To measure the thickness of the vibration screen ligaments, Sprouts nodes and NDT-modules are placed on the
steel layer underneath the mesh screen at each intersection, where they are shielded from direct contact with the
sand flow. When a thickness measurement is needed, Sprouts nodes request thickness readings from each channel of
the NDT-module or from all channels as specified by the server configuration. When a thickness reading is
requested from a particular channel, the NDT-module applies a fast voltage pulse to the PZT transducer by toggling
a digital logic port from low to high. The fast transition from logic-low to logic-high, less than 5.0 s rise time,
creates a wideband frequency response, which causes the PZT transducer (SMD10T04F5000S111) to resonate at
approximately 5MHz (+5%) with initial pulse magnitude voltage V0, as seen in Figure 5 (a). The initial pulse, which
occurs at time t0, travels through the steel layer until it reaches the end of the material boundary or a material of
different density, such as the tungsten layer, at time ta. The mismatch in material density causes a percentage of the
ultrasound energy, R1, to be reflected back to the transducer proportional to the acoustic impedance mismatch
between steel (Z1= 45.63MRayls) and tungsten (Z2= 99.72MRayls), as shown in equation (5)[2]. Therefore, at the
boundary between the two metals, or time location ta, the percentage of reflected energy is R1=0.1385, or 13.85%.
Acoustic impedance is a function of material density and velocity of sound, , in the given material, as shown in
equation (6). Note that and for a given material, such as steel or tungsten, can vary depending on manufacturing.