diff --git a/common-defs.tex b/common-defs.tex
index 3ef391c..43a8e13 100644
--- a/common-defs.tex
+++ b/common-defs.tex
@@ -149,12 +149,16 @@
 \DeclareRefcontext{patref}{labelprefix=P}
 \DeclareRefcontext{defref}{}
 \DeclareFieldFormat{labelprefix}{\textsuperscript{\sffamily#1}}
+\defbibfilter{webstuff}{
+    ( type=online or type=software )
+    and not keyword={preprint}
+}
 
 \newcommand{\chapterbibliography}{
     \FloatBarrier
     \addcontentsline{toc}{section}{References}
     \newrefcontext{webref}
-    \printbibliography[type={online},title={Web sources},heading=subbibliography,resetnumbers=false,segment=\therefsegment]
+    \printbibliography[filter={webstuff},title={Web sources},heading=subbibliography,resetnumbers=false,segment=\therefsegment]
     \newrefcontext{patref}
     \printbibliography[type={patent},title={Patent References},heading=subbibliography,resetnumbers=false,segment=\therefsegment]
     \newrefcontext{defref}
diff --git a/main.bib b/main.bib
index 8ffd22f..5ff42b0 100644
--- a/main.bib
+++ b/main.bib
@@ -8134,6 +8134,7 @@ Archive 2: https://web.archive.org/web/20250510104017/https://de.linkedin.com/pu
   abstract = {Litz wire planar spiral coils are widely used in inductive power transfer systems due to low power loss in high-frequency operation and low profile. However, the complicated structure of the litz wire coil imposes difficulties in estimating the frequency-dependent resistance and quality factor accurately. In this work, we present an 2D analytical model for calculating the frequency-dependent resistance and quality factor of multi-coil inductive power transfer systems based on superposition of different loss effects. Its accuracy is validated with multiple coils and litz wires over wide frequency range. Meanwhile, a fast and accurate multi-objective optimization method is developed to improve the product quality factor and coupling factor. From the optimization results, there are five factors affecting the quality factor and coupling factor. A set of design guidelines is proposed to cope with these design factors. The final prototypes show 33\textbackslash\% increase in quality factor and 23\textbackslash\% improvement in coupling factor compared with the state-of-the-art designs. Meanwhile, a 30W, 500kHz inductive power transfer system is designed with 91\textbackslash\% peak efficiency.},
   langid = {english},
   pubstate = {prepublished},
+  keywords = {preprint},
   file = {/home/jaseg/Zotero/storage/ZAQTS252/Zhao et al. - 2023 - Design and Optimization of Litz-Wire Planar Spiral.pdf}
 }