Ceramic Stack Research Articles

Development of SOFC Stack Using Low-Cost and Low-ASR Ceramic Interconnects

The multi-layer ceramic (MLC) interconnect is fabricated using multiple layers of YSZ tape, with each layer containing conductive vias to provide for electrical current flow through the interconnect. Fuel and air supply to cells is accomplished through the use of flow passages in the layers. MLC interconnect using low-cost conductive materials as vias was developed. All ceramic SOFC stacks utilizing electrolyte- supported cells and MLC interconnect with low-cost vias were built and tested, low-ASR and long term stable performance of which was demonstrated. pO2 simulation in low-cost vias was performed under different fuel utilization, and confirmed that low-cost conductive via materials have low ASR in normal SOFC stack operation conditions.

Silicon carbide face-cooled 4% ceramic Nd:YAG laser

It has been demonstrated that silicon carbide (SiC) may be used as an efficient heatsinking material for intracavity face cooling of gain media in solid-state lasers. Comparative thermal modelling and temperature distribution measurements of a diode-pumped 4% Nd:YAG ceramic laser medium face cooled by undoped YAG (as a baseline), diamond and SiC lead to the belief that SiC is an effective replacement for much more expensive diamond in this application. Laser performance of a SiC face-cooled 4% Nd:YAG ceramic press-fit stack without AR coatings was demonstrated to have 24% slope efficiency.

OS11-4 熱音響冷却システムにおけるエネルギー変換効率の向上を目指して : スタックの熱源との接触部に熱伝導率の大きい素材を設置した際のエネルギー変換特性(OS11 廃熱利用技術,循環型社会における動力エネルギー技術)

To improve the thermoacoustic cooling performance of loop tube cooling system, the structure of the stack in the prime mover, the energy conversion block from heat energy to sound energy, is focused. In this system, the stack is the most important part and when the gradient of heat flux in it is increased, the strong sound intensity is realized. Copper meshes are attached on top of the honeycomb ceramic stack as the active areas for the heat source to improve the energy conversion from heat energy to sound energy. Because of the copper mesh's heat conductivity is higher than the ceramic's one, the increase of heat flux is realized by multiplying the heat conductivity and the temperature gradient. It is confirmed that the effective gradient of heat flux in the stack becomes steep by using the copper mesh. Experimental results show that the efficiency of the amount of energy conversion is almost doubled by using presented structure of the stack.

Multi-layer ceramic acoustic transducer

A method for manufacturing a multi-layer acoustic transducer with reduced total electrical impedance. The method is based on the bonding of two piezoelectric ceramic layers with confronting metallized surfaces to a thin electrical conductor, then electrically connecting the top and bottom surfaces to form a wrap-around electrode while a center conductor forms a second electrode. The total electrical impedance of a two-layer ceramic stack comprised of piezoelectric layers connected in this manner is one-fourth that of a solid ceramic element of the same size. This provides for better matching of the acoustic stack impedance to that of the electrical cable, increased penetration depth for imaging within the body, and improved acoustic element sensitivity.

전기-기계 연성해석 코드 ATILA를 이용한 수중 음향 트랜스듀서 설계

Underwater acoustic transducers are widely used for SONAR application, whose important design parameters are shapes. materials, dimensions and supporting structures. Practical design method of transducers consists of manufacturing, experiments and modifications so that it requires much time and expenses. In this study, an analytical method was developed for the Tonpilz type transducers using the commercial finite element analysis code ATILA which can solve the electro-mechanical coupling problems. A finite element model was established including the transducer elements such as ceramic stack, head mass, tail mass, tensile bolt, and molding layers. The proposed model was verified and modified by comparing the in-air and in-water test results of prototypes. The developed analysis method will be effectively used for the sensitivity analysis of design parameters in transducer design process.

Optimisation of the Electrolyte Assembly at Ceramic Fuel Cells Limited

Ceramic Fuel Cells Limited has developed an all ceramic stack that has an electrolyte assembly consisting of an electrolyte support of 10 mol% Y 2 O 3 -ZrO 2 mechanically mixed with 15 wt% alumina to increase toughness, an LSM cathode, a Ni cermet dual layer anode, and gas distribution layers of LSM (air side) and Ni cermet (anode side). During the development phase, the power output of the electrolyte assembly was offset to achieve a structurally sound thermal cyclable stack. The electrolyte assembly has been demonstrated to thermal cycle at least 13 times in a stack environment. This paper describes the optimization development of Ceramic Fuel Cells electrolyte assembly aimed to provide more than 5 W per layer and about 300 We/L in stacks of 1-1.5 kWe size whilst retaining greater than 50% electrical efficiency and thermal cycling capability.

