Application Cases

Experiment Name: Application of Power Amplifier in Current-Injection Magnetoacoustic Imaging Research

Research Direction: Current-Injection Magnetoacoustic Imaging

Experimental Equipment:
ATA-4014 high-voltage power amplifier, ATA-5620 preamplifier for weak signals, function generator, ultrasonic sensor, water-immersion probe, stepper motor, etc.

Experimental Content:
Current-injection magnetoacoustic imaging utilizes the principle of magnetic-acoustic-electric coupling. By injecting current into a tissue phantom, ultrasonic signals are detected, and algorithms are designed for image reconstruction to obtain the internal electrical property information of the tissue phantom. In this experiment, a circular copper wire ring was used as the test sample. The diameter of the copper wire was 0.55 mm, and the outer diameter of the copper ring was 25.25 mm. The copper ring was placed in a water tank, with the sensor positioned parallel to the ring. Water was then added to the tank until both the copper ring and the sensor were submerged.

Figure: Block Diagram of the Experimental System

A sinusoidal pulse excitation signal generated by a function generator was applied to the copper ring. The sinusoidal signal had a peak-to-peak voltage of 50 V and a pulse width of 1 μs. A static magnetic field with a magnetic flux density of 0.4 T was applied perpendicular to the direction of the electric field. The ultrasonic sensor collected the ultrasound signals generated by the current-injection magnetoacoustic coupling. To improve the signal-to-noise ratio, the waveform was averaged 512 times at each position of the ultrasonic sensor. During the experiment, the rotation radius of the probe was 68.67 mm.

Experimental Procedure:

Figure: A typical time-domain waveform of the ultrasonic signal collected by the sensor under sinusoidal pulse excitation.

At the beginning of the signal, there is a strong narrow pulse. This is caused by the pulsed magnetic field interference generated when the pulse current passes through the coil and can be filtered out during image reconstruction. The first peak appears near point 5806, corresponding to the acoustic signal generated at the sample interface close to the probe. The second peak appears near point 7526, corresponding to the ultrasonic signal generated at the sample interface far from the probe. In the experiment, the sampling rate was 100 MHz, so the time interval between two adjacent points is 0.01 μs. The propagation velocity of ultrasound in water was approximated as a constant of 1.5 mm/μs.

Signal preprocessing includes noise filtering, magnetic field interference signal filtering, and normalization. In the figure, the points from 2000 to 3500 represent electromagnetic interference signals generated by the ultrasonic probe itself and should be discarded. The system also has some background white noise. This noise can be removed by averaging the signal when no excitation is applied and then subtracting this average value from the signal. The result after preprocessing is shown in the figure below.

Figure: Preprocessed waveform

Result Analysis:
The positions of the extracted boundary peak points were converted into corresponding coordinates. The average diameter of the boundary for peak 1 was 26.7993 mm, for peak 2 was 25.2920 mm, and for peak 3 was 23.6432 mm. The average diameter of the boundary at the first zero-crossing point was 26.0307 mm, and at the second zero-crossing point was 24.4429 mm. Comparing these with the actual copper ring sample, the average diameter of the second boundary (25.2920 mm) was very close to the average of the inner and outer diameters of the copper ring (25.25 mm). The result obtained by embedding a photo of the copper ring sample into the boundary reconstruction map is shown in the figure. It can be observed that the copper ring lies essentially between the first zero-crossing boundary and the second zero-crossing boundary, and the centerline of the copper wire in the ring closely coincides with the peak 2 boundary. Therefore, it can be generally confirmed that the peak 2 boundary represents the location of the copper wire centerline of the ring. The first zero-crossing boundary represents the upper limit of the outer boundary of the copper ring, and the second zero-crossing boundary represents the lower limit of the inner boundary of the copper ring.

Figure: Specifications of the ATA-4014C High-Voltage Power Amplifier