Droplet speed-shift keying: a modulation scheme for instantaneous microfluidic communications.

Microfluidics is a rapidly evolving research area that has attracted the attention of scientists for the huge range of potential applications ranging from medicine to biodefense and drug administration. However to enable the realization of devices that employ droplet microfluidics, efficient and effective methods for encoding information in droplet flows should be identified. So far a number of techniques to encode data have been proposed, e.g., exploiting droplet size, droplet composition, absence or presence of droplets. The above-mentioned methods, however, suffer for the propagation delay inside the channel so that data reception is far from being instantaneous. In fact, a relevant delay can exist in real systems which can be sometimes even in the order of minutes. This occurrence greatly limits the amount of applications that can take advantage of information transmission through microfluidic channels. To try filling the above gap towards a real and prompt deployment of a microfluidic systems, in this paper we propose a novel methodology for encoding information using an instantaneous variation in the properties of a train of droplets flowing in a continuous phase. In particular, taking advantage of the stable, laminar flow of the droplets, we aim to encode data in the instantaneous change of droplet velocity induced by changing the input pressures of the discrete-continuous phases according to the data to be encoded in the source side. This approach opens new perspectives for information transmission in microfluidic systems, which could lead to new applications.