This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT 1 Recovering of Corrupted Ultrasonic Waves, for Determination of TOF Using the Zero-Crossing Detection Technique Jean Carlos Fabiano dos Santos , Priscila Pagliari Pinheiro , and José Alexandre de França Abstract—Time-of-flight (TOF) measures are valuable in the estimation of displacements, distances, and moving fluids’ speed, e.g., the wind. Of the different types of methods that measure wind speed, the ultrasound is highlighted. As part of the calcula- tion required to acquire the wind speed, one must find the time that an ultrasonic wave takes to travel from one particular place to another. This time is known as TOF. The biggest challenge in measuring TOF is to determine the correct moment when the ultrasonic wave arrived at the reception because it will be immersed in noise and its envelope probably will be corrupted by the actions of the wind. The methodology proposed by this paper presents a combined algorithm between an extended Kalman Filter (EKF) and a zero-crossing detector (ZCD) technique. The EKF method is responsible for the noise elimination stage and estimation of the real ultrasound’s envelope, while the ZCD detects the correct TOF of the estimated signal. This paper also presents the flaws and solutions found for each technique. It was shown that for speeds up to 75 km/h, the coefficient that was found to be R 2 = 0.99977. Index Terms— Combined algorithm, envelope, fluid flow measurement, Kalman filter, ultrasonic transducers. I. I NTRODUCTION U LTRASOUND transducers are used in several fields of science [1]–[4], e.g., the measurement of fluids’ veloc- ity, such as the wind. Of the methods for measuring wind speed, the ultrasonic anemometers stand out because they can perform measurements in different environmental situations. The most common methods for ultrasonic fluid velocity measurement are phase difference, cross correlation, threshold level and, in particular, time-of-flight (TOF). The most usual practice of identifying the ultrasonic signal is by the method known as threshold-level detection [5]. In this technique, the signal is determined through the amplitude using a pre- defined minimum voltage level. The idea is simple: when the signal is greater than zero, means the pulse has arrived. However, in the presence of noise, this method does not work. The noise itself causes the signal to be higher than Manuscript received September 11, 2018; revised November 23, 2018; accepted December 3, 2018. This work was supported in part by CNPq and in part by CAPES. The Associate Editor coordinating the review process was Vedran Bilas. (Corresponding author: Jean Carlos Fabiano dos Santos.) The authors are with the Department of Electrical Engineering, State Uni- versity of Londrina, Londrina 86057970, Brazil (e-mail: jeancffs@gmail.com; priscilapagliari@gmail.com; franca@la2i.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIM.2018.2890326 zero. Thus, it is necessary to place a limit above a certain voltage level. However, this is not acceptable because it makes detection dependent on the amplitude of the ultrasonic signal, which alters with other variables. The noise, both external and electronic, in this system makes it very conducive to erroneous measures since it is necessary always to be careful to not exceed the threshold. This technique also requires periodic calibrations because the conditioning circuit components can cause the voltage threshold value changing over time. Another process known as phase difference consists in measuring the phase difference between the transmission and reception waves [6]–[9]. The difficulty of this procedure is that if the technique has a fixed reference, the maximum that the wave can delay is an entire period. This delay limits the maximum speed that the system will be able to measure. Also, regular calibrations are required in the system, since it is difficult to guarantee a uniform phase in fluids that have a constant velocity because the signal tends to be in continuous vibration [10]. Another technique, known as cross correlation, is a cross correlation methodology between the emitted and the received wave [11]. This technique is widely used to measure vibration levels, where it is simple to work with pairs of transduc- ers [12]. However, when measuring the wind speed, it requires the emitted wave to be measured at the exact moment it has been emitted in output, which is complicated to project without energy loss. In addition to this methodology, uncertainties are introduced due to interpolation techniques. A procedure based on the amplitude and envelope of the ultrasound is the technique of the TOF [13]. In this technique, a pulse train is applied to the emitter ultrasonic transducer in which a set of known oscillations will be generated that will travel by air. This signal arrives at the reception partially or entirely corrupted, and may also have a delay or advance of the ideal time of arrival. The scheme is best illustrated in Fig. 1. It is an advantageous technique when compared to oth- ers because other reference signals cannot restrict it. The same emitted wave, after a count of time, is expected in the reception. The difficulty in this system is to detect the ultrasound, as it may be immersed in the noise. Even if the signal is clear of noises, it is necessary to know the exact moment the ultrasound began to arrive at the reception, taking into account that the external actions may have caused an 0018-9456 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.