Patent Application
20240066554
The present invention relates to an array transducer arrangement, and associated methods of manufacturing the composite, suitable for use in a high temperature application or environment. In particular, but not exclusively, the present invention relates to an array transducer arrangement that includes kerfs cut through a piezoelectric layer arranged on a backing layer interspaced with an electrode layer. The kerfs extend though the electrode layer and into the backing layer and provide electrically isolated piezoelectric elements which are separated by a surrounding medium suitable for high temperature application. Optionally the backing layer may include a porous region and may exhibit performance characteristics (such as acoustic impedance and/or thermal expansion) that varies across its thickness.
Ultrasonic transducers are used in a variety of applications to perform, for example, fluid flow measurements, non-destructive testing, medical ultrasound testing, vibration control monitoring, diesel fuel injection and ultrasonic cleaning. A number of these applications require the transducers to operate in high temperature environments.
Ultrasonic array transducers conventionally include an ordered series or arrangement of many elements (an array) of a piezoelectric material, usually a lead zirconate titanate (PZT) ceramic, separated by a matrix medium, usually epoxy to make a composite thereof, housed in a polymer or metallic casing and assembled with epoxies, mechanical fixings, electronic components and soldered connections. These multi-element array assemblies can be used where each element is used as eletromechanical transducer elements individually or in multiple groups, as in the example of phased array ultrasonic testing (PAUT), or as a single group making use of the benefits of a composite transducer. Conventionally, the temperature of operation of these multi-element arrays is limited by several factors. In fact, conventional ultrasonic array transducers are typically limited to use below around 80° C.
For example, if the piezoelectric material is heated above its Curie temperature, the material can become depolarized causing the transducer to fail. At elevated temperature, the acoustic insulation between the array elements, usually, in conventional transducers, an epoxy resin or other polymeric material, can deform, delaminate or fail, causing distortion of the closely controlled pitch of a piezoelectric element utilised in a transducer, causing element failure or an unacceptable increase in cross-talk (inter-element noise).
Furthermore, the auxiliary components of the transducer such as, for example, the backing materials, housings and polymer fillers are also prone to failure, or to specification drift and displacement, when they are exposed to elevated temperatures. For example, increasing the temperature causes a dramatic decrease in the speed of sound, and subsequently acoustic impedance, which affects the sensor's sensitivity, frequency, bandwidth and acoustic transmission efficiency.
Certain high temperature ultrasonic transducers have been suggested which work by shielding critical internal components from excessive heat. This might be achieved by either cooling (by liquid or gas), through the addition of a thermal buffer or wedge (to distance the piezoelectric array from the source of heat), or by limiting the thermal exposure time (duty cycling). However, such methods would require the use of complex, oversized or inefficient external features in order to prevent the transducers from overheating, which restricts their use in many applications. Calibration would also be extremely complex and introduce substantial errors to obtained measurements, for example, due to the presence of significant thermal gradients.
Even where high temperature piezoelectric materials are used, the bonds which must be formed between a piezoelectric element and the other components of the transducer, such as the backing and/or the wear plate, are exposed to high temperatures such that the transducer cannot operate effectively at high temperatures for prolonged periods of time, further consideration and limiting any potential industrial application. In particular, the acoustic coupling between the transducer components is known to reduce significantly over time as the bonding between transducer components deteriorates due to high temperature degradation.
Multiple transducer elements can be arranged in a desired configuration, such as in matrix-like configuration, to provide an array of transducers. Transducer arrays are able to emit multiple pulses of sound via the transducer elements, and obtain multiple measurements based on reflections of the sound pulses along a region of a material to be measured. Individual transducer elements of a transducer array can be configured to emit and receive pulses of sound at different instances in time such as in phased array transducers. Applications of transducer arrays include, but are not limited to, medical imaging, industrial non-destructive testing, vehicle sensors and the like.
Arrays of transducers are known and these typically employ a piezo-composite configuration, where an epoxy material matrix exists between each of the piezoelectric regions or elements. This ultimately limits the operating temperature through either failure or excessive drift in ultrasonic properties or physical displacement which causes error in the composite performance, or focal laws which generate and/or govern a typical phased array ultrasonic transducer (PAUT), total focusing method (TFM), or full matrix capture (FMC) measurement.
Piezo-composite materials are used to increase the piezoelectric electro-mechanical coupling, sensitivity and ultrasonic (frequency) bandwidth of the transducer. This is helpful to achieve a short pulse length for each piezoelectric element that can be easily discerned and treated in the relevant focal law mathematics to produce faithful representations of the acoustic sound paths with accurate and precise times-of-flight. Acoustic backings are used to further increase the bandwidth or reduce the pulse length. Both the piezoelectric composite and backings are sensitive to changes in acoustic impedance which determines how the ultrasonic pulses are generated. Variation in temperatures can easily mismatch the impedance between the piezoelectric elements through the polymer matrix, or of the backing material causing crosstalk or ‘ringing’ and extended pulse lengths respectively which appear as noise in the final measurement.
