Conductive surfaces and patterns are at the forefront of electronics research with a need to go smaller and create more intricate electronic designs and devices while still maintaining easy manufacturability. This paper investigates an approach of patterning conductive traces for microsize electrically driven devices with the focus on enabling and patterning complicated geometries. The approach includes the design and fabrication of hydrophilic microstructures along the channels with hydrophobic borders on devices’ surfaces. The channels are connected to larger electrodes outside the device. When a conductive solution is applied to the outside electrode area, hydrophilic morphologies stimulate the solution to feed along the channels and fill the predesigned patterns. Therefore, the major objective of this study is to explore different designs of microstructures to increase surface hydrophilicity for liquid electrode patterning for variously oriented surfaces. Due to numerous physical forces, material domains, and interactions involved, experimental approach is selected to study the method of surface electrode micropatterning through wetting. Microstructured surfaces are fabricated using the two-photon polymerization 3D printing technique due to its superior resolution. Analysis of various morphologies is completed, a microsize electromechanical device with selected hydrophilic morphologies is fabricated, patterned with liquid electrode, and tested. The findings in this paper further the development of electrode patterning and help determine which hydrophilic microstructures show superior patterning ability along horizontal and vertical vectors.
Acoustic wave-based devices have attracted greater attention, particularly in the aerospace and bio-medical fields due to their passive and wireless capabilities. Interdigital transducer (IDT) is an integral part of the SHM wave-based sensor, as it transmits information about the structural state. Additionally, embedding the electrodes inside the piezoelectric substrate increases the acoustic coupling and protects the electrodes from potential external damage. This paper uses numerical analysis to discuss sensor responses with different IDT layouts in both frequency and time domains. The results investigate each type’s sensitivity towards mechanical strains and figure of merit, which facilitates the development of an efficient embedded electrode sensor through advanced additive manufacturing techniques.
This paper aims to investigate the performance of piezoelectric sensors with different shapes of 3D-printed microstructures. Based on the numerical analysis in the time-frequency domain, the microstructures are printed directly on the PVDF transparent film exhibiting higher piezoelectric coefficients using a high-resolution two-photon polymerization method. Bi-directional gold IDTs are fabricated by sputtering gold onto the substrate surface using a 3D-printed stencil. The mechanical properties of the film and surface morphology of printed microstructures are examined using a nanoindenter and a 3D profilometer. The change in frequency response due to the microstructure is measured using a network analyzer. This study will be a reference for developing an efficient wave-based gas sensor with enhanced sensitivity.
Efficient and flexible fabrication is critical to facilitate experimental research of dielectric elastomer actuators (DEAs). As a rapid prototyping technique, additive manufacturing enables autonomous fabrication of DEAs with controlled geometry and distributed actuation. Contact dispensing is currently the most utilized additive manufacturing method for fully printed DEAs due to its capability to utilize a wide range of materials. However, modest contact dispensing printers produce DEAs with reliable actuation by fabricating thicker dielectric layers. There is an evident need for other approaches to increase actuation performance and lower the driving voltage. While utilization of particulate dielectric composites is a known technique to increase DEA performance, it is not widely applied for 3D printed DEAs. Adverse effects of 3D printed dielectric particulate composites, such as stiffening and material flow interruption, can be diminished with lower operational strains and thicker layers, respectively. Additionally, composite DEAs with improved performance often possess lower driving voltage due to lower breakdown strength. In this study, various dielectric composites properties, such as compressive Young’s modulus, permittivity, and breakdown strength, were examined to evaluate the electromechanical performance of unimorph DEAs through the figures of merit (FOMs). Breakdown strength of both blade-casted films and 3D printed actuators were compared. Particle distribution was monitored using a scanning electron microscope. Unimorph DEAs with plain silicone and dielectric composites were fabricated using HYREL 30M printer. Printed actuators showed improved electromechanical performance and lowered the driving voltage.
Polymer-based composite incorporated with inorganic filler has shown great potential for developing high-performance piezoelectric sensors as they offer unique properties and design flexibility. The aim of this paper is to investigate the impact of nanoparticles on the piezoelectric property enhancement of the developed composite. The piezoelectric substrate made of PVDF-TrFE/ BaTiO3 is replicated reversely through a master mold made of IP-Q resin with IDT design printed using a two-photon polymerization (2PP) method. IDT channels are filled with a conductive material, and excess material on the surface is etched using oxygen plasma. The crystalline phase characteristics and surface morphology of fabricated substrate are examined using Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM). Strain detection of the developed sensor is evaluated by determining the change in scattering parameter using a network analyzer.
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.
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.
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