'Second-order adjoint sensitivities' (Electromagnetic Waves, 2017), 'Adjoint Sensitivity Analysis of High Frequency Structures with MATLAB®', Chap. 9, pp. 221-246, DOI: 10.1049/SBEW525E_ch9
IET Digital Library, https://digital-library.theiet.org/;jsessionid=1lkedqcxuwxn4.x-iet-live-01content/books/10.1049/sbew525e_ch9