The invention comprises a system and method for assessment of irregularity in a material surrounded by a substrate, from above a surface of the substrate, such as rot or decay in the in-ground part of wooden poles or other wooden elements buried below the ground surface.
Traditionally poles are tested using a sounding hammer and trained ear or microphone. Recently instruments have been developed to measure the speed of ultrasonic transmission across the pole or the resistance to drilling a hole. These tests are generally restricted to measuring in the cross-section of the pole above ground. Measurements based upon measuring the resistance to drilling a hole can be used to penetrate short distances below ground but are inherently destructive and are limited to detecting changes in resistance along the drill path. The ultrasonic tester is inherently non-destructive.
The best available technology today for detecting the physical condition of wooden structures below ground is to measure the resistance to drilling by a small diameter drill bit as it penetrates progressively into the structure using an instrument called a Resistograph. The drill bit has a length of up to approximately 45 cm and by drilling a hole at an angle downward from ground level it is possible to detect variations in resistance of up to approximately 30 cm below ground. A reduction in resistance to drilling indicates a region of weakness in the structure. However, this technique is inadequate to detect discontinuities more than 30 cm below ground or away from the drill path. The effective detection of defects below ground requires excavation. Many poles are set in concrete or asphalt and are not amenable to such examination. Drilling also inherently damages and weakens the structure being tested, and excavation can further weaken the foundation of the pole.
Currently used in the testing for above ground defects is the measurement of ultrasonic velocity between a source and receiver mounted on the surface of the pole, such that the path of the ultrasonic energy from source to receiver intersects the region of interest. By analysing the result of several such scans across the same cross-section it is possible to deduce a two-dimensional view of variations in density in that cross-section. This enables the remaining good wood to be visualised should the pole have been subjected to internal rot or insect infestation.
There is an unsolved problem of non-destructively detecting defects in wooden structures below the ground, where most decay occurs.
Ground penetrating radar has been used to detect rot in trees above ground and map the roots of trees below ground. However, it is the experience of the inventors that this technique when applied to wooden poles to inspect below ground defects provides only gross estimates of internal damage with little or no value in terms of estimating the fitness for use. When angled to the pole at ground level, ground penetrating radar has limited ability to effectively examine for defects beyond depths of approximately 30 cm. This is inadequate to reliably assess defects which are below this depth and which can adversely affect the load bearing capacity of the pole.
In broad terms the invention comprises in a first aspect a system for assessment of irregularity in material below a surface of a substrate, from above the surface of the substrate, the material being part of a body of the material surrounded by the substrate below the surface of the substrate, the body extending from below to above the surface of the substrate, and the assessment system being adapted to be positioned above the surface of the substrate, the system comprising:
In at least some embodiments the transmitter(s) or transducer(s) are arranged to transmit the transmitted energy in a focused beam shape and/or direction through the material of the body. The at least one transmitter and receiver or transducer may comprise an array of multiple transmitters and a receiver or receivers, or an array of multiple transducers, and may comprise an array of two or more arrays of multiple transmitters or multiple transducers. At least one array may be a phased array. The phased array may be a fixed phased array or a dynamically phased array enabling steering of the transmitted energy through the material of the body below the surface by varying the phase relationships.
In broad terms the invention comprises in a second aspect a method for assessment of irregularity in material below a surface of a substrate from above the surface of the substrate, the material being part of a body of the material surrounded by the substrate below the surface of the substrate and the body extending from below to above the surface of the substrate, the method comprising:
The substrate may be ground, and the material wood below the ground surface, of a wooden element such as a wooden pole extending from below the ground surface to above the ground surface. The ground surface may be covered by asphalt or concrete for example. The system may be for assessment for any rot, decay, insect infestation or damage, holes, or delamination in the wooden element below the ground. Alternatively, the substrate may be for example concrete. Alternatively again, the wooden element may be a pile in the sea floor (the substrate/ground comprises the seabed), supporting a wharf for example. Further alternatively, the wooden element may be a beam (a non-vertical element) an end of which is encased in a concrete column or simply inaccessible due to obstructions, and in this specification ‘above’ and ‘below’ the surface should be understood relatively.
In at least some embodiments the method or system includes calibrating the system by transmitting and receiving through the body above the surface of the substrate.
In at least some embodiments the system comprises a mount or mounts adapted to position the transmitter(s) and receiver(s) or transducer(s) adjacent the body above the surface of the substrate and at an angle to an axis of the body extending from below to above the substrate. The mount or mounts may be adapted to position the transmitter and receiver or transducer at an angle in the range above 0 to below 180 degrees to the surface of the substrate, such as for example at an angle in the range 30 to 60 degrees. The mount or mounts may be adapted to enable adjustably positioning the transmitter and/or receiver or transducer at multiple different angles. In at least some embodiments the mount or mounts are adapted to enable adjustably positioning the transmitter and/or receiver or transducer at multiple different vertical spacings above the surface of the substrate. In at least some embodiments the system comprises a mount or mounts adapted to position the transmitter(s) and receiver(s) or transducer(s) at locations spaced around an axis of the body extending from below to above the substrate, such as locations spaced substantially equidistantly around said axis of the body. In at least some embodiments the system may be arranged to assess irregularity in the material below the surface of the substrate to an extent or depth of at least 4 metres below the surface of the substrate.
