Xin Wang and  Yuanzhong Wang,  Horizontal Directivity of Pipa Radiation.   journal   = {International Journal of Humanities and Social Sciences}, [online]. World Academy of Science, Engineering and Technology.
    May 2015, vol. 101(5). 808 - 811
    [viewed 25 April 2024]. Available from: https://publications.waset.org/pdf/10001322.