Actuator Layers Research Articles

Multi-layered morphing soft structure with high-performance embedded electrothermal artificial muscles along with touch and temperature sensors

Abstract In this paper, we present a novel multilayered morphing structure, having similar topology resembling the structures found in nature to grasp delicate objects effectively as well as sense contact force and temperature. The structure consists of two actuation layers, two U-shaped cooling channel layers, piezoelectric based touch sensors and temperature sensors. Employing shape memory alloy (SMA) spring actuators for bending and twisted and coiled polymer fishing line with nichrome (TCPFL NMC) artificial muscles for antagonistic return, the soft silicone-based composite skin exhibits unique capabilities of large bidirectional movement, avoid rigid passive springs for return motion, soft grasping, safe interaction with humans, and ease fabrication. The SMA (0.38 mm wire diameter) serves as relatively fast actuating muscle and the TCPFL NMC (0.8 mm fiber diameter) as a slow actuating (considering mainly heating cycle), which was programmed/designed to mimic the fast and slow twitching muscles found in nature. Bending and return operations of skin samples of length 100 mm and thickness of 9 mm, with three different widths 20 mm, 25 mm, 30 mm, were experimentally studied. The 25 mm wide multilayered soft skin demonstrated cyclic actuation with a maximum bending angle of ∼70°, which was attributed due to the active cooling. The fluidic channels for active cooling were fabricated using 3D printed PVA tubes, casting within the silicone in a mold and subsequently dissolving in a circulating water. The study also included the integration and voltage response of mini-piezodisk sensor PIC255 having a diameter of 2 mm and thickness of 0.15 mm, which was embedded at different depths within the silicone (on the surface, 1 mm depth and 2 mm depth). The multilayered soft skin was also able to detect the temperature of the object during grasping, suggesting its potential application as a soft gripper in robotic systems.

Dynamic buckling active control of FGM spherical shell with piezoelectric sensor and actuator layers

The mechanical snap-through phenomenon represents one of the buckling modes inherent in shallow shells, exemplifying the shell's reaction to external loads, which can potentially have detrimental effects on structural performance. This article delves into the study of this phenomenon within the context of spherical shells. Leveraging functionally graded material (FGM) in the main layer of this structure proves instrumental in enhancing the shell's performance against rapid mechanical loads. Furthermore, the strategic placement of piezoelectric layers, both symmetrically and asymmetrically, coupled with the implementation of a proportional and derivative control system, facilitates the control of the shell's response. The formulation of displacement field and electric potential is grounded in the first-order shear deformation theory (FSDT) and second-order distribution, respectively. The strong form of nonlinear dynamic and electrostatic equations is derived using Hamilton's principle. Solving these equations is achieved through the implementation of the generalized differential quadrature (GDQ) method in the spatial domain and Newmark in the time domain. Additionally, the Newton-Raphson method is employed to tackle the inherent nonlinearity of the problem. The Budiansky's criterion is employed for the assessment of the load necessary for the buckling of the shell. Following the validation of results against numerical, analytical, and laboratory outcomes, a set of parametric results is presented. These results underscore the remarkable impact of the control system in mitigating shell deformation under time-dependent mechanical loads, as well as in postponing the occurrence of the snap-through phenomenon and damping the vibrations.

Slot‐Die‐Printed Electroactive Polymer Actuators with High‐Strain Sensitivity for Soft Robotic Applications

AbstractIonic electroactive polymer gels are widely employed as actuators in soft robotics due to their ability to undergo rapid mechanical deformation under low‐voltage. How to improve the performance of the ionic electroactive polymer actuators is always the focus of research in this field. Optimizing the migration of ions within the actuator is crucial for enhancing the actuation performance. In this regard, this study innovatively introduces slot‐die‐printing technology to fabricate gel actuation layers characterized by high smoothness and uniform particle distribution, achieving seamless integration between the electrodes and gel actuation layers, while mitigating issues associated with ion accumulation due to polymer clustering. Furthermore, this study attempts to add lactic acid to the traditional CS‐PVA‐IL gel, effectively strengthening the connection between CS and PVA, and promoting smooth ion transport within the gel. The results demonstrate that the actuators prepared in this study achieved a high‐bending‐strain of 0.35%, with a retention rate of 91% for actuation displacement after 10 000 cycles, showcasing superior actuation performance compared to existing research. The fabrication method proposed in this study is simple and highly reproducible, making it suitable for widespread industrial application, and providing a new approach for future industrial production of soft robotics.

