Electromagnetic Field Interference Research Articles

Analysis of Electromagnetic Field Characteristics of Wave Glider

A wave glider is an ocean observation platform that utilizes wave energy to drive and solar energy to power. Its metal structure will generate related electromagnetic fields due to corrosion and underwater motion. In the detection of weak electromagnetic field signals underwater, its own electromagnetic field characteristics will have an impact on signal detection. To study the applicability of electric field sensors and magnetic field sensors on wave glider platforms, the structural characteristics of the wave glider were analyzed, and the installation positions of electric field sensors and magnetic field sensors were designed based on the different motion states of the water surface mother body and underwater towing body. The measured electromagnetic field data of the wave glider platform were measured, and the measured data were analyzed. It was determined that the interference electric field energy under typical working conditions of the wave glider was mainly concentrated within 1 Hz, which decreased with increasing frequency, and the magnitude was mV/m. The magnitude of the interference magnetic field is several tens of nT, indicating that the electromagnetic field interference is significant during the working state of the wave glider. Installing an electric field sensor directly at the bottom of the wave glider will cause significant noise interference, while installing the magnetic field sensor directly at the bottom of the tractor will affect the servo and the shaking-induced magnetic field. Moreover, wave gliders should not use electric field signals below 1 Hz as signal sources, but they can utilize axial frequency electromagnetic fields to detect weak electromagnetic signals underwater.

Research on explosive electromagnetic field interference analysis based on field-circuit cooperated modeling and simulation

Research on explosive electromagnetic field interference analysis based on field-circuit cooperated modeling and simulation

Lightweight HfC nanowire-carbon fiber/graphene aerogel composites for high-efficiency electromagnetic interference shielding

Electromagnetic interference (EMI) and pollution triggered by electromagnetic waves are becoming a severe issue with the rapid development of various e-devices. Developing low-density and high-efficiency electromagnetic shielding materials is of great importance. Carbon aerogel materials have received worldwide attention due to their significant electromagnetic interference shielding properties and physicochemical stability. Herein, lightweight hafnium carbide nanowire (HfCnw)-carbon fiber (CF)/graphene aerogel (GA) composites with excellent electromagnetic shielding performance were fabricated by successively introducing CF via hydrothermal process, pyrolytic carbon (PyC) coating via chemical vapor infiltration (CVI), and HfCnw via catalytic chemical vapor deposition (CCVD) into GA. It was found that the electrical conductivity of the HfCnw-CF/GA composites with the HfCnw growth time of 4 h reached 94.0 S/cm, which was far higher than 1.1 S/cm of pristine GA and 2.7 S/cm of the CF/GA composites. The EMI shielding effectiveness (SE) of the HfCnw-CF/GA composites was as high as 66.4 dB in the X-band, which was 3 times that (25.4 dB) for GA and 1.5 times that (45.8 dB) for the CF/GA composites. The EMI shielding performance of the HfCnw-CF/GA composites was improved mainly due to the enhanced multiple reflection loss, conductance loss, and interfacial polarization loss. Moreover, the HfCnw-CF/GA composites had a specific SE (SSE) value of 364.1 dB cm3/g, which exhibits good application prospects in the EMI field to meet the needs for light weight and high SE.

A Simplified Method for the Preparation of Highly Conductive and Flexible Silk Nanofibrils/MXene Membrane.

Silk nanofibers (SNF) have great applications in high-performance functional nanocomposites due to their excellent mechanical properties, biocompatibility, and degradability. However, the preparation of SNF by traditional methods often requires the use of some environmentally harmful or toxic reagents, limiting its application in green chemistry. In this paper, we successfully prepared SNF using natural silk as raw material and solvent stripping technology by adjusting the solvent concentration and solution ratio (the diameter of about 120 nm). Using the above SNFs as raw materials, SNF membranes were prepared by vacuum filtration technology. In addition, we prepared an SNF/MXene nanocomposite material with excellent humidity sensitivity by simply coating MXene nanosheets with silk fibers. The conductivity of the material can approach 1400.6 S m-1 with excellent mechanical strength (51.34 MPa). The SNF/MXene nanocomposite material with high mechanical properties, high conductivity, and green degradability can be potentially applied in the field of electromagnetic interference (EMI) shielding, providing a feasible approach for the development of functional nanocomposite materials.

