Quartz Crystal Microbalance (QCM) has been used for detecting microgram level mass changes in gas and liquid phase. Conventional QCM design comprises a circular electrode configuration with an evenly distributed mass loading area. However, their mass sensitivity distribution is found to be non-uniform due to the inherent energy trapping effect. In this paper the recently developed QCM with a ring electrode and a ring-dot electrode configuration are evaluated. It is shown that this new configuration offers the ability to achieve a uniform mass sensitivity distribution while attaining a comparable mass sensitivity for a reduced mass loading area. Finite Element Analysis is used to design and evaluate the conventional circular electrode QCM and the proposed ring electrode and ring-dot electrode QCM configurations, where the mass loading area is reduced by 25% compared with the conventional sensor. Simulations are conducted to determine the sensor’s resonant frequency shifts for an added mass per unit area of 20 ug/mm². The results indicate that newly designed ring and ring-dot electrode configurations operate at a higher resonant frequency. The observed frequency shift for the designed circular electrode, ring electrode, and ring-dot electrode configurations on a 333 um thick quartz substrate are 85 kHz, 84 kHz, and 82 kHz, respectively. It is shown that the ring electrode and new ring-dot electrode configurations achieve a higher resonant frequency and offer a comparable sensing performance despite comprising of over 25% reduced mass loading area in comparison to the conventional circular electrode configuration.

Poly(3-hydroxybutyrate) (PHB) is a natural and biodegradable storage polyester, produced by numerous bacteria, which is considered a potential substituent for conventional plastics in the packaging industry. The improvement of the PHB material lifetime often involves the mechanical and tribological characterization which can be accurately performed on thin films. In this study, we aimed at the evaluation of the tribological properties, like adhesion force, friction coefficient and wear resistance, of different polyester films fabricated via the solvent casting method [1]. Three polyester films were designed in this study, each containing 1% w/v constituents as follows: a PHBh film prepared out of the PHB extracted from the extremely halotolerant bacteria Halomonas elongata DSM2581^T, a PHBc film fabricated using a commercially available PHB and a PHBVc film generated using the commercial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The spectroscopy-in-point of AFM was used for adhesion force measurement based on multiple tests performed in a matrix and the AFM lateral operating mode was applied for friction analysis under a controlled normal load. The fabricated PHBh film presented a thickness between 5 µm -7 µm, a lower adhesion force (14 nN) as well as a smaller friction coefficient (0.15) compared to the PHBc and PHBVc. The tribological investigations of PHBh film revealed a biodegradable material with low roughness as well as small adhesion and friction forces. Further optimization can be performed for the improvement of the PHBh film by copolymerization with other polymers, polyesters and reinforcers, thus generating a feasible material with advanced tribo-mechanical features.

References

[1] Cristea A, Pustan M, Birleanu C, Dudescu C, Floare CG, Tripon AM, Banciu HL. (2021) Mechanical evaluation of solvent casted poly(3-hydroxybutyrate) films derived from the storage polyesters produced by Halomonas elongata DSM 2581^T. J Polym Environ, Submitted: ID: JOOE-S-21-00260.

Ceramic materials have properties such as high hardness, high ratio between mechanical resistance/ density, wear and corrosion resistance, high stability to the action of corrosive agents and relatively low cost price. However, the use of technical ceramics has a rather limited area determined essentially by its tribomechanical behavior. The machine parts may failure and not fulfilling their functional role due to some limit states. This paper is based on the behavior of aluminum ceramics in terms of stress and strain in the contact area and the tribological behavior of these materials. A mathematical concept including multiobjective optimization based on Cuckoo Search Algorithm of breaking the ceramic materials in which there are defects in the form of internal cracks has been developed. A defect criterion has been formulated to allow the evaluation of the propagation of the semicircular crack which shapes the places where there are natural defects in the ceramic mass. The model highlighted is the contact between two curved surfaces, specific to the ball-ring contact in the bearings. It has highlighted tensions stress and the stress factors, taking into account the coefficient of conformity and the influence of the friction effects. The experimental study of the mechanical stress state in the contact areas was carried out of the ceramic friction couple ball - bearing ring (Al₂O₃ – 99.7% with the addition of SiO₂, Fe₂O and MgO). A large number of experimental tests were performed. The results of this research work are useful for the mechanical designers to identify the crack effect on the mechanical parts lifetime and to improve the reliability.

