Thick-film Strain Research Articles

Printing highly sensitive strain gauges with polymer-derived ceramics and In2O3 composites for high-temperature applications

The development of high-temperature thick film strain gauges (TFSGs) that offer both durability and a high gauge factor (GF) remains a formidable challenge. This study integrates polymer-derived ceramic technology with filler techniques to introduce the SiCNO/In2O3 TFSG. The proposed TFSG demonstrates a stable strain response and exceptional thermal stability, enabling its application at temperatures up to 1100°C. Notably, the SiCNO/In2O3 TFSG exhibits minimal resistance drift of 0.31%/h at 1100°C, and an impressive GF of 10.94 at 1000°C. These advancements underscore its significant potential for applications requiring precise strain monitoring under harsh thermal conditions, such as propulsion systems and industrial processes.

Strain regulates the photovoltaic performance of thick-film perovskites

Perovskite photovoltaics, typically based on a solution-processed perovskite layer with a film thickness of a few hundred nanometres, have emerged as a leading thin-film photovoltaic technology. Nevertheless, many critical issues pose challenges to its commercialization progress, including industrial compatibility, stability, scalability and reliability. A thicker perovskite film on a scale of micrometres could mitigate these issues. However, the efficiencies of thick-film perovskite cells lag behind those with nanometre film thickness. With the mechanism remaining elusive, the community has long been under the impression that the limiting factor lies in the short carrier lifetime as a result of defects. Here, by constructing a perovskite system with extraordinarily long carrier lifetime, we rule out the restrictions of carrier lifetime on the device performance. Through this, we unveil the critical role of the ignored lattice strain in thick films. Our results provide insights into the factors limiting the performance of thick-film perovskite devices.

Conformal Fabrication of Thick Film Platinum Strain Gauge Via Error Regulation Strategies for In Situ High-Temperature Strain Detection.

Monitoring high-temperature strain on curved components in harsh environments is a challenge for a wide range of applications, including in aircraft engines, gas turbines, and hypersonic vehicles. Although there are significant improvements in the preparation of high-temperature piezoresistive film on planar surfaces using 3D printing methods, there are still difficulties with poor surface compatibility and high-temperature strain testing on curved surfaces. Herein, a conformal direct ink writing (CDIW) system coupled with an error feedback regulation strategy was used to fabricate high-precision, thick films on curved surfaces. This strategy enabled the maximum amount of error in the distance between the needle and the substrate on a curved surface to be regulated from 155 to 4 μm. A conformal Pt thick-film strain gauge (CPTFSG) with a room-temperature strain coefficient of 1.7 was created on a curved metallic substrate for the first time. The resistance drift rate at 800 °C for 1 h was 1.1%, which demonstrated the excellent stability and oxidation resistance of the CPTFSG. High-temperature dynamic strain tests up to 769 °C revealed that the sensor had excellent high-temperature strain test performance. Furthermore, the CPTFSG was conformally deposited on an aero-engine turbine blade to perform in situ tensile and compressive strain testing at room temperature. High-temperature strain tests were conducted at 100 and 200 °C for 600 and 580 με, respectively, demonstrating a high steady-state response consistent with the commercial high-temperature strain transducer. In addition, steady-state strain tests at high temperatures up to 496 °C were tested. The CDIW error modulation strategy provides a highly promising approach for the high-precision fabrication of Pt thick films on complex surfaces and driving in situ sensing of high-temperature parameters on curved components toward practical applications.

All-Three-Dimensionally-Printed AgPd Thick-Film Strain Gauge with a Glass-Ceramic Protective Layer for High-Temperature Applications.

A high-temperature thin/thick-film strain gauge (TFSG) shows development prospects for in situ strain monitoring of hot-end components due to their small perturbations, no damage, and fast response. Direct ink writing (DIW) 3D printing is an emerging and facile approach for the rapid fabrication of TFSG. However, TFSGs prepared based on 3D printing with both high thermal stability and low temperature coefficient of resistance (TCR) over a wide temperature range remain a great challenge. Here, we report a AgPd TFSG with a glass-ceramic protective layer based on DIW. By encapsulating the AgPd sensitive layer and regulating the Pd content, the AgPd TFSG demonstrated a low TCR (191.6 ppm/°C) from 50 to 800 °C and ultrahigh stability (with a resistance drift rate of 0.14%/h at 800 °C). Meanwhile, the achieved specifications for strain detection included a strain sensing range of ±500 με, fast response time of 153 ms, gauge factor of 0.75 at 800 °C, and high durability of >8000 cyclic loading tests. The AgPd TFSG effectively monitors strain in superalloys and can be directly deposited onto cylindrical surfaces, demonstrating the scalability of the presented approach. This work provides a strategy to develop TFSGs for in situ sensing of complex curved surfaces in harsh environments.

