Development of ceramic microstructures

For the production of microstructured ceramic parts, development efforts are necessary in the field of powder synthesis as well as in the area of shaping. Several processes have been developed. Powder synthesis was performed starting from metal organic precursors and using a two stage thermal process. Shaping was performed by sol-gel methods, by pressing of a ceramic slurry or an organic precursor paste as well as by direct electrophoretic deposition of gels in a microstructured form. An overview is given on the methods and the results.     

Ceramic microstructures and potential applications

 The developed process of tape casting with subsequent stamping is a promising way to make three-dimensional ceramic microstructures. Examples of different ceramic materials illustrate, that a good quality of the moulding with high form fit can be attained after optimisation of the slurry and the stamping process. The sintered microstructures are characterised by lateral dimensions in the micron range and high aspect ratios. The unique properties of ceramic materials in combination with this new process can be used to produce microstructured ultrasonic transducers or micro heat exchangers/reactors. Received: 30 October 1995 / Accepted: 12 January 1996     

Ceramic microstructures and potential applications

The developed process of tape casting with subsequent stamping is a promising way to make three-dimensional ceramic microstructures. Examples of different ceramic materials illustrate, that a good quality of the moulding with high form fit can be attained after optimisation of the slurry and the stamping process. The sintered microstructures are characterised by lateral dimensions in the micron range and high aspect ratios. The unique properties of ceramic materials in combination with this new process can be used to produce microstructured ultrasonic transducers or micro heat exchangers/reactors.     

Replication processes for metal and ceramic micro parts

To cover the demand for effective manufacturing of metal and ceramic micro components two process technologies are described. The first one can be regarded as a special variant of micro powder injection molding (MicroPIM): inmold-labeling using powder filled feedstocks. Its basic procedures are the backfitting of powder filled foils by an injected PIM-Feedstock and the subsequent co-debinding and co-sintering steps. For example, two-material ceramic parts with microstructured surfaces could be produced and compacted with mostly tight interfaces. The second process conduct combines two-component and insert injection molding with an electroforming process. Since all process steps involved are based on technologies suitable for series production, low product costs per unit will be realistic. Surface qualities and dimensional accuracies are comparable or even better than achieved if applying alternative processes like MicroPIM.     

Ceramic micro parts produced by micro injection molding: latest developments

Powder injection molding is a preferred technology for the production of micro parts or microstructured parts. Derived from the well known thermoplastic injection molding technique it is suitable for a large-scale production of ceramic and metallic parts without final machining. To achieve good surface quality and control the part size and distortions is an important goal to allow mass production. This means that all process steps like part design adjusted for MIM/CIM-technology, appropriate choice of powder and binder components and injection molding simulation to design the sprue are required. Concerning the injection molding itself high quality mold inserts, high-precision injection molding with suitable molding machines like Battenfeld Microsystem50 or standard machine with special equipment like variotherm or evacuation of the molding tool and an adjusted debinding and sintering process have to be available. Results of producing micro parts by powder injection molding of ceramic feedstock will be presented.     

Surface micromachining of unfired ceramic sheets

Conventional surface micromachining techniques including photolithography and both wet and dry etching have been directly applied to an unfired sheet of yttria-stabilized zirconia ceramic material. Reversible bonding methods were investigated for affixing unfired ceramic samples to silicon handle wafers in order to perform photolithography. Three types of photoresist were investigated. Thin film photoresist allowed a line-width feature size of 8 μm to be obtained. Thick film photoresist exhibited a coverage gradient after being spun on. Chemical etching was successfully performed isotropically with concentrated hydrofluoric acid. A dry thick film resist applied by lamination provided coverage during plasma etching. Neither an oxygen plasma nor a mixture of sulfur hexafluoride and oxygen plasma proved successful at etching the unfired ceramic. Embossing was performed on the meso-scale with feature shrinkage of approximately 45% after sintering.     

