High Static Stiffness Research Articles

Optimization method of vibration isolation performance of the 6DOF vibration isolation platform based on different configurations

The configuration optimization methods are developed to design the six degree of freedom (6DOF) passive vibration isolation platform with superior isolation performance. According to different position arrangements, various configuration vibration isolation platforms, including the 33 type, 63 type, 66–1 type, and 66–2 type, are designed and systematically analyzed. Through analysis of the geometric characteristics of the configuration platforms, the nonlinear dynamical equations for each configuration vibration isolation platform are established using Hamilton's principle. Utilizing the transmission rate as an evaluation index, the isolation performance of each platform in six directions (three translational and three rotational) is systematically studied. The results indicate that: (a) Through the comparative analysis of different configuration vibration isolation platforms, it can be found that the 66–1 configuration not only has the largest loading capacity but also owns the best isolation performance in the x, y, and γ directions. The 33 configuration has better isolation performance in the z, α, and β directions, while having greater loading capacity; (b) Through configuration optimization, a 6DOF vibration isolation platform can be obtained with high static stiffness in the vertical direction and low dynamic stiffness in other external excitation directions. This kind of HSLDS characteristics will significantly enhance the isolation performance of the vibration isolation platform; (c) Workspace analysis under different configurations reveals that the 66–1 configuration offers the largest workspace in all six directions, followed by the 63 configuration, while the workspaces of the 33 and 66–2 configurations are similar.

Nonlinear static and dynamic response of a metastructure exhibiting quasi-zero-stiffness characteristics for vibration control: an experimental validation

This work introduces a novel metastructure designed for quasi-zero-stiffness (QZS) properties based on the High Static and Low Dynamic Stiffness mechanism. The metastructure consists of four-unit cells arranged in parallel, each incorporating inclined beams and semicircular arches. Under vertical compression, the inclined beams exhibit buckling and snap-through behavior, contributing negative stiffness, while the semicircular arches provide positive stiffness through bending-dominated behavior. The design procedure to achieve QZS is established and validated through finite element analysis and experimental investigations. The static analysis confirms a QZS region for specific displacement. Dynamic behavior is analyzed using a nonlinear dynamic equation solved using the Harmonic Balance Method, validated experimentally with transmissibility curves showing sudden jump down with effective vibration isolation. Parametric studies with varied payload masses and excitation amplitudes further verify the ability to of metastructure to attenuate vibrations effectively in low-frequency ranges.

Vibration isolation performance of silica aerogel blankets and boards, fumed silica, polymer aerogel and nanofoams

Buildings are often constructed on a continuous layer of vibration isolation to reduce vibrations and structure-borne noise. There are many vibration isolation products (rubber mats, textiles, polymer foams), but none fulfils all requirements in terms of load-bearing capacity, performance, and cost. In previous work, we have shown that silica aerogel particle beds display a low resonance frequency and correspondingly high vibration isolation performance. Loose silica aerogel granules are not a practical vibration isolation solution. In order to guide the future development of dedicated vibration isolation products based on aerogels, we determine the vibro-acoustic properties of a variety of existing commercial and R&D stage mesoporous composites, that have been developed for thermal insulation applications. The sample set includes monolithic aerogels (polyurethane), silica aerogel composites (aerogel – fibers, aerogel impregnated foams, aerogel bound with polymer foam), glued fumed silica-fiber boards, and nanoporous polymer foam composite boards. The silica aerogel and fumed silica composites display low resonance frequencies (down to 8 Hz for 40 mm, strongly dependent on composite type) and a low dynamic stiffness and loss factor over a wide range of static loads. The polymer aerogel, nanoporous foam and polymer-bound silica aerogel granule board all display higher resonance frequencies, consistent with their higher static stiffness. Although optimized for thermal insulation rather than vibration isolation, many of the tested silica aerogel and fumed silica composites are competitive with the best vibration isolation products on the market in terms of vibration isolation performance. The diversity of materials tested informs on which approaches, materials, and materials combinations are most promising to target vibration isolation.

