Electromechanical Devices Research Articles

Investigation of the influence of the number of poles on the external characteristic of a brushless DC machine in the generator mode

The article presents the results of a study on the generator mode of operation of a brushless DC machine (BLDC) when operating under active load. For analysis, two models were created with the number of permanent magnets on the rotor differing by a factor of two. The relevance of the research is due to the wide range of applications of BLDC in various fields. One of the key advantages of BLDC is the absence of a brush-commutator unit, which is replaced by a controller with semiconductor elements. This increases the reliability of BLDC and expands the range of operating modes. The main objective of this study is to determine the impact of the number of permanent magnets on the external characteristic of BLDC in generator mode. To achieve this goal, computer modeling was performed using ANSYS Maxwell software. This software is designed to study and calculate the magnetic field pattern using the finite element method in electromechanical devices, providing accurate results for analysis. For each BLDC model, the degree of saturation of the magnetic system elements was determined, and graphs of voltage, current, and braking torque at the generator shaft over time were obtained. Analysis of the calculation results for BLDC models with 46 and 92 permanent magnets demonstrated an impact on the voltage and current waveforms, leading to some slight distortion of their shape. The obtained calculation results allowed determining the efficiency and constructing the external characteristic for both BLDC models. Higher efficiency was obtained for the BLDC model with 92 permanent magnets on the rotor. The external characteristic for the generator mode of BLDC operation demonstrated a change in voltage when transitioning from idle to nominal current operation within the range of 15% and 21%, indicating the stiffness of the characteristic. The conclusions of the study indicate the potential for improving the efficiency of BLDC through optimization of the magnetic system design and cooling conditions, and can be useful for engineers and developers of electromechanical systems aiming to improve the performance of their products.

Design and development of thermo-electromagnetic system for spinodal decompositions of FeCrCo alloys

Permanent magnets are essential components of electromechanical devices. Majority of magnets are used in permanent magnet motors that have extensive application in relation to energy efficiency and sustainability like electric vehicles. This research is aimed for efficient manufacturing of FeCrCo permanent magnets. Electromagnets could be utilized for the generation of continuous magnetic field to use in number of manufacturing processes. A two-pole electromagnet, comprising of two solenoids each having 2200 turns of copper wire, was developed. The system was designed to produce magnetic field up to 10 kilo Gauss for spinodal decomposition of FeCrCo alloy samples under thermomagnetic treatment process. Being rare earth free alloys, FeCrCo magnet is gaining research focus as an alternative magnetic alloy for advanced applications. The electromagnetic system design was refined and confirmed by using the Finite Element Method. The experimental values, of magnetic field generated by the two-pole electromagnet setup, were well close to the simulation results. The magnetizing setup was utilized to treat the FeCrCo magnetic alloy samples simultaneously at high temperature (700 °C) and magnetic field (7 kilo Gauss). This thermo-magnetic setup helped to improve the metallurgical structures of FeCrCo to grow and develop more efficiently. Treated samples of FeCrCo alloy demonstrated enhanced magnetic properties due to effective spinodal decomposition. The improvement in magnetic properties was attributed to the elimination of retained alpha phase and formation of more alpha-1 phase.

Understanding and tuning negative longitudinal piezoelectricity in hafnia

Most piezoelectric materials exhibit a positive longitudinal piezoelectric effect (PLPE), while a negative longitudinal piezoelectric effect (NLPE) is rarely reported or paid much attention. Here, utilizing first-principles calculations, we unveil the origin of negative longitudinal piezoelectricity in ferroelectric hafnia by introducing the concept of weighted projected bond strength around cation in the c direction (WPBc), which is proposed to quantitatively characterize the asymmetric bonding stiffness along the strain direction. When the WPBc is anti-parallel to the direction of bulk spontaneous polarization, the polarization decreases with respect to tensile strain and leads to a negative piezoelectricity. Furthermore, to confirm the influence of WPBc on the piezoelectric effect and understand how the value of WPBc influences the piezoelectric coefficient e33, we acquire both the piezoelectric coefficient of doped hafnia and the corresponding bonding environment around each cation. The finding reveals that the more negative piezoelectric coefficient can be achieved through a concurrent achievement of the more negative average WPBc and the lower standard deviation (STD) of WPBc. In addition, the Sn-doped hafnia with the lowest average WPBc and smaller STD-WPBc is identified to have the highest piezoelectric coefficient (−2.04 C/m2) compared to other dopants, showing great potential in next-generation electromechanical devices.

