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Many variable-capacitance energy harvesters employ a large inductor to improve their power efficiency by reducing conduction losses, which is suboptimal in applications requiring a small form-factor, such as in implants. This article describes a variable-capacitance harvester that performs optimally using miniaturized inductors. The impact of scaling the inductor on the generated energy of conventional semisynchronous and fully-synchronous charge-constraint topologies is investigated analytically as well as experimentally. It is shown that the proposed harvester outperforms the semisynchronous and fully-synchronous charge-constraint harvesters while using very small inductance values. Using two reservoir capacitors to generate energy without requiring large inductors, as well as utilizing a different switching scheme are the main factors contributing to this advantage. Since harvesting energy from slow moving mechanical sources, such as body movements, constitutes a major challenge, all three harvesters are implemented and tested with an actuating frequency as low as 0.5 Hz and for inductance values between 1 $\mu$ H to 1 mH. The experimental results for sample designs corroborate the analytical expressions and show that to generate optimal harvested energy of the proposed harvester, the semisynchronous harvester requires a 15.6 times larger inductor.

This letter presents a methodology to model the effect of electromagnetic interference (EMI) on the wireline communication channels. The proposed simulation methodology incorporates the effect of EMI on the circuit during the design phase in EMI-sensitive applications. It allows simple and faster EMI simulations at the SPICE level which minimizes the post-fabrication failures. A TEM (transverse electromagnetic) cell is used to emulate the effect of EMI on the test circuit as provided in the standard IEC-62132. An analytical model is presented to quantify the effect of induced voltage and current on a transmission line placed in the TEM cell. The developed model is experimentally verified for a frequency range of 1 MHz to 1 GHz. As an experimental study, the proposed model is used to validate the effect of EMI on the wireline communication channel transmitting a pseudorandom binary sequence (PRBS) data generated from an FPGA board at 1 Gbps data rate for a wide range of EMI powers and frequencies.

Time-of-flight (ToF) sensors using light pulses or continuous waves allow accurate distance measurements. Three-dimensional imagers can be based on an array of timing or time-gated integration pixels. Single-photon avalanche diodes (SPADs) have been increasingly chosen as the pixel’s photodetector device to develop fast, long-range ToF sensors. Solid-state ToF cameras are replacing other alternatives, showing attractive characteristics and bringing up new potential applications. This paper presents the technical evolution of SPAD ToF 3D imaging sensors, and provides insight into their development over the last few decades. Starting with the first SPAD imagers reported in the early 2000’s, various direct and indirect arrays up to present day state-of-the-art prototypes are referenced. The existing methods, options and possible implementations are described, addressing their advantages and drawbacks, and showing the progress yet to be made. The performance of the different presented approaches are given and compared.

In some specific microelectronic applications, there is a demand for adhesive materials (glues/encapsulants) having very good thermal insulation properties. We have studied the properties obtained on epoxy-based samples loaded by several levels of xerogel filling. The thermal conductivity of these materials depends on the exact chemical composition and their manufacturing process. As a result, the thermal conductivity given in the manufacturer’s specifications or in the literature generally exhibits some dispersion. Therefore, we have developed a straightforward experimental rig, based on a vacuum chamber and miniature Pt100 sensors measurements, to precisely know the thermal conductivity of the various insulating materials used in the development and the assembly of select microsensors and microsystems. The results showed a decrease in the thermal conductivity of our xerogel-epoxy composites up to 35.8% compared with the value of the unfilled epoxy, corresponding to a thermal conductivity value of 107.9 mW m−1 K−1. In addition, cross-sectional images were observed by optical microscopy to characterize the specific microstructure of each sample to relate these observations to improvements in thermal conductivity.

Continuous navigation information for medical insertion methods including wireless capsule endoscopy is an important feature to guide a medical instrument/object to the targeted location within a hollow organ or internal cavity of the patient in the best possible way. Also, an autonomous medical insertion or swallowable device with a self-contained navigation system would reduce the role of the high-level operator and hence reduce the human-factor mistake and risk of injury. The navigation techniques suggested for Wireless Capsule Endoscopy are image-based that are required to transfer and process a significant amount of data in real-time operation. This would increase the complexity of the system and would be more difficult in dark or liquid environments. A novel navigation system for Wireless Capsule Endoscopy/ordinary endoscopy that does not depend on any external source for operation and can handle the uncertainties of the path even in a dark or liquid environment ( i.e .mucosa) of the human body is presented in this paper. The key element of the system is based on a capacitive-based pressure sensor array mounted on the capsule with the shape of semi-hemisphere. The place of each node is arranged to represent the variation in the latitude and the longitude of the travelling path. The system can acquire the required information to navigate the capsule in three-dimensional space and enhance the safety of the locomotion by monitoring the pressure between the capsule and the ambient environment. The system determines the variation of the path 180° in longitude and latitude with less than (

