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1. A self-powered wireless motion sensor based on a high-surface area reverse electrowetting-on-dielectric energy harvester

   https://doi.org/10.1038/s41598-022-07631-4  

   Tasneem, Nishat T.; Biswas, Dipon K.; Adhikari, Pashupati R.; Gunti, Avinash; Patwary, Adnan B.; Reid, Russell C.; Mahbub, Ifana (December 2022, Scientific Reports)

   Abstract This paper presents a motion-sensing device with the capability of harvesting energy from low-frequency motion activities. Based on the high surface area reverse electrowetting-on-dielectric (REWOD) energy harvesting technique, mechanical modulation of the liquid generates an AC signal, which is modeled analytically and implemented in Matlab and COMSOL. A constant DC voltage is produced by using a rectifier and a DC–DC converter to power up the motion-sensing read-out circuit. A charge amplifier converts the generated charge into a proportional output voltage, which is transmitted wirelessly to a remote receiver. The harvested DC voltage after the rectifier and DC–DC converter is found to be 3.3 V, having a measured power conversion efficiency (PCE) of the rectifier as high as 40.26% at 5 Hz frequency. The energy harvester demonstrates a linear relationship between the frequency of motion and the generated output power, making it highly suitable as a self-powered wearable motion sensor. 

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2. Self-Powered Motion Tracking Sensor Integrated with Low-Power CMOS Circuitry

   https://doi.org/10.1109/ISCAS51556.2021.9401440  

   Tasneem, Nishat T.; Biswas, Dipon K.; Mahbub, Ifana; Adhikari, Pashupati R.; Reid, Russell (May 2021, 2021 IEEE International Symposium on Circuits and Systems (ISCAS))

   null (Ed.)

   This paper presents a motion-sensing device with the capability of harvesting energy from low-frequency motion activities that can be utilized for long-term human health monitoring. The energy harvester used in the proposed motion sensor is based on the mechanical modulation of liquid on an insulated electrode, which utilizes a technique referred to as reverse electrowetting-on-dielectric (REWOD). The generated AC signal from the REWOD is rectified to a DC voltage using a Schottky diode-based rectifier and boosted subsequently with the help of a linear charge-pump circuit and a low-dropout regulator (LDO). The constant DC voltage from the LDO (1.8 V) powers the motion-sensing read-out circuitry, which converts the generated charge into a proportional output voltage using a charge amplifier. After amplification of the motion data, a 5-bit SAR-ADC (successive-approximation register ADC) digitizes the signal to be transmitted to a remote receiver. Both the CMOS energy harvester circuit including the rectifier, the charge-pump circuit, the LDO, and the read-out circuit including the charge amplifier, and the ADC is designed in the standard 180 nm CMOS technology. The amplified amplitude goes up to 1.76 V at 10 Hz motion frequency, following linearity with respect to the frequency. The generated DC voltage from the REWOD after the rectifier and the charge-pump is found to be 2.4 V, having the voltage conversion ratio (VCR) as 32.65% at 10 Hz of motion frequency. The power conversion efficiency (PCE) of the rectifier is simulated as high as 68.57% at 10 Hz. The LDO provides the power supply voltage of 1.8 V to the read-out circuit. The energy harvester demonstrates a linear relationship between the frequency of motion and the generated output power, making it suitable as a self-powered wearable motion sensor. 

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3. Output encoding for cochlear signal analysis

   https://doi.org/10.1109/BioCAS.2015.7348408  

   Wang, Yingying; Mandal, Soumyajit (October 2015, Biomedical Circuits and Systems Conference (BioCAS), 2015 IEEE)

   The biological inner ear, or cochlea, is an amazing sensor that performs auditory frequency analysis over an ultra-broadband frequency range of ~20 Hz to 20 kHz with exquisite sensitivity and high energy efficiency. Electronic cochlear models, which mimic the exponentially-tapered structure of the biological inner ear using transmission lines or filter cascades, have been shown to be fast and extremely efficient spectrum analyzers at both audio and radio frequencies (RF). Here we present improved output encoding methods for such cochlea-like analyzers. We have developed neuron-like asynchronous event-generation circuits to efficiently encode cochlear outputs, including ring-oscillator-based injection-locked frequency dividers (ILFDs) that accurately encode input frequencies and phase-sensitive detectors that encode both amplitude and phase information and thereby improve frequency resolution without reducing temporal resolution. 

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4. A Highly Efficient Dual-band Harmonic-tuned GaN RF Synchronous Rectifier with Integrated Coupler and Phase Shifter

   https://doi.org/10.1109/MWSYM.2019.8700900  

   Hoque, Md Aminul; Ali, Sheikh Nijam; Mokri, Mohammad Ali; Gopal, Srinivasan; Chahardori, Mohammad; Heo, Deukhyoun (June 2019, 2019 IEEE MTT-S International Microwave Symposium (IMS))

   This paper presents a dual-band RF rectifying circuit for wireless power transmission at 1.17 GHz and 2.4 GHz. A dual-band harmonic-tuned inverse-class F/class-F mode power amplifier using a 10 W GaN device has been utilized to implement the proposed rectifier with an on-board coupler and phase shifter. The matching circuit is precisely designed so that the circuit operates in inverse class F and class F mode in the lower and upper frequency bands using dual-band harmonic tuning, respectively. Measurement results show that the rectifier circuit has 78% and 76% efficiencies at 1.17 GHz and 2.4 GHz frequency bands, respectively. To the best of the authors' knowledge, this rectifier is the first demonstration of a dual-band harmonic-tuned synchronous rectifier using a GaN HEMT device with an integrated coupler and phase-shifter for a watt-level RF input power. 

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5. An Additively Manufactured Novel RFID-Based 3-D Printed Leaf Moisture Sensor for Smart Farming

   https://doi.org/10.1109/JSEN.2025.3562607  

   Maiti, Srabana; Mirazur_Rahman, Md; Dey, Shuvashis (June 2025, IEEE Sensors Journal)

   This work presents the design, analysis, and experimental validation of a novel chip-based 3-D printed ultra-high frequency (UHF) radio frequency identification (RFID) sensor designed for leaf moisture detection for smart farming applications. The presented sensor is designed to operate at a frequency of 915 MHz and utilizes an integrated circuit (IC) chip having a specified impedance of 18.06−j164 Ω at 915 MHz. The proposed sensor is fabricated by the state-of-the-art Nano Dimension DragonFly IV 3-D printer. The 3-D printer uses both dielectric and conductive inks in a single printer for producing additive manufactured electronics (AME). The performance of the sensor is validated by experiments conducted on Valley Oak, Japanese tree lilac, and Crabapple leaf samples. The sensor’s functionality is based on its ability to detect variations in the dielectric properties of leaves, which are caused by changes in moisture content. This is achieved by analyzing the radio frequency (RF) backscattered signal, measured in terms of the received signal strength indicator (RSSI) levels, using a standard RFID reader. Experimental results demonstrate a consistent linear relationship between RSSI levels and leaf moisture content that is used to obtain a calibration curve that can accurately determine unknown moisture levels. By integrating advanced fabrication techniques with reliable RF sensing mechanisms, this work offers a sustainable, and scalable solution for monitoring plant health and optimizing agricultural productivity. 

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