This study introduces a focused microjet droplet generator for forensic bloodstain applications.
In this work, the authors demonstrate a new focused microjet droplet generator that can produce such droplets using a blood simulant. Bloodstain investigation in a crime scene is an important part of forensic science. For gunshot wounds, bloodstains are produced by high speed (> 10 m/s), small diameter (< 1 mm) blood droplets that are difficult to produce experimentally. The generator is a small rigid liquid-filled container with a small-diameter glass capillary tube protruding from the lower end. The concave liquid-gas interface in the capillary tube is accelerated suddenly by a pressure impulse due to an impact on the upper surface of the container. The subsequent interfacial motion is focused into a high-speed microjet, which then pinches off into small droplets (Onuki et al., 2018). The authors explore this effect in low viscosity fluids (1 cSt) and control the droplet velocity by controlling the impact force and the distance between the concave interface and the end of the capillary tube. They observe the impact and spreading of these droplets on inclined textured solid surfaces, focusing specifically on the maximally spread droplet size and shape. (Published Abstract Provided)