Wide quasi-zero stiffness region isolator with decoupled high static and low dynamic stiffness

Quasi-zero stiffness (QZS) isolators can achieve the two goals of relatively high static and low dynamic stiffness (HSLDS). However, the static and dynamic stiffness of most QZS isolators remains coupled, causing conflicts in optimizing these dual objectives, especially in the case of large displacement excitations and heavy loads, leading to limited performance. To overcome these limitations, this paper presents an isolator with an extended QZS region that allows for the independent design of HSLDS. The positive stiffness provided by the cantilever beam with curve fixture (CBCF) precisely counteracts the negative stiffness offered by a pair of inclined springs, thereby achieving continuous and extensive QZS characteristics from a point to a region. Dynamic equations are established based on the Lagrangian principle and swiftly solved utilizing the Runge-Kutta-4 method. The proposed isolator exhibits a low resonance frequency, and superior performance when exposed to large displacement excitations compared to alternative isolators. Both static and dynamic experiments confirm a QZS region of 0.023 m and resonance frequencies of below 1 Hz. The proposed isolator facilitates effective vibration isolation for ultra-low-frequency and large displacement excitations.

Mechanical characteristics analysis of high dimensional vibration isolation systems based on high-static-low-dynamic stiffness technology

Large floating raft vibration isolation systems (FRVISs) based on high-static-low-dynamic stiffness (HSLDS) technology offer excellent low frequency vibration isolation performance with broad application prospects. However, the design process for these complex high-dimensional coupled nonlinear systems remains poorly developed, particularly when applied for ocean-going vessels that experience rolling and pitching motions. The present work addresses this issue by establishing a six-degree-of-freedom HSLDS vibration isolation model for FRVISs composed of eight isolators, and the model is applied to fully analyze the swing stability and multidimensional vibration isolation performance of these systems. The influence of nonlinearity on the mechanical properties of the vibration isolators is analyzed more clearly by assuming that each vibration isolator realizes nonlinear HSLDS characteristics in the z direction and linear characteristics in the x and y directions. The results demonstrate that the swing displacement responses of the system are greatly reduced under weak nonlinearity, which reflects the high static stiffness and high static stability characteristics of an HSLDS system. The multidimensional vibration isolation performance of the system is evaluated according to the impacts of nonlinearity, the installation height Hz of the isolators, and the relative position Dr of the two middle isolators. The results of analysis demonstrate that applying a value of Hz = 0 produces the best vibration isolation performance overall under strong nonlinearity by avoiding unnecessary secondary peaks in the force transmission rate under harmonic mechanical excitation and ensuring a maximum high-frequency vibration isolation effect. However, applying a weak nonlinearity is better than a strong nonlinearity if Hz is not zero. In contrast, Dr has little effect on the vibration isolation effect of the raft in the x, y, and z directions. Therefore, an equidistant installation with Dr = 0.5 would be considered ideal from the standpoint of installation stability.

Tunable stiffness design of curved-crease origami and extended quasi-zero stiffness vibration isolator

A kind of origami tube based on the curved crease, which has a tunable stiffness, was designed, fabricated, tested, and extended to the concept of a quasi-zero stiffness (QZS) vibration isolator. The regulating function of crease stiffness on the overall origami stiffness without changes in the crease pattern was verified by single-crease models. With various opening ratios along the creases, three tubes composed of mirrored single-crease origami were designed, fabricated by 3D printing, and compressively tested. The test results present the potential of the approach of QZS. Further, the elastic-frictionless origami tubes were redesigned and simulated to obtain the target stiffness. The cubic term fitting of the load curve was adopted by the harmonic balance method to solve the steady-state vibration response, and then the simulation results obtained by the finite element method (FEM) were compared. The study shows that the designed elastic-frictionless isolator has a good low-frequency vibration isolation performance. The concept of the simple stiffness control method of curved-crease origami provides more practice options for high static and low dynamic stiffness systems.

The dynamic properties and performance of the bellows-type hydraulic inerter-based dynamic anti-resonance vibration isolator

Aiming to effectively isolate disturbance vibrations for heavy machines with low frequencies, a novel bellows-type hydraulic inerter-based dynamic anti-resonance vibration isolation (I-DAVI) isolator is proposed, which consists of a primary supporting bellows container and an additional inerter subsystem comprising horizontal bellows and inertial mass, and the incompressible oil liquid is filled in the vacuum of both bellows as the working medium. First of all, the mathematic model of the presented I-DAVI device is established, and then the vibration transmissibility for the systems under force excitation and motion excitation are derived. The relevant results indicate that the anti-resonance appears at specific frequency, creating near-zero energy transmission and significantly reducing vibration transmission to the base or machines. Through the nondimensionalization analysis, the four parameters including the inertial mass ratio, damping ratio, ratio of effective cross-section areas, and number of the inerter subsystem completely dominate the isolation characteristics of the proposed device. Subsequently, a comparison study is carried out between systems with and without inertial mass located at the end of the additional horizontal bellows, and furthermore the operating mechanism of the I-DAVI is explained clearly. It is proven that the inerter-based DAVI isolator exhibits high static and low dynamic stiffness characteristics, which cause the resonance frequency of the isolation system to shift toward lower frequency without changing the static bearing stiffness and also reduce the peak value of the transmissibility. The further numerical simulation verifies that the optimal isolation effectiveness at the anti-resonance frequency is attributed to the dynamic equilibrium between the elastic restoring force of the primary bellows and the internal hydraulic pressure. In practice, the bellows-type hydraulic inerter-based I-DAVI isolator device investigated in this study is suitable for machines with the narrowband low-frequency vibration, such as the marine turbines.

