Harmonic　eddy　current　testing　(HECT)　is　an　electromagnetic　non-destructive　testing　method,　which　can　realize　non-contact　detection　of　metal　pipeline　defects.　Eddy　current　will　be　produced　at　the　metal　pipeline　affected　by　harmonic　excitation　with　multiple　frequencies.　Meanwhile,　the　eddy　current　generated　would　be　uneven　due　to　the　disturbance　of　the　defects.　In　order　to　detect　the　abnormalities　effectively,　the　relationship　model　among　the　diameter　of　the　pipeline　the　lift-off　height　of　the　probe　and　the　angle　of　excitation　coils　was　established　within　this　paper.　The　effect　of　the　magnetic　field　focusing　using　different　excitation　coils　models　were　studied　by　finite　element　simulation　and　the　optimal　structure　of　the　harmonic　excitation　coils　model　was　finally　achieved.　The　experimental　platform　was　established,　and　three　types　of　defects　were　designed　on　the　top　and　left　side　of　the　pipeline,　including　circular　holes,　rectangular　grooves,　and　45-degree　rectangular　grooves.　The　harmonic　eddy　current　magnetic　field　signals　were　acquired　by　the　3-axis　Tunnel　Magneto-Resistance　(TMR)　sensors　array.　The　frequency　bands　of　interference　and　original　excitation　signal　were　removed　by　using　Multi-Resolution　Analysis　(MRA),　and　thus,　the　useful　signal　frequency　bands　were　selected　for　fusion.　The　fused　signals　were　input　into　the　bistable　Stochastic　Resonance　(SR)　system　to　realize　the　noise　energy　transfer,　which　was　analyzed　by　the　fourth-order　Runge-Kutta　algorithm　and　the　scale　transformation,　so　as　to　enhance　the　energy　of　the　signals　at　the　pipeline　defects.　The　results　show　that　the　designed　harmonic　excitation　coils　model　improves　the　excitation　effect　of　both　sides　of　the　pipeline　and　expands　the　coverage　of　the　flaw　detection　of　the　pipeline.　Besides,　the　signal　processing　method　proposed　within　this　paper　can　extract　the　pipeline　defects　signal　effectively　and　improve　the　ability　of　defects　identification.　The　above　research　can　be　helpful　on　the　non-contact　non-destructive　testing　of　metallic　materials.　©　2019　IEEE.