A novel smart hybrid multimorph piezoelectric spherical shell cloak for broadband near-perfect underwater acoustic camouflage applications

Non-visual auditory camouflage plays a major role in the art of underwater deception. In this work, a hybrid active/semi-active omnidirectional cloaking shell structure composed of alternate complementary piezoelectric and smart viscoelastic (PZT/SVE) actuator layers is proposed that can effectively conceal a three dimensional underwater macroscopic object from broadband incident sound waves. The smart hybrid structure incorporates a finite sequence of fully active parallel-connected multimorph PZT constraining layers inter-stacked with semi-active SVE core layers both of which are collaboratively operative in the framework of a Particle Swarm Optimized (PSO) multiple-input multiple-output active damping control (MIMO-ADC) scheme. The elasto-acoustic modeling of the problem is conducted by coupling the spatial state space methodology based on the classical three-dimensional exact piezoelasticity theory with the wave equations for the inner and outer acoustic domains. The acoustic cloaking performance of proposed configuration is evaluated for four distinct classes of highly functional SVE interlayer materials with tunable (field-dependent) rheological properties, namely, magnetorheological elastomer (MRE), shape memory polymer (SMP), electrorheological fluid (ERF), and magnetorheological shear thickening polishing fluid (MRSTPF). Extensive numerical results reveal significant broadband reductions of the far-field backscattering amplitude in the (f∞θ=π,kexRex)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left|{f}_{\\infty }\\left(\ heta =\\pi ,{k}_{\ ext{ex}}{R}_{\ ext{ex }}\\right)\\right|)$$\\end{document} as well as the percentage error of external cloaked field (%Err)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\%\ ext{Err})$$\\end{document} by incorporating a sufficient number of smart multimorph PZT/SVE material layers. Furthermore, it is concluded that comparable low frequency acoustic cloaking effects is possible without expenditure of any external energy just by employing the entirely inactive MRSTPF-based cloak as an alternative to the semiactive or fully active multimorph PZT/SVE cloaks. The outcome of proposed study can advantageously serve as the first step towards practical development and experimental implementation of future high performance smart acoustic cloaking devices with expanded broadband near-perfect omnidirectional invisibility for three dimensional objects of diverse geometries.

Research on layered control of path tracking for unmanned industrial vehicles based on fully hydraulic steering leakage compensation

Industrial vehicles work in complex terrain, the variable centre of mass position, leakage nonlinearity of full hydraulic steering and other issues lead to poor path tracking stability and accuracy. In this paper, an intelligent hierarchical controller for industrial vehicles’ path tracking is designed with full hydraulic steering leakage compensation, including an upper decision layer and a lower execution layer. The upper decision layer observes the pavement-tyre adhesion coefficients through an extended Kalman filter algorithm, and uses the real-time observations of the adhesion coefficients to establish a variable constraint control for the linear time-varying MPC, and thus performs the path tracking control. The lower actuator layer receives the upper layer’s target steering wheel angle output and performs steering operations. Based on the establishment of a mathematical model of full hydraulic steering considering the leakage characteristics, it analyses the leakage disturbance factors and constructs a fuzzy feed-forward steering leakage compensation controller to compensate for the leakage disturbances in real time for path tracking steering. Simulation and experimental results show that the lateral acceleration, sideslip angle, tyre side slip angle and tracking error of intelligent industrial vehicles under different loads and working conditions are improved by more than 32.4%, 35.8%, 40.2% and 45.8% respectively, and the designed hierarchical controller for the path tracking of intelligent industrial vehicles, which considers the compensation of all-hydraulic steering leakage, can effectively improve the path tracking stability and tracking accuracy of intelligent industrial vehicles under different loads and working conditions.

