Field Mice: Extracting Hand Geometry from Electric Field Measurements

by International Business Machines Corporation. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions, of this paper may be copied or distributed royalty free without further permission by computer-based and other information service systems. Permission to republish any other portion of this paper must be obtained from the Editor. Several members of a family of techniques called Electric Field Sensing are described. Each sensing technique can be understood as a measurement of the value of a different component in an effective circuit diagram that summarizes all possible current pathways involving the body to be sensed and the sensing electrodes. An analytical model of the sensor response is presented, and then a probabilistic framework for inferring geometrical information from field measurements is described. The inference framework is demonstrated for the cases of a two-dimensional and a three-dimensional mouse. lectric Field Sensing has existed in some form since a musical instrument known as the there-min was invented circa 1917. 1-3 Before that time, only aquatic animals had used electric fields to sense their environments. 4 The theremin combined analog sound synthesis and an early form of Electric Field Sensing in a single clever circuit. It is surprising how little research attention has been focused since then on the use of electric fields for measuring the human body, because electric field sensors are safe, fast (millisecond time scales), high resolution (millimeters), and inexpensive (dollars per channel), and measure robust bulk properties of the body rather than ephemeral surface properties. Nevertheless, with the exception of the work of Matthews 5 and Vranish, 6,7 little effort has been made to improve upon the early, " capacitive " form of Electric Field Sensing until recently. There are two reasons why Electric Field Sensing has languished. The first is that at the time of its invention, very few devices were capable of being controlled electronically. The physical user interface problem of transducing voluntary human action into electronic signals had therefore not yet become important. Today, computers and other electronic devices are becoming increasingly ubiquitous, and in more and more application domains the factor that is limiting the performance of these systems is the physical human interface rather than raw processing power. …