Absorption Frequency Band Research Articles

Enhanced Electromagnetic Wave Absorption in Hexaferrite/LSMO Bilayers: Optimization of Structural Design Using a High Frequency Software Simulation

In this study, the electromagnetic (EM) wave absorption properties of a two-layered structure composed of La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub>-epoxy (10 wt.%) (LSMO) and SrFe<sub>9.5</sub>Co<sub>1.25</sub>Ti<sub>1.25</sub>O<sub>19</sub>-epoxy (10 wt.%) (SFCTO), both exhibiting distinct high-frequency magnetic and dielectric properties, were investigated using a High Frequency Simulation Software (HFSS) simulation tool. LSMO had a high dielectric constant (ε' >30) within the measurement range (0.1-18 GHz), indicating that dielectric loss mechanisms primarily contribute to EM wave absorption. In contrast, SFCTO is a material capable of significantly absorbing EM waves near 10 GHz due to ferromagnetic resonance (FMR). The simulations were validated by comparing the measured and simulated reflection losses (RL) of an unpatterned LSMO/SFCTO bilayer. The RL spectra were examined by varying the layer thickness and pattern size in three configurations: a continuous LSMO/SFCTO structure, a cross-patterned LSMO on SFCTO, and a square-patterned LSMO on SFCTO. In the continuous LSMO/SFCTO structure, tunable absorption frequency bands were achieved by adjusting the layer thickness. However, it was difficult to achieve broadband absorption due to the reflective characteristics of the high dielectric LSMO layer. The cross-patterned LSMO structure on SFCTO demonstrated broader bandwidth absorption, with layer thickness being more influential than pattern width. The square-patterned LSMO on SFCTO exhibited the best broadband EM wave absorption (max Δ<i>f</i> = 7.39 GHz). These results suggest that broader absorption is achievable by partially covering the high-dielectric layer with patterns on a hexaferrite sheet.

Enhanced electromagnetic wave absorption of La3+–Zr4+ cosubstituted M−type barium hexaferrite

The development and breakthrough of electronic information technology have led to a profound focus on exploring new millimeter-wave absorbing materials. Herein, La–Zr ions co-substituted barium ferrite BaxLa1−xZrxFe12−xO19 (BLZFO) was prepared using a sol–gel method. BaFe12O19 possesses a dual loss mechanism (electrical/magnetic) and exhibits a natural resonance frequency of ∼ 45 GHz, making it effective for millimeter-wave absorption. The presence of La–Zr ions enhances the electromagnetic parameters of the material, improving its attenuation ability and optimizing impedance matching. Consequently, a wide, effective absorption frequency band and a minimal matching thickness are achieved. Specifically, within the 26.5–40 GHz range (Ka-band), BLZFO (x = 0.4) demonstrates an effective absorption bandwidth of 12.15 GHz, an optimal reflection loss of − 21.17 dB, and a corresponding matching thickness of 0.6 mm. This material not only exhibits strong reflection loss but also meets the requirements of an effective absorption frequency bandwidth and a small matching thickness, underscoring its profound importance for millimeter-wave absorption material research.

Absorption frequency band switchable intelligent electromagnetic wave absorbing carbon composite by cobalt confined catalysis

The dielectric loss of carbon materials is closely related to the microstructure and the degree of crystallization, and the microstructure modulation of electromagnetic wave absorbing carbon materials is the key to enhancing absorption properties. In this work, a porous elastic Co@CNF-PDMS composite was prepared by freeze-drying and confined catalysis. The graphitization degree and conductivity loss of carbon nanofibers (CNFs) were regulated by heat treatment temperature and Co catalyst content. The construction of a heterointerface between Co and C enhances the interfacial polarization loss. The Co@CNF-PDMS composite with 4.5 mm achieves the minimum reflection loss (RLmin) of –81.0 dB at 9.9 GHz and RL no higher than –12.1 dB in the whole of the X-band. After applying a load of up to 40 % strain and 100 cycles to Co@CNF-PDMS, the dielectric properties of the composite remain stable. With the increase of compression strain, the distribution density of the absorbent increases, and the CNF sheet layer extrusion contact forms a conductive path, which leads to the conductive loss increase, finally, the absorption band moves to a high frequency. The absorption band can be bi-directionally regulated by loading and strain with good stability, which provides a new strategy for the development of intelligent electromagnetic wave absorbing materials.

