Prediction and measurement of acoustic transmission loss of acoustic window with composite sandwich structure

Underwater acoustic detection sensors are mounted on the outside of the submarine; the acoustic window for protecting these sensors must be structurally robust while also minimizing any deterioration of sensor's sound detection performance. These two conditions are typically satisfied simultaneously by using composite materials with acoustic window materials. However, since such composite material is manufactured by laminating fibers, there is the probability that delamination occurs, in which an air layer is formed inside, due to manufacturing process errors. Delamination inside the acoustic window degrades the sensor's acoustic performance and results in a failure of military operations. In the case of composites composed of sandwich structures located in the central part, the possibility of internal delamination is higher than in a single composite material. Therefore, it is very important to discriminate the presence or absence of internal delamination after producing an acoustic window. This article uses numerical and analytical methods to determine the internal delamination of the acoustic window fabricated with a sandwich structure. In addition, the results were analyzed and compared through ultrasonic measurement and acoustic transmission loss test.

Design and Analysis of an Active Reflection Controller That Can Reduce Acoustic Signal Refer to the Angle of Incidence

Techniques for reducing the reflection of acoustic signals have recently been actively studied. Most methods for reducing acoustic signals were studied using the normal-incidence wave reduction technique. Although the technique of canceling an object from the normal incidence wave is essential, research on reducing acoustic signals according to the angle of incidence is required for practical applications. In this study, we designed, fabricated, and experimented with an active reflection controller that can reduce acoustic signals according to the angle of incidence. The controller consists of a transmitter on one layer, a receiver sensor on two layers, and an acoustic window on three layers. To reduce the reflected signal, a combination of the time delay and phase was applied to the controller to minimize the acoustic signal by up to −23 dB at an angle of 10°. A controller array simulation was performed based on the results of a controlled experiment. In conclusion, our proposed controller can reduce acoustic signals according to the angle of incidence, which makes it suitable for many applications.

Ultrasonographic Assessment of the Normal Femoral Articular Cartilage of the Knee Joint: Comparison with 3D MRI

Objective. Ultrasonography (US) has a promising role in evaluating the knee joint, but capability to visualize the femoral articular cartilage needs systematic evaluation. We measured the extent of this acoustic window by comparing standardized US images with the corresponding MRI views of the femoral cartilage. Design. Ten healthy volunteers without knee pathology underwent systematic US and MRI evaluation of both knees. The femoral cartilage was assessed on the oblique transverse axial plane with US and with 3D MRI. The acoustic window on US was compared to the corresponding views of the femoral sulcus and both condyles on MRI. The mean imaging coverage of the femoral cartilage and the cartilage thickness measurements on US and MRI were compared. Results. Mean imaging coverage of the cartilage of the medial femoral condyle was 66% (range 54%–80%) and on the lateral femoral condyle 37% (range 25%–51%) compared with MRI. Mean cartilage thickness measurement in the femoral sulcus was 3.17 mm with US and 3.61 mm with MRI (14.0% difference). The corresponding measurements in the medial femoral condyle were 1.95 mm with US and 2.35 mm with MRI (21.0% difference), and in the lateral femoral condyle, they were 2.17 mm and 2.73 mm (25.6% difference), respectively. Conclusion. Two-thirds of the articular cartilage of the medial femoral condyle, and one-third in the lateral femoral condyle, can be assessed with US. The cartilage thickness measurements seem to be underestimated by US. These results show promise for the evaluation of the weight-bearing cartilage of the medial femoral condyle with US.

Ratio of Acceleration Time to Ejection Time of Transaortic Jet in Aortic Stenosis Depends on Acoustic Window

Background: Echocardiographic transaortic jet velocity (Vmax), mean pressure gradient (mPG), and aortic valve area (AVA) are routinely measured for severity of aortic stenosis (AS). Additionally, prolonged ejection time (ET), acceleration time (AT), and its ratio AT/ET are also known as indexes of AS severity. However, acoustic window dependency of AT/ET is not well studied. Methods: Eighty-one patients with AS assessed by transaortic jet tracing of all of three approaches (apical 3-chamber (3C), apical 5-chamber (5C), and right parasternal (R)) were included in this study. ET, AT, and AT/ET were measured on continuous Doppler recordings obtained by 3C, 5C, and R approaches. Also, ET and AT were corrected by dividing by (R-R interval)1/2, and they were named as cET and cAT. Results: No differences were observed in cET among 3 approaches. However, cAT was significantly longer in R (115+23 msec: p<0.05) compared to that of 3C (105+21 msec) or 5C (105+20 msec). AT/ET was significantly greater in R (0.340+0.058, p<0.05) compared to that of 3C (0.317+0.053) or 5C (0.316+0.055). AT/ET-peak V relation of R approach positioned significantly upward (ANCOVA, p<0.05) comparing to that of 3C or 5C. Also, AT/ET-AVAi relation of R approach positioned upward (ANCOVA, p<0.05) comparing to that of 3C or 5C. Conclusions: AT/ET by R approach was greater than that by 3C or 5C approach. Although multiple acoustic window’s approaches including R is recommended to obtain the maximal Vmax or mPG, AT/ET is better in 3C or 5C approach than R when AT/ET is used for AS severity.