diff --git a/SimPEG/EM/FDEM/FieldsFDEM.py b/SimPEG/EM/FDEM/FieldsFDEM.py
index 253b9984..6a39e00d 100644
--- a/SimPEG/EM/FDEM/FieldsFDEM.py
+++ b/SimPEG/EM/FDEM/FieldsFDEM.py
@@ -60,6 +60,20 @@ class Fields(SimPEG.Problem.Fields):
 
         return self._bPrimary(solution, srcList) + self._bSecondary(solution, srcList)
 
+    def _bSecondary(self, solution, srcList):
+        """
+        Total magnetic flux density is sum of primary and secondary
+
+        :param numpy.ndarray solution: field we solved for
+        :param list srcList: list of sources
+        :rtype: numpy.ndarray
+        :return: total magnetic flux density
+        """
+        if getattr(self, '_bSecondary', None) is None:
+            raise NotImplementedError ('Getting b from %s is not implemented' %self.knownFields.keys()[0])
+
+        return  self._bSecondary(solution, srcList)
+
     def _h(self, solution, srcList):
         """
         Total magnetic field is sum of primary and secondary
@@ -124,6 +138,21 @@ class Fields(SimPEG.Problem.Fields):
             return self._bDeriv_u(src, v, adjoint), self._bDeriv_m(src, v, adjoint)
         return np.array(self._bDeriv_u(src, du_dm_v, adjoint) + self._bDeriv_m(src, v, adjoint), dtype = complex)
 
+    def _bSecondaryDeriv(self, src, du_dm_v, v, adjoint = False):
+        """
+        Total derivative of b with respect to the inversion model. Returns :math:`d\mathbf{b}/d\mathbf{m}` for forward and (:math:`d\mathbf{b}/d\mathbf{u}`, :math:`d\mathb{u}/d\mathbf{m}`) for the adjoint
+
+        :param Src src: sorce
+        :param numpy.ndarray du_dm_v: derivative of the solution vector with respect to the model times a vector (is None for adjoint)
+        :param numpy.ndarray v: vector to take sensitivity product with
+        :param bool adjoint: adjoint?
+        :rtype: numpy.ndarray
+        :return: derivative times a vector (or tuple for adjoint)
+        """
+        # TODO: modify when primary field is dependent on m
+
+        return self._bDeriv(src, du_dm_v, v, adjoint = adjoint)
+
     def _hDeriv(self, src, du_dm_v, v, adjoint = False):
         """
         Total derivative of h with respect to the inversion model. Returns :math:`d\mathbf{h}/d\mathbf{m}` for forward and (:math:`d\mathbf{h}/d\mathbf{u}`, :math:`d\mathb{u}/d\mathbf{m}`) for the adjoint
@@ -471,6 +500,8 @@ class Fields3D_b(Fields):
             return 'E'
         elif fieldType == 'b':
             return 'F'
+        elif fieldType == 'bSecondary':
+            return 'F'
         elif (fieldType == 'h') or (fieldType == 'j'):
             return'CCV'
         else:
diff --git a/SimPEG/EM/FDEM/RxFDEM.py b/SimPEG/EM/FDEM/RxFDEM.py
index 53d6c722..318e62b7 100644
--- a/SimPEG/EM/FDEM/RxFDEM.py
+++ b/SimPEG/EM/FDEM/RxFDEM.py
@@ -97,6 +97,19 @@ class Point_b(BaseRx):
         self.projField = 'b'
         super(Point_b, self).__init__(locs, orientation, component)
 
+class Point_bSecondary(BaseRx):
+    """
+    Magnetic flux FDEM receiver
+
+    :param numpy.ndarray locs: receiver locations (ie. :code:`np.r_[x,y,z]`)
+    :param string orientation: receiver orientation 'x', 'y' or 'z'
+    :param string component: real or imaginary component 'real' or 'imag'
+    """
+
+    def __init__(self, locs, orientation=None, component=None):
+        self.projField = 'bSecondary'
+        super(Point_bSecondary, self).__init__(locs, orientation, component)
+
 
 class Point_h(BaseRx):
     """