Ultra-Flexible microwave absorber of PEDOT:PSS/Melamine composite film with wide tunable frequency controlled by Self-Strain sensing

The exploration of smart microwave (MW) absorption materials with excellent mechanical properties and wide frequency tuning ability is challenging work. Herein, an ultra-flexible MW absorber with wide frequency modulation by itself strain sensing has been successfully constructed, which is realized by introducing doped conductive poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT:PSS) with dimethyl sulfoxide (DMSO) into three-dimensional melamine foam (MF) network. The formed MF/P-D20 composite itself is a piezoresistive sensor with a high sensitivity. Most importantly, it is found that the absorption frequency band of the MF/P-D20 composite film can be controllably and reversibly modulated in a wide frequency range from S to Ku bands by changing the compression strain monitored by the value of ΔR/R0. Furthermore, theoretical simulations and experimental findings confirm that the variations of pore shape and size after compression serve as a crucial factor responsible for shifting the enhanced electron flux density and MW loss to higher frequency, which consequently induces the shift of impedance matching and sequent MW absorption to higher frequency. The MW absorber also shows excellent properties of mechanical robustness, thermal insulation, electro-thermal conversion and retardant. This study provides insights into the smart and reversible control of MW absorption properties and paves the way for tuning MW absorption frequency in wide frequency.

Design of an adjustable sound-absorbing structure with low frequency advantages

The thickness of microperforated panel absorbers with low-frequency sound absorption ability is often large and the absorption bandwidth is limited. To address this issue, a adjustable microperforated panel structure with low-frequency advantage (ASWLF) was designed. Compared to conventional structures, the introduction of inclined chambers allows the structure to absorb lower-frequency noise at the same thickness, enhancing spatial utilization efficiency. The addition of a rotating structure design broadens the frequency range over which the structure can operate effectively. The addition of a rotating structure design broadens the frequency range of the structure's action. The acoustic absorption coefficient of the model can be calculated using acoustic-electric analogy, which is used to predict the acoustic absorption coefficient of the ASWLF structure. The experimental results show that, with the same acoustic absorption performance, the thickness of the structure is reduced by 36.7%. The multi-stage combination allows the structure to achieve better acoustic absorption performance in a wider frequency band. By introducing the PSO optimization algorithm, the optimized ASWLF structure further improves the acoustic absorption frequency band by 32.9%. This study provides an effective method for solving noise environments under different conditions in industrial practical applications.

Random incidence sound absorption of micro-perforated panel absorbers backed with parallel-arranged cavities of different depths

This study investigates sound absorption performance of a kind of wideband micro-perforated panel (MPP) absorbers with parallel-arranged backing cavities at different depths in a diffuse field. An analytical prediction model is presented for evaluating the random incidence absorption coefficient of this type of absorbers, and it exhibits excellent agreement with finite element model and experimental measurements. Then, numerical cases were established using this model to investigate the absorption characteristics of this type of absorbers under random incidence, considering the influence of cavity depths and MPP parameters. Results show that the cavity depth and MPP perforation diameter in this absorber are primary influencing parameters controlling the overall sound absorption performance. Cavities at different depths introduce multiple resonant absorption peaks, while the perforation diameter determines matching conditions between the MPP and air impedance, which simultaneously broaden the absorption bandwidth of this MPP absorber. Although individually adjusting the panel thickness and perforation rate has a smaller impact compared to the perforation diameter, the interaction between these two parameters has significant influences across the entire absorption frequency band.

Far Infrared/Terahertz Spectroscopy as a Complementary Method for the Analysis of the Spectral Features of Thymol and Carvacrol Structural Isomers

