The engineers demonstrated the self-healing capabilities through tiny amplifiers; a total of 76 of them alongside everything else that is needed to carry out self-healing – all of it able to fit on a penny. The team went to the extremes in testing if their work actually yielded results for which they damaged the amplifiers at several places by zapping them with high-power lasers. Within a second, the chips were able to develop work-around thereby healing themselves.
The self-healing capabilities of the chips can be equated to that of the immune system of our body. The chips detected and quickly responded to assaults aka damage thereby repairing them to keep the larger system going. Engineers equipped the amplifiers with several sensors that would keep eye on temperature, current, power and voltage. They also built an Application Specific Integrated Circuit (ASIC) that acted as the brain of the system. The sensors feed the data into the ASIC which analyses the inputs thereby calculating the overall performance and checks whether any adjustment is needed in the system's actuators – the parts of the chip that are changeable.
The engineers haven’t programmed the ASIC with all the possible scenarios but, instead ASIC makes decision based on the data fed to it by the sensors. Engineers have programmed the chip with that they require in terms of desired results and it has been left onto the chip to figure out how to attain those results.
There are four classes of problems that the self-healing chips address: static variations caused due to variation across different sub-components; long-term aging problems caused due to changes in the internal properties of the system; short-term variations induced by environmental conditions; and accidental or deliberate destruction of parts of the circuits.
Another thing worth noting is that the engineers went about demonstrating their research using latest high-frequency integrated chips proving that their technology works even on advanced systems.
You can find more technical information through the research paper [PDF].