Conventional piezoelectric arrays are currently available for use at temperature up to approximately 80° C., above which the array at least falls outside of acceptable tolerances, or fails irreversibly. Such prior art arrays are commonly fabricated using the ‘dice and fill’ method which involves encasing a matrix of piezoelectric material in epoxy or a similar such substance to form a piezoelectric composite. Arrays produced by such manufacturing techniques are inherently not suitable for use in high temperature environments. For example, when a piezoelectric ceramic is subjected to a high temperature it sometimes will exhibit a change in shape which may be opposed by the surrounding epoxy. Similarly, the epoxy itself may exhibit physical change, for example thermal expansion, resulting in stresses, misalignment and similar problems within a piezoelectric array. Given the precise and sensitive nature of some piezoelectric transducer devices, mechanical and chemical issues associated with high temperature use of conventional transducer arrangements may result in failure and/or the distortion, drift, and high noise-to-signal ratio of obtained measurements.
A typical specification for a conventional ultrasonic phased array transducer for industrial applications is shown in the table below;
Conventional linear arrays, the most common for industrial applications, follow some common design rules and characteristic features. The frequency of operation is typically 1 to 20 MHz. The active aperture (A) is the total probe active length given by A=n.e+g·(n−1). The passive aperture or elevation (W) is the element length or probe width and is determined by the probe frequency and focal depth range. The pitch determines the beam steerability and beam characteristics, and as a general rule p<0.67λ. A practical value of the element width (e) is determined as e<λ/2 for a given frequency or wavelength (λ). It will be appreciated that the pitch of a piezoelectric element is given by the sum of the width of the element and the distance between the element and a neighboring element. The kerf (g) is the gap between elements.
The individual element centre frequencies, sensitivity and bandwidths (related by 1/pulse length) are required to be within a tight tolerance to give uniform performance, that is, the performance of each element must be similar. The higher the frequency the better resolution in the measurement due to the reduced cycle time and wavelength, but at the expense of penetration into the body under test; attenuation increases with increasing frequency. The array is often manufactured to have a pulse which is relatively short, ideally 1-1.5 wave cycles in length to achieve good measurement accuracy and sensitivity.
Such a prior art assembly has limited capability for high temperature use. At high temperatures the epoxy will denature. At intermediate temperatures (>80° C.), due to the significant thermal expansion coefficient miss-match between the piezoelectric ceramic and the epoxy, bowing and drift in ultrasonic performance may be observed. It is also noted that with increasing temperature of the component under test, often metal in construction, that the acoustic attenuation will increase, requiring high sensitivity, and potentially lower frequency operation (3-5 MHz, from 5-7 MHz at ambient) to reduce scatter and increase signal to noise—lower frequencies suffer lower attenuation.
Prior attempts for high temperature array transducers for PAUT are available in the literature, that have incorporated high-temperature piezoelectric materials, normally based on single crystals such as quartz, lithium niobate and gallium orthophosphate which exhibit high curie temperatures, but suffer from degradation, very low piezoelectric activity constants (orders of magnitude lower than PZT), which in turn produces low sensitivity transducers, and high quality factors which cause ringing and extended pulse lengths beyond an acceptable limit for most applications.
Thin-film based piezoelectric materials have also been tested in array configurations but, due to their inherent low thicknesses, have higher frequencies and lower activity constants thereby leading to lower signal to noise, and requiring much larger operating voltages respectively, than are acceptable for most industrial non-destructive testing applications.
Acoustic laws known to those skilled in the art propose that the ideal configuration for a 5 MHz array result in extremely fragile features and low tolerance to dimensional error. In conventional ambient temperature arrays, the gaps between each element are filled with epoxy providing mechanical strength and robustness. As discussed above, epoxy and other similar filling substances are not suitable for use in high temperature arrays.
It is an aim of the present invention to at least partly mitigate one or more of the above-mentioned problems.
It is an aim of certain embodiments of the present invention to provide an array transducer arrangement for high temperature use.
It is an aim of certain embodiments of the present invention to provide an array transducer arrangement for use above 80 degrees Celsius, for a prolonged period of time.
It is an aim of certain embodiments of the present invention to provide a bonding layer between a piezoelectric layer and a backing layer able to withstand high temperature use for a prolonged period of time.
It is an aim of certain embodiments of the present invention to provide a graded backing layer including a dense region proximate to a piezoelectric layer with an acoustic impedance that substantially matches the acoustic impedance of the piezoelectric layer to minimize sound reflection and a porous region distal to the piezoelectric layer to scatter and/or absorb incident sound.
It is an aim of certain embodiments of the present invention to provide a plurality of piezoelectric transducer elements in an array arrangement in which no epoxy or other filler material is utilised.
It is an aim of certain embodiments of the present invention to provide a method of providing piezoelectric elements by providing kerfs through a piezoelectric layer and into a backing layer.
It is an aim of certain embodiments of the present invention to provide a manufacturing technique suitable for production of multiple piezoelectric elements from a fragile piezoelectric ceramic without the need for epoxy reinforcement.
According to a first aspect of the present invention there is provided a method of manufacturing an array transducer arrangement for use in across a wide temperature range, including high temperature environments above 80° C., comprising: providing a piezoelectric layer (where Z=20-35 MRayls), providing a backing layer with substantially the same acoustic impedance as the piezoelectric layer across the temperature range at the interface with the piezoelectric layer, and substantially the same coefficient of thermal expansion (a mismatch of no more than +/−7 ppm/K); arranging the backing layer on a first face of the piezoelectric layer; and cutting a plurality of primary kerfs through the piezoelectric layer and into the backing layer, to provide a plurality of piezoelectric elements; whereby the primary kerfs define a pitch of the plurality of piezoelectric elements; cutting a plurality of secondary kerfs into piezoelectric layer (from 0 to 100% through) to tailor the acoustic properties for the given application.