Path optimizing of UAV inspection for 500kV AC transmission line cup-tower based on ant colony algorithm

To ensure unmanned aerial vehicles (UAVs) complete the inspection task of a high-voltage transmission line safely and effectively, it is necessary to consider the interference of a complicated electromagnetic field near a high-voltage transmission line and determine a reasonable inspection distance and path of the UAV. Taking the 500kV EHV AC power line as an instance, firstly, the three-dimensional model of the 500kV ZV1 cup-tower is built, and the finite element method (FEM) is used for computing the electric field and magnetic field of the UAV exterior. According to inspection specifications, the electromagnetic field protection threshold of the UAV is determined, and then the safety area between UAV and the split conductor is determined to be equal to 1.5 m. Combined with the UAV shooting field of view and safety distance, the spatial positions of UAV hovering shooting points are selected to ensure that UAV flies in a safe area. Finally, the path of UAV traversing hovering shooting points is optimized by the ant colony algorithm (ACO), and the optimal path distance is 109.4 m.

Modulus matching strategy of ultra-soft electrically conductive silicone composites for high performance electromagnetic interference shielding

Electrically conductive silicone composites have made significant advancements in the field of electromagnetic interference (EMI) shielding due to their excellent conductivity, elasticity, sealability and environmental reliability. Notably, chips and other miniature electronic components with limited pressure-bearing capacity often require composites with both low compressive stress and high EMI shielding performance. Unfortunately, conventional conductive silicone composites often exhibit high compressive stress as a result of the high modulus and high loading contents of fillers, which prevents them from fitting perfectly with the package cavity under low package stress conditions, resulting in inadequate EMI shielding. Herein, the elastic modulus of the silver@polydimethylsiloxane (Ag@PDMS) conductive filler can be adjusted by controlling the crosslinking ratio, which enables the creation-of-Ag@PDMS/Silicone-(APS)-conductive-composites-with-remarkable compressibility, EMI shielding and sealing capabilities. The-APS-composites exhibit a compressive stress of only 0.3 MPa under 50 % compressive strain, which is essential for the packaging-of-precision electronic components. The APS composites show a significant decrease in compressive stress (54 %) and elastic modulus (80 %) under 50 % compressive strain, in comparison to conventional polymer composites with hard fillers. Meanwhile, the APS composites exhibit a-satisfactory-EMI-shielding-effectiveness-(SE)-of-71-dB and demonstrate excellent electromagnetic sealing capabilities in practical electronics. This study provides an effective approach for developing and constructing high-performance ultra-soft composites for precision electronic components packaging.

Large‐Scale Ultralight and Flexible Metal Foil/Polymer Sandwich Composites with Excellent Electromagnetic Interference Shielding

AbstractMetal materials play an important role in electromagnetic interference (EMI) shielding due to their ultra‐high electrical conductivity, but they are rigid and inflexible, as well as of high density, which limits their application in some areas. In this study, a novel and simple method to fabricate the composites of metal foil and polymer is reported. A copper foil (Cuf) with micropores on the surface is used as a shielding matrix, then interpenetrating and interlocking nanostructure as well as reactive groups are introduced on its surface, and then silicone rubber (SiR) is coated on both surfaces to form a sandwich structure, and the obtained Cuf/SiR composites possesses high EMI shielding efficiency (SE), strong interface adhesion, and low density. The average EMI shielding efficiency of the obtained Cuf/SiR composites in the range of 1.13–18 GHz is 111.5 dB, with a high interface adhesion strength of 5.2 N cm−1 and low density of 1.3 g cm−3, and it also possesses bending and splicing properties, which exhibits broad potential application in the field of EMI shielding tents and shielding rooms. This preparation method of the composites is simple and efficient, and provides a guideline for the design and fabrication of metal foil/polymer composites in molding method.