Linear 3D piezo-elasticity theory for static and free vibration analysis of piezoelectric/GOP/CNTs panels submerged in fluid

The objective of this study is to analyze the bending and free vibration analysis of a new type of smart hybrid FG composite plate integrated with piezoelectric layers that are submerged in fluid. The proposed composites for some layers are carbon nanotubes (CNTs) and for some other are graphene oxide powder (GOP), along with two layers of piezoelectric sensors and actuators. Furthermore, two distinct combinations, namely GOP/CNTs/GOP and CNTs/GOP/CNTs, are analyzed. To capture the structural response of the system, exact linear three-dimensional piezoelasticity theory is employed to derive a semi-analytic solution for composite plates of arbitrary thickness, thereby avoiding simplifications in constitutive relations. The computation of fluid interaction components is performed using the Rayleigh integral method, and the coupling of structural and fluid interactions in the equations is addressed without imposing constraints on fluid density or assuming a far-field approximation. Parametric studies are carried out for the first time to investigate the impact of dimension ratios, reinforced distributions, and weight fractions of nanofiller on the natural frequency and static behaviour of the novel hybrid submerged smart composites.

Active vibration control of rotating smart bidirectional FGPTC subjected to internal mechanical shock

This study considers the active vibration control of a sandwich truncated cone, whose intermediate layer is made of bidirectional functionally graded (FG) porous material bonded with integrated piezoelectric actuator and sensor layers on its outer and inner surfaces. The material properties of the bidirectional functionally graded porous truncated cone (FGPTC), with even and uneven porosity distributions along the length and thickness directions, are changed using a power law function. The governing motion equations utilize the two-dimensional (2D) axisymmetric theory of elasticity rather than simple shell theories. The solving of the governing motion equations is accomplished through the utilization of graded finite element and Newmark methods. The study investigates the impact of dimensions, parameters, and porosity types on transient response behavior, including the semi-vertex angle and the ratio of truncated cone length to outer radius. Furthermore, the effects of power index, porosity volume fractions, rotational velocities, and boundary conditions are examined. Active vibration control (AVC) of the piezoelectric FGPTC is achieved by employing a closed-loop control algorithm based on velocity feedback. Several numerical simulations are conducted to evaluate the effectiveness of the proposed active vibration control system in reducing structural vibrations. The results demonstrate significant reductions in vibration amplitudes and improved structural stability achieved through the active control approach.

Nonlinear flutter response and reliability of supersonic smart hybrid nanocomposite rupture trapezoidal plates subjected to yawed flow using DQHFEM

In the realm of aerospace engineering, the analysis of flutter under supersonic flight conditions is of paramount importance. Hybrid nanocomposite materials, known for their lightweight and high-strength properties, are increasingly being employed in aerospace engineering. This article examines the supersonic flutter behavior and reliability of smart hybrid nanocomposite trapezoidal plates, considering various practical factors. The structure is subjected to yawed flow conditions, a scenario often encountered during supersonic flight. The importance of the hybrid nanocomposite in various applications such as aerospace, public security tools, and so on, therefore the hybrid nanocomposite core layer reinforced by carbon nanotubes (CNTs) and carbon fibers incorporates real-world material complexities such as agglomeration, waviness, and random orientation of fibers into the analysis. The complexities and the accurate characterization of the hybrid nanocomposite properties are determined by using the Halpin-Tsai model. Going beyond the current field of application, the core layer is integrated with actuators and sensors, respectively at the top and bottom layers. The structure is controlled by a Proportional-Derivative (PD) controller, simulating real-world control mechanisms used in aerospace systems for flight safety. The structure is modeled by the nonlinear Refined Zigzag Plate (RZP) theory. The advanced numerical technique of the Differential Quadrature Hierarchical Finite Element Method (DQHFEM) for the solution of the motion equations provides a robust framework for studying the intricate flutter and aerodynamic behavior of the smart hybrid nanocomposite trapezoidal plates. The examination of the reliability of the structure employs the three-term conjugate finite-step length (TCFS) method. This technique is constructed through the utilization of the conjugate gradient method, incorporating a controlled scalar parameter to ensure numerical stability. The results of this article have been validated against existing experimental and numerical studies, demonstrating the validity of the presented model and the numerical technique used. The effects of various parameters, such as the smart controller, applied output voltage to the actuator layer, volume percentage of CNTs, agglomeration, and waviness of carbon fibers, geometric parameters, the skew angle of the plate, rupture, and yawed angle flow are examined on the flutter behavior, critical aerodynamic pressure, nonlinear frequency, and reliability index. The results indicate that the controlled system exhibits an approximately 18% increase in the flutter critical aerodynamic pressure compared to the uncontrolled system, along with a significant 50% rise in flutter frequency. Additionally, the structure with rupture displays approximately 20% lower flutter aerodynamic pressure and a 25% lower flutter frequency compared to a healthy plate. In the absence of carbon nanotubes and under positive external voltage, a damage parameter exceeding 0.35 leads to a reliability index below 0.931, indicating a risk of structural failure. Two solutions involve switching to negative voltage or increasing the volumetric percentage of carbon nanotubes, resulting in a 43% or 118% increase in reliability, respectively.

