Combined passive detection and ultrafast active imaging of cavitation events induced by short pulses of high-intensity ultrasound

The activation of natural gas nuclei to induce larger bubbles is possible using short ultrasonic excitations of high amplitude, and is required for ultrasound cavitation therapies. However, little is known about the distribution of nuclei in tissues. Therefore, the acoustic pressure level necessary to generate bubbles in a targeted zone and their exact location are currently difficult to predict. To monitor the initiation of cavitation activity, a novel all-ultrasound technique sensitive to single nucleation events is presented here. It is based on combined passive detection and ultrafast active imaging over a large volume using the same multi-element probe. Bubble nucleation was induced using a focused transducer (660 kHz, f-number = 1) driven by a high-power electric burst (up to 300 W) of one to two cycles. Detection was performed with a linear array (4 to 7 MHz) aligned with the single-element focal point. In vitro experiments in gelatin gel and muscular tissue are presented. The synchronized passive detection enabled radio-frequency data to be recorded, comprising high-frequency coherent wave fronts as signatures of the acoustic emissions linked to the activation of the nuclei. Active change detection images were obtained by subtracting echoes collected in the unnucleated medium. These indicated the appearance of stable cavitating regions. Because of the ultrafast frame rate, active detection occurred as quickly as 330 μs after the high-amplitude excitation and the dynamics of the induced regions were studied individually.     

Towards a human factors and ergonomics integration framework in the early product design phase: Function-Task-Behaviour

Considering the existing methodologies’ hysteresis and cost of the human factors and ergonomics (HF/E) integration in the design phase, this paper attempts to develop a time-saving, less expensive and standard approach for designers to integrate the HF/E from the early design phase. In this study, the HF/E information is embodied by a user manual, which will be continuously improved with the refinement of design. A Function-Task-Behaviour framework is proposed to restate the design process, which involves three steps: (1) Functional specification involves function definition and decomposition according to initial user manual and other requirements; (2) Embodiment refers to conducting task definition and planning to achieve the intended function. SysML is used for task definition and PERT method is applied for task planning; (3) Detailed design refers to the interactions analysis between user’s behaviour and product’s behaviour in the work area. A case study is shown at the end of this paper to illustrate the feasibility of the proposed method in integrating the HF/E from the early design phase to improve the final performance of both product and user.