Patent Description:
Thermographic imaging has proven to be a generally useful technique for detecting structural abnormalities.

Document <CIT> discloses an inspection system <NUM> with a plurality of transducer elements <NUM>, <NUM>, <NUM> that are coupled to a structure <NUM> to be investigated via guided wave thermography in <FIG>. The guided waves are used to selectively deliver acoustic sonic or ultrasonic energy throughout the structure <NUM>, which can cause a thermal response upon impingement with a structural flaw which can be located in the structure <NUM>. The thermal response induced by the sonic or ultrasonic energy can be detected with the thermal imaging system <NUM>. For this reason, the system <NUM> includes a controller <NUM> for guided wave controlling <NUM> and for thermal imaging controlling <NUM> of a thermal imaging sensor <NUM>.

Document <CIT> discloses an ultrasonic guided wave system for defect detection in a plate-like structure <NUM> in <FIG>. The system includes at least one piezoelectric shear ring transducer element <NUM> coupled to a structure <NUM>. Furthermore, the system includes a controller with a processor, wherein the processor is configured to cause a pulse generator to pulse the shear ring element <NUM> such that the shear horizontal-type guided wave energy <NUM> is transmitted in all directions in the plate-like structure <NUM>. Additionally, the processor is configured to process at least one guided wave signal <NUM> to identify the presence and location of at least one possible defect <NUM> in the plate-like structure <NUM>.

For example, when exciting a structure with flaws using relatively high ultrasonic power, frictional heating may be generated at the flaws. The flaws can then become detectable under a thermal infrared camera. However, structurally weak regions that may be part of the structure may be vulnerable when subjected to such high ultrasonic power, which could lead to break up of the structure being inspected. Thus, there is a need for further improvements in connection with systems and methods for inspecting a structure.

Therefore, it is an object of the present invention to improve a system and a method for inspecting a structure.

The object is met by the independent claims. Further preferred embodiments of the invention are a part of the dependent claims.

It should be appreciated that the present inventor has recognized the above limitations, and now discloses a new solid state welding process, e.g., magnetic pulse welding, for additive manufacturing of superalloys.

In one embodiment, a system for inspecting a structure is provided as defined in claim <NUM>.

In yet a further exemplary embodiment, the system may include a plurality of transmitting transducer elements to transmit guided sonic or ultrasonic waves throughout the structure, wherein the energy is effective to cause a thermal response upon impingement with a structural flaw. The system may also include a means for simultaneously applying a plurality of signals to the plurality of transducer elements. The signals may include independent relative phase such that a plurality of predetermined phasing vectors may be implemented. The system includes at least one thermal imaging sensor arranged to sense the thermal response indicative of the flaw, and a controller operatively connected to the transducer elements and sensors to, e.g., control the sensing of the thermal response by the thermal imaging sensor and the phasing, and to control the plurality of predetermined phasing vectors in order to provide enhanced ultrasonic energy coverage across the structure by means of varying the ultrasonic vibration response.

In yet another exemplary embodiment, a method of inspecting a structure is provided as defined in claim <NUM>.

It should be appreciated that aspects of the exemplary inventive guided wave thermography system disclose herein may be implemented by any appropriate processor system using any appropriate programming language or programming technique. The system can take the form of any appropriate circuitry, such as may involve a hardware embodiment, a software embodiment or an embodiment comprising both hardware and software elements. In one embodiment, the system may be implemented by way of software and hardware (e.g., processor, sensors, etc), which may include but is not limited to firmware, resident software, microcode, etc..

Furthermore, parts of the processor system can take the form of a computer program product accessible from a processor-usable or processor-readable medium providing program code for use by or in connection with a processor or any instruction execution system. Examples of processor-readable media may include non-transitory tangible processor-readable media, such as a semiconductor or solid-state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk--read only memory (CD-ROM), compact disk--read/write (CD-R/W) and DVD.

The present inventors have identified the limitations of existing acoustic/ultrasonic thermography systems and recognized a need for systems and methods that may be selectively optimized to efficiently cause thermal responses at structural flaws with relatively low excitation power.

The present inventors propose innovative utilization of sonic or ultrasonic guided waves for performing thermography inspection on a variety of structures, which in one non-limiting application may comprise components of a combustion turbine engine, such as blades, vanes, etc. Ultrasonic guided waves comprise multi-mode structural resonances that propagate in a bounded structure, which effectively functions as a waveguide.

