Bernd Henning

SPICE model for lossy piezoceramic transducers

A transmission line equivalent circuit for piezoelectric transducers has been modified to provide modeling of lossy piezoceramic transducers. A lossy transmission line is used to model the mechanical losses. The equivalent circuit parameters are derived from analogies between electrical transmission lines and acoustic wave propagation. Implementation of the equivalent circuit model in SPICE is shown. Simulations and measurements in the time and frequency domain of a low-Q material and a multilayered ultrasonic sensor using a low-Q piezoceramic transducer are presented.

Ultrasonic density sensor for liquids

This paper presents an ultrasonic density sensor for liquids that unifies high accuracy with high durability and is suitable for on-line measurements in a wide range of tube diameters. The sensor consists of a transducer with a piezoceramic disk mounted between two reference rods of quartz glass. Additionally, a second transducer is used as a sound receiver. The density is obtained from the reflection coefficient of ultrasound at the interface between the quartz glass rod and the liquid and the transit time of sound between this interface and the second transducer. Parameters, such as high long-term stability and accuracy of /spl plusmn/0.1% of full scale, were obtained by an internal acoustic reference measurement. The reference signal is generated using the sound radiated from the rear side of the piezoceramic disk. Design aspects such as sensor materials and signal-to-noise ratio are discussed, and experimental results are given in this paper. Applications of the sensor include concentration measurement, and ultrasonic mass flow measurement.

Ultrasonic sensors for process monitoring and chemical analysis: state-of-the-art and trends

Abstract Ultrasonic sensors are used in a large variety of ways. New fields of ultrasonic: sensor and ultrasonic sensor system applications are process monitoring and control, automotive techniques and chemical analysis. These applications have enjoyed a rapid increase of interest in recent years. The development of new ultrasonic sensors or systems was and is essentially accelerated by the progress in electronics, by new piezoelectric materials, by exploitation of new technologies and by the need for new or more accurate analysis methods in many industrial branches. A review of ultrasonic sensors based on piezoelectric materials and resonators is presented. First, the physical background for ultrasonic wave propagation and corresponding technical applications is given. A definition of the ultrasonic sensor system is introduced later because an ultrasonic sensor alone makes no sense. For an efficient use of this sensor principle, a well-developed transmitter and receiver electronics and intelligent data-acquisition electronics are necessary. Secondly, it is shown that ultrasonic sensors can be divided into four groups depending on how the ultrasonic signal has been changed on its path during propagation or the transducer properties are changed by interaction with the surroundings. The present state of established sensors for flow, distance and level is discussed. Ultrasonic sensors for process monitoring are described. New application fields for these sensors can be predicted. Finally, ultrasonic microsensors are introduced. A description of their state-of-the-art and application examples are given. To conclude, the use of new technologies for the manufacture of miniaturized ultrasonic sensors and future developments are discussed.

In-line concentration measurement in complex liquids using ultrasonic sensors

Recently there has been increased demand for chemical sensors measuring in-line the concentration of selected substances in complex liquids in order to guarantee a high product quality in the process industry. At present there is a great interest in acoustic sensor systems for concentration measurements. This article presents a new ultrasonic sensor system consisting of a miniaturized multi-sensor arrangement for the comprehensive acoustic characterization of liquid mixtures. The sensor system measures sound velocity, impedance coefficient, attenuation coefficient and temperature.

Improved ultrasonic density sensor with reduced diffraction influence

The density of liquids can be measured with ultrasonic techniques. An important factor limiting the accuracy of the measurement is the effect of diffraction of acoustic waves in the transducer. This paper presents a method to minimize such effects. A simple geometric model is used to analyse the contributions of plane waves and diffraction waves as a function of the sensor geometry. Calculations using the model lead to an optimized sensor geometry where diffraction waves do not interfere with the measurement signals. To demonstrate the fundamental improvement of accuracy, selected measurements of optimized and non-optimized sensors are compared.