Aptly the backing layer comprises at least one region which is porous.
Aptly the backing layer comprises at least one region which is relatively dense.
Aptly the backing layer comprises at least one region having an acoustic impedance substantially similar to the acoustic impedance of the piezoelectric layer, and remains substantially similar as a function of temperature.
Aptly the method further comprises providing an electrode layer on the first face of the piezoelectric layer such that the electrode layer is locatable between the piezoelectric layer and the backing layer, whereby the primary kerfs extend through the electrode layer.
Aptly the method further comprises providing an electrode layer on a further face of the piezoelectric layer, whereby the primary kerfs extend through the electrode layer.
Aptly the method further comprises providing an electrode layer on a second face the piezoelectric layer and the backing layer and/or on top of the piezoelectric layer, whereby the primary kerfs extend through the electrode layer.
Aptly the method further comprises cutting a plurality of secondary kerfs into the first face or the second face or a further face of the piezoelectric layer, the further kerfs extending through a portion of a thickness of the piezoelectric layer.
Aptly the secondary kerfs provide a plurality of pillar-like sub-elements.
Aptly the method further comprises providing the piezoelectric layer from Ionix HPZ-580 material, but alternatively PZT, or any other piezoelectric material.
Aptly the method further comprises providing the backing layer from Ionix HPZ-580 material.
Other types of backings may be used, so long as the thermal expansion conforms to +/7 ppm/K and the acoustic impedance, Z, remains substantially matched.
Aptly the backing layer comprises Ionix HPZ-580 material in a depoled state.
Aptly the method further comprises providing a glassy frit bonding layer between the piezoelectric layer and the backing layer.
Aptly the piezoelectric elements are elongate pillar-like structures arranged perpendicularly to the major axis of the piezoelectric layer.
Aptly the piezoelectric elements include a plurality of elongate pillar-like structures which are connected along a distal end of each pillar-like structure.
Aptly the piezoelectric elements are box-like.
Aptly the piezoelectric elements have a maximum length parallel to the major axis of the piezoelectric layer and a minimum length perpendicular to the piezoelectric layer.
According to a second aspect of the present invention there is provided an array transducer arrangement for use in a high temperature environment, comprising: at least one piezoelectric layer; at least one backing layer arranged on a first face of the piezoelectric layer; and a plurality of primary kerfs extending through the piezoelectric layer and into the backing layer to provide a plurality of piezoelectric elements; wherein the primary kerfs define a pitch of the plurality of piezoelectric elements.
Aptly the plurality of piezoelectric elements form an array.
Aptly the piezoelectric layer comprises Ionix HPZ-580.
Aptly the backing layer comprises Ionix HPZ-580, optionally in a depoled state.
Aptly the backing layer includes at least one dense region proximate to the piezoelectric layer.
Aptly the backing layer includes at least one porous material distal to the piezoelectric layer.
Aptly the porosity of the backing layer is graduated/graded along its length, height or width.
Aptly the array transducer arrangement further comprises a plurality of secondary kerfs are cut into a further surface of the piezoelectric layer and extend though a portion of a thickness of the piezoelectric layer.
Aptly the secondary kerfs define pillar-like sub-elements.
Aptly the piezoelectric elements include a plurality of sub-elements.
Aptly the piezoelectric elements are box-like.
Aptly the piezoelectric elements are pillar like.
Aptly the piezoelectric array transducer arrangement is a 2D arrangement with primary kerfs extending along one axis in a plane provided by the further surface of the piezoelectric layer.
Aptly the piezoelectric array transducer arrangement is a 3D arrangement with primary kerfs extending along two axes in a plane provided by the further surface of the piezoelectric layer.
Aptly the array transducer arrangement further comprises a bonding layer between the piezoelectric layer and the backing layer.
Aptly the bonding layer comprises a frit layer.
Aptly the bonding layer can survive thermal mismatch strains up to +/−7 ppm/K, over the temperature range.
Aptly the array transducer arrangement further comprises at least one electrode layer.
Aptly the electrode layer is located proximate to the first face of the piezoelectric layer.
Aptly the electrode layer is located proximate to the further face of the piezoelectric layer.
Aptly the primary kerfs extend through the electrode layer and electrically isolate the piezoelectric elements.
According to a third aspect of the present invention there is provided a method of manufacturing an array transducer arrangement for use in a high temperature environment, comprising: providing an electrode layer, providing a piezoelectric layer on a first face of the electrode layer using additive manufacturing techniques.
Aptly the method further comprises providing a backing layer on a further face of the electrode layer.
Aptly the method further comprises curing the piezoelectric layer.
Aptly the additive manufacturing techniques include 3D printing.
Aptly the method further comprises providing a plurality of primary kerfs though the piezoelectric layer, through the electrode layer and into the backing layer to define a plurality of piezoelectric elements of a particular pitch.
Aptly the method further comprises providing a plurality of secondary kerfs into the piezoelectric layer, the secondary kerfs extending partially through the piezoelectric layer to provide a plurality of sub-elements.
Aptly the piezoelectric layer comprises Ionix HPZ-580.
Aptly the backing layer comprises Ionix HPZ-580, optionally in a depoled state.
