Haluk Kulah

Energy Scavenging From Low-Frequency Vibrations by Using Frequency Up-Conversion for Wireless Sensor Applications

This paper presents an electromagnetic (EM) vibration-to-electrical power generator for wireless sensors, which can scavenge energy from low-frequency external vibrations. For most wireless applications, the ambient vibration is generally at very low frequencies (1-100 Hz), and traditional scavenging techniques cannot generate enough energy for proper operation. The reported generator up-converts low-frequency environmental vibrations to a higher frequency through a mechanical frequency up-converter using a magnet, and hence provides more efficient energy conversion at low frequencies. Power is generated by means of EM induction using a magnet and coils on top of resonating cantilever beams. The proposed approach has been demonstrated using a macroscale version, which provides 170 nW maximum power and 6 mV maximum voltage. For the microelectromechanical systems (MEMS) version, the expected maximum power and maximum voltage from a single cantilever is 3.97 muW and 76 mV, respectively, in vacuum. Power level can be increased further by using series-connected cantilevers without increasing the overall generator area, which is 4 mm2. This system provides more than an order of magnitude better energy conversion for 10-100 Hz ambient vibration range, compared to a conventional large mass/coil system.

Noise analysis and characterization of a sigma-delta capacitive microaccelerometer

This paper reports a high-sensitivity low-noise capacitive accelerometer system with one micro-g//spl radic/Hz resolution. The accelerometer and interface electronics together operate as a second-order electromechanical sigma-delta modulator. A detailed noise analysis of electromechanical sigma-delta capacitive accelerometers with a final goal of achieving sub-/spl mu/g resolution is also presented. The analysis and test results have shown that amplifier thermal and sensor charging reference voltage noises are dominant in open-loop mode of operation. For closed-loop mode of operation, mass-residual motion is the dominant noise source at low sampling frequencies. By increasing the sampling frequency, both open-loop and closed-loop overall noise can be reduced significantly. The interface circuit has more than 120 dB dynamic range and can resolve better than 10 aF. The complete module operates from a single 5-V supply and has a measured sensitivity of 960 mV/g with a noise floor of 1.08 /spl mu/g//spl radic/Hz in open-loop. This system can resolve better than 10 /spl mu/g//spl radic/Hz in closed-loop.

An electromagnetic micro power generator for low-frequency environmental vibrations

This paper presents an electromagnetic (EM) vibration-to-electrical power generator which can efficiently scavenge energy from low-frequency external vibrations. The reported generator up-converts low-frequency environmental vibrations to a much higher frequency through a novel electro-mechanical frequency up-converter using a magnet, and hence provides efficient energy conversion even at low frequencies. Power is generated by means of electromagnetic induction using a magnet and coils on top of resonating cantilever beams. The expected maximum power from a single cantilever is 2.5 /spl mu/W in vacuum. The proposed system has been tested in milliscale and the frequency up-conversion technique has been verified.

A monolithic three-axis micro-g micromachined silicon capacitive accelerometer

A monolithic three-axis micro-g resolution silicon capacitive accelerometer system utilizing a combined surface and bulk micromachining technology is demonstrated. The accelerometer system consists of three individual single-axis accelerometers fabricated in a single substrate using a common fabrication process. All three devices have 475-/spl mu/m-thick silicon proof-mass, large area polysilicon sense/drive electrodes, and small sensing gap (<1.5 /spl mu/m) formed by a2004 sacrificial oxide layer. The fabricated accelerometer is 7/spl times/9 mm/sup 2/ in size, has 100 Hz bandwidth, >/spl sim/5 pF/g measured sensitivity and calculated sub-/spl mu/g//spl radic/Hz mechanical noise floor for all three axes. The total measured noise floor of the hybrid accelerometer assembled with a CMOS interface circuit is 1.60 /spl mu/g//spl radic/Hz (>1.5 kHz) and 1.08 /spl mu/g//spl radic/Hz (>600 Hz) for in-plane and out-of-plane devices, respectively.

An Electromagnetic Micro Power Generator for Low-Frequency Environmental Vibrations Based on the Frequency Upconversion Technique

This paper presents a microelectromechanical-system-based electromagnetic vibration-to-electrical power generator that can harvest energy from low-frequency external vibrations. The efficiency of vibration-based harvesters is proportional to excitation frequency, so the proposed generator is designed to convert low-frequency environmental vibrations to a higher frequency by employing the frequency upconversion (FupC) technique. It has been shown that the generator can effectively harvest energy from environmental vibrations of 70-150 Hz and generates 0.57-mV voltage with 0.25-nW power from a single cantilever by upconverting the input vibration frequency of 95 Hz-2 kHz. The fabricated generator size is 8.5×7×2.5 mm3, and a total of 20 serially connected cantilevers have been used to multiply the generated voltage and power. The generator demonstrated in this paper is designed for the proof of concept, and the power and voltage levels can further be increased by increasing the number of cantilevers or coil turns. The performance of the generator is also compared with that of a same sized custom-made traditional magnet-coil-type generator and with that of a traditional generator from the literature to prove its effectiveness.

