The Design and Construction of an Acoustic Imaging System for Imaging Underground Facilities

Document Type : Original Article

Authors

1 M.Sc., Hossein University, Tehran, Iran

2 M.Sc., Imam Hossein University, Tehran, Iran

3 Assistant Professor, Imam Hossein University, Tehran, Iran

Abstract

As underground hidden facilities are used for various applications, imaging systems are required
for the detection and recognition of these facilities. In this paper, imaging by mechanical wave
propagation in the soil is investigated. Most underground facilities can be considered as air
chambers located in the middle of the soil. Air and soil have a large difference in acoustic
impedance, so underground facilities can produce a large reflective signal because the amplitude
of the reflected signal depends on the difference in impedance of the two materials. Seismic and
non-destructive concrete testing systems also use the process of propagation of mechanical
waves in the material. Although seismic systems have been successful in the detection issue,
they require several meters of space for equipment layout, and transportation complexity is also
one of their problems. They are unsuitable for urban space because they are inherently designed
to detect water sources at depths of several hundred meters. On the other hand, while the
non-destructive concrete testing system equipment have suitable dimensions, they have low
penetration depth which is impractical for this purpose. Seismic and non-destructive testing
systems of concrete operate in the range of subsonic and ultrasonic waves, respectively. This
research project proposes the idea that by choosing an operating frequency between the two
mentioned ranges, it is possible to obtain equipment with the appropriate dimensions for
imaging underground facilities. In this project we managed to image an underground
constructed cylindrical cavity with the diameter of 1 meter and the depth of 4 meters. The
accuracy of this method depends on the sound propagation speed in the material. Since there are
accurate relationships for the propagation speed of sound in air, the diameter of the cylinder was
estimated with an accuracy of about 4%, but with the measurement of propagation speed being
infeasible in this project, leading to the ambiguity in the value of propagation speed of sound in
soil, the values cited in several reference sites were used, giving the accuracy of 4 to 20%.

Keywords

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References

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Radar
Volume 9, Issue 1 - Serial Number 25
September 2021
Pages 45-55

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History

  • Receive Date: 07 April 2021
  • Revise Date: 13 October 2021
  • Accept Date: 14 December 2021
  • Publish Date: 23 August 2021

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