Japan Radio Co Ltd. NJJ-105 Manual Do Utilizador
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4 Theory
4.1 Principle of Operation
The principle of this product is basically the same as for general radars widely used at present.
Electromagnetic waves are transmitted from the antenna toward the concrete as shown in Figure 4-1.
Electromagnetic waves are transmitted from the antenna toward the concrete as shown in Figure 4-1.
The electromagnetic waves are reflected by an interface with the reflecting objects (e.g., reinforcing steel
bars or cavities) whose electrical property is different from that of concrete. The waves are reflected back
onto the surface of concrete and received by the receiving antenna placed near the concrete surface. The
distance to the reflecting objects can be calculated from the time the reflected waves need to reach the
receiving antenna. The horizontal locations of the objects can be detected by moving the main unit on the
surface of concrete.
bars or cavities) whose electrical property is different from that of concrete. The waves are reflected back
onto the surface of concrete and received by the receiving antenna placed near the concrete surface. The
distance to the reflecting objects can be calculated from the time the reflected waves need to reach the
receiving antenna. The horizontal locations of the objects can be detected by moving the main unit on the
surface of concrete.
Since this product is designed to probe objects with high resolution that are near from the surface of
concrete, it transmits pulse waves having a width of only about one nanosecond (one-billionth of a
second) or less.
second) or less.
Figure 4-1 Diagram of Principle
Figure 4-2 shows a wave reflected by a reinforcing steel bar or the like in a concrete structure, which is
obtained by this product.
Figure 4-2 Sample of Reflected Waveform
T
Time
Reflected wave from rebar
Trans. wave
Reflection
Concrete surface
Inside concrete
Rebar
Trans antenna
Rec. antenna
Trans. Rec.