Formation mechanism of rhombohedral L11 phase in CoPt films grown on glass substrate

Abstract L11-CoPt(1 1 1) films were successfully fabricated on glass substrates at 300–400 °C, using Pt(1 1 1) underlayer. Magnetocrystalline anisotropy energy shows a maximum of 1.8 × 106 J/m3 at 350 °C. The mechanism of L11-CoPt ordering after introducing Pt underlayer is considered to be strain- or stress-induced ordering. The effect of CoPt layer thickness on phase structure and magnetic properties were investigated to confirm the ordering mechanism. Perpendicular magnetic anisotropy has been obtained in all CoPt films, while the squareness ratio and coercivity decrease with increasing film thickness, indicating decreased ordering due to the relaxation of strain or stress in thick films.

Depth Profiling of Strain in Textured Tungsten Films

ABSTRACTDevelopment of materials and engineering solutions in fusion technologies supports the use of high-Z elements as Plasma Facing Component to avoid tritium deposition with carbon. Tungsten is among the most promising candidates for these applications. Therefore, research in this area has gained increasing attention. It is then important to assess the structure and strain of thick W coatings as those parameters influence the adhesion on various substrates. This paper describes the status of investigations of strain in thick films of tungsten. Glancing incidence X-ray diffraction can be used to study W polycrystalline textured films, obtain information about their structure, and establish a depth profiling of residual strain. The actual strain at different depths within the coating can be extracted from the measured averaged strain using the inverse Laplace transform method applied to a set of measurements at different angles of the impinging X-ray beam. Results of measurements on films of different thicknesses are discussed.

Development of piezoelectric thick-film sensors to be embedded into adhesively bonded joints

Techniques have been developed for making a unique type of piezoelectric thick-film strain sensor in the form of a ‘piezoelectric adhesive’ to be embedded into a bonded joint. Lead zirconate titanate (PZT) powder is used as the active ingredient of the piezoelectric composite and epoxy resin as the matrix. The sensors have been fully characterised (i.e. type of piezoelectric powder, the surface area of the sensor, its thickness, weight fraction and the poling field) through an extensive testing programme in order to determine the optimum formulation for enhancing the sensitivity of the sensor. One of the main challenges was to effectively incorporate those sensors into the adhesive layer of a lap joint without greatly affecting the joint's mechanical properties. This application would allow the direct measurement of the stress field in a joint along the bond area, aiming at the optimisation of the adhesively bonded joint design as well as serving as an in-service structural health monitoring device. In the present work, the sensors were tested using the dynamic four-point bending test and preliminary results demonstrate the feasibility of this approach, achieving a satisfactory performance of the piezoelectric sensors applied on a metal substrate.

Low-cost carbon thick-film strain sensors for implantable applications

The suitability of low-cost carbon thick-film strain sensors embedded within a biomedical grade silicone rubber (Silastic® MDX4-4210) for implantable applications is investigated. These sensors address the need for robust cost-effective implantable strain sensing technology for the closed loop operation of function-restoring neural prosthetic systems. Design, fabrication and characterization of the sensors are discussed in the context of the application to strain/fullness measurements of the urinary bladder as part of the neuroprosthetic treatment of lower urinary tract dysfunction. The fabrication process, utilizing off-the-shelf screen-printing materials, is convenient and cost effective while achieving resolutions down to 75 µm. This method can also be extended to produce multilayer embedded devices by superposition of different screen-printable materials. Uniaxial loading performance, temperature dependence and long-term soak testing are used to validate suitability for implantation while proof-of-concept operation (up to 40% strain) is demonstrated on a bench-top latex balloon bladder model.

Investigation on critical failure thickness of hydrogenated/nonhydrogenated amorphous silicon films

Thick films of polycrystalline silicon for solar cells can be made by crystallization of amorphous silicon. Due to the high internal stress of amorphous silicon films, deposition of such thick films is challenging. In this paper, we investigate the failure behavior of thick amorphous silicon films. Depending on the deposition method of amorphous silicon films, they can be cracked or delaminated. While nonhydrogenated amorphous silicon films deposited by an evaporator are cracked when the accumulated strain in thick films reaches a critical point, hydrogenated amorphous silicon films deposited by plasma enhanced chemical vapor deposition are delaminated from the substrate. Critical cracking/delamination thicknesses of amorphous silicon films are theoretically derived and excellent agreement with experimental results is shown.

