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In recent years, consumer drones have gained widespread popularity for capturing breathtaking footage, delivering emergency supplies, and even competing in aerial races. Most modern drones rely on a range of sensing technologies to enable autonomous navigation, obstacle avoidance, and various other functions. Among these, ultrasonic sensors play a crucial role, especially when it comes to landing, hovering, and ground tracking.
The drone landing aid is a key feature that helps the drone determine the distance between its bottom and the landing surface, assess the safety of the landing spot, and then descend smoothly to the ground. While GPS, barometric sensors, and other technologies contribute to the landing process, ultrasonic sensing remains the most accurate and reliable method for UAVs. Many drones also use hover and ground tracking modes to maintain a consistent altitude during filming or navigation, with ultrasonic sensors playing a vital role in this functionality.
This blog post explores the reasons why ultrasonic sensing is widely used in drone applications. We’ll start by explaining the basic principles of ultrasound and how it works, followed by an in-depth look at the Time of Flight (ToF) technique used in drone landing systems. We'll also discuss the advantages of using ultrasonic sensors, including their cost-effectiveness, reliability, and ability to detect surfaces that other technologies might miss.
Ultrasonic waves are sound waves with frequencies above the human hearing range—typically above 20 kHz. These waves can travel through different media such as air, water, and solid objects, making them ideal for detecting obstacles and measuring distances. In dry air at 20°C, the speed of sound is approximately 343 meters per second. However, ultrasonic waves in air tend to attenuate more at higher frequencies, which is why most applications limit the frequency to below 500 kHz.
When it comes to drone landing, ultrasonic sensors use the Time of Flight (ToF) principle. The sensor emits an ultrasonic pulse, which travels to the target surface and reflects back. By measuring the time it takes for the echo to return, the system can calculate the distance to the surface. This method is both simple and effective, making it a popular choice for drones.
One of the main challenges with ultrasonic sensing is the "ringing" effect, where the sensor continues to vibrate after emitting a signal, making it difficult to detect incoming echoes immediately. To overcome this, many drone designers use separate transmitter and receiver sensors. This allows the drone to detect objects even while the transmitter is active, improving accuracy and performance.
Texas Instruments’ PGA460 is a powerful solution for ultrasonic sensing in drones. It supports both half-bridge and H-bridge drive configurations, as well as transformer-based driving for sealed sensors. The device also includes a complete analog front end for processing received signals and calculating ToF through digital signal processing.
Another advantage of ultrasonic technology is its ability to detect reflective surfaces like glass. Unlike optical sensors, which may pass through transparent materials, ultrasonic waves reliably reflect off glass, allowing drones to hover safely near buildings and other structures.
While ultrasonic sensing is primarily used for landing and hovering, its cost-performance ratio is driving innovation in other areas of drone technology. As the drone industry continues to grow, we can expect to see even more creative applications of this versatile sensing method.