According to a fourth aspect of the present invention there is provided an array transducer arrangement for use in a high temperature environment, comprising: at least one piezoelectric layer; at least one electrode layer; and at least one backing layer; wherein the at least one backing layer includes a first region proximate to the piezoelectric layer and a further region distal to the piezoelectric layer, the further region including a plurality of pores.
Aptly the further region is porous.
Aptly the first region has an acoustic impedance being substantially similar to the acoustic impedance of the piezoelectric layer.
Aptly the piezoelectric layer comprises a region of Ionix HPZ-580 material.
Aptly the backing layer comprises a region of Ionix HPZ-580 material, optionally in a depoled state.
Aptly the array transducer arrangement further comprises a plurality of primary kerfs though the piezoelectric layer, through the electrode layer, through and into the backing layer to define a plurality of piezoelectric elements of a particular pitch.
Aptly the array transducer arrangement further comprises a plurality of secondary kerfs into the piezoelectric layer, the secondary kerfs extending partially through the piezoelectric layer to provide a plurality of sub-elements.
According to a fifth aspect of the present invention there is provided a method of producing a porous backing layer for a high temperature array transducer arrangement, comprising: providing a sinterable powder into a pellet forming die; providing a mixture of sinterable powder and a pore former on top of the sinterable powder; pressing the mixture together to form an unsintered block; removing the pore former to provide cavities; and sintering the unsintered block.
Aptly the backing layer comprises Ionix HPZ-580, optionally in a depoled state.
Aptly the method further comprises providing a piezoelectric layer to/over at least one face of the backing layer.
Aptly pore former is removed by burning and/or ashing.
According to a sixth aspect of the present invention there is provided a backing layer for an array transducer arrangement, comprising: a first region; a further region; wherein the first region is relatively dense, the further region being relatively porous, the further region including pores to scatter/absorb sound.
Aptly the backing layer comprises Ionix HPZ-580, optionally in a depoled state.
According to a seventh aspect of the invention there is provided an array transducer arrangement for use in a high temperature environment or on a component under test with a high surface temperature, the transducer arrangement comprising: many piezoelectric elements comprising a piezoelectric material, the piezoelectric material being arranged for generating and receiving acoustic energy. A backing material to absorb and/or scatter, rearward facing acoustic energy, with an acoustic impedance substantially similar to that of the piezoelectric through the operating temperature range. A means of bonding the piezoelectric elements to the backing material, in such a way the array elements are able to withstand high temperature and maintain acoustic coupling. This bond may be either electrically conductive, or electrically resistive. A means of addressing each element electrically, and individually. This connection may be made at the interface to the backing (the rear) or on the front face. There may be a common earth, or multiple common earths on the opposite side of the elements to the actuation/sensing electrical elements.
Aptly there may be a wear plate on the front face of the piezoelectric array for protecting the piezoelectric elements from the article which is under inspection from interface wear.
Aptly there may be a metal housing which contains the array assembly.
Aptly there may be other electrically insulating or electrically isolating materials included within the assembly.
Aptly there may be a harness and/or strain relief to connect the array to an ultrasonic controller.
Aptly the wear plate may be in the form of a wedge to cause refraction of the ultrasonic beam to produce longitudinal and shear mode waves according to Snells law.
Aptly the piezoelectric element may have a Curie temperature of at least 350° C. making it a high temperature transducer of ultrasonic signals.
The piezoelectric material may have a Curie temperature of at least 400 or 500° C. The piezoelectric element may exhibit a Curie temperature which is at least any one of the following temperatures: at least 450° C., at least 550° C., at least 600° C., at least 650° C., at least 675° C. and at least 700° C.
The piezoelectric material may comprise a ceramic having a solid solution of formula: x(BiaK1-a)TiO3-yBiFeO3-zPbTiO3; wherein 0.4≤a≤0.6; 0<x<1; 0<y<1; 0<z≤0.5; and x+y+z=1; wherein the ceramic is substantially free of non-perovskite phases, other than porosity.
The array may be placed on a hot body, to send and receive ultrasonic energy, to detect for example a flaw. Aptly the temperature of the hot body may be >80° C. Aptly the temperature of the hot body is >200° C. Aptly the temperature of the hot body is >350° C. Aptly the temperature of the hot body may is >500° C. Aptly the body may be <0° C., <100° C., <200° C.
The array may be designed to work at a range of ultrasonic frequencies. Aptly the range of frequencies is between 1 and 20 MHz, optionally between 2 and 12 MHz.
Optionally the thickness of the bonding layer between the piezoelectric elements and the backing, and the front face is around <¼λ to help avoid interference with a measurement.
Aptly the acoustic impedance of the backing can be substantially matched to that of the piezoelectric materials. The backing may be formed from the same material as the piezoelectric. Optionally the backing material may contain internal porosity, and be unpoled. The porosity may be <30 vol %, and may be <20 vol %. The porosity may be >5 vol %, and may be >10% vol.
The backing may be <10% porosity, <5% or essentially no porosity. The backing may optionally be a composite, a ceramic, a metal or a high temperature polymer.
Aptly the porosity may be highly ordered. Optionally, the porosity is scattered and forms no set pattern.
Aptly the porosity of the backing may be graded. That is, the face of the backing which is attached to the active piezoelectric elements may have no, or lower, porosity than the region of the backing material which is furthermost from the piezoelectric material/layer. In this manner, a strong bond and high acoustic energy transmission interface, may be formed and the acoustic impedance is substantially well matched.
