An inkjet-printed, fully passive sensor capable of either humidity or gas sensing is presented herein. The sensor is composed of an interdigitated electrode, a customized printable gas sensitive ink and a specialized dipole antenna for wireless sensing. The interdigitated electrode printed on a paper substrate provides the base conductivity that varies during the sensing process. Aided by the porous nature of the substrate, a change in relative humidity from 18% to 88% decreases the electrode resistance from a few Mega-ohms to the kilo-ohm range. For gas sensing, an additional copper acetate-based customized ink is printed on top of the electrode, which, upon reaction with hydrogen sulphide gas (H2S) changes, both the optical and the electrical properties of the electrode. A fast response time of 3 min is achieved at room temperature for a H2S concentration of 10 ppm at a relative humidity (RH) of 45%. The passive wireless sensing is enabled through an antenna in which the inner loop takes care of conductivity changes in the 4–5 GHz band, whereas the outer-dipole arm is used for chipless identification in the 2–3 GHz band.
A novel dynamically reconfigurable bandpass filter (BPF) employing stepped impedance resonators (SIRs) that can operate as either a single-band or a dual-band filter is demonstrated. The reconfigurable BPF uses four p-in diodes as switching elements. With the four p-in diodes in the "OFF" state, the filter behaves as a low-loss (0.85 dB) single-band BPF with a passband around 2.45 GHz. The reconfigurable SIR filter can operate as a dual-band bandpass filter with two center frequencies at 1.6 GHz and 2.45 GHz. The diodes are dynamically set to the "ON" state in the presence of a 1.6 GHz RF signal that is received by an RF triggered power management unit (PMU), integrated on the back side of the microstrip filter in a dual-layer architecture. The RF triggered PMU consists of a PIFA antenna, a highefficiency voltage doubler rectifier (47% at-13 dBm) and an active dc-to-dc power booster. The rectified output voltage is used as the enabling voltage for the dc-to-dc power booster. This, in turn, provides the required dc power for the diodes biasing. The filter switches from single-band to dual-band when a wireless input RF signal (>-13 dBm) is received by the RF triggered PMU's antenna. Index Terms-Microwave filter, reconfigurable, rectenna wireless power transfer. I. INTRODUCTION HERE has been an increasing demand for switchable and reconfigurable microwave devices, such as filters for wireless communication systems, where several different wireless devices co-exist and share the same frequency spectrum. Band pass filters (BPFs) with multi-frequency response and high stopband rejection are widely used, therefore reconfigurable BPFs can be utilized for controlling either standalone signals or combinations of information signals, with different frequency spectrum characteristics [1], [2]. In [1] a
A dynamically reconfigurable dual-layer UWB antenna integrated with an energy harvesting system for powering a GaAs FET switch is presented. The UWB antenna dynamically creates a notch-band in the presence of an interfering signal at 5.6 GHz and it goes back to normal UWB operation when the interferer is removed. For the switching operation, the FET switch is powered using only harvested energy carried by the interfering signals. The UWB antenna on the front layer is a microstrip-fed monopole with an embedded elliptical slot. Inside the slot a quarter wavelength linear stub acts as a resonator and it is connected and disconnected using the low-power FET switch. The UWB antenna shares the RF ground with a very compact energy harvesting system, that consists of a planar inverted-F antenna, a very compact voltage doubler rectifier and a passive DC-to-DC boost converter. The boost converter elevates the rectified voltage to above the 3.3 V threshold, which is the minimum voltage needed for the actuation of the FET switch. The dynamic notch-band reconfiguration of the UWB antenna without the need for any external DC power source is made possible when the collected power at the input of the rectifier is higher than -12 dBm.
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