Ali Abdallah

Characterization of Viscous and Viscoelastic Fluids Using Parallel Plate Shear-Wave Transducers

We introduce a recently devised approach for viscosity and viscoelasticity measurement using a device based on the excitation of acoustic shear waves in fluids, which opens up opportunities for rheological applications in the low kilohertz range. Two in-plane plate resonators, which are driven and read out electromagnetically, are aligned in parallel and are separated by a well-defined gap filled with the fluid sample. The lower plate is actuated, generating a shear wave in the viscous or viscoelastic fluid. The response on the second side is recorded in a frequency range, where intrinsic resonances of this setup are observed. The coupling of the two resonators increases with viscosity, yielding a, for resonator viscosity sensors unprecedented, high viscosity measurement range (measured up to 17.6 Pa · s). Analytical modeling and experimental results are presented.

Resonator sensor array for synovial fluid characterization

We introduce a resonating viscosity-density sensor array measurement setup for the characterization of synovial fluid, the joint-lubricant in humans and animals, in an isolated and protective environment to prevent degradation of the fluid sample due to exposure to air. Our measurement technique requires very low sample volumes of 28 μl or less, and offers a more reliable alternative to capillary breakup tests already in use. The described method can be extended to characterize other biological and non-Newtonian fluids.

Concept study on an electrodynamically driven and read-out torsional oscillator

In this contribution a concept study for an electrody-namically driven and read-out torsional oscillator is presented. The fundamental mechanical and electrodynamical theory is explained in detail and measurements results obtained with first prototypes are discussed.

Application of resonant sensors for magnetic flux density measurements

This contribution discusses the influence of the magnetic flux density on Lorentz force driven resonant sensors. A closed form model describing the physical behavior of the resonating wire shows the quadratic influence of magnetic flux density on the readout signal, which in our case is the motion induced voltage in the oscillating wire. It is furthermore shown that the resonating wire sensor is well suited for magnetic field measurements, even at high temperatures.

Viscosity measurement cell utilizing electrodynamic-acoustic resonator sensors: Issues and improvements

Miniaturized viscosity sensors operating at frequencies in the KHz-range offer portability and results comparable to existing lab viscometers. In this paper we will briefly describe a viscosity measurement cell utilizing electrodynamic-acoustic resonator sensors and provide a modified design with interchangeable resonator cards, which allow for ease of maintenance of the device and provides higher measurement repeatability. Some basic experiments made with the new resonator cards are presented, which show the clear dependence of the resonance frequency and Q factor on viscosity. In addition, an approach is taken to optimize the magnetic circuit for the measurement cell using finite element simulations and experiments. A temperature dependence comparison is made between straight beam resonators and S shaped (Meander) beam resonators the result of which is the adoption of the S shaped beam design for further investigation. Finally the data processing approach using a curve fitting function designed for low quality factors is briefly described.

Parallel plates shear-wave transducers for the characterization of viscous and viscoelastic fluids

We present a novel sensor design for viscosity measurements using shear-waves, which opens up opportunities for rheological applications in the low kHz range. Two electrodynamic in-plane plate resonators are aligned in parallel and separated by a defined gap filled with the fluid sample. The lower plate is actuated, generating a shear-wave in the viscous or viscoelastic fluid. The response on the upper plate, which is coupled to the lower plate with the viscous fluid in between, is recorded in a frequency range where resonances are observed. The coupling of both resonators increases with viscosity, allowing a, for resonator sensors unprecedented, high viscosity measurement range measured up to 17.1 Pa.s. In this contribution we will introduce the sensor concept, present an analytical model and discuss the results of measurements made with various fluids.

A levitating sphere viscometer operating in a rotational mode

We present a special operation mode of a levitating sphere viscometer which allows steady rotations of a levitated magnet around its vertical axis. In contrast to miniaturized oscillatory viscosity sensors, this mode of operation allows to obtain viscosity measurements more comparable to standard laboratory viscometers. Moreover, the measurement range is increased to higher viscosities, where no resonance peak is detectable in with oscillatory sensors. Using electromagnetical actuation and the readout, all fluids except ferrofluids are measurable. Due to the levitation and the contactless readout, only the measurement body has to be in contact with the fluid, all readout and actuation parts can be placed outside the measurement cell, which makes the setup particularly useful for, e.g., sterile, toxic or poisonous fluids.

Electrochemical impedance spectroscopy for in situ monitoring of early zeolite formation

Zeolites are crystalline materials with internal pore structures finding widespread application from everyday products like laundry detergents to large scale catalytic and adsorption processes. Up to today however, zeolite formation is not fully understood. Especially the early stages of zeolite formation remain elusive. Although electrochemical impedance spectroscopy (EIS) has already proven to be a versatile tool for characterization of ionic solutions, it has, to the current knowledge of the authors, never been used before for in situ monitoring of zeolite growth. The linear relation between the measured impedance and Si/OH ratio of clear solutions shows that all added silica in taken out of solution and involved in the formation of nano-aggregates. Electrochemical impedance spectroscopy data for clear solutions has been proven to be complementary with ex situ dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) data and moreover allows for quantitative monitoring of nano-aggregate formation, especially in the crucial early steps where traditional methods fail.

Acoustic sensor for in-line monitoring in polymer extrusion dies

We present a pressure-wave-based acoustic sensor device for inline monitoring of polymer flow behavior. The device is made to be integrated in a slit capillary of an in-line-extrusion-rheometer, but could be implemented in any die used for extrusion. It was manufactured to withstand the high pressures involved in the extrusion process by employing a boundary reflection based acoustic measurement to determine the viscosity of the polymer. A high temperature graded PZT disc transducer was used and the whole system was designed to measure viscosities at the temperatures of the extruder without the need for external cooling of the PZT element.

U-shaped wire based resonators for mass density and viscosity sensing

In this contribution, U-shaped resonators used for viscosity and mass density sensing are presented. These devices were especially designed to reduce and overcome spurious instabilities, which were observed in previous sensor designs. Five sensor designs are presented and their sensitivities to viscosity and mass density are examined. The setups are discussed regarding their working principle, sensitivity, cross-sensitivity to temperature and repeatability. The measurement results in liquids featuring different viscosities and mass densities are shown and the theory necessary to relate the measured data to viscosity and mass density is outlined.