Precision readout circuits for capacitive microaccelerometers

This paper presents a review of capacitive readout front-end circuits for high-precision accelerometers. The primary design parameters and the trade-offs affecting the resolution are presented. The discussions apply to all capacitive microsensor interfaces. Also, a high-sensitivity capacitive accelerometer interface circuit for hybrid-integration with a surface/bulk micromachined micro-g accelerometer is described. The first generation of the circuit resolves 75 aF of capacitance on /spl sim/120 pF parasitic capacitance with a 200 kHz sampling rate, and the second generation resolves 20 aF with 1 MHz sampling rate. The overall sensor-circuit module has a noise floor of 1.6 /spl mu/g//spl radic/Hz at ambient atmosphere.

An in-plane high-sensitivity, low-noise micro-g silicon accelerometer with CMOS readout circuitry

A high-sensitivity, low-noise in-plane (lateral) capacitive silicon microaccelerometer utilizing a combined surface and bulk micromachining technology is reported. The accelerometer utilizes a 0.5-mm-thick, 2.4/spl times/1.0 mm/sup 2/ proof-mass and high aspect-ratio vertical polysilicon sensing electrodes fabricated using a trench refill process. The electrodes are separated from the proof-mass by a 1.1-/spl mu/m sensing gap formed using a sacrificial oxide layer. The measured device sensitivity is 5.6 pF/g. A CMOS readout circuit utilizing a switched-capacitor front-end /spl Sigma/-/spl Delta/ modulator operating at 1 MHz with chopper stabilization and correlated double sampling technique, can resolve a capacitance of 10 aF over a dynamic range of 120 dB in a 1 Hz BW. The measured input referred noise floor of the accelerometer-CMOS interface circuit is 1.6/spl mu/g//spl radic/Hz in atmosphere.

Noise analysis and characterization of a sigma-delta capacitive silicon microaccelerometer

This paper reports a high-sensitivity low-noise capacitive accelerometer system with one micro-g//spl radic/Hz resolution. The system operates as a 2/sup nd/-order electromechanical /spl Sigma/-/spl Delta/ modulator together with the interface electronics. A detailed noise analysis of electromechanical /spl Sigma/-/spl Delta/ capacitive accelerometers with a final goal of achieving sub-/spl mu/g resolution is also presented. The circuit has more than 120 dB dynamic range and can resolve better than 10 aF. The complete module operates from a single 5V supply and has a measured sensitivity of 960 mV/g with a noise floor of 1.08 /spl mu/g//spl radic/Hz in open-loop. This system can resolve better than 10 /spl mu/g//spl radic/Hz in closed-loop.

Breath sensors for lung cancer diagnosis

The scope of the applications of breath sensors is abundant in disease diagnosis. Lung cancer diagnosis is a well-fitting health-related application of this technology, which is of utmost importance in the health sector, because lung cancer has the highest death rate among all cancer types, and it brings a high yearly global burden. The aim of this review is first to provide a rational basis for the development of breath sensors for lung cancer diagnostics from a historical perspective, which will facilitate the transfer of the idea into the rapidly evolving sensors field. Following examples with diagnostic applications include colorimetric, composite, carbon nanotube, gold nanoparticle-based, and surface acoustic wave sensor arrays. These select sensor applications are widened by the state-of-the-art developments in the sensors field. Coping with sampling sourced artifacts and cancer staging are among the debated topics, along with the other concerns like proteomics approaches and biomimetic media utilization, feature selection for data classification, and commercialization.

Fully Self-Powered Electromagnetic Energy Harvesting System With Highly Efficient Dual Rail Output

This paper presents a vibration-based energy harvesting system composed of a compact electromagnetic (EM) power generator and highly efficient full-wave interface electronics in a system-on-package. The system harvests energy from ambient vibrations, and delivers a smooth and reliable dual rail DC supply to power up a practical load. The energy harvester module is an in-house double-coil EM transducer which generates AC voltage in response to low frequency ambient vibrations. Voltage regulation is achieved by the interface electronics at the core of the system, which is designed to rectify the input AC voltage with peak amplitude ranging from several hundred mVs to several Volts, with maximum efficiency. The interface electronics contains an active rectifier with high conversion efficiency (>;80%) for a wide range of load currents (0-42 μA). A passive network, built from low threshold-voltage chip diodes and capacitors, generates a dual supply voltage from one of the coils to power up the active rectifier. The autonomous system of 16 cm3 volume (comparable to the size of a C-Type battery), delivers 54 μW to a 37-μA load through a dual rail 1.46 V DC voltage with total system efficiency of 81%, when subjected to low frequency (8 Hz) external vibrations. The maximum overall system power density has been validated to be 6.06 μW/cm3, three times what was previously reported for a batteryless vibration driven system.