Interaction of a guided acoustic wave with an intrusion. Sound intensity cross section is plotted through the water, steel, oil, and an air-filled plastic sphere above the pipeline.

NRL researchers have developed an intrusion detection system for undersea pipelines that detect intruding objects as well as leakage effects from the pipelines.

Existing detection systems attempt to fully maintain the security and physical integrity of the pipelines. However, intrusions by undersea vehicles, underwater robots, divers, diver delivery vehicles, directed or intense sound waves, or leaking fluid warrants the need for a reliable, continual monitoring system that is able to detect objects or disturbances in proximity to the pipeline.

The innovative NRL intrusion detection system utilizes low-frequency (LF) structure-guided acoustic waves for detecting the intrusion since the waves propagate great distances without suffering geometrical signal attenuation. As a result, these waves can excite resonant characteristics in intruding objects that are a few wavelengths long or contain very compressible substances such as air.


  • Enhanced sensitivity to pipeline intrusions
  • Lower cost system requiring less maintenance than existing systems


  • Intrusion Detection
  • Leak Detection

Snapshot from a time-domain simulation of low-frequency guided wave development in an undersea oil-filled steel pipeline. The oil-steel-water borne mode propagates just under the speed of sound in water and is faster than the oil-borne mode which is conveyed at the lower speed of sound in oil. More water penetration is provided by the faster mode.

Generation of a low-frequency guided wave in an undersea oil pipeline using a sound source located above the pipe upstream. Downstream the guided wave insonifies an intrusion (pressure in symmetry plane shown). The wavelength of sound is comparable to the pipe diameter.

Acoustic intensity of a low-frequency guided wave mode in an underwater oil-filled steel pipeline that is half-buried in sand. Significant evanescent penetration into the water is observed.

Licensing and Collaborative Opportunities

  • US Patent No. 8,578,759 is available for license to companies with commercial interest
  • Potential for collaboration with NRL researchers

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