U.S. Air Force Research Laboratories
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USAF Researchers Shrink RF Isolators

March 31, 2021
In defense-related electronics, reducing SWaP is an all-consuming goal. Consider the RF isolator part handled.

The continuing quest to reduce size, weight, and power (SWaP) in electronic systems is often a challenge when it comes to certain passive components such as attenuators and filters, which are typically constructed from materials that do not lend themselves to miniaturization. But researchers at the U.S. Air Force Research Laboratory (AFRL) recently discovered how to produce an often-used high-frequency passive component, the RF isolator, in a size akin to that of semiconductor devices. RF isolators are vital for minimizing unwanted signal reflections in systems operating at microwave and mmWave frequencies.

The AFRL research team of Dr. Derek A. Bas, Dr. Piyush J. Shah, and Dr. Michael R. Page (left to right; Dr. Bas's tweezers hold a chip with an array of four RF isolators) developed an isolator that is approximately one-sixth the size of miniature RF isolators based on currently available magnetic materials, such as yttrium-indium-garnet (YIG) materials, which also consume higher amounts of power. The same research team previously applied their design strategy to develop a patented tunable filter to replace the much larger YIG-tuned filters commonly used in high-frequency systems and test equipment.

The researchers used a layer of piezoelectric material along with a thin film of permanently magnetized material to achieve high isolation from a chip-sized passive component. As Dr. Page reports, “The novel device in our work is essentially an RF isolator.” Dr. Shah adds: “The core area of the science of our technology is called acoustically driven ferromagnetic resonance phenomena.” Research in this area of replacing larger ferromagnetic components with lower-power composites of magnetic and piezoelectric materials, which was begun by German scientists, has been ongoing for about a decade. Their team has reported isolation of close to 50 dB for the tiny components, a significant improvement over earlier isolators fabricated on the composite materials. As Shah notes, the high isolation translates into minimal signal reflections in high-frequency circuits and systems: “In our device, the signal is essentially completely blocked when returning or reflected in the opposite direction.” The AFRL team is pursuing the research with Sandia National Laboratories in quest of a circulator based on the same material. 

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