Infra-Through Ultrasonic Piezoelectric Acoustic Vector Sensor Particle Rejection System

Sensor elements which employ fine filaments are often vulnerable to particulate fouling when used in certain operational field conditions. Depending on the size, attraction level, thermal and electrical conduction, and charge accumulation properties of the particles, erroneous readings can be easily generated in such “dirty” environments. This paper describes the design, development, and testing of an ultrasonic system which dynamically rejects highly tenacious electrostatically charged particles of a wide variety of sizes and even water. The paper starts with a brief introduction to the field of acoustic vector sensing, outlining its outstanding characteristics and history. Operational challenges including a statistical analysis of typical Middle-Eastern wind-blown desert sand and charge density are laid out. Several representative subscale hot-wire filaments were fouled with calibrated dust representing desert sand. The fouled elements were then exposed to airflows of 13？ft/s (4？m/s) and showed highly erratic shifted conduction levels with respect to baseline (clean) levels. An ultrasonic cleaning system was designed specifically resonate the filament and cantilever so as to mechanically reject foulants. When operated at resonance, the ultrasonic cleaning system showed 98.6% particulate rejection levels and associated restoration of uncorrupted filament resistance levels to within 2% of baseline resistance measurements. 1. Introduction Over the past decade, a new class of acoustic sensors has evolved. Conventional microphone technologies simply measure pressure as a function of time. These scalar measuring devices must be used in sizable clusters with powerful computers detangling this limited information [1]. A new approach using acoustic vector sensors (AVSs) employs fundamentally different sensor physics. These AVS elements are capable of not only determining pressure as a function of time (as do conventional microphones), but they can divide acoustic source directionality by measuring particle velocity in x, y, and z coordinates with time at very high rates and phenomenal dynamic range [2]. Acoustic vector sensors use a number of different techniques to determine acoustic source direction. One of the leading acoustic vector sensors employs an advanced dual hot-wire anemometry setup to measure particle movement in multiple directions. The device is used in many applications ranging from acoustic holography to tracking airborne vehicles as well as aquatic applications. Most of the applications currently employing these AVS devices are limited to