Near-field Acoustic Holography (NAH)

Microscopic Holographic Perspective

Contents

1. Core Technology: Near-field Acoustic Holography (NAH)

2. I. Core Technical Principles

3. II. Cross-Industry Application Value

4. III. Summary of Technical Advantages

Core Technology: Near-field Acoustic Holography (NAH)

When focusing on core components, engineers have long faced the dilemma of “microscopic holographic perspective”: constrained by the physical diffraction limit, conventional techniques remain stuck at “meter-level blur” in localization accuracy, making it difficult to pinpoint the specific excitation point and impossible to achieve root-cause diagnosis. The GroupCore Acoustic NAH2048 large-array near-field acoustic holography system specializes in low-frequency source tracing and precision measurement of complex structures, delivering a revolutionary leap in localization accuracy from “meter-level blur” to a “centimeter-level precise origin.”

I. Core Technical Principles

The core breakthrough of Near-field Acoustic Holography (NAH) lies in the following: conventional far-field measurement can capture only “propagating waves” that travel to the far field, and its resolution is therefore limited by wavelength; NAH, by contrast, performs dense-array measurement in the near field of the sound source, capturing not only propagating waves but also the evanescent waves that carry fine vibration information about the source. Evanescent waves exist only in the near field of the source and decay rapidly with increasing distance, yet they are precisely what carries the source’s sub-wavelength fine-structure information. By capturing this “vanishing” wave, NAH breaks through the Rayleigh diffraction limit and achieves reconstruction resolution that is not constrained by wavelength.

The NAH2048 system goes a step further: equipped with an ultra-large planar microphone array of 2048 high-density acquisition channels, its “wrapping” coverage enables millisecond-level synchronous, full-area acquisition over the surface of the component under test. A single trigger completes full-field data acquisition, reducing the hours required by conventional point-by-point scanning to just a few seconds. The captured hologram-plane sound pressure data, which contains evanescent-wave information, is then reconstructed into a complete three-dimensional sound field through an inverse mathematical transform, ultimately outputting a high-resolution 3D sound field contour map.

II. Cross-Industry Application Value

• Power industry: The low-frequency noise (50–500 Hz) of large power equipment such as power transformers has long been a localization challenge. NAH2048 can precisely capture, in the near field of a transformer, the noise sources generated by core vibration and winding electromagnetic forces, raising localization accuracy to the centimeter level and precisely identifying the specific fault excitation point. Combined with acoustic holographic imaging, it can rapidly distinguish transformer body noise from cooling-system noise, providing a quantitative basis for targeted noise reduction and fault repair.

• Oil & gas and petrochemical industries: For micro-leaks and wall-thickness corrosion in large pressure-bearing equipment such as pipelines and storage tanks, NAH2048 delivers high-resolution sound field reconstruction in the near field of the equipment surface. By capturing the weak acoustic emission signals produced by leaks, the system precisely locates leak points and corrosion zones, upgrading the traditional empirical practice of “locating by listening” to scientific diagnosis with “centimeter-level quantitative” accuracy.

• Machinery and industrial manufacturing: Early faults in core mechanical components such as gearboxes, bearings, and engines (e.g., gear tooth surface wear, bearing pitting) often manifest as weak low-frequency anomalous signals. NAH2048 performs high-precision sound field reconstruction over the component surface; by comparing holograms under faulty and normal states, it identifies changes in source characteristics at specific locations and, in combination with characteristic frequencies, determines the specific fault type. Experimental studies show that NAH-based gearbox fault diagnosis can achieve 97.3% accuracy.

• Production-line quality inspection: At the end of production lines for home appliances such as air conditioners and refrigerators and for industrial products, the NAH2048 system performs a rapid acoustic “CT scan” of finished goods, using millisecond-level synchronous acquisition and AI pattern recognition to precisely determine whether a product exhibits abnormal noise. The system has already been deployed in cooperation with an air-conditioner production line for abnormal-noise inspection, achieving a detection accuracy of 99.99%.

III. Summary of Technical Advantages

NAH2048 large-array near-field acoustic holography handles microscopic precision measurement and fault confirmation for core equipment and components, elevating fault diagnosis from the phenomenological judgment of “locating by listening” to essential analysis at the level of physical mechanisms, thereby providing a scientific, quantitative technical path for precise fault diagnosis.