High Power Ultrasonic Devices for Consumer Products

High power ultrasonic systems (HPUS) operate over a diverse industrial landscape and with a wide range of transducers and system capabilities. The most common use of high power ultrasound is for cleaning, with systems available at the small scale level, for example cleaning jewellery, up to large tanks for industrial scale cleaning. Diversification of applications into ultrasonic reactors for the chemical industry for reaction enhancement is a growth area and ultrasound can be applied in atomisation systems to provide an efficient, controllable spray/mist. Moreover, medical applications of high power ultrasound are also undergoing a significant period of development and acceptance. These techniques have even found their way into the cosmetic surgery world! So, the case has been made that HPUS is a growing sector, but an interesting development is in the consumer product domain where ultrasonic devices are becoming increasingly more common.
The programme will be structured around five topics:
1. Calibration or characterisation of HPUS. This are solutions for this in reactors or single transducer systems operating into a water load, but they are primarily invasive and/or band limited. For the consumer market products a different approach would have to be adopted, with non-invasive techniques the priority: acoustic emission and air-coupled ultrasonic detection will be investigated as potential solutions.
2. It has recently been reported that in addition to the convention three phases of water - gas, liquid, and solid - there exists a fourth phase that occurs at interfaces. The depth of this phase can be controlled through the application of light (UV, visible and IR). Our interest is from a cavitation perspective, where cleaning activity would be at this interface and hence, an investigation on the potential impact that this 4th phase of water would have on the cleaning performance of a high power ultrasonic system would be of interest. This would be an experimental programme considering optical stimulation of an interface and assessing cavitation performance.
3. The key component related to performance in a high power ultrasonic system is the active piezoelectric element. There are three main aspects to the transducer design that have to be addressed in order to improve the overall system performance and typically, these are inter-related: piezoelectric material; geometry; and loading/matching materials. However, the most significant is the active material itself and in recent years, advances in piezoelectric materials offer potential for a step change in performance in high power systems for industrial applications. New ternary compositions (e.g. PIN-PMN-PT [2]) have been reported with increased mechanical-Q and higher energy densities which opens new possibilities to produce a new generation of ultrasonic transducer designs with enhanced sensitivity. Importantly, the ternary materials have a curie temperature >100oC, which is sufficient for many commercial applications. A combination of finite element modelling and prototype manufacture/testing will evaluate new designs and configurations and compare to standard conventional high power ultrasonic devices.
4. A significant driver for consumer products would be device miniaturisation. However, this is not a straight-forward process - with smaller devices operating at higher frequencies, which have poorer high power performance (higher cavitation threshold). A comprehensive finite element modelling study will be undertaken considering various piezoelectric material options, piezoelectric geometries and constituent materials. Prototype devices will be fabricated, characterised and tested in the CUE laboratories.
5. The application of array technology to provide control of the high power ultrasonic field will be investigated. This approach has been implemented in the biomedical domain (HIFU), but would require lower operating frequencies for typical HPUS applications.