The clamp-on transit-time ultrasonic flow meters are widely applied for the advantage of noninvasive measurement and convenient deployment. Its key point lies on measuring of the time difference between the upstream and downstream. While high quality of the transducer transmitting/receiving ultrasonic signals is the premise of measuring time difference accurately. This paper studies on the main factors contributing to the uncertainty of the transducer's output signal and focuses on the transducer's frequency, incident angle and the separate distance. The selection principle of transducer's frequency is presented by the analysis of the ultrasonic attention characteristics in the liquid. The incident angle range and precise installation distance of the transducers are calculated and analyzed by Snell's law.Experiments are also carried out with the 1MHz transducers clamped on the aluminium pipe of 20mm outer diameter. The results show that the accurate calculation separate distance 18.16mm is effective to guarantee the output of high quality ultrasonic wave. If the axial installation error reaches more than 3mm, the one beam of ultrasonic signal cannot be guaranteed.
Soft tissue sarcomas which are serious hazard to human are aggressive and difficult to control. Traditional ways of treatment can bring great pain to the patients. Radiofrequency(RF) ablation has become a feasible and minimally invasive treatment for soft tissue sarcomas. However, there are few literatures to study the energy and temperature distributions in the sarcomas. In this paper, sarcomas simulation model was established based on the prototype of gastrointestinal stromal sarcoma. Parameters of electric and thermal properties of the sarcomas were set appropriately by considering its thermal sensitivity. Temperature of 323.15K is chosen as a border edge to evaluate the efficacy of RF ablatio. Results indicate that the maximum temperature point occurs at the apex of RF probe. Growth of temperature at the probe apex decreases with the increment of ablation time. In addition, a local maximum temperature point is presented at the interface of the sarcoma and muscle tissue, which is meaningful for RF ablation to keep the normal tissue undamaged. Effects of electrode insertion depth on the RF ablation were studied in this paper. Results indicate that area of tumor cell necrosis is expanded gradually with the increase of insertion depth and RF power radiated. However, the temperature of the apex of probe drops with the increasing of the depth inserted. As a result, probe insertion depth and RF ablation power must be cooperated to achieve desired RF ablation effect.
Robust and efficient tracking of continuum robots is important for improving patient safety during space-confined minimally invasive surgery, however, it has been a particularly challenging task for researchers. In this paper, we present a novel tracking scheme by fusing fiber Bragg grating (FBG) shape sensing and stereo vision to estimate the position of continuum robots. Previous visual tracking easily suffers from the lack of robustness and leads to failure, while the FBG shape sensor can only reconstruct the local shape with integral cumulative error. The proposed fusion is anticipated to compensate for their shortcomings and improve the tracking accuracy. To verify its effectiveness, the robots' centerline is recognized by morphology operation and reconstructed by stereo matching algorithm. The shape obtained by FBG sensor is transformed into distal tip position with respect to the camera coordinate system through previously calibrated registration matrices. An experimental platform was set up and repeated tracking experiments were carried out. The accuracy estimated by averaging the absolute positioning errors between shape sensing and stereo vision is 0.67±0.65 mm, 0.41±0.25 mm, 0.72±0.43 mm for x, y and z, respectively. Results indicate that the proposed fusion is feasible and can be used for closed-loop control of continuum robots.
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