# Conceptual Design and Preliminary Verification of Distributed Wireless System of Weigh-in-Motion
## 2 Self-Powered Wireless WIM Sensor  
Traditional WIM systems are installed by excavating the road surface, positioning the sensors, and laying the power and signal transmission cables, which has a significant impact on traffic flow. The strain energy produced by the tire load of a moving vehicle is supposed to be absorbed by piezoelectric materials through the electromechanical coupling effect and converted into electrical energy to power a WIM system, making the sensor self-powered. Numerous works have been published in this field [23; 24], and based on these discoveries, an energy-capture device is created, negating the need for power lines by meeting the demands of dynamic load cells for self-energy supply. In addition, wireless communication technology has been very mature. The test signals could be transmitted wirelessly, eliminating the need for signal transmission cables. It is important to further miniaturize the design to enable rapid deployment by using equipment for coring asphalt pavement rather than digging the road for traditional sensor replacement. Additionally, the coring device can be redesigned into a more practical shape for enhanced signal acquisition and energy capture. Figure 1 depicts the self-powered wireless load cell's conceptual design. The cap, buffer layer, sensor layer, and base are the four components that make up the cylindrical sensor. The cap is subjected directly to the vehicle wheel load force, which is passed through the buffer layer to the sensor layer for energy capture and signal acquisition. Since the cap is immediately subjected to the vehicle's wheel stress and is exposed to a rather severe environment, it is essential that the cap has certain levels of tensile strength, stiffness, and durability. The buffer layer is designed to protect the sensor and energy capture device from excessive mechanical stresses. It is often composed of more durable material, such as rubber, and its thickness can be determined by testing. Core sensing and energy-capturing components of the complete sensor are supported by a sensing and energy capturing-layer with adequate strength and rigidity. By employing specialized equipment to drill holes in the pavement's construction layer, the entire sensor may be rapidly and easily installed without the need for power and signal lines. In order to remove it from the pavement construction layer for maintenance or replacement, specialized equipment must be constructed. Figure 2 shows a trial prototype with a 304 stainless steel lid, base, and rubber buffer layer. The sensing captive energy layer is composed of a multi-layer sandwich of rubber, in which the sensors and captives are arranged with a line groove of a specified width between them. In addition, the center of the 6 mm diameter through-hole, the sensor, and the capturer can be inserted via the hole between the wires into the base. Figure 1: Schematic diagram of a wireless WIM sensor. The piezoelectric sensing and energy harvesting unit is designed as a disc structure, with a piezoelectric ceramic of PZT-8 (25 mm diameter, 10 mm aperture, and 5 mm thickness), two copper electrodes, two stainless steel gaskets, two wires, and external room temperature curing silicone rubber. The Piezoelectric properties of PZT-8 are listed in Table 1. The detail of the structure is shown in Figure 3. Considering the brittleness of piezoceramics, brass electrodes with pins are used. Additionally, wires are welded on the pins of the brass electrodes, which can avoid the unevenness of electrode welding spots. A stainless-steel spacer slightly larger than the PZT piezoelectric ceramic sheet is used to prevent the piezoelectric material and electrode from the influence of external environments such as rain. A stainless-steel spacer with the dimension of \(\varphi\)35 \(\times\) 3 mm is employed, which can be filled with flexible room-temperature cured silicone rubber on the side of the PZT piezoelectric sheet, thus avoiding lateral force.