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1. A Miniaturized Highly Efficient Headstage Based Wireless Power Transfer (WPT) System for Optogenetic Stimulation of Freely Moving Animals

   https://doi.org/10.1109/DCAS51144.2020.9330642  

   Biswas, Dipon K. ; A Martinez, Jose H. ; Kaul, Ishani ; Kaul, Arnav ; Mahbub, Ifana ( November 2020 , 2020 IEEE 14th Dallas Circuits and Systems Conference (DCAS))

   For the treatment of chronic neuropathic diseases, long-term behavior study of the patient is very important. The behavior study is performed using neural stimulation and simultaneously recording the response from the neural cells. Headstage-based neuromodulation device has become one of the popular methods for neural stimulation in recent times. In this work, a wirelessly powered system is presented that provides constant power to a headstage based optogenetic stimulator, which includes a receiver (RX) coil, a rectifier, and an mm-sized light-emitting-diode (LED). A multi-layered transmitter (TX) coil is designed to provide uniform power transmission over the 20.7 cm × 14 cm mouse behavioral cage area. A maximum of ~49% efficiency is achieved using the proposed system at 3 cm distance through the air media at 13.56 MHz operating frequency. The proposed system uses less number of headstage resonators on the 3-D printed light-weight headstage which is able to achieve higher efficiency compared to the other state-of-the-art. 

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2. Wirelessly Powered 3-D Printed Headstage Based Neural Stimulation System for Optogenetic Neuromodulation Application

   https://doi.org/10.1109/JERM.2022.3225972  

   Biswas, Dipon K. ; Saha, Nabanita ; Mahbub, Ifana ( January 2023 , IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology)

   This work presents a miniaturized wireless power transfer (WPT) system integrated with a neuromodulation headstage for duty-cycled optical stimulation of freely moving rodents. The proposed WPT system is built using the commercially available off-the-shelf components (COTS) for the optogenetic neuromodulation system consisting of a bridge rectifier, a DC-DC converter, an oscillator circuit, an LED driver, and a μLED. The total power consumption of the stimulation system is 14 mW which is provided using the WPT method. The WPT system includes a novel transmitter (TX) coil implemented on a printed circuit board (PCB), and a solenoid receiver (RX) coil wrapped around a customized 3-D printed headstage. The proposed TX coil is designed in such a way that the magnetic field all across the TX coil is sufficient to provide the required power to the optical stimulation system that is worn as a headstage by the freely moving rat. The headstage device's dimension is 18.75 mm × 21.95 mm, weighing 4.75 g. The ratio of the weight of the headstage and rat is 4.75:300. The proposed system is able to achieve a maximum overall efficiency of ∼63% at 5 cm separation between the TX and RX coils, where the maximum power transfer efficiency (PTE) of the WPT system is ∼88% and the power conversion efficiency (PCE) of the rectifier is 71.6%. The proposed system with reconfigurable stimulation frequency is suitable for exciting different brain areas for long-term health monitoring. 

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3. Design, Modeling, and Simulation of a 2.4 GHz Near-field Phased-Array based Wireless Power Transfer System for Brain Neuromodulation Applications

   https://doi.org/10.1109/WMCS55582.2022.9866412  

   Saha, Nabanita ; Mahbub, Ifana ( April 2022 , 2022 IEEE Texas Symposium on Wireless and Microwave Circuits and Systems (WMCS))

