A research team at Los Alamos National Laboratory has developed an inexpensive method for generating a high-power, low-frequency, collimated sound beam. In addition to penetrating deeply, this beam can create high-resolution images for applications such as biomedical diagnosis, borehole monitoring, evaluating explosives threats, and underwater communications. The new technique, dubbed Acoustic Collimated Beam (ACCObeam), is a major advance over ultrasound imaging tools. These current tools cannot image deeply into cement, rock formations, or bone and the human body. That’s because high frequencies attenuate significantly in solids.The trick ended up being fairly simple. They put the piezoelectric disk that generates the sound into a fixture that clamps it along its circumference.
By simply clamping the circumference of a piezoelectric disc inside a hard material and exciting concentric ring-like ripples in the disc, the team determined that it could produce a highly collimated, powerful sound beam that also minimizes unwanted side lobes.10 kHz is going to be lower resolution than 250 kHz (higher frequencies are always shorter wavelengths, and resolution depends on the physical size of the waves - sound or radio), but the narrow 6 degree beamwidth and lower sidelobes help the performance as well. For comparison, you may have heard of the sonar "fish finders" that have become essential equipment for most fishermen, and are on millions of recreational boats. Those are ultrasonic sonars, too. The fishing sonars work at twice the highest frequency of the ACCObeam as their low frequency ends, not quite 500 kHz, more like 450 kHz, 800 kHz for their narrow beams, and are now pushing above 1000 kHz for higher resolution imaging.
The resulting device, called ACCObeam, operates at a low frequency of 10–250 kHz, so the sound it produces does not attenuate significantly in any medium. In fact, ACCObeam is capable of imaging underground in almost any medium and has been shown to image two to three meters of rock without compromising image resolution.
LANL produced a well done little video that shows some details about the ACCOBeam and how it could be used for oil wells, fracking, and other energy industry-related tasks, which is LANL's reason for being.
Still, this isn't a fishing sonar, and while the commercial grade sonars have capabilities that ACCObeam doesn't, direct comparison isn't fair. These are different tasks, and the LANL scientists are looking for applications where it fits better than existing technology.
Using mock material, the team has proven that ACCObeam can noninvasively establish the 3-D thermal field inside a closed container. ACCObeam’s portability could significantly change how emergency responders analyze explosive threats.My only gripe about the story is they shared no images captured through rocks or ground. The video is worth watching, though.