Aptly in the case of a graded backing, a face of the backing which attaches to the piezo may have <10% porosity. Optionally the porosity is <5% or <2% or zero porosity. The porosity of the face of the backing which attaches to the piezo may optionally have the same level of porosity as the active piezo element. The thickness of this low porosity region may be <10 mm or <5 mm. Aptly the thickness is <3 mm or <2 mm or <1 mm. The thickness of this low porosity region may be >λ/4. It may be >0.1, 0.2, 0.3, 0.5, or 1.0 mm.
Optionally the thickness of the backing is sufficient such as to scatter and absorb any rearward acoustic energy such that a reflection from the rearward face of the backing does not interfere with the measurement.
Aptly the thickness of the low porosity region of the backing may be <50% of the total thickness of the backing. Aptly the thickness is <40%, or optionally <30%. The thickness of the low porosity region of the backing may optionally be >1%, >2%, >5%, >10%, >20%, >30%, >40% or >50% of the total thickness of the backing material.
Optionally the graded backing may be made by bonding a dense material to a porous material, both materials of which have a similar acoustic impedance in dense form.
Optionally the graded backing may be made by the steps of:
The bonding layer between the active piezo element and the backing and/or the wear face may have an acoustic impedance of between 5 MRayl and 50 MRayl. The bonding layer may further comprise a porosity of less than 10%. The bonding layer may be suitably configured to provide an efficient medium through which ultrasonic signals may be transmitted. The bonding layer may have an acoustic impedance which is matched, or substantially matched, to both the piezoelectric element and the backing or the wear face.
Aptly The bonding layer may be formed from a ceramic containing melted or sintered glass powder, such as a FRIT. The bonding layer may be formed from a high temperature solder.
The bond layer may be an active braze. The bond layer maybe epoxy, or substantially epoxy with ceramic fillers. The bonding layer may be electrically conductive, or electrically insulating.
Aptly the bonding layer may exhibit substantially the same thermal expansion coefficient as the piezoelectric and backing layer, within +/−7 ppm/K, over the temperature range of interest.
According to an eighth aspect of the invention, there is provided a method of manufacturing a transducer arrangement via the steps of:
1. Forming a Bulk Ceramic Array
2. Forming a Ceramic Coating.
Rather than using a traditional bulk ceramic (sintered, ground, electrode, poled, cut into arrays) certain embodiments of the present invention manufacture using a coating directly onto an electrode backing. Individual elements can either be formed in the green state, or in the case of a deposition technique, the elements may be formed by masking. The coating can optionally be deposited by additive manufacturing such that the material is deposited only in areas required to form elements, controlled by a computer. Optionally, the elements may be formed in the green, unfired, state.
Such a coating method has the following advantages
Examples of means by which to coat a backing with a piezoelectric ceramic material include
According to a ninth aspect of the present invention there is provided a method of manufacturing an array transducer arrangement for use in a high temperature environment, comprising: providing a region of piezoelectric material, providing a backing layer over a first surface of said a piezoelectric region; and cutting a plurality of spaced apart primary slits through said a piezoelectric region and into the backing layer; wherein respective portions of the piezoelectric region between adjacent slits each provide respective piezoelectric elements.
Aptly a pitch of the piezoelectric elements is determined by a spacing distance between the primary slits.
Aptly a pitch of the piezoelectric elements is provided by a spacing distance between the primary slits and the width of at least one slit.
Aptly the slits are kerfs.
Aptly the portions of the piezoelectric region have an aspect ratio that is plate like or bar like.
Aptly a first layer of electrode material is disposed between said a region of piezoelectric material and the backing layer prior to cutting said a plurality of slits and the method includes cutting through said a first layer when the primary slits are cut.
According to a tenth aspect of the present invention there is provided apparatus for selectively emitting ultrasonic waves in a high temperature environment, comprising: at least one region of a piezoelectric material; at least one backing layer arranged over a first surface of said a region of piezoelectric material; and a plurality of primary slits extending through said a region of piezoelectric material and into the backing layer; wherein respective portions of the piezoelectric region between adjacent slits each provide respective piezoelectric elements.
Aptly a pitch of the piezoelectric elements is determined by a spacing distance between the primary slits.
Aptly a pitch of the piezoelectric elements is provided by a spacing distance between the primary slits and the width of at least one slit.
According to an eleventh aspect of the present invention there is provided a method of manufacturing an array transducer arrangement for use in a high temperature environment, comprising: providing a piezoelectric layer, providing a backing layer; arranging the backing layer on a first face of the piezoelectric layer; and cutting a plurality of primary kerfs through the piezoelectric layer and into the backing layer, to provide a plurality of piezoelectric elements; whereby the primary kerfs define a pitch of the plurality of piezoelectric elements.
Aptly the backing layer comprises at least one region which is porous.
Aptly the backing layer comprises at least one region which is relatively dense.
Aptly the backing layer comprises at least one region having an acoustic impedance substantially similar to the acoustic impedance of the piezoelectric layer.
Aptly the method further comprises providing an electrode layer on the first face of the piezoelectric layer such that the electrode layer is locatable between the piezoelectric layer and the backing layer, whereby the primary kerfs extend through the electrode layer.