Polymethylmethacrylate/polyethyleneglycol-based partially water soluble binder system for micro ceramic injection moulding

In micro powder injection moulding polyethylene-wax binder systems have been widely established for many years enabling the fabrication of dense ceramic or metal micro structured parts. With respect to complete organic moiety removal a solvent debinding step prior to thermal decomposition using hexane as organic solvent has to be applied dissolving the wax prior to thermal decomposition of the polyethylene. The development of environmentally friendly binder systems must consider the substitution of any organic solvent or even the solvent pre-debinding. In this work a modified process chain, starting with a reactive feedstock mixture consisting of a thermally curable methylmethacrylate/polymethylmethacrylate resin, low molecular mass polyethyleneglycol and submicron-sized zirconia as ceramic filler, followed by feedstock polymerization at elevated temperature, pelletizing, injection moulding, debinding and sintering, will be presented. Prior to replication important feedstock properties like temperature and solid load dependent melt viscosity as well as the real solid load was measured guaranteeing a successful mould filling. Two different debinding strategies—with and without water-assisted predebinding—were pursued and the resulting sinter part densities as well as surface qualities were compared. Zirconia test specimen parts with a density around 99 % of the theoretical density could be obtained successfully.     

Reversible circuit synthesis by genetic programming using dynamic gate libraries

We have defined a new method for automatic construction of reversible logic circuits by using the genetic programming approach. The choice of the gate library is 100% dynamic. The algorithm is capable of accepting all possible combinations of the following gate types: NOT TOFFOLI, NOT PERES, NOT CNOT TOFFOLI, NOT CNOT SWAP FREDKIN, NOT CNOT TOFFOLI SWAP FREDKIN, NOT CNOT PERES, NOT CNOT SWAP FREDKIN PERES, NOT CNOT TOFFOLI PERES and NOT CNOT TOFFOLI SWAP FREDKIN PERES. Our method produced near optimum circuits in some cases when a particular subset of gate types was used in the library. Meanwhile, in some cases, optimal circuits were produced due to the heuristic nature of the algorithm. We compared the outcomes of our method with several existing synthesis methods, and it was shown that our algorithm performed relatively well compared to the previous synthesis methods in terms of the output efficiency of the algorithm and execution time as well.     

Magneto-optical behavior of microstructure spun fibers

The simple design of a microstructured spun fiber with air channels has been developed. For the first time a magneto-optical response of the microstructured spun fiber with high built-in linear birefringence has been experimentally studied. Most valued magneto-optical properties of this fiber to be discovered are high sensitivity resistance at bent deformations and sensitivity value is nearly to a theoretical value. It is showed that such microstructured fiber accumulates effectively Faraday phase shift in magnetic field even when the fiber is coiled into a loop of a very small diameter. For example, a fiber coil of diameter 5 mm with 100 turns has a magneto-optical sensitivity of about 70% of “ideal” value and well agrees with model calculations. Results are of a great significance for a fiber-optic current sensor.     

Injection molding of microstructured components from plastics, metals and ceramics

 Micro injection molding is presently on its way to become an established manufacturing process in commercialising Microsystem Technologies. Enhanced products from plastics for micro optical or medical applications are entering the market. New developments like the different kinds of injection molding for microstructured components from plastics, metals or ceramics will increase the material range available in microdimensions. This will open up opportunities for increasing economic efficiency, for new fields of applications as well as for innovative products in the future. Received: 30 April 2001/Accepted: 30 August 2001     

Quasi-static and cyclic testing of specimens with high aspect ratios produced by micro-casting and micro-powder-injection-moulding

