Wireless Power Transfer for Autonomous Wearable Neurotransmitter Sensors

Abstract

In this paper, we report a power management system for autonomous and real-time monitoring of the neurotransmitter L-glutamate (L-Glu). A low-power, low-noise, and high-gain recording module was designed to acquire signal from an implantable flexible L-Glu sensor fabricated by micro-electro-mechanical system (MEMS)-based processes. The wearable recording module was wirelessly powered through inductive coupling transmitter antennas. Lateral and angular misalignments of the receiver antennas were resolved by using a multi-transmitter antenna configuration. The effective coverage, over which the recording module functioned properly, was improved with the use of in-phase transmitter antennas. Experimental results showed that the recording system was capable of operating continuously at distances of 4 cm, 7 cm and 10 cm. The wireless power management system reduced the weight of the recording module, eliminated human intervention and enabled animal experimentation for extended durations.

Keywords: L-glutamate sensors; multi-transmitter antenna; neurotransmitter sensor recorder; wireless power transmission.

Figure 1

(a) Scanning electron microscopy (SEM) photo of the probe tip indicating two working electrodes (WE), two self-reference electrodes (SRE) and a reference electrode (RE) [4]; (b) A photo of the assembled devices with the probe lengths of 7 and 12 mm [4].

Figure 2

Photo of the neurotransmitter sensor recording device with a dimension of 25 × 27 × 6 mm³. The module included multi-stage amplifiers and a system-on-chip (SoC) processor with an integrated radio-frequency (RF) transceiver.

Figure 3

Block diagram of the wireless power harvester for the wearable neurotransmitter sensor module.

Figure 4

Illustration of the experiment setup with a freely-moving rat wearing the neurotransmitter sensor module inside an acrylic box with a dimension of 40 × 40 × 15 cm³.

Figure 5

Radiation patterns of the normal field components H_z generated by the transmitter (TX) spiral antenna at different distances z of (a) 4, (b) 7, (c) 10 and (d) 11 cm.

Figure 6

Measured load voltages at different distances z of (a) 4; (b) 7; (c) 10 and (d) 11 cm when a load of 745 Ω was connected to the receiver side.

Figure 7

Angular misalignment θ between the TX and receiver (RX) antennas.

Figure 8

Measured load voltages at different distances z = 4, 7, 10 cm when a load of 745 Ω was connected to the receiver side. (a) The angle θ between the TX and RX antennas was 90°. Measured load voltages at the planes of y = 0 cm and (b) z = 4 cm; (c) z = 7 cm; and (d) z = 10 cm; with different angular misalignment θ = 0°, 30°, 60° and 90°.

Figure 9

Two identical TX antennas were arranged 20 cm apart driven by the same power supply and identical amplifier circuitry.

Figure 10

Simulation of the normal component of magnetic fields at a distance z = 4 cm from the two TX antennas when two antennas were (a) in-phase and (b) out-of-phase.

Figure 11

Measured load voltages at different planes at z = 4, 7 and 10 cm when using two TX antennas were (a) in-phase and (b) out-of-phase.

Figure 12

Simulation of the normal component of magnetic fields at a distance z = 4 cm from (a) three TX antennas; and (b) four TX antennas.

Figure 13

(a) Electrical current response of the L-Glu sensor which were wirelessly recorded with the neurotransmitter sensor module powered by the WPT system; (b) Calibration curve shows a sensitivity of 1.7 pA/µM with standard deviation (SD) less than 6.7 pA.