Fig. 9: Flexible acoustic sensors and ultrasound devices.

a Exploded view diagram of a flexible acoustic sensor for detecting heart sound. b Heart sounds (bottom) and ECG (top) signals measured simultaneously and their magnified views. A.U. arbitrary units, MC mitral valve closure, AO aortic valve opening, RE rapid ventricular ejection, AC aortic valve closure, MO mitral valve opening, RF rapid ventricular filling. c Schematic (left) and photograph (right) of the flexible wearable wireless device for bowel sound detection. d Waveform lines of detected bowel sounds from one normal subject (blue line) and two patients with mechanical ileus (red line) and paralytic ileus (pink line). e Long time monitoring results of bowel sounds after meal. The red histogram shows the variation of number of peaks and the red broken line indicates the short-time energy of bowel sounds over time. f A stretchable ultrasonic device for monitoring of the central blood pressure. g Schematic illustration to measuring blood pressure by using pulse-echo method. Ant. anterior, Post. posterior. h Blood pressure measurements from carotid artery and brachial artery, and validation with a commercial tonometer. a, b Reproduced with permission¹⁷² (Copyright 2016, the American Association for the Advancement of Science). c–e Reproduced with permission¹⁷⁴ (Copyright 2019 Science China Press and Springer-Verlag GmbH Germany). f–h Reproduced with permission¹⁷⁵ (Copyright 2018, Nature Publish Group).