## 5 Conclusions  
Based on the working principle of a sensorized prodder that is used for landmine detection, a mathematical analysis method is proposed to analyze the influences of each of the prodder's components on the measured signal. The calculated results meet well with the published electromechanical analogy simulation results and experimental results respectively, proving the feasibility of the proposed numerical analysis method. According to the analysis results, we can draw the following conclusions:  
If the mass of the moving part of prodder increases, the main resonance frequency of the measured signal would decrease while the corresponding vibration intensity would increase. Therefore, the mass of the moving part of prodder should be reasonable large to acquire greater signal strength to obtain larger detection depth.  
The stiffness of prodder's adjusting spring has no effect on the vibrational characteristics of the measured object, but the damping effect of spring can attenuate the vibration intensity. Thus, the spring of an optimized prodder should have a smaller damping coefficient.  
The steel rod's coupling effects generate a second resonance of the measured signal, while its influence on the main resonance vibration could be ignored. However, the measured signal strength would decrease with the increase of the stiffness of the steel rod. As a result, a better performing prodder should adopt a steel rod with smaller stiffness, for example, a hollow steel rod with conic-shaped tip.  
The analysis results of the effects of the measured object's stiffness and damping coefficient show that the theoretical signal strength for the plastic mine is larger than the related value for metal mine, which indicates that the prodder might be better suited for non-metallic landmine detection.  
According to the above analysis results, when the mass of the prodder's moving part is 0.1 kg, the adjusting spring is still the same, and the stiffness of the rod is 100 kN/m, the measured signal strength would increase approximately 122.78% resultantly, which means that a greater depth of detection could be achieved, and this optimal design is verified by the simulation experiment that was conducted with the optimization function of Adams software. It should be mentioned that, although many prodders have been proposed, prodder with force feedback is more of an exploration solution for landmine detection and is under consideration by some mine clearance organizations at this stage for its safety as a contact method. However, this optimized prodder could be of considerable interest in landmine detection training, other shallow buried landmine detection, and nondestructive testing for structural health. In our future work, we will develop an optimized prodder and dedicate it to these fields.  
Conceptualization, J.Z. and Z.W.; methodology, Z.W.; writing-original draft preparation, Z.W.; writing-review and editing, J.L.; project administration, C.W.; simulation experimental validation, H.M.  
This research was funded, in part, by the NATIONAL NATURAL SCIENCE FOUNDATION OF CHINA, grant number 61773249; the NATURAL SCIENCE FOUNDATION OF SHANGHAI, grant number 16 ZR1411700; the SCIENCE AND TECHNOLOGY ON NEAR-SURFACE DETECTION LABORATORY, grant numbers 6142414090117, TCGZ2017A006; and the NATIONAL YOUTH FUNDATION OF CHINA, grant number 41704123.  
Thanks are due to [PERSON] and [PERSON] for their valuable discussion and help.  
The authors declare no conflict of interest.