Low-power FM transmitter for use in neural recording applications

Journal ArticleWe present a low power FM transmitter for use in neural recording telemetry. The transmitter consists of a low noise biopotential amplifier and a voltage controlled oscillator used to transmit the amplified neural signals at a frequency of 433 MHz. The circuit is powered through a transcutaneous, inductive link. The power consumption of the transmitter is measured to be 465 μW. Using a 1/8-wavelength monopole antenna, a received power level was measured to be -54.5 dBm at a distance of one meter

Coaxial microwave resonant sensor design for monitoring ionic concentration in aqueous solutions

Nitrate efflux from agricultural lands mixes with surface streams and adversely affects both human health as well as aquatic life. Currently, there is a lack of low-cost, effective, real-time systems for monitoring ion concentration. In this work, a microwave resonant sensor is designed using an open-ended coaxial transmission line, which can be evanescently perturbed by a liquid sample, and a suitable coupling structure which allows transmission measurements. The sensor is developed to have high sensitivity at agriculturally relevant concentrations, low manufacturing costs, and small dimensions to be potentially field deployable. Finite Element Analysis simulations are carried out using ANSYS HFSS, employing complex permittivity data of aqueous solution samples with varying concentrations of nitrate, sulfate, and chloride ions. Appropriate functions are determined that model the correlations between resonant frequency and ion concentration, and discussion on the feasibility of the sensor for field deployment is presented

Architecture comparison for concurrent multi-band linear power amplifiers

In this paper, a comparison between the concurrent multi-band and parallel single-band power amplifier architectures is analyzed. A generalized framework in which these two architectures can be compared in terms of cost, drain efficiency, output power, and linearity is developed. Results show that in general, a concurrent multi-band power amplifier will have worse performance than a parallel single-band amplifier for class-A operation, to the point that it is not a viable substitution. Class-B and class-C operation, however, remain viable alternatives for area savings without a large drop in efficiency and output power

Highly Sensitive Readout Interface for Real-Time Differential Precision Measurements with Impedance Biosensors

Field deployment is critical to developing numerous sensitive impedance transducers. Precise, cost-effective, and real-time readout units are being sought to interface these sensitive impedance transducers for various clinical or environmental applications. This paper presents a general readout method with a detailed design procedure for interfacing impedance transducers that generate small fractional changes in the impedance characteristics after detection. The emphasis of the design is obtaining a target response resolution considering the accuracy in real-time. An entire readout unit with amplification/filtering and real-time data acquisition and processing using a single microcontroller is proposed. Most important design parameters, such as the signal-to-noise ratio (SNR), common-mode-to-differential conversion, digitization configuration/speed, and the data processing method are discussed here. The studied process can be used as a general guideline to design custom readout units to interface with various developed transducers in the laboratory and verify the performance for field deployment and commercialization. A single frequency readout unit with a target 8-bit resolution to interface differentially placed transducers (e.g., bridge configuration) is designed and implemented. A single MCU is programmed for real-time data acquisition and sine fitting. The 8-bit resolution is achieved even at low SNR levels of roughly 7 dB by setting the component values and fitting algorithm parameters with the given methods

Positionally-independent and extended read range resonant sensors applied to deep soil moisture monitoring

Here we detail an inductively coupled extender (ICE) and resonant (LC) sensor to monitor soil moisture using a portable reader. Significant advances of this ICE-LC design are extending typical LC sensor read range over a meter and reducing positional alignment sensitivity between reader and sensor. An analytical model validates the working principle and feasibility of the ICE-LC system. Prototypes of the ICE-LC sensor were built and optimized in terms of sensitivity and power transfer (single and four turns for ICE top and bottom coils, respectively). Soil moisture tests validated the ICE-LC improvements on minimized positional alignment sensitivity and extended read range, transducing a decrease in resonant frequency with increasing soil moisture. When calibrating with existing wired approaches, the ICE-LC sensor had a reproducible, linear sensor gain of 4.52%moisture content/MHz with an R2 of 0.745 and RMSE of 2.41%. A smaller, planar form factor of the ICE-LC sensor was also tested and exhibited reduced positional alignment sensitivity between reader and sensor at shorter read ranges. This initial study demonstrates the feasibility of the ICE-LC resonant sensor as a cost-effective method to monitor soil moisture content throughout the growing season at many field locations.This is a manuscript of an article published as Chan, Yee Jher, Adam R. Carr, Subhanwit Roy, Caden M. Washburn, Nathan M. Neihart, and Nigel F. Reuel. "Positionally-independent and extended read range resonant sensors applied to deep soil moisture monitoring." Sensors and Actuators A: Physical 333 (2022): 113227. DOI: 10.1016/j.sna.2021.113227. Copyright 2021 Elsevier B.V. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). Posted with permission