Calibration of therapeutic ultrasonic transducers with the modified radiation force balance system

A modified radiation force balance (RFB) system was established for physiotherapy and high intensity therapeutic ultrasound (HITU) power measurements in the Medical Metrology Laboratory at the National Metrology Institute of Turkey (UME). The system was found to be highly stable up to a power level of 500 Watts. The measuring system consists of a Plexiglas cylindrical balancer, target mounted scale disks, conical reflector and absorbent targets, adjustable nuts and a hanging monofilament line‥ The balance is entirely symmetric with identical sizes and weight targets on both sides of the equilibrium point. The balance of the balance arm can be adjusted with adjustment screws on each side. The transducer was mounted beneath the water reservoir. Absorbing liners were used in the bottom and the near walls of the tank for reflecting target case. Ultrasound force is applied to a scale of equilibrium to which the reflector/absorber target is mounted, and the corresponding force is measured on the other scale of the equilibrium to which the equilibrium is connected by a thin wire while standing on a thin resting support. Ultrasound power of a HITU transducer at frequencies of 1.1 MHz was measured with conventional and new system. The measurement results were compared and uncertainty components were evaluated in this paper. A lower uncertainty value has been achieved in ultrasound power measurements for physiotherapy and HITU.