1. Introduction

Ultrasonic sensor technology has experienced significant growth and innovation in recent years, finding widespread use in areas such as automotive systems, industrial automation, and precision agriculture.

These sensors operate by emitting high-frequency sound waves and detecting the reflected signals to measure distances and identify objects. Their ability to function without physical contact makes them highly valuable in environments where traditional sensors might struggle, such as those involving smoke, dust, harsh lighting, or confined spaces. Ultrasonic sensors are especially popular for their cost-effectiveness, reliability, and ability to operate under various challenging conditions, making them indispensable in numerous applications[1]. However, despite their numerous advantages, ultrasonic sensors are not without limitations. They frequently encounter impediments in the realm of long-range detection and may be susceptible to environmental influences such as temperature fluctuations, humidity, precipitation, or interference from various substances. These limitations raise important questions about the technology's future potential, especially as it increasingly becomes part of more complex and dynamic systems like autonomous vehicles and smart farming.

This paper will explore ultrasonic sensors by drawing on existing literature and case studies, focusing on three key areas: optimizing sensor performance under varying environmental conditions, integrating ultrasonic sensors with other sensor technologies, and evaluating their current and potential applications in automotive and agricultural fields.

2. The concept of ultrasonic sensors

An ultrasonic sensor is a device capable of measuring distance and detecting the presence of objects without physical contact, utilizing the physical properties of ultrasonic waves. It emits high-frequency sound waves (typically above 20 kHz, beyond the range of human hearing) and receives the reflected waves from the object’s surface to measure information such as the distance, speed, position, and material characteristics of the target object [1].The operating principle of the ultrasonic sensor is based on variations in the speed of sound in different media, as well as the physical phenomena of reflection, scattering, and attenuation. Operating as a piezoelectric transducer, it facilitates the conversion between electrical and mechanical vibrational energy. In monostatic systems, the ultrasonic sensor functions as both a transmitter and a receiver at a single frequency, acting as both a speaker and a microphone. One of its primary advantages is its ability to operate in a wide range of environmental conditions, including dust, smoke, and bright light. Consequently, ultrasonic sensors find extensive application across sectors such as industrial automation, robotic navigation, vehicle obstacle detection, level measurement, and medical imaging[2].

The sensor captures the time difference between the emission and reception of the echo. Since the speed of sound is a known variable, the time delay captured can be used to calculate the distance between the sensor and the object. \( d=\frac{Vt}{2} \) demonstrates how the distance is calculated using ultrasonic waves.This approach is identified as the Time-of-Flight (ToF) measurement, which is contingent upon the propagation duration of sound waves. It should be noted that the speed of sound in air varies with temperature. In dry air at 20°C (68°F), the speed of sound is 343 m/s, which means it takes approximately 2.91 seconds to travel one kilometer[3].

3. Ultrasonic sensors in different fields of application

Ultrasonic sensors use sound waves exceeding 20 kHz to detect nearby objects, similar to how bats avoid obstacles through echolocation. In the automotive sector, ultrasonic sensors are prevalent in Advanced Driver Assistance Systems (ADAS), especially in parking assistance, where typically 4 to 16 sensors are used to detect obstacles during parking maneuvers. In industrial applications, ultrasonic sensors are used in robotics and other systems requiring reliable presence, proximity, or position sensing[4].

3.1. Ultrasonic sensors in automotive applications

3.1.1. Parking assistance systems

During parking, drivers face various obstacles, especially when reversing or parallel parking in tight spaces with limited visibility. Ultrasonic sensors, installed in multiple units on the front and rear bumpers, detect obstacles by emitting and receiving ultrasonic signals[4]. When the sensors detect an obstacle, they provide the driver with a warning signal based on the distance and direction of the object. This technology substantially enhances the convenience and safety of parking by diminishing the incidence of accidents resulting from limited visibility during such maneuvers.

3.1.2. Automated driving system

In autonomous vehicles, ultrasonic sensors are used alongside other sensors, such as radar, lidar, and cameras, to provide comprehensive environmental awareness[5]. Ultrasonic sensors are particularly effective in short-range obstacle detection and precise control in low-speed environments, such as in automated parking. They contribute to the vehicle’s capacity to accurately gauge distances from surrounding obstacles, thereby enabling safe and dependable automated parking procedures.

3.1.3. Blind spot monitoring system

Blind spot monitoring systems help drivers detect vehicles or obstacles in the blind spots on the sides and rear of the vehicle, reducing the risk of collisions during lane changes or turns. Ultrasonic sensors are mounted on the sides and rear of the vehicle, continuously emitting and receiving ultrasonic signals to monitor these areas[6] . When an object is detected in the blind spot, the system alerts the driver through flashing lights or sound warnings, enhancing driving safety, particularly in complex urban environments.

3.1.4. Existing problems

However, ultrasonic sensors have limitations. Their detection range is typically restricted, which can diminish their efficacy in identifying distant obstacles at high vehicular speeds. Additionally, environmental factors such as rain, snow, or dust can affect their accuracy. Therefore, in practice, ultrasonic sensors are often integrated with other sensor types to improve system reliability and safety[7]. Overall, due to their excellent short-range detection capabilities and low cost, ultrasonic sensors are widely used in automotive applications, especially in parking assistance and blind spot monitoring systems. As autonomous driving technology advances, the use of ultrasonic sensors will expand further, providing safer and more reliable solutions for intelligent driving.

