Handheld 3D scanner
Infrastructures such as bridges, railways and roads are vital to every country’s economic growth and development. These structures are usually reinforced concrete structures which need continuous monitoring for regular operation and safely. The large concrete structures pose many challenges for inspection due to wide distribution in size of aggregates and its nature. Non-destructive testing (NDT) is one of the most effective ways for inspecting such concrete structures.
Elop AS is developing a novel transducer design for fast data acquisition while maintaining good coupling to the concrete surfaces. To minimize the loss due to scattering in the aggregates, low frequency ultrasonic transducers (50-250 kHz) are used. The image quality is improved using SAFT algorithm for image reconstruction. The scanner uses separate transmitter and receiver array sealed inside a filled liquid cylinder and a segmented dry coupling to the material under inspection (patented).
Our scanner system is able to send and receive signals at any chosen time as coupling between the transducers and target material is always maintained. The use of separate transmitter (Tx) and receiver (Rx) rollers is another advantage in our concept as the reflection from transmitted pulses against the polymer, elastomer and the concrete surface will not interfere with the receiving signals on the other roller.
• Very fast inspection. From 10 cm/sec to 100 cm/sec depending on resolution.
• Only one instrument will be required to detect different concrete faults (rebar, rust, cracks, delaminations and voids).
• Data will be easy to interpret and thus less special training will be needed.
• 3D real-time video can be obtained with high resolution of ~ 1 cm.
• The handheld roller system will provide a high coverage rate (up to 1 m2 in 10 sec).
• A trolley version will later be developed for even faster coverage rate.
• Evaluations can be done at the inspection site using an integrated display.
Elop AS is currently working on two different research and development projects.
1. Research project with funding from Regionale Forskningsfond Innlandet. The scope is to develop a rolling scanner with use of an OEM digital platform. Project period 2014-2016.
2. The Innovation project “COBRI” funded by the EU program Horizon2020. The scope here is to develop a proprietary scanner system completed with electronics and software. Project period 2015-2017.
The scanner system is based on an innovative transducer design suited for low frequency applications using a piezoelectric polymer material, PVDF. The transducer is non resonant and broadband, but has low piezoelectric properties compared to a PZT composite. The input impedance of the PVDF is very high, thus to generate an equal amount of acoustic power, a much higher drive voltage is needed. This problem is minimized in our transducer design by the use of multiple layers. The layers are connected acoustically in series and electrically in parallel thereby reducing the electrical input impedance.
Electronics and Software
The ultrasound electronics and software/firmware will partly be based on existing OEM product with an adaption to the lower frequency range required for the concrete material. The electronics will contain a rotational encoder which keeps track of positional information with reference to a starting point and this can be recorded along with the 3D data of any located defects. This allows any discovered defects to be further analyzed and monitored periodically.
Synthetic aperture focusing technique (SAFT)
Synthetic apertures offer a different way of focusing compared to shaping of the transducer or using an acoustic lens. A synthetic aperture imitates a large transducer by sampling its area at many points. SAFT is based on subsequent focusing of the data measured on an aperture to every point of the reconstructed area through superposition of the time records. Compared to A-scan and B-scan techniques, SAFT is able to suppress the stochastic noise. The broad divergence angle of the transducer which is drawback in both A and B-scan is a useful property as it allows the object to be insonified from various sides.