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Continuous imaging of cardiac functions is highly desirable for the assessment of long-term cardiovascular health, detection of acute cardiac dysfunction and clinical management of critically ill or surgical patients1–4. However, conventional non-invasive approaches to image the cardiac function cannot provide continuous measurements owing to device bulkiness5–11, and existing wearable cardiac devices can only capture signals on the skin12–16. Here we report a wearable ultrasonic device for continuous, real-time and direct cardiac function assessment. We introduce innovations in device design and material fabrication that improve the mechanical coupling between the device and human skin, allowing the left ventricle to be examined from different views during motion. We also develop a deep learning model that automatically extracts the left ventricular volume from the continuous image recording, yielding waveforms of key cardiac performance indices such as stroke volume, cardiac output and ejection fraction. This technology enables dynamic wearable monitoring of cardiac performance with substantially improved accuracy in various environments.

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Refill friction stir spot welding (FSSW) is a solid state joining technology recently derived from conventional FSSW. In the present study, refill FSSW was performed in a 0?8 mm thick AA7075-T6 aluminium alloy with varying welding parameters (welding time and plunge depth). The influence of welding parameters on the microstructure and mechanical properties of the weld was investigated in terms of nugget thickness, hardness and overlap shear strength. The microstructural features and fracture mechanism were observed by optical microscopy and scanning electron microscopy. The results indicate that the nugget thickness increases with increasing welding time and plunge depth. Furthermore, melted films observed in the stir zone (SZ) were consistent with a maximum temperature of 470?9uC measured 2?6 mm away from the SZ. The overlap shear strength increases with the increase of weld time and plunge depth due to increasing nugget diameter.