Blood pressure (BP) is a critical vital sign in health, measured millions of times per day worldwide. Current BP measurement requires cumbersome tools, is painful and can be inconvenient. Non-invasive cuffless BP measurement based on pulse arrival time (PAT) techniques allow an alternative way of monitoring BP in healthcare settings with refined wearability and user-friendly features. PAT extraction requires at least two measurements, one as a time reference and another to obtain time delay; there are several approaches to calculate the PAT from various sensors placed on the body. Commonly used signals are electrocardiography (ECG) and photoplethysmography (PPG), which can be recorded from a patients body using more than two separate sensors attachment set-ups. In this work, cuffless BP calculation based on five different PAT readings using Bio-impedance (BImp) at the shoulder as an alternative to PPG, has been investigated. Sensor placement is on the patients chest; which hides them beneath the patient’s clothes making them more suitable for ambulatory monitoring systems. Technology performance was assessed using different postures, exercises and Glyceryl Trinitrate (GTN) spray doses; which provided stable, rising and falling BPs for evaluation. Data were collected from 41 participants who were sitting, standing and supine. Twenty-four of 41 participants undertook experiments including a handgrip task (isometric exercise), three periods of cycling on an exercise bike with light, moderate and heavy resistance settings and an observed rest period at the end. The remaining 17 of 41 subjects received GTN spray for predefined times with variable recovery periods afterwards. Different methods of PAT extraction from BImp data were compared for accuracy. Comparisons were made between PAT readings alone and PAT combined with Heart Rate and the combination model performed better when calculating BP. Simultaneously, data were collected using PPG-based PATs compared to BImp-based PATs. BImp-based PATs proved 3% more accurate than PPG-based PATs, demonstrating the potential superiority of BImp-based BP calculations.

This work presents the modeling and the experimental validation of a linear electromagnetic energy harvester (EMEH) actuated by random low-g external acceleration or by a very slow imposed movement. By combining these two different ways of energy scavenging, the system is particularly suited for powering wearable and biomedical electronic devices where the human-motion and movement can be considered as random and non predictable. The design is composed of a mobile stack of head-to-head ring-shaped permanent magnets in which a fixed wounded ferromagnetic core, composed of two coils, is located. A custom co-simulation is presented: a finite element analysis (FEA) and a one dimension (1D) two degrees of freedom (2DOF) system model. The FEA is used to optimize the geometry of the EMEH and its form factor, allowing an significative down-scaling. The 1D 2DOF model describes the dynamics of the EMEH in its real environment by considering all the leading mechanical and electrical parameters. The geometry can drastically change the behavior of the system as well as its dynamics: the goal of this double structure is to reduce the magnetic force exerted between the fixed part and the moving part while keeping the magnetic flux gradient in each coil as large as possible. This force was characterized experimentally by using a custom designed test bench, to validate the FEA results. It was observed that the maximum produced energy is reached when the system sweeps across different equilibrium positions rather than oscillating around a given stable position. The second degree of freedom helps the system to settle in a large number of equilibrium positions when submitted to random external accelerations and therefore broadens the frequency response of the EH. Results show a theoretical electrical power output (RMS) of 2 mW for a 10 cm3 cylindrical harvester submitted to a short external acceleration pulse of 27.5 m/s2.

Low-power wide-area network protocols, such as LoRa, Sigfox, and NB Internet of Things, have become a popular technology for long range and limited data communication. Those protocols have been optimized for low power consumption and offer competitive subscription prices. This article presents the development of an autonomous Sigfox sensor node capable of transmitting data collected by a range of sensors directly to the cloud. The device is powered by a solar cell and can transmit data every 5 min under cloudy conditions (

Micro-scale generators are becoming more popular for harvesting energy to power bio-implantable devices and sensor networks. Most electrostatic generators (ESGs) use constant capacitors as storage or reservoir components in conjunction with a variable capacitor. The main issue with some existing ESG topologies is that these capacitors deplete and discharge over time. This paper studies a typical ESG and derives the charge depletion problem mathematically. Subsequently, a new ESG capable of circumventing this problem is proposed. Closed-form formulas expressing the output voltage and generated power are derived and validated. The proposed ESG harvests 25% of the power that the mechanical energy source generates by actuating the variable capacitor when the maximum-to-minimum capacitance ratio of the variable capacitor is optimized. In the presented case study, the ESG generates 9.75 mW optimally when a variable capacitor with a maximum/minimum capacitance ratio of 39/ $9.75~\mu \text{F}$ is used for energy harvesting from a 1-Hz knee joint movement of a walking person. The overall volume of the ESG is estimated to be 125 mm3, and the variable capacitor is charged to 5 V at its maximum capacitance. A control mechanism and a self-starting circuit are presented for this ESG architecture, which allows it to generate any desired output voltage. This capability can be used to harvest the maximum available kinetic energy and compensate load variations.

