two ends of the piezoelectric block. The multilayer piezoelectric ceramic was layered in the direction of the width, which lowered the driving voltage of the piezoelectric motor. However, when the motor works, a shear force between the piezoelectric ceramic layers caused by the resistance of the mover would do damage to the multilayer piezoelectric ceramic, which reduces the lifetime of the motor. [PERSON] et al. [17] proposed a piezoelectric motor with a similar structure to that reported in [16]. In addition, [PERSON] et al. extended the lifetime of the multilayer piezoelectric motor, and a higher efficiency was obtained by using the \(\mathrm{d}_{33}\) piezoelectric stack, which has a higher electromechanical coupling factor than the \(\mathrm{d}_{31}\) one. [PERSON] et al. [18] proposed a piezoelectric motor with multilayer piezoelectric ceramic layered in the direction of the thickness, mainly aiming to excite the two desired vibration modes separately, so as to improve the controllability of the motor. In this study, a multilayer monolithic ultrasonic linear piezoelectric actuator (hereinafter referred to as a multilayer linear piezoelectric actuator, MLPA) working under the first longitudinal and the second bending modes was analyzed, and related experiments were conducted to research its properties.