Fabrication of Flexible FCI/PDMS Electromagnetic Shielding Composites Based on Pulsed Magnetic Field-Induced Alignment

Conductive polymer composites have been utilized in the field of electromagnetic interference (EMI) shielding, albeit requiring a high concentration of conductive fillers to achieve desirable EMI performance. To address this issue and enable the creation of superior EMI shielding composites with reduced filler loadings, this study employed a pulsed magnetic field featuring an amplitude of 0.7 T, a pulse width of 10 μs, and a frequency of 100 Hz to align flaky carbonyl iron (FCI) in poly(dimethylsiloxane) (PDMS). This method resulted in an improved EMI shielding performance of the composites. The outcomes revealed that the pulsed magnetic field effectively controlled the orientation of the FCI, forming a conductive network structure, with the average orientation angle of the FCI reaching 69.3°. The aligned composites exhibited a significant improvement in EMI shielding effectiveness, with the enhancement effect reaching 37.53% and the EMI shielding effectiveness reaching 24.87 dB. Moreover, the flexible tensile properties of the aligned composites were superior to those of the unaligned composites, particularly the elongation at break, which reached 197.46%. The concordance between the theoretical analysis and experimental results affirms the efficacy of the microsecond pulsed magnetic field in enhancing the EMI shielding performance of composite materials. Ultimately, the high-performance, flexible electromagnetic shielding composite materials prepared in this study demonstrate potential for use in advanced electronic equipment.

On-Chip Mirror Enhanced Multiphoton Upconversion Super-Resolution Microscopy

Multiphoton upconversion super-resolution microscopy (MPUM) is a promising imaging modality, which can provide increased resolution and penetration depth by using nonlinear near-infrared emission light through the so-called transparent biological window. However, a high excitation power is needed to achieve emission saturation, which increases phototoxicity. Here, we present an approach to realize the nonlinear saturation emission under a low excitation power by a simply designed on-chip mirror. The interference of the local electromagnetic field can easily confine the point spread function to a specific area to increase the excitation efficiency, which enables emission saturation under a lower excitation power. With no additional complexity, the mirror assists to decrease the excitation power by 10-fold and facilities the achievement of a lateral resolution around 35 nm, 1/28th of the excitation wavelength, in imaging of a single nanoparticle on-chip. This method offers a simple solution for super-resolution enhancement by a predesigned on-chip device.

Multifunctional shape memory foam composites integrated with tunable electromagnetic interference shielding and sensing

Porous polymer-based conductive composites are highly regarded for their accomplishments of being applied in the field of electromagnetic interference (EMI) shielding, but fabrication of high-performance porous EMI shielding materials with the ability to realize self-fixable shielding effectiveness (SE) adjustment is still challenging. Herein, ethylene–vinyl acetate copolymer (EVA)@polypyrrole (PPy)@Ag (EPA) foam composites are fabricated by modifying EVA foams with PPy and Ag nanoparticles (AgNPs) in succession. In this system, EVA foam serves as shape memory frameworks to endow this composite with shape memory effect (SME), and PPy is employed to reinforce the interaction between the Ag layers and the EVA foam. Profiting from the reinforced conductive network, the EPA foam composites exhibit electro-thermal performance with a heating temperature of 81.1 °C at a voltage of 1 V and EMI shielding performance with a SE of 107.45 dB within the X-band. Importantly, depending on the SME, the SE of the EPA foams can be easily tuned by controlling and fixing the compressive strain. Moreover, the EPA foams can also serve as sensors for monitoring different actions. By virtue of the above merits, the EPA foams are promising to serve as multifunctional electronics, involving smart EM protection devices and wearable sensors.

Graphene/carbon nanotube/polypyrrole composite films for electromagnetic interference shielding

AbstractPolypyrrole (PPy), an ideal organic electroactive material, shows limited application in the field of electromagnetic interference (EMI) shielding for its relatively low shielding effectiveness (SE), significant stiffness, difficult solubility, and poor processing performance. A strategy is proposed to construct three‐dimensional network structures of graphene/CNT/polypyrrole by electrochemical deposition to improve the EMI SE of polypyrrole composite films. In the graphene/CNT/polypyrrole films, the graphene/CNT substrates form the skeletons, and polypyrrole acts as bridges between graphene sheets and CNTs to form percolation networks in the multiphase and multihierarchical nanocomposites. When the deposition time increases to 80 min, the content of polypyrrole increases to 30 wt%, the conductivity improves by 27.7%, and the EMI SE improves by 11.4% at X‐band. The final film thickness is 249 μm, the conductivity is 3.06 S/mm, and the average EMI SE is 59.6 dB.