Aptly the method further comprises providing an electrode layer on a further face of the piezoelectric layer, whereby the primary kerfs extend through the electrode layer.
Aptly the method further comprises providing an electrode layer on a second face the piezoelectric layer and the backing layer and/or on top of the piezoelectric layer, whereby the primary kerfs extend through the electrode layer.
Aptly the method further comprises cutting a plurality of secondary kerfs into the first face or the second face or a further face of the piezoelectric layer, the further kerfs extending through a portion of a thickness of the piezoelectric layer.
Aptly the secondary kerfs provide a plurality of pillar-like sub-elements.
Aptly the method further comprises providing the piezoelectric layer from Ionix HPZ-580 material.
Aptly the method further comprises providing the piezoelectric layer from PZT, or any other piezoelectric material.
Aptly the method further comprises providing the backing layer from Ionix HPZ-580 material.
Aptly the backing layer comprises Ionix HPZ-580 material in a depoled state.
Aptly the thermal expansion of the backing conforms to +/7 ppm/K and the acoustic impedance, Z, remains substantially matched.
Aptly the method further comprises providing a glassy frit bonding layer between the piezoelectric layer and the backing layer.
Aptly the piezoelectric elements are elongate pillar-like structures arranged perpendicularly to the major axis of the piezoelectric layer.
Aptly the piezoelectric elements include a plurality of elongate pillar-like structures which are connected along a distal end of each pillar-like structure.
Aptly the piezoelectric elements are box-like.
Aptly the piezoelectric elements have a maximum length parallel to the major axis of the piezoelectric layer and a minimum length perpendicular to the piezoelectric layer.
Certain embodiments of the present invention describe an array suitable for long durations of use through varying temperatures and at high temperatures. They may be employed for use in applications, for example on-stream, in-service a) crack and corrosion/erosion monitoring and imaging in high-temperature components, b) high-temperature flow measurements and c) weld and bolt/fastener inspections operating at high-temperature.
Certain embodiments of the present invention provide a relatively robust method of manufacturing array transducer arrangements for high temperature application.
Certain embodiments of the present invention provide an array transducer arrangement with for us in high temperature application.
Certain embodiments of the present invention provide a grading backing layer for an array transducer arrangement for use in a high temperature environment including at least one dense region and at least one porous region.
Certain embodiments of the present invention provide a manufacturing technique wherein piezoelectric ceramic is provided directly onto an electrode layer by additive manufacturing.
Certain embodiments of the present invention provide an array transducer arrangement with an advantageous k33/kt ratio.
Certain embodiments of the present invention provide a method of manufacturing an array transducer arrangement which eliminates a need for epoxy or filler reinforcement.
Certain embodiments of the present invention provide an array transducer arrangement for prolonged use above 80 degrees.
For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:
Certain embodiments of the present invention relate to an array transducer arrangement suitable for use in high temperature environments. Certain embodiments of the present invention relate to an array of piezoelectric elements, a bonding layer, a backing material (or acoustic absorber) a front face (or wear face or wedge) and electrical connections.
At stage 1 of
At stage 2 120 of
A conventional conductive silver frit layer 130 is applied to the piezo 110 and/or the backing 125 and air dried. Optionally, successive layers maybe provided and dried to achieve the desired thickness. The conductive layers are optionally provided as an ink by screen printing. Optionally, conductive silver frit 135 can be extended to the sides of the backing to offer a high-temperature electrical connection to the piezo-backing interface, and air dried.
At stage 3 140 of
At stage 4 150 of
At stage 5 160 of
At stage 6 175 of
The first array transducer includes a plurality of piezoelectric elements 235. Primary kerfs/gaps 240 are provided through the piezoelectric layer 215 to produce a plurality of elongate pillars or plate like elements, or sub elements, 245 of piezoelectric material. The primary kerfs 240 extend through the piezoelectric layer 215 and into the backing layer 220. It will be appreciated that the primary gaps/kerfs/slits 240 extend through both electrode layers 225, 230. Each pillar 245 is therefore electrically isolated and thus constitutes a piezoelectric element 235. Alternatively, each piezoelectric element is made up of a number of pillars, or sub elements which may be electrically connected using electrodes, cabling, wires and the like. The forming of an air-filled composite serves to improve the bandwidth, and provides a higher performance. Additionally, the air-filled composite does not suffer limitations associated with epoxy deformation and the like and can therefore operate at a higher temperature. In this configuration, the array utilizes the ‘33’ mode coupling coefficient, k33, as the piezoelectric ceramic is less constrained in a direction perpendicular to the poling direction. It is noted that, although these arrays are capable of high temperature use, they have applicability at all temperatures and have similar performance to epoxy based systems at near ambient temperatures. Alternative fluids such as noble gasses or other neutral gasses can optionally be provided between adjacent piezoelectric elements.
The small footprint of each element 235 or pillar 245 is well bonded to the backing layer 220 due to the glass frit bonding method and is robust enough to resist the cutting process in which the primary gaps/kerfs 240 are provided. The arrangement, including the glass frit bonding between the piezoelectric layer and the backing layer, provides support such that the extremely fragile piezoelectric material can withstand the cutting process.