Implementation of a unilateral hip flexion exosuit to aid paretic limb advancement during inpatient gait retraining for individuals post-stroke: a feasibility study

BackgroundDuring inpatient rehabilitation, physical therapists (PTs) often need to manually advance patients’ limbs, adding physical burden to PTs and impacting gait retraining quality. Different electromechanical devices alleviate this burden by assisting a patient’s limb advancement and supporting their body weight. However, they are less ideal for neuromuscular engagement when patients no longer need body weight support but continue to require assistance with limb advancement as they recover. The objective of this study was to determine the feasibility of using a hip flexion exosuit to aid paretic limb advancement during inpatient rehabilitation post-stroke.MethodsFourteen individuals post-stroke received three to seven 1-hour walking sessions with the exosuit over one to two weeks in addition to standard care of inpatient rehabilitation. The exosuit assistance was either triggered by PTs or based on gait events detected by body-worn sensors. We evaluated clinical (distance, speed) and spatiotemporal (cadence, stride length, swing time symmetry) gait measures with and without exosuit assistance during 2-minute and 10-meter walk tests. Sessions were grouped by the assistance required from the PTs (limb advancement and balance support, balance support only, or none) without exosuit assistance.ResultsPTs successfully operated the exosuit in 97% of sessions, of which 70% assistance timing was PT-triggered to accommodate atypical gait. Exosuit assistance eliminated the need for manual limb advancement from PTs. In sessions with participants requiring limb advancement and balance support, the average distance and cadence during 2-minute walk test increased with exosuit assistance by 2.2 ± 3.1 m and 3.4 ± 1.9 steps/min, respectively (p < 0.017). In sessions with participants requiring balance support only, the average speed during 10-meter walk test increased with exosuit by 0.07 ± 0.12 m/s (p = 0.042). Clinical and spatiotemporal measures of independent ambulators were similar with and without exosuit (p > 0.339).ConclusionsWe incorporated a unilateral hip flexion exosuit into inpatient stroke rehabilitation in individuals with varying levels of impairments. The exosuit assistance removed the burden of manual limb advancement from the PTs and resulted in improved gait measures in some conditions. Future work will understand how to optimize controller and assistance profiles for this population.

Adaptive ferroelectric states in KNN-based piezoceramics: Unveiling the mechanism of enhancing piezoelectric properties through multiple phase boundary engineering

Developing high-performance lead-free piezoceramics, such as (K,Na)NbO3 (KNN) material, is critical to achieving environmental sustainability in next-generation electromechanical devices. Although substantial advancements have been made in KNN-based ceramics, a general coherent framework is lacking that links microscopic structure to the enhancement of macroscopic properties. Our findings indicate that the enhanced performance of KNN-based ceramics in multiphase coexistence boundaries can be attributed to the formation of self-adjusting nanodomains in response to strong local structural heterogeneity. The self-adjusting behavior of domain structure is an outcome of minimizing the local stress generated by the lattice mismatch within KNN-based ceramics, which conforms to the thermodynamic principles that favor minimizing total free energy. Guided by this strategy, the present work achieves a significant improvement of electromechanical properties, including a piezoelectric coefficient (d33) of ∼585 pC N−1, an electromechanical coupling factor (kp) of ∼62 %, and a figure of merit (d33 × g33) of ∼12.78 ×10−12 m2 N−1. This study offers a new strategy for developing lead-free piezoceramics through dedicated design of novel phase boundaries.

Programming Piezoelectric Phase of Poly(Vinylidene Fluoride) via Hybrid Metal Halide Perovskite for Enhanced Electromechanical Performance

AbstractFluoropolymers and metal halide perovskites (MHPs), as two classes of important piezoelectric materials, suffer from active phases through a facile process and brittleness led poor manufacturability, respectively. Here, TMCM‐CdCl3/PVDF nanocomposites (TMCM = trimethylchloromethyl ammonium, PVDF = polyvinylidene fluoride) are synthesized to overcome the above shortcomings. The abundant hydrogen (H) and chlorine (Cl) sites in TMCM‐CdCl3 can interlock with H and fluorine (F) atoms within PVDF via C─H···Cl and C─H···F interactions. This programming effect augments the dipole alignment and consequently promotes the formation of polar phases within PVDF. The devices made by these nanocomposites exhibit high energy harvesting properties surpassing established MHP/PVDF analogues, and prominent performance in sensing delicate human motions. Moreover, the devices show exceptional capabilities for detecting underwater ultrasound waves. The signal intensity is ≈4 times that of commercial PVDF film devices, and the frequency distortion is only a quarter of that observed in commercial ceramic transducers. This study opens up new possibilities for developing high‐performance piezoelectric nanocomposites and the creation of advanced electromechanical devices.

