A Radiation Force Balance Target Material for Applications below 0.5 MHz

Abstract

Acoustic output power is an important safety-related parameter whose standardised measurement method involves use of a radiation force balance in conjunction with a special target that is typically designed to be totally absorbing to ultrasound. International Standard International Electrotechnical Commission (IEC) 61161 specifies important performance criteria for such an absorber, such as transmission loss and reflection loss. Currently, there is a lack of acoustic absorbers meeting these requirements at low frequencies (<0.5 MHz). This is unsatisfactory given emerging clinical applications, particularly therapeutic. Described here is an acoustic absorber appropriate for application below 0.5 MHz. Through use of two National Physical Laboratory measurement facilities, the absorber transmission loss and reflection loss have been derived over the frequency range 50–500 kHz. Results are presented and compared with performance requirements specified in IEC 61161, revealing the efficacy of the new material as an absorbing radiation force balance target down to a frequency of approximately 120 kHz.