As indicated above, each primary kerf (for the elements 235 and pillar) is made though the piezoelectric layer 215, which optionally is composed of ceramic material, through the bonding layer, and into the backing layer 220. A number of sub-elements or pillars are optionally then electrically joined together to provide piezoelectric elements of the required/desired pitch. The pitch of a piezoelectric element in which three pillars 245 are electrically connected (the electrical connection not being shown in
Optionally a number of sub-elements or pillars are joined together electrically to form an array element upon application of appropriate electric connections.
Optionally the backing layer is graded and/or includes pores.
The second array transducer arrangement provides an alternative in terms of machinability when compared to the first array transducer arrangement illustrated in
In the further cutting stage, primary kerfs 350 are cut through the piezoelectric layer and into the backing layer 320. The primary kerfs 350 provide a plurality of piezoelectric elements 345. Each element is electrically separated, by the cutting of the primary kerfs through the ceramic/piezoelectric layer, through at least one electrode layer 325, 330, through the bond layer, and into the backing 320 at the required element pitch. The pitch of a piezoelectric element which includes 3 pillars 336 is denoted by p in
The first cutting stage (in which the secondary kerfs are cut) therefore provides the pillars or sub-elements which are a substructure of each piezoelectric element. The further cutting stage (in which the primary kerfs are cut) provides the piezoelectric elements of a desired pitch which can be individually electrically addressable.
The second array transducer arrangement is hybrid mode which provides much more reliable cutting when compared to the first array transducer arrangement illustrated in
Optionally an amount of uncut material is minimised, whilst attaining reliable machining.
Optionally the backing layer is graded and/or includes pores.
The third array transducer arrangement illustrated in
An Ionix HPZ580 piezoelectric layer included in the third array transducer arrangement has a higher performance than would be expected due to the above noted k33/kt ratio.
In the third array transducer arrangement no sub-elements or pillars are used. The array is machined directly to the correct pitch.
Optionally the backing layer is graded and/or includes pores.
It will be appreciated that the first, second or third array transducer arrangements described above (and illustrated in
It will be appreciated that the first, second or third array transducer arrangements described above (and illustrated in
The acoustic impedance of the backing 500 is substantially matched to that of the piezoelectric materials used in a particular array transducer arrangement, and maintained through the temperature range. The backing may be formed from the same material as the piezoelectric layer, but contains internal porosity, and is unpoled. Optionally the porosity is <30 vol %, optionally being <20 vol %. Optionally the porosity is >5 vol %, optionally being >10% vol.
The backing 500 may be <10% porosity, <5% or essentially no porosity. The backing may optionally be a composite, a ceramic, a metal or a high temperature polymer.
The pores of the porous region of the backing layer are randomly arranged/scatted and form no set pattern. That is to say that the porosity is scattered and forms no set pattern. Optionally porosity may be highly ordered.
The porosity of the backing is graded. That is to say, the region of the backing material proximate to the active piezoelectric elements/layer has no, or lower, porosity than a region of the backing material which is further from the piezoelectric material/layer. In this manner, a strong bond and high acoustic energy transmission interface, is formed and the acoustic impedance is substantially well matched.
The face 530 of the backing proximate to the piezoelectric layer may is around <10% porosity. Optionally the porosity is <5%. Optionally the porosity <2% or zero porosity.
The porosity of the face 530 of the backing proximate to the piezoelectric layer has substantially the same level of porosity as the active piezoelectric elements. The thickness of the low porosity region is optionally <10 mm, or <5 mm. Optionally the thickness of the low porosity region is <3 mm, or <2 mm, or <1 mm. The thickness of this low porosity region is optionally >λ/4. Optionally the thickness is >0.1, 0.2, 0.3, 0.5, or 1.0 mm.
An increased bandwidth, or decreased pulse length, is observed in the second array transducer element assembled from sub-diced pillars when compared to the third array transducer element, in line with an increased k; recall that the second array utilizes predominantly the k33 mode, whilst the third predominantly the kt mode, where kt<k33. The increased damping also suppresses the centre frequency. It is understood that the array modes presented therefore are tailorable to the application.
A drop in gain from 18 to 7 dB with increasing temperature from 20 to 200° C. is observed for the array manufactured in accordance with the third array transducer arrangement. This constitutes an increase in voltage sensitivity of a factor of 3.5. The reason for this increase is due to a combination of:
Optionally the piezoelectric layer and/or piezoelectric elements of the array transducer arrangement illustrated in
Transducers and array transducers comprising piezoelectric elements may optionally be formed with BF-KBT-PT included in the piezoelectric region/layer and may be able to operate within, and/or above, a temperature range of 250° C. to 500° C. BF-KBT-PT piezoelectric elements may be able to withstand higher temperatures compared with piezoelectric elements made from PZT. The BF-KBT-PT piezoelectric elements may also be more sensitive and demonstrate increased activity and functional performance compared with piezoelectric elements made from other bismuth titanate materials. For example, BF-KBT-PT may offer up to 2-15 times the activity of other bismuth titanate materials when used in a transducer operating under the same conditions.
The piezoelectric activity may describe temperature dependent actuation of the piezoelectric material and may be related to the piezoelectric charge constant d33, which may describe the mechanical strain experienced by a piezoelectric material per unit of electric field applied. Alternatively, it may refer to the polarization generated per unit of mechanical stress applied to a piezoelectric material.
A piezoelectric layer/region, piezoelectric element, or backing layer for an array transducer arrangement according to certain aspects of the present invention may optionally be fabricated utilising a method whereby a sinterable form of a mixed metal oxide containing Bi, K, Fe and Ti (and optionally Pb) is sintered at an appropriate temperature in order to produce the required piezoelectric material. An example of such a method is described below.
