Buried Object Detection Method Using Optimum Frequency Range in Extremely Shallow Underground

Abstract

We propose a new detection method for buried objects using the optimum frequency response range of the corresponding vibration velocity. Flat speakers and a scanning laser Doppler vibrometer (SLDV) are used for noncontact acoustic imaging in the extremely shallow underground. The exploration depth depends on the sound pressure, but it is usually less than 10 cm. Styrofoam, wood (silver fir), and acrylic boards of the same size, different size styrofoam boards, a hollow toy duck, a hollow plastic container, a plastic container filled with sand, a hollow steel can and an unglazed pot are used as buried objects which are buried in sand to about 2 cm depth. The imaging procedure of buried objects using the optimum frequency range is given below. First, the standardized difference from the average vibration velocity is calculated for all scan points. Next, using this result, underground images are made using a constant frequency width to search for the frequency response range of the buried object. After choosing an approximate frequency response range, the difference between the average vibration velocity for all points and that for several points that showed a clear response is calculated for the final confirmation of the optimum frequency range. Using this optimum frequency range, we can obtain the clearest image of the buried object. From the experimental results, we confirmed the effectiveness of our proposed method. In particular, a clear image of the buried object was obtained when the SLDV image was unclear.

Proposal of Non Contact Inspection Method for Concrete Structures Using High-Power Directional Sound Source and Scanning Laser Doppler Vibrometer

“…The frequency response range 22) of the defective part is detected. The measurement result of a center point on the defective part is standardized by the average result of all points.…”

“…The system consisting of an air-borne sound wave and the LDV has also been employed for a study on the land mine detection in shallow areas under the ground surface. [18][19][20][21][22][23] A potential disadvantage of this method is that a sound wave has a heavy attenuation in air. When targeting a tunnel, for example, the floor to roof height is at least 5 m. By using a loudspeaker, a sufficient sound pressure to excite the concrete wall cannot be maintained at a practical long distance.…”

“…Moreover, using a scanning laser doppler vibrometer (SLDV), is a scanningtype LDV, efficient scanning over a wide area will be possible. [20][21][22][23] Therefore, we propose a non contact inspection method consisting of a high-power directional sound source and an SLDV. [24][25][26][27][28][29] In this paper, we describe two types of experiment on the feasibility of our proposed method.…”

Study on Water Distribution Imaging in the Sand Using Propagation Velocity of Sound with Scanning Laser Doppler Vibrometer

“…Therefore, we propose a method for the monitoring and imaging of the water content in the rooting zone of plants using sound vibration. 1) Shallow underground imaging using the sound wave vibration has been already performed, and there are techniques using a shear horizontal wave, [2][3][4][5][6][7][8][9][10] an electromagnetic sound source, [11][12][13][14] a giant magnetostriction vibrator, [15][16][17] and an air-borne wave [18][19][20][21][22] have been developed. However, no research in which irrigation is controlled by measuring the water distribution in the rooting zone of plants using sound vibration has been performed yet.…”

Basic examination of noncontact inspection in solid material by using high-intensity aerial ultrasonic waves and optical equipment

“…We have developed a new method [13,14] of aerial ultrasonic inspection that uses high-intensity aerial ultrasonic waves and optical equipment. This method [15,16] differs from existing methods in that it detects solid material defects by analyzing vibrations on the surface of the object, which is excited using high-intensity aerial ultrasonic waves.We also developed a point-converging acoustic source [17] with a stripe-mode vibration plate to generate the high-intensity aerial ultrasonic waves, an essential component of the method. While the sound source operates at a single resonance frequency, the generated ultrasonic wave has nonlinear acoustic characteristics because sound intensity greatly increased by converging sound wave at the one point and generates nonlinear higher harmonics at the focal point.…”