Jens Strobel

Ultrasound transducers based on ferroelectret materials

Ferroelectret materials can be utilized to set up electroacoustic transducers. The materials offer both, a rather large bandwidth and a high piezoelectric strain constant. Due to its cellular structure, the material is flexible and exhibits an excellent matching to air. Therefore, this polymer is appropriate for many sound as well as ultrasound transducer applications. Our research is concentrated on the simulation based design and characterization of ultrasound transducers. In this contribution, we present a finite element based modeling of the cellular structured ferroelectret materials. In particular, a microscopic as well as a macroscopic model is discussed. We fabricate single element and array transducers based on ferroelectret materials, namely the so-called EMFi (Electro- Mechanical-Film) material. To show the applicability of ferroelectret materials for ultrasound transducers, different applications in air and water are presented. An emitter-receiver-unit is introduced which is utilized in an artificial bat head and allows the functional reproduction of the biosonar system found in bats. Moreover, a robust sensor array consisting of 16 single elements (4x4) is studied. With the aid of this sensor array, cavitation effects in ultrasonic cleaning systems can be investigated on the specimens surface, which is not possible with common ultrasound sensors, e.g., hydrophones.

Ferroelectret sensor array for characterization of cavitation effects in ultrasonic cleaning

The demand for an increasing efficiency of ultrasonic cleaning in industrial manufacturing cannot be satisfied with the current empirical design approaches. This article describes the development of tools for the characterization of cavitation effects, which are the most important mechanisms of cleaning impact. The approach is based on the measurement of cavitation intensity by the assessment of characteristic acoustic spectral components. For this purpose, a sensor array using a novel, cellular structured ferroelectret is developed that can be easily applied to component surfaces. The electrical and acoustic characteristics of the sensor array are analyzed by measurements and finite element simulations. The correlation between acoustic spectral components and cavitation erosion on surfaces is deducted from cleaning experiments.

Ferroelektretsensor zur Messung der Kavitation in UltraschallreinigungsbädernFerroelectret Sensor for Measurement of Cavitation in Ultrasonic Cleaning Systems

Zusammenfassung Bisherige empirische Ansätze zur Auslegung von Ultraschallreinigungsanlagen werden der in der industriellen Fertigung geforderten Reinigungseffizienz nicht mehr gerecht. Die vorliegende Arbeit beschreibt die Entwicklung von Werkzeugen zur Charakterisierung von Kavitationseffekten, welche die Hauptmechanismen der Reinigungswirkung sind. Die Kavitationsintensität wird anhand des Auftretens charakteristischer Anteile im Druckspektrum bestimmt. Hierfür wird die Entwicklung eines Sensorarrays auf Basis eines neuartigen, zellular strukturierten Ferroelektrets vorgestellt, das flexibel auf Bauteiloberflächen aufgebracht werden kann. Mittels Reinigungsuntersuchungen wird die Korrelation spektraler Druckanteile mit der Erosionswirkung auf Probekörpern abgeleitet und die Abhängigkeiten von diversen Einflussparametern ermittelt.