Aerospace Ultrasonic Test Equipment Basics

The components of aerospace ultrasonic test equipment.

PC-based and external components make up an aerospace ultrasonic test system. Each of these components has features and considerations when put together to build custom flexible ultrasonic test equipment.

Assembling Ultrasonic Immersion Test Equipment.

Ultrasonic test equipment can take several forms, but the most common type of ATE is immersion test equipment. Squirter systems are the commonest used for aerospace composite material inspection and complex geometry composite parts. To achieve effective acoustical impedance matching between the couplant and the composite component or titanium plate that is the subject of the test (unit under test), and to achieve free range over the entire surface of the UUT, many test systems use an immersion tank filled with water. This equipment uses one or more ultrasonic transducers, which are moved over the surface of the UUT. It receives echoes from the surfaces. This process is repeated many times a second with one pulse and subsequent echoes. Application software sets up the test and presentation. Motion control moves the ultrasonic transducers. The signal from the ultrasonic transducer is amplified and filtered before it is sent back to the PC. The waveform is converted from voltage to bits using an analog-to-digital converter. The application software handles the data.

The scale of immersion test equipment can vary enormously in aerospace including, for example, anything up to 17 axis scanning bridges. Acoustic microscopes use high ultrasonic frequencies and high resolution scanning units.

Ultrasonic Transducers

Ultrasonic transducers are built around piezoelectric ceramics that vibrate at ultrasonic frequencies. Piezoelectric ceramics in ultrasonic transducers used in field service are commonly contact sensors, and are contoured to the surface to be inspected. Standard Immersion Ultrasonic Transducers works on the principal that in ultrasonics, the voltage amplitude is proportional to the amount of energy echoed by the flaw. In immersion testing, the ultrasonic wave must travel through water before arriving at the UUT. If the distance is known, a trigger delay can be implemented to minimize the amount of unnecessary data that is recorded and stored. There is a trade-off between resolution, speed, channel count, data throughput, and cost. However, the technology is evolving and many of these trade-offs will become insignificant with respect to cost.

Motion Control and switching

Most automated ultrasonic test systems use motion control to gather multiple data points with one transducer. For instance, acquiring B- or C-scans requires movement of the ultrasonic sensor 

over the UUT surface to create a surface map.

As for switching, in ultrasound applications that have one digitizer and pulser/receiver for multiple ultrasonic sensors, switching is required to route the signals properly. This is used for equipment like acoustic microscopes that use arrays of sensors to create images. Arrays of ultrasonic sensors are common in aerospace NDT applications because the sound energy can be steered in multiple directions without moving the sensor array. Multitransducer applications are also common when speed of test is an issue.

Application software

One of the main trends in non-destructive testing, and ultrasonic test equipment, in particular, is full test automation. ATE includes not only data collection and presentation automation but also pass/fail 

automation. Setting pass/fail templates increases statistical accuracy and eliminates much of the subjectivity that is commonly found with NDT.