Objective: The conventional method for the characterization of volatile compounds has been mostly limited to the use of gas chromatography. This work offers an alternative method to address the limitations that might be encountered with the use of the gas chromatography method. Furthermore, this work addresses the scarcity of the analysis of these materials in the far infrared/terahertz region as previous studies have been focused mainly on the mid-infrared region. Methods: The far infrared/terahertz spectra of carvacrol and thymol were analyzed using the Fourier transform infrared (FTIR) and gas chromatography-mass spectroscopy (GC-MS). Density function theory (DFT) calculations were employed for the interpretation of the FTIR experimental spectra. Results: Thymol and carvacrol spectra were characterized by distinct absorption bands in the 200-600 cm−1 (6-18 THz). There were appearances of bands at similar energies for these isomers. These bands appeared at 320.7 cm−1 (9.6 THz), 439.2 cm−1 (13.2 THz), 525.2 cm−1 (15.8 THz), and 586.8 cm−1 (17.6 THz) for thymol and at 313.6 cm−1 (9.4 THz), 419.8 cm−1 (12.6 THz), 521.2 cm−1 (15.7 THz), and 566.9 cm−1 (17.0 THz) for carvacrol. Despite these similarities, there were also significant differences in the spectra of these materials. The theoretical peak frequencies were in agreement with the experimental absorption band frequencies. Two seemingly common absorption bands were observed in the spectra of thymol and carvacrol. However, peak assignments revealed that these bands have different vibrational modes. The GC-MS results show that the retention time of thymol and carvacrol are very close at 18.5 and 18.8 respectively. Conclusion: This work underscores the ability of far infrared/terahertz waves in identifying materials with similar structural features. Furthermore, it supplements the limited studies of these isomers in the far infrared/terahertz region. The GC-MS results emphasize the need for a complementary method that can improve the characterization of these materials.

Controlled growth of polyaniline nanofibers on the surface of alkali pre-treated PI fabric as electromagnetic wave-absorbing fabrics

The electromagnetic wave attenuation network composed of PANI NFs is an efficient wave-absorbing structure. Constructing PANI NFs networks on the surface of flexible fabrics is a potential approach to improve the wave-absorbing properties of fabrics, but there are few related reports on this. In this paper, we proposed a facile method to grow PANI NFs (average diameter of 80–100 nm) on the polyimide (PI) fabric surface through a controlled nucleation and growth process. The results of FESEM, FTIR, XPS, and UV–vis indicated that the PANI and PI may first combine at the initial nucleation centers through electrostatic interactions, hydrogen bonding, and π-π stacking, and then the PANI grows linearly into elongated nanofibers under suitable polymerization conditions. As expected, the PANI NFs coated fabric achieved a strong reflection loss (RL) of -34.20 dB (>99.999 % absorption) and a broad effective absorption frequency band of 5–18 GHz. The excellent absorption performance originated from the conduction loss, scattering loss, and polarization relaxation loss of the PANI NFs network. In addition, the fabric exhibits good thermal stability (Td beyond 570 °C) and long-term stability ((90.57 % retention of conductivity after 500 bending cycles). This study provides a viable approach for designing next-generation microwave-absorbing fabric.

Ultra-thin water-based metasurface with dual-broadband perfect absorption

The rapid development of the 5 G technology can be attributed to its outstanding penetration in the low frequency bands ranging from 600 MHz to 6 GHz, particularly in specific frequency ranges like 700 MHz, 2.3 GHz, and 3.5 GHz. Simultaneously, the technology excels in the millimeter-wave spectrum, spanning from 24 GHz to 52 GHz, notably in bands such as 24.25–27.5 GHz and 37–40 GHz, showcasing impressive capabilities for high-speed data transmission. Nevertheless, these signals frequently encounter electromagnetic interference from electronic equipment in practical applications, which compromise the quality of communication. To address these issues, this paper presents the design, fabrication, and measure of a dual-broadband ultra-thin water-based metasurface absorber (WBMA). The unit cell is composed of a 4 mm thick photoresist shell encasing a water layer and metal plate, and features an irregular octagonal prism and a rectangular annulus cavity within the water layer. Simulation and experimental outcomes indicate that the proposed metasurface achieves near-perfect absorption at frequencies from 4.2 GHz to 4.8 GHz and from 23.6 GHz to 51.1 GHz in the transverse electric mode. Additionally, the proposed metasurface exhibits more than 90% absorption in the transverse magnetic mode for frequency ranges from 4.3 GHz to 4.9 GHz and from 23.2 GHz to 50.8 GHz. The designed water-based metasurface also exhibits features of polarization insensitivity and capability to handle wide-angle incidence. Analysis of the electric and magnetic field distribution within the metasurface suggests that the absorption mechanism is driven by strong magnetic resonance within the water layer’s structure. Furthermore, the effective impedance of the metamaterial absorber is explored. Given the unique absorption frequency bands, the proposed WBMA has potential applications in the realm of 5G communication.

Preparation, Structure and Properties of Epoxy/Carbonyl Iron Powder Wave-Absorbing Foam for Electromagnetic Shielding.