Vibration Characteristics of FML Cylindrical Shell Bonded by Thin Piezoelectric Actuator and Sensor Layer with and Without Fluid–Structure Interaction Resting on Pasternak Elastic Foundation

The present study investigates the vibration analysis of cylindrical shells composed of fiber metal laminate (FML) with embedded piezoelectric layers, undergoing fluid-structure interaction (FSI) and resting on a Pasternak elastic foundation based on the principles of three-dimensional elasticity theory. Using the state space approach, the equations of motion were derived under simply supported boundary conditions. The natural frequencies of the FML cylindrical shell, accounting for the presence of a moving fluid, were computed by solving the eigenfrequency equations. The study examined the influence of various parameters, including boundary conditions, length-to-radius ratio, fluid type, fluid velocity, circumferential wave number, and radius-to-thickness ratio, on glass-reinforced aluminum laminate (GLARE), aramid-reinforced aluminum laminate (ARALL), and carbon-reinforced aluminum laminate (CARALL). A constant composite/metal volume ratio was assumed. The results obtained were validated by comparing with natural frequency values from the existing literature, confirming the agreement and convergence with previous studies. The results confirm that the highest natural frequency values are assigned to the CARALL, ARALL and GRALE structures in descending order. Furthermore, an increase in fluid flow velocity through the cylindrical shell correlates with a reduction in natural frequency.

A self-healing artificial muscle was realized by fitting the electrode membrane with the self-healing actuating membrane with a folded structure

As a part of biomimetic gelatinous polymer actuator (BGPA), hydrogel artificial muscle has the advantages of extreme flexibility, low driving voltage and controllable driving direction. However, such artificial muscles do not have self-healing properties and it is difficult to continue using them if they break, which considerably reduces their lifespan. In this paper, we propose a hydrogel artificial muscle with self-healing capability by gluing a membrane of electrodes with a pleated structure to a self-healing actuator layer. The crosslinking reaction between polyacrylic acid molecular chains and carboxylated chitosan (CLC) molecular chains was utilized to fabricat e self-healing actuator layers, while multi-walled carbon nanotubes and chitosan were employed for electrode films. The impact of CLC doping content on the self-healing properties, mechanical properties, electrical response output force properties, and electrochemical properties of self-healing artificial muscles was investigated. Experimental results demonstrated that the output force density of the self-healing artificial muscle could reach 14.7 mN g−1 with an addition of 0.2 g CLC; even after fracture-self-healing, the maximum output force density of the artificial muscle still remained above 90%, and the maximum stretching stress of the actuator film maintained a range from 91% to 99%, showcasing exceptional self-healing performance.

Hybrid Fuzzy PID Sound Radiation Control of a Functionally Graded Porous GPL-Reinforced Plate with Piezoelectric Sensor and Actuator Layers

This paper is the first attempt to investigate the sound radiation control of a functionally graded porous graphene platelet-reinforced composite (FGP-GPLRC) plate integrated with piezoelectric face sheets. A spatial state-space formulation based on the linear 3D piezoelasticity theory is utilized to derive a semi-analytic solution for the coupled vibroacoustic response of the simply-supported arbitrarily thick composite plate. A comprehensive parametric study examines the effect of GPLs’ distribution, weight fraction, and porosity parameters of the core layer on the radiated sound power. Then, the best material configuration is selected to be actively controlled. A hybrid Fuzzy Proportional-Integral-Derivative (FPID) controller, which utilizes an FPID controller integrated with a classical PID controller, is employed to mitigate sound radiation from the smart sandwich plate via the volume velocity approach. The gain parameters of the proposed controller are tuned using the Bat optimization algorithm. Finally, the performance of the active control strategy in attenuating radiated sound power is investigated through several numerical simulations. Results show the proposed control scheme's robustness and rapid disturbance rejection performance.