Marine Diesel Engine Fault Detection Based on Xilinx ZYNQ SoC

Marine diesel engines are the preferred power equipment for ships and are the most important component among the numerous electromechanical devices on board. Accidents involving these engines can potentially cause immeasurable damage to the vessel, making fault detection in marine diesel engines crucial. This design enables the detection and reporting of faults in marine diesel engines at the earliest possible time through the computation of convolutional neural networks, which is of great significance for ensuring the safe navigation of ships. For this functionality, the Xilinx ZYNQ-7000 XC7Z010 is selected as the main control chip, and the LoRa wireless network is used as the transmission module. The FreeRTOS embedded operating system is ported, with sensor data collection completed on the PS side of the ZYNQ chip and algorithm acceleration calculations on the PL side. Data are then transmitted to the host computer via the LoRa module paired with a custom protocol. Experimental test results show that the program provides stable data transmission, with each module of the algorithm generally accelerating by more than 95% and an accuracy rate of 92.86%. Additionally, the host computer can display the received data in real time. The custom protocol’s header also allows for precise judgments about the completeness and origin of messages, facilitating the expansion of other SOC’s message uplink and the host computer’s message downlink.

Boosting piezoelectric response and electric-field induced strain in PMN-PT relaxor ferroelectrics

High-performance piezoelectric materials are essential for diverse electromechanical devices, from actuators to sensors and transducers. Here, we synthesized Ce2O3-doped Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (xCe-PMNT29) solid solutions via conventional solid-state methods. In the x = 2.5 % modified composition, we achieved a notable electrostrain-hysteresis trade-off, enhancing electrostrain (0.2 %), equivalent piezoelectric coefficient d33* (1701 pm V–1 at 3 kV cm–1), and reducing strain hysteresis to 8.1 %. Additionally, direct high-temperature piezoelectric characterizations revealed real-time variations in piezoelectric coefficient (d33) and the actual depolarization temperature, with d33 reaching 859 pC N−1 at 53 °C and planar electromechanical coupling coefficient (kp) exceeding 70 % within 30−85 °C. Leveraging x-ray diffraction (XRD) and piezoelectric force microscopy (PFM), we elucidated synergistic effects between complex nanodomains and local structural heterogeneity, enhancing piezoelectric activity. This study presents a promising approach for improving electromechanical performance and electrostrain in ferroelectrics, with significant potential for practical piezoelectric applications.

A review on the magnetorheological materials and applications

Magnetorheological materials refer to field-response smart materials whose properties are controllable with a magnetic field, including fluid, grease, elastomer, and gel. The unique magnetorheological effect exhibited by these smart materials is a physical phenomenon where physics and engineering intersect and has extensive application prospects in modern machinery. In electro-mechanical systems, magnetorheological materials offer a superior design method for mechanical devices used in the fields of transmission, damping, and braking. It is important to control the magnetorheological materials for advancing the design philosophy of modern electro-mechanical devices. Hence, this paper presents a recent progressive review on the fundamentals of magnetorheological materials and numerous applications. Firstly, an introduction to the magnetorheological effect and different types of magnetorheological materials are presented in this review. Then, the individual and coupled effects of sedimentation, temperature, and magnetic field on magnetorheological materials are discussed. Finally, magnetorheological materials-based devices have been extensively reviewed, including actuator, clutch, damper, brake, pump, valve, and robot, thus aiming to provide useful information for facilitating the design of complex electro-mechanical systems.

