Sensitivity Enhancement of an Inductively Coupled Local Detector Using a HEMT‐Based Current Amplifier

Abstract

Purpose To improve the signal transmission efficiency and sensitivity of a local detection coil that is weakly inductively coupled to a larger receive coil. Methods The resonant detection coil is connected in parallel with the gate of a HEMT transistor without impedance matching. When the drain of the transistor is capacitively shunted to ground, current amplification occurs in the resonator by feedback that transforms a capacitive impedance on the transistor’s source to a negative resistance on its gate. Results High resolution images were obtained from a mouse brain using a small, 11 mm diameter surface coil that was inductively coupled to a commercial, phased array chest coil. Although the power consumption of the amplifier was only 88 µW, 14 dB gain was obtained with excellent noise performance. Conclusion An integrated current amplifier based on a High Electron Mobility Transistor (HEMT) can enhance the sensitivity of inductively coupled local detectors when weakly coupled. This amplifier enables efficient signal transmission between customized user coils and commercial clinical coils, without the need for a specialized signal interface.

Sensitivity Analysis of the Simply Noise-matched Receiving Coil for NMR Experiments

“…For our example the value ܸ = 10 ି V has been adopted. Other quantities: ݂ = 4.45 ‫ݖܪܯ‬ ܳ = 250 is quality factor of the unloaded coil ܺ = ߱ ‫ܮ‬ = 75 Ω is reactance of the coil ܴ ௨௧ is output resistance of the tuning and matching circuit, corresponding to ܴ ܴ = ఠ బ ொ is resistance of the unloaded coil Values of the capacitances ‫ܥ‬ ଵ and ‫ܥ‬ ଶ are given by (10) and (11): Auxiliary voltage ܸ ଷ is given by (12):…”

Analysis of NMR Signal for Static Magnetic Field Standard

“…Significant part of the NMR equipment are the RF coils. Many authors studied arrangements of coils to improve the resulting sensitivity [7], [8]. Authors [9]- [11] present different experiments based on the NMR technique.…”

Calibration of NMR Receiver using Spectrometer Characteristics

“…A quality coil system can solve many problems [6], [7]. If using a commercial NMR scanner, the RF coils are the only facility which can be changed [8], [9]. Experiments may be based on presentation of a new technique which solves problems independently of the scanner or it can be part of it [10]- [13].…”