Aspects of the present invention utilize at least one actuator to deliver acoustic sonic or ultrasonic energy throughout the structure, which can cause a thermal response (e.g., heating) upon impingement with a structural flaw which may be located in the structure. As elaborated in greater detail below, the thermal response induced by the sonic or ultrasonic energy can be detected with a thermal imaging system, which may be effective for high flaw detection sensitivity while utilizing at least one of frequency sweeping, actuator phasing, and shear energy excitation in order to minimize the ultrasonic energy introduced to the structure under test.

For general background information, reference is made to U. Patent <CIT>.

Referring now to the drawings wherein the showings are for purposes of illustrating embodiments of the subject matter herein only and not for limiting the same, <FIG> illustrates a schematic representation of a guided wave thermography system <NUM>, which may be used to practice aspects of the present disclosure.

In one exemplary embodiment, the system <NUM> includes one or more transmitting-transducers coupled to a structure <NUM> (an object being inspected) for transmitting ultrasonic guided waves through the structure. The transmitting-transducers may be arranged as a distributed array of single-element transmitting-transducers <NUM>; or may comprise multi-element transmitting-transducers, such as an annular array transducer <NUM> comprising a plurality of individually-actuated transmitting elements <NUM> (as may be better appreciated in <FIG>); or a circular array transducer <NUM> comprising a plurality of individually-actuated transmitting elements <NUM> (as may be better appreciated in <FIG>). The transmitting-transducers could include, but are not limited to piezo-stack transducers, piezo-ceramic bars, disks, rings, or cylinders, magnetostrictive transducers, electromagnetic acoustic transducers (EMATs), controlled mechanical impact devices, piezo-composites, etc. It will be appreciated that aspects of the present disclosure are not limited to any particular configuration for the transmitting-transducers, or to any particular shape of structure <NUM>, apart from what is defined in claim <NUM>. Accordingly, the configuration of transmitting-transducers, or the shape of structure <NUM> as illustrated in the figures should be construed in an example sense and not in a limiting sense.

The system <NUM> may further include a signal conditioner <NUM>, which in one non-limiting embodiment may be configured to provide appropriate signal amplification by way of one or more amplifier circuits <NUM>, and impedance matching by way of one or more impedance matching networks <NUM> to electrical signals which may be respectively applied to transmitting-transducers <NUM>, <NUM>, <NUM> from a signal generator <NUM> (e.g., a multi-channel signal generator). A system controller <NUM> may include a guided wave controller <NUM>, (labeled GW controller) which may be configured to control signal generator <NUM>, such as may be configured to control one or more signal parameters of one or more signals that may be applied to the one or more transmitting-transducers to generate the ultrasonic guided waves transmitted through structure <NUM>. Non-limiting examples of signal parameters that may be controlled to determine signal characteristics for the signals that may be applied to the one or more transmitting-transducers may comprise a phase delay, a frequency, and a combination of phase delays and frequencies, such as may involve a phase delay sweep, frequency sweep or both. The system controller <NUM> may further include a thermal imaging system comprising a thermal imaging controller <NUM> to control a thermal imaging sensor <NUM> (e.g., an infrared (IR) camera) configured to sense a thermal response indicative of the flaw.

It will be appreciated that for thermography to effectively detect structural flaws, the magnitude of certain vibration variables (e.g., in-plane displacement, shear stress, etc.) appropriate to the geometry and/or the spatial orientation of a given structural flaw, should be set sufficiently high in the immediate vicinity of the given flaw to ensure that a sufficient thermal response (e.g., heating) is induced.

As will be appreciated by one skilled in the art, during ultrasonic vibration of plate-like or other waveguide-like structures, the magnitude of the generated vibration fields can vary throughout such structures. For example, such variations may occur both through the thickness of the structure and as a function of distribution relative to the other dimensions of the structure. Accordingly, the variation in the vibration fields can lead to regions of relatively high stress, displacement, etc., as well as to regions of practically no stress, displacement, etc. In order for a structural flaw located in a given region of the structure to be appropriately acousto-thermally excited, the pertinent vibration variables of the vibration field delivered to such a region should have sufficiently high amplitude. As suggested above, the pertinent vibration variables may vary depending on the geometry of the structural flaw and/or the spatial orientation of the flaw.

