Background High‐intensity focused ultrasound (HIFU) for non‐invasive treatment of a range of internal pathologies including cancers of major organs and cerebral pathologies is in exponential growth. Systems, however, operate at relatively low frequencies, in the range of 200‐2000 kHz as required for deep axial penetration of the body. HIFU utilizing frequencies in excess of 15 MHz has so far not been explored, but presents an opportunity to extend the HIFU modality to target specific dermal lesions and small animal research. Materials and methods A new 20‐MHz HIFU system (TOOsonix ONE‐R) with narrow focus corresponding to the dermis was studied in acoustic skin equivalents, for example, in a tissue‐mimicking gel and in bovine liver. HIFU lesion geometry, depth, and diameter were determined. The temperature increase in the focal point was measured as a function of acoustic power and the duration of HIFU exposure. Results The system produces highly reproducible ultrasound lesions with predictable and configurable depths of 1‐2 mm, thus corresponding to the depth of the human dermis. The lesion geometry was elongated triangular and sized 0.1‐0.5 mm, convergent to a focal point skin deep. Focal point temperature ranged between 40 and 90°C depending on the chosen setting. Observations were confirmed ex vivo in bovine liver and porcine muscle. Variation of acoustic power and duration of exposure produced linear effects in the range of the settings studied. Thus, effects could be adjusted within the temperature interval and spatial field relevant for clinical therapy and experimental intervention targeting the dermal layer of human skin. Conclusion The tested 20‐MHz HIFU system for dermal applications fulfilled key prerequisite of narrow‐field HIFU dedicated to cutaneous applications regarding reproducibility, geometry, and small size of the applied ultrasound lesions. Controlled adjustment of acoustic lesions within the temperature range 40‐90°C qualifies the system for a range of non‐ablative and ablative applications in dermatological therapy.

Porous ceramics are of interest for ultrasonic transducer applications. Porosity allows to decrease acoustical impedance, thus improving transfer of acoustical energy to water or biological tissues. For underwater applications, the d h g h figure of merit can also be improved as compared to dense materials. In the case of high frequency transducers, namely for high resolution medical imaging, thick film technology can be used. The active films are generally porous and this porosity must be controlled. An unpoled porous PZT substrate is also shown to be an interesting solution since it can be used in a screen-printing process and as a backing for the transducer. This paper describes the fabrication process to obtain such materials, presents microstructure analysis as well as functional properties of materials. Modelling is also performed and results are compared to measurements. Finally, transducer issues are addressed through modelling and design of several configurations. The key parameters are identified and their effect on transducer performance is discussed. A comparison with dense materials is performed and results are discussed to highlight in which cases porous piezoceramics can improve transducer performance, and improvements are quantified.

The development towards smaller devices with more functions integrated calls for new and improved manufacturing processes. The screen-printing process is quite well suited for miniaturised and integrated devices, since thick films can be produced in this manner without the need for further machining. On the other hand, the process of screen printing thick films involves potential problems of thermal matching and chemical compatibility at the processing temperatures between the functional film, the substrate and the electrodes. As an example of such a miniaturised device, a MEMS accelerometer based on PZT thick film will be presented. The design and process flow of this accelerometer has been optimised by means of finite element modelling (FEMLAB©). Consequently it has proved possible to eliminate post-processing steps after the screen printing of the PZT thick film.

Non-invasive high-intensity focused ultrasound (HIFU) operating at frequencies from 500 kHz to approximately 3 MHz has gradually been established as an efficient non-invasive treatment of internal cancers of major organs, bone metastases, and cerebral pathologies over the last decade. 1-9 HIFU focal points are positioned deep within the body with the anatomical location guided by MRI scanning or ultrasound imaging. In the focal point, temperatures of about 65°C are achieved, which is enough to kill

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