Sensors Team Up to Thwart Trespasser Drones

Here’s how sensors can help prevent unwelcome drones turning up.

Low-cost consumer drones is a fantastic new technology that many of us enjoy, but the free-flying nature of drones also lets them quickly become a nuisance or even hazard if misused.

What can we do when a drone flies where it shouldn’t?

A wayward drone can be a benign nuisance—such as a neighbor’s drone hovering over your family pool—or something more serious. Drones flying near aircraft may affect lives, and weaponized drones could potentially affect humans in an urban setting. There’s no doubt that the easy access to low-cost drones has added a problematic third dimension to security and privacy equations.

As drones are a relatively new phenomenon, lawmakers are still playing catchup. Regulations are unevenly applied and vary from place to place. Most jurisdictions outlaw drones from flying near airports, prisons, and sensitive political or military zones. However, if an unknown drone is buzzing in your backyard or hovering at the window of your corporate boardroom, it may be less clear what law it is violating.

While we wait for the law to catch up, there are practical measures which are available today.

Detection: The First line of Defense
The first step in drone defense is detection—knowing that a drone is there. Of course, you may well see or hear the unwanted drone, but if not, a multitude of sensors can help.

If the drone is in active communication with a pilot, detection is significantly easier. Most consumer-class drones use the same ISM radio frequencies as WiFi and Bluetooth, namely the 2.4GHz and 5.8GHz bands. Therefore, a source broadcasting on unlicensed frequencies is of particular interest to our drone detector.

If we can achieve some directional discrimination to de-emphasize radio sources that are at ground level or permanently immobile, then drones should stand out more clearly. A simple ‘cantenna’ tube can provide directional discrimination, with the drawback that it must be physically scanned across the sky.

Alternatively, an array of widely spaced antennas can estimate the direction of a radio source based on relative signal strength, without the need to move the antennas. There’s even the (more difficult) possibility of using the same hardware to locate the drone’s owner.

For an off-the-shelf drone using standard communications protocols, some essential elements of its transmissions, such as Media Access Control (MAC) address and Basic Service Set Identifier (BSSID), may even let us identify the model, though these can easily be altered. Researchers have even suggested cunning ideas such as flashing a laser at the drone and listening for a corresponding change in its transmitted video stream to verify that the drone is actively watching you.

While these detection methods might be feasible, they are impractical because you don’t know when or where a drone might appear.

Locating Autonomous Drones
How can we automatically detect autonomous drones which are not currently transmitting radio signals? This is more difficult and expensive. Makers of commercial drone detectors combine a variety of sensors, including machine vision, radar, and lidar.

Fortunately, typical drones are loud, so if you’re building a budget drone detector, then a relatively simple directional array of microphones could be a surprisingly easy way to discover a drone buzzing nearby. The distinctive sound signature of quadcopter electric motors is an additional data point enhancing the chance of detection, even in a noisy urban area.

Perhaps the lowest cost method for detecting radio-silent drones would be directional microphones combined with a simple camera backed by machine vision software. While adequate for most purposes, notable drawbacks are that the system may be triggered by birds or distant aircraft, will have more difficulty picking out a low-flying drone from background objects and will perform poorly at night.

Taking Action Against Unwanted Drones
Assuming we have detected an intrusive drone, and we want to take active measures, then the next step is defense—forcing the drone to back away or land, or even disabling or destroying it somehow. The legality of these techniques depends on the situation and your local laws, so you need to familiarize yourself with your local regulations.

A simple step up from detection is jamming. The same directional device may even perform both tasks. This is a relatively good solution because almost all drones will either return to their owner or land after they lose radio communications. A variety of DIY directional radio jamming projects can be found online.

Commercial drone defense solutions include more sophisticated radio jammers, GPS (and GNSS) spoofing, dazzling camera lasers, and interceptor drones. Military and police forces employ the most aggressive techniques. These include using projectiles such as nets fired from a small cannon, or even small anti-aircraft missiles.

Bringing Drones Down to Earth
While consumer drones have undoubtedly improved many industries from surveying to aerial photography, real estate and more, their easy maneuverability has also created privacy and safety issues. Techniques such as drone detection and signal jamming provide businesses, government organizations, airports, and private citizens with ways to defend against wayward drones.

Rudy Ramos is the project manager for the Technical Content Marketing team at Mouser Electronics and holds an MBA from Keller Graduate School of Management. He has over 30 years of professional, technical and managerial experience managing complex, time critical projects and programs in various industries including semiconductor, marketing, manufacturing, and military. Previously, Rudy worked for National Semiconductor, Texas Instruments, and his entrepreneur silk screening business.


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