This paper describes a hybrid mass sensing system comprising a QCM (quartz crystal microbalance) mass sensor operating under atmospheric pressure and a 3-DOF mode localized coupled resonator operating in vacuum. Nanoparticles as consecutive mass perturbations are added onto the QCM, the output signals with respect to the amount of mass change are then being manipulated to generate electrostatic forces. Subsequently, the electrostatic forces act on the 3-DOF mode localized coupled resonator as external stiffness perturbations. The output metrics of the hybrid system were defined as: the resonant frequency shifts, vibration amplitude changes, and the changes in resonance amplitude ratio. Measured data was analyzed for these metrics and compared. This work demonstrated that the proposed hybrid mass sensing system attained a ${2.5\times }10^{\text 6}{N}{(\text{m}\bullet \text{kg})}^{-1}$ mass to stiffness transduction factor, and has the potential to be employed as a direct liquid contact biochemical transducer.

We have developed a straightforward die-level thinning process suitable for Silicon-On-Insulator (SOI) dies. The process has been demonstrated on SOI CMOS die assembled on rigid and flexible PCBs using previously-developed anisotropic conductive adhesive flip-chip method. Unlike standard wafer-level thinning processes, in the demonstrated process the full thickness SOI die is directly mounted on PCB and after that thinned. The demonstrated process is simple and robust; it comprises fewer process steps compared to conventional die thinning process. The ultra-thinning process has no effects on the assembly integrity and device performance.

State of the art bioelectronic implants are using thin cables for therapeutic electrical stimulation. If cable insulation is thin, biological tissue surrounding cables can be unintentionally stimulated. The capacitance of the cable must be much less than the stimulating electrodes to ensure stimulating currents are delivered to the electrode-tissue interface. This work derives and experimentally validates a model to determine the capacitance of parallel cables implanted in biological tissue. Biological tissue has a high relative permittivity, so the capacitance of cabling implanted in the human body depends on cable insulation thickness. Simulations and measurements demonstrate that insulation thickness influences the capacitance of implanted parallel cables across almost two orders of magnitude: from 20 pF/m to 700 pF/m. The results are verified using four different methods: solving the Laplacian numerically from first principles, using a commercially available electrostatic solver, and measuring twelve different parallel pairs of wires using two different potentiostats. Cable capacitance simulations and measurements are performed in air, a porcine blood pool and porcine muscle tissue. The results do not differ by more than 30% for a given cable across simulation and measurement methodologies. The modelling in this work can be used to design cabling for minimally-invasive biomedical implants.

This paper proposes a wireless wearable sensor system for the continuous beat-to-beat blood pressure (BP) monitoring. The real-time BP can be estimated utilising a 2-parameter regression model based on the pulse arrival time (PAT) and heart rate (HR). The PAT is defined as the time interval between the electrocardiogram (ECG) R-peak and the corresponding maximum inclination point of photoplethysmography (PPG) signal. A wireless wearable sensor patch designed to be attached to the subject’s chest is used for the measurement of ECG and PPG signals. The sensor data are transmitted through a Bluetooth low energy (BLE) module to a computer for the real-time online estimation of BP. To verify the feasibility and performance of the proposed system, a 5-day period experiment is conducted on two healthy male subjects for the training and validation of the BP estimation model. On each day, there are two 15 minutes offline sessions for data collection from the sensor patch, which are compared with the reference BP to calibrate the estimation model parameters. After that, a 10 minutes online session is carried out to validate the regression model against the reference BP device. Eventually, the 5-day period data are combined together for an overall BP estimation model, which has good correlation (r=0.82) with the reference BP measurements. The experimental results show the proposed sensor patch with the BP estimation model is capable of the online real-time BP monitoring after an initial calibration procedure.

A wearable continuous beat-to-beat blood pressure (BP) monitoring system on the arm, based on a 4-channel photoplethysmography (PPG) array is presented in this paper. Three pulse transit time (PTT) values have been derived from the combinations of PPG signals from the sensors array. We evaluated the system on a group of 5 healthy male subjects. The result suggests that there is a strong correlation between the pulse wave velocity (PWV) derived from PPG signals of the sensors array and the reference systolic and diastolic BP. With the PPG-sensor array, PWV along the arm is divided into several segments. Therefore, more detailed PWV along the arm is found, which can potentially facilitate the accuracy of estimating BP based on the PWV principle.