   To avoid interruption of experiment and risk of infection, wireless power transfer (WPT) techniques have been used to eliminate the bulky wires and batteries attached to the animals in rodent electrophysiological applications for long-term in-vivo electrophysiological recordings. Headstage-based neuromodulation device has become one of the most popular methods for neural stimulation in recent times. In this work, a wireless power transfer system is designed which provides a constant power to a headstage based optogenetic stimulator. The proposed research is composed of two parts: i) a unidirectional 28 cm × 21 cm phased array transmitter antenna, and ii) an electrically small bi-directional 2.4 cm × 2.4 cm receiver antenna. A phased array transmitter antenna is designed to provide a uniform power transmission over the 27 cm × 23 cm × 16 cm rat behavioral cage area. The proposed WPT scheme utilizes a near-field power transmission scheme at 2.4 GHz frequency. Simulation results show that the transmitter antenna achieves a -24 dB and receiver antenna achieves a −27 dB return loss (S 11 ) at the resonating frequency. The proposed WPT system shows a maximum of 24.5% power transfer efficiency (PTE) when the receiver is in the center position and is 10 cm distance apart from the transmitter, which is much higher compared to the other state-of-the-art works. The transmitter antenna steers beam from −21° to 27° in ϕ axis and −108° to 74° in θ axis which covers the maximum 6.27 cm 2 area of the cage. The preliminary simulation results of the proposed WPT module show a better prospect for future optogenetics based applications. 

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4. Modeling and Optimization of the Steering Range of a Phased Array Antenna for Neuromodulation Applications in the Near-Field Region

   https://doi.org/10.1109/USNC-URSI52151.2023.10238083  

   Saha, Nabanita ; Mahbub, Ifana ( July 2023 , 2023 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (USNC-URSI))

   This paper presents modeling and optimization of the steering range of a microstrip planar phased array antenna to steer the unidirectional near-field focused beam towards a certain direction. This antenna can be implemented in headstage-based neural stimulation system and wireless recording system for optogenetic neuromodulation applications. The proposed phased-array antenna consists of sixteen elements that are designed to provide a uniform power transmission over the 27 cm×23 cm×16 cm rat behavioral cage area. The proposed transmitter (TX) antenna implements a near-field-based wireless power transmission system operating at 2.4 GHz frequency. The phased array antenna steers the beam from -30° to 60° in the elevation plane by feeding the individual elements with different phases using four 4-bit phase shifters. A design analysis of the beam-steering approach of the phased array antenna is presented and the corresponding simulation and measurement results are included in this paper. 

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5. Multichannel Electrophysiological Recording With Spike Detection and Sorting in a Duty-Cycled Wireless Optogenetic Headstage

   https://doi.org/10.1109/JSEN.2023.3313520  

   Tasneem, Nishat T. ; Biswas, Dipon K. ; Reza, Sakib ; Becker, April ; Mahbub, Ifana ( November 2023 , IEEE Sensors Journal)

   Neural signal recording and optical stimulation using implantable devices have become a ubiquitous method to treat brain disorders, yet there lie some shortcomings, such as size, weight, and functionalities of the implants. This work presents a commercial off-the-shelf (COTS) component-based miniaturized wireless optogenetic headstage with simultaneous optical stimulation and electrophysiological recording for freely moving rats. The system includes a battery-based neural stimulator consisting of a low-dropout (LDO) regulator, an oscillator, and a μ LED. The electrophysiological signal recording system includes an intracortical neural probe implemented on a shape memory polymer (SMP) substrate, an array of neural amplifiers with an integrated analog-to-digital converter (ADC), a transceiver IC, and a ceramic antenna. A digital sub-1-GHz transceiver integrated with a low-power microcontroller (MCU) is used to transmit the acquired neural data to a remote receiver unit, followed by offline spike detection and sorting in LabVIEW. The front-end recording amplifiers provide a gain of 45.7 dB with the input-referred noise of 2.4μVrms . The integrated multiplexer (MUX) with the ADC allows sampling of the amplified voltage at a configurable sampling rate of 160–480 kSamples/s. The total power consumption of the stimulation and the recording system is 23 mW. The dimension of the headstage device is 13.5×21.3 mm, weighing 4 g without the battery. The system is experimentally validated in an in vivo setting by placing the headstage on the head of a male rat and recording the neural signals from the ventral tegmental area (VTA) of the brain. This integrative neural signal recording and spike sorting approach would be useful for the development of a closed-loop neuromodulation system. 

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