It is well documented that the lift force of hovering micro aerial vehicles can be enhanced by increasing their air-flow velocities. This is commonly accomplished using nozzles and other flow-manipulating geometries with Reynolds numbers above order 100. [1,2] However, the effects of nozzles and other geometries are not well characterized for lower Reynolds numbers within the Stokes’ regime. In general, controlled flight in low-Reynolds number conditions using conventional propulsion methods such as propellers is difficult. Instead, levitation at ultra-low Reynolds number conditions has been accomplished through other means, including photophoretically as demonstrated recently by Cortes et al. [3] and Azadi et al. [4]. These works levitated planar materials without macroscale geometric enhancements and relied strictly on the lift force created through a temperature or accommodation coefficient difference across the planar structure. In the current work, we numerically explored the feasibility of multi-scale structures operating at low-to-moderate Reynolds numbers that pair microscale photophoretic gas pumping with macroscale jet-inducing nozzles.

We used ANSYS Fluent to simulate the lift forces in centimeter-scale porous membrane discs (no macroscale enhancements) and in conical nozzles created from porous membranes. Our results indicate that porous conical nozzles provide an order of magnitude lift enhancement relative to flat discs with inlet velocities as low as 10^-6 m/s. In addition, we developed a semi-analytical flow model and found good agreement with the simulations. We are currently fabricating mylar structures analogous to the simulation geometries, laser machined to create porosity and adhered to lightweight frames to maintain their shape. The multi-scale structures we create will be of critical importance for exploring low-pressure environments such as Earth’s mesosphere and the Martian atmosphere.

References:

[1] Benedict, Moble, et al. "Experimental investigation of micro air vehicle scale helicopter rotor in hover." International Journal of Micro Air Vehicles3 (2015): 231-255.

[2] Seddon, John M., and Simon Newman. Basic helicopter aerodynamics. Vol. 40. John Wiley & Sons, 2011.

[3] Cortes, John, et al. "Photophoretic levitation of macroscopic nanocardboard plates." Advanced Materials16 (2020): 1906878.

[4] Azadi, Mohsen, et al. "Controlled levitation of nanostructured thin films for sun-powered near-space flight." Science Advances7 (2021): eabe1127.

The earcanal mechanical deformation induced by the temporomandibular joint movement constitutes a promising source of energy to power in-ear devices (hearing aids, communication earpieces, etc.). The large morphological variability of the human earcanal and its intrinsic dynamic characteristics - with displacement frequencies below 1.5 Hz with average volume variation of 60 mm³ - motivate the development of non-conventional dedicated energy harvesting methods. This paper demonstrates the concept and design of a modular hydraulic-piezoelectric self-actuated frequency up conversion micromachine for energy harvesting. The mechanical energy is conveyed using a liquid-filled custom fitted earplug, which can be considered as a hydraulic pump. A dedicated hydraulic circuit drives two micro-pistons (MP) while ensuring the impedance matching between the earplug available pressure and swept volume and the MP required displacement and force. These MP actuate a mechanical oscillator associated to a piezoelectric transducer allowing the low frequency mechanical excitation to be efficiently converted into electric energy through frequency up-conversion. An innovative mechanical feedback selects the actuated MP depending on the mechanical oscillator position. By doing this, each jaw motion can be harvested. A complete theoretical multiphysics model of the machine has been established for the design and evaluation of the potential of the proposed approach. Global analytical and refined FEM approaches have been combined to integrate the fluid and mechanical behaviors. Based on simulation and preliminary experimental data, the harvested energy is expected to be 8 µJ for one jaw closing, with a theoretical 40 % end-to-end conversion efficiency.

