No abstract

Unfocused/weakly focused pressure pulses (UPP) are generated by an air-gun like mechanism, with a projectile accelerated by pressurized air and impinging on a metal applicator. They were introduced in 1998 for the treatment of orthopedic soft tissue pain. The patient side of the applicator (a circular piston of 630 mm diameter) releases single pressure pulses of 210 MPa and 45 µs duration. Up today, there is no standard for the measurement of UPP sources (UPPS), so data are often reported on the basis of the focused lithotripter standard IEC61846. The purpose of this research is to establish methods to reliably measure UPPS acoustic parameters and establish a parameter set based on denitions from focused lithotripsy sources as applicable. Therefore, acoustic characteristics and wave elds of the pressure pulses of UPPS from dierent manufacturers were measured in a water bath and in a dry test bench. It was demonstrated by comparison with optical hydrophones that piezoelectric hydrophones are appropriate for the measurements of UPP. For on-axis measurements at a xed distance, measurements in the dry test bench can replace water-bath measurements. Additionally, the dry test bench allows for reliable results at pulse rates > 1 Hz.

The measurements of ultrasonic elds are often performed using polyvinylidene uoride (PVDF) membrane hydrophones. Recently, optical hydrophones have gained popularity. Refractive type optical hydrophones are based on the change of refractive index at a glasswater interface when the shockwave passes the sensitive area. A major disadvantage of the optical and the PVDF hydrophones is the fact that they provide a single spot sensitive area, with the result that eld measurements need a repositioning of the probe. In this work we introduce a multispot optical hydrophone with six measurement spots, for the single shot eld measurement of shockwave elds. We measure a highly stable shockwave source with a calibrated hydrophone and the multi-spot optical hydrophone and we nd good agreement for the calculated energy values of the shockwave eld (depending on the energy settings 4% ± 1%).