A nested cantilever piezoelectric MEMS speaker

To address the challenge of insufficient full-range sound pressure level (SPL), particularly in the low-frequency range (20–100 Hz), in piezoelectric micro-electromechanical system (MEMS) speakers with limited area, a novel quasi-closed diaphragm design is proposed. The 6.25 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sup> diaphragm incorporates double-drive electrodes, a flexible coupling structure, and a central mass, subdivided by slits. Parylene-C acts as an acoustic isolation layer to prevent air leakage, a flexible coupling structure to reduce diaphragm stiffness, and significantly lowers the stress at the ends of the slits, enabling higher excitation voltages for improved SPL. Additionally, the flexible coupling structure reduces both electrode area and power consumption, compared to the rigid coupling structure. Tests conducted on an ear canal simulator show that compared to the rigid coupling design, the proposed speaker achieves a 13–15 dB SPL improvement from 20 Hz to 1 kHz under 2 Vpp excitation, with a 20% reduction in power consumption. Under 60 Vpp excitation, the proposed speaker produces SPL > 93 dB across the frequency range from 20 to 100 Hz, and SPL > 100 dB from 100 Hz to 20 kHz. Under 100 Vpp excitation, the design delivers SPL > 97 dB across the frequency range from 20 to 100 Hz. This work demonstrates the advantage of achieving high full-range SPL with a small diaphragm area through optimized design, offering a promising solution for the advancement of MEMS speakers.

One of the challenges for piezoelectric MEMS speakers is their relatively low sound pressure level (SPL) due to the relatively small piezoelectric constants of sol-gel or sputtered lead zirconate titanate (PZT). In this paper, we present a piezoelectric MEMS speaker with improved SPL that is enabled by high-piezoelectric-coefficient ceramic PZT as well as a dual-electrode configuration with phase tuning. A dual-electrode piezoelectric MEMS speaker based on 4 μm thin ceramic PZT has been designed and fabricated with top electrodes consisting of an inner circular-shaped electrode and an outer ring-shaped electrode. The maximum SPL at 9.7 kHz reaches 121 dB with both electrodes activated simultaneously. Measurements have also revealed that 180° is not always the optimal phase delay between the two driving signals to yield the highest SPL. Instead, the output SPL of the MEMS speaker changes significantly with the phase delay and is frequency dependent, peaking at different phase delays for different frequencies. The optimal phase delays in the frequency band from 600 Hz to 10 kHz have been obtained by phase tuning experiments, which shows 2 to 10 dB SPL improvement compared with the single-electrode driving method.

Piezoelectric MEMS loudspeakers based on cantilever diaphragms have demonstrated promising electroacoustic efficiency and low-frequency sound pressure level (SPL). However, their total harmonic distortion (THD) significantly increases near the first resonant frequency, and high-frequency SPL (above 10 kHz) rapidly decreases due to the resonance frequency and bandwidth limitations, severely affecting sound quality. This work presents a piezoelectric MEMS loudspeaker featuring a 2.7 µm-thick sputtered PZT film, comprising a cantilever diaphragm and four sets of Double-S actuators. The first resonance frequency of the cantilever diaphragm is 3.2 kHz, and the Double-S actuators introduce an additional resonance frequency at 21.3 kHz, addressing the issues of insufficient high-frequency SPL and poor THD performance. Testing on a 711-ear simulator reveals that, under 1–3 Vpp excitation, incorporating the Double-S actuators leads to an average SPL increase of 23 dB and an average THD reduction of 80% that remains below 0.6% across the 3.2–20 kHz range. Thus, both SPL and THD performance in the mid- to high-frequency range are improved. This work paves the way for the development of high-fidelity piezoelectric MEMS loudspeakers, offering new opportunities to improve sound quality and extend the frequency range for in-ear applications.

One of the key requirements for MEMS speakers is to increase the sound pressure level (SPL) while keeping the size as small as possible. In this paper we present a MEMS speaker based on piezoelectric bimorph cantilevers that produces a higher SPL than conventional unimorph cantilever speakers. The active diaphragm size is 1.4 × 1.4 mm2. The bimorph cantilevers are connected in parallel to make full use of the actuation voltage. At 1 kHz, the measured SPL reached 73 dB and the peak SPL reached 102 dB at the resonance frequency of 10 kHz in a 711 ear simulator under a driving voltage of 10 Vrms. The total harmonic distortion of the MEMS speaker was less than 3% in the range from 100 Hz to 20 kHz. Although the absolute SPL was not the highest, this work provides a better SPL for all piezoelectric MEMS speakers.

