sensor reliability increases

Scanning Acoustic Microscopy testing ensures that oilfield and optical sensors are built without essential material defects.

Edited by: Mike Santora • Managing editor

Electro-mechanical sensors, such as pressure, flow, and vacuum switches, composed of electrical and mechanical parts, interact and transmit information or commands to other components of a larger, more complex system. To keep the entire system functioning safely, sensor producers must manufacture these devices to deliver accurate measurements. Traditionally, however, if there was an issue with a sensor, it was often found when the product failed the field.

Now, sophisticated testing like Scanning Acoustic Microscopy (SAM) is being used to assess the physical sensing elements to determine that the components are sound before they are assembled into sensors that will be used in critical applications.

SAM is a non-invasive and non-destructive ultrasonic testing method. The testing is already the industry standard for 100% inspection of semiconductor components to identify defects such as voids, cracks, and the delamination of di erent layers within microelectronic devices. Now, the same rigor of failure analysis and quality testing is being applied to specialty metals and materials to detect subsurface flaws, dis-bonds, cracks, and other irregularities.

“Previously, sensor manufacturers had no way to test the functionality of a sensor until it was in the field. If it gave incorrect results on a known good test, they called it a failure. They had no metrology to test the sensors elements during the manufacturing process,” said Hari Polu, President of OKOS, a Virginia-based manufacturer of SAM and industrial ultrasonic non-destructive (NDT) systems.

Sensors

Oil Field Sensors

For example, SAM can be used to ensure sensor quality in oil drilling equipment. These sensors are sensitive to vibrations or generate vibrations at a specific frequency. These sensors provide metrology attributes of fluid properties in real-time.

Electro-mechanical advanced sensors are used in critical areas such as oilfield exploration and production processing to take pressure data and fluid samples from the bottom of highpressure and high-temperature wells. The sensors establish the hold-up of fluids using the density and electrical properties of oil, gas, and water. The characteristics of the vibration can help to determine the density of the wellbore fluid mixture.

“If a manufacturer is building defective sensors and anything fails anywhere in the process upstream, that’s extremely costly for an oilfield application,” said Polu.

Oil drilling equipment manufacturers can test tuning fork sensors’ piezoelectric crystals with SAM to determine if flaws exist before shipping. Since piezoelectric ceramics are fragile, sensitive components may present internal cracks undetectable to visual inspection. Ceramics presenting cracks, even if internal and invisible, must be discarded to avoid the premature fault of ultrasonic transducers and converters in which they are mounted and the resulting losses from repairs and technical assistance.

Scanning acoustic microscopy works by directing focused sound from a transducer at a small point on a target object. The sound hitting the object is either scattered, absorbed, reflected, or transmitted. By detecting the direction of scattered pulses as well as the “time of flight,” the presence of a boundary or object can be determined as well as its distance.

To produce an image, samples are scanned point by point and line by line. Scanning modes range from singlelayer views to tray scans and crosssections. Multi-layer scans can include up to 50 independent layers. Depthspecific information can be extracted and applied to create two- and threedimensional images without the need for time-consuming tomographic scan procedures and more costly X-rays. The images are then analyzed to detect and characterize flaws such as cracks, inclusions, and voids.

When high throughput is required for 100% inspection, ultra-fast single or dual gantry scanning systems are used along with 128 sensors for phased array scanning. Multiple transducers can also be used to simultaneously scan for higher throughput.

Ensuring lithium niobate wafer quality

Lithium niobate (LiNbO₃) is one of the most versatile and well-developed active optical materials and is widely used in electro-optics, acousto-optics, nonlinear optics, waveguides, and fiber optic gyroscopes (FOGs).

Scanning Acoustic Microscopy testing ensures that oilfield and optical sensors are built without essential material defects.