Cuffless blood pressure (BP) estimation using pulse arrival time (PAT) has become popular in recent years. There are several approaches to calculate PAT from various sensors placed on the body. In this chapter, the shoulder’s bio-impedance (BImp) signal is used as a surrogate together with ECG to estimate cuffless systolic BP (SBP) based on four different PAT readings. Different BP trends have been experimentally validated for varying postures and physical exercises. Data was collected from 43 participants in supine, sitting, or standing postures. Among all these participants, 26 were asked to undertake light, moderate, and heavy cycling on an exercise bike. SBP calculation results using each PAT calculation have been compared in terms of estimation accuracy. Overall, the results of SBP calculation with PAT obtained from the maximum value of the first derivative of BImp pulse signal are at least 2% more accurate than other methods.

The power supply plays an important role in wireless sensor nodes because they are mainly powered by rechargeable batteries and require regular charging. For uninterrupted and convenient system design, energy harvesting for wearable devices is of great importance. This paper presents an indoor energy harvesting module designed for safety applications (called WE-Safe project). The whole system is designed and configured to consume minimum power. The energy harvesting module is able to harvest energy from ambient light at low illumination and store the energy into a super-capacitor. The energy harvesting module can provide sufficient power for sensing and data transmission via a LoRa network. In addition, the duty cycle can be adjusted automatically based on the current voltage level and light intensity.

The article addresses the development of highly sensitive, low-light and efficient, miniature single-photon sensor technology based on Single Photon Avalanche Diode (SPAD) arrays, its integration on a Flash Light Detection and Ranging (LiDAR) system mounted on a custom built multi-rotor Unmanned Aerial System (UAS) platform, for the collection of real time imagery and performance of neuromorphic processing for accurate target detection and classification.

This study presents a method of calculating the pre-ejection period (PEP) from simultaneous records of the electrocardiogram (ECG) and continuous wave radar (CWR). The PEP is derived as the interval between R-wave peak of ECG and the foot of CWR signal measured at the sternum. Data collected from 40 subjects participating in different postural experiments, mainly sitting, standing, and supine, has been analyzed. Among subjects, 23 were selected to participate in exercise experiments such as handgrip, light cycling, moderate cycling, heavy cycling, and recovery 1 and 2. The mean and standard deviation values of the PEP are presented for different postural and exercise conditions. The results of postures showed that the lowest PEP value (mean 47.24 ms) is obtained in supine posture and the highest PEP (mean 66.22 ms) is obtained in the standing situation. The PEP for sitting position (mean 64.8 ms) was between these two measurements; however, it was closer to standing. Different exercise tasks showed a significant effect of body activities on the measured PEP values. Any condition which increased cardiac activity led to decreasing PEP. This study indicates that CWR is a reliable noninvasive method to measure the PEP during daily activities.

We developed a low-cost process for assembling versatile sensors without expensive, thick metal finish on rigid and flexible PCB using anisotropic conductive films (ACF) flip-chip (FC) process. This allows a lower temperature budget than conventional FC assembly. The ACF FC process requires no expensive set up, is quick to implement and suits perfectly for sensor prototyping and low-scale manufacturing. The process was directly applied to assemble the bare die of a CMOS strain gauge sensor on flexible PCB without compromising its integrity.

Stents are a common biomedical device used to treat atherosclerosis, but they are typically passive and employ no electronics. This article details the design, fabrication, and testing of a miniaturized circuit board capable of telemetry via a stent antenna. The circuit is less than 1.1 mm in diameter making it sufficiently miniaturized to be delivered via a catheter. Experiments in porcine tissue achieved a data rate of 277 kb/s with a 280-MHz carrier. The implant was tested at depths of 3, 6, and 9 mm, requiring a transmitter power of 44, 48, and 63 mW, respectively, to operate, surpassing specifications reported in previous electronic stent-based works. These measurements confirm that stents incorporating a power and data link could be used to monitor biological indicators such as blood pressure, blood glucose, or even neural signals.

This paper presents two electromagnetic interference (EMI) resisting current mirror topologies that use a linearization technique to filter out the EMI without producing any offset at the output. A proposed current mirror illustrating the linearization concept is implemented in standard $\text{0.18}\;\mu \text{m}$ mixed-mode CMOS technology. Measurement results show that for a frequency range of 10 kHz–10 MHz, the EMI-induced offset current produced by the proposed current mirror is negligible as compared to the traditional current mirror.

This paper presents a unique methodology to calculate the filtering capacitances of the OpAmp already reported in the literature. The methodology aims to show that there is an optimal solution that can be used to increase the electromagnetic interference (EMI) immunity of any OpAmp for a wide range of frequencies. By using this proposed methodology, an OpAmp structure that reduces the EMI effect is designed in standard $0.18\ \mu \text{m}$ mixed-mode CMOS technology. Detailed mathematical analyses and simulation results are presented and discussed. Simulation results show that the maximum EMI-induced offset voltage in the frequency range from 1 MHz to 1 GHz for the OpAmp is 4.4 mV. In contrast, the standard Miller OpAmp exhibits a maximum EMI-induced offset voltage of 92.4 mV under the same operating conditions.