Ground penetrating radar (GPR) is valuable for the detection of subsurface objects with little or no metal content, such as plastics, ceramics, and concrete piping. However, the effects of antenna configuration parameters, such as height and angle, are not well studied for all sensing applications. GPR simulations and laboratory GPR experiments are performed to evaluate the effects of antenna angle and height on the sensitivity of bistatic air-launched GPR, to search for buried nonmetallic objects. The results presented provide guidance for the development of air-launched GPR systems installed on unmanned aerial vehicles for in-flight subsurface scanning of buried targets.
Ground penetrating radar (GPR) subsurface sensing is a promising nondestructive evaluation (NDE) technique for inspecting and surveying underground utilities in complex urban environments, as well as for monitoring other key infrastructure such as bridges and railroads. A challenge of such technique lies on image formation from the recorded GPR data. In this work, a fast back projection algorithm (BPA) for three-dimensional GPR image construction is explored. The BPA is a time-domain migration method that has been effectively used in GPR image formation. However, most of the studies in the literature apply a computationally intensive BPA to a two-dimensional dataset under the assumption that an in-plane scattering occurs underneath the GPR antennas. This assumption is not precise for 3D GPR image formation as the GPR radiation scatters in multiple directions as it reaches the ground. In this study, a generalized form for an approximation to determine the scattering point in an air-coupled GPR system is developed which considerably reduces the required computations and can accurately localize the scattering point position. The algorithm is evaluated by applications on GPR data synthesized using GprMax, a finite-difference time domain (FDTD) simulator.
Many cities seek utilities monitoring with centrally managed Internet of Things (IoT) systems. This requires the development of many reliable low-cost wireless sensors, such as water temperature and flow meters, that can transmit information from subterranean pipes to surface-mounted receivers. Traditional radio communication systems are either unable to penetrate through multiple feet of earthen and manmade material, or have impractically large energy requirements which necessitate either frequent replacement of batteries, or a complex (and expensive) built-in energy harvesting system. Magnetic signaling systems do not suffer from this drawback: low-frequency electromagnetic waves are shown to penetrate well through several feet of earth and water. In the past, these signals were too weak for practical use; however, this has changed with the recent proliferation of high-sensitivity magnetometers and compact antennas using mechanically actuated rare-earth magnets. A permanent magnet can be either rotated or vibrated to create an oscillating magnetic field. Utilizing this phenomenon, two flow meter designs are proposed: one which uses a propeller to directly rotate a diametrically magnetized neodymium magnet; and, another which uses an oscillating tail to move a permanent magnet back-and-forth across a novel soft-magnet Y-stator, which projects a switching magnetic field. These oscillating magnetic fields are used to send water flow rate information to an above ground LoRa-capable Arduino receiver equipped with a magnetometer. Simulation software is used to model the oscillating electromagnetic fields. Complete system performance with remote datalogging is tested, with the aim of integrating many sensors and surface receivers into a single LoRa wireless IoT network.
Ground penetrating radar (GPR) has been shown to be an effective device for detecting buried objects that have little or no metal content, such as plastic, ceramic, and concrete pipes. In this paper, buried non-metallic object detection is evaluated for different antenna elevation angles and heights using a bistatic air-launched GPR. Due to the large standoff distance between antennas and the ground surface, the air-launched GPR has larger spreading loss than the hand-held GPR and vehicle-mounted GPR. Moreover, nonmetallic objects may have similar dielectric property to the buried medium, which results in further difficulty for accurate detection using air-launched GPR. To study such effects, both GPR simulations and GPR laboratory experiments are performed with various setups where antennas are placed at different heights and angles. In the experiments, the test surface areas are configured with and without rocks in order to examine surface clutter effect. The experimental results evaluate the feasibility and effectiveness of bistatic air-launched GPR for detecting buried nonmetallic objects, which provide valuable insights for subsurface scanning with unmanned aerial vehicle (UAV) mounted GPR.
This paper explores a low-rank and sparse representation based technique to remove the clutter produced by rough ground surface for air-coupled ground penetrating radar (GPR). For rough ground surface, the surface clutter components in different A-Scan traces are not aligned on the depth axis. To compensate for the misalignment effect and facilitate clutter removal, the A-Scan traces are aligned using cross-correlation technique first. Then the low-rank and sparse representation approach is applied to decompose the GPR data into a low-rank matrix whose columns record the ground clutter in A-Scan traces upon alignment adjustment, and a sparse matrix that features the subsurface object under test. The effectiveness of the proposed clutter removal method has been evaluated through simulations.