Computer-assisted design of transducers for ultrasonic sensor systems

In this contribution, possibilities and methods for computer-assisted design of ultrasound transducers are described. These transducers are essential for an ultrasonic sensor design, e.g. for continuous non-invasive determination of quantities that are important in process technology. To achieve technical reliability and robustness, the precise determination of all acoustic properties of the used sensor materials is of great importance. Problem-oriented modeling, numerical simulation, special optimization algorithms and improved methods for the visualization of propagating waves offer new and promising possibilities for developing ultrasonic transducers with enhanced properties.

Ultrasonic density sensor—analysis of errors due to thin layers of deposits on the sensor surface

Abstract The density of liquids can be measured with ultrasonic techniques. Such sensors determine the reflection coefficient of ultrasound at the boundary between a reference material and the investigated liquid. An important question for application of these sensors is the influence of thin layers which may be deposited at the sensor–liquid interface. This article analyses the measurement errors of an ultrasonic liquid density sensor utilising simulation techniques.

Multi Reflection of Lamb Wave Emission in an Acoustic Waveguide Sensor

Recently, an acoustic waveguide sensor based on multiple mode conversion of surface acoustic waves at the solid—liquid interfaces has been introduced for the concentration measurement of binary and ternary mixtures, liquid level sensing, investigation of spatial inhomogenities or bubble detection. In this contribution the sound wave propagation within this acoustic waveguide sensor is visualized by Schlieren imaging for continuous and burst operation the first time. In the acoustic waveguide the antisymmetrical zero order Lamb wave mode is excited by a single phase transducer of 1 MHz on thin glass plates of 1 mm thickness. By contact to the investigated liquid Lamb waves propagating on the first plate emit pressure waves into the adjacent liquid, which excites Lamb waves on the second plate, what again causes pressure waves traveling inside the liquid back to the first plate and so on. The Schlieren images prove this multi reflection within the acoustic waveguide, which confirms former considerations and calculations based on the receiver signal. With this knowledge the sensor concepts with the acoustic waveguide sensor can be interpreted in a better manner.

Ultrasonic sensor properties characterized by a PC-controlled scanning measuring system

The use of ultrasonic sensors for process control is currently widespread for flow, level or distance measurements. Recently, interest has increased, too in the application of ultrasonic sensors to concentration measurements in complex liquids. In this application there are high demands for a defined and stable quality of the properties of both the sensor transfer function and the sound field characteristic. For a detailed investigation and characterization of ultrasonic sensor propertiess, an efficient PC-controlled measuring system was developed by the Institut fur Automation und Kommunikation (IFAK). In this contribution, this high performance approach is presented to make visible the vibrating ultrasonic sensor surface as well as the sound field in front of acoustic sensors in liquids.

Transient modeling of ultrasonic guided waves in circular viscoelastic waveguides for inverse material characterization

In this contribution, we present an efficient approach for the transient and time-causal modeling of guided waves in viscoelastic cylindrical waveguides in the context of ultrasonic material characterization. We use the scaled boundary finite element method (SBFEM) for efficient computation of the phase velocity dispersion. Regarding the viscoelastic behavior of the materials under consideration, we propose a decomposition approach that considers the real-valued frequency dependence of the (visco-)elastic moduli and, separately, of their attenuation. The modal expansion approach is utilized to take the transmitting and receiving transducers into account and to propagate the excited waveguide modes through a waveguide of finite length. The effectiveness of the proposed simulation model is shown by comparison with a standard transient FEM simulation as well as simulation results based on the exact solution of the complex-valued viscoelastic guided wave problem. Two material models are discussed, namely the fractional Zener model and the anti-Zener model; we re-interpret the latter in terms of the Rayleigh damping model. Measurements are taken on a polypropylene sample and the proposed transient simulation model is used for inverse material characterization. The extracted material properties may then be used in computer-aided design of ultrasonic systems.