Strain Relaxation in Thin Films of La1.85Sr0.15CuO4Grown by Pulsed Laser Deposition

X-ray diffraction, resistivity, and susceptibility measurements are used to examine the effects of film thickness d (from 17 to 250 nm) on the structural and superconducting properties of La1.85Sr0.15CuO4 films grown by pulsed laser deposition on SrLaAlO4 substrates. For each d the film sgrow with a variable strain, ranging from a large compressive strain in the thinnest films to a negligible or tensile strain in thick films. Our results indicate that the tensile strain is not caused by the off-stoichiometric layer at the substrate–film interface. Instead, it may be caused by the extreme oxygen deficiency in some of the films.

LTCC Post Load Cell

This paper presents the development of a force post compressive load cell, fabricated using Low Temperature Cofired Ceramics (LTCC) technology. It was implemented as an LTCC mechanical load cell structure with a z-axis thick film strain gage using two different approaches. Fabrication methods and materials are explored in this work and fabricated devices are presented. This paper will also present the results of initial electromechanical sensitivity to load force and temperature tests. Compressive force behavior is consistent, in a strain level up to 1.500 micro-strain.

Piezoelectric paint: Ceramic-polymer composites for vibration sensors

A piezoelectric ceramic-polymer composite has been developed for use as a novel thick film strain sensor for vibration monitoring of structures. The material is in the form of a paint that can be applied to a wide range of substrates using conventional spraying equipment. The sensor properties depend on the morphology of the composite and on the electrodes that are used to couple it to the charge amplifier. Electrodes of various kinds have been tested. Interaction between the electrode and the piezoelectric paint sometimes occurs (for example, the organic vehicle for spray-coated electrodes may interact with the paint binder). The morphologies of the piezoelectric paint and of the electrode materials have been studied using light optical microscopy and scanning electron microscopy to investigate the effect of different compositions and of different processing conditions (e.g., paint mixing schedule). Preliminary work is reported on the characteristics of the piezoelectric particles and on the effect of heat treatment applied to anneal out defects produced by milling. X-ray analysis and particle size analysis have been used to characterize the changes that take place on heat treatment. X-ray diffractometry has also been used to follow the effect of poling on the paint sensors. At the present state of development, sensors made using the paint have a dynamic range of at least 40–4000 microstrain and a bandwidth of at least 1 Hz–2 kHz, and piezoelectric coefficient d31 of approximately 20 pC/N. The sensors are resistant to outdoor exposure and a successful field trial has been conducted.

An explanation of thermal behaviour of thick film strain gauges

Earlier study shows that resistor thickness of the thick film strain gauge can affect its temperature characteristic, which is usually a roughly parabolic curve. Thicker resistors tend to exhibit a higher positive temperature coefficient of resistance (TCR) and a lower T min , the temperature at which the TCR changes to zero in the curve. This paper presents a possible explanation of this observation based on an analysis of strain profiles and resistivity behaviour difference in resistors with different thicknesses subjected to temperature variation.

An evaluation of materials and processes employed in the construction of novel thick film force sensors

Novel thick film strain gauges have been constructed using a z‐axis orientation on insulated stainless steel for a variety of force sensing applications. These devices exhibit high gauge factor and good thermal stability compared with conventional x‐axis devices and offer other mechanical advantages due to their mode of operation. The work reported here investigates the characteristics of different types of stainless steel substrate and different types of insulating material used in the construction of the sensors. Both ferritic and austenitic steels have been investigated, together with different resistive and insulative compositions. The temperature coefficient of resistance of the devices has been shown to be a complex function of device thickness, surface area and the difference between the thermal coefficients of expansion of the various materials employed.

On the zero offset stability of thick film strain gauges

This paper presents results of work aimed at characterising the zero offset stability in novel thick film strain gauges. The devices studied arez‐axis (k33) load sensors fabricated on insulated stainless steel substrates and include examples of novel commercially developed force sensors. Devices loaded with compressive strains using a purpose designed test jig were found to exhibit a significant zero offset shift, which is negative up to a certain level (typically 1,000 micro strains) and then increasingly positive when strained beyond this point. Repeated cycles of loading then produced a certain level of stability until the previous maximum value of applied strain was exceeded. Temperature coefficient of resistance (TCR) measurements showed the devices to exhibit characteristics that depend significantly on the device geometry. The TCR was found to increase positively with increasing device thickness and surface area. The effect of overglazing the devices was found to decrease the TCR.

A study of some production parameter effects on the resistance-temperature characteristics of thick film strain gauges

Experiments aimed at investigating the possible factors affecting the temperature performance of thick-film resistors are presented. Particular emphasis is given to the temperature coefficient of resistance (TCR) of thick film strain gauges printed on both alumina and stainless steel substrates. The results confirmed that the resistance versus temperature curve is nearly parabolic, but showed that Tmin, the temperature at which the TCR changes to zero, is largely affected by the choice of resistor and substrate materials and also the thickness of the thick-film resistors. A possible explanation is proposed for the observed relationship between resistor thickness and TCR. Other factors, such as the thickness of the substrates, the choice of conductor materials, and whether single- or double-sided printing of the substrate was employed in fabrication were found to make little difference to the temperature performance of the thick-film resistors.

