IEEE Trans Ultrason Ferroelectr Freq Control. 2017 Apr;64(4):736-748. doi: 10.1109/TUFFC.2017.2661383. Epub 2017 Jan 30.
Pulse compression has been used for decades in radar, sonar, medical, and industrial ultrasound. It consists in transmitting a modulated or coded excitation, which is then cross-correlated with the received signal such that received echoes are time compressed, thereby increasing their intensity and hence the system resolution and signal-to-noise ratio (SNR). A central problem in pulse-echo systems is that while longer coded excitations yield higher SNRs, the length of the coded excitation or sequence is limited by the distance between the closest reflector and the transmitter/receiver. In this paper, a new approach to coded excitation is presented whereby receive intervals or pauses are introduced within the excitation itself; reception takes place in these intervals. As a result, the code length is no longer limited by the distance to the closest reflector and a higher SNR increase can be realized. Moreover, the excitation can be coded in such a way that continuous transmission becomes possible, which reduces the overall duration of the system response to changes in the medium. The optimal distribution of the receive intervals within the excitation is discussed, and an example of its application in industrial ultrasound is presented. The example consists of an electromagnetic-acoustic transducer driven with 4.5 V, where a clear signal can be obtained in quasi-real-time (e.g., ~9-Hz refresh rate), while commercially available systems require 1200 V for a similar performance.
脉冲压缩在雷达、声纳、医学和工业超声中已经使用了几十年。它包括发射调制或编码的激励，然后与接收到的信号进行互相关，从而使接收到的回波时间压缩，从而提高其强度，进而提高系统分辨率和信噪比（SNR）。在脉冲回波系统中，一个核心问题是，虽然更长的编码激励会产生更高的 SNR，但编码激励或序列的长度受到最接近的反射器与发射器/接收器之间的距离的限制。在本文中，提出了一种新的编码激励方法，即在激励本身中引入接收间隔或暂停；在这些间隔中进行接收。因此，码长不再受最接近的反射器的距离限制，可以实现更高的 SNR 增加。此外，激励可以以这样一种方式进行编码，即连续传输成为可能，从而减少了系统对介质变化的整体响应时间。讨论了在激励中最佳分配接收间隔，并给出了其在工业超声中的应用示例。该示例由一个 4.5V 的电磁声换能器驱动，其中可以在准实时（例如，~9Hz 的刷新率）获得清晰的信号，而类似性能的商业系统则需要 1200V。