During the daily activities, such as chewing, eating, speaking, etc., the human jaw moves and the earcanal is deformed by its anatomic neighbor called the Temporomandibular Joint (TMJ). Given the frequency of those jaw-joint activities, the earcanal dynamic movement is a promising source of energy at close vincinity of the ear, and such envery can be harvest by using a mechanical-electrical transducer, dubbed energy harvester. Yet, the optimal design of such micromachine requires to characterize the TMJ’s range of motion, its mechanical action on the earcanal and its mechanical power capability. For that purpose, this research presents two methods to analyse the earcanal dynamic movements: first, an in-situ approach based on measuring the pressure variation in a water-filled earplug fitted inside the earcanal; and second, an anatomic-driven mechanism in the form of a chewing test fixture capable to reproduce the TMJ kinematics with great precision. The pressure earplug system provides the earcanal global dynamics which can be derived as an equivalent displaced volume while the chewing test fixture provides the discrete displacement along the earcanal wall. Both approaches are complementary and contribute to a better analysis of the interaction between TMJ and earcanal. Ultimately, the knowledge of the maximum displacement area and the derived generated power within the earcanal will lead to the design of a micromachine allowing to further investigate in-ear energy harvesting strategies.

Photophoretic or light-driven levitation has been studied extensively in the context of the motion of illuminated micron-sized particles, such as dust grains in the atmosphere under sunlight [1,2], and in relation to Crooks radiometers [3]. When heated by incident light, a micron-sized particle experiences a temperature gradient that in turn results in uneven gas-surface interactions and a net propulsive force [4]. Though thoroughly investigated for micron-sized particles, this phenomenon has rarely been studied to controllably levitate macroscopic objects.

We report light-driven levitation of 0.5-um thick mylar samples that have been modified by depositing a 300-nm-thick layer of carbon nanotubes (CNTs) on a single side. The CNT layer serves three key purposes: 1) It acts as a lightweight light absorber, absorbing ~ 90% of the incident light and elevating the temperature of the sample. 2) It increases the structural rigidity of the mylar film, allowing cm-scale discs with submicron thicknesses to hold their shape. 3) It creates a structured porous surface that traps impinging gas molecules, which results in an accommodation coefficient difference between the top and bottom surfaces for gas-surface interactions. Air molecules that rebound from the CNT-coated side have on average higher velocities than those departing from the opposing uncoated mylar surface. We show that the net force thus created can be used to levitate the mylar films. Moreover, we will demonstrate our ability to manipulate a light field in order to control the flight of levitating samples for extended periods of time.

References:

1. Jovanovic, O. Photophoresis—Light induced motion of particles suspended in gas. Journal of quantitative spectroscopy & radiative transfer 110, 889–901, (2009)
2. Horvath, Photophoresis – a forgotten force ??, KONA powder and particle journal, 31, 181–199 (2014)
3. Ketsdever, N. Gimelshein, S. Gimelshein, and N. Selden, “Radiometric phenomena: From the 19th to the 21st century”, Vacuum 86, 1644-1662 (2012).
4. Loesche, G. Wurm, T. Jankowski, M. Kuepper, Photophoresis on particles hotter/colder than the ambient gas in the free molecular flow. J. Aerosol Sci, 97, 22–33 (2016)

Energy harvesting from wasted or unused power has been the topic of discussion for a long time. We have developed ‘damper devices’ for precision machinery and automobile engine mats in 1980s. However, after getting into 1990s, we realized that just electric energy dissipation was useless, and started to accumulate the converted electric energy into a rechargeable battery? This is the starting point of ‘piezoelectric energy harvesting devices’ historically.

As one of the pioneers in the piezoelectric energy harvesting, Uchino feels a sort of frustration on many of the recent research papers from the following points:

(1) Though the electromechanical coupling factor k is the smallest among various piezo-device configurations, the majority of researchers primarily use the ‘unimorph’ design. Why?