Polyvinylidene fluoride—An advanced smart polymer for electromagnetic interference shielding applications—A novel review

AbstractEmerging technology and modernization have become a worldwide threat to human life in all aspects. Worldwide, all countries are in the race to develop the most advanced electronic devices and gadgets as they reflect the country's superiority and economic development. Specialists have forecasted that during and after the pandemic, the addiction toward modern gadgets have increased by 40% among the people irrespective of age. A few researchers have reported that the world economy is dependent on and dominated by countries manufacturing semiconductors, mobiles, electronic chips, and so on. People started sensing that modern devices are like a boon, as their lives seem to be more connected and comfortable with all their needs and wants being fulfilled at their doorsteps. But this boon is slowly whirling as a severe threat to human lives. Due to this rapid usage of electronic devices, electromagnetic interference (EMI) is drastically growing, which is considered a global warning issue for commercial and biological systems. So advanced countries have decided to make EMI shielding a compulsory entity to be implemented in all advanced electronic devices. Though traditional materials like metals and carbon allotropes have excellent shielding properties, they cannot cope with today's mass production of modern devices. Thus, researchers had to find a suitable substitute material that should possess properties such as sustainability and biocompatibility to overcome problems faced by the conventional materials. Thus, polymers have come into the world of EMI shielding applications. Polyvinylidene fluoride (PVDF), a non‐conductive polymer from the family of Fluorocarbons, is creating history in the field of EMI shielding applications. PVDF astonished researchers with its versatile features, such as light weight, flexibility, and easy processibility with excellent dielectric and piezoelectric properties. Though they are poor in electrically conductive properties, incorporating metals, carbon allotropes, and metal oxides as fillers make them superior to the existing conventional materials. Thus, the main objective of this review article is to highlight the uniqueness of PVDF as an advanced polymer for EMI shielding applications. It has been noted that PVDF is more suitable for EMI shielding in X, K, and Ku band frequencies. But overall, we noticed that the performance of PVDF has a great impact by incorporating a combination of metal and carbon allotrope enhances the shielding effectiveness up to 65 dB in the Ku‐band (Kurz‐under) frequency band range of (12–18 GHz).

Ultrathin Wood‐Derived Conductive Carbon Composite Film for Electromagnetic Shielding and Electric Heating Management

AbstractRecently, wood‐based composites have absorbed widespread concern in the field of electromagnetic interference (EMI) shielding due to their sustainability and inherent layered porous structure. The channel structure of wood is often used to load highly conductive materials to improve the EMI shielding performance of wood‐based composites. However, there is little research on how to use pure wood to prepare ultrathin EMI shielding materials. Herein, ultrathin veneer is obtained by cutting wood in parallel to the annual rings. Then, carbonized wood film (CWF) is prepared by a simple two‐step compressing and carbonization. The specific EMI shielding effectiveness (SSE/t) of CWF‐1200 with an ultrathin thickness (140 µm) and high electrical conductivity (58 S cm−1) can reach 9861.41 dB cm2 g−1, which is much higher than other reported wood‐based materials. In addition, the zeolitie imidazolate framework‐8 (ZIF‐8) nanocrystals are grown in situ on the surface of the CWF to obtain CWF/ZIF‐8. CWF/ZIF‐8 exhibits an EMI shielding effectiveness (SE) of up to 46 dB and an ultrahigh SSE/t value of 11 330.04 dB cm2 g−1 in X band. In addition, the ultrathin CWF also shows an excellent Joule heating effect. Therefore, the development of ultrathin wood‐based film provides a research basis for wood biomass to replace traditional non‐renewable and expensive electromagnetic (EM) shielding materials.

Effects of pore structure on wide-frequency electromagnetic interference shielding performance of carbonized wood

Carbonized wood attracts widespread attention in the field of electromagnetic interference (EMI) shielding thanks to its layered porous structure and high electrical conductivity. Understanding the correlation between pore structure and shielding performance is crucial for constructing efficient EMI shielding materials. Herein, pore structures are monitored by changing the compression ratio during the hot pressing. Carbonized wood with a 40% compression ratio displays a superior EMI shielding effectiveness (SE) up to 71.69 dB in K-band, owing to the optimal structure. EMI shielding characteristics of carbonized wood in different frequency ranges are also studied. The effects of pore structure on the shielding performance are further illuminated by finite element analysis. After structure optimization, carbonized wood can demonstrate high EMI shielding performance, wide-frequency coverage, terahertz band use, and excellent heat dissipation. This work inspires the design of next-generation sustainable EMI shielding materials.

