# Ultrasonic Pulse-Echo Signals for Quantitative Assessment of Reinforced Concrete Anomalies
Pulse-echo testing is a nondestructive technique that uses ultrasonic waves to detect material defects. The technique works by analyzing the amplitude of the echo signal and the time it takes for the signal to reach the receiver. This information helps determine the defect's presence, size, and location. One of the primary advantages of the pulse-echo technique is its flexibility in testing large and irregularly shaped objects. However, the technique has a significant drawback: the loss of sensitivity near the test surface due to the  
Figure 1: Schematic of the principles of UPC device. coupling of the transducer with the test specimen. The ultrasonic signal passes through several materials before reaching the test specimen, including a coupling element and a transducer body. The reflected signals create near-field noise in the A-scan, which shows a reflector at each material interface. The amplitude of the received echo depends on several factors, such as the transmitter power, direction of the transmission, size of the reflector, surface irregularities of the reflector, the reflector's position and orientation, the receiver's size and orientation, loss of signal at the receiver due to re-reflection and lack of coupling, attenuation of the sound wave due to absorption and scattering, and shadow effects [17; 18; 19; 20; 21]. Ultrasonic testing is an effective method for detecting internal defects in concrete structures. However, interpreting ultrasonic testing data is a crucial task requiring extensive expertise. Various methods have been developed to overcome this challenge, including the widely used mature industrial ultrasonic imaging method, SAFT. These methods have shown promising results in detecting internal defects of concrete structures. However, it is essential to note that most of these methods can only qualitatively determine the presence of defects in concrete and cannot quantitatively detect the position and size of these defects. Accurate positioning, precise evaluation, and clear visualization of void defects are essential for assessing the safety and performance of concrete structures. Unfortunately, the conventional SAFT method is often plagued by background noise and image artifacts, primarily due to the low-frequency ultrasonic pulse with a long wavelength. Consequently, the resulting image tends to droop, resulting in suboptimal quality outcomes. Ultrasonic array devices are now widely employed to visualize the insides of concrete structures nondestructively. However, the data collected by these devices may sometimes need to be clarified, requiring the use of image reconstruction algorithms to achieve clear images. Low-frequency UPE devices can combat the issue of signal attenuation in concrete structures. These devices emit low-frequency ultrasonic pulses that reduce signal attenuation, pulse duration, and image sagging, resulting in fewer image distortions and an overall improvement in quality. The UPE device has an impressive collection of ultrasonic transducers that can measure multiple pulse-echo signals in a single scan. This advanced process results in a comprehensive cross-sectional image of the tested object. The device runs on the cutting-edge SAFT-C algorithm, which uses a time-domain approach that relies on the delay-and-sum method to focus on delayed reflections effectively. This algorithm was selected for its user-friendliness and low-performance requirements, making it an excellent microprocessor option. While the interpolated image provides an intuitive and immediate visualization of the inside of concrete structures, the reliability of the information in the interpolated area decreases as the spacing between 2D images increases. Using a polarized shear wave by the UPE device makes it highly unlikely for a reflector to be arranged in a specific direction. Additionally, the UPE device software cannot combine data collected from multiple orientations to generate an image. Existing detection methods often use ultrasonic body waves.