Precision at Every Layer: How Piezoelectric Sensors Are Redefining Industrial NDT and Structural Health Monitoring

1.Introduction
2.The Key for Piezoelectric Ceramics in Industrial Ultrasonic Testing
3.Where These Technologies Are Applied in Practice
4.Bestarsensor: Expert Knowledge in Piezoelectric Ceramics
5.Every Inspection Counts

Introduction
The word "Industry" is used when the size and complexity of the equipment is considerable. Pipes transport liquid at high pressure over thousands of kilometres. Pressure vessels are subjected to very high temperatures and pressures over the course of years. A common source of cyclic loading on aircraft structural components is each and every flight. In all of these scenarios, a tiny fault can expand into a disaster.
The effects of unforeseen equipment breakdowns on the economy are significant. That is why non-destructive testing (NDT) and structural health monitoring (SHM) are key for the risk management of modern industrial processes. Normally in engineering, the state of the inside of a product without cutting, or removing it from use for inspection. SHM takes it one step further. Installs sensors on or inside a structure and continuously monitors the condition over time. 
It is a technology that one suspects they're using all the time, yet you would have to read a large number of blogs to find out: the piezoelectric ceramic transducer. To appreciate the use of piezoelectric sensors to inspect industry requires an understanding of how they work and why they are so specifically suited to the requirements of industrial environments.

The Key for Piezoelectric Ceramics in Industrial Ultrasonic Testing
The ability of certain materials to change mechanical energy into electrical energy and vice versa is called the piezoelectric effect. When voltage is applied to a piezoelectric ceramic element, the element physically deforms. Squeeze the same element and a measurable electrical signal is generated. This conversion is repeatable, it is accurate and it is fast.
This property is exploited in a simple manner in the practical application of ultrasonic testing as related to industrial applications. A pulse of electricity is passed through a piezoelectric sensor. That electrical pulse is transmitted to the transducer which translates it into a high-frequency sound wave. This sound wave enters the object being tested. In areas where the density, an internal crack, void or boundary is encountered; some of the wave reflects back to the transducer. The returning sound wave is then transmitted back to an electrical signal as a result of the action of the transducer. Using the time of that return and the amplitude (the brightness) and frequency (the resolution) of the signal, the engineer can discover the location, size and type of any discontinuity within the body.
It is a process known as material integrity assessment and one of the most significant techniques used in industrial safety management analysis.
There are a number of practical considerations advantages that explains why piezoelectric ceramics are used in this application.
The first is sensitivity. A well-formulated piezoelectric ceramic can be used to construct a precise ultrasonic transducer which is capable of detecting cracks as narrow as a fraction of a millimeter, pores in composite materials that can't be seen on any surface, and even corrosion that hasn't intruded on the structural cross-section. This is the level of detection which is not possible with any other transduction technologies at a comparable cost and form.
The second is the frequency range. Piezoelectric ceramics can be made to work over a very broad range of ultrasonic frequencies. A piezoelectric transducer made of piezoelectric ceramic can be modified to the desired frequency range for a specific inspection task.
The third one is reaction time. Piezoelectric ceramics react in micro seconds with an electrical signal. The high response frequency makes them the obvious choice for the real-time sensing applications related to structural health monitoring(SHM) where the sensor is required to sense fast events like stress wave propagation, occurrence of microcracks or impact events. This temporal resolution is far greater than can be achieved at practical sensitivities with traditional sensors based on other principles.
The fourth is physical form factor. Piezoelectric ceramic elements can be produced in extremely thin profiles and a very small size. They can be incorporated in sensors arrays, into probe structures for inspection access sensitive locations or bonded directly to structural surfaces for permanent SHM installations. The small packaging is useful in field conditions that would hinder larger or more fragile sensor technologies.

Where These Technologies Are Applied in Practice
1. Non-Destructive Testing(NDT) in Industrial Inspection
The most common application of the piezoelectric ultrasonic transducers in NDT is the inspection of welds. Fabricated structures are composed of welds—connections. A variety of defects can be generated at the welding process such as incomplete fusion, porosity, slag inclusion and cracks. A cross-section of the weld may be scanned from the outside simply and effectively with ultrasonic (piezoelectric) probes, without any cutting or chemical processing.
Another key NDT application is thickness measurement. Over time pipes, tanks, pressure vessels become subject to corrosion and will lose thickness. This piezocontour attachment for ultrasonic thickness gaging measurement is a non-contacting method, in which the remaining wall thickness can be measured by the piezo-electric transducer from one side of the structure. This is necessary in the inservice inspection of pipelines and storage vessels where internal inspection is not feasible.
2. SHM in Dynamic Service Environments
SHM is fundamentally different to periodic NDT inspection. Instead of sending an inspector with a probe to investigate a structure at periodic testing times, SHM consists of sensors which are installed on or in a structure and kept monitoring the structure continuously. This is an ideal application for piezoelectric sensors.
Piezoelectric accelerometers and acoustic emission sensors are used in referring to vibration signatures and high-frequency stress events in rotating machinery. Vibrations with these signatures reveal the occurrence of developing faults before it can be seen in the conventional vibration measurements. The stability of the piezoelectric materials are important in these applications. 

Bestarsensor: Expert Knowledge in Piezoelectric Ceramics
Bestarsensor has built its position in the piezoelectric ceramics industry on a foundation of material science expertise. Its own multilayer piezoelectric ceramic formulation and proprietary low-temperature co-firing (LTCC) technology and ultra-high multilayer stacking processes make the company's own development and manufacturing process. 
This is significant for a specific reason for applications in industrial NDT and SHM. The level of repeatability depends directly on the consistency of the transducer. This requirement is resolved by direct addressing of the material level manufacturing control by Bestarsensor. Consistent electromechanical properties of production batches will achieve sensor-to-sensor repeatability, which are at the core of the company's ceramic formulation and firing processes.
From a practical point of view, manufacturing discipline allows to fulfil the stability requirements of the industrial field applications for Bestarsensor's transducer elements. Sensors working in environments that experience relatively large temperature changes, mechanical vibrations and exposure to humidity must remain sensitive to their task and as calibrated. There is no guarantee that piezoelectric material will be stable under these conditions just by selecting the piezoelectric material. A careful control of the ceramic composition, as well as the selection of the electrode materials, bonding processes and approach of encapsulation, all is required. 

Every Inspection Counts
Industrial safety is at the heart of the ability to identify small changes in the rating or to detect them before they become big problems. The early detection is made possible by a high performance piezoelectric transducer. Their role is to convert the physical reality that exists at the microscopic level to an electrical signal which is analyzed, recorded and acted on by engineers. Therefore, the process of translation influences the quality of inspection data, and the quality of inspection data influences the quality of the safety decision.
Bestarsensor produces its products based on the premise that only the reliability of the sensor that conducts the inspection can determine the value of the inspection. The company guarantees industrial customers the performance the inspectors require for a product through consistent materials, controlled manufacturing and application-specific engineering.
For more information about Bestarsensor's product line and engineering abilities, you can visit us at www.global-bestarsensor.com