In at least some embodiments the transmitter and receiver or transducer operate at a frequency or frequencies above about 200 Hz or above about 2 kHz or above about 5 kHz or above about 10 kHz or above about 20 kHz and/or at a frequency or frequencies below about 500 kHz or below about 300 kHz or below about 100 kHz or below about 20 kHz and/or at other sonic or ultrasonic frequency or frequencies. In at least some embodiments the system comprises the transmitter(s) or transducer(s) is/are arranged to transmit energy as a pulse or series of pulses. In at least some embodiments the transmitter(s) or transducer(s) has a Q factor of not more than about 4.
In this specification:
The invention is further described with reference to the accompanying figures and by way of example, in which:
As stated the invention comprises a system and method for assessment of irregularity in a material surrounded by a substrate and on one side of a surface of the substrate, from another side of a surface of the substrate.
As stated in at least some embodiments the transmitter(s) or transducer(s) are arranged to transmit the transmitted energy in a focused beam shape and/or direction through the material of the body. The at least one transmitter and receiver or transducer may be a single transmitter and receiver or transducer or may comprise an array of multiple transmitters and a receiver or receivers, or an array of multiple transducers, and may comprise an array of two or more arrays of multiple transmitters or multiple transducers. At least one array may be a phased array. The phased array may be a fixed phased array or a dynamically phased array enabling steering of the transmitted energy through the material of the body below the surface by varying the phase relationships. In the embodiment shown in
The transducers may operate at a single frequency or a range of frequencies in the range above about 200 Hz or above about 2 kHz or above about 5 kHz or above about 10 kHz or above about 20 kHz and/or below about 500 kHz or below about 100 kHz or below about 100 kHz or below about 20 kHz and/or at other sonic or ultrasonic frequency or frequencies for example. The frequency is e.g. a relatively low frequency so that the ultrasonic energy will penetrate into the pole for example up to four metres below ground, and preferably detect defects with dimensions on the order of a centimetre or more. The transducers may operate over a wide bandwidth so that the pole can be tested over a broad band of frequencies with a single pulse. The transmitter(s) or transducer(s) may have a Q factor of not more than about 4.
The transducers may emit a short pulse of energy which is of a shorter length than the time required for the pulse to return to the transducer after being reflected in the pole, or series of such pulses, such as of duration less than about 250 milliseconds or less than about 100 milliseconds or less than about 50 milliseconds or less than about 2 or 1 millisecond(s) for example. This gives lower reverberations and ensures that the transducer is receiving as much of an uninterrupted signal as possible and is not picking up unwanted reflections or signals. Alternatively, the transducers may emit a longer or in some embodiments a continuous pulse into the pole. Preferably, the short pulse of energy comprises a chirp of multiple different frequencies to facilitate differentiation of true reflections from reverberations. The preferred pitch (i.e. the distance between adjacent transducers in a phased array) of the transducers is a function of the central frequency.
There are different waveforms of interest, each of which can interact with defects in a different way. These waveforms of interest can include compression and shear waves. Characteristics of interest in the reflected signals may be the time of flight and intensity of the reflected beams which may be interpreted in terms of the extent, position and nature of any discrepancy in the density of the pole in the path of the beam. Transducers may be arranged to direct two or more beams, as indicated by 4 in the Figures, at different angles, and/or may be positioned at different diametric and/or vertical positions to map the discrepancy in three dimensions for more precise information. The amount of power supplied to the transducers may be varied so that signal returns can be algorithmically compared. Variations in the form of reflected energy may be interpreted in terms of the type and distance of defects from the probe. Information from multiple scans may be integrated into 2D or 3D representations of the below ground structure of the pole (e.g. tomographic views). Animations of representations of the pulse echoes may also be used to display the results of the scan reflections.
The transducers are preferably designed to be heavily damped by providing absorptive backing and/or a forward-facing surface with good coupling to wood.
