Scientists at the Massachusetts Institute of Technology (MIT) have developed an acoustic system that functions like an underwater GPS but does not require a battery to operate. The Underwater Reverse Scatter Positioning (UBL) system generates binary pulses by reflecting modulated audio signals. GPS navigation has been very successful. In addition to helping motorists from point A to point B, the technology has also discovered confusing applications, from battlefields to warehouses.
However, GPS cannot work underwater. This is because water can block and disperse the radio waves on which GPS depends, making them inastive. That’s why submarines use sonar instead of radar to detect their surroundings. Radar beams can be swallowed up within a few yards, and acoustic signals can spread thousands of miles under the right conditions.
According to MIT scientists, the problem with using acoustics to create an underwater signal generator equivalent to GPS is that acoustic signal generators are very power-hungry. This may not be important for nuclear submarines, but it can be a real problem for small devices that rely on batteries to carry out tasks, such as tracking animals.
To help overcome this problem, MIT researchers, with the support of the Naval Research Office, turned to pyelectronic materials, which generate electrical charges under mechanical stress, including the effects of sound waves. For UCL systems, the team used a ballast sensor to selectively reflect back the sound waves emitted from the environment as a reverse scattering, using the sound waves themselves as a power source. These sound waves are then received by the receiver in binary mode, with 1 reflecting sound waves and 0 reflecting sound waves.
This binary signal allows the UCL system to carry information, time the sound waves reflected from the sensor, and then return the time required by the observation device to secure the position. However, the team points out that the underwater environment is extremely complex and sound waves bounce off the surface and the ocean floor. Especially in shallow waters, the rebound signal is strong, which is more difficult.
To solve this problem, the team used a “frequency hopping” approach, in which signals are sent at a series of frequencies in one mode, so they return in different phases. The combination of timing data and phase data allows for more precise fixation. In shallow waters, the bit rate of the signal is slowed down so that the echo has time to fade without interfering with the signal.
So far, the UBL system has passed the concept verification test of shallow water, and its estimated distance is nearly 50 cm. MIT will work with the Woodhall Oceanographic Institute to increase the distance before starting field testing. The ultimate goal is a navigation technique that will allow autonomous underwater spacecraft to map the ocean floor in detail.
“Why can’t we send autonomous underwater spacecraft to carry out missions to explore the ocean?” The answer is yes. We’re going to lose them. Team leader Reza Ghaffarivardavagh said.
Papers on the study were presented at the Computational Machinery Association’s Web Hotspot Symposium.