Abstract: As microscale devices, such as wireless microsensors and noninvasive biomedical implants, continue to shrink and incorporate more functions, energy becomes scarce, thereby shortening operation life. Furthermore, the limited volume space available constrains the stored energy available in state-of-the-art microbattery technologies, such as thin-film lithium ion �Li Ion�. For long-lasting life, it is, therefore, necessary to replenish continuously the energy consumed by harnessing, storing, and delivering energy from the environment in situ, i.e., in the package, alongside the application electronics. Operation life would ultimately be independent from storage limitations. The proposed self-contained, system-in-package solution is composed of three different energy-harvesting sources �light, vibrations, and thermal gradients � that sustain the system, while a charger stores the harnessed energy into an in-package Li Ion. Since substantially low-power levels are expected, the sensor must minimize energy consumption and the system, therefore, must be power moded into various operational modes to consume power only when necessary. Experimental measurements show how an electrostatic harvester sources nanoscale currents that can supply 1.18 �W from typical vibrations and, thus, recover the system consumption within 37.3 s.

Abstract: This paper presents the key design challenges encountered in system-in-package (SiP) wireless sensors. These sensors show tremendous promise for the test and evaluation of military equipment. These sensors should be small and autonomous to maximize utility; in this environment, energy management and system integration pose the greatest challenge. Fundamental limits exist on the amount of power required to process and transmit a signal a given distance with given accuracy, and approaching those limits requires careful energy use. Incorporating all necessary components on-chip or inpackage will require examining the trade-offs between volume and energy in many cases, as well as processing and packaging technology limitations. To illustrate these constraints, they are evaluated in the context of designing an EMI sensor.

Is it possible, are indefinite operational life and wireless power grids possible? Maybe not for every application, but how about for micro-scale devices? The fact is in situ energy sources like MEMS vibrational and thermoelectric generators can potentially achieve these goals for small footprint systemin-package (SiP) solutions like bio-implantable devices and wireless sensor transceiver network nodes. The key objective is to scavenge sufficient energy from the environment to sustain the micro-power system indefinitely, or at least extend life to practical levels. The problem, however, is micro-scale harvesters can only generate low-to-moderate power, and the energy-storage and power-delivery processes of the system inherently consume a portion of that, which is why the various functions of a loading application must be power-moded, that is, multiplexed, duty-cycled, and turned off when not needed. Fortunately, low frequency ambient vibrations are relatively abundant, stable, and predictable, and tuned MEMS- and CMOS-compatible electrostatic harvesters, for instance, can generate moderate power levels [1], but only if they prevail over the power losses associated with energy storage and power delivery. The focus of this article is to therefore identify, quantify, and discuss the power-consuming mechanisms present in a harvester circuit. Harvesting energy