31 research outputs found
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
Time-Domain Analysis of Optimum Bias Point in Inverse Class-F Power Amplifiers
The optimum bias point for an inverse class-F power amplifier is discussed in this paper from a time-domain point of view. It is shown that the inverse class-F power amplifier should be biased in shallow triode region where the bias current is slightly higher than DC current when driven into compression. Lower bias currents can cause significant efficiency degradation due to peaking in the drain-source voltage. Simulation results show that drain efficiency at 6dB over drive drops from 83.4% to 65.2% when bias current is reduced by 34% from optimum bias current. Moreover, it is shown that if the bias current is too high, then the efficiency under power back off is reduced
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
Towards Wireless Characterization of Solvated Ions with Uncoated Resonant Sensors
Uncoated resonant sensors are presented here for wireless monitoring of solvated ions, with progress made toward monitoring nitrates in agricultural runoff. The sensor, an open-circuit Archimedean coil, is wirelessly interrogated by a portable vector network analyzer (VNA) that monitors the scattering parameter response to varying ionic concentrations. The sensor response is defined in terms of the resonant frequency and the peak-to-peak amplitude of the transmission scattering parameter profile (|S21|). Potassium chloride (KCl) solutions with concentrations in the range of 100 nM – 4.58 M were tested on nine resonators having different length and pitch sizes to study the effect of sensor geometry on its response to ion concentration. The resonant sensors demonstrated an ion-specific response, caused by the variations in the relative permittivity of the solution, which was also a function of the resonator geometry. A lumped circuit model, which fit the experimental data well, confirms signal transduction via change in solution permittivity. Also, a ternary ionic mixture (composed of potassium nitrate (KNO3), ammonium nitrate (NH4NO3), and ammonium phosphate (NH4H2PO4)) response surface was constructed by testing 21 mixture variations on three different sensor geometries and the phase and magnitude of scattering parameters were monitored. It was determined that the orthogonal responses presented by resonant sensor arrays can be used for quantifying levels of target ions in ternary mixtures. Applications of these arrays include measuring the concentration of key ions in bioreactors, human sweat, and agricultural waters. Preliminary results are shown for calibration standards and real waterway samples in Iowa, USA