In one non-limiting embodiment, control of phase delay and/or frequency (e.g., phase delay and/or frequency sweep) may be performed on the signals (e.g., continuous signals) applied to the one or more transmitting-transducers coupled to structure <NUM>. This phasing action when performed on the transmitting-transducers may be conducive to enhanced spatial selectivity for the locations of low or high sonic or ultrasonic energy throughout such structures (e.g., enhanced spatial selectivity for the location of nodes for enhancing the intensity of the sonic or ultrasonic energy delivered to a given region of the structure, and the location of anti-nodes for attenuating the intensity of the sonic or ultrasonic energy delivered to other regions of the structure). In one non-limiting embodiment, the phasing can be performed in conjunction with frequency sweeping to provide maximum spatial selectivity to intensity variation throughout the structure of the generated vibration fields.

The combination of signal phasing and frequency sweeping effectively allows spanning of a multi-dimensional phasing-frequency space. This allows for an ability to form a relatively greater range of vibration states --which for example may be selectively formed throughout the structure being inspected-- than would be feasible if operating at a single frequency, or just performing frequency sweeping. These vibration states allow substantial versatility regarding selectivity of different vibration fields throughout the thickness of the structure, such as displacement wavestructure, stress wavestructure, vibration mode shape, etc. This is conducive to an increased likelihood of detecting a broad range of structural flaws, regardless of structural flaw geometry, depth, and other flaw characteristics.

<FIG> is a schematic representation of one non-limiting embodiment for implementing a respective phase delay on signals <NUM> respectively applied to single-element transmitting transducers <NUM> distributed on a structure <NUM> being inspected. In this embodiment, continuous wave signals <NUM> may be respectively applied to transmitting transducers <NUM> each having a different phase delay. Without limiting aspects of the present disclosure to any particular theory of operation, it is believed that in this case the effect of phasing may be to excite various natural modes of the structure by changing a loading distribution across its surface. Any combination of phase delay values applied to the plurality of transmitting transducers <NUM> may be referred to as a "phasing vector". For general background information in connection with phasing, reference is made to U. Patent <CIT> and <CIT>.

Significant improvements in response can be obtained by utilizing guided wave energy concentration via a phased transducer array with the appropriate frequency and phasing. One example of this is provided in <FIG>, which compare two finite element models of an identical structure upon which identical actuator arrays are installed. Structure <NUM> (<FIG>) features the cumulative stress field coverage achieved by means of frequency sweeping, in which the darker areas <NUM> indicate higher stresses and the lighter areas <NUM> indicate lower stresses. Alternatively, structure <NUM> (<FIG>) features the cumulative stress field coverage achieved by means of frequency sweeping, in which the darker areas <NUM> indicate higher stresses and the lighter areas <NUM> indicate lower stresses. The benefit of actuator phasing is, as illustrated here, is that a much greater variety of vibration states can be induced, which allow the maximum stresses, or other measure of energy concentration, to be distributed across the structure to a greater degree without increasing the ultrasonic power induced in the structure at any given time.

With respect to <FIG>, consider a case in which a defect <NUM> requires a certain minimum level of local ultrasonic energy concentration to be detectable by a thermal imaging system. A conventional acoustic thermography system may apply at least one actuator to structure <NUM> (<FIG>) and excite the at least one actuator over a range of frequencies. Based on the bandwidth of the actuator, the geometry of the structure, and location at which it is coupled to the structure, the maximum ultrasonic energy concentration in structure <NUM>, considering all frequencies at which the actuator is excited, may be as shown in <FIG>. In this case, the local ultrasonic energy concentration at the location of defect <NUM> never exceeds the minimum threshold and the defect is undetectable. One conventional way to address this limitation is by increasing the overall ultrasonic input power, which at some point will increase the amplitude of the energy field of <FIG>, but will not change its distribution. As a result of this increase in overall ultrasonic energy, the darker high-intensity regions <NUM> will be exposed to very high ultrasonic energy levels, which may damage the structure. In many cases, the overall ultrasonic energy cannot be increased due to limitations of the actuator or amplification systems, in which case defect <NUM> is undetectable.

However, by implementing the method and system described herein, various actuator phasing combinations can be applied across a plurality of actuators along with frequency sweeping in order to greatly increase the number of and variety of ultrasonic vibration states of structure <NUM> (<FIG>), in which the net ultrasonic energy coverage is greatly improved. Utilizing this approach, the defect <NUM> becomes detectable without increasing the overall power level and without necessarily exposing any regions of the structure <NUM> to unnecessarily high energy levels.