The paper is focused on a sophisticated switched mode power supply with a pure sinusoidal output voltage waveform with frequency (40-65 Hz) and voltage range (30-500 V). In order to cope with stringent voltage (10.2%) and distortion constraint (THD<0.7%) in a modern calibration system, traditional inverter design with an output LC filter is upgraded with a feedback-feedforward control principle. The paper presents the voltage source topology, analyzes its steady-state response and gives its comprehensive evaluation. Using a simple sensor that is capable to detect a small voltage asymmetry at the presence of a high AC component (500 VRMS), the parasitic DC component is limited below 5 mV. Experimental results demonstrate exceptional voltage accuracy (<0.2%) and low total harmonic distortion (THD).

To reduce total harmonic distortion (THD) and improve the power factor (PF) of a boost power factor correction (PFC) converter, here, the authors propose a non‐linear control algorithm that includes the feedforward correction (FC) algorithm in the continuous conduction mode (CCM) and the non‐linear frequency variation (FV) algorithm in the mixed conduction mode (MCM). The proposed FC algorithm achieves current out of distortion through zero crossing with a lower current loop bandwidth. The proposed non‐linear FV algorithm achieves high PF and low THD under minimal load conditions. The non‐linear FV algorithm comprises a third harmonic extraction algorithm, a harmonic control loop for reducing THD and a frequency production algorithm. By using this non‐linear FV algorithm, the inductor size is reduced, which leads to lower cost and also achieves better THD and PF. The proposed algorithms are verified experimentally in terms of current tracking, current THD, PF, heating and loss on a 2000‐W boost PFC converter hardware prototype.

This research compared the performance of PWM (Pulse Width Modulation) inverter and multilevel inverter in terms of their output voltage and current total harmonic distortion (THD). The inverters were designed to have the output voltage of 220 V at 50 Hz. The input voltage for both inverters are 400 VDC. For PWM inverter, the PWM technique utilized was sinusoidal PWM (SPWM) and for multilevel converter, the number of voltage level is five with diode-clamped topology. The study included circuit implementation, analysis, and THD calculation, all of which were carried out through simulation using PSpice software. In controlling the SPWM inverter output, the adjusted parameters included amplitude modulation ratio, frequency modulation ratio, and filter components’ parameters. On the other hand, the firing angles of the switching components were designated as controlling parameters in multilevel inverter. From the study, it was found that the best THD values of the designed SPWM inverter are 4.2% (voltage) and 1.7% (current), while those of multilevel inverter are 27% and 11%, for voltage and current, respectively. Thus, it can be concluded that SPWM inverter is better than 5-level inverter for the application in solar panel due to its lower THD. In our study, 5-level inverter did not satisfy the THD requirement specified in IEEE 512-1992, i.e. 5%.

This paper presents the mathematical and harmonic analyses of output phase voltages of three-phase voltage source inverters which employ a hybrid two-dimensional-three-dimensional (2-D-3-D) space vector modulation (SVM) voltage control algorithm. The explicit time-domain representation of the harmonic components in addition to the total harmonic distortion (THD) of the output phase voltages is given in terms of system and control parameters. This paper also investigates the harmonic characteristics and THD performance against the linearity of the modulation region which helps in the harmonic performance and design studies of such inverters employing the hybrid 2-D-3-D SVM. The fundamental component of the output voltages follows the reference with lower THD in the linear modulation region rather than the overmodulation region. Experimental results are used to validate these analyses as well as the effectiveness of the hybrid 2-D-3-D SVM algorithm for generating balanced and low THD phase voltages.

Light load efficiency and total harmonic distortion (THD) of AC-DC converters is of increasing importance when considering the increase in non-linear electronic loads on the modern grid. Efficiency and THD standards are becoming stricter in their requirements to account for this increase in non-linear loads. To address the increasing requirements for higher efficiency and lower THD without increasing the cost or complexity of the design, a Line Cycle Skipping (LCS) method is proposed and its digital control implementation presented. A 100W universal line input voltage PFC boost converter prototype is built to demonstrate the effectiveness of the proposed control method.

This paper presents the design guidelines of electronic ballast for HID lamps. High efficient electronic ballast with high power factor and low THD (total harmonic distortion) is presented. The use of input current shaper converters (ICSC) working in Discontinuous-Conduction Mode (DCM) to stabilize the discharge arc in High Intensity Discharge (HID) lamps is proposed. The analysis of how the ICSC stabilizes the lamp current through the analysis of the output capacitor Co and model lamp is presented. The results indicated the feasibility to stabilize the lamp and obtaining high efficiency, high power factor and low THD in a single stage is presented.

