This document presents a guided wave pulse position modulation (PPM) system using American Wire Gauge 12 (AWG12) cables for long-distance communication. It discusses using guided waves for structural health monitoring and non-destructive testing applications. The system transmits a 60 kHz tone signal encoded with PPM over AWG12 cables. Experimental results showed successful transmission and reception of a 10-bit PPM symbol over 4m and 1m cable lengths, identifying the propagated longitudinal and flexural wave modes. Further development is needed for real-time automatic PPM demodulation.

1. GUIDED WAVES PPM ENCODED
SYSTEM USING AWG12 CABLES AS
COMMUNICATION CHANNEL
Gianpiero Trane
Rito Mijarez

2. Introduction
• Guided waves long distance
propagation application:
– Structural Health Monitoring
(SHM)
– Non-Destructive Testing
(NDT)
• SMH communication
necessities:
– Wireless communications
– Harsh environments
• Fixed offshore oilrigs
• Downhole oil reservoirs
– Use of existing infrastructure
• This work presents:
– Guided wave
– Pulse Position Modulation
(PPM)
– Multiple-strand American
Wire Gauge (AWG)
– Smart PZT based modulator
– Real time off-line PZT based
demodulator
– Experiments with 4m and 1m
multiple strand wire AWG12

3. Guided waves theory
• American Wire Gauge
(AWG) 12 cables:
– 19 copper wires
– Polyvinyl chloride (PVC)
insulator
• Analytical solution for the
wave propagation does
not exist
– Inter-wire coupling
– Dispersive nature
– Multi-mode presence
– Mode coupling

4. Wave propagation
• Dispersion curves were
obtained with the
commercial software
Disperse©.
• Wave propagation in
single wires
– The so-called Pochammer
frequency equation of a
solid, isotropic,
homogeneous and traction
free cylindrical rod
• Propagation modes:
– Longitudinal L(0,m)
– Torsional T(0,m)
– Flexural F(0,m)

5. Frequency and signal selection
• Guided waves in long range
applications require
frequencies under 100 kHz
• For frequency selection on the
dispersion curves
– Spectrum of the transducer
source (PZT 5-H)
• Surface pressure loadings will
excite longitudinal and flexural
modes
• Under 300 kHz the number of
excited modes increases
– Multi-mode presence
• The frequency selected: 60
kHz
• The signal generated: tone
pulse pulses

6. Pulse Position Modulation (PPM)
• Information modulated in the time delay
between pulses (TDBP)
– Effective in signals power limited rather than
band limited
• Δt = time slot
• tr = time
reference
• ±ε = temporal
position of an
acoustic pulse

7. PPM guided wave system
• Active smart piezoelectric
– 9V Battery
– Microcontroller
– Signal buster
– PZT element
• AWG12 cable
– Insulator silicone
• Preamplifier
• DAQ
• LabVIEW based demodulator

8. PPM symbol codification
• 10 bit frames
• Start and stop pulses
– 40 square pulses of 60 kHz (666 µs)
• 8 data pulses
– 20 square pulses of 60 kHz (333 µs)
• Time slot Δt of 1998 µs (six times bit pulse width)
• Quantified values of ±ε of 999 µs (three times bit
pulse width)

9. PPM demodulation
• Finite Impulse Response (FIR) band pass digital filter (35
kHz – 50 kHz)
• Autocorrelation to increase SNR
• Low pass filter tuned to the baud rate
– Smooth out the filtered signal
• RMS operation threshold
– Continuous square pulse for each acoustic pulse
• Temporal position demodulation of TDBP for each digital
bit

10. Experiment setup an results

11. Guided waves propagation modes
identification
• Dispersion curves 60 kHz: L(0,1) and F(1,1)
– L(0,1) vg = 3.3718 m/ms
– F(1,1) vg= 1.4760 m/ms

12. Guided wave symbol PPM
identification
• 4BH ( 0 0 1 0 1 1 0 1 )

13. Conclusions
• Novel guided waves PPM system using multiple-wire
AWG12 cables as a communication channel has been
designed, implemented and evaluated
• The system uses the electrical cable infrastructure as
communication channel
• Successful transmission and reception of guided waves
encoded PPM information
• Experimental results match with the theoretical Disperse©
results
• The feasibility of detecting dispersive energy guided wave
packets, provided sufficient SNR, has been proved
• Next stage of this work is to carry out automatic real time
PPM demodulation

14. References