diff --git a/FDTD/excitation.cpp b/FDTD/excitation.cpp
index e05e2e6..cc16078 100644
--- a/FDTD/excitation.cpp
+++ b/FDTD/excitation.cpp
@@ -32,6 +32,8 @@ Excitation::Excitation()
 
 	dT = 0;
 	m_nyquistTS = 0;
+	m_f_max = 0;
+	m_foi = 0;
 }
 
 Excitation::~Excitation()
@@ -51,6 +53,8 @@ void Excitation::Reset( double timestep )
 
 	dT = timestep;
 	m_nyquistTS = 0;
+	m_f_max = 0;
+	m_foi = 0;
 }
 
 bool Excitation::setupExcitation( TiXmlElement* Excite, unsigned int maxTS )
@@ -146,6 +150,9 @@ void Excitation::CalcGaussianPulsExcitation(double f0, double fc, int nTS)
 		Signal_curr[n] = cos(2.0*PI*f0*(t-9.0/(2.0*PI*fc)))*exp(-1*pow(2.0*PI*fc*t/3.0-3,2));
 	}
 
+	m_foi = f0;
+	m_f_max = f0+fc;
+
 	SetNyquistNum( CalcNyquistNum(f0+fc,dT) );
 }
 
@@ -164,6 +171,9 @@ void Excitation::CalcDiracPulsExcitation()
 	Signal_curr[0]=0.0;
 	Signal_curr[1]=1.0;
 
+	m_foi = 0;
+	m_f_max = 0;
+
 	SetNyquistNum( 1 );
 }
 
@@ -181,6 +191,9 @@ void Excitation::CalcStepExcitation()
 	Signal_curr[0]=1.0;
 	Signal_curr[1]=1.0;
 
+	m_foi = 0;
+	m_f_max = 0;
+
 	SetNyquistNum( 1 );
 }
 
@@ -215,6 +228,8 @@ void Excitation::CalcCustomExcitation(double f0, int nTS, string signal)
 		Signal_curr[n] = fParse.Eval(vars);
 	}
 
+	m_f_max = f0;
+	m_foi = f0;
 	SetNyquistNum( CalcNyquistNum(f0,dT) );
 }
 
@@ -238,7 +253,8 @@ void Excitation::CalcSinusExcitation(double f0, int nTS)
 		t += 0.5*dT;
 		Signal_curr[n] = sin(2.0*PI*f0*t);
 	}
-
+	m_f_max = f0;
+	m_foi = f0;
 	SetNyquistNum( CalcNyquistNum(f0,dT) );
 }
 
diff --git a/FDTD/excitation.h b/FDTD/excitation.h
index d9c9e34..d27c2ef 100644
--- a/FDTD/excitation.h
+++ b/FDTD/excitation.h
@@ -55,6 +55,12 @@ public:
 	//! Get the length of the excitation signal
 	unsigned int GetLength() const {return Length;}
 
+	//! Get the max frequeny excited by this signal
+	double GetMaxFrequency() const {return m_f_max;}
+
+	//! Get the frequency of interest
+	double GetFrequencyOfInterest() const {return m_foi;}
+
 	FDTD_FLOAT* GetVoltageSignal() const {return Signal_volt;}
 	FDTD_FLOAT* GetCurrentSignal() const {return Signal_curr;}
 
@@ -68,6 +74,11 @@ protected:
 	FDTD_FLOAT* Signal_volt;
 	FDTD_FLOAT* Signal_curr;
 
+	// max frequency
+	double m_f_max;
+	// frequency of interest
+	double m_foi;
+
 	//! Calculate a custom signal
 	virtual void CalcCustomExcitation(double f0, int nTS, string signal);
 	//! Calculate an excitation with center of \a f0 and the half bandwidth \a fc
diff --git a/openems.cpp b/openems.cpp
index 6eeb683..85c0cdf 100644
--- a/openems.cpp
+++ b/openems.cpp
@@ -646,11 +646,7 @@ int openEMS::SetupFDTD(const char* file)
 	if (m_CSX->GetQtyPropertyType(CSProperties::LORENTZMATERIAL)>0)
 		FDTD_Op->AddExtension(new Operator_Ext_LorentzMaterial(FDTD_Op));
 	if (m_CSX->GetQtyPropertyType(CSProperties::CONDUCTINGSHEET)>0)
-	{
-		double f_max=0;
-		FDTD_Opts->QueryDoubleAttribute("f_max",&f_max);
-		FDTD_Op->AddExtension(new Operator_Ext_ConductingSheet(FDTD_Op,f_max));
-	}
+		FDTD_Op->AddExtension(new Operator_Ext_ConductingSheet(FDTD_Op,m_Exc->GetMaxFrequency()));
 
 	//check all properties to request material storage during operator creation...
 	SetupMaterialStorages();