In 2004, Larry was challenged with developing a tag system to be used for identifying assets, where the tag could not transmit a signal yet had to convey asset identifying information over relatively long distances.  After some research, Larry settled on developing a system based upon modulating reflector (MR) tags, which do not transmit signals but instead vary their radar cross-sections in accordance with time-varying codes thereby enabling interrogating radar having a priori knowledge of the codes to receive information from the MR tags.  As part of the development, Larry made substantial improvements to previous MR tag systems including incorporating the antennas of the MR tags into retroreflectors to increase the signal-to-noise (SNR) of the MR tags.  CRR refers to these improved MR tags as modulating retroreflector (MRR) tags.

Larry filed a provisional patent application for MRR tags in August of 2004.   When CRR was founded in December 2006, Larry assigned the pending MRR tag technology patent application to CRR.  CRR successfully prosecuted the patent application resulting in U.S. patent 7,479,884.  In 2008, Larry conceived of another improvement to his MRR tag system that involved embedding the retroreflectors into a dielectric material in order to enable the MRR tags to be read from interrogation angles approaching ±90°.  CRR filed a continuation-in-part patent application in October 2008, which resulted in issued U.S. patents 8,395,484 and 8,730,014. 

 
Antenna inside retroreflector embedded in dielectric material

Antenna inside retroreflector embedded in dielectric material

 

In recent years, fast-evolving advances in unmanned aerial vehicle (UAV), or drone, technologies has raised serious issues with government and commercial entities, where drones have been flown near aircraft in violation of federal rules, which has caused safety concerns, while companies are also moving forward to use drones for business purposes.  For example, Amazon and DHL plan to use drones for small package delivery and many other companies either plan or are already using drones for farming, monitoring traffic, building construction, searching for missing people, bridge monitoring, railway monitoring, building monitoring, oil rig monitoring, news gathering, and wildlife area monitoring. 

Four British Airways pilots have opened a drone training school for training drone pilots.  Currently, the U.S. Department of Transportation regarding is accessing proper ways for monitoring drones.  In 2015, Larry recognized that CRR’s MRR tag technology lends itself for monitoring drones and CRR began an initiative to demonstrate use of its MRR tag technology for drone monitoring.  It is important to note that U.S. Patents 7,479,884 and 8,730,014 each have dependent claims involving use of a modulating retroreflector tag to convey information about an unmanned air vehicle.

As part of the drone monitoring initiative, Larry first undertook an effort to upgrade CRR’s X band MRR tag, where he replaced a diode used to switch the state of the antenna with a microwave transistor.  Microwave transistor technology has advanced substantially over the last decade and such transistors are now less expensive and smaller.   Because a microwave transistor is voltage driven as opposed to a diode, which must be current driven, the microwave transistor requires less power, which is very important for most applications given that power consumption determines battery life and power available for sensors.  Importantly, because modern microwave transistor ON resistance is considerably lower than ON resistance of the diode a significant 20 dB (100x) gain in path loss was achieved.  Overall, the upgrade effort resulted in a smaller, lower cost X band MRR tag that has substantially improved performance while using less power.  

CRR’s MRR tag has a substantial advantage over conventional tags in high multi-path environments, where there is a lot of metal.  Whereas the performance of active and passive RFID tag systems suffers in high multi-path environments, CRR’s MRR tag system thrives because most of the energy received at a given MRR tag from the multiple paths is reflected back to an interrogator by the MRR tag’s retroreflector.  Generally, as the amount of multipath increases, CRR’s MRR tags have increasing gain while conventional tags have decreasing gain. 

Comparison of RFID, Reflector, and Retroreflector Tags

Comparison of RFID, Reflector, and Retroreflector Tags

From April to December 2017, CRR put forth a substantial effort to increase the Technology Readiness Level (TRL) of CRR’s MRR tag technology.  As part of that effort, CRR developed a MRR tag system test bed including an automated test fixture for rotating a tag about three axes relative to a fixed tag reader location in order to measure system performance for different view angles of the tag reader relative to the tag. A base having a processor, batteries, and quick connects was designed to attach to the automated text fixture and to enable easy interchange of test component tags having various tag characteristics such as different antenna shapes and configurations, different retroreflector sizes, and different dielectric materials, where the performance of different tag designs could be directly compared.

Various dielectric materials were tested in order to select a material having a desirable dielectric constant and corresponding refractive index to be used to fill the retro-reflectors of the various test components. Below is an informative picture of a jig used to measure the dielectric constant/refractive index of a sample material.

Jig used to measure dielectric constant and refractive index of a sample material.

Jig used to measure dielectric constant and refractive index of a sample material.

Below are pictures of the base, the test component, and a test component mounted on the base attached to the test fixture.

Base

Base

Front and Side Views of a Test Component attached to the Base

Front and Side Views of a Test Component attached to the Base

Test Component Mounted in the Test Fixture

Test Component Mounted in the Test Fixture

CRR also developed an alpha prototype Inphase - Quadrature (IQ) tag reader for receiving output from two receive antennas and processing output into digital signals provided to proprietary post-processing software. The prototype utilized a modified shell of a Bushnell® Radar Gun. The tag reader and processing software are shown below.

Alpha Prototype MRR Tag Reader

Alpha Prototype MRR Tag Reader

MRR Tag Automated Test System Post-processing Software

MRR Tag Automated Test System Post-processing Software

In December 2017, the MRR Tag System project was suspended in order to focus company resources on a novel truncated retroreflector array technology that was conceived as a result of retroreflector research performed as part of the MRR Tag System effort.

Parties interested in receiving licenses to or acquiring CRR’s modulating retroreflector tag technology or establishing a strategic partnership relating to CRR’s MRR tag technology should contact Mark Roberts at mark@cr-res.com.