(2) Though the typical noise vibration is in a much lower frequency range, the researchers measure the amplified resonance response (even at a frequency much higher than 1 kHz) and report these ‘unrealistically’ harvested electric energy. Why?

(3) Though the harvested energy is much lower than 1 mW, which is lower than the required electric energy to operate a typical energy harvesting electric circuit with a DC/DC converter (typically around 2 – 3 mW), the researchers report the result as an energy ‘harvesting’ system. Does this situation mean actually energy ‘losing’? Why?

(4) Few papers have reported successive energy flow or exact efficiency from the input mechanical energy to the final electric energy in a rechargeable battery via the piezoelectric transducer step by step. Why?

Interestingly, the unanimous answer from these researchers to my question ‘why’ is “because the previous researchers did so!”.

This paper focuses on how to rectify the above common “misconceptions” in the piezoelectric energy harvesting system. We will consider comprehensively three major phases/steps associated with piezoelectric energy harvesting: (i) mechanical-mechanical energy transfer, including mechanical stability of the piezoelectric transducer under large stresses, and mechanical impedance matching, (ii) mechanical-electrical energy transduction, relating with the electromechanical coupling factor in the composite transducer structure, and (iii) electrical-electrical energy transfer, including electrical impedance matching, such as a DC/DC converter to accumulate the energy into a rechargeable battery. In order to provide comprehensive strategies on how to improve the efficiency of the harvesting system, the author conducted detailed energy flow analysis in piezoelectric energy harvesting systems with stiff “Cymbals” (~100 mW) and flexible piezoelectric transducers (~1 mW) under cyclic mechanical load, in order to improve the efficiency of the harvesting system. Energy transfer rates are practically evaluated for all three steps above. The former “Cymbal” is to be applied to the automobile engine vibration, while the latter flexible transducer is to the human-wearable energy-harvesting system.

We should also point out that the commercially-successful piezo-energy harvesting devices are for signal transfer applications, where a pulse input load is applied to generate instantaneous electric energy for transmitting signals for a short period (100 ms ~ 10 s) without accumulating the electricity in a rechargeable battery. Present products include “Lightning Switch” from Face International and the 25 mm caliber “Programmable Ammunition” from Micromechatronics Inc.

Additive manufacturing (AM) makes enormous advancements in technology and materials development, thus requires attention in developing functionalized printed materials. AM can assist in manufacturing complex designed tailored-shaped electrodes efficiently for electrochemical sensing in the food industry. Herein, we used commercial fused deposition modelling (FDM) filament, polylactic acid (PLA) for FDM 3D printing of self-designed electrode with minimal time and cost compared to commercial electrodes. Surface functionalization on the 3D printed PLA electrode was done using GnP to enhance the electrical conductivity. Scanning electron microscopy confirms the homogenized surface coating of GnP that provides electron flow behaviour for the 3D printed electrode. The electrochemically functionalized 3D printed electrode was tested against standard 3-monochloropropane-1,2-diol (3-MCPD) with known concentrations and characterized using cyclic voltammetry and differential pulse voltammetry methods. Results showed a basis for promising application to detect and quantify 3-MCPD, a food contaminant known for its potential of being carcinogenic. Fabrication of functionalized 3D printed polymer electrodes paves way for the development of complete 3D-printable electrochemical systems.

Magnetic microrobots with versatile mechanical motion will enable many ex- and in vivo applications. Unfortunately, monolithic integration of multiple functions in a streamlined microrobotic body is still challenging due to the compromise between fabrication throughput, device footprints, and material choices. In this talk, I will present a unified framework architecture for microrobotic functionalization to enable magnetically steered locomotion, chemical sensing and in-vivo tracking. This has been achieved through stratifying stimuli-responsive nanoparticles in a hydrogelmicro-disk. We uncovered the key mechanism of leveraging spatially alternating magnetic energy potential to control a Euler’s disk-like microrobot to locomote swiftly on its sidewall. The results suggest great potential for microrobots to locomote while cooperating a wide range of functions, tailorable for universal application scenarios.