Calibration of an ultrasonic transducer in a standing wave field

Abstract

Acoustofluidics is one of the emerging technologies for cell sorting. Most of the acoustofluidics platforms use an acoustic standing wave field for the separation. The calibration of the standing wave field is a challenging task. In the past, there have been few studies to quantify the standing wave indirectly using particle tracing in the field. In the present work, we attempt to calibrate the standing wave field using acoustic techniques. Hydrophones are used to find the pressure in an acoustic field. They are designed and constructed in a way that they do not alter the field. Most of the commercial hydrophone in market is made of PVDF (polyvinylidene fluoride): an acoustically transparent material. When a hydrophone is inserted in a standing wave field, the field in front of the tip is no longer a standing wave field as PVDF is acoustically transparent. This was observed in our acoustic chamber also. Here, we propose to use the receiving characteristics of a transducer to quantify the standing wave field. In brief, two identical PZT transducers are used to generate the standing wave field: one as a transmitter and other as a receiver (reflector). The receiving characteristics of the transducer used as a reflector are calibrated using a needle hydrophone. Using the signal recorded by the receiving PZT transducer in the standing wave field and the calibration value, the pressure at the surface of reflecting transducer can be found. For the sake of comparison, the field will be quantified also by the particle tracing method.