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‘Fantastic voyage’ of Technion professor

Prof Weihs correctly predicted a critical speed above which dolphins jump out of the water to improve their swimming efficiency.  Photo: Courtesy of

 Distinguished Professor Daniel Weihs at the Technion Institute of Technology, Israel, is a world renowned expert in the mechanics involved with how birds fly and how fish swim. One of the early discoveries to come out of his laboratory was the solution to the problem of dolphins being accidentally caught by the tuna fishery. Prof. Weihs correctly predicted a critical speed above which dolphins jump out of the water to improve their swimming efficiency. By chasing the tuna and the dolphins in smaller boats – at sufficient speed – the dolphins jump to escape the net while the tuna dive deeper into the net. This simple method of separating dolphins from tuna helped to solve the problems that led to widespread tuna boycotts in the 80s. However, even though dolphins were no longer being caught in the nets, the dolphin population did not increase as expected. One of the reasons suggested for the lack of growth in the dolphin population was baby dolphins being separated from their mothers.

It was once again Prof. Weihs who provided the solution. He showed that baby dolphins need to "draft" their mothers in order to swim at high speeds. By swimming near the side of its mother, the baby can gain energy from its mother who willingly does a bit of extra work. It is a similar idea to car racing where the car out in front uses more energy than the cars behind. With Prof. Weihs' analysis confirmed by numerous observations, it became necessary to ensure that the mother and baby were not separated when being chased out of the tuna nets. Based on these experiences, it is no surprise that when Prof. Weihs sets out to engineer devices to solve a particular problem he first looks to nature.

When thinking of great advances in engineering history it is typical to think of monumental achievements such as long bridges, trains, cars or airplanes. Yet, in recent years it is the development of machines and the furthering of our understanding of transportation at the smallest scales that offers the most exciting technological developments.

Prof. Weihs is at the forefront of the development of these small devices. In fact, one of his nano-parachutes was featured on the stamp from the Israel Postal Service commemorating the 100 year anniversary of the founding of the Technion. Typically, engineering achievements like airplanes or bridges need to be significantly scaled down for the size of a stamp; however, the nano-parachute designed by Prof. Weihs had to be scaled up! One of the reasons for developing the nano-parachutes is to use them in tracking air movement in the atmosphere. For example, if an accident happens at an industrial facility, or a terrorist attack releases a toxic chemical into the air, these nano-parachutes could be dropped into the toxic cloud allowing officials and civilians to easily track the movement of the toxin by eye.

The Israeli stamp featuring nano-parachutes

The nano-parachute is made up of several small nano-fibers laid out like a ladder with several of the nano-fibers making up the rungs – each fiber being thinner than the diameter of a human hair. According to Prof. Weihs, the design inspiration for the nano-parachute comes from nature where dandelion seeds are carried long distances by the wind. The reason that dandelion seeds can travel so far is that it takes a long time for them to fall to the ground. However, these dandelion seeds do not float in the same way that one might float in a swimming pool or the Dead Sea, rather they float using drag forces. Prof. Weihs offers a simple analogy for how it works. The easiest way to visualize it at larger scales is to take a regular comb and drop it into a barrel of honey – the highly viscous honey slows the descent of the comb. By shrinking the bristles in the comb down to the nano scale, the air effectively becomes increasingly viscous and the behavior is similar to the comb in the honey.

Prof. Weihs has developed mathematical models to optimize the size and spacing of the bristles in his nano-parachute to make them fall as slowly as possible since the slower they fall to the ground the longer they will be able to track potentially dangerous pockets of air. In addition to conceiving and optimizing the design of these nano-parachutes, Prof. Weihs' lab at the Technion has developed the expertise required to construct these devices which are made up of strands barely visible to the human eye. 

A small world ... a nano-parachute compared to a household battery

As with the nano-parachutes, the focus of Prof. Weihs' recent research on swimming has considerably shrunk in size. As part of his current research efforts, he is actively involved in developing a "micro-swimmer". Micro-swimmers could be used to deliver medicine to targeted locations in the body, which is often much more effective than conventionally taken medication. By using carefully controlled magnets, a surgeon could guide the micro-swimmer to the desired location in the body and guide it back out again. The real challenge is to ensure that the "robot" is small enough. For example, if a surgeon loses control of one of these micro-swimmers, they must be small enough to ensure that they will not create a blockage which could lead to a stroke.

These tiny-scale miniature robots are just two examples of the advances possible due to the advent of nanotechnology. The Technion has long been a world-leading institution in many fields of science and engineering. As the attention of engineers shifts to designing devices at these tiny scales, Prof. Weihs and his colleagues ensure that the Technion will remain at the forefront of these developments. In the future, these nano-scale devices will be commonplace – even if they are not seen – and it will be today's researchers who lead the way to remarkable advances in fields as diverse as anti-terrorism to medicine. 



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Saturday, 29 January 2022

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