科学家们在概念验证实验中证明，有可能在没有能量损失的情况下捕捉并储存机械波，然后将其导向特定位置。
这一突破——在《华尔街日报》上有所描述科学进步—可以提高我们操纵波浪的能力，这将对广泛的领域产生影响。
实验装置由一根长的碳钢棒组成，中间有一个空腔，两端各有两个致动器——将能量转化为运动的装置。研究人员利用这些向相反方向行进的致动器产生了两种机械波。
“机械波类似于在海洋表面传播的波，但它携带着在固体物质中传播的振动，”纽约城市大学该项研究的主要作者安德里亚·阿尔告诉记者新闻周刊。"一个很好的例子是波浪沿着吉他弦传播."
“通常情况下，在谐振腔中储存能量效率很低，并且很难积累信号并在以后按需释放，”他说。“我们的实验证明，有可能在给定的区域有效地储存能量，然后根据需要向优选的方向释放。”
在他们的研究中，该团队意识到吸收能量的材料可以被设计成从一个源头提取所有的“撞击能量”。
这个短语本质上是指波浪携带的所有能量。典型地，如果波被它撞击的材料吸收——即与之接触——一些能量就损失了。
“[吸收材料]以其他形式转化这种能量。在这里，我们想从效率的角度模拟吸收过程，但是使用一个系统，以同样的形式保存能量，然后可以按需释放它，”阿尔说。“两年前，我们从理论上证明，通过控制和调整波浪的时间演变来实现这一目标是可能的，这样当它们与非吸收性材料接触时，它们会有效地堆积在材料中而不会反射，就好像它们被吸收了一样。"
实验装置，由带空腔的波导杆组成。沿着杆行进的弹性波的激励由放置在系统两端的致动器提供。
“我们把这个概念命名为相干虚拟吸收。这种方法可以防止撞击到结构上的波逃逸，并且有效地被截留在内部，就像被吸收一样。存储的波可以按需释放，”她说。
本质上，通过模拟吸收，研究人员设法捕捉到了所有的波的能量，而没有转化成特定形式的能量——比如热量。
在实验中，研究小组使用致动器激发碳素钢棒——产生两个方向相反的机械波——并仔细控制每个波的时间变化，以确保空腔能保留所有撞击能量。
“然后，通过停止激励或使两个信号中的一个与另一个失谐，我们能够控制储存能量的释放，并将其发送到所需的方向，”阿尔说。
据研究人员称，这项研究的结果可能会导致几个领域的进展。
“我们对机械波的实验显示了对振动的新程度的控制，振动通常用于监测桥梁等结构的完整性，因此我们的工作可以提高这些完整性控制系统的效率，”阿尔说。
“此外，我们目前正在探索将类似概念应用于其他类型的波，包括光。我们设想基于类似原理的高效光学计算和量子计算设备，并提高无线充电、存储器和开关的效率，”他说。
SCIENTISTS HAVE COME UP WITH A WAY TO STORE AND RELEASE MECHANICAL WAVES WITH NO ENERGY LOSS
Scientists have demonstrated, in a proof-of-concept experiment, that it is possible to capture and store a mechanical wave without energy loss and then guide it towards a specific location.
The breakthrough—described in the journal Science Advances—could improve our ability to manipulate waves, which would have implications for a broad range of fields.
The experimental setup consisted of a long, carbon steel bar with a cavity in the middle and two actuators—devices that turn energy into motion—at each end. The researchers produced two mechanical waves using these actuators that traveled in opposite directions.
"A mechanical wave is similar to a wave propagating on the surface of the ocean, but it carries vibrations that travel in solid materials," Andrea Alù, lead author of the study from the City University of New York, told Newsweek. "A good example is the wave traveling along a guitar string."
"Typically, storing energy in resonant cavities is inefficient, and it is challenging to accumulate signals and release it on-demand at a later time," he said. "Our experiment proves that it is possible to efficiently store energy in a given region and then release it on-demand towards a preferred direction."
In their research, the team realized materials that absorb energy can be designed to extract all the "impinging energy" coming from a source.
This phrase essentially means all of the energy being carried by a wave. Typically, if a wave is absorbed by the material upon which it's impinging—i.e. comes into contact with—some of the energy is lost.
"[Absorbing materials] transform this energy in other forms. Here, we wanted to mimic the absorption process in terms of efficiency, but using a system that preserves the energy in the same form, and can then release it on demand," Alù said. "Two years ago we showed, theoretically, that it is possible to achieve this goal by controlling and tailoring the waves' time evolution, so that when they came in contact with non-absorbing materials, they would efficiently pile up in the material without reflections, as if they were absorbed."
Experimental setup, consisting of a waveguide bar with a cavity. The excitation of elastic waves traveling along the bar is provided by actuators placed at the two ends of the system.
"We named this concept coherent virtual absorption. This method prevents the wave impinging on the structure from escaping, and it gets efficiently trapped inside as if it were being absorbed. The stored wave could then be released on demand," she said.
Essentially, by mimicking absorption, the researchers managed to capture all of the wave's energy and not convert into a specific form of energy—such as heat.
In the experiment, the team excited the carbon steel bar using the actuators—producing two mechanical waves traveling in opposite directions—and carefully controlled the time variations of each wave to ensure that the cavity would retain all of the impinging energy.
"Then, by stopping the excitation or detuning one of the two signals from the other, we were able to control the release of the stored energy and send it towards a desired direction," Alù said.
According to the researchers, the results of this study could lead to advances in several areas.
"Our experiment with mechanical waves shows a new degree of control of vibrations, which are commonly used for monitoring the integrity of structures like bridges, so our work can improve the efficiency of these integrity control systems," Alù said.
"In addition, we are currently exploring the application of similar concepts to other types of waves, including light. We envision efficient devices for optical computing and quantum computing based on similar principles, and improving the efficiency of wireless charging, memories and switches," he said.
