Structural health monitoring has become an important factor in the assessment of defects/damage in material components. Ultrasonic methods generally incorporate a sparse array of sensors/transducers as they provide a low number of piezoelectric sensors per area, thus providing savings with regard to system costs and weight. Many structural health monitoring techniques rely on linear ultrasonic effects such as reflections, amplitude changes, time of arrival and wave scattering effects which rely on precise baseline measurements. In this work, a nonlinear ultrasonic method based on a sparse array of surface-bonded ultrasonic transducers was used to evaluate the second harmonic and modulated elastic responses from a damaged medium. A complex composite stiffened panel with barely visible impact damage was evaluated. The points closest to damage are found on the paths between transmitter–receiver pairs through a reciprocal relationship of nonlinear elastic parameters and a statistical approach was used to select a cloud of points so that a two-dimensional image of the damaged region is created. Experimental results revealed that the second-order nonlinear parameter provided accurate damage localisation and imaging and the use of modulation bands further improved imaging accuracy and damage localisation. The maximum error between the calculated and the real damage area centres was only 1.3 mm. The proposed nonlinear elastic multi-path imaging technique based on higher harmonic generation and modulation coupled with a statistical approach provides damage detection without a priori knowledge of the material characteristics, which is in direct contrast to conventional linear ultrasonic methods which rely on precise measurement of elastic wave effects both before and after the initiation of damage.

结构健康监测已成为评估材料组件缺陷/损坏的重要因素。超声波方法通常包含稀疏的传感器/换能器阵列，因为它们在每个区域提供的压电传感器数量较少，因此可以节省系统成本和重量。许多结构健康监测技术都依赖于线性超声效应，例如反射，振幅变化，到达时间和波散射效应，这些依赖于精确的基线测量。在这项工作中，基于表面粘结超声换能器稀疏阵列的非线性超声方法被用于评估受损介质的二次谐波和调制弹性响应。评价了几乎看不见的冲击损伤的复杂复合材料加劲板。通过非线性弹性参数的倒数关系，可以在发射器-接收器对之间的路径上找到最接近损坏的点，并使用统计方法选择点云，以便创建损坏区域的二维图像。实验结果表明，二阶非线性参数提供了准确的损伤定位和成像，调制带的使用进一步提高了成像精度和损伤定位。计算出的和实际损坏区域中心之间的最大误差仅为1.3毫米。所提出的基于高次谐波生成和调制的非线性弹性多径成像技术，再加上统计方法，可在不事先了解材料特性的情况下提供损伤检测，