Mechanical behavior of a cellular composite under quasi-static, static, and cyclic compression loading

The quasi-static, static, and cyclic compressive behavior of a novel epoxy matrix cellular composite reinforced with glass foam granules is investigated. Three different grain-size fractions of the granules are used: 0.5–1, 1–2, and 2–4 mm. The density of the cellular composite varies between 0.65 and 0.82 g/cm3. The material exhibits high specific compressive strength and stiffness within the class of cellular materials; these properties can be varied using appropriate size of granules. The glass foam granules increase the stiffness of the cellular composite compared to neat epoxy foam with the same weight. The measured elastic properties are in good agreement with results obtained from analytical and numerical homogenization methods. The fatigue behavior is determined in static tests and in cyclic tests at 1 and 20 Hz on one type of cellular composite. The fatigue process for cyclic loading is a result of an interaction between static and cyclic damage. The sensitivity to static damage is found to be higher than to cyclic damage. The damage behavior is investigated by evaluation specimen’s stiffness and using scanning electron microscopy.     

A novel, single-mode piezoceramic plate actuator for ultrasonic linear motors

A new type of piezoelectric plate actuator for ultrasonic linear motors has been developed. These new piezoelectric actuators use the principle of asymmetric resonant excitation of the piezoceramic plate in a special resonant mode consisting of a standing two-dimensional extensional wave in a piezoceramic plate. The behavior of the actuator has been simulated with finite-element method (FEM) software and the simulation results checked with single-point contact measurements on the surface of the actuator. This paper describes this work and closes by describing the new ultrasonic translation stages based on this design.     

Implementation of self-sensing SPM cantilevers for nano-force measurement in microrobotics

Micromanipulation tasks have to be solved in the assembly of microsystems, the handling of biological cells and the handling of specimens for scanning electron microscopy. For these applications, we have developed a flexible micromanipulation station, including direct-driven robots a few cubic centimeters small. The robots are able to perform high-precise manipulation and positioning of microobjects. Force-controlled microgripping strategies are now necessary to develop robust microassembly strategies. Microgripping is different from conventional gripping in two ways. First, microparts with dimensions less than 100 microm are often fragile and can easily be damaged during gripping, thus special grasping techniques are needed. Second, the mechanics of manipulation in the microworld are much different than in the macro-world. Part interactions in the microworld are dominated by adhesive forces making it difficult to release parts during manipulation tasks. Several microgrippers that do not employ force feedback have been developed; force-controlled microgrippers are much less common. Grippers with integrated piezoresistive force sensors and with attached strain gauges have been reported. These approaches, however, are limited in their ability to resolve the gripping force. Hence, we are currently integrating self-sensing SPM cantilevers into a gripper of our microrobots. These cantilevers operate by measuring stress-induced electrical resistance changes in an implanted conductive channel in the flexure legs of the cantilever. The real-time force feedback provided by these sensors enables us to better understand the prevailing nano forces and dynamics, what is indispensable for reliable micromanipulation strategies.     

Improving the Out-Coupling of a Metal-Metal Terahertz Frequency Quantum Cascade Laser Through Integration of a Hybrid Mode Section into the Waveguide

A hybrid mode section is integrated into the end of the metal-metal waveguide of a terahertz (THz) frequency quantum cascade laser (QCL) by removing sub-wavelength portions of the top metal layer. This allows a hybrid mode to penetrate into the air, which reduces the effective index of the mode and improves the out-coupling performance at the facet. The transmission of the hybrid section is further increased by ensuring its length fulfills the criterion for constructive interference. These simple modifications to a 2.5-THz metal-metal QCL waveguide result in a significant increase in the output emission power. In addition, simulations show that further improvements in out-coupling efficiency can be achieved for lower frequencies with effective refractive indices close to the geometric mean of the indices of the metal-metal waveguide and air.     

Software for Small-scale Robotics: A Review

In recent years, a large number of relatively advanced and often ready-to-use robotic hardware components and systems have been developed for small-scale use. As these tools are mature, there is now a shift towards advanced applications. These often require automation and demand reliability, efficiency and decisional autonomy. New software tools and algorithms for artificial intelligence (AI) and machine learning (ML) can help here. However, since there are many software-based control approaches for small-scale robotics, it is rather unclear how these can be integrated and which approach may be used as a starting point. Therefore, this paper attempts to shed light on existing approaches with their advantages and disadvantages compared to established requirements. For this purpose, a survey was conducted in the target group. The software categories presented include vendor-provided software, robotic software frameworks (RSF), scientific software and in-house developed software (IHDS). Typical representatives for each category are described in detail, including SmarAct precision tool commander, MathWorks Matlab and national instruments LabVIEW, as well as the robot operating system (ROS). The identified software categories and their representatives are rated for end user satisfaction based on functional and non-functional requirements, recommendations and learning curves. The paper concludes with a recommendation of ROS as a basis for future work.     

