This article is part of our exclusive IEEE Journal Watch series in partnership with IEEE Xplore.
It’s safe to say that most people do not want to get up close and personal with a shark when they take a dip in the ocean. Finding ways to deter these curious creatures from coming too close to humans—in a way that doesn’t harm the sharks—can be challenging, but researchers are exploring an intriguing option: electrical fields.
In a study published 31 October in IEEE Sensors Letters, a team in Australia characterized the nature of underwater electrical fields under different salinities. One of their goals is to develop a small device that swimmers could wear to repel sharks.
“We are interested in electric fields as a deterrent because they directly interact with one of the shark’s most sensitive sensory systems–electroreception,” explains Hugo Espinosa, deputy dean of learning and teaching at Griffith University in Australia who participated in the research.
Sharks are able to detect weak electric signals using the pores on their snouts that act as electroreceptors, which helps them with navigation and prey detection. “Introducing a controlled, stronger electric stimulus can disrupt this process in a way that encourages avoidance without harming the animal,” Espinosa explains.
The threshold for an electrical field to repel a shark can vary by species but ranges from about 3 V/m (to deter bull sharks) to 18.5 V/m (to deter scalloped hammerheads), with some species requiring even higher field strengths. These field levels are well below established human exposure limits and are not expected to produce physiological effects in humans under normal, nonconductive exposure conditions, Espinosa says.
The key challenge, however, is to create an electric field that extends far enough into the surrounding water. Generating long-range electric fields in seawater is inherently difficult because seawater is highly conductive. The electric current disperses rapidly through the surrounding medium, causing a voltage gradient that drops sharply with distance.
A Shark Repellent Device Under Study
In their study, Espinosa and his colleagues conducted experiments using a small, portable pulsed electric-field generator, delivering an output of 5,000 V at 8.5 kHz, and measured the electrical field it produced across three different salinities of water. The salinities ranged from those found in freshwater systems used by river-adapted sharks, estuarine environments where infant sharks are born and grow, and coastal marine waters where most human-shark encounters occur.
Similar to what many studies in the past have shown, the pulsed electric fields diminished rapidly with distance.
But the results hint at some good news too: The device was able to create similar electric fields across different salinities. This suggests that if scientists can boost the range of underwater electric fields, the same electric field-generating device could be used in different marine environments. The researchers also quantified in detail how pulsed electric fields that deter shark species attenuate in conductive environments.
Their calculations align closely with theoretical models and point toward potential ways to boost the range of underwater electrical fields. This includes focusing on optimizing electrode configuration, waveform design, and power delivery to create an effective shark deterring device, says David Thiel, a professor emeritus of electronic engineering at Griffith University, who was involved in the study.
He acknowledges that each of these design features comes with trade-offs in terms of battery life, heating, and device size. “For wearable systems, these constraints are significant,” he notes, adding that the team plans to study the influence of these different design factors on underwater field generation in future work.
The research team also has visions for scaling up this technology beyond wearable devices for individual swimmers. In particular, they are suggesting that a network of electric field generators could be used to form a controlled boundary near beaches and swimming areas.
Espinosa says, “While each device has a short range, a distributed array could create a larger protective zone if spacing, overlap, and power requirements are properly optimized.”
For people with shark phobias—likely traumatized by movies like Jaws—such advances could help make getting in the water a little easier.
Michelle Hampson is a freelance writer based in Halifax. She frequently contributes to Spectrum's Journal Watch coverage, which highlights newsworthy studies published in IEEE journals.
