Microwave absorbing characteristics of porphyrin derivates: a loop of conjugated structure

Abstract

Microwave absorbing architectures have gained a great deal of attention due to their widespread application in diverse fields, especially in refining electromagnetic pollution. The aim of this study is to investigate the metamaterial characteristics of porphyrin derivatives as conjugated rings in the microwave region and evaluate the influence of electron-withdrawing and donating groups on microwave attenuating performance. Initially, an innovative microwave curing procedure was applied to synthesize the derivates; following that, the phenyl, aniline, and nitrophenyl-coupled structures were identified by XRD, FTIR, FESEM, and DRS analyses. The optical features illustrated that the characteristic band gap of the conjugated loops is obtained and that the optical performance can be manipulated by coupling the functional groups. Eventually, the achieved results demonstrated that the best microwave absorbing performance is related to aniline-coupled porphyrin with a maximum reflection loss (RL) value of -104.93 dB at 10.09 GHz with 2.80 mm in thickness attaining an efficient bandwidth (EB) (RL ≤ 10 dB) higher than the X-band. Noticeably, polyethylene (PE) was applied as an absorbing matrix presenting a meaningful idea for the development of practical microwave absorbers as a new generation of electromagnetic refining and stealth materials. The presented research provides precious inspiration to tailor novel microwave absorbing materials with metamaterial capability to promote their microwave absorbing performance.

Fig. 1. Synthetic routes of TPP (a), TNPP (b), and TAPP (c) structures.

Fig. 2. FTIR spectra of the TPP, TNPP, and TAPP.

Fig. 3. FE-SEM micrographs of the TPP (a₁, a₂), TNPP (b₁, b₂), and TAPP (c₁, c₂).

Fig. 4. XRD patterns of the porphyrin derivates.

Fig. 5. UV-vis absorption (a) and energy band gaps (b) of the samples.

Fig. 6. RL values of the porphyrin derivates at X-band.

Fig. 7. Matching thickness associated with the efficient bandwidth (RL > 10 dB) (a) and maximum RL (b) of the samples.

Fig. 8. Complex permittivity (a and b) as well as complex permeability (c and d), impedance matching (Z) (e), attenuation constant (α) (f), and Cole–Cole plot (g) of the architected samples.

Fig. 9. General scheme related to the microwave absorption (a) and possible microwave absorbing mechanisms (b) modified to clearly show the mechanism.