Owing to their intrinsic actuation capability and outstanding electromechanical characteristics, dielectric elastomer actuators (DEAs) are promising smart materials with the potential to outperform conventional mechanical and electrical actuation systems for certain engineering applications, such as soft robotics and biomedical engineering. As a single-layer, planar DEA produces only one-dimensional deformation, i.e., contraction-expansion, with a moderate actuation force, different actuation mechanisms, such as rolling or stacking DEAs, have been implemented to obtain larger deformations and higher actuation forces. However, these DEA configurations do not alter the fundamental type of thickness-wise deformation. In some applications, DEA’s out-of-plane actuation motion, such as bending, is often desired for effective system operation. Currently, the desired types of DEA deformation are generally attained by implementing additional members or mechanisms using various means, e.g., stiff frames, unimorph or bimorph, multistable structures, preloaded mechanisms. Although the methods above enable DEAs to achieve desired motions, they can considerably constrain deformation and actuation force and mostly require manual assemblies. This paper demonstrates a novel DEA capable of generating the needed range of motions without introducing additional elements within the actuator. This was accomplished by tailoring the electrode-elastomer pattern and thereby deforming the elastomer in the desired manner. Studied DEA design was first developed using theoretical basics about flat capacitors and then verified through finite element analysis. The designed actuator was additively manufactured using a contact microdispensing 3D printer and tested to validate its bending due to the tailored electric field.
The development of a flexible surface acoustic wave (SAW) sensor as microelectromechanical systems (MEMS) device has been gradually emerged due to its unobtrusive size, passive, and wireless competencies. The concept behind this work is to additively develop a flexible surface acoustic wave (SAW) device with enhanced electromechanical properties capable of detecting mechanical strain occurring in aerospace applications. The nanocomposite substrate is made of polyvinylidene fluoride (PVDF) owing to its flexibility, piezoelectricity, long-term stability, and easy processing incorporated with carbon nanotubes (CNTs) as nanofillers. Adding CNTs to the polymer matrix for electromechanical properties enhancement is investigated through additive manufacturing (AM) process. Both the thin substrate and the interdigital transducer (IDT) are fabricated through direct digital manufacturing (DDM), exhibiting favorable piezoelectric and electrical properties. Various device characteristics of fabricated SAW sensor, including the generation and propagation of Rayleigh waves and the changes in wave characteristics, such as frequency, admittance, and impedance, are discussed in this paper. The effects of IDT dimensions and the resonant frequency response of the developed SAW device are also examined with numerical analysis.
Having a multitude of electromechanical and robotic applications, most flexible elastomer actuators require electrically conductive electrode components as well as nonconductive substrate components to operate. Various analytical models of flexible actuators typically show that several properties of the elastomer, such as thickness, permittivity, and softness, directly influence the actuation capability. As such, the optimization of flexible actuators, particularly in dielectric elastomer actuator (DEA), has focused on improving the elastomer while electrodes are often overlooked. However, the electrodes with high modulus of elasticity, thickness, and low stretchability can reduce the amount of actuator performance. In addition, inadequate electrical conductivity increases the actuator’s power requirement and influences the viscoelastic properties of DEA materials through resistive heating. Furthermore, besides material composition of electrode, manufacturing methods also govern the actuator performances. Therefore, a thorough investigation of both electrode properties and manufacturing methods is crucial to attain high-performance DEAs. In this work, a microdispensing additive manufacturing technique was used to produce high-quality electrodes and to fabricate test coupons composed of PEDOT:PSS (conductive and transparent polymer) and Triton X-100 (surfactant plasticizer). These coupons, as well as some molded coupons, were used to investigate important mechanical, electrical, and thermal properties of DEAs. Through the testing, the electrode showed satisfactory stretchability up to 55% for a PDMS-supported sample. Although Young’s modulus of PEDOT:PSS was decreased largely by adding Triton X-100, the value was still relatively high (8.3 MPa) that needed to be lowered more to be effectively used for DEA application. The electrode maintained its conductivity above 50 S/cm when tested in the deformed state (up to 50% of strain) or at different temperatures (25-55 °C). Finally, the applicability of electrode composition was verified by electromechanical tests performed on a fully printed single layer DEA with 20 microns thick electrodes.
Surface acoustic wave (SAW) sensors offer overwhelming advantages over other competitive sensing technologies due to its small size, cost-effectiveness, fast response time, passive and wireless capabilities. Development of SAW sensors allows investigation of their potential not only for measuring less-time dependent parameters, such as pressure and temperature, but also dynamic parameters like mechanical strains. The concept behind this work is to develop a passive flexible SAW sensor with optimized materials selection that can be used in harsh environments to measure mechanical strains occurring in aerospace applications. A flat 0-3 composite thin substrate is fabricated using a hot-press, an interdigital transducer (IDT) finger deposition is made through additive manufacturing. The sensor substrate comprises polyvinylidene fluoride as a polymer matrix, lead zirconate titanate powders as well as carbon nanotubes as nanoparticle fillers, exhibiting favorable flexibility and piezoelectric properties. The electromechanical property is enhanced using a non-contact corona poling technique with high electric field. IDT fingers are printed using direct printing additive manufacturing technique of conductive paste. Design parameters of SAW IDTs are optimized using a second-order transmission matrix approach. Rayleigh waves, generated on the fabricated substrate by an RF excitation signal, travel through the substrate and can provide useful information for desired parameters. In this work the sensing mechanism is based on the radio frequency scattering parameters response of the device. Results show a correlation between the amplitude and phase frequency response of the scattering parameters, and the mechanical strain. Experimental study on SAW substrate fabrication and analysis of sensed results with phase shift in wave speed due to strains are discussed.
Surface acoustic wave (SAW) sensor has increasing demand in structural health monitoring due to its passive, reliable life-cycle, high accuracy, and small size. The ongoing demands of sensor’s adaptability with flexible substrates, which is capable of wireless monitoring, is the basis of the research. The SAW device assembly includes a piezoelectric composite substrate that aids in wave transmission and two interdigital transducers (IDTs) capable of actuating and sensing radio frequency (RF) signals. The SAW substrate is fabricated by integrating lead zirconate titanate ceramic nanoparticles into polyvinylidene fluoride polymer matrix using dimethyl sulfoxide as the solvent. Hot-pressing the mixtures produces a thin 0-3 composite substrate that exhibits flexibility and optimum dielectric properties. The substrate material properties are studied by conducting FTIR scanning. Delay-line IDTs are incorporated on the surface of the substrate by a conventional photolithographic technique. With the sensor fabricated, RF signals are passed onto the device through the input transducer generating Rayleigh waves. The transmission and reflection characteristics of the device is determined through the S-parameter reading obtained using a network analyzer. This paper discusses about the development process of a flexible piezocomposite SAW sensor.