This paper presents a piezoelectric energy harvesting circuit, which integrates a Synchronized Switch Harvesting on Inductor (SSHI) circuit and an active rectifier. The major design challenge of the SSHI method is flipping the capacitor voltage at optimal times. The proposed SSHI circuit inserts an active diode on each resonant loop, which ensures flipping of the capacitor voltage at optimal times and eliminates the need to tune the switching time. The diodes of the SSHI circuit are also used as a rectifier to further simplify the controller. The key advantage of the proposed circuit is a simple controller, which leads to low power dissipation of the proposed circuit to result in high efficiency. The proposed circuit is self-powered and capable of starting even when the battery is completely drained. The circuit was fabricated in BiCMOS 0.25 μm technology with a die size of 0.98 × 0.76 mm ² . Measured results indicate that the proposed circuit increases the amount of power harvested from a piezoelectric cantilever by 2.1 times when compared with a full bridge (FB) rectifier and achieves a power conversion efficiency of 85%. The proposed circuit dissipates about 24 μW while the controller alone only 1.5 μW.

This paper presents an ultra low power IC design for piezoelectric (PE) energy harvesting, which integrates a maximum power point tracking (MPPT) circuit and a synchronized switch harvesting on inductor (SSHI) circuit. The proposed circuit also has three different operation modes to extend the range of the harvestable power level generated by a PE transducer. The circuit is designed in CMOS and fabricated in BiCMOS 0.25 μm technology with the die size of 2 mm2. The measurement results indicate the circuit can harvest energy with the input power ranging from 10 μW to 34 μW during MPPT. It achieves peak efficiency of 77 % under a PE cantilever voltage of 3.5 V and the battery voltage of 4.2 V.

This paper proposes alternating resistive impedance matching for an impact-type microwind piezoelectric energy harvester (PEH). The proposed PEH is composed of a piezoelectric cantilever and a small wind turbine, which strikes the free end of the cantilever to generate vibrations. The motion of the cantilever is divided into two action periods, impact and vibration, whose optimal resistive loads are different. The impact period detector, in collaboration with a wake-up circuit, identifies the current period and sets the frequency and duty cycle of the oscillator to provide the optimal load for each period. When the cantilever generates energy, the wake-up circuit activates the converter to charge the battery. Otherwise, the circuit goes into sleep mode to save power. The proposed circuit is able to cold start even if the battery is completely drained. Experimental results indicate that the efficiency of the proposed circuit is 70.3% for a wind speed of 1.3 m/s, which is 6.3% higher than that of an existing resistive matching circuit with sleep mode and 7.7% higher than that of a circuit without sleep mode. The proposed circuit is intended for low-speed winds, but it also achieves high efficiency for higher wind speeds.

Postural control is a key aspect in preventing falls. The aim of this study was to determine if obesity affected balance in community-dwelling older adults and serve as an indicator of fall risk. The participants were randomly assigned to receive a comprehensive geriatric assessment followed by a longitudinal assessment of their fall history. The standing postural balance was measured for 98 participants with a Body Mass Index (BMI) ranging from 18 to 63 kg/m², using a force plate and an inertial measurement unit affixed at the sternum. Participants’ fall history was recorded over 2 years and participants with at least one fall in the prior year were classified as fallers. The results suggest that body weight/BMI is an additional risk factor for falling in elderly persons and may be an important marker for fall risk. The linear variables of postural analysis suggest that the obese fallers have significantly higher sway area and sway ranges, along with higher root mean square and standard deviation of time series. Additionally, it was found that obese fallers have lower complexity of anterior-posterior center of pressure time series. Future studies should examine more closely the combined effect of aging and obesity on dynamic balance.

Real-time system identification is desirable for designing a proper feedback controller in a practical system. Digital control provides the potential advantages of on-line programmability to apply adaptive control. The digital nature of the feedback signal facilitates the communication between the converter and the processing unit (e.g., microcontroller). These features of digital control make it possible to estimate the real-time system parameters by means of system identification in situ (in-place), and then design and configure the controller accordingly. In this paper, an automated system identification method for digitally-controlled multi-phase DC-DC converters is set forth. Fourier analysis is utilized because of the potential for closed-loop identification and high measurement signal-to-noise ratio. The phase loss and zero-order-hold due to digital control are considered. The identification results for single- and multi-phase DC-DC converters closely match those obtained from conventional network analyzer and models. The proposed method can be done by a stand-alone digital controller; therefore it eliminates the expense of external test equipment. The identification results can be used for controller configuration without pre-existing knowledge of the power stage parameters. This opens up a possibility of moving the determination of the loop compensation from a lab bench to a factory floor or even to an end customer's application.