Thermomechanical behaviour of ceramic breeder pebble stacks for HICU

This paper reports on the thermomechanical behaviour of small pebble beds or pebble stacks in order to lay out irradiation test specimens. Uniaxial compression tests (UCTs) of the pebble stacks with relatively small diameters are performed at 27 and 800 °C i.e. the maximum irradiation temperature. The H/D ratio of the specimens influences the thermomechanical behaviour because of the friction between the pebbles and the steel tube. The results are compared with the thermomechanical data obtained from standard UCTs, which apply for larger pebble-beds. The outcome of the comparison will be used for the detailed design of the constrained pebble-beds in the high fluence irradiation. In addition, the compatibility between the ceramic breeder materials and the containment is studied. It has been shown that platinum has the best compatibility at 800 °C for both the lithium meta-titanate and lithium ortho-silicate ceramics.

A sound projector for acoustic tomography and global ocean monitoring

Long-range underwater acoustic systems, such as those used in ocean acoustic tomography, require low-frequency signals covering a broad frequency band. To meet this requirement, a novel design based on a tunable narrow-band high-efficiency sound projector has been used. The projector transmits a frequency sweep signal by mechanically tuning a resonator tube (or organ pipe) to match the frequency and phase of a reference signal. The resonator tube projector consists of a symmetrical pressure-balanced Tonpilz driver placed between two coaxially mounted tubes. The Tonpilz acoustic driver is composed of two pistons separated by preloaded ceramic stacks. The resonant tube is a simple, efficient, narrow-band, medium-output projector that operates at any ocean depth. Both projector tubes have slots (or vents) which are progressively covered or uncovered by sliding coaxial tubular sleeves. The frequency varies with the sleeve position. A computer-controlled electromechanical actuator moves the cylindrical sleeves along the tubes, keeping the projector in resonance at the instantaneous frequency of a swept frequency signal. The actuator smoothly tunes the resonator tube frequency in a bandwidth of 200 to 300 Hz during a 135-s transmission. A computer synthesizes the linear frequency-modulated signal; compares the phase between transmitted and reference signals; and, using a phase-lock loop (PLL) system, keeps the resonator tube frequency in resonance with the driver frequency. The estimated PLL precision is better than 3/spl deg/ phase error. The system was analyzed by means of finite element analysis and electrical equivalent circuit simulation. The projector prototype was first tested at the Woods Hole Oceanographic Institution (WHOI) dock in Woods Hole, MA and later in the Pacific Ocean during a voyage of the R/V Point Sur in November 2001.

Modeling Piezoceramic Actuators for Smart Applications

The development of a self-sensing piezoceramic actuator requires the development of a model, which completely characterizes the electrical and mechanical properties of piezoceramics. A model that characterizes the nonlinear mechanical and electrical coupling inherent to piezoelectric ceramic stack actuators is presented. The behaviour of the piezoceramic stack actuator is established through experimentation, where the charging and loss processes are modeled with the use of complex permittivity. The piezoceramic model presented characterizes the coupling of the mechanical and electrical properties of the piezoceramic actuator when subject to variable load conditions, under a range of voltage excitations at frequencies up to 5kHz.

Piezoelectric Linear Motor with Two Motional Functions of Small Displacement and Large Displacement

In precise positioning equipment such as an XY stage, the linear actuator (motor) is indispensable. In the practical application of such a linear motor, two motional functions of small displacement and large displacement are usually required. Both such functions have fundamentally been achieved by changing the input-voltage driving the linear motor, because it usually has only one motional function. However, in such a case, the utility of the motor having one motional function is not smooth in practice; therefore, if the linear motor is constructed by combining two motors with such different functions into one form so that it has two motional functions of small displacement and large displacement, it is presumed that the utility can be much improved. From the viewpoint of this engineering requirement, we have developed a new concept of a linear motor inherently having two motional functions of small displacement and large displacement. That is, we deal with, herein, a linear motor consisting of three or two multilayer piezoelectric ceramic stacks and one piezoelectric ceramic disk-type motor; concretely, two motor constructions based on this new concept are presented and their characteristics are experimentally investigated.

Active vibration control of a space truss using a lead zirconate titanate stack actuator

This paper presents design, implementation and experimental results of active vibration control of Naval Postgraduate School (NPS) space truss using a piezoelectric ceramic stack actuator. The NPS space truss represents a flexible spacecraft structure that may support interferometer, antenna and other vibration-sensitive instrumentation. To simulate the effects of a spacecraft disturbance on the truss, a proof mass actuator is incorporated on the structure to excite the truss. To reduce the vibrations caused by the proof mass actuator, an active strut member is installed along a diagonal of the base bay of the truss. The active strut element consists of a piezoelectric ceramic actuator stack, a force transducer and mechanical interfaces. An integral plus double-integral force controller is designed to suppress vibration of the truss. Experimental results demonstrate that the active piezoceramic strut actuator can effectively reduce truss vibration.

