Ultrasonic sensors are simple, convenient, and inexpensive to use. However, current ultrasonic sensors have some drawbacks, such as reflection problems, noise, and cross-talk issues.

　　1. Reflection Problems

　　If the object being detected is always at the right angle, the ultrasonic sensor will obtain the correct angle. Unfortunately, in practice, it is rare for the object being detected to be correctly detected.

　　Several errors may occur:

　　2. Triangular Error

　　When the object being measured is at a certain angle to the sensor, there is a triangular error between the detected distance and the actual distance.

　　3. Specular Reflection

　　This problem is the same as the reflection of light learned in high school physics. At a specific angle, the emitted sound waves are specularly reflected by a smooth object, so no echo is generated, and no distance reading can be generated. In this case, the ultrasonic sensor will ignore the existence of this object.

　　4. Multiple Reflections

　　This phenomenon is more common when detecting objects such as corners or similar structures. The sound waves bounce multiple times before being received by the sensor, so the actual detected value is not the true distance value.

　　These problems can be solved by using multiple ultrasonic rings arranged at a certain angle. By detecting the return values of multiple ultrasonic waves, the correct reading can be filtered out.

　　5. Noise

　　Although the operating frequency of most ultrasonic sensors is 40-45Khz, which is far higher than the frequency that humans can hear, the surrounding environment can also produce similar frequency noise. For example, motors produce certain high frequencies during rotation, wheels produce high-frequency noise due to friction on hard ground, the robot itself shakes, and even when there are multiple robots, the sound waves emitted by other robot ultrasonic sensors can cause the sensor to receive incorrect signals.

　　This problem can be solved by encoding the emitted ultrasonic waves, such as emitting a group of sound waves of different lengths. Only when the detection head detects the same combination of sound waves is the distance calculated. This can effectively avoid misreading due to environmental noise.

　　6. Cross-talk Issues

　　Cross-talk issues occur when multiple ultrasonic sensors are installed on a robot at a certain angle. The sound waves emitted by ultrasonic sensor X are specularly reflected and received by sensors Z and Y. At this time, Z and Y will calculate the distance value based on this signal, thus failing to obtain the correct measurement.

　　The solution is to encode the signals emitted by each sensor, allowing each ultrasonic sensor to only listen to its own sound.