Application Cases

Experiment Name: Application Experiment of Multi-Sensor Information Stress Wave Communication in Solid Structures

Research Direction:
With rapid economic development and advancements in science and technology, various large and complex industrial structures continue to emerge. Factors such as environmental loads, material aging, sudden natural disasters, and other human-induced damages can affect the safety, applicability, and durability of these structures, leading to reduced resistance and even sudden accidents that threaten the safety of lives and property. Therefore, establishing effective structural health monitoring systems to assess the condition of large industrial structures has become a key research focus. Structural monitoring systems typically require monitoring multiple parameters, such as damage, vibration, stress, displacement, and tilt. Early structural monitoring systems mainly relied on bus communication protocols, forming wired sensor networks. However, wired transmission systems are often damaged due to excessive external forces and require extensive pre-installation of communication cables within structural layers, which not only increases system costs but also demands significant installation time. Currently, wireless sensor networks, built with sensor nodes equipped with microprocessors and wireless communication modules, are widely used in large solid structure health monitoring due to their low cost, rapid deployment, simple maintenance, and strong scalability. Nevertheless, wireless sensor nodes are prone to failure due to power issues, leading to data loss. Furthermore, in specific structural monitoring environments such as sealed metal containers, underwater or offshore platforms, and underground metal pipelines, wireless electromagnetic signals are easily shielded. Additionally, electromagnetic waves experience severe attenuation in special environments like water or soil, resulting in very short transmission distances. Therefore, in scenarios where wireless sensor networks cannot effectively transmit structural state information, exploring new communication methods for solid structure state monitoring is highly significant.

In recent years, with in-depth research on piezoelectric materials (PZT, piezoelectric ceramic transducer), stress wave-based structural health monitoring sensing technology has opened a new research avenue for solid structure state monitoring due to its low cost, ease of use, high sensitivity, and wide measurement range. PZT not only functions as both a transmitter and receiver but can also harvest energy from signals. When embedded in large, complex industrial solid structures and interconnected into a sensor network, it combines the advantages of wireless sensor networks with the ability to achieve acoustic-electric conversion via the piezoelectric effect. This makes it less prone to damage and capable of providing real-time, critical information about the integrity of the monitored solid structure. Therefore, using PZT to generate stress waves for sensor data communication in large industrial solid structures holds immense research potential. Since monitoring large industrial solid structures requires deploying numerous sensors of different types to provide integrity information, variations in sensor node counts and frequent potential data connections necessitate more complex communication architectures for independent multi-sensor information communication in solid structures. To avoid interference between multi-sensor signals, there is an urgent need to explore new multi-sensor communication architectures that can distinguish signals from different channels within the same medium.

Spread spectrum theory represents a novel communication approach, alongside optical fiber and satellite communication, hailed as one of the three high-tech communication transmission methods of the information age. It offers strong anti-interference, anti-fading, anti-multipath performance, low intercept probability, and high spectral efficiency, currently widely used in large-scale communication systems for navigation, secure communication, ranging, and positioning. Therefore, aiming for independent communication of sensor information in large industrial solid structure health monitoring sensor networks, using stress waves as the information transmission medium, and exploring the mechanism of multi-sensor information stress wave communication in large solid structures based on spread spectrum theory expands the application of spread spectrum theory into new domains. This has significant academic value and practical implications for the development of theories and methods for large industrial solid structure health monitoring.

Experiment Objective:
To verify the feasibility of a novel multi-sensor stress wave communication method for structural state monitoring based on spread spectrum theory, providing a foundation for subsequent experiments.

Testing Equipment:
Power amplifier, signal generator, host computer, data acquisition card, fixed pulley, 7-strand steel cable, PVC pipe, receiving-end PZT (piezoelectric material), transmitting-end PZT, etc.

Experimental Procedure:
To verify the feasibility of applying the multi-sensor information stress wave communication mechanism based on spread spectrum theory in special water environment structures, an experimental platform for multi-sensor information stress wave communication in a water environment was established, as shown in Figure 1-1. This platform includes PZT (piezoelectric ceramic transducer), a 7-strand steel cable, PVC pipe (inner diameter 10 cm), KEYSIGHT 33500B signal generator, Antai AT-2042 power amplifier, data acquisition card, and a host computer responsible for spread spectrum modulation and information recovery. The host computer is connected to the signal generator and data acquisition card. It transmits excitation and modulation signals to the signal generator and receives signals collected by the data acquisition card. The piezoelectric amplifier, connected to the signal generator, amplifies the excitation signal by 50 times. The PZT used measures 5*8 mm and functions as both an actuator and a sensor, attached to the surface of the steel cable structure, with a distance of 80 cm between the transmitting and receiving ends.

Figure 1-1: Stress Wave Communication Experiment in an Underwater Steel Cable Environment

Figure 1-2: a) LabVIEW Virtual Instrument Interface for Receiving Signal Settings;

Figure 1-3: Noise Signal Received at the Signal Acquisition End

The receiving end captures signals through the stress wave communication data acquisition system, as shown in Figure 1-2. Using LabVIEW virtual instruments, parameters such as channel selection, sampling frequency, and sampling period for stress wave signal acquisition are configured. After correctly setting the acquisition parameters, a noise signal with an amplitude of 5 mV and a frequency of 50 Hz is received, as shown in Figure 1-3.

Experimental Results:

Figure 1-4: Dispersion Test Results of Five-Peak Signals at Different Frequencies in Steel Cable Medium

Figure 1-4 shows the dispersion test results of five-peak signals at different frequencies in the steel cable medium. It can be observed that as the frequency of the five-peak detection signal increases, the signal splits into several signals of different frequencies during propagation in the solid structure. This indicates that dispersion becomes more severe, leading to greater signal distortion, which affects signal transmission quality. Therefore, signals in the low-frequency band below 15 kHz are more conducive to stress wave propagation in steel cable solid structures.

Figure: Specifications of the ATA-2042 High-Voltage Amplifier

The experimental materials in this article were compiled and published by Xi'an Antai Electronics. For more experimental solutions, please continue to follow the Antai official website.