Innovative lead-free ultrasonic bending transducers for low to medium power applications

Nowadays ultrasound technology is established in various fields of application like industrial production or medical technology. Besides high power ultrasound applications like ultrasonic cleaning and ultrasonic welding, which are often not strongly restricted regarding their weight, costs, and construction space, there are many applications in the low to medium power range like handheld surgical instruments, medical inhalers, or ultrasonic cutters. For the latter there is often a strong demand for low weight and construction space and low costs to be competitive in mass production. Another challenge that arises from the RoHS-directive [1] is, that new ultrasonic devices should avoid the use of lead-containing PZT-materials. Against this background there is a demand for lead-free, small and lightweight and cost-effective ultrasonic transducers. In many of the above-mentioned applications, pre-stressed Bolted-Langevine-Transducers (BLT) based on lead-containing PZT-materials are established to generate ultrasonic vibrations. These are quite advantageous in many ways and can be built tailored to each application and even for high power of thousands of watts. But due to the required steps during their manufacturing process (machining parts, assembly, pre-stressing, frequency tuning, …), these transducers remain expensive. Furthermore, due to the operation in resonance, the construction space of these transducers is linked to their wavelength and cannot be reduced remarkably. For these reasons, our aim is to present an innovative lead-free ultrasonic transducer for low to medium power applications, that is based on bending vibrations instead of longitudinal vibrations. This design enables to build very small transducers. Furthermore, due to their simple construction, these transducers can be built at low manufacturing costs and are well suited for industrial mass production. The use of lead-free piezoelectric materials makes this transducer design ready for future applications. In our contribution we will present the model-based design of a lead-free 30 kHz bending transducer for applications up to 10 W. Furthermore, the comprehensive experimental analysis of this transducer-prototype in applications like mist generation or ultrasonic drilling will be presented. The results will be compared to a PZT-based bending transducer and a classical BLT to show the potential and limits of these kind of transducers and lead-free materials.