- What is Ultrasound?
Ultrasound or ultrasonic waves are sound waves with a higher frequency than humans can hear. In the case of Toposens‘ sensors, frequencies above 40kHz are being used.
- What is an Ultrasound Sensor?
In general, ultrasound sensors are sensors that make use of the characteristics of high-frequency sound for a range of applications such as distance measurement, non-destructive testing of materials, or medical applications.
For distance measurement, a typical ultrasound sensor uses a transducer to periodically send out ultrasonic pulses in the air. These pulses get reflected from objects in the detection area of the sensor and are received back by the sensor. By measuring the time it takes an ultrasonic pulse to travel to the object and get reflected to the sensor, the distance to the object can be calculated. This principle is called time-of-flight measurement.
- How are Toposens’ 3D Ultrasound Sensors different?
In addition to measuring the distance to an object, 3D ultrasound sensors can also calculate the horizontal and vertical position of an object relative to the sensor itself (i.e. they provide 3D coordinates for detected objects). The localization of objects in three-dimensional space also allows a 3D ultrasound sensor to detect and distinguish between multiple objects in a single scan. In that sense, the principle of 3D ultrasound sensors is similar to echolocation, as applied for example by bats. In comparison, a typical ultrasonic sensor, as described in the previous section, will normally only give the distance to the nearest object. Because of this, a limited opening angle is usually applied for this type of sensor. In contrast, 3D Ultrasound Sensors allow for opening angles of up to 180°.
- What are benefits of ultrasound sensors?
Especially for close range sensing, ultrasound sensors complement other sensors, such as Lidar, Radar and 3D cameras:
1. Since ultrasound does not rely on visual components, Toposens‘ ultrasound sensors can „see“ in the dark, through dust and dirt and in varying lighting conditions
2. The sensor units can detect objects with transparent or reflecting surfaces
3. The sensors are robust, energy efficient and can be used in a wide variety of applications.
Characteristics of 3D Ultrasound Sensors
- How does a 3D Ultrasound Sensor work?
Toposens’ 3D Ultrasound Sensors work by combining the time-of-flight principle of conventional ultrasound sensors with triangulation and advanced signal processing algorithms.
At the beginning of each measurement cycle, a transducer on the sensor sends out an ultrasonic pulse. This pulse is reflected by surrounding objects and received by an array of microphones on the sensor. Based on the different times of when echoes arrive at the individual microphones, the origins of the echoes are calculated as 3D coordinates. These 3D coordinates are put out at the end of each measurement cycle.
A 3D Ultrasound Sensor detects an object only at the strongest points of reflection. This explains why there are less points (i.e. the point cloud is sparse) for 3D Ultrasound Sensors compared to other sensors, which scan a grid (i.e. Lidar or 3D cameras).
- What are limitations of 3D Ultrasound Sensors?
The limitations of 3D Ultrasound Sensors are mainly based on the physical properties of ultrasound and the respective reflection characteristics of objects. For the sensor to detect an object, the sent out ultrasonic pulses have to be reflected by the object and received back by the sensor. The reflection characteristics of an object depend on object properties, such as the object’s surface size, orientation and distance to the sensor, and the material characteristics of the object.
The surface size of an object plays a pivotal role in reflecting the ultrasonic wave that is sent out by the transducer. An object, for which only a small surface faces the sensor, has a lower chance of detection.
The orientation of an object determines which part of the ultrasonic pulse gets reflected to the sensor. At an adverse angle (= surface not perpendicular to sensor), a smaller proportion of the pulse is received by the sensor, in which case the object has a lower chance of detection.
Ultrasonic pulses are attenuated in air, which limits the detection range that can be achieved by 3D Ultrasound Sensors. The further away an object is from the sensor, the lower its chance of detection becomes.
Material characteristics of an object also determine which part of the ultrasonic pulse gets reflected to the sensor. For weakly reflecting or sound absorbing materials, such as foam, the chance of detection decreases.
- What is the data output of 3D Ultrasound Sensors?
Generally, the output of a 3D Ultrasound Sensor is a list of detected reflections for each frame, with each frame containing the output of one full measuring cycle. A graphical representation of the sensor output is a sparse point cloud.
The information put out by the sensor for each detected reflection contains the 3D coordinates of the origin of the reflection and its relative signal strength. A marker is added to each frame in case it is registered as “noisy”, meaning that the level of ambient noise affected the accuracy of the measurement. The number of reflections and their strengths depend on the reflection characteristics of the object.
Watch Toposens‘ Automotive DevKit Demo video to get a sense for how 3D Ultrasound Sensors perceive their environment.
- Where can I get more specific information about Toposens 3D Ultrasound Sensors?