Polar orientation and extension in a novel crystallographic model for PbTiO3-based perovskites explaining the experimental ferroelectric thermal anomalies

PbTiO3-based ferroelectric solid-solution ceramics have been widely used for electromechanical devices. However, it is still challenging to separate and control the contributions to the electromechanical functionalities, mainly as a function of temperature, where thermal anomalies and phase transitions can be observed. This study investigates the ultrasonic velocity and attenuation and the dielectric, ferroelectric and structural features of Pb0.55Ca0.45TiO3 ceramics from low temperatures (10 or 115 K) up to room temperature as an example of A-site isovalent substitution in PbTiO3. Such a combination of information makes possible the phenomenological deconvolution of the effects of ferroelectric domain wall pinning and structural features on spontaneous electric polarization. The room-temperature symmetry was determined as Pna21. The results show that this model refined by the Rietveld method for synchrotron X-ray diffraction patterns from 115 K to room temperature can explain the polarization extension features of these materials during heating. This study shows a correlation between structural thermal anomalies and low-temperature electric polarization in PbTiO3-based ferroelectric ceramics.

Phosphate mine by-products as new cementitious binders for eco-mortars production: Experiments and machine learning approach

Phosphate mining industry generates different types of by-products that have significant environmental impacts such as ecosystems destruction and soil contamination. To reduce their environmental footprint, these wastes were investigated as supplementary cementitious materials (SCMs). The generated by-products included a clayey material and calcareous marl which were used in the current study. Blends of the abovementioned materials with cement (ratio of 1:1) were investigated using X-Ray Fluorescence spectrometry (XRF), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TDA-TG), Mercury Porosimetry, Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Electromechanical testing device. Using these results, a learning model based on multiple linear regression (MLR) was proposed to predict the compressive strength and the specific surface area from the constituents of the material, the additives, the L/S ratio, and the hardening regime. The accuracy of the models was assessed using the correlation coefficient (R2), mean absolute error (MAE), and root mean square error (RMSE). Compressive strength results confirmed that the sample's strength improved with the amount of calcined clay. Unlike the water demand where the mixtures required more water than the OPC mixture. SEM-EDS examinations proved the existence of the C–S–H gel, responsible for the specimen strength. The used machine learning model demonstrated excellent performance and practical potential to predict both compressive strength (CS) and specific surface area (SS) by capturing both linear and nonlinear relationships. As well as time and plasticizer were the most influential factors on the properties studied (CS and SS) and their effect was positive. This sensitivity study provides important information on the critical factors influencing compressive strength and specific surface area in the different ranges considered.

A mechanical manipulated electromechanical coupling design with stretchable electret film: mechanical sensing, energy harvesting, and actuation

Electrical and mechanical energy converts around the nature, and electromechanical coupling effect is applied in various conditions such as mechanical sensing, electrical actuation, and self-powering. During the energy type conversion, electromechanical parameters are among the key issues, such as enlarging the sensitivity and range of mechanical sensing, and energy harvesting efficiency. In this work, a mechanical manipulated approach with stretchable electret is proposed to continuously manipulate the electromechanical parameters. An electromechanical coupling demonstration with pre-stretched electret films and non-contact electrodes are applied, verifying high and regulable electromechanical coupling parameters, and it is advantaged from large deformable and overload permissible capability. This mechanical manipulation approach proposes a new possibility on simplifying the structural and mechanical design of various electromechanical devices, and further enhancing the general applicability with certain geometry and material with ultra-high and tunable electromechanical coupling parameters.

Electromechanical energy storage device

Introduction. Short-term peak loads of machines and mechanisms create the need to accumulate mechanical energy for its subsequent pulsed use. This is quite relevant, for example, for tractors at the initial stage of towing heavy trailers. The use of a mechanical energy accumulator will reduce the power of the tractor engine and expand its functionality.Target. Development of a mathematical model of a mechanical energy accumulator.Research methods. The mechanical energy accumulator can be made in the form of a direct current electric machine or a valve machine, on the shaft of which a superflywheel is attached. When a machine is connected to a power source, a non-stationary process occurs, described by two differential equations: one for mechanical quantities, the other for electrical ones. Solutions of differential equations repeat the relationships for charging and discharging an electric capacitor.Results. From the resulting formulas it follows that for an electrical circuit, the mechanical energy accumulator in question is indistinguishable from an electrical capacitor. It follows from this that in this case we can talk about artificial electrical capacitance. In addition, artificial electrical resistance arises (which is not related to the resistivity, length and cross-sectional area of the conductors). In connection with the above, a mechanical energy accumulator can be interpreted as an artificial electric capacitor, which stores not the energy of the electric field, but the kinetic energy of rotation of the superflywheel.Conclusion. There are superflywheel designs that can store significant kinetic energy. Even the possibility of installing them on passenger vehicles was studied. In this sense, massive tractors have an undeniable advantage, since the increase in weight is not only not problematic for them, but in some cases it is desirable.

