Modern day systems often require reconfigurability in the operating parameters of the transmit and receive antennas, such as the resonant frequency, radiation pattern, impedance, or polarization. In this work a novel approach to antenna reconfigurability is presented by integrating antennas with the ancient art of origami. The proposed antenna consists of an inkjet printed center-fed spiral antenna, which is designed to resonate at 1.0GHz and have a reconfigurable radiation pattern while maintaining the 1.0GHz resonance with little variation in input impedance. When flat, the antenna is a planar spiral exhibiting a bidirectional radiation pattern. By a telescoping action, the antenna can be reconfigured into a conical spiral with a directional pattern and higher gain, which gives the antenna a large front-to-back ratio. Construction of the antenna in this manner allows for a simple, lightweight, transportable antenna that can expand to specifications in the field.

This paper presents the design, simulation, and preliminary measurement of a passive (battery-free) frequency doubling antenna sensor for strain sensing. Illuminated by a wireless reader, the sensor consists of three components, i.e. a receiving antenna with resonance frequency f 0 , a transmitting antenna with resonance frequency 2 f 0 , and a matching network between the receiving and transmitting antennas. A Schottky diode is integrated in the matching network. Exploiting nonlinear circuit behavior of the diode, the matching network is able to generate output signal at doubled frequency of the reader interrogation signal. The output signal is then backscattered to the reader through the sensor-side transmitting antenna. Because the backscattered signal has a doubled frequency, it is easily distinguished by the reader from environmental reflections of original interrogation signal. When one of the sensor-side antennas, say receiving antenna, is bonded to a structure that experiences strain/deformation, resonance frequency of the antenna shifts accordingly. Through wireless interrogation, this resonance frequency shift can be measured by the reader and used to derive strain in the structure. Since operation power of the diode is harvested from the reader interrogation signal, no other power source is needed by the sensor. This means the frequency doubling antenna sensor is wireless and passive. Based on simulation results, strain sensitivity of this novel frequency doubling antenna sensor is around −3.84 kHz/με.