非线性工作状态压电换能器匹配技术

针对压电换能器在大功率下存在复杂非线性而导致匹配参数难以优化的问题,以大功率超声金属焊接为例,通过采集测试焊接过程换能器两端电压的幅值与频率,建立换能器反谐振电阻与驱动电压有效值、频率之间的数学模型;提出基于反谐振电阻模型的最优功率匹配方法,推导了匹配电感电容的计算公式。最后实验验证了数学模型的准确性,且当换能器输入功率在最优功率附近时,匹配网络电能传输效率最高。     

Einsatz von DMS- und Piezomeßtechnik zur direkten Schubspannungsermittlung in der Kapillarrheometrie

Zusammenfassung Der Stand der Kapillarheometrie mit den Vor- und Nachteilen der einzelnen Systeme und Meßverfahren wird dargestellt. Ausgehend von diesem Stand werden zwei alternative Meßverfahren, nämlich Piezo-Einzelkraftund DMS-Meßverfahren, zur direkten Schubspannungsermittlung besprochen und eine nach diesem Prinzip konzipierte Versuchsdüse vorgestellt. Die mit dieser Düse erhaltenen Meßergebnisse zeigen im Vergleich zu konventionell, d. h. unter Anwendung des Bagley-Verfahrens, ermittelten Fließkurven im Falle der Einzelkraftmessung gute Übereinstimmung. Das Problem der Einlaufdruckkorrektur ist bei diesem Konzept von vornherein nicht vorhanden, und der ununterbrochene Fließkanal erlaubt, bei entsprechender Erweiterung auf zwei Kraftaufnehmer, einen unproblematischen Einsatz im On-line- oder sogar im In-line-Betrieb in der Polymerverarbeitung.Schlüsselwörter Rheometrie; Kapillarrheometrie; Schubspannungsermittlung; Piezokraftmessung; DMS-Anwendung; Kunststoffschmelzen; On-line-Rheometrie

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The state-of-the-art of capillary rheometry, especially the advantages and disadvantages of different systems, is presented. Two measuring methods, a piezo single-force transducer, and a strain-gauge device combined in a testing die are compared. The strain gauges are fixed at the outside of a small capillary to detect the resulting wall shear stress between inner surface of the die and polymer flow by measuring the axial strain in the wall of the die. The single force method uses an elastic section of the die which uncouples the die from the supporting structure without changing the cross-section of the flow. The uncoupled part of the die is supported by a stiff, piezo-force transducer that detects the integral effect of wall shear stress. The resulting flow curves compare well with those using the Bagley method. With the novel die no entrance pressure-loss correction is needed. In principle, it also could be used as an on-line device for polymer processing.

Vortrag, gehalten auf der Jahrestagung der Deutschen Rheologischen Gesellschaft, TH Darmstadt, 19.–21. April 1989.     

Interactions of DNA with graphene and sensing applications of graphene field-effect transistor devices: A review

Graphene field-effect transistors (GFET) have emerged as powerful detection platforms enabled by the advent of chemical vapor deposition (CVD) production of the unique atomically thin 2D material on a large scale. DNA aptamers, short target-specific oligonucleotides, are excellent sensor moieties for GFETs due to their strong affinity to graphene, relatively short chain-length, selectivity, and a high degree of analyte variability. However, the interaction between DNA and graphene is not fully understood, leading to questions about the structure of surface-bound DNA, including the morphology of DNA nanostructures and the nature of the electronic response seen from analyte binding. This review critically evaluates recent insights into the nature of the DNA graphene interaction and its affect on sensor viability for DNA, small molecules, and proteins with respect to previously established sensing methods. We first discuss the sorption of DNA to graphene to introduce the interactions and forces acting in DNA based GFET devices and how these forces can potentially affect the performance of increasingly popular DNA aptamers and even future DNA nanostructures as sensor substrates. Next, we discuss the novel use of GFETs to detect DNA and the underlying electronic phenomena that are typically used as benchmarks for characterizing the analyte response of these devices. Finally, we address the use of DNA aptamers to increase the selectivity of GFET sensors for small molecules and proteins and compare them with other, state of the art, detection methods.     

Coupling of Biomolecular Logic Gates with Electronic Transducers: From Single Enzyme Logic Gates to Sense/Act/Treat Chips

The integration of biomolecular logic principles with electronic transducers allows designing novel digital biosensors with direct electrical output, logically triggered drug‐release, and closed‐loop sense/act/treat systems. This opens new opportunities for advanced personalized medicine in the context of theranostics. In the present work, we will discuss selected examples of recent developments in the field of interfacing enzyme logic gates with electrodes and semiconductor field‐effect devices. Special attention is given to an enzyme OR/Reset logic gate based on a capacitive field‐effect electrolyte‐insulator‐semiconductor sensor modified with a multi‐enzyme membrane. Further examples are a digital adrenaline biosensor based on an AND logic gate with binary YES/NO output and an integrated closed‐loop sense/act/treat system comprising an amperometric glucose sensor, a hydrogel actuator, and an insulin (drug) sensor.     

