Aptflex F48
The NPL’s acoustic absorber Aptflex F48 has been designed to meet the need to reduce reflections in sub MHz frequency test tanks.
Overview
The Aptflex F48 is an acoustic absorbing tile designed to meet the requirements of applications in frequency range 50 kHz to 1.5 MHz. It is a microbubble filled, pre-cast polyurethane sheet that provides a cost effective balance between echo reduction and insertion loss.
Ultrasonic tank linings
For long toneburst or continuous-wave ultrasonic applications, acoustic output measurements or ultrasonic testing in general can be strongly affected by reflections or echoes from test tank walls. To overcome this, test tanks are coated with ultrasonically absorbent linings which must be of low ultrasonic reflection yet highly absorbing to ultrasound. The Aptflex F48 material is specifically designed to meet this requirement. Its simple design, being a single-ply layer, ensures that the material is the cost-effective solution for coating large areas such as the walls of an ultrasonic test tank.
Physical specification
- Based on a polyurethane rubber material
- Single-ply nominally homogeneous layer
- Thickness of tile: 10 mm or 26.5 mm
- Tile dimensions: 1200 mm x 600 mm
- Density: 1910 ± 20 kg/m3
* Minimum order quantities apply if there is no stock or if longer expiry dates are required.
Acoustical specification
Insertion Loss of a 26.5 mm thick tile (IL)
This limits or affects the performance at low frequencies, as IL goes down with frequency.
At 100 kHz, single pass insertion loss of a 26.5 mm thick layer of the material is 21 dB, which means that double (the wave which goes through, bounces off the tank wall and comes back out) is 42 dB (0.8% amplitude).
The insertion loss increases rapidly with frequency in the following way: 500 kHz: 100 dB single pass; 1 MHz: 200 dB single pass and 3 MHz: >500 dB single pass.
Echo-Reduction of a 26.5mm thick tile (ER)
Note the structure shown below; 200 kHz is caused by the reflected wave from the front surface interfering with the reflected wave from the back surface of the tile.
The echo-reduction limits or affects the performance of the tank wall lining at high frequencies (>1 MHz).
For a 26.5 mm tile the ER is better than 20 dB below 0.5 MHz. The peak in the ER is sensitive to temperature and it is possible to match the performance to the temperature of the customer’s test tank. If matched, then it is possible to obtain an ER better than 30 dB.
At 1 MHz, the echo-reduction of a 26.5 mm tile is 20 dB (10% reflected amplitude) and at 3 MHz, it is 15 dB (18% reflected amplitude). Careful angling of the flat panels will improve performance greatly. Anything twice reflected will come down in amplitude to 1% at 1 MHz and about 3% at 3 MHz.
