A-1A P P E N D I XACHAPTER 0A COUSTIC D ROPLET EJECTIONTECHNOLOGYA.1 ADE historySimple ADE (Acoustic Droplet Ejection)—liquid transfer using acousticenergy—dates back to early experiments with high-intensity acousticbeams at the Tuxedo Park laboratory of Alfred Lee Loomis in 1927. It wasobserved that immersing a high-power acoustic generator in an oil bathwould create a mound at the surface “erupting oil droplets like a miniaturevolcano.”Improvements in the 1950s and early 1960s localized the energy with“exponential” acoustic horns or focused it with acoustic lenses, but stillmaintained the high intensity of earlier devices. These devices created dropswith a continuous application of acoustic energy to form geysers of smalldroplets or patterns of disturbances on the liquid surface where some ofthe swells grew large enough to pinch off and become drops.The introduction of a lower-intensity process that both focused and pulsedthe acoustic energy to create a single “drop-on-demand” was developed inthe early 1970s. Drop-on-demand technology has been extended to createtoday’s “ink jet” printing.The increasingly automated nature of life science research during the1990s, with its need for precise and reliable robotic liquid dispensing, led tothe application of focused-acoustic, drop-on-demand technology to lifescience liquid handling in the 2000s.
