Remote passive sensing of a vibration signature using modulated light US8488123

Patent US8488123

Description

AFRL has developed an optical detector that senses the intensity of scattered light reflected by a surface coupled to a vibration source. If the vibration source is operating, the coupled surface vibrates at the same frequency. The vibration signature of the vibration source, if present, is discerned from a graphical display of the foregoing function.

Typical methods of measuring vibration require placing a device such as a seismometer or microphone with a transmitter, at a location of interest; measuring modulation from solar glints, i.e., when the angle subtended by incident sunlight and a surface normal is equal to the angle subtended by the normal and the reflected light; or using an active detector that either emits light or microwave radiation, and subsequently analyzing the reflected light or radiation.

Abstract

An optical detector senses the intensity of scattered light reflected by a surface coupled to a vibration source. If the vibration source is operating, the coupled surface vibrates at the same frequency. Incident light reflected by the surface is modulated by the vibration at a hypertemporal frequency. The detector produces a direct electrical current as a temporal function of the detected modulated light intensity. A transimpedance amplifier converts the current into a voltage. A voltage amplifier amplifies the voltage. An analog-to-digital converter converts the amplified voltage into digital signal. A digital signal processor converts the digital signal into a function of power spectral density and frequency using Fourier transform and principle component analyses. The vibration signature of the vibration source, if present, is discerned from a graphical display of the foregoing function.

  • Measuring vibration at a site for which it is difficult or impossible to obtain physical access
  • Identifying vibration source (through glass, earth, concrete, plaster, etc.)

TECHNOLOGY READINESS LEVEL (TRL)

TRL 4: Component and/or breadboard validation in laboratory environment Basic technological components are integrated to establish that they will work together. This is relatively “low fidelity” compared with the eventual system. Examples include integration of “ad hoc” hardware in the laboratory.
Air Force Research Laboratory- Directed Energy Directorate (RD) logo

Air Force Research Laboratory- Directed Energy Directorate (RD)

Kirtland AFB, NM

Advantages

  • Concealing of measurement possible
  • Accurate
  • Can be used at all times of the day
  • Usable without physical access