The application of absorbing materials for electromagnetic shielding is becoming extensive, and the use of absorbents is one of the most important points of preparing absorbing foam materials. In this work, epoxy resin was used as the matrix and carbonyl iron powder (CIP) was used as the absorbent, and the structural absorbing foam materials were prepared by the ball mill dispersion method. Scanning electron microscopy showed that the CIP was evenly dispersed in the resin matrix. The foam structures formed at pre-polymerization times of 10 min, 30 min and 50 min were analyzed, and it was found that the cell diameter decreased from 0.47 mm to 0.31 mm with the increase in the pre-polymerization time. The reflectivity of the frontal and reverse sides of the foam gradually tends to be unified at frequencies of 2-18 GHz. When the CIP content increased from 30 wt% to 70 wt%, the cell diameter increased from 0.32 mm to 0.4 mm, and the uniformity of CIP distribution deteriorated. However, with the increase in the CIP content, the absorption properties of the composite materials were enhanced, and the absorption frequency band broadened. When the CIP content reached 70 wt%, the compression strength and modulus of the foam increased to 1.32 MPa and 139.0 MPa, respectively, indicating a strong ability to resist deformation.

Improvement of the sound absorption performance of sandwich panel using inhomogeneous micro-perforations

Sandwich structures are widely used in several fields because of their mechanical performance with low weight. In this paper, a sandwich panel made of a core and a top and a back panel is investigated using the finite element method. The core consists of 33 hexagonal cells and each cell is connected to a micro-perforation. To improve the sound absorption, inhomogeneous micro-perforations are considered within the top panel. It is shown that with homogenous micro-perforations made of the same diameter, the sound absorption coefficient presents only one resonant peak. When 2, 3, and 6 different sets of micro-perforation diameters are considered, the sound absorption coefficient presents, respectively, 2, 3, and 6 resonance peaks where the surface impedance is close to that of the air. When each micro-perforation diameter is different resulting in inhomogeneous distribution of micro-perforations within the top panel, the sound absorption frequency band is widened and the absorption coefficient value increases while without micro-perforations the absorption coefficient of the sandwich panel is zero over the entire frequency range. The studied structure can offer high mechanical stiffness and good sound absorption performance.

Sound absorption performance of double layer sandwich structure containing micro-perforations and extended necks

In this study, a double layer sandwich panels made of micro-perforated plate and perforated plate with extended necks is proposed and its acoustic attenuation is studied using the finite element method. The top panel of the structure is micro-perforated and is connected to a first honeycomb structure cells. The internal panel is perforated, and a neck is connected to each perforation and extends into each cell cavity of the second honeycomb structure. The proposed material design is made of 33 micro-perforations and 33 extended necks and has excellent mechanical stiffness due to the honeycomb structure performance. This study shows how to design the parameters of the necks and the micro-perforations to widen the sound absorption frequency band. With identical micro-perforation diameters and identical necks, the sound absorption coefficient presents two resonance peaks where the surface impedance is close to the impedance of air. The number of the sound absorption peaks increases when different micro-perforation diameters and different necks are used while the sound absorption of conventional double layer sandwich structure is zero over the entire frequency range. The proposed material design can be used to attenuate the noise in various engineering fields that require good bending stiffness.

Semi-self-similar fractal cellular structures with broadband sound absorption

Honeycomb core materials, recognized for their excellent sound absorption and load-bearing capabilities, are widely employed in engineering applications. The back cavity shape of honeycomb structure absorbers plays a crucial role in their sound absorption performance. In this study, the honeycomb structure absorbers are re-designed using fractal design principles, enabling a modification of the acoustic properties of traditional honeycomb-type absorbers and a significant enhancement in the sound absorption frequency band. The theoretical predictions of the semi-self-similar fractal honeycomb absorber structure are validated through finite element simulations and experimental studies, exhibiting remarkable consistency. The findings indicate that compared to single-layer first-order structures, the performance of dual-layer second-order fractal element Helmholtz resonators is significantly improved. Relative to conventional honeycomb panel structures, the fractal design approach markedly enhances the semi-absorption bandwidth of the absorbers, with an increase in the fractal order further broadening the sound absorption frequency band. The innovation of achieving broadband absorption through fractal resonators not only represents a new direction in the design of advanced honeycomb core materials but also holds substantial promise in the field of noise control.