Observations on the characteristics of thick film k33 strain sensors fabricated on steel substratesThis paper is based on a poster presentation made at the IMAPS 2001 Symposium, Baltimore.

Results are presented from a programme of research aimed at establishing the mechanisms behind the effects of fabrication parameter variation on the performance of thick film strain gauges on steel substrates. The research is aimed at describing the effect on the repeatability of the device characteristics due to different choices of materials, thicknesses of printed layers, firing regimes and geometry of the gauges. In particular the effects of load and temperature on the offset and gain characteristics of a variety of different sensor constructions have been explored. The sensors described here are of a type where the applied strain is parallel to the measured resistance path but orthogonal to the substrate (k33). It has been found that these devices exhibit different characteristics to conventional thick film strain gauges that can help explain the mechanisms affecting gain and offset changes caused by temperature fluctuations and mechanical deformation.

Effects of aspect ratio on the temperature coefficient of resistance matching and low frequency noise levels in thick film strain sensors

An experimental study of thick film strain sensitive resistors as typically employed in resistive bridge interface circuits has been undertaken. It has been found that the chosen aspect ratio (length to width ratio) of these screen printed and fired thick film resistors has a significant effect on both the temperature coefficient of resistance and the low frequency noise characteristics of the devices. This sensitivity to aspect ratio has been attributed to metal end contact migration in the devices during firing and hence a relationship between the sensitivity and the choice of end contact material and the firing regime employed in device fabrication has also been identified.

Computational Methods for Smart Structures and Materials

SECTION 1: ANALYSIS TOOLS - On the modelisation of the piezoelectric effect with control system and some applications Simulation of flexible fibers by discrete cyllindrical segments An adaptive fuzzy logic control synthesis Fundamental solutions for infinite transversely isotropic piezoelectric media. SECTION 2: PHYSICAL SYSTEMS MODELLING AND ANALYSIS - Design and analysis of a travelling wave ultrasonic motor for space applications Finite element based modelling and analysis of structronic systems A finite element approach for multilayered plates including piezo-layers Tuned liquid damper (TLD) using heavy mud On the analytical solution of a cubic nonlinear structure controlled by linear tuned mass damper. SECTION 3: SENSOR AND ACTUATOR TECHNOLOGIES - Piezoelectric stiffener-actuators for the suppression of the vibration of laminated composite beams Thick-film strain transducers made using piezoelectric paint Evaluation of piezoelectric active control systems for vibrations suppression. SECTION 4: DAMAGE DIAGNOSIS - Smart structure integrity monitoring using transient response Truss bridge fatigue evaluation using acoustic strain gauges Diagnosis of structural damage in smart structures Cumulative damage diagnosis of smart structures under dynamic loading. SECTION 5: ACTIVE AND PASSIVE CONTROL - On the optimal placement of piezoelectric elements for active flutter suppression Active noise control by modal state feedback using piezo-electric actuators Passive structural control strategies using seismic steel energy dissipators On the sound radiated by electrical equipment:an active structural acoustic control of harmonic sound. SECTION 6: INTELLIGENT CONTROL SYSTEMS - Applications of quasi-optimizing control method to structural response control systems for seismic excitations Wind-resistant active structural response control by installing active rotor fin system. SECTION 7: ADAPTIVE MATERIALS AND STRUCTURES - Optimum design of deployable structures using genetic algorithms The effect of shape memory alloys in vibration suppression of a cantilever beam Generation and stability of reversible shape change in NiTi memory alloys Electrical discharge machining of smart materials parts.

The electrical response of thick-film resistors to hydrostatic pressure and uniaxial stress between 77 and 535 K

The longitudinal gauge factor for a thick-film resistor material (Heraeus 8241) printed on an alumina substrate is found to be 12.6 at 295 K. The piezoresistive coefficient G, the unit change in resistivity per unit change in strain is 19.5, with a negative temperature coefficient of −0.00335 K −1, measured between 77 and 535 K. Thick-film resistors of different geometry were subject to hydrostatic pressure, and by the use of the piezoresistive equation based on elastic theory, and elastic modulus data for Heraeus 8241, G was calculated and found to be 19.7 at 295 K, thus validating the piezoresistive equations and the elastic modulus value for Heraeus 8241. Hydrostatic pressure tests at elevated temperature were believed to be subject to some error, 10% at 500 K, due to adiabatic heating effects. However, it is apparent that resistance change can be predicted with a knowledge of strain in the x, y and z axes. This will prove useful for thick-film strain sensor design, where the thick-film resistor is simultaneously stressed in more than one direction.