The low-frequency ultrasonic pulse-echo tomography is applicable to all heterogeneous materials where "regular" ultrasonic flaw detectors (frequency range 1 – 10 MHz) cannot be applied. The following materials can be considered as "inspectable" by A1040 MIRA 3D Pro:

• Concrete, rock, marble, stones
• Refractory materials/ceramics, such as fireproof bricks
• Composite materials, e.g., glass-fiber components with significant wall thickness (e.g., wind turbines)
• Large carbon electrodes

The ultrasonic tomograph A1040 MIRA 3D Pro can be applied for:

• Measuring the thickness of concrete walls
• Locating structural metallic elements (reinforcement, tendon ducts, pipes)
• Detecting material voids in concrete (e.g., delaminations, cracks, honeycombs, cold joints).
• Further advanced applications of MIRA include:
• Assessment of the tendon ducts
• Measuring the depth of the open cracks with one-side access

The detection and resolution capability of ultrasonic tomography depends on several factors, such as:

• Material properties (e.g., aggregate size), and thus, the applied inspection frequency
• Reflectivity of the defect/structural element, which, in turn, depends on its shape and orientation in the inspection volume.
• Depth position of the reflector
• Effective aperture of the tomograph

In an "average" case, we can state that for an elongated cylindrical reflector (like rebar), the detectable diameter might be 15 mm, while for a "round air bubble," the detectable diameter might be 20 mm.

Keeping in mind that sound attenuation in concrete depends on material properties, such as aggregate size or density of the ceramic blocks, the inspection range must always be considered as a derivative of the optimal inspection frequency. When using an optimal inspection frequency in combination with a sufficient effective aperture of the ultrasonic instrument, the achievable inspection range can be up to 2 – 3 meters. Advanced signal generation and processing techniques, like using coded excitation sequences (E-Boosting), may double the inspection range of the instrument to up to 4 – 6 meters.

Both available software packages for visualization and analysis of UT data perform three-dimensional image reconstruction, when the scans are collected in so called MAP mode – when equidistant measurement points are distributed over the region of interest. The 3D representation of the UT results by overlapping multiple scans provide the most comprehensive information about the inspected volume.

Pulse echo testing is included in the European standard EN 12504-4 for pulse velocity determination. This is then subsequently included in the standard EN13791 for in-situ compressive strength estimation. Though, there are no international standards for pulse-echo imaging and flaw detection yet. The only available guideline for pulse-echo flaw detection is the German Society for Non-Destructive Testing Guideline B4. It is also covered in a German highway authority guideline for measuring tunnel lining thickness (ZTV-ING Teil 5 Tunnelbau) and ACI 228.2R.

Any void filled with the material having different density then concrete can be visualized and detected by ultrasonic tomograph A1040 MIRA 3D Pro, supposed those voids have sufficient spatial dimensions exceeding the ½ of ultrasonic wavelength.

The image below represents detecting steel rebar of ∅16 mm at 17 mm depth (25 mm to the center of rebar).

The ultrasonic pulse-echo tomography is the most suitable technology for detecting voids, honeycombs, and delaminations even below the several rebar grid. While a dense rebar structure will shield a GPR signal from penetrating deeper into the structure, an ultrasonic pulse-echo signal passes through is able to detect deeper-lying voids.