Pressure transducer for measuring acoustic radiation force based on a magnetic sensor

Abstract

This work presents a pressure transducer based on a magnetic sensor to measure acoustic radiation force (ARF) and small displacements. The methodology presented in this paper allowed this transducer to be calibrated for use as an acoustic pressure and intensity meter. It can control the acoustic intensity emitted by ultrasound used, for example, in ARF impulse imaging, vibro-acoustography and high-intensity focused ultrasound techniques. The device comprises a magnet, a membrane, a magnetoresistive sensor and a coil to cancel the external magnetic field. When ARF is applied to the membrane, the magnetic field on the sensor changes due to the magnetic target displacement. The variation of the output signal from the magnetic transducer is proportional to the acoustic pressure applied to the membrane. A focused ultrasound transducer with a central frequency of 3 MHz was used to apply a continuous ARF. The sensitivities of the magnetic transducer as an acoustic pressure and intensity meter, evaluated in water, were respectively 0.597 µV MPa−1 and 0.073 µV (W cm−2)−1/2, while those of the needle hydrophone (Onda model HNP-0400) used in the magnetic transducer calibration were respectively, 0.5024 mV MPa−1 and 6.153 mV (W cm−2)−1/2. The transducer resolution to displacement is 5 nm and 6 dB of signal attenuation occurs for 7° of misalignment. The transducer responded well to acoustic pressure in water above 200 kPa.

Measurement of focused ultrasonic fields based on colour edge detection and curve fitting

“…Jiang [5] measured the field distribution of ultrasound and key parameters of the focal region using an automatic measurement system based needle hydrophone. Kamimura [6] proposed a methodology to measure acoustic radiation force and small displacements using a transducer based on a magnetic sensor. Clement [7] designed a measurement device suitable for characterizing narrowband ultrasound signals in air by introducing a binary plate lens including a target and planar receiver.…”

Estudos de técnicas ultrassônicas para análise de propriedades mecânicas de meios viscoelásticos

“…Based on the idea of using acoustic radiation force to move a magnetized object and measuring its position through a magnetic sensor, we developed a device to monitoring acoustic pressure and force [50]. A cubic magnet was attached to a thin latex sheet, which was connected to a magnetoresistive sensor.…”

“…Based on Oestreicher's theory [48], they simulated a magnetic-sensor response due to the vibration of a spherical magnet embedded in water and in a viscoelastic medium. Based on the use of acoustic radiation force to move a magnetized object and the measurement of its position using a magnetic sensor, we developed a device to monitor acoustic pressure and force [50]. A cubic magnet was attached to a thin latex sheet, which was connected to a magnetoresistive sensor.…”

Imagens acústicas geradas pela interação da radiação ultrassônica com o meio material

“…A norma IEC-61161 † é a referência internacional dos procedimentos de medição cujo princípio físico é baseado na força de radiação[57]. Um outro método inovador[58] de medir a pressão de força de radiação é baseado em um transdutor que mede a força a † Ultrasonic Power Measurement in Liquids in the Frequency Range 0,5 MHz to 25 MHz, publicada inicialmente em 1992 e revisada em 1998…”