The corresponding frequency response characteristics of these three materials are shown in Figs. 2(a), 2(b), and 2(c), respectively. All the figures are plotted such that at each frequency ($\Omega t,\Omega l$, and $\Omega s$), the TMH, LMH, and SMH produce their maximum power by operating against the optimal electrical loads ($\alpha t,\alpha l$, and $\alpha s$), as predicted by Eqs. (18), (20), and (22) for the TMH, LMH, and SMH, respectively.