Many places in the world are heavily contaminated with landmines, which cause that many resources are not utilized. Much recent research acknowledges that the contact sensors have promising potential for landmine detection. To guarantee reliable landmine sensing system, deep analysis and many test cases are required. The proposed concept is based on application of 1kPa external constant pressure (lower than the landmine activation pressure) to the sand surface. The resultant contact pressure distribution is dependent on the imbedded object characteristics (type and depth). Then Neural Networks (NN) is trained to find the inverse solution of the sand-landmine problem. In other words when the contact pressure is known, NN can estimate the imbedded object type and depth. In this work, using finite element modeling, the existence of landmines in sand is modeled, and analyzed. The resultant contact pressure distribution for five objects in sand at different depths is used in training NN. Three NN are developed to estimate the landmine characteristics. The 1st one is perceptron type which classifies the introduced objects in sand. The other two feed-forward-NNs are developed to estimate the depth of two landmine types. The NN detection rates of Anti-tank and Anti-personnel landmines are 100% and 67% in training, and 95% and 70% in validation, respectively. As test cases, the detection rates of the NN in case of landmine inclination angles (0o-30o) and random noises 10%-20% of the average signal are studied.
Also, this work introduces a new concept for landmine detection with contact sensor. The sensor main principle is based on the concept of 2-DOF vibration absorber system (two springs and two masses), to detect the existence of an object (ex: landmine) in sand which is modeled as a 3rd spring in the 2-DOF vibration absorber system. The sand stiffness (the 3rd spring stiffness ko) can be acquired as a function of the vibration absorber mode frequency ωAbs (the frequency at which the 2nd mass has the lowest amplitude (mathematically proven: zero)). When the sand stiffness changed due to the presence of the landmine, the vibration absorber frequency ωAbs changes, and consequently the landmine can be detected. The mathematical derivation of the (ωAbs-ko) relation is verified by simulations with Matlab and finite element COMSOL Multi-physics. The system is succeeded to measure the sand stiffness up to 2 MN/m. A prototype for the sensor is developed with sensitivity 7.58 (N/m)/Hz at range of 200 N/m. Also, design procedure for the contact stiffness sensor for landmine detection is developed for selecting and optimizing the sensor parameters (masses and springs). Finally, feasibility study is developed for sensor fabrication with MEMS technology, including design and fabrication process. |
