Test & Measurement
attenuative material. These often have the largest focal lengths.
PVDF transducers use a gold-tipped exposed element for high-frequency imaging, operating between 35 MHz and 75 MHz. These are ideal for thin, attenuative materials like silicon-based chips. Focal lengths typically range from 0.25 to 1.5 inches, enabling precise internal inspection.
Delay line transducers are quartz lens tipped transducers with internal crystals manufactured to a precise thickness to control frequency. These transducers can range from 35 MHz to 300 MHz, have the best depth of field, and can have custom focal lengths.
Phased array transducers use multiple elements, unlike the single-element design of standard types, and can be curved to improve scanning over contoured surfaces. Multiple elements sweep the sample simultaneously, enabling faster scans. Constructive interference allows real-time focal length adjustment for optimal imaging. These transducers typically operate at 20 MHz or below.
Multiple transducers speed scanning Unlike conventional scanning acoustic microscopy systems that utilize a single- element transducer, phased array systems employ multiple transducers that can be combined to scan the sample simultaneously. In a phased array system, multiple elements can be activated either simultaneously or sequentially to synthesize a focused acoustic beam. The number of transducer elements incorporated into the array varies significantly depending on the specific application and system design. Common configurations typically include arrays with 16, 32, 64, 128, or 256 elements.
Software
Software coordinates all the pieces of an ultrasonic scanning system like SAM. It interacts with the digitizer, motion control, and digital pulser/receivers in order to coordinate their operations. Software is used to adjust the position of the sample or the probe (transducer) in three-dimensional space, trigger the transducer, and process the resulting waveform data into 2D and 3D images.
The effectiveness of SAM depends on the strategic integration of three core components: transducers, digitizers, and software.
“A conventional 5 MHz sensor could take up to 45 minutes to inspect an 8–10-inch square or disc alloy. Today, however, an advanced phased array with 64-128 sensors and innovative software to render the images can reduce inspection time to five minutes, with more granular detection of small impurities or defects,” says Polu. A phased array scanning system consists of multiple ultrasound transducer elements arranged in an array. Each element within the array is independently controlled with respect to the timing (phase) and amplitude of excitation. This configuration allows for electronic steering and focusing of the ultrasound beam by adjusting the timing and amplitude applied to each element. Phased array SAM systems offer significant advantages for applications that demand high-throughput inspection. These systems are particularly well-suited for non-destructive evaluation of composites, bonded structures, and electronic assemblies. They also support real-time imaging with adjustable depth of focus, which enhances their effectiveness in assessing internal
features at various depths within the material.
“To produce an image, samples are scanned point by point and line by line,” explains Hari. “Scanning modes range from single layer views to tray scans and cross-sections. Multi-layer scans can include up to 50 independent layers. Depth-specific information can be extracted and applied to create two-and three-dimensional images without the need for time-consuming tomographic scan procedures or costly X-ray equipment. The images are then analyzed to detect and characterize flaws such as cracks, inclusions, and voids.”
According to Polu, SAM can also be custom designed to be fully integrated into high volume manufacturing systems. When high throughput is required for 100 per cent inspection, ultra-fast single or dual gantry scanning systems are utilized along with 128 transducers for phased array scanning.
Digitizers
In a scanning acoustic microscopy, the digitizer takes the analogue voltage signals received from the transducer – after amplification by the pulser/receiver – and converts them into digital format. This digital data is then used for image reconstruction and analysis, enabling accurate visualization of the internal features of the inspected object. The digitizer is critical for translating raw acoustic information into usable, high-resolution imaging. Digitizers convert analog signals into digital form by sampling the input waveform at specific intervals, known as the sampling rate. A higher sampling rate captures more data points per second, allowing for a more accurate reconstruction of the original signal. To avoid distortion and preserve signal integrity, the sampling rate usually must be at least twice the highest frequency present in the signal, according to Polu.
Each component must be selected and calibrated according to the specific demands of the application to maximize system performance.
www.cieonline.co.uk
“More data is generated as the sampling rate is increased, so the lowest sampling rate that can accurately reproduce the original signal will improve throughput,” says Polu.
As important as the physical and mechanical aspects of conducting a scan, the software is critical to improving the resolution and analyzing the information to produce detailed scans.
Multi-axis scan options enable A, B, and C-scans, contour following, off-line analysis, and virtual rescanning for a variety of materials. This results in highly accurate internal and external inspection for defects and thickness measurement via the inspection software.
Various software modes can be simple and user friendly, advanced for detailed analysis, or automated for production scanning. An off-line analysis mode is also available for virtual scanning. Polu estimates that OKOS’ software- driven model enables them to drive down the costs of SAM testing while delivering the same quality of inspection results. Consequently, this type of equipment is well within reach of even modest testing labs.
The bottom line
In scanning acoustic microscopy, performance depends not solely on the quality of individual components but on their effective integration.
Scanning acoustic microscopy achieves peak effectiveness when transducers, digitizers, and software operate in seamless coordination. Performance depends not only on the quality of individual components, but on how well they are integrated as a unified system. When properly matched, these elements enable higher scanning speeds, enhanced defect detection at smaller scales, and improved imaging clarity. This level of performance allows manufacturers to identify issues early, enhance product quality, and maintain a competitive edge in industries where minor defects can result in significant consequences.
www.pvatepla-okos.com
OKOS is a wholly owned subsidiary of PVA TePla AG, Germany.
By Del Williams, a technical writer based in Torrance, California.
Components in Electronics October 2025 39
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60