Electro-Mechanical Buckling of Shallow Segments of Functionally Graded Porous Toroidal Shell Covered by Piezoelectric Actuators

The current work deals with the mechanical buckling behavior of saturated porous toroidal shell segments sandwiched by piezoelectric actuator layers. Material properties of the porous shells with nonuniform distributed porosities are assumed to vary as a specific function of the thickness and porosity parameters. The nonlinear equations of the sandwich toroidal shell having either positive or negative Gaussian curvature are obtained on the basis of Biot’s poroelasticity theory. The energy method as the minimum potential energy principle is applied to derive the governing equations of the sandwich shells. The buckling equations of the piezo-porous sandwich shells under various types of mechanical loading are established by employing the adjacent equilibrium criterion. The governing equations as a set of the coupled partial differential equations are solved using an analytical method including the Airy stress function. Closed-form solutions are derived for shallow segments of the sandwich toroidal shell with positive/negative Gaussian curvature under lateral pressure, axial compression, and hydrostatic pressure loadings. Novel numerical results are presented in this work to show the effects of important factors such as the piezoelectric layer thickness, applied voltage, shell geometrical ratio, and variation of the porosity coefficient on the buckling behavior of these structures.

Applications of internet of things (IoT) and sensors technology to increase food security and agricultural Sustainability: Benefits and challenges

Agriculture must overcome escalating problems in order to feed a growing population while preserving the environment and natural resources. Recently, it has become clear that sensors and the Internet of Things (IoT) are effective tools for boosting agricultural sustainability and food security. This study provides insights into the global market size for smart agriculture in future years from 2021 to 2030, In addition, this research offered four levels of the IoT architecture for smart agriculture: the perception or sensing and actuator layer, the network layer, the cloud layer, and the application layer. The state of the art in IoT and sensor technologies for agriculture is examined in this review paper, along with some of their potential uses, including 1) irrigation monitoring systems, 2) fertilizer administration, 3) crop disease detection, 4) monitoring (yield monitoring, quality monitoring, processing monitoring logistic monotoring), forecasting, and harvesting, 5) climate conditions monitoring, and 6) fire detection. Additionally, this review offers a number of sensors for agriculture that can detect parameters like soil NPK, moisture, nitrate, pH, electrical conductivity, CO2, temperature, humidity, light, weather station, water level, livestock, plant disease, smoke, flame, flexible wearable. Subsequently, this study highlights the advantages of IoT in smart agriculture, including superior efficiency, expansion, reduced resources, cleaner method, agility, and product quality improvement. However, there are still issues that need to be resolved in order for IoT technology to be used in agriculture where covered in this paper, and also provide insights into future research directions and opportunities. This study will contribute to helping future readers and researchers to better understand the state of academic achievement in this subject.

Vibration Analysis of Two-dimensional Functionally Graded Plate with Piezoelectric Layers using the Classical Theory of Plates

In this article, two-dimensional functional materials have been used using the power law in them, which is a good measure to obtain the properties of a composite material of metal and ceramic. At first, the equations of motion were obtained using Hamilton's method and solved by the GDQ method, and finally, the accuracy of the obtained answers was compared with the existing articles. In the following, the dynamic model of the sheet with two piezoelectric actuator layers at the top and bottom was investigated and the obtained equations were solved using the Ritz method.

Vibration control of an axially loaded composite beam bonded with Piezoelectric actuator and sensor layers on a Winkler–Pasternak foundation and under transverse excitation force based on first-order shear deformation theory

Vibration control of an axially loaded composite beam bonded with Piezoelectric actuator and sensor layers on a Winkler–Pasternak foundation and under transverse excitation force based on first-order shear deformation theory

An Ultrathin Internal Dielectric Actuator for Extended Range Deflection Pull-in Free Actuation

MEMS electrostatic actuators suffer from pull-in instability, making them highly nonlinear and limiting their useful range of motion. This report resolves the performance-limiting issues of the gap-closing transducer by using an ultrathin dielectric layer (UDL) for actuation. The device has an electromechanical coupling coefficient of 4.26% and an average deflection sensitivity of 119 nm/V over a range of 350 nm for upto 3.3 V dc bias. The UDL capacitance and deflection show a square law dependence on voltage. The device can thus be used as an actuator upto the full range of motion with better performance. Additionally, the UDL or gap capacitance can be used for feedback to maintain constant gap or strain. UDL actuation may also be combined with gap actuation to lower the pull-in voltage without changing the gap or the actuator thickness. 2022-0213

Thermo-Electro-Mechanical Analysis of Micropolar FGP Cylindrical Shell Covered with Piezoelectric Actuator Layers

