Rad AJ et al, 2014: Investigation on the comparability of the light spot hydrophone and the fiber optic hydrophone in lithotripter field measurements
Rad AJ, Ueberle F, Krueger K
Department Life Sciences, Hamburg University of Applied Sciences, Hamburg 21033, Germany
Department Mechanical Engineering, Helmut Schmidt University, Hamburg 22043, Germany
Optical hydrophones are optimized pressure-pulse-sensors used for high-power shockwave sources, such as lithotripters. Recent investigation of Smith et al. ["A Comparison of light spot hydrophone and fiber optic probe hydrophone for lithotripter field characterization," Rev. Sci. Instrum. 83, 014301 (2012)] show discrepancies in the negative pressure peak and tensile pulse duration regarding measurements carried out with two optical hydrophones: the Light Spot Hydrophone (LSHD) and the fiber optic hydro-phone. It was assumed that the differences arise from cavitation effects at the end-face of the LSHD glass-block and filter characteristics of the trans-impedance amplifier of the LSHD. The present study investigates the transfer-function of the LSHD. It is shown that the filter characteristics of the amplifier cause discrepancies in the rarefaction pressure pulse fraction (depending on the energy settings of the source 15 ± 2%).
Rev Sci Instrum. 2014 Jan;85(1):014902. doi: 10.1063/1.4861355.
PMID:24517798[PubMed - in process]
This paper digs into the problems of measuring shock wave pressure profiles. Contemporary lithotripters feature extreme high pressures (up to 100 MPa and more) very short time duration (several nanoseconds up to some microseconds) and require a spatial resolution in the millimetre range. Conventional pressure probes are suffering from limited durability, time resolution and often insufficient response to tensile wave fractions of medical shock waves.
Laser optical hydrophones such as light spot hydrophones (LSHD) and fibre optic hydrophones (FOPH) seem to be best suited to match with the needs of shock wave measuring. However, certain precautions have to be taken into account as reported.