Electrical arc discharge in air between Pt-coated NEMS electrodes at nanoscale separation

A thorough understanding of arc discharge mechanism as well as determination of arc discharge voltage at the nanometer scale remains challenging due to the complexities associated with electrode preparation and precisely maintaining nanoscale separations in experiments. This work addresses this challenge through a novel approach by accurately measuring electric breakdown/discharge voltages between Pt-coated Si electrodes with separations ranging from ∼5 nm to 370 nm using a combination of fixed and flexible nano-electrodes while inherently creating an ideal environment to mitigate the effect of mechanical vibrations on the measurement results. For separations of 10, 100, and 300 nm, the corresponding discharge voltages are ∼15, 75, and 160 V, respectively, with the apparent electric field for the 10 nm separation exceeding 1.5 GV m−1. The results acquired from the investigated electrode configuration closely resembling the laterally actuated nanoelectromechanical system (NEMS) cantilever relays reveals strong agreement with NEMS relay breakdown characteristics, emphasizing the importance of arc discharge considerations while designing micro/nano electromechanical devices. Furthermore, deliberately applied arc discharge is shown to provide electrode nano-welding for realization of configurable NEMS circuits.

Fabrication of in situ polymerized polyaniline‐based functional nanofibrous structures for flexible electromechanical devices

AbstractRecently, flexible electromechanical devices (EMDs) emerged as alternatives to rigid electronics, promoting polymeric materials over traditional semiconductors. This study develops EMDs using conductive nanofibrous membranes of thermoplastic polyurethane (TPU), polyaniline (PANI), and multi‐walled carbon nanotubes (MWCNTs) in various structures. The fabrication technique included the combination of electrospinning and in situ polymerization to create random and aligned conductive membranes. Morphological, mechanical, thermomechanical, and electrical characterizations were conducted to assess their potential in EMDs applications. Mechanical testing revealed that, in comparison to aligned pure TPU mats, aligned TPU/PANI and TPU/MWCNTs/PANI membranes exhibited maximum strains of 26% and 19%, respectively. Meanwhile, randomly oriented mats, TPU/PANI and TPU/MWCNTs/PANI demonstrated maximum strains of 18% and 27%, respectively. Moreover, incorporating PANI and/or MWCNTs increased the Young's modulus. Thermogravimetric analysis showed thermal stability up to 250°C for all mats, with TPU/PANI mats demonstrating superior stability. Dynamic mechanical analysis revealed that PANI incorporation increased the storage modulus from 119 and 180 MPa to 2012 and 1367 MPa for aligned and random mats, respectively, compared with pure TPU mats. The combination of MWCNTs and PANI yielded moduli of 1501 and 1096 MPa, respectively. All conductive mats exhibited symmetric ohmic behavior, with conductivities varying based on orientation and composition. Specifically, TPU/PANI and TPU/MWCNTs/PANI mats exhibited conductivities of 0.83 and 1.78 S/cm for aligned mats, and 0.35 and 0.67 S/cm for random mats, respectively. Pure TPU, on the other hand, displayed a conductivity of 1.8 × 10−10 S/cm, indicating a significantly lower conductivity compared with the other mats.

Efficiency of multi-armature linear pulse electromechanical power and speed converters

Introduction. High-speed linear pulse electromechanical converters (LPEC) provide acceleration of the executive element in a short active section to high speed with significant displacement, while power-purpose LPECs create powerful power impulses of the executive element on the object of influence with minor movements. One of the areas of improvement of LPEC is the creation of multi-armature structures. Methodology. To analyze the electromechanical characteristics and indicators of LPEC, a mathematical model was used, which takes into account the interconnected electrical, magnetic, mechanical and thermal processes that occur when connected to a pulse energy source with a capacitive energy storage. The main results of the calculations were performed in the COMSOL Multiphysics software environment and confirmed by experimental studies in laboratory conditions. Results. The features of the electromechanical processes of multi-armature LPECs are established and their indicators are determined. With the help of efficiency criteria, which take into account electrical, power, speed and magnetic indicators in a relative form with different options for their evaluation strategy, it was established that multi-armature LPECs for power purposes have increased efficiency, and for high-speed LPECs the use of multi-armature configurations is impractical. The conducted experimental studies confirm the reliability of the calculated results. Originality. It has been established that almost all multi-armature LPECs for power purposes have higher efficiency compared to a converter with one armature, and for high-speed LPECs it is advisable to use traditional LPECs with one armature. Practical value. On the basis of multi-armature LPECs, models of an electromagnetic UAV catapult, a magnetic pulse press for ceramic powder materials, an electromechanical device for dumping ice and snow deposits from a power line wire, a device for destroying information on a solid-state digital SSD drive have been developed and tested. References 20, tables 4, figures 8.