Atomic resolution imaging using a novel, compact and stiff scanning tunnelling microscope in cryogen-free superconducting magnet.

We present the design and performance of a novel scanning tunnelling microscope (STM) operating in a cryogen-free superconducting magnet. Our home-built STM head is compact (51.5mm long and 20mm in diameter) and has a single arm that provides complete openness in the scanning area between the tip and sample. The STM head consists of two piezoelectric tubes (PTs), a piezoelectric scanning tube (PST) mounted on a well-polished zirconia shaft, and a large PT housed in a sapphire tube called the motor tube. The main body of the STM head is made of tantalum. In this design, we fixed the sapphire tube to the frame with screws so that the tube's position can be changed quickly. To analyse the stiffness of the STM head unit, we identified the lowest eigenfrequencies with 3 and 4kHz in the bending modes, 8kHz in a torsional mode, and 9kHz in a longitudinal mode by finite element analysis, and also measured the low drift rates in the X-Y plane and in the Z direction. The high performance of the home-built STM was demonstrated by images of the hexagonal graphite lattice at 300 K and in a sweeping magnetic field from 0 T to 9 T. Our results confirm the high stability, vibration resistance, insensitivity to high magnetic fields and the application potential of our newly developed STM for the investigation of low-frequency systems with high static support stiffness in physics, chemistry, material and biological sciences.

Kinematics design and statics analysis of novel 6-DOF passive vibration isolator with S-shaped legs based on Stewart platform

Optical payloads are widely used in many fields, such as aerospace, drones, autonomous vehicles, or other highly precise instrumentation. Vibration is one of the causes that greatly affect the quality of data of highly precise optical payloads. Recently, many researcher focuses on isolating the vibration for the precise equipment, those study just only mention the overcoming of vibration in one or two directions, but in reality, an object will exist vibration in six directions in space. Therefore, it is necessary to find a new mechanism that can isolate vibration in six axes in space. The parallel mechanism is considered a viable system because of its strengths in accuracy, rigidity, and stability. In this research, the author proposes a novel 6-DOF passive vibration isolator based on the Steward platform with S-shaped legs. We have developed a 6-DOF passive vibration isolator using the S-shaped non-linear stiffness and damping characteristics. In this study, the model parameters of a vibration isolator device with legs using an S-shaped will be proposed. Based on geometrical parameters and vibration sources and some loads assuming the structure's durability problem will be calculated and evaluated the efficiency of the isolator at different frequencies. With the specially designed S-shaped it can be deformity like a spring, and with the change of structural and material parameters, we can adjust the system's stiffness and damping capacity. Due to the high static stiffness and low dynamic stiffness of each leg, and thus it is designable to isolate very well vibration isolation performance in all six directions. This research is organized as firstly the kinematics and 3D model are introduced. Secondly, the stiffness matrix of the novel 6-DOF passive vibration isolators is presented. Statics analysis of the 6-DOF passive vibration isolators revealed that the S-shaped structure provides sufficient load-carrying capacity and isolation due to its very good static nonlinear stiffness. The dynamic stiffness of the isolator in this study in each direction is very low but does not reduce the load-carrying capacity of the structure. By changing the structure and material parameters (which is very simple in a purely passive manner), we can completely adjust both the dynamic and static stiffness of the mechanism. The last series of numerical simulation results on displacement and a statics response in random excitation is carried out to show the effectiveness of the proposed 6-DOF passive vibration isolator, as well as the influence of structural parameters on vibration attenuation performance. The simulation results with the different exciting are shown to demonstrate the efficiency of the 6-DOF passive vibration isolators. Considering its simulation results A proposed new 6-DOF isolator will be applied in various engineering practices with multi-degree of freedom vibration isolation such as for precise optical payloads.