Oscillations in radiative damping of plasma resonances in a gated disk of a two-dimensional electron gas

We calculate the absorption spectra of a conductive disk in the presence of a metal gate. In our analysis, we use the conductivity described by the Drude model. We examine the frequency and line width of the absorption resonances associated with the excited plasma waves. They are estimated both numerically and analytically for the fundamental and axisymmetric plasma modes. The line width is determined by the collisional and radiative losses. In high mobility samples, the latter may dominate even when the resonant frequencies can be described by a standard quasistatic approximation, i.e., neglecting electromagnetic retardation. Placing a metal near the disk drastically affects the radiative broadening of the line width due to the interference of electromagnetic fields created by the disk and the metal charges. Bringing the disk in close proximity to the gate makes the total field almost vanish. In that case, the line width is defined solely by the collisional broadening. As the disk is moved away from the gate, the line width first shows a reduction since the plasmon transforms into plasmon-polariton, which is dressed with undamped electromagnetic field surrounding the disk. Then it increases and exhibits decaying oscillations, reaching the asymptotic value of the ungated disk.

Temperature‐ and Ambient Pressure‐Independent Sensing of Hydrogen in Fluids Using Cascaded Interferometers Incorporated in Optical Fibers

AbstractPractical gas sensors are indispensable for the healthy operation of cutting‐edge hydrogen‐based systems. An optical fiber‐based hydrogen sensor incorporating a robust Fabry–Perot interferometric structure on a fiber tip with high sensitivity, selectivity, and reliability of operation and a micrometer‐scale footprint is demonstrated. The hydrogen‐sensitive volume expansion of palladium provides bi‐metal operation with a silicon nitride mirror to tune the interferometer cavity and therefore the resonance modes by switching the mirror form factor from a flat to convex shape. It does not require any peripherals, including a power supply or data communication modules. In addition to fiber‐inherent advantages, such as remote and multiplexed monitoring without electromagnetic field interference, the sensor guarantees temperature‐ and pressure‐independent operation by adding a simple glass sub‐cavity and microwindows in the mirror layer, respectively. Critically, the sensor highlights reliable operation in a liquid fluid (electrical transformer oil) to monitor hydrogen as its “damage marker” escaping from a mechanical shield or selective gas screen. The detection limit, sensitivity, and response time of the sensor under atmospheric conditions are 15 ppm, 29.6 nm/%, and 12.5 s, respectively. In addition, the unimpaired operation of the sensor in 60 °C transformer oil is verified experimentally.

A double crosslinking MXene/cellulose nanofiber layered film for improving mechanical properties and stable electromagnetic interference shielding performance

With the discovery of the two-dimensional (2D) MXene, it shows a great application potential in the field of electromagnetic interference (EMI) shielding, but the mechanical brittleness and easy oxidation of MXene limit its wide application. For this reason, a double crosslinking strategy is provided to solve the above problems in a nacre-like “brick-mortar” layered MXene/cellulose nanofiber (MXene/CNF) film. Typically, the film was firstly suffered by dopamine modification, then was further reinforced by secondary Ca2+ bridging, so as to obtain excellent mechanical properties and antioxidative EMI shielding performance. Comparing with the single crosslinking, the double crosslinking strategy reveals a higher efficiency in improving the mechanical property. The mechanical strength and toughness of the double crosslinking MXene/CNF film can increase to 142.2 MPa and 9.48 MJ/m3, respectively. More importantly, while achieving good mechanical properties, the MXene composite film still holds a very stable EMI shielding performance of more than 44.6 dB when suffering from the oxidation treatment of high-temperature annealing, showing excellent anti-oxidation ability and environment tolerance. Therefore, this work provides a universal but effective double crosslinking strategy to solve the mechanical brittleness and easy oxidation of MXene-based composites, thus showing a huge potential in flexible EMI shielding applications.