In the embodiment shown in
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In one embodiment, the direction of the ultrasonic beam of energy may be directed with the use of a mount or mounts used to couple the phased array(s) of transducers at an angle to the pole. The angle may be from above 0 to below 180 degrees such as for example about 30 to about 60 degrees, to assess the pole below the surface to a depth of up to four metres, for example, but also enable the pole above the transducers to be examined in the same way. The angle may depend on the depth to which the pole or other element is to be assessed. The mount or mounts may hold the phased array(s) of transducers in a fixed position or may comprise for example a rotating carriage arranged to enable manual moving of the phased array(s) of transducers around the circumference of the pole, or having an associated motor drive system and controller arranged to step the phased array(s) of transducers around the circumference of the pole. A system with manual or automatic repositioning may comprise a built in digital compass to record position and a laser distance finder to record position above ground level for example. The transducer mount(s) may be adjustable to enable a range of different angles between these extremes to be used to inspect different regions of the pole by producing beams with different angles. For example, a transducer could be located at multiple different positions around the circumference of the pole and at multiple different vertical locations over a range of heights above ground, to enable most if not all of the region of interest to be probed with the ultrasonic beam(s). Another embodiment may use arrays of ultrasonic transducers that can be phased to produce beams that can sweep through the wood. However, in a simplest embodiment the mounts may comprise or include wedges between the surface of the pole and the transmitter(s), receiver(s) and/or transducer(s), which position the transmitter(s), receiver(s) and/or transducer(s) at an angle to the pole, and are acoustically coupled to the transmitter(s), receiver(s) and/or transducer(s) to the pole. A range of wedges may be provided with different angles. The material of the wedge should be selected to minimize reflection or refraction at the interface with the pole. This would typically require the wedge to be made of a material with similar acoustic properties, such as refractive index, to the wood in the pole (e.g. a fibre composite).
The acoustic coupling of the transducer(s) with the pole can be increased by using a high viscosity fluid such as a gel, or a compliant pad, which can conform to both surfaces, and which ideally has acoustic properties, such as refractive index, close to that of the wood in the pole.
Alternatively, the acoustic coupling between the transducer(s) and pole may be achieved or improved by the end(s) of the probe(s) being shaped such as pointed, to penetrate the surface of the pole. As shown in
The shaped, such as pointed interface elements 7, are designed and shaped to reduce the amount they resonate as much as possible. For example, they may be tapered and sized to reduce resonance. The material's acoustic properties, such as refractive index, should also be preferably close to wood (for example, a fibre composite may be used).
The transducer interface elements described above may be low cost and designed to be robust so that they can be removed and reused on other poles, or may be left in the pole after inspection has been completed so that such poles can be more easily inspected in the future, or as a time saving measure to simply dispose of the transducer elements. The transducer elements may also be shaped to direct energy from the transducers in order to accommodate the anisotropy of wood. In general, the speed of sound in the wood grain direction is approximately twice that across the grain. In practice the principal access of the transducer is between 0 and 45 degrees. The angle of insertion can be adjusted to assist with directing the energy towards the region of interest.
In another embodiment for example the transducer(s) or the transducer interface elements may be flat edge transducer inserts into the pole with the flat edge pointing in the direction of interest.
As shown in
The information can not only provide an analysis of the residual strength of a pole (e.g. residual effective diameter) but, combined with a knowledge of the stresses that a particular pole is under due to both the static loading of transmission cables and supporting guys and dynamic loads from wind shear, may predict fitness for use. This is one example of how the digital information available from this test can be entered into a Cloud data base and be combined with other sets of data such as weather patterns, climate change, geo positioning, etc. and analytical packages such as predictive maintenance schemes, capital planning, etc. to increase its value.
The information can be used to develop a library of scan data in order to develop a body of knowledge based on different pole types, species, strength classes, lengths and known defects. This library can be used to give further insight into future results and to help give more accurate readings. Machine learning techniques may also be used for ongoing analysis of existing and previously scanned poles to fine tune the results from both current and previous pole scans.
This invention may have application for a range of structures involving the analysis of the interior structure of wood and similar materials with comparably low densities (e.g. between 0.01 to 2.5 g/cm3, such as many polymers, asphalt, some ceramics, graphite, etc.) where it is difficult to probe the region of interest. These other uses may include pilings for buildings, wharf pilings, structural timber that is encased in other materials or located in difficult to access areas, inspection of tree trunks and root systems, etc.
In at least some embodiments the method or system also includes calibrating the system by transmitting and receiving through the body above the surface of the substrate.
The electronics can be programmed to produce a series of horizontally or vertically planar images of the ultrasonic echoes which will reveal the remaining side and lower boundaries of the pole and any internal discontinuities. The combination of the planar images provides a three-dimensional view of the below ground structure of the pole, which is useful for determining its fitness for use.
A specialised form of a phased array may be possible whereby two surface mounted transducers operate so as to produce a wave that transmits axially near to the surface of the pole to detect the rot on the surface of the pole, since rot would transmit ultrasonic energy differently than solid wood.
The information received for each pole can be used to identify changes in the pole over its life by comparing records of this information taken at different times during the life of the pole including prior to use.
The foregoing description of the invention includes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention as defined in the accompanying claims.
Number | Date | Country | Kind |
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713995 | Nov 2015 | NZ | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2016/056633 | 11/4/2016 | WO | 00 |