The improvement in ultrasonic energy coverage by implementing one embodiment of the frequency sweeping and phasing system and method described herein is quantified in <FIG>, which plots experimental data comparing the ultrasonic energy coverage over a structure using three methods of actuator excitation: 'single frequency', 'frequency sweeping', and 'phasing and frequency sweeping' at various input power levels. This graph demonstrates that for a given input power level, much greater energy coverage above the predetermined threshold level is achievable by implementing a frequency sweeping and phasing excitation method.

It should be noted that the appropriate frequency and phasing combination can excite certain structural flaws and not others. One example of this phenomenon is depicted in <FIG>, in which two cracks <NUM> and <NUM> are present above and below hole <NUM>, respectively. A first frequency and phasing combination applied to the actuators in <FIG> yield sufficient thermal excitation at both cracks <NUM> and <NUM> to be detected with moderate intensity. In comparison, a second frequency and phasing combination applied to the same actuators in <FIG> yield insufficient thermal excitation to detect crack <NUM>, but the thermal intensity at crack <NUM> is much higher than in <FIG>, in which the first frequency and phasing combination was applied. Therefore, the appropriate frequencies of excitation in conjunction with appropriate actuator phasing can be used to thermally excite flaws in the structure that may be otherwise undetected by conventional acoustic thermography systems and methods.

In another non-limiting embodiment, in lieu of continuous signals, respective streams of pulses may be applied to the one or more single or multi-element transmitting-transducers coupled to the structure being inspected. In this embodiment, transient guided waves may be propagated throughout the structure to avoid causing steady-state vibration. This may be accomplished by applying relatively narrow, high-power excitation pulses. It is contemplated that a similar effect (e.g., no steady-state vibration) may be achieved in applications involving large and/or attenuative structures, in which there may be insufficient interaction with the boundaries of the structure to induce structural resonance. These excitation pulses may be repeated at a repetition frequency sufficient to cause the accumulation of thermal energy in the vicinity of a given structural flaw to allow the thermal imaging system to detect the structural flaw. As will be appreciated by one skilled in the art, appropriate imaging techniques may be utilized to increase the signal-to-noise ratio and detect relatively weak thermal gradients.

To implement the phasing system and method most efficiently, the band over which the frequency is swept must be adjusted for each new phasing combination, as the forced vibrational spectrum is shifted by applying phasing. The optimal frequency band can be selected by means of an impedance analyzer sweep or by analyzing the forward and reflected power measured between the amplifiers and the actuators. For further details regarding frequency optimization as part of a phasing system and method, reference is made to doctoral dissertation by C. Borigo, titled A Novel Actuator Phasing Method for Ultrasonic De-lcing of Aircraft Structures, available from The Pennsylvania State University (<NUM>).

In one non-limiting embodiment, it is contemplated that the sensing of the thermal response by the thermal imager may be synchronized (e.g., frequency lock, phase lock) relative to a frequency of the stream of excitation pulses which may be applied to the one or more transmitting transducers. It is further contemplated that such a frequency may comprise a time-varying frequency (e.g., a chirping frequency). This temporal synchronicity is believed to enhance a signal-to-noise ratio in connection with the sensing of the thermal response by the thermal imager. In one example embodiment, the synchronicity may be performed relative to an expected energization time of a region being excited in response to the guided ultrasonic wave.

One further aspect of the present disclosure is the utilization of shear actuators to generate shear horizontal-type guided waves in a structure, as well as the vibration states induced by the waves in the structure if the excitation signal is applied for a sufficient period of time. Shear horizontal-type guided waves are a class of guided wave modes that can exist in plate-like structures. The characteristics of a shear-horizontal guided wave mode and the means by which it may be excited for the purposes of the present disclosure are described below.

More generally, guided waves may be defined as elastic waves propagating in a medium (a waveguide structure) in which distinct wave modes can exist that satisfy the boundary conditions of the waveguide structure. Guided waves differ from traditional bulk waves at least by the fundamental fact that an infinite number of distinct wave modes may exist with wavestructures (e.g., displacement, stress, energy, etc. distributions through the thickness of the waveguide) that may vary as a function of mode and/or frequency. Dispersion curves, such as the ones shown in <FIG>, illustrate a relationship between phase (or group) velocity and mode and frequency for a given structure. Each waveguide has its own unique set of dispersion curves, which may be useful for identifying various mode-frequency possibilities in a waveguide. Wavestructure variations can yield substantial flexibility for utilizing guided waves, since, for example, particular wave mode and/or frequency combinations can be selected with desirable properties through the thickness of the structure.