A large solar/heat-driven thermoacoustic cooler

Based on the success of an earlier solar-powered thermoacoustics prime mover which used a direct-illumination stack and no hot-side heat exchanger [Chen and Garrett, Proc. 16th Int. Cong. Acoust., Vol. II, 813–814 (1998)], a large solar/heat-driven thermoacoustic cooler was designed and fabricated. Target cooling powers of 10 to 60 W, over a 25-deg temperature span, were based on a thermal input power of 150 to 600 W. To concentrate the required amount of solar power on an 11-cm-diameter ceramic stack, a 10-ft diameter fiberglass parabolic dish, used for satellite TV, has been converted by gluing aluminized MylarTM on its surface over a 2-m diameter. A two-axis coordinated solar tracking system, driven by two computer-controlled motors, has produced the required 600 W of solar power to illuminate the hot side of the stack for a maximum of 3 h. Measured performance of the solar refrigerator will be compared to DeltaE models. [Work supported by the Office of Naval Research.]

A flexure-based gripper for small-scale manipulation

A small-scale flexure-based gripper was designed for manipulation tasks requiring precision position and force control. The gripper is actuated by a piezoelectric ceramic stack actuator and utilizes strain gages to measure both the gripping force and displacement. The position and force bandwidths were designed for ten Hertz and one hundred Hertz, respectively, in order to afford human-based teleoperative transparency. The gripper serves effectively as a one degree-of-freedom investigation of compliant mechanism design for position and force controlled micromanipulation. Data is presented that characterizes the microgripper performance under both pure position and pure force control, followed by a discussion of the attributes and limitations of flexure-based design.

Piezoelectric pseudo-shear mode actuator made by L-shape joint bonding

A new type of pseudo-shear mode piezoelectric actuator is described which uses a particular bonding design on a multilayer piezoelectric ceramic stack. In this actuator, long thin rectangular surface electroded PZT piezoelectric sheets are stacked and epoxy bonded at alternate ends. The poling directions in the sheets are selected such that a common potential difference applied to the plates produces alternate lengthening and contraction through the action of d31 and thus a cumulative displacement over the whole length of the effectively “folded” ceramic. The rectangular stack of plates thus “shears” over to produce a substantial shear angle, hence the title of pseudo-shear mode actuator. In this paper, a new higher strength bonding for the anchoring of the alternate ends is discussed, and shown to permit the generation of large unloaded surface displacements and a high blocking force.

A 3-kHz class VII flextensional transducer

A 3-kHz class VII flextensional transducer was developed at NUWC. The class VII flextensional is a modified class IV shape having concave radiating surfaces rather than convex. This transducer is commonly referred to as a ‘‘dogbone‘‘ flextensional because of its similar shape. This design, originally described by Merchant in U.S. Patent 3,258,738 (28 June 1966), has the advantages that all the surfaces of the shell radiate in-phase and a positive compressive stress is maintained on the ceramic driver as the operation depth increases. The shell can support thinner walls, since hydrostatic pressures do not have to be overcome in order to keep the piezoelectric ceramic driver under compression, as in a conventional class IV transducer. The transducer was designed using two different modeling approaches: finite element modeling (using ATILA) and an equivalent circuit model based on plane-wave and lumped parameters. Based on the modeled results, a transducer was fabricated and then tested in August 1996. The transducer volume is 5 in. (12.7 cm) high, 5 in. (12.7 cm) long, and 2.5 in. (6.35 cm) wide, the shell material is stainless steel, and the ceramic stack is composed of 30 0.1-in. (2.54-mm)-thick PZT-8 plates, two of which are unpoled and used for insulators. The in-air weight is 10 lbs. The transducer performed exceptionally, matching the modeled data while producing an SL of 202 dB at 10 kV/in., a resonance frequency of 3050 Hz, a mechanical Q of 5, an in-water effective coupling coefficient of 30% (typical of class IV transducers), and an electro-acoustic efficiency of 80%. [Work supported by ONR.]

