Remote passive sensing of a vibration signature using modulated light US8284405

Patent US8284405

Description

AFRL has developed 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. 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. Each of the foregoing methods has an inherent shortcoming which compromises its utility.

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.

TECHNOLOGY READINESS LEVEL (TRL)

TRL 3: Analytical and experimental critical function and/or characteristic proof of concept Active R&D is initiated. This includes analytical studies and laboratory studies to physically validate the analytical predictions of separate elements of the technology. Examples include components that are not yet integrated or representative.
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 at sites without physical access
  • Can obtain an accurate vibration measurement for an object in the presence of background vibration