Piezoelectrically actuated micro-electromechanical systems (MEMS) loudspeakers have experienced significant advancements in recent years, achieving acoustic performance for in-ear applications comparable with traditional electrodynamic microspeakers. Despite their advantages in compactness, power efficiency, and ease of integration, these devices are limited by nonlinear hysteretic effects inherent to piezoelectric transduction, which often lead to undesirable distortion. Accurate and computationally efficient models are crucial for enabling digital signal processing (DSP) precompensation algorithms to address this challenge. While well-established nonlinear lumped-element models of electrodynamic loudspeakers have supported DSP techniques for equalization and linearization, the lack of analogous models for MEMS loudspeakers has constrained their broader application. This article presents a nonlinear discrete-time circuital model for a piezo-actuated MEMS loudspeaker designed for in-ear applications. The proposed model integrates two key processing components: a neural network (NN)-based block that accurately captures the nonlinear hysteretic behavior of piezoelectric transduction, and a linear circuit-equivalent block that represents the loudspeaker’s vibration and acoustic environment. The discrete-time implementation of the model, including a wave digital filter (WDF) realization of the circuit-equivalent block, enables efficient and accurate simulation of nonlinear hysteretic dynamics under arbitrary input signals. Validation against experimental data—including time-domain pressure waveforms, frequency-domain sound pressure level (SPL), and total harmonic distortion (THD)—demonstrates the model’s accuracy and effectiveness across a wide range of operating conditions.

Fluvial biological habitat types are classified using the diversity in physical characteristics of a water channel. Recent ecological management studies have highlighted the potential of underwater sound as a quantitative indicator of habitat characteristics. We investigate the relationship between underwater acoustic characteristics and hydraulic factors of 12 habitat types in the Namdae Stream in Yangyang, Korea, namely riffles, pools, and step riffle habitats. In the riffles and pools, the underwater sound levels were measured as sound pressure levels (SPLs). SPL(RMS) and 1/3 octave band have been measured in the frequency range between 8 Hz and 20 kHz. Among riffles, high SPL corresponded to the descending level of flow velocity. Pools generally had a low SPL. Low-frequency sound waves in the upper regions are better transmitted in the deeper water. To quantitatively analyze the water depth and flow velocity, we used a regression between the observed water depth, flow velocity, and acoustic SPL. The application of this study was certificated. The correlation coefficients between SPL and flow velocity/water depth revealed specific frequency bands with very strong positive correlations between SPL and flow rate in riffles and very strong negative correlations between SPL and pool water depth. Consequently, underwater sound can be used as an alternative for evaluating biological habitats.

This paper presents a single-stage flyback power-factor-correction circuit with a variable boost inductance for high-brightness light-emitting-diode applications for the universal input voltage (90–270 Vrms). The proposed circuit overcomes the limitations of the conventional single-stage PFC flyback with a constant boost inductance, which cannot be designed to achieve a practical bulk-capacitor voltage level (i.e., less than 450 V) at high line while meeting the IEC 61000–3–2 Class C line current harmonic limits at low line. According to the proposed variable boost inductance method, the boost inductance is constant in the high-voltage range and it is reduced in the low-voltage range, resulting in discontinuous-conduction-mode operation and a low total harmonic distortion (THD) in both the high-voltage and low-voltage ranges. Measurements obtained on a 24-V/91-W experimental prototype are as follows: PF = 0.9873, THD = 12%, and efficiency = 88% at nominal low line (120 V rms ); and PF = 0.9474, THD = 10.39%, and efficiency = 91% at nominal high line (230 V rms ). The line current harmonics satisfy the IEC 61000–3–2 Class C limits with enough margin.

This paper analyzes the Total Harmonic Distortion (THD) performance of a single phase 5-level CHB MLI. The multi level inverter is simulated using the carrier overlapping APOD Pulse Width Modulation (PWM) switching control technique. The total harmonic distortion (THD) of the output voltage is observed for the PWM control technique at varying modulation index of 0.7-1.0. The performance of a 5-level CHB MLI is simulated using MATLAB/SIMULINK. It is observed that the carrier overlapping APODPWM provides output with relatively low THD.

In order to break limited step-down ratio range and poor regulation capacity in the conventional resonant switched-capacitor converters for rectifier application, a single-stage ac/dc rectifier based on the dual-resonance switched-capacitor converter is proposed in this article. Through utilizing a dual-resonant structure and nonoverlapping strategy to realize wide continuous voltage gain of the proposed converter, high power factor (PF) and low total harmonic distortion (THD) based on the narrow dead zone are guaranteed by operating at high step-down conversion ratio in this converter topology. Moreover, the voltage gain is concentrated between resonant frequency and double resonant frequency to achieve a narrow switching frequency range for rectifier application. Furthermore, operating at flat voltage stress curves to obtain low voltage stress character. Comprehensive mode analysis, input PF and THD, and stress analysis are given, and analysis results indicate that the proposed power factor correction converter can work with soft turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and zero-current turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ; high efficiency is realized. Finally, an experimental prototype with 85–130 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ac</sub> input and 47 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub> /44 W output is built and tested for verifying the operation modes and PFC performance, and the comparison between different rectifiers and the proposed one is provided.