Fabrication technology and performance tests for optical fiber-encapsulated, high-temperature superconducting tapes

Realizing fast and accurate quench detection is a great challenge for the application of long high-temperature superconducting (HTS) conductors. The combination of a distributed temperature sensing (DTS) system and optical fiber-encapsulated HTS (OFE-HTS) tape may become a promising approach to solve this problem. As a recently proposed composite HTS tape, its properties have not been studied systematically yet. Therefore, in this study, the electromagnetic and thermal behaviors of the OFE-HTS and traditional HTS tapes are compared by finite element simulation technology. The simulation results predict that the embedded optical fibers will hardly change the original electric, magnetic and thermal characteristics of the HTS tapes. In addition, a detailed fabrication method for OFE-HTS tape is introduced, and the composite tape performances including structural integrity, critical current uniformity, anti-bending/tensile force and quench response are tested seriatim. According to the microscope and x-ray detection results, the optical fibers are fully embedded in the OFE-HTS tape through the presented fabrication process. The critical current uniformity test results show the average critical current of the prepared 76 m long OFE-HTS tape is about 520 A, and the uniformity variation is about ±4%. The prepared OFE-HTS and traditional tapes have similar anti-bending/tensile properties. Finally, to check the effectiveness of the embedded optical fiber for quench detection, the fabricated OFE-HTS coil is tested. The quench detection results show that the temperatures in the same area measured by the optimized DTS system and a thermocouple are similar. Moreover, the temperature response ability of the optimized DTS system is better than that of the thermocouples, and the optimized DTS system is able to effectively avoid environmental electromagnetic field interference.

Regulating bifunctional flower-like NiFe2O4/graphene for green EMI shielding and lithium ion storage

• A novel flower-like composite with adjustable structure is fabricated. • The composite is a potential and adjustable green EMI shielding material. • Fast energy storage and long-cycle stability under high current density are realized. • The composite achieves EM energy conversion-storage and lithium ion energy storage. Environment and energy are the eternal hot topics in the world, multiloculated microscale materials have attracted great attention in the field of electromagnetic interference (EMI) shielding and lithium ions storage. Herein, a novel flower-like NiFe 2 O 4 /graphene composite with adjustable structure was fabricated as EMI shielding material and anode material of lithium-ion batteries. NiFe 2 O 4 /graphene composite is a potential green EMI shielding material. The EMI shielding effectiveness ( SE ) increases with the increase of graphene content in NiFe 2 O 4 /graphene composite, and the total EMI SE of NiFe 2 O 4 /graphene with 73.6 wt.% graphene increases from 26.5 to 40.6 dB with the increase of frequency in 2–18 GHz. Furthermore, it exhibits long-life and large capacity lithium storage performance at high current density. The capacity reaches 732.79 mAh g −1 after 100 cycles at 0.1 A g −1 , recovering to more than 139% from the minimum capacity value. After 300 cycles at 0.5 A g −1 , the capacity increases to 688.5 mAh g −1 . The initial capacities at 2 and 5 A g −1 are 704.9 and 717.8 mAh g −1 , and remain 297.9 and 203.2 mAh g −1 after 1000 cycles. The distinguished EMI shielding performance and electrochemical performance are mainly ascribed to the structure regulation of NiFe 2 O 4 /graphene composite, as well as the synergistic effect of graphene and NiFe 2 O 4 . This research opens up infinite opportunities for the application of multifunctional and interdisciplinary materials.

An RF Amplifier Circuit for Enhancement of Echo Signal Detection in Bathymetric LiDAR

The echo signal from the water bottom in bathymetric light detection and ranging (LiDAR) onboard unmanned boat is very weak. As a result, the signal’s amplitude cannot be resampled using an analog-to-digital (AD) sampling module after being detected by the photomultiplier tube (PMT). In addition, the traditional methods, which adopt the trans-impedance circuit, cannot provide sufficient gain and bandwidth, resulting in incorrect detection of echo signals. For the reasons above, this article presents an radio frequency (RF) amplifier circuit for signal amplification, in which a dc paranoid network associated with a matching circuit is used to ensure the stable operation of the circuit; the ac-coupled and low-noise voltage stabilizers are adopted to ensure a low-noise signal output; the shielding is adopted to suppress the interference of electromagnetic fields and static electricity. The validations are conducted in indoor and outdoor laboratories, including a simulated amplitude and bandwidth using a signal generator in the indoor laboratory, the water tank, the test well, the pond, and the pool. The experimental results show that the proposed RF amplifier circuit can amply the gain of 25.31 dB when using a signal generator in the bandwidth range of 500 MHz, 650 MHz, and 800 MHz; 1 GHz; and 34.63, 31.62, and 25.78 dB under the experiments in the water tank, in the test well, and in the pond when the PMT control voltages are 0.4, 0.5, and 0.7 V, respectively, and amplify the echo signals to 451–568 mV under the bandwidth of 500 MHz.