Testing

Before conducting ND tests, survey design is critical. Time should be spent considering the five major factors of survey design, which are detailed below:

1. The required depth of penetration into the structure

-Assume that penetration distance through air is negligible, therefore total penetration required is simply the width of the moveable wall. Note: Detection of the far side of the stationary wall is not required. Due to the toroid scattering of the EM wave from the antenna, as the target gets further away, less EM waves hit the 'target' and as such less are reflected back to the receiver. This form of attenuation will increase in proportion to the increase in void width and therefore the test will have limits to it's penetration.

2. The vertical and lateral resolution required for the anticipated targets

-This relates to the thickness of the void between both walls. This will be varied and is what will be under investigation.

3. The contrast in physical properties between the target and its surroundings

-EM properties of the walls and void are known

4. Signal to noise ratio for the physical property measured at the structure under investigation

-The radar antenna/receivers used in this investigation are shielded, hence there will be no problems with external noise.

5. Historical information concerning the methods used in the construction of the structure

-Full details recorded of construction procedure. This is a new wall and will therefore not have any history of structural stress (i.e. local vibrational activity, creep or weathering).

 

The experiment apparatus will consist of two walls, one thicker than the other, contained within a moveable frame. The two walls will represent a multi-leaf structure, commonly used in masonry buildings. The frame will allow the thinner wall to move relative to the stationary thicker wall, thus varying the gap between them and modelling the phenomenon of leaf delamination.

It is planned that the movable wall could be positioned at set distances from the fixed wall, providing a known width void. This twin leaf wall will then be analysed using the radar system and the traces recorded. As the precise void width is known conclusions of the radars effectiveness can then be drawn from the resulting recorded data. A diagram of the intended test rig is shown below.

The radar antenna/receiver box will be attatched to the movable wall in a central location in order to overcome edge effects.

The test rig we intend to use looks something like the diagram above.

The pictures below show the equpiment we will be using

The above picture shows the processing and display equipment.

The above picture shows two antennas we will be using in the tests.

The test procedure will consist of moving the wall to a set location (corresponding to a pre-determined void width), then introducing a radar pulse into the wall from the antenna and recording the receiver response. The wall can then be moved as necessary to another location and the test repeated.

Various factors can cause distortion in the trace, such as the breakthrough effect. Filtering will be conducted to minimise the problems in interpretation associated with this distortion.