Without breaking the rules of physics, a device broadcasts radio waves with practically no power

 By 

Joshua R. Smith, University of Washington, Zerina Kapetanovic, Stanford University

January24, 2023

                                             At first look, a novel ultra-low-power communication technique appears to defy the rules of physics. By simply opening and closing a switch that links a resistor to an antenna, it is feasible to wirelessly send data. No need to provide the antenna with electricity.

All kinds of data-transmitting devices, including small sensors and implanted medical devices, might be created using our methodology in combination with methods for obtaining energy from the environment without the use of batteries or other power sources. These include sensors for intelligent agriculture, implantable electronics that never need batteries, improved contactless credit cards, and perhaps even new satellite communication techniques.

No further energy is required to transfer the information outside the energy used to flick the switch. In this instance, the switch is a transistor, a switch that is electrically operated, has no moving components, and uses a very small amount of electricity.

A switch links and disconnects a powerful electrical signal source, such as an oscillator that generates a sine wave that changes 2 billion times per second, to the transmit antenna in the most basic version of conventional radio. The antenna generates a radio wave when the signal source is attached, which represents a 1. There is no radio signal while the switch is off, which represents a 0.

We demonstrated that the absence of a powered signal source is sufficient. The signal driving the antenna can be replaced by random thermal noise, which is present in all electrically conductive materials due to the migration of electrons driven by heat.

No free lunch

We study wireless systems as electrical engineers. Reviewers questioned us about the method's compliance with the second law of thermodynamics, the fundamental physical principle that explains why perpetual motion machines are impossible, during the peer review of our paper describing this research, which was recently published in Proceedings of the National Academy of Sciences.

Theoretically, perpetual motion machines are capable of operating without the need for external energy. The reviewers expressed concern that if information could be transmitted and received without the need of any powered components and with both the transmitter and receiver operating at the same temperature, it could be conceivable to build a perpetual motion machine. Since this is implausible, it would suggest that our work or our comprehension of it was flawed.

The spontaneous transfer of heat only occurs between hotter and colder substances, according to the second law. Our transmitter's wireless transmissions carry heat. In defiance of the second rule, you could collect any spontaneous signal flow that occurred from the transmitter to the receiver in the absence of a temperature differential between the two.

The fact that the receiver in our system is powered and functions like a refrigerator provides the answer to this seeming paradox. Similar to how a refrigerator maintains its internal temperature by continually pumping heat out, the powered amplifier successfully maintains the signal-carrying electrons on the receive side at a low temperature. The receiver uses up to 2 watts of electricity, while the transmitter uses nearly none. Receivers in various ultra-low-power communication systems are comparable to this. A base station without energy use restrictions is where almost all of the electricity is consumed.

A simpler approach

Backscatter is a term for similar passive communication techniques that have been the subject of much investigation globally. Our data transmitter gadget resembles a backscatter data transmitter in appearance. The distinction is that a backscatter communication system also includes a third component that produces a radio wave in addition to the data transmitter and data receiver. The data transmitter switches in a way that causes that radio wave to reflect, which the receiver then picks up.

The energy efficiency of a backscatter device is identical to that of our system, but the backscatter setup is significantly more difficult since a signal-generating component is required. However, compared to traditional radios and backscatter radios, our device has a lower data rate and range.

What's next

Future work will include increasing the data rate and range of our system and testing it in scenarios like implanted devices. Our novel approach has the benefit of not subjecting the patient to a powerful external radio signal for implanted devices, which might result in tissue heating. Even more intriguing, we think that similar concepts may enable new types of communication that allow for the modulation of other natural signal sources, such thermal noise from biological tissue or other electrical components.

Finally, this approach may result in new linkages between the study of communication and the study of heat (thermodynamics) (information theory). Although both domains are frequently seen as comparable, our research shows some more direct linkages between them.

Under the terms of a Creative Commons licence, this article has been taken from THE CONVERSATION. Go here to read the original article.