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In this study, a planar ultrasonic motor platform is presented that uses three half-side excited piezoelectric hemispherical shell resonators. To understand the working principle and the harmonic vibration behavior of the piezoelectric resonator, the trajectory of the friction contact was measured in free-oscillating mode at varying excitation frequencies and voltages. The driving performance of the platform was characterized with transport loads up to 5 kg that also serve as an influencing downforce for the friction motor. The working range for various transport loads and electrical voltages up to 30 V is presented. Undesirable noise and parasitic oscillations occur above the detected excitation voltage ranges, depending on the downforce. Therefore, minimum and maximum values of the excitation voltage are reported, in which the propulsion force and the speed of the planar motor can be adjusted, and noiseless motion applies. The multidimensional driving capacity of the platform is demonstrated in two orthogonal axes and one rotary axis in open-loop driving mode, by measuring forces and velocities to confirm its suitability as a planar motor concept. The maximum measured propulsion force of the motor was 7 N with a transport load of 5 kg, and its maximum measured velocity was 77 mm/s with a transport load of 3 kg.

Reverse electrodialysis (RED) is one of the techniques able to harvest energy from the salinity gradient between different salt solutions. There is a tradeoff between efficiency and generated power in a RED stack. This paper focuses on efficiency. A simple model is presented to calculate the efficiency in a co-flow or counterflow operated stack. Moreover, the efficiency can be improved by applying multistaging; the stacks in such a system can also be interconnected externally in co- and counterflow. The four combinations of internally and externally flow modes are the base of further considerations concerning procedures for optimization of these configurations. Three methods for optimization the energy efficiency in a multistage system are discussed: (A) successively maximizing the power of each individual stage, (B) maximizing the power of the whole system by adjusting the electrical current in all stages simultaneously, and (C) maximizing the power of the whole system by adjusting the same current through each stage. Method C is the most attractive because it only requires one converter (cheaper and easier to control) while the results are hardly inferior to B and much better than A. An alternative to multistaging is electrode segmentation and the advantages and disadvantages of both systems are briefly discussed.

A novel design of a multiple degrees of freedom (multi-DOF) piezoelectric ultrasonic motor (USM) is presented in the paper. The main idea of the motor design is to combine the magnetic sphere type rotor and two oppositely placed ring-shaped piezoelectric actuators into one mechanism. Such a structure increases impact force and allows rotation of the sphere with higher torque. The main purpose of USM development was to design a motor for attitude control systems used in small satellites. A permanent magnetic sphere with a magnetic dipole is used for orientation and positioning when the sphere is rotated to the desired position and the magnetic field synchronizes with the Earth’s magnetic dipole. Also, the proposed motor can be installed and used for robotic systems, laser beam manipulation, etc. The system has a minimal number of components, small weight, and high reliability. Numerical simulation and experimental studies were used to verify the operating principles of the USM. Numerical simulation of a piezoelectric actuator was used to perform modal frequency and harmonic response analysis. Experimental studies were performed to measure both mechanical and electrical characteristics of the piezoelectric motor.

A new concept of a self-sensing bending actuator is introduced. This self-sensing approach enables to control the deflection of a loaded piezoelectric cantilever operated in a wide frequency band. Furthermore, the tip force, moment and angular velocity can also be estimated. Thereby, the determination of the applied load impedances becomes possible. The novel concept is based on the segmentation of actuator electrodes. This provides additional information about the charge distribution in the piezoelectric material and hence the operational mode shape of the loaded actuator can be determined. To obtain the desired state variables, at least two segments are required. [ABSTRACT FROM AUTHOR]

• Numerical method for analyzing a real-scale RED including vast micropatterns. • Successful simulation of 40 cm RED with 4000 micropatterns. • Length optimization of the real-scale RED resulting 251% net power enhancement. • 352% net power enhancement by electrode segmentation with micropatterns. • Net power improvement analysis through Sherwood number. Here we present an improved numerical method by exploiting periodicity to analyze a real-scale reverse electrodialysis (RED), including an unlimited number of microstructures and electrode segmentations. Flow and current (or voltage) distributions are calculated for a unit cell with on-demand adjustment of applied voltage (or current), and the calculations are repeated by mapping the outflow's data to the inflow's one. By laying end to end those results, a real-scale RED with vast microstructures and segmented electrodes can be simulated. 4-mm length RED was analyzed by exploiting periodicity and a conventional method, and we verified that the errors were within 1%, requiring 1/n memory usage and < 50% computing time (n: number of repeating units). Such reduced computational cost allows us to calculate 400-mm length RED filled with 4,000 microstructures of woven mesh spacer, 2D horizontal or 3D cross patterns and 10 segmented electrodes. We confirmed that the relative superiority of the local power generation of spacers/patterns varies from location, and the net power density (and net energy efficiency) can be enhanced up to 251 % by optimizing a system's size and 352 % by electrode segmentation. In addition, we verified that the degree of performance enhancement as segmenting the electrode is proportional to the Sherwood number, which represents the convective mass transfer governed by a flow velocity and spacer/pattern structures. To be best of our knowledge, this is the first numerical analysis of a real-scale RED with spacer/patterns and electrode segmentations simultaneously, and it firmly established the existence of coupled effects of patterns and electrode segmentation. [ABSTRACT FROM AUTHOR]