Quasi-zero stiffness interval optimization design and dynamics analysis of a new bi-directional horizontal isolation system

The quasi-Zero Stiffness (QZS) isolation system is a typical nonlinear isolation system, which has high static stiffness characteristics to improve the bearing capacity and deformation resistance, and its low dynamic stiffness characteristics can reduce the inherent frequency of the system to realize a wider vibration isolation frequency band, so it has a more excellent low-frequency vibration isolation performance compared with the linear system. In this paper, a horizontal QZS isolator is constructed based on a pre-compressed oblique spring system, and two sets of the horizontal QZS isolators are mechanically assembled to work together to achieve a bi-directional horizontal QZS isolation system. Considering that the construction of two sets of horizontal vibration isolators is approximately the same, we focus on one of the isolators for the static analysis and derive the parameter conditions to be satisfied for achieving quasi-zero stiffness characteristics. We considered the effect of each adjustable parameter of the horizontal vibration isolator on the mechanical performance of the QZS system, and sought to optimize the QZS interval to improve the vibration isolation performance. A comparative study of the dynamical properties between the QZS system with ordinary and optimized parameters, as well as the equivalent linear system, is further carried out by means of nonlinear approximate analysis. Finally, the dynamic characteristics of the bi-directional horizontal QZS system and the equivalent linear system are compared by shaker tests on the prototype device, which proved the excellent vibration isolation performance of the proposed QZS isolation system.

Parametric study of the axial force and negative stiffness of an electromagnetic mechanism for vibration isolation applications

Nonlinear vibration isolators that take advantage of negative stiffness elements can provide high static stiffness to bear high static loads and quasi-zero dynamic stiffness to widen the isolation frequency band and hence are desirable for vibration isolation. Electromagnetic negative stiffness elements can be used to design and fabricate quasi-zero-stiffness vibration isolators. Different combinations of permanent magnets and electromagnetic coils in attractive or repulsive configurations can lead to negative stiffness. The magnitude of the electromagnetic restoring force and negative stiffness is dependent upon many geometric and electromagnetic parameters and is controllable by adjusting the current in the electromagnetic coils. The present work compares the negative stiffness properties of three different configurations and provides a general guideline for selecting the appropriate configuration. The finite element method is used to simulate the magnetic fields and electromagnetic force acting on the permanent magnet. Numerical results are presented, and findings are validated by analytical solutions.

Optimization of the mechanical properties of machine tool with steel reinforced mineral concrete

High damping and high static stiffness are essential to improve the static and dynamic characteristics of machine tools. Traditionally, the structural parts of machine tools are usually made of cast iron and steel, which may lead to poor surface finish and inaccurate dimensions of finished products. Therefore, many scholars have investigated other alternatives of structural material for machine tools, such as concrete, polymer concrete and epoxy granite. Although epoxy granite has better damping properties, its structural stiffness (as measured by Young’s modulus) is only 1/3 of the gray cast iron. Thus, this study would introduce several steel bar designs into epoxy granite to improve the static stiffness and quantitatively review the performance by finite element analysis. The results showed that the equivalent static stiffness and natural frequency were about 12 to 20% higher than the structural material of cast iron. Therefore, the proposed finite element model of vertical machining center (VMC) column in epoxy granite could serve as a feasible alternative to achieve higher damping or static stiffness, as it was also more environmentally friendly to the manufacturing process.

Optimal Design and Dynamic Analysis of a New Quasi-Zero-Stiffness Isolation Device

Compared with the linear isolation system, the quasi-zero-stiffness (QZS) nonlinear isolation system has the characteristics of high static stiffness and low dynamic stiffness, which has better low-frequency vibration isolation performance. However, most of the existing QZS isolators only consider the quasi-zero-stiffness characteristic at the static equilibrium position achieved by the parallel connection of positive and negative stiffness structures. To optimize the isolation performance of the QZS system, a new isolation device based on the parallel connection of oblique springs and vertical springs was proposed. The device can not only achieve quasi-zero-stiffness at the static equilibrium position but also expand the interval of quasi-zero-stiffness through parameter optimization design to optimize the stiffness characteristics of the QZS system, thus effectively improving the vibration isolation performance. The QZS nonlinear systems with the optimal parameters were analyzed dynamically, and the nonlinear motion equations were approximately solved based on the fifth-order polynomials fitted by the restoring force curves. A prototype was further designed and fabricated to compare and analyze the vibration isolation performance of the QZS system and the equivalent linear system through a shaking table test.