Examples of three guided wave modes comprising different vibration characteristics are shown in <FIG>. The deformation of a plate-like structure with an anti-symmetric (A-type) guided wave mode propagating through it is shown in cross-section in <FIG>. Alternatively, the deformation of a plate-like structure with a symmetric (S-type) guided wave mode propagating through it is shown in cross-section in <FIG>. Note that the vibration in <FIG> is solely in the x-z plane. Finally, the deformation of a plate-like structure with a shear horizontal (SH-type) guided wave mode propagating through it is shown in cross-section in <FIG>; note that the vibration in <FIG> is solely in the y direction.

Furthermore, it can be shown that for shear horizontal waves in isotropic, homogeneous plates of uniform thickness, the only non-zero stresses induced by the waves are the in-plane shear stresses τxz and τyz. Therefore, such waves induce pure shear into the structure for the case of isotropic, homogeneous plates of uniform thickness. It will be appreciated that in the case of structures that do not meet the definition of isotropic, homogeneous plates of uniform thickness, the stress components of shear horizontal-type waves are generally predominantly shear instead of pure in-plane shear. For further details on guided waves, reference is made to textbook by <NPL>).

It will be appreciated that for thermography to effectively detect structural flaws, the magnitude of certain vibration variables (e.g., in-plane displacement, shear stress, etc.) appropriate to the geometry and/or the spatial orientation of a given structural flaw, should be set sufficiently high in the immediate vicinity of the given flaw to ensure that a sufficient thermal response (e.g., heating) is induced. As illustrated in <FIG>, the in-plane shearing <NUM> is ideal for generating surface rubbing at a crack <NUM> in a structure <NUM>, which in turn generates a detectable level of heat <NUM>. The shearing-induced friction illustrated in <FIG> can occur for cracks perpendicular to the local surface plane of the part as well as cracks or delaminations parallel to the local surface plane of the part. Furthermore, the efficiency of heat generation <NUM> at crack <NUM> is dependent on the relative orientation of the crack and the shearing motion <NUM> induced by the ultrasonic vibration. The phasing and frequency sweeping described above can address this by varying the vibration field, as illustrated in <FIG>.

The inventors note that the transient propagating guided wave solution for shear horizontal-type ultrasonic guided waves is not directly applicable to the steady-state ultrasonic vibration solution, but the two may be intimately related.

Conventional acoustic thermography technology utilizes a piezo-stack actuator with an acoustic horn actuator, including those produced under the brand name Branson. These types of actuators generate predominantly flexural (A-type) and compressional vibrations (S-type), which are composed only of in-plane and out-of-plane particle displacements that are less well-suited to induce crack heating in many cases than the shearing energy of the SH-type modes. Less efficient crack heating means more energy is required to gain the same level of detectability and thus the chances of unintentional part damage are higher. Additionally or alternatively, in some non-limiting embodiments of the present disclosure, shear horizontal-type energy may be introduced into the structure by means of d15 piezoelectric shear actuators.

In one non-limiting embodiment, the piezoelectric d15 shear actuator may be a "shear bar", in which the d15 piezoelectric coefficient is employed in a laterally-polarized piezoceramic block <NUM> such as the one illustrated in <FIG>. Here the piezoceramic element <NUM> is polarized in the direction indicated by the arrow <NUM> and an electric potential is applied across the electrode faces <NUM> and <NUM> using the alternating voltage source <NUM> attached with leads <NUM>. As illustrated in <FIG>, when the voltage is applied to the undeformed element <NUM>, it shears into a deformed state <NUM>. The various dimensions and the piezoceramic material selected for the bars can all be adjusted to suit the specific requirements of the application as will be understood by people of ordinary skill in the art.

In a second non-limiting embodiment, the piezoelectric d15 shear actuator is a "shear ring", in which the d15 piezoelectric coefficient is employed in a circumferentially-polarized piezoceramic ring <NUM> such as the one illustrated in <FIG>. The shear ring element is fabricated from two half rings that are polarized quasi-circumferentially, in accordance with arrow <NUM> and subsequently bonded together to form a full ring element <NUM>, which can be excited with voltage source <NUM> applied to the upper and lower electrode surfaces <NUM> and <NUM> via leads <NUM>. The torsional vibration <NUM> of the shear ring element under a voltage applied by the source <NUM> is illustrated in <FIG>. This torsional deformation effectively excites SH guided waves omnidirectionally when coupled to a structure. The inner and outer radii, the thickness, and the piezoceramic material selected for the rings can all be adjusted to suit the specific requirements of the application as will be understood by people of ordinary skill in the art. Additional variations upon this transducer design also are possible, and the specific embodiment detailed herein is non-limiting and used as one example of an omnidirectional piezoelectric d15 shear ring element for SH-type guided wave generation in accordance with some embodiments. Additional embodiments may include shear rings that are fabricated from more than two segments, shear rings that are poled through the radius instead of the thickness dimension, and shear rings that are polygonal instead of truly circular.

