Research Of A Differential Frequency Ultrasonic Power Supply For Vibro-acoustography Instrument

Recently, the technology of ultrasonic imaging based on the elasticity of the bio-tissue has become an interesting area. Nevertheless, the ultrasonic imaging is limited on the axis of the ultrasound beam, besides the disadvantages such as the low special resolution, scattering speckle and the ultrasound bean phase distortion on the sound path, the small lesion can not be detected easily.Fatemi and Greenleaf propose the principle of Vibro-Acoustography which has been published on the Science. In their jobs, two confocal ultrasound with little frequency difference⊿f are focused on the spot inside the bio-tissue, resulting in the vibration of this spot caused by the alternating radiation force, this vibration generates the acoustic wave with the frequency⊿ f. The phenomenon is called Ultrasound-simulated Acoustic Emission (USAE). These signals includes the information of the elasticity and sound attenuation of the confocal tissue which can be collected by the hydrophone outputting the image reflect the information of the tissue. This process is called Vibro-acoustogram.We developed the Power Supply based on the Differential Frequency. This device provides the high stability of the frequency and high resolution of the frequency and two channels of the triggering signals that can be adjusted widely. This work compared the advantages and disadvantages of several schemes of the Frequency Synthesis and chose the Direct Digital Frequency Synthesizer (DDS) as the core of our system. This system is composed by several parts as follows: The digital module of the little frequency difference; the amplification module of radio frequency; the module of peak detecting and UART to USB converter. We introduce the principle of vibration imaging, compare the schemes of frequency synthesis; analyze the operation and programming method of AD9852; develop an 7-stages low pass filter and power amplification circuits; simulate the peak detecting circuits; develop the interface between human and machine; establish the communication between the URAT and USB; test the software systematically.During the experiments, we test the hardware successfully; meanwhile we generate the frequency by the AD9852 which is measured by the frequency meter. Such experiments have also been applied to the signal being amplified.