GUIDED WAVES PPM ENCODED SYSTEM USING AWG12 CABLES

AS COMMUNICATION CHANNEL Gianpiero Trane

Rito Mijarez

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

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

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)

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

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

PPM guided wave system• Active smart piezoelectric

– 9V Battery– Microcontroller– Signal buster– PZT element

• AWG12 cable– Insulator silicone

• Preamplifier• DAQ• LabVIEW based demodulator

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)

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

Experiment setup an results

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

Guided wave symbol PPM identification

• 4BH ( 0 0 1 0 1 1 0 1 )

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

References