A control system for ultrasound devices utilized for inactivating E. coli in wastewater.

Sonochemical processes applied to wastewater treatment have an influence on the behavior of ultrasonic systems. This is especially due to the load characteristic of the sonochemical process itself and the temperature increase caused by internal damping within the converter. Hence, a controlling device is needed to guarantee the operation in resonance and to keep the vibration amplitude constant. This paper presents a digital control system for the operation of weak to strong damped ultrasonic devices and its application for inactivating Escherichia coli in wastewater. In an experimental investigation, the electric data during a sonochemical process to inactivate E. coli in wastewater is taken into account to analyze the efficacy of the treatment process and the reaction of the vibration system to the process. Frequency response measurements depict that the resonance frequency changes with the sonicated medium and the vibration amplitude decreases with driving current. In addition to a common continuous operation of the system, different pulsed modes are investigated. The experiments prove the common dependencies between inactivation and power level or treatment time. Additionally, it is pointed out that the control of the sonochemical device is of utmost importance to guarantee an efficient treatment of water, because fast process changes, especially in pulsed operation modes, need to be controlled to a steady state as fast as possible. Although a water treatment efficiency increase using pulsed modes was not proved, it is shown, that the performance of the control unit is capable of using different driving modes in water treatment.

Piezoelectric transducer design via multiobjective optimization.

The design of piezoelectric transducers is usually based on single-objective optimization only. In most practical applications of piezoelectric transducers, however, there exist multiple design objectives that often are contradictory to each other by their very nature. It is impossible to find a solution at which each objective function gets its optimal value simultaneously. Our design approach is to first find a set of Pareto-optimal solutions, which can be considered to be best compromises among multiple design objectives. Among these Pareto-optimal solutions, the designer can then select the one solution which he considers to be the best one. In this paper we investigate the optimal design of a Langevin transducer. The design problem is formulated mathematically as a constrained multiobjective optimization problem. The maximum vibration amplitude and the minimum electrical input power are considered as optimization objectives. Design variables involve continuous variables (dimensions of the transducer) and discrete variables (the number of piezoelectric rings and material types). In order to formulate the optimization problem, the behavior of piezoelectric transducers is modeled using the transfer matrix method based on analytical models. Multiobjective evolutionary algorithms are applied in the optimization process and a set of Pareto-optimal designs is calculated. The optimized results are analyzed and the preferred design is determined.

The effect of friction reduction in presence of ultrasonic vibrations and its relevance to travelling wave ultrasonic motors.

In many ultrasonic applications frictional effects play an important role (e.g. ultrasonic machining, ultrasonic motors). For optimising the applications in terms of quality, efficiency and lifetime it is important to understand the frictional coupling of the vibrating and the non-vibrating part. This contribution is devoted to give an explanation for the reduction of friction forces which is often observed when ultrasonic vibrations are superimposed to macroscopic motions. Usually adopted coefficients of friction are used for modelling such conditions suggesting special frictional mechanisms for high frequency oscillations, whereas the present paper shows that Coulomb's friction law provides a very good description of the observed phenomena if the kinematics of the system is taken into account. Two systems are investigated. In the first system the ultrasonic and macroscopic movements are parallel and in the second they are perpendicular to each other but also within the plane of contact. Both systems were investigated analytically and experimentally using a specially designed test rig. The measurements confirmed the analytically derived equations and therefore the validity of Coulomb's friction law even for ultrasonic conditions.

Survey of the present state of the art of piezoelectric linear motors

Piezoelectric ultrasonic motors have been investigated for several years and have already found their first practical applications. Their key feature is that they are able to produce a high thrust force related to their volume. Beside rotary drives like the travelling wave motor, linear drives have also been developed, but only a few are presently commercially available. In the present paper, we first describe the state of the art of linear piezoelectric motors. The motors are characterized with respect to their no-load velocity, maximum thrust force, efficiency and other technical properties. In the second part, we present a new motor, which is judged to be capable of surpassing the characteristics of other piezoelectric motors because of its unique design which allows the piezoelectric drive elements to be pre-stressed in the direction of their polarization. The piezoelectric elements convert energy using the longitudinal d33 effect which allows an improved reliability, large vibration amplitudes and excellent piezoelectric coupling. Energy loss by vibration damping is minimized, and the efficiency can be improved significantly. Experimental results show that the motor characteristics can be optimized for a particular task by choosing the appropriate operating parameters such as exciting voltage, exciting frequency and normal force.