Millimeter-Scale True 3-D Antenna-in-Package Structures for Near-Field Power Transfer

This paper describes the modeling, fabrication, and measurement of a method to construct true 3-D antennas for radio frequency (RF) power harvesting in millimeter-scale sensors. The goal is to create an omnidirectional RF power-harvesting structure, which can provide power even if the sensor and external power source are not perfectly aligned. Because the orientation of the sensor is not known in advance, the antenna must work equally well in all directions. To realize such a structure, antennas will be built into the packaging of the sensor, and this allows for the largest possible antenna without increasing the size of the sensor and by combining antennas which are orthogonal to each other. This construction results in a cubic structure, where the power-transfer efficiency can be increased by 22 dB over a traditional single-coil setup at the worst case orientations for the sensor. The presented structures will range from 3 to 5 mm cubes.