How Does Ultrasonic Detection Work?

In the world of ultrasonic detection, sound conveys lots of crucial information. All we have to do is listen.

At its core, the PROSARIS Solution includes an ultrasonic sensor – a device that can detect these ultrasonic emissions. We call this sensor the “Puck”. The Puck features 24 MEMS (Micro-Electro-Mechanical Systems) microphones that can “hear” ultrasonic anomalies, and whose proprietary arrangement and processing allows them to punch far above their weight class. The Puck connects to your tablet or mobile device where the detected ultrasonic frequencies are visualized on-screen. This allows you to triangulate the exact source that the ultrasonic emission is coming from. It’s critical to ensure that your ultrasonic detection tool is set to the correct frequency range to match the issue type you’re detecting (e.g., compressed air leaks emit a frequency of around 36 - 42 kHz). However, for leak detection, it’s decibels that are important to observe for determining the severity of the issue. For example, both a minor and severe air leak will have a frequency of ~39 kHz, but the decibel levels will be low for the minor leak and higher for the severe leak. Additionally, ultrasonic issues do not have objective decibel levels of their own – they are completely dependent on the distance and angle that you are detecting them from. For example, detecting the same leak directly straight on from 1 meter away will provide a much higher decibel reading than from 8 meters away at a 45° angle (This is due to the “Inverse Distance Law of Attenuation” of the signal). PROSARIS generally excels at detecting ultrasonic issues from approximately 10 meters and in – but make sure you’re at least 1 foot away to accurately measure your calculations.

The OL2 Puck and PROSARIS App

PROSARIS is filled with smart features that allow you to adjust the detection frequency range, record dB levels, calculate $ loss, and much more. You can learn about the PROSARIS Solution and all these features by visiting our various product pages. However, there's one feature that we’ll continue to dive into here, as it pertains to this subject matter. The default detection mode that PROSARIS offers is Visual mode. As seen in the image above, the direction of the ultrasonic frequencies is overlaid on your tablet’s camera feed, allowing you to follow the trail and centralize on the source of the emissions. However, we offer a second mode of detection: Audio mode.

The down conversion process

As we learned in our previous blog, we can’t hear sounds in the ultrasonic range. So how does Audio mode work? To answer this question, it’s time to learn about heterodyned down conversion.

Simply put, heterodyned down conversion allows you to shift a section of soundwaves from one frequency range to a lower range. For example, recorded sound in the 25 kHz – 45 kHz range (ultrasound) can be down shifted to 0 Hz – 20 kHz (audible), allowing you to effectively hear it. The range is still 20 kHz wide, but has been shifted down and into the Audible range.

A visual representation of the down conversion process

The Puck's ability to switch from Visual mode to Audio mode allows the user to hear exactly what’s happening within a range of ultrasonic frequencies that are normally outside our hearing range.

While there are other techniques out there, we've found that our heterodyning process results in high-fidelity audio that preserves spectral quality to support more advanced post-processing analysis of harmonic indications of the fault condition. And it sounds great.