The piezoelectric shear transducer elements described above are one or more of the components within a transducer module, such as the non-limiting example shown in cross-section in <FIG>. In the embodiment shown in <FIG>, transducer module <NUM> is comprised of a housing <NUM> that contains at least one piezoelectric shear bar element <NUM> bonded to at least one faceplate <NUM>, which is comprised of a metallic or ceramic material and allows the ultrasonic shear energy to be efficiently transmitted from element <NUM> to the structure under test by means of mechanical pressure coupling. Module <NUM> is further comprised of a cavity <NUM> through which a connector <NUM> is electrically connected to the upper and lower electrode faces <NUM> and <NUM> by means of a flexible circuit <NUM> or jumper wires. In some embodiments, module <NUM> may be further comprised of magnets <NUM> that aid in retaining a clamping device in pocket <NUM> for the purposes of coupling the module to the structure under test. <FIG> is another view of the module <NUM> shown in cross-section in <FIG>. Here the faceplate <NUM> is shown with the rectangular coupling surface <NUM>. In additional non-limiting embodiments, similar module design may be adapted to accommodate a shear ring transducer, in which case the coupling surface <NUM> and faceplate <NUM> would be circular instead of rectangular.

It should be noted that another advantage of utilizing one or more piezoelectric shear elements as part of a guided wave thermography system is that they are much smaller than the piezo-stack transducers utilized as part of conventional acoustic thermography systems. This affords the opportunity to conduct in situ inspections or perform inspections with fewer limitations due to access issues.

Additional embodiments may include shear horizontal-type excitation by means of magnetostrictive or EMAT (electromagnetic acoustic transducer) devices, as will be understood by those of ordinary skill in the art.

<FIG> provide examples of thermal images collected using one embodiment of the invention. The images are of turbine blades with crack-like defects along the trailing edge. In all three images, the cracks <NUM> are indicated by the dark areas of higher temperature indicated by the arrows. The rectangular areas <NUM> are calibration strips.

While specific embodiments have been described in detail, those with ordinary skill in the art will appreciate that various modifications and alternative to those details could be developed in light of the overall teachings of the disclosure. Methods and systems based on guided wave thermography for non-destructively inspecting structural flaws that may be present in a structure are described herein. Such systems may include the ability to sweep a frequency-phase space in order to maximize ultrasonic energy distribution across the structure while minimizing input energy by means of a plurality of actuators. Moreover, such systems include transducer elements configured to predominantly generate shear horizontal-type guided waves in the structure to maximize thermal response from the flaws. In the foregoing detailed description, various specific details are set forth in order to provide a thorough understanding of such embodiments.

However, those skilled in the art will appreciate that embodiments of the present disclosure may be practiced within the scope of the claims without some of the aforementioned specific details, that the present disclosure is not limited to the depicted embodiments, and that the present disclosure may be practiced in a variety of alternative embodiments. In other instances, methods, procedures, and components, which would be well-understood by one skilled in the art have not been described in detail to avoid unnecessary and burdensome explanation. Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention.

Claim 1:
An inspection system (<NUM>) comprising:
a piezoelectric shear transducer element (<NUM>, <NUM>) contained in a housing (<NUM>), a controller (<NUM>) and a thermal imaging sensor (<NUM>), wherein the controller (<NUM>) is operably connected to the piezoelectric shear transducer element (<NUM>, <NUM>),
wherein the piezoelectric shear transducer element (<NUM>, <NUM>) is configured to receive at least one signal for generating shear horizontal-type guided sonic or ultrasonic waves throughout a structure (<NUM>) to cause a thermal response upon impingement with a structural flaw,
wherein the thermal imaging sensor (<NUM>) is configured to sense the thermal response indicative of the structural flaw,
wherein the controller (<NUM>) is configured to control one or more parameters of the at least one signal and a phasing thereof, and for controlling the sensing of the thermal response, characterized in that
the shear transducer element (<NUM>, <NUM>) comprises a faceplate (<NUM>) for coupling the shear horizontal-type guided sonic or ultrasonic waves into the structure (<NUM>) via a mechanical pressure coupling.