A procedure for inductive wireless powering of single-chip systems is presented. An integrated spiral coil is used as the power receiving component. An external resonator formed by a wire-loop inductor connected to a capacitor is placed in close proximity to the chip. The sinusoidal magnetic field generated at a distant transmitting loop is amplified by the resonator. The present approach enables delivering power in the order of tens of microwatts to a few milliwatts at distances longer than $10\mathrm{cm}$ using a frequency of $13.5\mathrm{MHz}$ . The integrated coil used here can be fabricated with any integrated circuit fabrication technology.

A scheme to enhance a wireless passive sensor's readout is presented. This alternative consists of the addition of a passive inductive-capacitive resonator placed between the sensor and readout antenna. A discrete model is proposed and used in simulations to study the effects of the resonator in the sensor-antenna interaction. A resonator was fabricated at 28 MHz to test the enhancement of the sensor's signal. Increases in the sensor's signal and the power transmitted to the sensor were always obtained for frequencies below 28 MHz. All experimental results were consistent with the simulation outcomes.

In this paper we present the design of an open-source and low-cost buoy prototype for remote monitoring of water quality variables in fish farming. The designed battery-powered system periodically measures temperature, pH and dissolved oxygen, transmitting the information locally through a low-power wide-area network protocol to a gateway connected to a cloud service for data storage and visualization. We provide a novel buoy design that can be easily constructed with off-the-shelf materials, delivering a stable anchored float for the IoT device and the probes immersed in the water pond. The prototype was tested at an operating fish farm, showing promising results for a low-cost remote monitoring tool that enables automatic data acquisition and storage in fish farming scenarios. All the elements of this design, including hardware and software designs, are freely available under permissive licenses as an open-source project.

We report on the design and characterization of the building blocks of a single-chip wireless chemical sensor fabricated with a commercial complementary metal-oxide-silicon (CMOS) technology, which includes two types of transducers for impedimetric measurements (4-electrode array and two interdigitated electrodes), instrumentation circuits, and a metal coil and circuits for inductive power and data transfer. The electrodes have been formed with a polycrystalline silicon layer of the technology by a simple post-process that does not require additional deposition or lithography steps, but just etching steps. A linear response to both conductivity and permittivity of solutions has been obtained. Wireless communication of the sensor chip with a readout unit has been demonstrated. The design of the chip was prepared for individual block characterization and not for full system characterization. The integration of chemical transducers within monolithic wireless platforms will lead to smaller, cheaper, and more reliable chemical microsensors, and will open up the door to numerous new applications where liquid mediums that are enclosed in sealed receptacles have to be measured.