Salisbury screen | A resistive sheet is placed in front of a metal ground plane, usually separated by some lossless dielectrics. The reflectivity drops to zero due to destructive interference between the scattering paths in the device. | (a) Narrow band(b) Destructive interference(c) Easy to process |
Jaumann absorber | The Jaumann absorber, an extension of the Salisbury screen, primarily comprises multiple thin impedance layers, lossless dielectric layers, and a metal layer. The electromagnetic characteristics of each impedance layer and the thickness of the dielectric layer are designed to operate at distinct frequencies, enabling destructive interference absorption across multiple frequency points and achieving broadband absorption. | (a) Broadband frequency(b) Destructive interference(c) Substantial thickness and intricate processing methods |
Dällenbach absorber | The impedance matching layer is designed for specific high imaginary part of dielectric constant and permeability, while matching the free-space impedance. | (a) High imaginary part of dielectric constant and permeability ,(b) Free-space impedance matching(c) The absorption bandwidth is related to the conduction-frequency characteristics(d) Easy to process |
| Classification | Absorbing mechanism | Remark |
Impedance gradient multilayer absorber | Similar to the Dällenbach absorber, the layer-by-layer impedance matching design minimizes the reflected component of the interface when waves are incident. | (a) Gradient interface impedance matching(b) The absorption bandwidth is related to the conduction- frequency characteristics(c) Complicated process |
Pyramidal type absorber | The pyramidal-type absorber, an evolution from the Dällenbach absorber framework, adopts a specific angle design to maximize incident wave capture, minimizing reflection. Electromagnetic waves undergo multiple reflections along the cone structure. Both pyramidal and tetrahedral pyramidal configurations exhibit reduced demands concerning the polarization direction of electromagnetic waves. | (a) The macrostructure captures the incident wave and reduces scattering (b) The absorption bandwidth is related to the conduction- frequency characteristics(c) Easy to process |
Metamaterial absorber | The resonant response exhibited by distinctive metamaterial structure serves the purpose of dissipating incident electromagnetic waves. Owing to the notably high degree of freedom within this characteristic structure, metamaterials can be engineered for either single-frequency or wide-band resonant absorption. To achieve broadband absorption, multiple distinct single-frequency resonant structures are employed and combined. However, due to practical limitations in the manufacturing process, there remains a gap in absorption between the multiple resonant frequencies, leading to partial absorption within specific frequency bands. | (a) Electromagnetic resonance characteristic structure(b) Adjustable electromagnetic parameters ()(c) The processing difficulty is related to the wavelength |
Coherent perfect absorber | When two normal incidence plane waves with an odd times π phase difference enter the impedance layer from both ends, interference cancelation occurs, and all electromagnetic waves will be absorbed. | (a) Coherent wave(b) Phase difference:(c) The absorption bandwidth is related to the conduction- frequency characteristics |
Artificial blackbody | In the domain of artificial black holes, spheres and cylinders stand as prevalent design frameworks. Multi-layer spheres and cylinders are designed to increase the dielectric constant of the medium layer by layer from the outside to the inside. The center is full of material with high imaginary part of dielectric constant, and the incident wave is deflected to the center layer by layer and converges and loses. | (a) Gradient dielectric constant(b) The overall geometry is larger than the wavelength diffraction limit |
![Schematic illustration of a THz-TDS system for electromagnetic interference shielding efficiency (a) and reflection loss measurements (b)[57]](/Images/icon/loading.gif){kind=icon}