An absolute-zero-stiffness vibration isolator for continuously varying mass: Theoretical design and numerical simulation

Nonlinear quasi-zero-stiffness (QZS) vibration isolators can provide low dynamic but high static stiffness, and thus attract much attention in the fields of vibration isolation and reduction. However, it seems difficult for QZS isolators to protect continuously varying mass from the surrounding vibratory disturbance of relatively large amplitude. In this article, an adjustable absolute-zero-stiffness vibration isolator is designed by updating the classical QZS isolator in two steps. First, each hinged constraint in the QZS isolator that connects the oblique spring with the outer rigid framework, is released and replaced by a sliding constraint supported on an additional vertical linear side-spring. Second, the two oblique springs in the QZS isolator are further replaced by two identical oblique cam-roller-spring units, which can synthetically provide a constant negative-stiffness at will in the vertical direction. Once the stiffness ratios among the main-spring (as in the QZS isolator), side-springs and oblique-units of the new isolator are rationally determined, for a target object with any weight to be protected, absolute zero stiffness and transmittance can always be achieved by appropriately exerting an additional time-independent vertical force on each sliding constraint. The validity and efficiency of the theoretical design are fully verified by numerical simulations for both fictitious loads and real seismic spectra. This work provides a possible means for nonlinear vibration isolations of continuously varying mass.

Transverse vibration of axially loaded beam with parallel-coupled nonlinear isolators

To improve low-frequency vibration isolation when the excitation source and the isolation object are not co-located, transverse vibration of axially loaded beam with parallel-coupled nonlinear isolators is explored both experimentally and analytically. The nonlinear isolators use double annular magnets and spiral springs aligned on the same axis to achieve high static and low dynamic stiffness, which is suitable for low-frequency vibration isolation. Using the Galerkin truncation, harmonic balance analysis, and arc-length continuation, an approach is developed to analyze the frequency response functions of power flow for the strongly nonlinear discrete and continuum coupled systems. Both analytical and numerical results demonstrate that frequency response function of power flow can be used to deal with transverse vibration which excitation source and isolation object are not co-located. Parallel-coupled nonlinear vibration isolator can decrease the energy transmission of high order modal vibration of continuum, compared with the discrete isolation system. The axially loaded beam with parallel-coupled nonlinear isolators achieves significant vibration suppression at low frequency. Parametric studies of strongly nonlinear discrete and continuum coupled systems demonstrate that increasing the length of the beam and increasing the initial axial force can reduce the resonant frequency, which broadens the vibration isolation frequency band. An experiment is implemented to verify the accuracy of the theoretical model.

A theoretical framework for joining multiple locally resonant bandgaps of metamaterials towards a super-wide bandgap

In this paper, we establish a theoretical framework for joining multiple locally resonant bandgaps of composites that consist of a continuous matrix and discrete particles towards a super-wide bandgap through the damping effect of the inclusions or interphases. The binary locally resonant material is taken as an example. The analytical expressions of its first bandgap, effective mass and transmission characteristics are obtained by virtue of the equivalent discrete models. The theoretical framework and the optimized results are validated by numerical examples and experiments. Then, the theoretical framework is further used to design composite metamaterials that have the merits of small characteristic size, light weight, high static stiffness, and low-frequency bandgaps simultaneously which are characterized by a dimensionless comprehensive performance index. The results demonstrate that the generalized bandwidth can be increased by four folds, and the comprehensive performance index can be doubled through optimization. The methods developed in this work are applicable to other kinds of locally resonant metamaterials, and can be used to guide the design of high-performance metamaterials.

Dynamic characteristics analysis of magnetorheological semi-active vibration isolator with high-static-low-dynamic stiffness

High static and low dynamic stiffness vibration isolators have the advantages of high load-bearing capacity and small static displacement, but their negative stiffness components will cause a jump phenomenon at the resonance frequency. A semi-active vibration isolator with high-static-low-dynamic stiffness based on magnetorheological (MR) damper is proposed. The equivalent dynamic model of the MR semi-active vibration isolator is established, and the main resonance steady solution and stability conditions of the vibration isolation system are obtained using the average method. The influences of the basic excitation amplitude, excitation frequency, coulomb force, viscous damping coefficient, load-bearing mass, nonlinear elastic force coefficient and linear elastic force coefficient on the stability and performance of vibration isolation systems are analyzed. The results will provide a certain theoretical basis for the design of semi-active control strategies.

