User Manual

Page 26
Figure 26. Piezo cable construction
PIEZOELECTRIC CABLE AND PROPERTIES
One of the most recent developments in piezo polymer technology is piezo cable. The cable has the
appearance of standard coaxial cable, but is constructed with a piezoelectric polymer insulator between the
copper braid outer shield and the inner conductor (Figure 26).
Protected by a rugged polyethylene jacket, the cable is used in buried or fence security systems, traffic
sensors including vehicle classification and weight-in-motion systems, and taxiway sensors for aircraft
identification, safety and security applications. Other applications include sensors for anti-tampering, door
edge safety monitoring, floor mats, touch pads
and panels, and patient mattress monitors. The
new cables feature the same piezoelectric
properties that are characteristic of piezo film
sensors. The electrical output is proportional to
the stress imparted to the cable. The long, thin
piezoelectric insulating layer provides a relatively
low output impedance (600 pF/m), unusual for
a piezoelectric device. The dynamic range of the
cable is substantial (>200 dB), sensing distant,
small amplitude vibrations caused by rain or hail,
yet responding linearly to the impacts of heavy
trucks. The cables have withstood pressures of
100 MPa. The typical operating temperature
range is -40 to +125bC. Table 4 lists typical
properties for piezo cable.
Table 4. Piezo Cable Typical Properties
Parameter Units Value
Capacitance @ 1KHz
Tensile Strength
Young's Modulus
Density
Acoustic Impedance
Relative Permittivity
tan δ
e
Hydrostatic Piezo Coefficient
Longitudinal Piezo Coefficient
Hydrostatic Piezo Coefficient
Electromechanical Coupling
Energy Output
Voltage Output
pF/m
MPa
GPa
kg/m
3
MRayl
@1KHz
@1KHz
pC/N
Vm/N
Vm/N
%
mJ/Strain (%)
kV/Strain (%)
600
60
2.3
1890
4.0
9
0.017
15
250 x 10
-3
150 x 10
-3
20
10
5