In this study, a planar ultrasonic motor platform is presented that uses three half-side excited piezoelectric hemispherical shell resonators. To understand the working principle and the harmonic vibration behavior of the piezoelectric resonator, the trajectory of the friction contact was measured in free-oscillating mode at varying excitation frequencies and voltages. The driving performance of the platform was characterized with transport loads up to 5 kg that also serve as an influencing downforce for the friction motor. The working range for various transport loads and electrical voltages up to 30 V is presented. Undesirable noise and parasitic oscillations occur above the detected excitation voltage ranges, depending on the downforce. Therefore, minimum and maximum values of the excitation voltage are reported, in which the propulsion force and the speed of the planar motor can be adjusted, and noiseless motion applies. The multidimensional driving capacity of the platform is demonstrated in two orthogonal axes and one rotary axis in open-loop driving mode, by measuring forces and velocities to confirm its suitability as a planar motor concept. The maximum measured propulsion force of the motor was 7 N with a transport load of 5 kg, and its maximum measured velocity was 77 mm/s with a transport load of 3 kg. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis harvests energy from salinity gradients establishing a renewable energy source. High energy efficiencies are fundamental to up-scale the process and to minimize feedwater pre-treatment and pumping costs. The present work investigates electrode segmentation to strategically optimize the output power density and energy efficiency. Electrode segmentation allows the current density to be tuned per electrode segment. Segmentation experiments were performed with a dedicated electrode configuration in a cross-flow stack using a wide range of residence times. Moreover, an experimentally validated model was extended and used to further compare single and segmented electrode configurations. While operating the electrode segments, the highest efficiencies were obtained when considering the overall power, i.e. not maximized by segment. Results show that at a given net power density (0.92 W·m−2), electrode segmentation increases the net energy efficiency from 17% to 25%, which is a relative increase of 43%. Plus, at 40% net energy efficiency the net power output for a segmented electrode configuration (0.67 W·m−2) is 39% higher than in a single electrode configuration. Higher power density reduces capital investment and higher energy efficiency reduces operating costs. Electrode segmentation increases these parameters compared to a single electrode and can be potentially applied for up-scaling. Unlabelled Image • Electrode segmentation improves the reverse electrodialysis process. • Validated model for reverse electrodialysis using cross-flow stacks. • Highest efficiencies found when segments work for the overall maximum power. • + 39% relative increase in net power density at 40% net energy efficiency. • + 43% relative increase in net energy efficiency at 0.92 W·m−2 net power density. [ABSTRACT FROM AUTHOR]

Reverse electrodialysis (RED) is one of the techniques able to harvest energy from the salinity gradient between different salt solutions. There is a tradeoff between efficiency and generated power in a RED stack. This paper focuses on efficiency. A simple model is presented to calculate the efficiency in a co-flow or counterflow operated stack. Moreover, the efficiency can be improved by applying multistaging; the stacks in such a system can also be interconnected externally in co- and counterflow. The four combinations of internally and externally flow modes are the base of further considerations concerning procedures for optimization of these configurations. Three methods for optimization the energy efficiency in a multistage system are discussed: (A) successively maximizing the power of each individual stage, (B) maximizing the power of the whole system by adjusting the electrical current in all stages simultaneously, and (C) maximizing the power of the whole system by adjusting the same current through each stage. Method C is the most attractive because it only requires one converter (cheaper and easier to control) while the results are hardly inferior to B and much better than A. An alternative to multistaging is electrode segmentation and the advantages and disadvantages of both systems are briefly discussed. [ABSTRACT FROM AUTHOR]

A novel design of a multiple degrees of freedom (multi-DOF) piezoelectric ultrasonic motor (USM) is presented in the paper. The main idea of the motor design is to combine the magnetic sphere type rotor and two oppositely placed ring-shaped piezoelectric actuators into one mechanism. Such a structure increases impact force and allows rotation of the sphere with higher torque. The main purpose of USM development was to design a motor for attitude control systems used in small satellites. A permanent magnetic sphere with a magnetic dipole is used for orientation and positioning when the sphere is rotated to the desired position and the magnetic field synchronizes with the Earth's magnetic dipole. Also, the proposed motor can be installed and used for robotic systems, laser beam manipulation, etc. The system has a minimal number of components, small weight, and high reliability. Numerical simulation and experimental studies were used to verify the operating principles of the USM. Numerical simulation of a piezoelectric actuator was used to perform modal frequency and harmonic response analysis. Experimental studies were performed to measure both mechanical and electrical characteristics of the piezoelectric motor. [ABSTRACT FROM AUTHOR]