The Radio Assay: Josh Griffin kicked off the microwave backscatter research with his famous “Radio Assay” — custom hardware that could measure link degradations experience by RFID tag antennas when placed upon card- board, wood, metal, etc. In 2004, Josh Griffin began the first of many UHF/microwave backscatter experiments involving the “Radio Assay” of an antenna. The radio assay was a series of tests involving antennas radiating against different types of materials: cardboard, wood, water containers, plastic, meat, and metal.
The goal was to demonstrate how an antennas radiation characteristics — impedance, efficiency, and pattern — change when placed against different substances. During this “dark period” of RFID antenna design, many RFID antennas (and non-RFID antennas) were designed for free space but expected to operate in close proximity to materials that significantly altered electrical performance. Moreover, the range of materials for operation is varied and unpredictable.Thus was born the idea of the radio assay. An antenna would be tested against a standard set of materials that represent the range of lossless to lossy dielectric, light to heavy conductor — all formulated from readily available objects. The work was highly cited and still influences antenna design today.
Fun fact #1: We coined the term “radio assay” because we were collaborating with chemists in printable electronics. The analogy with a chemical assay — where an unknown substance’s properties are gaged by mixing them with a standard test set of chemicals — was judged to be the best way to explain our proposed experiment to our scientific collaborators.
Fun fact #2: We wanted to get an idea of how the antennas radiated in the presence of human tissue, but tests with live subjects was out of the question, since this adds multiple layers of institutional review, test time, and human labor. Since the goal was to formulate a standard set of tests that any lab could apply with ready-made materials, we used the next best thing: blocks of ground beef. On a subsequent presentation in India about the work, the identity of the meat was kept confidential.