The NPL's acoustic absorber Aptflex F48 has been designed to meet the need to reduce reflections in sub MHz frequency test tanks.
The combination of the acoustic properties of the new material and its simple design makes it the cost-effective solution for large-scale applications. This new material is only available from Precision Acoustics.
Ultrasonic Tank Wall 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 specifically 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.
- based on a polyurethane rubber material
- single-ply nominally homogeneous layer
- thickness of tile: 10mm or 26.5mm
- tile dimensions: 1200mm by 600mm
- density of 1.91gm/ml +/-0.03
Transmission Loss of a 26.5mm thick tile (TL)
This limits or affects the performance at low frequencies, as TL goes down with frequency.
At 100kHz, single pass transmission loss of a 26.5mm thick layer of the material is 21dB, which means that double (the wave which goes through, bounces off the tank wall and comes back out) is 42dB (0.8% amplitude).
The transmission loss increases rapidly with frequency in the following way: 500kHz: 100dB single pass; 1MHz: 200dB single pass and 3MHz: >500dB single pass.
Echo-reduction of a 26.5mm thick tile (ER)
Note the structure shown below; 200kHz 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 (>1MHz).
For a 26.5mm tile the ER is better than 20dB below 0.5MHz. 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 30dB. Please contact us for more information.
At 1MHz, the echo-reduction of a 26.5mm tile is 20dB (10% reflected amplitude) and at 3MHz, it is 15dB (18% reflected amplitude). Careful angling of the flat panels will improve performance greatly. Anything twice reflected will come down in amplitude to 1% at 1MHz and about 3% at 3MHz.
Speed of Sound