Global dynamics for a class of tristable system with negative stiffness

Tristable system with negative stiffness has attracted extensive attention in the low frequency vibration isolation and vibration energy harvester. As a low frequency vibration isolator, it can achieve high static stiffness and low dynamic stiffness. As a vibration energy harvester, it had a wider bandwidth for resonance than the bistable one. The introduction of negative stiffness may induce subharmonic resonance and chaos in the tristable system. Chaos usually brings disorder to mechanical vibration system. Subharmonic resonance plays the negative effect on low frequency vibration isolation because they will transfer the high frequency energy of the system to the low frequency, but it is beneficial to broaden the working frequency band of vibration energy harvester. In this paper, the subharmonic bifurcation and chaos of a class of tristable system with negative stiffness are studied. The piecewise linearized systems are established to approximate the system with tristable potential. In order to conduct Melnikov analysis, the homoclinic-heteroclinic orbits and periodic orbits for the unperturbed piecewise linearized system are obtained respectively. The subharmonic Melnikov method for nonsmooth systems with four switched manifolds is developed. The thresholds for homoclinic-heteroclinic chaos and subharmonic resonance are derived by using non-smooth Melnikov method. It provides a theoretical support not only for design of the vibration energy harvester to obtain wider working frequency band, but also for design of the vibration isolation system to avoid high frequency energy transfer to low frequency. Moreover, the phenomena for infinite subharmonic bifurcations to chaos from odd order subharmonic orbit and the coexistence for chaotic and subharmonic attractors are revealed. The subharmonic Melnikov method with four switching manifolds developed in this paper lays a foundation for the subharmonic resonance analysis of other nonsmooth tristable systems.

Design of quasi-zero stiffness compliant shock isolator under strong shock excitation

The quasi-zero stiffness (QZS) mechanism can rely on the combination of negative and positive stiffness elements to achieve very low dynamic stiffness while obtaining high static stiffness to support the isolated payload. It is a nonlinear shock isolation method with good shock isolation performance. In this paper, a new QZS compliant shock isolator is designed for shock isolation under strong acceleration shock excitation(>1000g), by paralleling a fixed-guided beam with negative stiffness and a Roberts configuration compliant beam with positive stiffness. The force-displacement characteristics of the QZS compliant shock isolator is analyzed and calculated theoretically using an elliptic integration method, and are verified by comparison using finite element simulation. The dynamic time-domain response characteristics of the QZS compliant shock isolator under the excitation of ideal shock excitation with different amplitudes, different periods, different payloads, and actual shock excitation are calculated, and compared with the performance of a general positive stiffness compliant shock isolator under the same excitation. The results show that the proposed QZS compliant shock isolator can be applied to shock isolation under strong shock excitation, and exhibits good constant force characteristics in the whole stroke during the shock isolation process, and is less affected by the amplitude and period of shock excitation. Compared with the general positive stiffness compliant shock isolator, the proposed QZS compliant shock isolator can significantly reduce the peak of the shock, reduce the maximum acceleration ratio and improve the shock isolation performance. It can provide some theoretical guidance for the design of the QZS compliant shock isolator under strong shock excitation.

A bending stiffness criterion for sandwich panels with high sound insulation and its realization through low specific modulus layers

The sound transmission loss of a sandwich panel is usually much lower than that given by the mass law for a homogeneous panel with the same weight in the mass-controlled frequency range. How to make the sound transmission loss of the sandwich panel close to the mass law and maintain a high static stiffness is a key acoustic issue in its design. In this paper, the critical apparent bending stiffness is defined as the apparent bending stiffness at which the sound transmission loss of a sandwich panel approaches that of the mass law. Then, a method is given to determine the critical apparent bending stiffness of sandwich panels, based on which a range of structural parameters can be obtained to guide the design of sandwich panels with high acoustic performance. Compared with the apparent bending stiffness of a typical sandwich panel, the critical apparent bending stiffness decays more rapidly with the increase of frequency, exhibiting a relatively high static stiffness and a relatively low dynamic stiffness. In order to make the apparent bending stiffness of a typical sandwich panel close to the critical apparent bending stiffness, the concept of introducing an elastic layer with low specific modulus in the middle of the core layer is proposed. Both theoretical and experimental results show that the introduced elastic layer with low specific modulus reduces the dynamic bending stiffness of the sandwich panel while a high static bending stiffness is maintained, thus significantly improving the broadband sound-insulation performance of the panel.