Wolfgang Burger

Motional capacitance of layered piezoelectric thickness-mode resonators

The Butterworth-Van Dyke equivalent circuit for description of the electrical behavior of piezoelectric bulk resonators is considered. The motional capacitance, C/sub 1/, in the circuit characterizes the strength of piezoelectric excitability of a vibration mode. For layered one-dimensional (1-D) structures this parameter can be calculated from the admittance given by the transfer matrix description of H. Nowotny and E. Benes (1987). Introducing the equivalent area of a vibration mode, the calculation is generalized for the three-dimensional (3-D) case of thickness-mode vibration amplitudes varying only slowly in the lateral directions. Detailed formulae are given for the case of singly rotated quartz crystals or ultrasonic transducers with additional layers on one or two sides. Good agreement of the calculated C/sub 1/ with experimental data is shown for mass-loaded planoconvex AT-cut quartz crystals.<<ETX>>

Separation of Suspended Particles by use of the Inclined Resonator Concept

A resonant ultrasonic field is applied to a suspension of micron size particles. The nodal planes of the sound field are slightly inclined to the main fluid flow. Since the acoustic forces cause the particles travelling along the planes, the particles are deflected from the fluid flow. An enriched suspension and the cleaned fluid can be obtained at different outlets. With the described resonator and 40 micron Polystyrene particles a separation efficiency higher than 80% was achieved.

Trapping of Suspended Biological Particles by use of Ultrasonic Resonance Fields

A layered piezoelectric resonator is introduced, that works as a cell retending filter in bioreactor flow loops. The resonator comprises two chambers; the first (passive volume) contains the cooling liquid, the second (active volume) the cell suspension. A separation efficiency of 99% has been achieved. The influence of the ultrasonic field on hybridoma cell viability was determined for three different cell cultures (R03 Virgil, 2F5, 1B1) up to ultrasonic field energy densities of 60 J/m3.

Aggregation and Separation of Hybridoma Cells by Ultrasonic Resonance Fields - Eifect on Viability, Growth Rate and Productivity.

An acoustic resonator was used to generate an ultrasonic standing wave field within a suspension of hybridoma cells. Acoustically induced aggregation and increased cell sedimentation rates were observed. Exposure of cells to ultrasonic resonance fields did not influence viability, growth rate, glucose consumption and antibody productivity. This paper demonstrates the potential of utilizing acoustic resonance separation methods in bioprocessing applications. Parameters investigated include time of ultrasound exposure, power level and cell concentration.

Frequency Dependence of the Acoustic Loss Distribution in Piezoceramic/Liquid Resonators

During the past decade, several separation methodes based on the response of fine particles to ultrasonic standing wave fields have been developed. The forces acting on the particles depend beside other quantities on the energy density and therefore on the stored energy in the liquid. Since separation cells are mainly constructed as layered piezoelectric resonators, a model is presented, which can describe the frequency dependence of the quality factor of a composite piezoelectric resonator. In addition, using this model, the stored (elastic) energy in each of the layers related to the electric input power can be calculated.

Review on the viability of mammalian cells in ultrasonic standing wave fields

Ultrasonic standing waves have been used in a number of applications for the separation of suspended particles, such as the separation of animal cells in fermentation processes. This technology has led to the development of high cell density, continuous perfusion fermentation systems with increased volumetric productivity. The ultrasonic separation device additionally can be used for controllable selective retention of viable cells and selective removal of cell debris. A key issue with this technology is the question if the ultrasound fields applied can be stressful to animal cells growing in suspension, thereby decreasing cell viability or impeding metabolic functions. This issue is also of interest to regulatory bodies concerned with quality assurance and quality control of pharmaceuticals derived from animal cell culture. Available data concerning cell viability, productivity, and metabolic activities will be reviewed and put into perspective to regulatory and fermentation technological concerns, such ...

Building-up Time of Standing Waves in Composite Piezoelectric Resonators

The present work investigates the transient behaviour of composite piezoelectric resonators, especially referring to the application of the so called Drifting Resonance Field cell. The building-up time is calculated considering the Butterworth-Van-Dyke equivalent-circuit of the piezoelectric resonator and assuming a step function in the driving frequency. Computed results are compared to measurements taken by means of a high resolution Frequency and Time Interval Analyzer.