Effect of Reduced Graphene Oxide on Microwave Absorbing Properties of Al1.5Co4Fe2Cr High-Entropy Alloys.

The microwave absorption performance of high-entropy alloys (HEAs) can be improved by reducing the reflection coefficient of electromagnetic waves and broadening the absorption frequency band. The present work prepared flaky irregular-shaped Al1.5Co4Fe2Cr and Al1.5Co4Fe2Cr@rGO alloy powders by mechanical alloying (MA) at different rotational speeds. It was found that the addition of trace amounts of reduced graphene oxide (rGO) had a favorable effect on the impedance matching, reflection loss (RL), and effective absorbing bandwidth (EAB) of the Al1.5Co4Fe2Cr@rGO HEA composite powders. The EAB of the alloy powders prepared at 300 rpm increased from 2.58 GHz to 4.62 GHz with the additive, and the RL increased by 2.56 dB. The results showed that the presence of rGO modified the complex dielectric constant of HEA powders, thereby enhancing their dielectric loss capability. Additionally, the presence of lamellar rGO intensified the interfacial reflections within the absorber, facilitating the dissipation of electromagnetic waves. The effect of the ball milling speed on the defect concentration of the alloy powders also affected its wave absorption performance. The samples prepared at 350 rpm had the best wave absorption performance, with an RL of -16.23 and -17.28 dB for a thickness of 1.6 mm and EAB of 5.77 GHz and 5.43 GHz, respectively.

Near-infrared H2S telemetry system under non-cooperative target with a novel mixed heterodyne optical structure scheme for high efficiency

A gas leakage telemetry system under non-cooperative target was designed and developed based on laser absorption spectroscopy technology, targeting the combination frequency absorption band of Hydrogen sulfide (H2S) gas molecules. A distributed feedback (DFB) laser centered at 1578 nm was adopt, with mature packaging process and high market maturity. The returned signal of diffuse reflection is extremely weak, decreasing exponentially with the increase of telemetry distance, and direct detection technology is difficult to achieve ideal performance at telemetry distance and lower detection limit. Thus, heterodyne detection technology was introduced to significantly amplify diffuse reflection signal and improve the signal-to-noise ratio (SNR) of telemetry system. For further detection sensitivity, wavelength modulation spectroscopy (WMS) technology was combined to suppress background noise through the electrical modulation of DFB laser. Alternating signal was applied to the laser to alter its output characteristics during the process of laser oscillation. Compared with exterior modulation methods, this interior modulation method does not require additional modulator, which avoids optical loss and is more economical. Combining the advantages of fiber structure and space optical path structure, a novel mixed heterodyne optical structure which was more applicable to this system was independently designed after the specific analysis of main noise sources. Then, the effect of heterodyne detection technology was verified in contrast of direct detection technology. Sensor performance was validated through calibration and stability experiments. The limit of detection (LoD) reached a minimum of 3.44 parts-per-million (ppm·m) with a 98 s averaging time. And the packaged system was fully capable of detecting the hazardous critical concentration of H2S and acting as an alarm mechanism.

Multilayer Bolometric Structures for Efficient Wideband Communication Signal Reception.

It is known that the dielectric layer (resonator) located behind the conducting plate of the bolometer system can significantly increase its sensitivity near the resonance frequencies. In this paper, the possibility of receiving broadband electromagnetic signals in a multilayer bolometric meta-material made of alternating conducting (e.g., silicon semiconductor) and dielectric layers is demonstrated both experimentally and numerically. It is shown that such a multilayer structure acts as a lattice of resonators and can significantly increase the width of the frequency band of efficient electromagnetic energy absorption. The parameters of the dielectric and semiconductor layers determine the frequency bands. Numerical modeling of the effect has been carried out under the conditions of our experiment. The numerical results show acceptable qualitative agreement with the experimental data. This study develops the previously proposed technique of resonant absorption of electromagnetic signals in bolometric structures.

