The use of ultrasonic longitudinal critically refracted (LCR) waves is one approach used for near surface material characterization. It has been shown to be sensitive to stress and, in general, less sensitive to the effects of the texture of the material. Although the LCR wave is increasingly widely applied, in experiments the factors that influence the formation of the LCR beam are seldom discussed. This paper reports a new numerical model used to investigate the transducers’ parameters that can contribute to the directionality of the LCR wave and hence enable performance optimization when used for industrial applications. An orthogonal experimental method is used to study the sensitivity to the transducer parameters which influence the LCR wave beam characteristics. This method provides a design tool used to study and optimize multiple parameter experiments and it can identify which parameter or parameters are of most significance. The effects of incident angle, the aperture and the center frequency of the transducer were all studied. It is shown that the aperture of the transducer, the center frequency and the incident angle are the most important factors in controlling the directivity of the resulting LCR wave fields. The model was validated by comparision of data to those obtained with a finite element model. Experiments were also performed to confirm the numerical results. The model and experimental data provided improve understanding of the transducer selection and positioning in the optimization of LCR wave fields in experiments, which can be used to give signals which exhibit higher sensitivity for near-surface stress characterization.

超声纵向临界折射（LCR）波的使用是用于近表面材料表征的一种方法。已经显示出它对应力敏感，并且通常对材料质地的影响不那么敏感。尽管LCR波的应用越来越广泛，但是在实验中很少讨论影响LCR光束形成的因素。本文报告了一种新的数值模型，该模型用于研究换能器的参数，这些参数可有助于LCR波的方向性，从而在工业应用中实现性能优化。使用正交实验方法来研究对影响LCR光束特性的换能器参数的敏感性。该方法提供了一种用于研究和优化多参数实验的设计工具，并且可以识别出哪些参数最为重要。研究了入射角，孔径和换能器中心频率的影响。结果表明，换能器的孔径，中心频率和入射角是控制所得LCR波场方向性的最重要因素。通过将数据与使用有限元模型获得的数据进行比较来验证该模型。还进行了实验以确认数值结果。提供的模型和实验数据有助于在实验中优化LCR波场时更好地了解换能器的选择和位置，