Solid-state damper for reducing vibration activity of an electromechanical device of a life support system of oil and gas stations

Relevance. Mechanical vibrations are a common and technically important process that has a negative acoustic effect on human health and in some cases is a harmful production factor. In devices, the presence of vibration is caused by exciting influences of various physical nature: mechanical, electromagnetic, aerodynamic. The reason for their occurrence are defects in parts and assemblies, the technical principle of the ball bearing device, as well as the coincidence of the operating frequency of the device with natural frequency of the structural elements. Since it is technically impossible to completely eliminate the vibration activity of an electromechanical device, the actual topic of scientific research is the technical task of developing a damping device with determining its effectiveness to reduce the vibration activity of an electromechanical device, thereby minimizing the effects of concomitant harmful production factors on humans. To study this problem, a 3D model of the construction of a solid-state damper based on aluminum foam has been developed, according to which two layouts are made with different depths of cylindrical ducts used to install screws. The results of measuring vibration characteristics showed that the material used as a vibration dampener has damping properties and can be used to reduce the level of vibration activity of an electromechanical device. A comparison of the test results of the solid-state damper layouts showed that using layout No. 1 reduces the vibration amplitude up to 3 times compared with layout No. 2. Object. Fragment of the damping element of the vibration damper of a solid-state damper based on aluminum foam. Aim. To develop a design for a solid-state damper based on aluminum foam and determine the effectiveness of its use to reduce the level of vibration activity of an electromechanical device of the life support system of oil and gas stations. Methods. Modern approaches of vibration diagnostics, computational mathematics and measuring instruments. Results. There is a possibility of creating a solid-state damper based on aluminum foam to solve the problems of reducing the amplitude of vibration in the operating frequency range of the rotor of an electromechanical device compared with the corresponding vibration characteristics without damping elements.

Review of Vision-Based Environmental Perception for Lower-Limb Exoskeleton Robots.

The exoskeleton robot is a wearable electromechanical device inspired by animal exoskeletons. It combines technologies such as sensing, control, information, and mobile computing, enhancing human physical abilities and assisting in rehabilitation training. In recent years, with the development of visual sensors and deep learning, the environmental perception of exoskeletons has drawn widespread attention in the industry. Environmental perception can provide exoskeletons with a certain level of autonomous perception and decision-making ability, enhance their stability and safety in complex environments, and improve the human-machine-environment interaction loop. This paper provides a review of environmental perception and its related technologies of lower-limb exoskeleton robots. First, we briefly introduce the visual sensors and control system. Second, we analyze and summarize the key technologies of environmental perception, including related datasets, detection of critical terrains, and environment-oriented adaptive gait planning. Finally, we analyze the current factors limiting the development of exoskeleton environmental perception and propose future directions.

M2BIST-SPNet: RUL prediction for railway signaling electromechanical devices

M2BIST-SPNet: RUL prediction for railway signaling electromechanical devices

Biodegradable ferroelectric molecular crystal with large piezoelectric response.

Transient implantable piezoelectric materials are desirable for biosensing, drug delivery, tissue regeneration, and antimicrobial and tumor therapy. For use in the human body, they must show flexibility, biocompatibility, and biodegradability. These requirements are challenging for conventional inorganic piezoelectric oxides and piezoelectric polymers. We discovered high piezoelectricity in a molecular crystal HOCH2(CF2)3CH2OH [2,2,3,3,4,4-hexafluoropentane-1,5-diol (HFPD)] with a large piezoelectric coefficient d33 of ~138 picocoulombs per newton and piezoelectric voltage constant g33 of ~2450 × 10-3 volt-meters per newton under no poling conditions, which also exhibits good biocompatibility toward biological cells and desirable biodegradation and biosafety in physiological environments. HFPD can be composite with polyvinyl alcohol to form flexible piezoelectric films with a d33 of 34.3 picocoulombs per newton. Our material demonstrates the ability for molecular crystals to have attractive piezoelectric properties and should be of interest for applications in transient implantable electromechanical devices.