An investigation is performed in this paper to analyze the nonlinear thermo-electro-mechanical response of long sandwich cylindrical shells with functionally graded porous (FGP) core and thin piezoelectric actuator layers. The FGP core of the sandwich shell is assumed to be temperature- and microstructure-dependent. It is assumed that the sandwich shell is subjected to uniform lateral pressure loading in a thermo-electrical environment. The equilibrium equations of the shell with infinite length are established with the aid of the virtual displacement principle and von Kármán kinematic assumptions. The governing equations are obtained in terms of displacement components based on the first-order shear deformation model of shallow cylindrical shells and the modified couple stress theory. These nonlinear differential equations are analytically solved for a sandwich shell having both the simply-supported and clamped–clamped edge conditions by employing a two-step perturbation technique. Analytical closed-form solutions are determined as a relationship including the load parameter and the mid-span deflection. The comparison examples are made with the existing results in the literature for a simple functionally graded shell, where good agreement is obtained. It is shown that the nonlinear response of the sandwich shell is highly dependent upon the temperature variation, power law index, porosity coefficient, couple stress parameter, piezoelectric layers, and geometrical parameters of the shell.

Modular shape-switching architected materials toward programmable acoustic properties

Next-generation acoustic devices and systems have utilized the recent advances in shape-switching and reconfigurable origami-inspired architected materials. Motivated by those efforts, we herein develop a hybrid material design strategy by combining two types of architected materials for their potential applications in tunable acoustic diffusion. The bilayered modular material consists of bistable/multistable blocks as the actuation layer and the origami sheet as the function layer. Guided by numerical simulations and physical prototyping, we proved the feasibility of controllable acoustic properties induced by programmable shape-switching sequences and customized corrugations in prototypes of linear units and planar units. Such programmability could offer the on-demand modification of scattering field directivity and variation of diffusion coefficients at various states compared to their traditional fixed counterparts. Overall, the proposed strategy opens the route to developing acoustic devices and systems with tailorable properties at different length scales.

A robust-based configuration design method of piezoelectric materials for mechanical load identification considering structural vibration suppression

Piezoelectric materials have received considerable attention to structural vibration suppression and health monitoring by virtue of their transform ability between electric energy and mechanical energy. This study investigates a novel robust-based configuration design method for piezoelectric materials under the assumption of identical configurations for actuator and sensor layers. Firstly, underlying the inverse piezoelectric effects, a load-independent layout design framework of piezoelectric actuators is developed in the context of topology optimization, in which the desired structural vibration suppression can be achieved and the robustness of system performance index representing actuating energies may be guaranteed once uncertainties are involved. Then, based on the direct piezoelectric effects, some piezoelectric sensors are effectively selected from the optimized distributed piezoelectric elements for mechanical load identification considering inevitable signal noises and material dispersion To improve the accuracy of identified results, an adaptive load identification method and an independence-driven sensor selection strategy are conducted. To strengthen the robustness of identified results, an uncertain-oriented load identification method and variance-driven sensor selection strategy are completed. Moreover, interval quantification and propagation methods are adopted to deal with multi-source uncertainties. Eventually, two numerical examples are discussed to demonstrate the validity and feasibility of the developed approach.

A Piezoelectric MEMS Speaker with a Combined Function of a Silent Alarm.

To explore the versatility of speakers, a piezoelectric micro-electro-mechanical system (MEMS) speaker combining the function of a silent alarm is proposed, which mainly comprises a lead zirconate titanate (PZT) actuation layer and a rigid-flexible coupling supporting layer. Measurements performed on encapsulated prototypes mounted to an artificial ear simulator have revealed that, compared to a speaker with a rigid supporting layer, the sound pressure level (SPL) of the proposed piezoelectric MEMS speaker with a rigid-flexible coupling supporting layer is significantly higher and is especially higher by 4.1-20.1 dB in the frequency range from 20 Hz to 4.2 kHz, indicating that the rigid-flexible coupling supporting layer can improve the SPL significantly in low frequency. Moreover, the spectral distribution characteristic of its playback audio is similar to that of the commercial electromagnetic type. The device can also function as a silent alarm based on oral airflows in dangerous situations, as it performs well at recognizing words according to their unique voltage-signal characteristics, and can avoid the effects of external sound noise, body movement, long distance, and occlusion. This strategy provides inspiration for functional diversification of piezoelectric MEMS speakers.