The Case for Wireless Power Transfer

By Henry Boger, Independent Consultant

In 1864, James C. Maxwell predicted the existence of radiowaves by means of a mathematical model. The so-called Maxwell equations are the most famous and most successful formulas. In 1884, John H. Poynting realized that the Poynying vector would play an important role in quantifying electromagnetic energy. In 1888, bolstered by Maxwell’s theory, Heinrich Hertz first succeeded in showing experimental evidence of radiowaves using his spark-gap radio transmitter. The prediction and evidence of radiowaves was the beginning of wireless power transfer (WPT).

During the same period, when Marchese G. Marconi and Reginald Fessenden pioneered communication via radiowaves, Nicola Tesla suggested the idea of wireless power transfer and carried out the first WPT experiments in 1889.

To focus on the transmitted power and to increase the transfer efficiency, a higher frequency than that used by Tesla is required. In the 1930s, a great deal of progress in generating high-power microwaves in the 1-10 GHz range was achieved by the invention of the magnetron and klystron. After World War II, high-power and high- efficiency microwave tubes were advanced by the development of radar technology. The power delivered to a receiver can be concentrated with microwaves. WPT using microwaves is called microwave power transfer (MPT).

On the basis of development of microwave tubes during World War ii, W.C. Brown introduced the first MPY research and development in the 1960’s. First Brown developed a rectifying antenna, which he named a “rectenna” for receiving microwaves and rectifying microwaves. With the rectenna, Brown successfully applied MPT to a wired helicopter in 1964 and to a free-flying helicopter in 1968.

During the 1960’s, numerous MPT laboratory and field experiments were carried out all over the world. A Canadian group successfully conducted a fuel-free airplane flight experiment using MPT in 1987. In Japan, several field MPT experiments were conducted, such as fuel-free airplane experiments with MPT phased arrays.

Much current work is centered on charging of electric vehicles.

Existing Wireless Process Devices

The introduction of battery powered field devices in September 2008 has enabled manufacturers in the process control industry to add instruments to applications where the cost of wired field devices could not be justified. As a result, the use of wireless technology has increased dramatically.

Because of the conservative nature of the process industry, wireless analog and discree field devices were initially installed to better monitor process operation. However, as plants have gained experience with wireless technology there has been a growing interest in using wireless measurement and wireless actuators in closed loop control. The cost advantages along with the proven reliability of wireless communication are key factors behind this change in attitude.

Wireless field devices are offered by several suppliers such as Rosemount, Siemens, Pepperel+Fuchs, TopWorks, Fisher Controls, Yokogawa, Honeywell, and GE Measurement and Control.

The Concept

The way things work is illustrated in the added figures.

Figure 1 illustrates exemplary process control apparatus including a power supply, rectifier, source, receiver, and field device.

Figure 2 illustrates source and receiver. As illustrated in the figure, the rectifier inputs a voltage signal, which is sinusoidal, into a source. The source further includes a capacitor and inductor in series to resonate in response to the voltage signal in order to produce an oscillating magnetic field.

Figure 3 illustrates exemplary process control apparatus that includes field devices disposed about the industrial process to communicate power wirelessly to receivers as illustrated. Receivers convert power signals into electrical power and then flow the electrical power into the field devices.

Advantages of Wireless Power Transfer

Wireless power transfer eliminates the need for batteries and the replacement of batteries by a skilled technician who is required to go part way up a 100-foot distillation tower on the midnight shift. Personnel safety is an issue here.

Because of the desire to prolong battery life, update timing is sacrificed. Improved process control will offset the cost of WPT.

Summary

It is obvious to this author that wireless power transfer will be adopted in the process control industry. In the meantime, we are losing the benefits and the cost savings that are in the grasp of opportunity.

About the Author

Henry Boger is a former VP of Masoneilan and is now an independent consultant. He is credited with 23 US patents and authored many published articles.

References

1. Wireless Power Transfer Via Radiowaves, Shinohara, N. Wiley 2014
2. Wireless Control Foundation, Blevins, etal, ISA, 2015
3. US Patent No. 9,923,418, Boger, 2018

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