The need for low-cost sensors and ID tags is ongoing. Our work explores how ID and sensor information can be encoded in the electromagnetic spectrum of inexpensive material structures without the need for electronic chips. Through the use of novel electromagnetic structures and active materials, it is possible to manipulate and to control the electromagnetic response of structures in order to create a "representation language" for conveying ID and sensor information. Applications include smart packaging, automatic inventory systems, and low-cost sensors for home, industrial, and environmental uses.