David Novotny

Power consumption plays a pivotal role in a variety of applications that use magnetometers (e.g., space applications, wearables, $\text {drones}, \ldots $ ). In this article, a novel approach to reduce power consumption in magnetometers is proposed. We primarily focus on the anisotropic magneto-resistance (AMR) based magnetometer, which was subjected to a series of tests. Nevertheless, this algorithm is broadly applicable to any magnetometer that employs a fast-enough feedback compensation. In precise magnetometers, feedback compensation is almost always utilized to obtain stability and linearity. Traditionally, this feedback compensation remains active for the entire duration the magnetometer is powered on. We propose an algorithm that disables this feedback for the majority of the time and enables it briefly only when necessary. This approach leads to a significant reduction in power consumption (20%) while maintaining full accuracy and low noise.

An improvement in data processing utilizing gradient information rather than only homogenous field values and calibration of the response of each individual sensor in the AMR sensor array yields significant improvement in positioning accuracy (from about +/−3 to +/−0.6 mm) of a piston-like apparatus with ferromagnetic piston rod. The approach uses low-frequency ac excitation from an external coil allowing sensing through a 2 mm thick aluminum wall.

Characterizing the noise and long-term offset stability of a fluxgate sensor are two of many important tasks during its development and manufacturing. For this purpose, it is advantageous to use synchronous demodulation realized by a lock-in amplifier. Commercial lock-in amplifiers are very complex, expensive, bulky, and frequently generate unpleasant acoustic noise. Additionally, these instruments are often heavily utilized in the lab. We, thus, present the development and testing of a specific instrument tailored for fluxgate sensor measurements. It combines a low-noise data acquisition front-end module with an excitation unit featuring variable parameters (frequency, H-bridge voltage) and a precise feedback current source module for possible closed-loop operation. With this configuration, it forms a single-axis digital magnetometer with up to 26-bit resolution. Furthermore, a Cyclone V FPGA development kit controls all the modules and performs the necessary signal processing. The presented lock-in amplifier uses only internal signal reference coupled with excitation unit signals – a solution that greatly simplifies the design. The user interface is based on LabVIEW software and provides real-time signal and spectrum charts. The results of the instrument’s characterization as well as the testing of a race-track fluxgate sensor are presented herein.

In this paper, we present research, development, calibration and characterization of a novel concept of a digitally compensated, low-noise magnetometer based on anisotropic magnetoresistance sensors that is suitable for space applications. The main idea of the design was to reduce the number of precise analog components while using the digital signal processing power available in a modern microcontroller. Our most recent effort targeted lowering power consumption, enhancement of radiation hardness and overall improvement of the parameters. The principle of operation is presented in detail, along with a detailed description of the instrumentation used to characterize the real instrument, including its noise, linearity, and temperature stability in the range of -20 to +70 °C. The results of total ionizing dose (TID) testing at a gamma-ray irradiation facility are discussed at the complete magnetometer and part levels. This is an extended version of a paper presented at I2MTC 2020 that contains the results of a second radiation test done with a slightly modified design. The instrument worked well throughout the entire irradiation session (TID of 1.05 kGy over 72 hours), and the stability of main parameters was very good (50 pT/Gy offset and 1 ppm/Gy sensitivity stability).

The article presents testing of a miniature fluxgate sensor developed and manufactured by Texas Instruments as well as an application of the sensor in a compact magnetic field probe with USB interface and LabView based software. Several basic properties of the sensor were evaluated and compared with the datasheet specifications. Offset stability measurements have indicated some possible problems for applications that require very high DC and low-frequency precision. Jumps in offset were present for some of the devices, frequency and duty of the jumps varying between individual pieces and with respect to the supply voltage. Magnetic probe for fast and handy measurements of DC and AC (up to 30 kHz) magnetic fields (up to ±1 mT) is also presented. The probe contains 24-bit analog to digital converter, microcontroller and high-speed USB interface which allows a live view of the signal in time and spectral charts. The probe proved to be very useful for the DRV425 debugging, application development, EMC measurements and magnetic field demonstrations activities.

This paper considers the possibilities of using digital feedback for precise anisotropic magneto-resistance (AMR) magnetometers using commercial off-the-shelf (COTS) components. Requiring only a few analog parts, most of the signal processing is done digitally within an STM32 microcontroller. Because most of the precision is made by the feedback circuit, the analog-to-digital converter (ADC) can be a low-cost type. The compensation source is made with a pulsewidth modulation-driven H-bridge sourced from a voltage reference, so the cost reduction when compared to a “full-analog” design is large. The demodulation of a flipped-AMR signal is done with software after the AD conversion because it improves the offset stability and brings the reduction of the preamp's and ADC's LF noise. This paper presents the full characterization of a real instrument, including its noise, linearity, stability, and power consumption.