With the rapid development of the transportation industry, the demands for traffic monitoring, management, and vehicle performance optimization are increasing. As a sensitive component that can convert mechanical energy into electrical energy, piezoelectric sensors, with their many advantages such as high sensitivity, fast response, simple structure, and strong reliability, show great application potential in the transportation field. From vehicle detection and traffic flow monitoring in intelligent transportation systems, to vibration measurement and fault diagnosis in vehicle engineering, and to the health monitoring of road infrastructure, piezoelectric sensors are playing an increasingly important role, providing strong technical support for the intelligence, efficiency, and safety of the transportation industry.

I. Working Principle of Piezoelectric Sensors

The working basis of piezoelectric sensors is the piezoelectric effect, that is, when certain materials are subjected to mechanical stress, the phenomenon that the amount of charge generated on their surfaces is proportional to the applied stress occurs. Materials with the piezoelectric effect can be divided into piezoelectric crystals (such as quartz crystals), piezoelectric ceramics (such as barium titanate, lead zirconate titanate, etc.), and piezoelectric polymers (such as polyvinylidene fluoride).

Take piezoelectric ceramics as an example. There are many electric domains inside. When there is no external force, the electric domains are arranged randomly, and the material as a whole is electrically neutral. When an external force is applied, the electric domains will be regularly arranged, causing the material to be polarized, and thus bound charges are generated on its surface. According to the different external forces received, the piezoelectric effect can be divided into the direct piezoelectric effect and the inverse piezoelectric effect. The direct piezoelectric effect refers to the phenomenon that a material generates charges when it is stressed, while the inverse piezoelectric effect means that when an electric field is applied to the material, the material will generate strain or stress proportional to the electric field strength. In transportation applications, the direct piezoelectric effect is mainly used to detect and measure various transportation – related physical quantities.

II. Applications of Piezoelectric Sensors in Intelligent Transportation Systems

1. Vehicle Detection and Traffic Flow Monitoring

Road – Embedded Piezoelectric Sensors

Piezoelectric sensors are embedded at appropriate positions under the road surface. When a vehicle passes by, the pressure generated by the contact between the vehicle tires and the road surface will cause the piezoelectric sensors to generate charge signals. By detecting, amplifying, and analyzing these charge signals, information such as the presence of the vehicle, the driving direction of the vehicle, and the number of vehicle axles can be accurately determined. By arranging multiple piezoelectric sensors on the road at a certain interval, the driving speed of the vehicle can also be calculated. By statistically analyzing the vehicle detection data of different lanes and different time periods, the traffic management department can keep abreast of the traffic flow on the road in real – time, providing accurate data basis for traffic signal control, traffic guidance, and traffic planning.

For example, piezoelectric sensors are embedded at the entrance of intersections on major urban roads to monitor the traffic flow of each lane in real – time. When the traffic flow of a certain lane is large, the traffic signal control system can automatically extend the green light time of that direction to relieve traffic congestion. At the same time, through the long – term analysis of traffic flow data, the peak and off – peak periods of traffic flow can be found, providing a reference for the traffic planning department to develop reasonable traffic construction and renovation plans.

Vehicle Detection at Bridge and Tunnel Entrances

Installing piezoelectric sensors at the entrances of bridges and tunnels can detect and count the vehicles entering the bridges or tunnels. This is not only helpful for mastering the real – time traffic flow of bridges and tunnels and reasonably arranging maintenance plans, but also can accurately count the number of vehicles trapped in the bridges or tunnels in case of emergencies (such as fires, traffic accidents, etc.), providing important information for rescue work.

For example, a piezoelectric sensor detection system is set up at the entrance of a large – scale cross – sea bridge to monitor the vehicles entering the bridge in real – time. Once an abnormal situation occurs, such as a vehicle breakdown or a traffic accident on the bridge, the monitoring center can quickly take corresponding rescue measures according to the vehicle information detected by the sensors, avoiding further aggravation of traffic congestion and ensuring the safe operation of the bridge.

2. Auxiliary for Electronic Toll Collection (ETC) System

Traditional ETC systems mainly rely on Radio – Frequency Identification (RFID) technology to identify vehicle identities and complete toll collection operations. However, in practical applications, due to factors such as the high driving speed of vehicles and the limited identification range of antennas, identification errors or missed readings may occur. Piezoelectric sensors can be used as an auxiliary means for ETC systems to improve the accuracy and reliability of toll collection.

Piezoelectric sensors are embedded under the road surface of the toll collection area in the ETC lane. When a vehicle enters this area, the piezoelectric sensors will detect the presence of the vehicle and generate signals. Combining with the vehicle information read by the RFID system, the system can further confirm whether the vehicle is a legitimate ETC user and whether the vehicle has passed through the toll collection area normally. If the piezoelectric sensors detect that a vehicle has passed through but the RFID system fails to read the vehicle information, the system can take timely manual intervention measures to prevent vehicle toll evasion. This ETC system based on the combination of piezoelectric sensors and RFID technology can effectively improve the toll collection efficiency, reduce the vehicle queuing waiting time, and enhance traffic fluidity.

III. Challenges and Solutions of Piezoelectric Sensors in Transportation Applications

1. Signal Interference and Noise Problems

In the actual traffic environment, piezoelectric sensors are easily affected by various electromagnetic interferences and the noise generated by vehicle driving, resulting in errors in the collected signals and affecting the measurement accuracy. To solve this problem, shielding technology can be used to conduct electromagnetic shielding on piezoelectric sensors and their transmission lines to reduce external electromagnetic interference. At the same time, advanced signal processing algorithms, such as filtering algorithms and adaptive noise cancellation algorithms, are used to denoise the collected signals and improve the signal – to – noise ratio. In addition, during the sensor selection and installation process, traffic environment factors should be fully considered. Piezoelectric sensors with strong anti – interference ability should be selected, and the installation position of the sensors should be reasonably determined to avoid excessive noise interference to the sensors.

2. Long – Term Stability and Durability

Traffic application scenarios usually require piezoelectric sensors to work stably for a long time and withstand various complex environmental factors such as vehicle loads, climate changes, and road construction. However, some piezoelectric materials may experience performance degradation during long – term use, affecting the measurement accuracy and reliability of the sensors. To improve the long – term stability and durability of piezoelectric sensors, on the one hand, piezoelectric materials with excellent performance and good stability should be selected, and appropriate surface treatment and packaging should be carried out to enhance the anti – aging ability of the materials. On the other hand, during the sensor design process, the structure of the sensor should be optimized to improve its anti – fatigue performance. At the same time, a regular sensor detection and maintenance mechanism should be established to timely detect and replace sensors with degraded performance, ensuring the stable operation of the entire traffic monitoring system.

3. Data Transmission and Processing

With the continuous deepening of the application of piezoelectric sensors in the transportation field, a large amount of sensor data needs to be transmitted and processed quickly and accurately. In some remote areas or complex traffic environments, there may be problems such as insufficient coverage of the data transmission network or unstable signals. In addition, the massive sensor data also poses higher requirements for data processing capabilities. For the data transmission problem, a combination of multiple communication technologies, such as Wireless Sensor Networks (WSN) and cellular mobile communication networks (4G/5G), can be used to ensure reliable data transmission. For the data processing problem, advanced technologies such as cloud computing and edge computing are introduced. Some data processing tasks are offloaded to sensor nodes or edge devices for real – time processing, reducing the data transmission volume and improving the data processing efficiency. At the same time, big data analysis and artificial intelligence algorithms are used to deeply mine the processed data, extract valuable information, and provide support for traffic management and decision – making.