# Multilayer Bolometric Structures for Efficient Wideband Communication Signal Reception
## 3 Experimental Setup and Measurements; Results and Discussion
### Results and Discussion  
We initiate our analysis of the resonant absorption effect by considering a structure composed of a doped semiconductor layer positioned behind the dielectric plate, as depicted in expression (3). The experimental and simulation data of the radiation absorption by such a structure as a function of its frequency are shown in Figure 2a. It is evident that the absorption experiences resonance in the presence of the dielectric plate approximately at the linear frequency of \(f=\omega/2\pi\approx 4.3\) GHz. Figure 2b illustrates that the presence of a dielectric rearranges the field of the electromagnetic wave in the vicinity of the semiconductor plate, thereby leading to an augmented level of absorption within it. The field modulus distribution inside the resonant structure clearly shows that the resonance corresponds to the condition when an integer number of half-wavelengths fits along the length of the resonator (three half-wavelengths). Figure 2: \(Cont.\)  
Another part of the work is devoted to investigating the possibilities of controlling the fraction of the signal absorbed as well as the absorption bandwidth, which is important for the detection of broadband signals. To this end, we have studied the characteristics of the resonant absorption of radiation in the presence of four-layer structures whose dielectric permittivity is described by Formulas (4) and (5). The measured and simulated radiation absorption data for structure (4) are shown in Figure 3. A significant increase in the fraction of the absorbed signal can be observed compared to the previous case, as well as a slight shift in the resonance frequency (Figure 3a). In this case, the resonance condition (three half-wavelengths) is fulfilled independently for both dielectric plates (see Figure 3b). By contrast, the dielectric plate located between the two semiconductors acts as a \"booster\", providing effective penetration (and absorption) of the wave field inside the far (concerning the incident wave) semiconductor plate (plate \"1\"). Nevertheless, it is clear from Figure 3b that the value of the field distribution in the left dielectric plate is considerably lower than in the right one, so the absorption is mainly determined by the semiconductor plate \"2\", which is placed closer to the incident wave. Of note, this version of \"anti-reflection coating\" with good matching of \"distributed detector impedance\" to \"open space impedance\" provides a noticeable increase in absorption. A different situation arises when the order of the doped wafers is changed, i.e., wafer \"1\" is placed closer to the incident wave; see expression (5). The absorption data for this case are shown in Figure 4a. Here, we observe a splitting of the resonant absorption peak into two sub-peaks, forming a wider absorption bandwidth. Analysis of the field modulus distribution in Figure 4b shows that the dielectric layers are better-coupled. In particular, for the first sub-peak, the resonance condition is found to be distributed over the whole region \(a+d_{1}+a\). Figure 2: **(a)** Experimental (dots) and theoretical (curves) data on the absorbed GHz radiation normalized to the incident radiation flux measured at the output of the waveguide in the presence of either a bolometric or our resonant structure; see Equation (3). **(b)** The field modulus distribution along the waveguide for the resonant frequency \(f\approx 4.3\) GHz in the case with/without the dielectric plate. The electric field strength is normalized to the amplitude of the incident wave. For 100% reflection from the structure, the maximum value of the electric field modulus is two. In addition, the value of the field modulus in the left and right dielectric resonators is comparable since wafer \"1\" provides less signal attenuation than \"2\". Consequently, in this case, the contribution of wafer \"2\", located at the end of the structure concerning the incident radiation, to the total absorption becomes essential.