Analysis and Design of Coupled Inductive Bridges for Magnetic Sensing Applications

Abstract

This paper presents the analysis and design of a novel magnetic sensor. We study the underlying physics of inductance shift sensors as a special case of the broader family of magnetic energy deviation sensors. The result is a quantitative definition of performance metrics with all assumptions and approximations explicitly stated. This analysis is then used to design a modified ac Wheatstone bridge that uses two inductorpairs in a cross-coupled configuration, to half its size and double its transducer gain while maintaining a fully differential structure with a matched frequency response. A proof-of-concept sensor was fabricated with peripheral circuitry in a 65-nm bulk CMOS process to operate between 770 and 1450 MHz with an effective sensing area of 200 μm × 200 μm. The new bridge sensor is fully characterized at a frequency of 770 MHz and demonstrates a reliable and continuous detection of 4.5-μm iron-oxide magnetic beads over time periods longer than 30 min, appreciably longer than previously reported works.

Effect of the Coil Excitation Method on the Performance of a Dual-Coil Inductive Displacement Transducer

“…The dual-coil series three-wire (DCSTW) excitation method applies an excitation signal to both ends of the transducer, and the public terminal and the negative terminal of the excitation signal are used as outputs [ 26 ], as shown in Figure 8 . Vin is the excitation signal, and Vout is the output signal.…”

The next generation of hybrid microfluidic/integrated circuit chips: recent and upcoming advances in high-speed, high-throughput, and multifunctional lab-on-IC systems

“…3D) with two channels that successively measure passing cells at 0.9 GHz and 2.6 GHz. 75,76 Instead of using an oscillator for readout (which measures the shift in the resonator's stored energy and therefore is only sensitive to the particle's susceptibility magnitude 77 ), the chip measures cells by observing their effect on the coupling between two on-chip concentric coils, realizing an integrated transformer. Both the magnitude and phase of the MNP label susceptibility can be extracted using a quadrature receiver to downconvert the GHz signals to low frequencies for detection (Fig.…”