Proc. SPIE. 9437, Structural Health Monitoring and Inspection of Advanced Materials, Aerospace, and Civil Infrastructure 2015
KEYWORDS: Finite-difference time-domain method, Soil science, Reflection, Signal attenuation, Dielectrics, Interfaces, Wave propagation, Signal detection, Ground penetrating radar, General packet radio service
In this paper, a method using the instantaneous phase information of the reflection ground penetrating radar (GPR) signal to detect the variation of sand moisture is developed. The moisture changes the permittivity of the medium, which results in different speed when the GPR electromagnetic (EM) wave propagates in the medium. In accordance to this principle, we develop an analytical method to extract GPR reflection signal’s instantaneous phase parameters utilizing Hilbert Transform for sand moisture characterization. For test evaluation, Finite Difference Time Domain (FDTD) numerical simulations using a 3rd party open source program GprMax V2.0, and laboratory experiments on sand samples are conducted using a commercial GPR (2.3 GHz Mala CX) as the data acquisition system.
Climbing on concrete, masonry and brick with automated machines is difficult due to the uneven surfaces that prevent
getting a good grip. This paper describes developments in using dual-durometer pneumatic suction feet for gripping
onto concrete surfaces as part of a multi-legged robotic climbing system for inspecting concrete structures with vertical
walls. The dual durometer technique presents a compliant suction tip to the concrete thereby producing a good seal
against an irregular surface, and stiff component to deliver the structural rigidity needed for walking and climbing.
Individually actuated pneumatic Venturi vacuum generators provide the suction from positive pneumatic pressure in a
manner that is robust against leaks that cause the systemic vacuum collapse that can plague other vacuum configurations.
The feet are attached to a six-legged robot that with a nominal floor walking capability and gait. Climbing a wall
requires modification to leg actuation and gait, along with suction feet. System design, integration, concrete wall
climbing performance and sensor deployment in the form of a lightweight ground penetrating radar system are
Proximity lithography places a thin membrane mask into close proximity (5-100 micron) to a wafer for exposure to radiation and pattern placement. Efficient production practices require that the wafer be positioned relative to the mask as quickly as possible. The positioning maneuvers involve both a lateral motion and a closing of the mask-to-wafer gap. Gap closing requires forcing the exposure chamber gas (usually air or helium, possibly at a mild vacuum) between the mask and wafer out through the edges of the gap in a squeeze film process that can substantially deflect and damage the membrane mask. Moving laterally, i.e. stepping, would be more efficient if it were performed at the close proximity gap. The buildup of hydrodynamic pressures while stepping at gap can deform and possibly damage the mask. This paper discusses methods to model, measure and control aeroelastic effects due to gap closing and lateral stepping at gap. The analysis considers an aeroelastic model based on coupling Reynolds' hydrodynamic lubrication theory with membrane mechanics. A principal result of the analysis is the prediction that it is possible to step at gap and produce minimal aeroelastic out-of-plane deflections, if the wedge angle is zero, and both the membrane and mask have a flat profile. The aeroelastic models are confirmed with experiments that measure out-of-plane stepping of a membrane versus wedge angle, gap and speed. Non-flat mask profiles, such as buttes and mesas raise additional aeroelastic issues are also examined.
Electrical, optical and hydraulic conductors are vital components of most modern engineered systems. Damage to wiring and other conductors can degrade system performance, require expensive maintenance, and may cause catastrophic failures. This paper describes some efforts at developing active methods for self-healing wiring and conductor insulation. The concept is that there may be situations where it is beneficial to use self-healing cabling. One-part and two-part self-healing systems are fabricated and tested. Localized toughening in the face of localized damage has been realized in bench top experiments.
Mechanical actuators are integral components of many engineered systems. Many of the presently available actuator systems lack the desired stroke, power, controllability and reliability. The hierarchical actuator is a natural extension of the trend toward improving the performance of actuators through increments in geometric complexity and control. The hierarchical concept is to build integrated actuators out of a combination of smaller actuators. The smaller actuators are arranged geometrically and controlled so as to extend the performance of the total actuator into ranges that are not possible with actuators that are based on a few active elements and levels of control. Precision, speed increase, force output, load sharing, efficiency under smooth load/displacement control, smooth motion, stroke amplification/reduction and redundancy are all possible. Mechanics and mechanisms of hierarchical actuators are examined, along with a few experiments to demonstrate the operating principles.