Beamforming Explained Simply: How an Ultrasound Camera Works for Leak Detection

Beamforming refers to the process of focusing a beam. In an ultrasound camera, the analysis is computationally aligned with many points in space without the need to mechanically move microphones or the camera. For each pixel, the system performs a calculation to determine how a sound signal from that direction in space should arrive at the individual microphones. 

This creates an acoustic map: points from which the microphone signals consistently arrive are assigned a higher level. Points from which the signals do not match are attenuated. The result is superimposed on the camera image as a colored heat map.

A single microphone can measure sound pressure, but cannot unambiguously determine the direction from which the sound source is coming. A microphone array uses multiple highly sensitive digital MEMS microphones positioned at known, geometrically calibrated locations. The compact UltraCam LD 500/510 uses 30 microphones; the LeakCam 600 uses 64 digital microphones.

The precisely known geometry of the microphone array forms the basis for evaluating time-of-flight and phase differences. The spatial arrangement, number, and distribution of the microphones significantly influence the directional resolution and thus the accuracy of sound source localization.

Standard beamforming: microphone array, signal processing, filtering, and calculation of the acoustic map.

To perform the calculation, the system requires fixed boundary conditions: focal length or distance to the object, horizontal and vertical field of view, and the desired acoustic resolution. These parameters are used to generate a grid of acoustic pixels.

For each pixel on the ultrasound map, the processor performs a calculation to determine the physical path from each microphone to that point in space. When a sound signal arrives, the microphone signals are corrected for the calculated time-of-flight differences. In the classic delay-and-sum approach, this is done in the time domain; in the LeakCam’s power beamforming, phase shifts are used in the frequency domain. At the same time, the signal is digitally filtered to the selected target frequency window.

After the runtime or phase correction, the signals from all microphone channels for the pixel in question are summed. If the sound is actually coming from this direction, the signals are in phase with one another and reinforce each other constructively. If the sound comes from a different direction, the signals interfere out of phase and partially cancel each other out destructively.

Constructive interference: phase-corrected signals add together and amplify the actual sound source.	Destructive interference: Noise from other directions is attenuated by the summation.

To provide a smooth, real-time display, the system performs calculations to generate acoustic images in rapid succession. The acoustic data is superimposed as a colored heat map directly over the live optical image. The display guides the user directly to the most likely position of the ultrasound source.

From the calculated ultrasound image to the heat map: Dynamic range and threshold determine which levels are displayed.

The image produced by an ultrasound camera can be compared to that of a thermal imaging camera. An infrared camera measures thermal radiation and assigns temperature values to individual pixels. An ultrasound camera measures frequency-dependent sound pressure levels and assigns these acoustic values to spatial directions or pixels.

In both cases, the user sees a visual image with overlaid color information. With a thermal imaging camera, the color indicates temperature differences. With an ultrasound camera, the color indicates the intensity of the calculated sound source. The heat map is therefore not a photograph of the leak, but rather an acoustic localization overlay that is superimposed on the video image.

Analogy: visual image of the system and thermal or acoustic color image. With ultrasound, the color represents sound pressure, not temperature differences.

Standard beamforming can effectively locate individual dominant sound sources. In practice, however, multiple leaks or noise sources with different sound pressure levels often occur simultaneously. A system’s dynamic range determines the maximum level difference that can be displayed between the strongest and weakest visible sound sources.

A high dynamic range improves the simultaneous detection of leaks of varying loudness. A low display dynamic range can highlight weak sources more strongly but reduces the level range visible in the image.

The LeakCam 600’s Power Beamformer is designed for high spatial resolution and the simultaneous visualization of multiple sound sources. This allows even weaker leaks to remain visible alongside dominant sound sources and be located more easily.

Comparison from the webinar: Power beamforming visualizes multiple leaks more clearly than standard beamforming.