especially irreplaceable role in the area of precision actuations, such as in lens driving in optical assemblies and optical communication, micro/nanopositioning in semiconductor and microelectromechanical system (MEMS) manufacturing, nanoscanning probes in scanning electron microscopy, etc. [1,2] Due to the huge market demand for piezoelectric actuators, the progress of piezoelectric materials and devices is new every year. New piezoelectric material compositions, novel fabrication processes and full assessments of materials are widely studied to improve the material properties or make devices more suitable for actuation applications. Pb(Zr,Ti)O 3 (PZT)-based ceramics are still dominant in the market because of their high piezoelectric properties, low cost, and stable thermal performance. Although single crystals' piezoelectric and electromechanical coupling coefficients show great advances compared with ceramics, actuation applications are limited to only some special cases due to high cost of single crystals. [3] Lead-free ceramics have also experienced fast development, and some compositions have been found to exhibit large strains, but they also result in large energy losses under high electric fields. This type of ceramic may have potential for use in nonresonant actuator applications. Additionally, various actuation configurations operating via different working modes or mechanisms have been developed.In this review, we first introduce materials used for the corresponding actuators and motors, and then, recent developments in the area of actuators including nonresonant multilayer ceramic actuators, step motors and inertial motors, and resonant ultrasonic motors, such as linear motors, rotary motors, multi-DOF motors, and MEMS actuators, are discussed. Actuation performance parameters such as the stroke length, resolution, loading force, velocity, lifetime, and power efficiency are the main concerns. We try to clarify and compare differences between devices. Finally, the challenges and outlook for the piezoelectric actuators are discussed. Piezoelectric Materials for ActuatorsPiezoelectricity in materials can be attributed to an asymmetric center of the crystalline structure or molecular chain, which Piezoelectric actuators are unique driving force-generation devices, which can transfer input electric energy into force, displacement, or movement outputs efficiently and precisely via piezoelectric effect-based electromechanical coupling instead of electromagnetic induction. In comparison with traditional electromagnetic actuators, the most important features of the piezoelectric actuators are their compact size, flexible design, and ability to provide nanometer or sub-micrometer positioning. Here, recent progress in nonresonance piezoelectric actuators including multilayer ceramic actuators, step motors, inertial motors, and resonance ultrasonic motors, such as linear motors, rotary motors, multidegree of freedom motors, and microelectromechanical system actuators, is comprehensively presented. The working p...

It is well known that the piezoelectric performance of ferroelectric Pb(Zr,Ti) O 3 (PZT) based ceramics is far inferior to that of ferroelectric single crystals due to ceramics' polycrystalline nature. Herein, it is reported that piezoelectric stress coefficient e 33 = 39.24 C m −2 (induced electric displacement under applied strain) in the relaxor piezoelectric ceramic 0.55Pb(Ni 1/3 Nb 2/3 ) O 3 -0.135PbZrO 3 -0.315PbTiO 3 (PNN-PZT) prepared by the solid state reaction method exhibits the highest value among various reported ferroelectric ceramic and single crystal materials. In addition, its piezoelectric coefficient d 33 * = 1753 pm V −1 is also comparable with that of the commercial Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (PMN-PT) piezoelectric single crystal. The PNN-PZT ceramic is then assembled into a cymbal energy harvester. Notably, its maximum output current at the acceleration of 3.5 g is 2.5 mA pp , which is four times of the PMN-PT single crystal due to the large piezoelectric e 33 constants; while the maximum output power is 14.0 mW, which is almost the same as the PMN-PT single crystal harvester. The theoretical analysis on force-induced power output is also presented, which indicates PNN-PZT ceramic has great potential for energy device application.

Bulk-magnetoelectric (ME) composites consisting of various piezoelectric and piezomagnetic materials with (3-0), (3-1), (2-2), and (2-1) connectivity are proposed in a bid to realize strong ME coupling for next-generation electronic-device applications. Here, 1D (1-1) connectivity ME composites consisting of a [011]-oriented Pb(Mg,Nb)O -PbTiO (PMN-PT) single-crystal fiber laminated with laser-treated amorphous FeBSi alloy (Metglas) and operating in L-T mode (longitudinally magnetized and transversely poled) are reported, which exhibit an enhanced resonant ME coupling coefficient of ≈7000 V cm Oe , which is nearly seven times higher than the best result published previously, and also a superhigh magnetic sensitivity of 1.35 × 10 T (directly detected) at resonance at room temperature, representing a significant advance in bulk magnetoelectric materials. The theoretical analyses based on magnetic-circuit and equivalent-circuit methods show that the enhancement in ME coupling can be attributed to the reduction in resonance loss of laser-treated Metglas alloy due to nanocrystallization and the strong magnetic-flux-concentration effect in (1-1) configuration composites.

Various microfluidic cell culture devices have been developed for in vitro cell studies because of their capabilities to reconstitute in vivo microenvironments. However, controlling flows in microfluidic devices is not straightforward due to the wide varieties of fluidic properties of biological samples. Currently, flow observations mainly depend on optical imaging and macro scale transducers, which usually require sophisticated instrumentation and are difficult to scale up. Without real time monitoring, the control of flows can only rely on theoretical calculations and numerical simulations. Consequently, these devices have difficulty in being broadly exploited in biological research. This paper reports a microfluidic device with embedded pressure sensors constructed using electrofluidic circuits, which are electrical circuits built by fluidic channels filled with ionic liquid. A microfluidic device culturing endothelial cells under various shear stress and hydrostatic pressure combinations is developed to demonstrate this concept. The device combines the concepts of electrofluidic circuits for pressure sensing, and an equivalent circuit model to design the cell culture channels. In the experiments, human umbilical vein endothelial cells (HUVECs) are cultured in the device with a continuous medium perfusion, which provides the combinatory mechanical stimulations, while the hydrostatic pressures are monitored in real time to ensure the desired culture conditions. The experimental results demonstrate the importance of real time pressure monitoring, and how both mechanical stimulations affect the HUVEC culture. This developed microfluidic device is simple, robust, and can be easily scaled up for high-throughput experiments. Furthermore, the device provides a practical platform for an in vitro cell culture under well-controlled and dynamic microenvironments.