The Smart Dust project is exploring the limits of autonomous detection and communication by packaging a complete system in one cubic millimeter at a relatively low cost. These volumetric constraints correspond to energy constraints in the system. Therefore, the motto "intelligence" must operate on the absolute minimum energy while providing the necessary characteristics. The mote can be divided into four subsystems: sensors and analog signal conditioning, power system, front end of the transceiver and the core. The core is essentially all digital circuits in the system, including the rear end of the receiver, sensor processing circuits, calculation circuits and memory. A basic requirement is that it has an on-the-fly degree of reconfigurability determined by the changing needs of the mission. In this project we define an ultra low energy architecture for the mote core that will satisfy the needs of the military base monitoring scenario.
The objective of the Smart Dust project is to build cubicmillimetric scale and measurement platforms (Figure 1) that form a network of distributed sensors and can monitor environmental conditions in both military and commercial applications. These networks will consist of hundreds to thousands of "dust motes" and some interrogation transceivers. Dust specks are made up of several subsystems of different manufacturing technologies. Many sensors, including temperature, pressure and acceleration sensors, of MEMS and CMOS processes can be connected to a motorcycle. An ASIC handles measurement recording, data storage and system control. A receiver circuit converts the photocurrent of an incoming laser into a data stream that will be used to interrogate or reconfigure the mote. Several transmission systems, such as a passive corner hub reflector (CCR) may also be used for communication to a base station or an integrated laser with beam direction MEMS structures for intermobile communication. Finally, all components are mounted on a thick film battery charged by a solar cell. The most difficult restrictions in the Smart Dust design are the minimum power consumption required to drive circuits and MEMS devices. When the entire spec is set within a volume of 1 mm3, the power density of the power supply is the main issue. Current technology provides batteries with ~ 1J / mm3 power and high series resistance. Modern capacitors can reach up to 10mJ / mm3 with low resistance in series. The series resistance affects the peak power that can be drawn from the source. In typical low-power mixed signal systems, most designers consider performance in terms of cycles, samples or bits, maximizing performance first and minimizing power in the second place. With strict power restrictions for Smart Dust, we are forced to consider performance in terms of Joules: given a cubic millimeter battery, there is a Joule of energy to use. With the CCR, the communication costs over 1nJ / bit, while the detection can be reached in ~ 1nJ / sample. Modern processors, such as Strong ARM SA1100 , can perform calculations as low as ~ 1nJ / instruction. With these energy figures, you can make cost exchanges between the amount of calculation, the amount of data transmitted and the sampling frequency of the sensor.