13 research outputs found
Shear wave sensors for viscoelastic properties
AbstractElectromechanical resonators are sensitive to the properties of the surrounding medium due to interaction forces onto the surface caused by motions in the medium. In the present contribution, fully metallic Lorentz force resonators exhibiting in-plane oscillation are used to excite shear waves to measure the linear viscoelastic storage and loss-moduli at specific frequencies in the kHz range of complex fluids (e.g. aqueous polymeric solutions). Reflected shear waves in a well defined gap are employed to extend the measurement range as well as the capability to measure at multiple frequencies. Numerical methods and reduced order models are employed to solve for the velocity field and interaction forces to determine the required quantities from the measured frequency response
Modeling and Experimental Investigation of Resonant Viscosity and Mass Density Sensors Considering their Cross-Sensitivity to Temperature
AbstractIn this contribution we discuss a generalized, reduced order model for resonant viscosity and mass density sensors which considers also the devices’ cross sensitivities to temperature. The applicability of the model is substantiated by experimental results from measurements obtained with a circular steel tuning fork in various liquids and temperatures. Advantages of this model are its simplicity, its general applicability for resonant mass density and viscosity sensors which furthermore facilitates the comparison of different sensors
Characterizing Vibrating Cantilevers for Liquid Viscosity and Density Sensing
Miniaturized liquid sensors are essential devices in online process or condition monitoring. In case of viscosity and density sensing, microacoustic sensors such as quartz crystal resonators or SAW devices have proved particularly useful. However, these devices basically measure a thin-film viscosity, which is often not comparable to the macroscopic parameters probed by conventional viscometers. Miniaturized cantilever-based devices are interesting alternatives for such applications, but here the interaction between the liquid and the oscillating beam is more involved. In our contribution, we describe a measurement setup, which allows the investigation of this interaction for different beam cross-sections. We present an analytical model based on an approximation of the immersed cantilever as an oscillating sphere comprising the effective mass and the intrinsic damping of the cantilever and additional mass and damping due to the liquid loading. The model parameters are obtained from measurements with well-known sample liquids by a curve fitting procedure. Finally, we present the measurement of viscosity and density of an unknown sample liquid, demonstrating the feasibility of the model
Miniature flow-through resonator cell for density and viscosity sensing
AbstractMiniaturized physical sensors for precise density and viscosity analysis are required as supplement or replacement for complex and expensive laboratory instruments. Utilizing miniature mechanical resonators as transducers, one can greatly reduce the necessary liquid volume, measurement time, and complexity of the experimental setup. In this contribution, we describe the development of a miniature, modular measurement setup for a large viscosity range. We devised and fabricated an inexpensive flow-through cell using milling technology of multiple PCB layers and Parafilm sealing for easy assembly and disassembly. The mechanical resonator is designed as a suspended plate using Lorentz force excitation and movement induction detection. The Qfactor of the resonator is evaluated and related to the density-viscosity product of different test liquids at multiple resonant modes of vibration at low operating frequencies for over a wide range of different viscosities
Acoustic Streaming Actuator and Multifrequency Resonator Sensor
We introduce an analysis platform for the viscoelastic properties of biological fluids such as the synovia found in articular joints. Small sample volumes are available for diagnostic purpose. Our approach uses a thickness shear mode quartz crystal integrated in an electrodynamically actuated spring structure. This combines the sensitivity of the quartz resonator operating at several overtones in the MHz range with previously introduced low kHz frequency multimode resonators. The latter is not only advantageous for characterizing viscoelastic fluids but is also used as an acoustic streaming actuator. Particulate matter in the sample thus can be resuspended and their settling is observed by tracking the resonance frequencies and Q-factors of both the quartz and electrodynamic resonator sensors
Monitoring of Monosodium Urate Crystallization for the Detection of Crystal Arthropathies in Human Joints
A piezoelectric tuning fork sensor is evaluated as a physical excitation and sensing device aiming at the detection of crystals and their nucleation behavior in joint fluids, as observed in gout. This device allows to study the crystallization tendency at varying temperatures or at increased uric acid concentrations as predominant in real human joints. In this work, a tuning fork resonator is characterized to enable spatially resolved viscosity and density measurements by calculating the mode shape of the vibration from resonance frequency measurements when immersed in test liquids
Viscoelasticity Sensor with Resonance Tuning and Low-Cost Interface
AbstractElectromechanical resonators are sensitive to the material parameters of a surrounding medium and therefore can be used as sensors for viscoelastic properties and density. In our recent work, we presented a metallic plate resonator excited by Lorentz forces in a permanent magnetic field. We improved the interface circuitry by using signal transformers, so that it is now possible to make accurate measurements using a commonly available low-cost audio- interface. Beside that, the necessary sample volume is reduced to a maximum of 50μl, so that a drop of liquid covers the sensitive area. Using a reflector parallel to the oscillation plane, standing waves in the gap could be generated. A desirable feature of resonator sensors is tunability over a significant frequency range. We investigated mechanisms to change the resonance frequency, e.g. an electric current that induces thermal stress. These advancements pave the way for a versatile low-cost, easy-to-use solution to measure viscoelastic properties in numerous applications
Does Solution Viscosity Scale the Rate of Aggregation of Folded Proteins?
Viscosity effects on the kinetics of complex solution
processes
have proven hard to predict. To test the viscosity effects on protein
aggregation, we use the crystallization of the protein glucose isomerase
(gluci) as a model and employ scanning confocal and atomic force microscopies
at molecular resolution, dynamic and static light scattering, and
rheometry. We add glycerol to vary solvent viscosity and demonstrate
that glycerol effects on the activation barrier for attachment of
molecules to the crystal growth sites are minimal. We separate the
effects of glycerol on crystallization thermodynamics from those on
the rate constant for molecular attachment. We establish that the
rate constant is proportional to the reciprocal viscosity and to the
protein diffusivity. This finding refutes the prevailing crystal growth
paradigm and illustrates the application of fundamental kinetics laws
to solution crystallization