The ceramic is optionally obtainable by a process comprising the following steps: (A) preparing an intimate mixture of a substantially stoichiometric amount of a compound of each of Bi, K, Ti and Fe (and optionally Pb); (B) converting the intimate mixture into an intimate powder; (C) inducing a reaction in the intimate powder to produce a mixed metal oxide; (D) manipulating the mixed metal oxide into a sinterable form; and (E) sintering the sinterable form of the mixed metal oxide to produce the ceramic. Optionally, in step (A), one or more of the compounds of Fe, Ti, K and Bi (and optionally Pb) departs from a stoichiometric amount. For example, one or more of Fe, Ti, K and Bi (and optionally Pb) is optionally present in excess of the stoichiometric amount. For example, the atomic % may depart from stoichiometry by ±20% or less, or by ±10% or less or by ±5% or less. By departing from stoichiometry, the ceramic may be optionally equipped with oxide phases (e.g. perovskite phases).
In step (A) the substantially stoichiometric amount of the compound of each of Bi, K, Ti and Fe (and optionally Pb) may be expressed by the compositional formula: x(BibKc)TiO3-y(BiFe1-dBdO3)-zPbTiO3 wherein: B is a B-site metal dopant, such as optionally Ti, Mn, Co or Nb; b is optionally in the range 0.4 to 0.6; c is optionally in the range 0.4 to 0.6; d is optionally in the range 0 to 0.5; and x, y and z are optionally as hereinbefore defined.
The compound of each of Bi, K, Ti and Fe (and aptly Pb) may be independently selected from the group consisting of an oxide, nitrate, hydroxide, hydrogen carbonate, isopropoxide, polymer and carbonate, optionally an oxide and carbonate. Some non-limiting examples are Bi2O3 and K2CO3.
The intimate mixture may be slurry (e.g. milled slurry), a paste, a suspension, dispersion, a sol-gel or a molten flux. Step (C) may include heating (e.g. calcining). Optionally step (C) includes stepwise or interval heating. Step (C) may include stepwise or interval cooling. Where the intimate mixture is a slurry, the compound may be a salt (e.g. a nitrate). Where the intimate mixture is a sol-gel, the compound may be an isopropoxide.
Where the intimate mixture is a molten flux, the compound may be an oxide dissolved in a salt flux. The mixed metal oxide from step (C) may be precipitated out on cooling. Optionally the intimate powder is a milled powder. Step (A) may be: (A1) preparing a slurry of a substantially stoichiometric amount of a compound of each of Bi, K, Ti and K (and optionally Pb); (A2) milling the slurry; and step (B) may be (BI) drying the slurry to produce the milled powder.
Step (D) may include milling the mixed metal oxide. Step (D) may include pelletising the mixed metal oxide. Step (D) may include suspending the mixed metal oxide in an organic solvent.
Step (D) may include painting, spraying or printing the mixed metal oxide suspension to prepare for sintering.
Step (E) may be stepwise or interval sintering. Optionally step (E) includes stepwise or interval heating and stepwise or interval cooling. Step (E) may be carried out in the presence of a sintering aid. The presence of a sintering aid may promote densification. The sintering aid may be CuO2.
Aptly, the ceramic further comprises a pre-sintering additive which is present in an amount of 75 wt % or less, optionally 50 wt % or less, or 25 wt % or less, or 5 wt % or less. The pre-sintering additive may be present in a trace amount.
The pre-sintering additive may be a perovskite or, alternatively, optionally a layered perovskite such as Bi4Ti3O12. The pre-sintering additive may also be a lead-containing perovskite such as PbTiO3 or PbZrO3. The pre-sintering additive may be added post-reaction (e.g. post-calcination) in order to form the mixed metal oxide containing Bi, K, Fe and Ti (and optionally Pb). In this way, the pre-sintering additive may act as a sintering aid to fabrication process.
The transducer may be configured to be operable as at least one of a contact transducer, a single element transducer, a dual element transducer, as an angle beam transducer, a delay line transducer, a flexural mode transducer, and an immersion transducer. The transducer may also be configured to be operable as a 1 dimensional or 2 dimensional array suitable for use as a composite single element transducer, a full matrix capture sensor, or as a phased array.
The glass bonding layer of any of the above described transducer arrangements may be configured such that it can be cured at a temperature below 600° C., or optionally below 580° C., which may remove a need to re-polarize the piezoelectric element. Alternatively, configuring the bonding layer so that it is cured at a temperature below 450° C. may enable the transducer to be bonded, in air, to a substrate comprising 400 series steel without causing significant corrosion to the substrate. Furthermore, configuring the bonding layer such that it may be cured at 350° C. or more, may enable the transducer to be used for monitoring the components of a nuclear power plant, including the monitoring of low pressure steam, for example. A curing temperature of the bonding layer between 350° C. and 400° C. may enable the transducer to be used for monitoring the components of chemical processing plant. Alternatively, configuring the bonding layer such that it can be cured within a range of temperatures between 550° C. and 565° C. may enable the transducer to be used for the permanent monitoring of conditions within a conventional gas or coal fired power station.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019016.1 | Dec 2020 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2021/053115 | 11/30/2021 | WO |
