  The Compressed Baryonic Matter (CBM) experiment is one of the major
scientific spectrometers of the future Facility for Antiproton and Ion Research
(FAIR) in Darmstadt. As one of the core sub-systems in CBM experiment for
charged hadron identification, the Time-of-Flight (TOF) system is required to
have a time resolution better than 80 ps. According to the final state particle
flux distribution, the CBM-TOF will be constructed with several types of
Multigap Resistive Plate Chambers (MRPC). In the outer region of the TOF wall
where the particle fluxes are around 1 kHz/cm2, MRPCs with ultra-thin float
glass electrodes are considered as a cost effective solution. MRPC3b prototypes
have been developed and tested with excellent performance which could meet all
the requirements. Before the construction of CBM-TOF, approximately 80 MRPC3bs
are assembled for the STAR endcap TOF (STAR-eTOF) upgrade at RHIC as part of
the FAIR Phase-0 programs for CBM-TOF which provides a valuable opportunity for
detector stability test under high flux environments. This paper will introduce
the batch test of the MRPC3bs for STAR-eTOF upgrade. Time resolution of better
than 70 ps and efficiency of around 95% are achieved. Notably, during the batch
test, it has been observed that the noise rates of the two edge strips in each
counter are significantly higher than those of the middle strips. Simulations
with Computer Simulation Technology (CST)Studio Suite are carried out and
several kinds of MRPC prototypes are designed and tested accordingly. Based on
the simulation and test results, the design of the MRPC3b has been further
optimized, resulting in a significant suppression of noise rates in the edge
strips.