 The presented investigations of material properties of micro-components have been carried out in one project of the DFG Collaborative Research Centre (SFB) 499 “Development, production and quality assurance of moulded micro-components made out of metallic and ceramic materials” [SFB01]. The aim of this SFB is to develop production methods for micro-components in large-, middle and short-batches, where the applied metallic and ceramic materials can sustain high stresses and are wear-resistant, e.g. in relation to plastics. A micro-turbine and a sun-and-planet gearing with three stages (outside diameter: 1.9 mm; already realised in plastic [THü99]) are planned as a demonstration device. However, for the design of such micro-components, no reliable data for material states in small dimensions are available. Therefore, bending-specimens made out of micro-cast Stabilor G and out of micro-powder-injection-moulded ZrO₂ were investigated with respect to their behaviour under quasi-static as well as under cyclic loading. Received: 10 August 2001/Accepted: 24 September 2001     

微结构固体中孤立波的动力学稳定性

描述微结构固体中波传播的一种KdV类方程作为控制方程并利用积分因子方法,对微结构固体中传播的孤立波的动力学稳定性进行了数值模拟研究。主要以高斯波、Ricker子波以及双曲正割波作为初始扰动,考察了不同小扰动下孤立波能否较长时间保持波形结构和传播速度而稳定传播问题。模拟结果表明,不同的小扰动对孤立波的影响不同,孤立波的稳定传播与扰动幅度和宽度都有关系,只有受到幅度和宽度都非常小的扰动下在微结构固体中传播的孤立波才能显现出一定程度的抗干扰性和动力学稳定性,可在微结构固体中较长时间稳定传播。     

Study of mechanical response in micro-indentation of laminated ceramic green substrates

Micro-indentation at elevated temperature is an effective method for studying the mechanical response of a material used in micro embossing. In this study, micro-indentation was performed on co-firable green ceramic substrates for the purpose of simulating micro embossing process and investigating the mechanical response at certain temperature. The laminated low temperature co-firable ceramic (LTCC) green tapes were used as the testing materials, the correlations of indentation depth versus applied force at various temperatures ranging from 25 to 75°C were studied. The results showed that permanent indentation cavities could be formed and retained at the temperatures ranging from 25 to 75°C; the depth of cavities created was applied force, temperature and holding time dependent. Creep during holding period occurred and made a significant contribution to the plastic deformation at elevated temperatures. There were instantaneous recoveries during the unloading and cooling processes, and retarded recovery in the first day after indentation as well. No significant pile-up around the indented cavities at the temperatures up to 75°C was observed, suggesting that there was little material flow during indentation at this temperature range. The indented cavities on green ceramic substrates were formed mainly due to the plastic deformation under compression. The findings could be used as a guideline for micro embossing of ceramic green substrates.     

Ferroelectric thin film fabrication by direct UV-lithography

Due to their use in the fields of sensors, energy harvesting, capacitors and FeRAMs the fabrication of microstructured ferroelectric thin films is an important research field. Therefore a modified sol–gel process chain has been developed to produce fine patterned ferroelectric PZT (PbZr_0.52Ti_0.48O₃) thin films by direct UV-lithography. A sol based on methacrylic acid was developed to provide a photosensitive metal organic PZT precursor. The sol was used to obtain photosensitive xerogel films by spin-coating, which were patterned using conventional UV-photolithography equipment. After development the patterned xerogel films were pyrolized and crystallized in air via rapid thermal annealing in order to obtain crystalline PZT thin films. The patterned PZT films were investigated by XRD technique and SEM-micrographs. Finely patterned, crack free, crystalline PZT thin films were obtained.     

