Imagine shining a light down a dark hallway. The light source transmits the light and your eyes receive the light. Even if you were able to bounce the light off the walls, it would be difficult to see everything in that hallway with a single beam of light. But, if you bring a few friends that also have lights, together you would be able to illuminate and view the entire hall.
This is how phased array works. It makes use of multiple sensors angled at varying degrees in order to obtain greater coverage. In doing this, it electronically directs a sound beam to every corner of the hall, providing complete inspection coverage and better probability that operators will detect the object or defect they are seeking.
The BeginningPhased array technology was first introduced in the early 1970s into the medical field using ultrasounds. Although the idea of phased array has been around since the 1800s, the industry was not able to harness this technology for inspection means until more than 100 years later. This advanced method of inspection has now expanded from the medical field into the industrial arena, proving to enhance results, speed inspections and provide productivity.
In the industrial environment, the traditional means of inspection have changed drastically during the past few decades. Early inspections were restricted to the application of the probe. The probe itself would have been a single-element transducer, containing one operating element. This element would have been transmitting and receiving a single ultrasonic pulse. Multiple probes with various focusing, apertures and angles often were needed to perform every inspection.
The data also was simplistic for these single-element transducers in the form of an A-scan, essentially an oscilloscope trace with a time and amplitude component. Inspections were time-consuming and tedious.
Probes Expand FunctionalityThe introduction of angle beam and dual-element probes greatly expanded the functionality of ultrasonic inspection. Defects could not only be detected, but also measured. The inspection data also evolved from simplistic A-scans to B-scans and C-scans. Even with this development, multiple probes often were necessary to fully inspect a part that needed inspections from multiple angles. The task of changing probes, recalibrating and re-measuring still proved to be tedious.
Conventional probes are composed of a single crystal, or element. An element is the active component in the probe that vibrates to generate ultrasonic energy. In order to change the sound angle, an inspector changes the angulation of the probe relative to the inspection surface by either changing probes or changing the ultrasonic wedge fixture attached to the probe.
For phased arrays, the crystal is cut into many parts. Each of these elements is individually driven by a pulser that is capable of delivering the excitation pulses to each element with minute time-shifts.
Many elements can be pulsed together at once to mimic the acoustic output of a single probe, or they can be pulsed as a group with each element receiving its pulse time-shifted from its neighbors. A specific set of time-shifted pulses is referred to as focal law, or phasing sequence.
These focal laws allow one multi-element array to produce many different sound angles within a test piece and can be changed electronically and very rapidly. In other words, one array does the job of many single-element transducers.
Advances ContinueAdvances in electronics and computerization have helped the advances in inspection methods and results. Today, data is processed, displayed, analyzed and stored all within the same instrument. The instrument also can transmit data to remote locations for further analysis, reporting or archiving.
The phased arrays also are advancing; today there are dialogue probes that are preprogrammed with setup information to assist the inspector in setup and hasten the calibration process. Phased arrays also are available in many configurations to optimize the acoustic and mechanical performance to provide the best solution for an inspection application.
There are many advantages to phased array, but speed is probably the most prevalent. The inspection process that used to take three, four or five different probes can now be done with one phased array probe. The need to change probes, recalibrate and re-inspect is eliminated with phased array. Quicker inspections equate to less downtime, which in turn equates to real savings for the customer.
The second largest advantage is the quality of the inspection results. As mentioned earlier, the probability of detection is higher because of the complete coverage of the part with the phased array. Also, the results are presented as an image instead of an A-scan, which offers more information to the inspector and is much more intuitive. This allows inspectors to make more confident decisions and enables the improved probability of detection and inspection speed. The more an inspector can see and understand about the component, the more confident he can be about the quality of his inspection.
Phased array decreases total inspection time, improves the inspection results and increases the confidence in the inspector’s decision-making. Phased array also helps to eliminate the need to purchase multiple probes for the inspection of one part. This means more standardization since there are fewer parts to purchase and maintain.
As phased array technology improves and the inspector becomes more accustomed to the technology, it will soon become a standard in the inspection world. Traditional inspection means will not necessarily go away, but the power and impact of phased array in industry will be more important.Q