Numerical method for the solution of the regulator equation with application to nonlinear tracking

A numerical method to solve the so-called regulator equation is presented here. This equation consists of partial differential equations combined with algebraic ones and arises when solving the output-regulation problem. Solving the regulator equation is becoming difficult especially for the nonminimum phase systems where reducing variables against algebraic part leads to a potentially unsolvable differential part. The proposed numerical method is based on the successive approximation of the differential part of the regulator equation by the finite-element method while trying to minimize a functional expressing the error of its algebraical part. The method is analyzed to obtain theoretical estimates of its convergence and it is tested on an example of the “two-carts with an inverted pendulum” system. Simulations are included to illustrate the suggested approach.     

Optimization of industrial‐scale deodorization of high‐oleic sunflower oil via response surface methodology

Optimization of industrial‐scale deodorization of high‐oleic sunflower oil (HOSO) via response surface methodology is presented in this study. The results of an experimental program conducted on an industrial‐scale deodorizer were analyzed statistically. Predictive models were derived for each of the oil quality indicators (QI) in dependence on the studied variable deodorization process parameters. The deodorization behavior of some minor components was analyzed on a pilot‐scale deodorizer. For comparison, a similar experimental program was also performed on the laboratory‐scale. The results of this study demonstrate that optimization of the deodorization process requires a suitable compromise between often mutually opposing demands dictated by different oil QI. The production of HOSO with top‐quality organoleptic and nutritional values (high tocopherol and phytosterol contents and low free and trans fatty acid contents) and high oxidative stability demands deodorization temperatures in the range between 220 and 235 °C and a total sparge steam above 2.0% (wt/wt in oil). The response surface methodology provides the tools needed to identify the optimum deodorization process conditions. However, the laboratory‐scale experiments, while showing similar response characteristics of QI in dependence on the process parameters and thus helpful as a guide, are of limited value in the optimization of an industrial‐scale operation.     

Direct observation and mapping of spin waves emitted by spin-torque nano-oscillators

Dynamics induced by spin-transfer torque is a quickly developing topic in modern magnetism, which has initiated several new approaches to magnetic nanodevices. It is now well established that a spin-polarized electric current injected into a ferromagnetic layer through a nanocontact exerts a torque on the magnetization, leading to microwave-frequency precession detectable through the magnetoresistance effect. This phenomenon provides a way for the realization of tunable nanometre-size microwave oscillators, the so-called spin-torque nano-oscillators (STNOs). Present theories of STNOs are mainly based on pioneering works predicting emission of spin waves due to the spin torque. Despite intense experimental studies, until now this spin-wave emission has not been observed. Here, we report the first experimental observation and two-dimensional mapping of spin waves emitted by STNOs. We demonstrate that the emission is strongly directional, and the direction of the spin-wave propagation is steerable by the magnetic field. The information about the emitted spin waves obtained in our measurements is of key importance for the understanding of the physics of STNOs, and for the implementation of coupling between individual oscillators mediated by spin waves. Analysis shows that the observed directional emission is a general property inherent to any dynamical system with strongly anisotropic dispersion.     

Strain as a Global Factor in Stabilizing the Ferroelectric Properties of ZrO2

Since the discovery of ferroelectricity in doped HfO₂ and ZrO₂ thin films over a decade ago, fluorite-structured ferroelectric thin films have attracted much research attention due to their excellent scalability and complementary metal-oxide semiconductor compatibility compared to conventional perovskite ferroelectric materials. Although various factors influencing the formation of the ferroelectric properties are identified, a clear understanding of the causes of the phase formation have been difficult to determine. In this work, ZrO₂ films deposited by atomic layer deposition and chemical solution deposition have resulted in films with completely different structural properties. Regardless of these differences, a general relationship between strain and phase formation is established, leading to a more unified understanding of ferroelectric phase formation in undoped ZrO₂ films, which can be applied to other fluorite-structured films.