A supervised approach for automated surface defect detection in ceramic tile quality control

Surface defect detection is very important to guarantee the quality of ceramic tiles production. At present, this process is usually performed manually in the ceramic tile industry, which is low efficiency and time-consuming. For small surface defects detection of high-resolution ceramic tiles image, an intelligent detection method for surface defects of ceramic tiles based on an improved you only look once version 5 (YOLOv5) algorithm is presented. Firstly, the high-resolution ceramic tile images are cropped into slices, and the Bottleneck module in the YOLOv5s network is optimized by introducing depthwise convolution and replaced in the whole network. Then, feature extraction is performed using the improved Shufflenetv2 backbone, and an attention mechanism is added to the backbone network to improve the feature extraction ability. The path aggregation network (PAN) and Feature Pyramid Networks (FPN) neck are used to enhance the feature extraction, and finally, the YOLO head is used to identify and locate the ceramic tile defects. The multiple sliding windows detection method is proposed to detect the original ceramic tile image which is faster than the single sliding window detection method. The experimental results show that compared with the original YOLOv5s detection algorithm, the parameters of the model are reduced by 20.46 %, the floating point operations are reduced by 26.22 %, and the mean average precision (mAP) of the proposed method is 96.73 % in the ceramic tile image slice test set which has 1.93 % improvement in mAP than the original YOLOv5s. Compare with other object detection methods, the method proposed in this paper also has certain advantages. In the high-resolution ceramic tile images test set, the mAP of the proposed algorithm is 86.44 % by using the multiple sliding window detection method. The ceramic defect detection experiment has verified the feasibility of the method proposed in this paper.     

人脸画像合成研究的综述与对比分析

人脸画像合成通常是在给定一些训练画像-照片的前提下,将一张输入的人脸照片转换为画像的过程.目前并没有一个系统性的实验对比分析揭示当前此过程面临的挑战以及可能的解决思路.文中对具有代表性的各类方法进行综合深入对比与分析.人脸画像合成方法归纳为2类:数据驱动类方法(即基于样本的方法)和模型驱动类方法.数据驱动方法由3类方法组成:基于子空间学习的方法、基于稀疏表示的方法和基于贝叶斯推断的方法.模型驱动方法直接学习照片到画像的映射关系.文中给出一些之前文献中并未发现的有意义的结论和展望.     

LPV model-based robust diagnosis of flight actuator faults

A linear parameter-varying (LPV) model-based synthesis, tuning and assessment methodology is developed and applied for the design of a robust fault detection and diagnosis (FDD) system for several types of flight actuator faults such as jamming, runaway, oscillatory failure, or loss of efficiency. The robust fault detection is achieved by using a synthesis approach based on an accurate approximation of the nonlinear actuator–control surface dynamics via an LPV model and an optimal tuning of the free parameters of the FDD system using multi-objective optimization techniques. Real-time signal processing is employed for identification of different fault types. The assessment of the FDD system robustness has been performed using both standard Monte-Carlo methods as well as advanced worst-case search based optimization-driven robustness analysis. A supplementary industrial validation performed on the AIRBUS actuator test bench for the monitoring of jamming, confirmed the satisfactory performance of the FDD system in a true industrial setting.     

Finite element investigations of the dynamical properties of microstructured membranes

 Microstructured membranes (microdia-phragms) are a tool for measuring quantities such as temperature, strain, or density by ultrasound, i.e. without any contact (e.g. by a wire connection). In this paper we study the dynamical properties of such microstructured membranes numerically by means of the finite element method. In particular, we consider the shape of the eigenmodes of the system and study the dependence of the corresponding eigenfrequencies on material and geometry parameters. Received: 28 January 1997 / Accepted: 2 March 1997     

Selective adsorption of solvents in a multiscale device

We have incorporated microspheres, from 50 to 80 μm in diameter, of periodic mesoporous organosilica (inner surfaces up to 1,000 m²/g and pore sizes in the nanometre range) with two types of organic functionalities (benzene and ethane bridges, respectively) inside microstructured channels (each 200 μm wide and 100 μm deep) and, exemplarily, monitored by Raman microscopy (Raman spectroscopy through microscope optics) that the temperature characteristics of the adsorption–desorption equilibria of benzene and ethanol vary significantly with the type of organic functionality of the microspheres and the pore morphology. The integration of this class of nanostructured material into devices by means of microchannels is a promising novel approach to, among others, substance separation in analytics, micro process engineering, and micro chemistry.