# Frequency Sensitivity and Mode Characteristics of Body Structure for a Piezoelectric-Based UUV
## 2 Operating Principle of the UUV  
The structure of the proposed UUV is shown in Figure 1. It consists of a bow (2), stern (19), sonar (1), diving-surfacing system, control, and storage system, propelling system, visual detection system, piezoelectric energy collection system, and piezoelectric vibration reduction system. The diving-surfacing system is composed of a buoyancy cabin (3), water container (9), pushing device (10), fixed plate (11), and magnetic valve (8). The control and storage system is made up of an upper cover (25), battery cover (15), body structure (13), battery (21), energy storage (14), and controller (22). The propelling system includes a propeller (20) and a propulsion motor (16). In the case of the visual detection system, it contains a camera lens (6) and lens support (7). The piezoelectric energy collection system is composed of quadrate piezoelectric ceramics (4), a support ring (23), and annular piezoelectric ceramics (24). The piezoelectric vibration reduction system consists of piezoelectric ceramics integrated with a shunt circuit. The operating principle of the proposed UUV is presented as follows: in the initial state, the buoyancy of the vehicle is greater than its weight. Therefore, the UUV floats on the surface of the water, and the pushing device is in its elongated state, while the magnetic valve is in a closed state. When the circuit between the controller and the pushing device is connected, the pushing device retracts, whereas the magnetic valve is powered on under the command of the controller. At this moment, the water container starts to be filled with water, and the weight of the UUV exceeds its buoyancy. Hence, the UUV dives underwater. When the UUV achieves a preset depth, the controller sends a reverse voltage to the pushing device. This device again extends outward, thus pushing on the water-emptying container of the UUV to maintain underwater balance. Then, the controller regulates the magnetic valve and the pushing device in a stage of the outage, and the pushing device remains extended. Meanwhile, the propulsion motors are powered on and they all rotate with the same speed, which causes the UUV to move forward. When the rotation speed of the two motors on one side is larger than that of the motors on the other side, the UUV swerves based on the difference of velocity principle. Upon completion of underwater operations, all of the propulsion motors of the UUV are powered off, the pushing device and magnetic valve are powered on, and the pushing device is extended to its initial length As such, the water container is emptied. At this time, the buoyancy of the UUV exceeds its gravity, and the UUV floats to the water surface. In this report, piezoelectric energy harvesting, and piezoelectric vibration reduction are introduced for application to the UUV. Considering the working characteristics of this vehicle as well as increasing the vibration effectiveness of the piezoelectric ceramics, quadratic and annular piezoelectric ceramics are added to the piezoelectric energy collection system. Meanwhile, in the case of the annular piezoelectric ceramics, eighteen flabellate blades are joined onto the annular piezoelectric ceramic at the inner ring (see Figure 2a). Besides, the quadratic rubber mat and annular rubber mat are installed on the back of the quadrate and the annular piezoelectric ceramics to increase the energy collection effect. During the operation of the UUV, the wave motion of the water induces a reciprocating motion of the piezoelectric ceramics. This motion is transformed into electrical energy that is stored in reserve for later UUV use. In addition, to isolate the vehicle from the effect of the operation of the propeller, piezoelectric ceramics are utilized for vibration reduction based on an ultrathin piezoelectric fiber structure design. Furthermore, the resistance and inductance of the shunt circuit are set as adjustable values to adapt to different sea conditions (see Figure 2b).