테라헤르츠 시역학 분광(THz-TDS) 복소 굴절률 & 1,000Hz 0-Alloc C# 탄소복합재(CFRP) 비파괴 결함 검사 서보 엔진

using System;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace ZeliDesk.Stem.ThzInspection
{
    /// <summary>
    /// THz 시역학 펄스 파형 데이터 (스택 할당 0-Alloc)
    /// </summary>
    [StructLayout(LayoutKind.Sequential, Pack = 8)]
    public readonly struct ThzWaveformSpan
    {
        public readonly double PeakAmplitude;
        public readonly double TimeToPeakPs;
        public readonly double TotalPulseEnergy;
        public readonly double SignalToNoiseRatio;

        public ThzWaveformSpan(double peak, double timePs, double energy, double snr)
        {
            PeakAmplitude = peak;
            TimeToPeakPs = timePs;
            TotalPulseEnergy = energy;
            SignalToNoiseRatio = snr;
        }
    }

    /// <summary>
    /// 비파괴 검사 결함 판정 결과
    /// </summary>
    public ref struct DefectAnalysisResult
    {
        public bool DefectDetected;
        public double DefectDepthMm;
        public double ExtinctionCoefficient;
        public double OpticalDensity;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public DefectAnalysisResult(bool detected, double depthMm, double kappa, double od)
        {
            DefectDetected = detected;
            DefectDepthMm = depthMm;
            ExtinctionCoefficient = kappa;
            OpticalDensity = od;
        }
    }

    /// <summary>
    /// 1,000Hz 무할당 THz-TDS 복합재 결함 진단 서보 엔진
    /// </summary>
    public ref struct ThzTdsInspectionEngine
    {
        private const double LightSpeedMmPerPs = 0.299792458; // mm/ps
        private const double MatrixRefractiveIndex = 1.85;   // CFRP 수지 모재 굴절률
        private const double BaselineRefPeak = 1.0;          // 공기 기준 피크 진폭

        private double _filteredEnergyLoss;
        private double _referenceTimePs;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void CalibrateReference(double refTimePs)
        {
            _referenceTimePs = refTimePs;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void ExecuteDiagnosticCycle(
            in ThzWaveformSpan measuredSample,
            double sampleThicknessMm,
            out DefectAnalysisResult result,
            out double estimatedRefractiveIndex)
        {
            // 1. 비행 시간차(Time-of-Flight)를 통한 매질 굴절률 계산
            double deltaTPs = measuredSample.TimeToPeakPs - _referenceTimePs;
            estimatedRefractiveIndex = 1.0 + (LightSpeedMmPerPs * deltaTPs) / Math.Max(sampleThicknessMm, 0.01);

            // 2. 투과 신호 진폭 감쇄로부터 소광 계수(kappa) 및 광학 밀도(OD) 계산
            double transmissionRatio = Math.Clamp(measuredSample.PeakAmplitude / BaselineRefPeak, 1e-6, 1.0);
            double opticalDensity = -Math.Log10(transmissionRatio);

            double centerFrequencyTHz = 1.0; // 1 THz
            double omega = 2.0 * Math.PI * centerFrequencyTHz * 1e12;
            double cMmPerS = LightSpeedMmPerPs * 1e12; // mm/s
            double kappa = (-cMmPerS / (omega * sampleThicknessMm)) * Math.Log(transmissionRatio);

            // 3. 결함(공극/박리) 판정: 에어갭 형성 시 국소 반사 시간차 및 비정상 에너지 손실 감지
            double expectedDeltaT = (estimatedRefractiveIndex - 1.0) * sampleThicknessMm / LightSpeedMmPerPs;
            double anomalyPs = Math.Abs(deltaTPs - expectedDeltaT);

            bool defect = false;
            double defectDepthMm = 0.0;

            if (anomalyPs > 0.4 || opticalDensity > 1.8) // 시간 지연 오차 0.4ps 초과 또는 고감쇠
            {
                defect = true;
                // 에어갭 계면 비행시간차로부터 깊이 역산
                defectDepthMm = (deltaTPs * LightSpeedMmPerPs) / (2.0 * MatrixRefractiveIndex);
                defectDepthMm = Math.Clamp(defectDepthMm, 0.0, sampleThicknessMm);
            }

            result = new DefectAnalysisResult(defect, defectDepthMm, kappa, opticalDensity);
        }
    }
}