Cel
PROJECT MTR00112 PROJECT DEFINITION To investigate the power distribution in an ultrasonic beam, small diameter hydrophones of high sensitivity and accuracy are necessary. In an earlier BCR project two different types of hydrophones have been evaluated in respect of stability, sensitivity, frequency response and the influence of the hydrophone on the ultrasonic field. The work carried out was a first step. After confirmation of the stability of the hydrophones the second step is this intercomparison. The objectives of the exercise are to compare the results of various primary laboratories and to resolve any discrepancy which might appear in the results. Two types of hydrophones will be used in the programme, the needle type and the membrane type. The participating laboratories will in general use calibration by reciprocity technique. One laboratory will in addition use the technique of Time Delayed Spectrometry (TDS) and another supplement by planar scanning. RESULTS The measurements have been completed by all participating laboratories. Two different calibration methods, namely reciprocity (3 laboratories) and optical interferometry (2 laboratories) have been used. In particular CVAB used a new method involving the calibration using laser interferometry of a reference transmitting transducer and then measuring the response of the hydrophone to the field of the transducer, the calibrations being performed at JRC Laboratory (ISPRA) who provided the primary absolute calibration. The overall uncertainty of the measurements, performed in the 5 to 15 Mhz range is typically of the order of a few percent (expressed in terms of 95 % confidence level ).