Electric Field Imaging Electric Field Imaging Electric Field Imaging

The physical user interface is an increasingly signiicant factor limiting the eeectiveness of our interactions with and through technology. This thesis introduces Electric Field Imaging, a new physical channel and inference framework for machine perception of human action. Though electric eld sensing is an important sensory modality for several species of sh, it has not been seriously explored as a channel for machine perception. Technological applications of eld sensing, from the Theremin to the capacitive elevator button, have been limited to simple proximity detection tasks. This thesis presents a solution to the inverse problem of inferring geometrical information about the connguration and motion of the human bodyfrom electric eld measurements. It also presents simple, inexpensive hardware and signal processing techniques for making the eld measurements, and several new applications of electric eld sensing. The signal processing contribution includes synchronous undersampling, a narrowband, phase sensitive detection technique that is well matched to the capabilities of contemporary microcontrollers. In hardware, the primary contributions are the School of Fish, a scalable network of microcontroller-based transceive electrodes, and the LazyFish, a small footprint integrated sensing board. Connecting n School of Fish electrodes results in an array capable of making heterodyne measurements of any or all nn , 1 oo-diagonal entries in the capacitance matrix. The LazyFish uses synchronous undersampling to provide up to 8 high signal-to-noise homodyne measurements in a very small package. The inverse electrostatics portion of the thesis presents a fast, general method for extracting geometrical information about the connguration and motion of the human body from eld measurements. The method is based on the Sphere Expansion, a novel fast method for generating approximate solutions to the Laplace equation. Finally, the thesis describes a variety of applications of electric eld sensing, many enabled by the small footprint of the LazyFish. To demonstrate the School of Fish hardware and the Sphere Expansion inversion method, the thesis presents 3 dimensional position and orientation tracking of two hands. 3 For Dad, who invented the busybox and showed me my rst circuit.