Microwave differential dilatometer measures 10−12 m, at 1 Hz

To check and measure the converse piezoelectric effect in bone samples, we had to detect displacements in the range of 1–100 pm with three kinds of restrictions: (1) the biological nature of the samples imposes severe limits in selecting a suitable device and method; (2) such a method has to take into account some clinical applications to which the experiment is devoted; (3) the piezoelectric behavior of bone samples is particularly interesting at low frequencies, around 1 Hz. For such reasons we modified an existing dilatometer based on a microwave differential spectrometer. A 14 GHz klystron, linearly modulated in frequency by a triangular 50 Hz voltage applied to the repeller, is connected, via magic T, to two identical cavities tunable around 14 GHz and whose resonance curves are recorded by crystal detectors. When one of the two cavities changes its height according to the length variations of the sample, its resonance frequency varies resulting in a shift of the resonant curve with respect to the resonance curve of the other cavity acting as reference. The comparison between the cavities’ responses is performed by a pulse technique transforming the frequency shifts into time intervals, that are then converted into dc voltages. The differential character of this measurement avoids the need for the microwave source stabilization. The relative shift in frequency is measured with an accuracy better than 500 Hz. This accuracy allows us to measure displacements smaller than 7 nm in the cavity’s height. After 2 h of warmup, thanks to the differential arrangement of the system, thermal or other drifts are not detectable within a lapse of time of 12 h. This feature allows coherent signal averaging over long periods. With a piezoelectric ceramic stack moving 100 pm in square wave fashion at 50 mHz we found that the signal to noise ratio was 20 dB after 1000 cycles of signal averaging, when our bandpass filter was tuned at 1 Hz. In conclusion, this system can detect periodic displacements as small as 1 pm in a short time and reliably. Due to the operational simplicity and stability, at room temperature and humidity, the device is suitable for dilatometric measurements on biological samples.

Experimental studies on thermoacoustic refrigeration

Thermoacoustic refrigeration phenomena in a resonance tube were studied experimentally. A horizontal brass tube of 400 mm in length and 40 mm in diameter was closed at one end and attached to the acoustic driver (audio speaker) at the other end. Atmospheric air was enclosed in the tube as a working fluid. Stacks which were made of a bundle of ceramic tubes, a rolled abrasive paper with garnet, or a rolled copper metal netting, were set in the tube. Driven acoustic frequency was varied from 100 to 300 Hz, and electric power to the driver was varied from 0 to 7.8 W. Pressure and temperature distributions in the tube were measured by an axially movable pressure transducer and a Copper–Constantan thermocouple. The relation of refrigeration capacity and refrigeration temperature was also measured. It was found that the maximum cooling temperature was obtained when the stack was located near the closed end equivalent to the pressure antinode. Maximum refrigeration capacity was found to be made by the ceramic tubes stack composed of a bundle of ceramic tubes 0.8 mm in hydraulic diameter. A maximum temperature difference of 12 °C was achieved in this experiment.

Composite properties of ceramic stacks

Abstract The assembly of ceramic stacks as the driver in acoustic transducers necessitates the interleaving of electrodes and jointing compounds with ceramic plates. In modelling transducers for the purpose of finite element (FE) analysis, the designer is faced with the choice either of modelling the stack in detail, leading to excessive computing demands, or of neglecting the detail of the stack construction, with consequential lack of accuracy. An approach which maintains simplicity and accuracy is to use a simple model of the stack but with material properties which represent the stack as a composite. This paper describes the methods of deriving values for these properties, with the aim of matching various performance characteristics of a simple model to those of a detailed model using known values for the properties of each material. Results are presented for a particular stack.

Acoustic transducer for sending and receiving acoustic communication signals

A uniquely designed acoustic transducer comprising a stack of piezoceramic elements (other piezoelectric materials may be used) mounted upon a tuned, shaped transmit/receive head made of hardened metal alloy. The ceramic stack is preloaded to the head via a stress bolt. Insulator electrodes used in the ceramic stack are selected to minimize compliance in the stack for maximum efficiency. All the material properties, sizes, weights, etc., as well as the overall transducer design are carefully selected to act in combination to match the impedance of the load (i.e. metal structural framework). The diameter of the tip of the tuned, shaped driving head is sized such that when clamped to a metal framework, the base metal of the material just under the tip is compressed to or slightly beyond its yield point. This eliminates the requirement for surface preparation because any coatings will be displaced under the applied pressure and any surface irregularities will be flattened out. The underside of the clamping member used to hold the transducer assembly in place consists of a half wave length reflecting waveguide designed to reflect any absorbed energy back into the load. Thus, the attachment points for both the reflector and the transducer head of the clamping device effectively appear invisible to the driving transducer under load.

Study of the sandwiched piezoelectric ultrasonic torsional transducer

The sandwiched piezoelectric ultrasonic torsional transducer was studied. The transducer consists of front and back metal cylinders, and coaxially segmented, tangentially polarized, piezoelectric ceramic tubes. The torsional vibration of the tangentially polarized piezoelectric ceramic slender tube was studied first and its electromechanical equivalent circuit was derived. Based on the network theory and the electromechanical equivalent circuit, the torsional vibration of the piezoelectric ceramic cylinder, formed by stacking a number of identical short piezoelectric ceramic rings, was analysed and the electromechanical equivalent circuit of the piezoelectric ceramic stack in torsional vibration was developed. Finally, the sandwiched ultrasonic torsional transducer was studied and resonance frequency equations were derived which can be used to design and calculate the torsional transducers for different applications.