diff --git a/docs/source/input_api.rst b/docs/source/input_api.rst
index 06be22c0..94f6790e 100644
--- a/docs/source/input_api.rst
+++ b/docs/source/input_api.rst
@@ -175,6 +175,10 @@ Fractal Box
 -----------
 .. autoclass:: gprMax.cmds_geometry.fractal_box.FractalBox
 
+.. note::
+
+    * Currently (2024) we are not aware of a formulation of Perfectly Matched Layer (PML) absorbing boundary that can specifically handle distributions of material properties (such as those created by fractals) throughout the thickness of the PML, i.e. this is a required area of research. Our PML formulations can work to an extent depending on your modelling scenario and requirements. You may need to increase the thickness of the PML and/or consider tuning the parameters of the PML (:ref:`pml-tuning`) to improve performance for your specific model.
+
 Add Grass
 ---------
 .. autoclass:: gprMax.cmds_geometry.add_grass.AddGrass
@@ -220,7 +224,7 @@ Transmission Line
 
 Excitation File
 ---------------
-.. autoclass:: gprMax.cmds_singleuse.ExcitationFile
+.. autoclass:: gprMax.cmds_multiuse.ExcitationFile
 
 Receiver
 --------
diff --git a/docs/source/input_hash_cmds.rst b/docs/source/input_hash_cmds.rst
index 5fc551ef..47002aba 100644
--- a/docs/source/input_hash_cmds.rst
+++ b/docs/source/input_hash_cmds.rst
@@ -620,6 +620,10 @@ Allows you to introduce an orthogonal parallelepiped with fractal distributed pr
 
 For example, to create an orthogonal parallelepiped with fractal distributed properties using a Peplinski mixing model for soil, with 50 different materials over a range of water volumetric fractions from 0.001 - 0.25, you should first define the mixing model using: ``#soil_peplinski: 0.5 0.5 2.0 2.66 0.001 0.25 my_soil`` and then specify the fractal box using ``#fractal_box: 0 0 0 0.1 0.1 0.1 1.5 1 1 1 50 my_soil my_fractal_box``.
 
+.. note::
+
+    * Currently (2024) we are not aware of a formulation of Perfectly Matched Layer (PML) absorbing boundary that can specifically handle distributions of material properties (such as those created by fractals) throughout the thickness of the PML, i.e. this is a required area of research. Our PML formulations can work to an extent depending on your modelling scenario and requirements. You may need to increase the thickness of the PML and/or consider tuning the parameters of the PML (:ref:`pml-tuning`) to improve performance for your specific model. 
+
 #add_surface_roughness:
 -----------------------
 
diff --git a/gprMax/cmds_multiuse.py b/gprMax/cmds_multiuse.py
index 385f6f92..e7689a0d 100644
--- a/gprMax/cmds_multiuse.py
+++ b/gprMax/cmds_multiuse.py
@@ -871,7 +871,7 @@ class Rx(UserObjectMulti):
 
         try:
             r.ID = self.kwargs["id"]
-            outputs = list(self.kwargs["outputs"])
+            outputs = self.kwargs["outputs"]
         except KeyError:
             # If no ID or outputs are specified, use default
             r.ID = f"{r.__class__.__name__}({str(r.xcoord)},{str(r.ycoord)},{str(r.zcoord)})"
diff --git a/toolboxes/GPRAntennaModels/GSSI.py b/toolboxes/GPRAntennaModels/GSSI.py
index 1bbaa5f2..582b839d 100644
--- a/toolboxes/GPRAntennaModels/GSSI.py
+++ b/toolboxes/GPRAntennaModels/GSSI.py
@@ -432,7 +432,7 @@ def antenna_like_GSSI_1500(x, y, z, resolution=0.001, **kwargs):
                 material_id="rxres",
             )
             scene_objects.append(e1)
-        r1 = gprMax.Rx(p1=(tx[0] - 0.059, tx[1], tx[2]), id="rxbowtie", outputs="Ey")
+        r1 = gprMax.Rx(p1=(tx[0] - 0.059, tx[1], tx[2]), id="rxbowtie", outputs=["Ey"])
         scene_objects.append(r1)
 
     elif resolution == 0.002:
@@ -443,7 +443,7 @@ def antenna_like_GSSI_1500(x, y, z, resolution=0.001, **kwargs):
                 material_id="rxres",
             )
             scene_objects.append(e1)
-        r1 = gprMax.Rx(p1=(tx[0] - 0.060, tx[1], tx[2]), id="rxbowtie", outputs="Ey")
+        r1 = gprMax.Rx(p1=(tx[0] - 0.060, tx[1], tx[2]), id="rxbowtie", outputs=["Ey"])
         scene_objects.append(r1)
 
     return scene_objects
@@ -900,7 +900,7 @@ def antenna_like_GSSI_400(x, y, z, resolution=0.002, **kwargs):
         )
         scene_objects.extend((w2, tl2))
     else:
-        r1 = gprMax.Rx(p1=(tx[0] + 0.162, tx[1], tx[2]), id="rxbowtie", outputs="Ey")
+        r1 = gprMax.Rx(p1=(tx[0] + 0.162, tx[1], tx[2]), id="rxbowtie", outputs=["Ey"])
         scene_objects.append(r1)
 
     # Geometry views
diff --git a/toolboxes/GPRAntennaModels/MALA.py b/toolboxes/GPRAntennaModels/MALA.py
index 937ec7b0..cbee5f06 100644
--- a/toolboxes/GPRAntennaModels/MALA.py
+++ b/toolboxes/GPRAntennaModels/MALA.py
@@ -649,7 +649,7 @@ def antenna_like_MALA_1200(x, y, z, resolution=0.001, **kwargs):
     scene_objects.append(vs1)
 
     # Output point - receiver bowtie
-    r1 = gprMax.Rx(p1=(tx[0] + 0.076, tx[1], tx[2]), id="rxbowtie", outputs="Ey")
+    r1 = gprMax.Rx(p1=(tx[0] + 0.076, tx[1], tx[2]), id="rxbowtie", outputs=["Ey"])
     scene_objects.append(r1)
 
     # Geometry views