Electron irradiation modified point defects of SiC nanoparticles with tunable high electromagnetic wave absorption

Silicon carbide nanoparticles (SiC nps) were modified by changing the injection amount using 1 MeV high-energy electron as radiation source. When the injection volume reaches 5ⅹ1013 cm−2, the irradiated particles produce defect structures sufficient to optimize the electromagnetic wave absorption performance. With the increase of beam amount, the value of g detected by electron paramagnetic resonance (EPR) energy spectrum moves towards the silicon suspension bond, and the macroscopic electromagnetic wave absorption peak gradually moves towards the low frequency, accompanied by the enhancement of absorption intensity and the increase of absorption bandwidth. When the injection volume reaches 3ⅹ1014 cm−2, the loss value of −62.79 dB is achieved at the optimal thickness of 2.56 mm, and the absorption frequency band covers the entire Ku band. SiC presents point defects, and carbon atoms leave the original lattice position due to electron irradiation, forming carbon vacancies, resulting in uneven charge distribution inside the material, resulting in dipoles of orientation polarization, which further affects the electromagnetic wave absorption performance. As the irradiation dosage increases, the defects become denser and purer. This leads to higher electromagnetic wave absorption intensity and a correspondingly lower optimal absorption frequency. Thus, the modification of SiC nps through irradiation achieves tunable absorbers.

Optimization design and analysis of the broadband acoustic absorber of the microperforated panel with an interpolated straight tube

The microperforated panel (MPP) structure is widely used in the field of noise reduction. The traditional MPP structure has a fixed absorption peak, and the optimized MPP structure has an improved absorption band, but the frequency range of the absorption is not ideal. For the design of broadband absorption in MPP structures, this paper presents a MPP acoustic absorber structure (N-MH) with an interpolated straight tube (IST) designed for superior broadband acoustic performance. The N-MH structure combines the advantages of the MPP and the embedded necked Helmholtz resonator, as well as having a sub-wavelength thickness of only 60 mm, which is only 1/14th of the wavelength at the first resonant frequency. The N-MH structure is optimized based on the particle swarm optimization (PSO) algorithm. In comparison to traditional microperforated panel structures, the N-MH structure exhibits a significantly broader sound absorption frequency band. Additionally, we thoroughly investigate the factors influencing the mid-low-frequency sound absorption performance of the N-MH structure. Through theoretical prediction, simulation analysis, and experimental testing, it is verified that the N-MH structure has excellent broadband sound absorption characteristics in the frequency interval of 0–2000 Hz, and the percentage of sound absorption bands with absorption coefficients exceeding 0.9 can reach 78.2%.

Sound attenuation analysis of a honeycomb structure with extended necks

In this paper, a honeycomb structure metamaterial consisting of 95 necks that are attached to the perforated top panel is presented and its sound absorption coefficient and transmission loss are investigated using the finite element method. Helmholtz resonators are therefore created by each honeycomb cell (cavity) and the attached neck, which is protruding within each cell. The structure has therefore a high bending stiffness due to the honeycomb mechanical performance and constitutes a sound absorber based on the parallel assembly of multiple Helmholtz resonators. This study demonstrates the importance of properly designing the diameter and the length of each neck to create a broadband sound absorption. One resonant sound absorption peak is observed when all the necks are identical, and two absorption peaks are obtained using two different sets of neck parameters. When the number of different necks increases, the sound absorption frequency band improves and when the parameters of all the necks are different, resulting in a parallel assembly of 95 different Helmholtz resonators, the sound absorption frequency band broadens. The material design studied in this paper can be useful in various applications where available space is limited and high mechanical stiffness and noise reduction are required in one structural element.

Study on the acoustic performance of bending metasurface with ultra-thin broadband quasi-perfect sound absorption

In order to achieve low-frequency broadband noise control under subwavelength thickness, this paper established a theoretical model for calculating the sound absorption coefficient of curled acoustic metasurface (CAM) composed of embedded hole, equal width curled channel, and gradient width curled channel, which is based on the thermal viscosity equivalent model and impedance equivalent model. Considering the over resistance effect caused by multi-unit composite structure, a multi-parameter control strategy was used to design bending acoustic metasurface (BAM) units for perfect sound absorption at four discrete frequencies of 546 Hz, 563 Hz, 585 Hz, and 601 Hz, which is based on the complex frequency plane method. and the thicknesses of these unites are only (1.2 cm). The broadband and efficient sound absorption effect of the four parallel composite BAM units was theoretically studied. The simulation and experiment verified that the composite BAM not only achieved perfect sound absorption at 573 Hz with a subwavelength thickness of 12 mm, but also had an efficient sound absorption(α > 0.8) frequency band of 512Hz-621Hz, with a bandwidth up to 109 Hz. The research in this paper provides a certain theoretical basis for the design of low-frequency broadband compact acoustic structures, and has certain reference value for low-frequency broadband noise control.