The research team started from the idea that cycles that have periods set by different prime numbers cannot develop a fixed phase relationship. Surprisingly, this principle seems to have emerged in the evolution of several species of cicadas, whose life cycles follow prime numbers of years, to avoid synchronizing with each other and with predators. For example, if one tries to "tie together" oscillators with periods set to the first three prime numbers (3, 5 and 7), the resulting signals are very complicated and chaos can readily be generated (Figure 1).
The design started from the most traditional oscillator found in integrated circuits, called the "ring oscillator," which is small and does not require reactive components (capacitors and inductors). Such a circuit was modified so that the strengths of ring oscillators having three, five and seven stages could be controlled independently, along with the tightness of their linkages. The device could generate chaotic signals over a wide frequency spectrum, from audible frequencies to the radio band (1 kHz to 10 MHz).
"Moreover, it could do so at a rather low power consumption, below one-millionth of a watt," explains Dr. Hiroyuki Ito, head of the laboratory where the prototype was designed.