3.2. Application of ultrasonic sensors in agriculture

In recent years, with the development of smart agriculture, ultrasonic sensors have been increasingly applied in the agricultural field. These sensors use the propagation characteristics of ultrasonic waves, emitting pulses and receiving the reflected signals to measure the distance between the sensor and the target[7]. With high precision and real-time capabilities, ultrasonic sensors provide precise data support in agricultural production, improving accuracy and efficiency.

3.2.1. Unmanned aerial plant protection

Ultrasonic sensors can monitor crop growth and density in real time. By measuring the distance between the drone and the crops, ultrasonic sensors automatically adjust the amount and height of pesticide or fertilizer spraying, achieving precise application. This reduces resource waste and minimizes environmental pollution. Additionally, ultrasonic sensors can detect obstacles ahead of the drone and changes in terrain, helping the drone adjust its flight path to avoid collisions with crops or the ground.

3.2.2. Irrigation system

Ultrasonic sensors are widely used in irrigation systems to monitor water levels in tanks or reservoirs. When the water level falls below a set point, the system automatically activates the irrigation equipment to replenish water. Conversely, if the water level exceeds the set limit, the system halts irrigation to prevent wastage. These sensors can also detect soil moisture by measuring the distance between the soil surface and the sensor, allowing farmers to more accurately control irrigation frequency and water volume, improving water efficiency[8].

3.2.3. Precision sowing

The uniformity and depth of sowing directly affect crop growth and yield. Ultrasonic sensors facilitate the monitoring of the distance between the seeding machine and the soil surface, aiding in the adjustment of row spacing and sowing depth to ensure even seed distribution. This reduces manual intervention and significantly improves germination rates and yields[9].

3.2.4. Existing problems

Despite these advantages, ultrasonic sensors face challenges in complex agricultural environments, such as terrain variability and dense vegetation that may affect measurement accuracy. Moreover, weather conditions, such as wind speed and temperature, can impact ultrasonic wave propagation and measurement results[10]. Selecting suitable sensor types, optimizing algorithms, and integrating multiple technologies can mitigate these issues.

4. The future of ultrasonic sensors

With the rapid development of artificial intelligence and machine learning, ultrasonic sensors will not be limited to simple distance measurement and obstacle detection. By combining ultrasonic sensors with intelligent algorithms, more complex scene perception and decision-making can be achieved. For instance, in agriculture, ultrasonic sensors integrated with drones and ground robots can monitor crop growth and soil moisture in real-time, providing intelligent irrigation and fertilization recommendations. In the automotive sector, ultrasonic sensors will be integrated with onboard computing systems and other sensors, offering smarter environmental awareness and decision support to enhance the safety and reliability of autonomous driving.

In the future, the development of ultrasonic sensors will depend not only on technological advancements but also on integration with other sensor technologies. For instance, the fusion of ultrasonic sensors with infrared, lidar, and optical sensor technologies has the potential to enhance environmental perception with a greater degree of comprehensiveness and accuracy. This multi-sensor fusion technology has vast applications in autonomous driving, smart security, and smart homes, promoting the innovative use and market expansion of ultrasonic sensors.

The successful application of ultrasonic sensors in the automotive and agricultural fields demonstrates their strong potential and market prospects.

As technology continues to advance and cross-sectoral applications expand, ultrasonic sensors will play a crucial role in the trends of automation, intelligence, and cost reduction, bringing more innovative solutions to various industries. he milestones and advancements in ultrasonic sensor technology are anticipated to furnish more dependable and efficient perception instruments, thereby contributing to the construction of a more intelligent and interconnected world.

5. Conclusion

This paper investigates the use of ultrasonic sensors in both automotive and agricultural applications, focusing on their roles in advanced driver assistance systems (ADAS), such as parking assistance and blind spot monitoring, and in precision agriculture, including irrigation management and crop monitoring. The key research questions addressed in this study involve optimizing the accuracy of ultrasonic sensors under varying environmental conditions and exploring their integration with other sensor technologies to enhance overall functionality.

Through the analysis of case studies and existing literature, this research finds that ultrasonic sensors are highly effective for short-range detection in controlled environments, yet their performance is often limited by factors such as adverse weather and long-range detection.

Although ultrasonic sensors confer distinct advantages in terms of cost-effectiveness and dependability in proximate-range applications, the current inquiry identifies several impediments. One major drawback is the sensors' reduced accuracy in harsh conditions like rain, snow, or dust, and their difficulty detecting objects at longer distances. To overcome these challenges, future research could focus on improving sensor fusion techniques—integrating ultrasonic sensors with radar, LiDAR, or AI-driven systems to enhance detection capabilities in diverse environments. Additionally, the development of more resilient sensors capable of operating under extreme conditions would be crucial for expanding their practical applications. Lastly, future studies should explore the broader integration of ultrasonic sensors within emerging smart systems, such as fully autonomous vehicles and advanced precision farming, to address current limitations and unlock the full potential of this technology.