Piezoelectric cable and its characteristics

One of the latest research results of piezoelectric copolymer technology is a piezoelectric cable, the piezoelectric cable shape and the same standard coaxial cable (16~24 gauge). However, a piezoelectric copolymer is used as an insulator between the copper braided cover and the inner and the inner conductors (Figure 26). The outside of the cable and polyethylene sheath used in embedded or electronic fence security system, including vehicle classification and traffic sensor detector and a moving weighing system and aircraft classification, safety and security of airport runway applications such as aircraft classification, safety and security of sensor etc.. Other applications include anti-interference, door safety monitoring, ground pad, touch template, bed monitoring and other sensor detectors. The characteristics of this new type of cable are the same as that of a piezoelectric film sensor. The output is proportional to the force received by the cable. A long, thin piezoelectric insulating layer can produce a relatively low output impedance (600nF/m), which is rare for a piezoelectric device. The dynamic range of cables is the most important (>200dB), which can detect small amplitude vibration caused by rain or hail at long distance, and also can shake the vibration of heavy trucks linearly. The cable can pressure 100Mpa pressure, the standard working temperature is ~40~+125 C. Table 4 lists the standard characteristics of the cable.

Parameter unit value

Capacitance PF/m 600

Strain strength MPa 60

Young modulus GPa 2.3

Density Kg/m3 1890

Acoustic impedance MRay1 4

Relative dielectric constant @1kHz 9

Tan delta e @1kHz 0.017

Hydrostatic pressure and piezoelectric coefficient pC/N 15

Longitudinal piezoelectric coefficient Vm/N 250 x 10-3

Pressure coefficient of hydrostatic pressure Vm/N 150 x 10-3

Electromechanical coupling% 20

Energy output mJ/Strain (%) 10

Voltage output kV/Strain (%) 5

Cable standard characteristics: the output sensitivity of piezoelectric cable when the impact load is increased is indicated in Figure 27a, figure 27b shows the output linearity when stress increases, which is the standard case of all specifications of piezoelectric cable.

Diagram 27a. relation between sensitivity and load diagram 27b. voltage cable linearity

Piezoelectric Foundation

Electromechanical transformation

Like a sponge can extrude water, when the piezoelectric material is pressed to produce charge, the amplitude and frequency of the signal are directly proportional to the mechanical change of the piezoelectric material. The deformation of the material changes the charge density on the surface of the material, resulting in a voltage between the surface of the added electrode. When the added force is reversed, the polarity of the output voltage is also reversed simultaneously. A reciprocating force will get the output voltage of the alternating.

A piezoelectric film, like all piezoelectric materials, is a dynamic material. The charge generated is proportional to the change in the mechanical stress added. Because of the internal impedance of the material, it is not suitable for static measurement (pure DC). The decay time constant of the charge produced by a piezoelectric film depends on the dielectric constant and internal resistance of the membrane itself, and the input internal resistance of the interface circuit of the piezoelectric film. In fact, the minimum detectable frequency of the piezoelectric film can reach 0.001Hz. There are many ways to achieve pure DC response, but the piezoelectric membrane is required not only as an actuator but also as a sensor to monitor the change of exec