diff --git a/meanas/fdfd/eme.py b/meanas/fdfd/eme.py
index f834973..cb1b99e 100644
--- a/meanas/fdfd/eme.py
+++ b/meanas/fdfd/eme.py
@@ -55,7 +55,13 @@ def get_abcd(
     B = r21 @ t21i
     C = -t21i @ r12
     D = t21i
-    return sparse.block_array(((A, B), (C, D)))
+    return sparse.block_array(
+        [
+            [sparse.csr_array(A), sparse.csr_array(B)],
+            [sparse.csr_array(C), sparse.csr_array(D)],
+            ],
+        format='csr',
+        )
 
 
 def get_s(