基于声表面波技术实现数字微流体多基片间输运

建立了声表面波实现多基片间输运微流体的新方法.由3个128(0)YX-LiNbO3压电基片组成,一个基片为接口基片,另两个为工作基片,每个基片光刻一个中心频率为27.5 MHz叉指换能器和一个反射栅.采用微量进样器将待输运的数字微流体进样到工作基片2,调节接口基片使得其与工作基片2位于同一高度,并使其间隙尽可能小,在工...     

Micromechanical modelling of remanent properties of morphotropic PZT

The present paper investigates the capability of micromechanical material models to predict the ferroelectric behaviour of morphotropic PZT ceramics in a rate-independent approximation based on realistic microscopic material parameters. Starting point is a three-dimensional tetragonal model, which builds on the model of Pathak and McMeeking [2008. Three-dimensional finite element simulations of ferroelectric polycrystals under electrical and mechanical loading. Journal of the Mechanics and Physics of Solids 56, 663-683]. Volume fractions of the crystallographic variants represent the domain structure inside the grains. Interactions between the grains are taken into account by means of a representative volume element of the grain compound. A simplified set of realistic microscopic material parameters of the lattice in terms of Young's modulus, Poisson's ratio, dielectric constant, and spontaneous strain and polarisation is derived from experimental data and theoretical results given in the literature. The simulation of the macroscopic remanent polarisation and strain response due to two load cases shows explicitly that the tetragonal model is not capable to reproduce the behaviour of morphotropic PZT. Therefore, the model is extended by the rhombohedral phase, allowing a mixture of both phases with varying quantities inside the grains. A comparison of our results with experimental data shows a remarkably good agreement, revealing the capability of the extended model.     

介电高弹聚合物理论

软材料受刺激会发生变形, 该变形会引起相应的功能, 这种材料称为活性软材料(soft active material, SAM). 本综述主要讨论介电高弹聚合物这一类活性软材料. 当介电高弹聚合物薄膜受到厚度方向的电压作用时, 薄膜厚度减小同时面积增大, 可导致超过100{\%}的应变. 介电高弹聚合物作为转换器被广泛应用, 包括柔性机器人、智能光学器件、盲文显示屏、发电机等. 本文综述了建立在连续介质力学和热力学框架内的、并且基于分子理论描述和经验观测的介电高弹聚合物理论. 该理论耦合了大变形和电势, 描述了非线性和非平衡行为, 如力电失稳和黏弹性. 采用该理论能够通过有限元方法模拟实际构型的转换器, 计算力电能量转换的效率, 给出电致大变形的可行途径. 该理论有助于材料和器件设计.     

An instrumentation system to measure the loads acting on the tractor PTO bearing during rotary tillage

Application of rotary tillage has been increased due to less tillage passes required, reduced draft, and greater efficiency through reduction in wheel slippage. Early failure of the bearing of tractor power take-off (PTO) shaft was observed in tractors of power range 30–35 horsepower during rotary tillage. An instrumentation setup involving an extended octagonal ring transducer (EORT) was developed and installed at the bottom of the bearing to measure the axial load and the vertical component of the radial load. The horizontal component of radial load was measured by strain gauges. Based on measured loads, the bearing life was assessed. Independent variables were: operating depth, number of blades, gear setting, engine speed, and tyre size. The average axial and radial loads varied from 786–3869 N, and 134–430 N, respectively. However, bearing experienced very high peak loads during each trial. The peak axial and radial loads was recorded between 1081–7534 N and 566–1794 N, respectively. The estimated bearing life based on peak loads was 171.98–28341.39 h. Based on the findings, it may be concluded that the average loads were not sufficient to cause quick failure of PTO bearing, rather sudden peak loads might be the root cause of early failure.     

多极子阵列声波成像测井技术研究*

多极子阵列声波成像测井已经成为测井中主要方法之一,在地层评价与油气田开发中有重要作用。在已有理论与数值模拟的基础上,经过近十年的技术攻关,我们已经在多极阵列声波成像仪器制造、测试与数值处理等主要关键技术方面都取得了长足的进展,具体包括高温正交偶极子发射换能、高温低频单极子换能器、声系测试、多极子阵列声波测井高温电路及仪器集成、资料处理及解释等主要方面。所研制的仪器及资料处理方法,经过与国外同类仪器的测井结果进行了对比分析,验证了所研发的仪器的可靠性和处理方法的正确性,这些关键技术为我国声学测井仪器装备技术研发和快速发展打下了基础,提供了技术支撑。     

基于最小电压法的超声换能器谐振频率自动跟踪*

首先分析了最大电流法跟踪超声换能器谐振频率的原理及应用范围。研究了基于由串联电感和并联电容匹配电路下,不同频率时换能器两端电压电流的变化规律。研究表明在串联电感和并联电容匹配电路下发生谐振时,换能器两端的电压最小而电流并非最大。由此形成了采用最小电压法跟踪谐振频率的自动跟踪策略,并给出了该方法的具体实施步骤。论文研究结果为换能器谐振频率的自动跟踪方法提供了新的选择。