Effect of Heat Transfer on Materials Selection for Bimaterial Electrothermal Actuators

Abstract

Abstract-Bimaterial electrothermal actuation is a commonly employed actuation method in microsystems. This paper focuses on optimal materials selection for bimaterial structures to maximize the thermomechanical response based on electrothermal heat-transfer analysis. Competition between different modes of heat transfer in electrothermally actuated cantilever bimaterial is analyzed for structures at the microscale (10 µm ≤ L ≤ 1 mm) using a lumped heat-capacity formulation. The choice of materials has a strong influence on the functional effectiveness and the actuation frequency even though the electromechanical efficiency is inherently small (∼10 −5 ). Frequencies on the order of ∼100 Hz to 15 kHz can be obtained for bimaterial structures at small scales by varying either the operating temperature range or the rate of heat dissipation. It is found that engineering alloys/metals perform better than other classes of materials for high-work high-frequency (∼10 kHz) actuation within achievable temperature limits.[

Optimal Materials Selection for Bimaterial Piezoelectric Microactuators

“…Since the BPE actuators operate at mechanical resonance, an actuation frequency of ∼100 kHz can be achieved even for a cantilever length of a few hundred micrometers; however, the work/volume per cycle is relatively small. On the other hand, BET actuators have the ability to actuate at ∼10 kHz only if their length is less than 60 µm [17]; however, the work/volume per cycle is larger than that of the BPE actuator. Unlike BET actuators which are characterized by high losses due to the Joule heating effect, the losses associated with BPE actuators due to charge leakage are very small.…”

“…These have not yet been established for microsystems despite the hitherto limited available choices of the active materials [13]- [15]. This paper is aligned with the aims of previous studies on identifying promising candidate materials for bimaterial electrothermal (BET) actuators to meet defined functional requirements [16], [17], properly accounting for the discrete nature of the properties of engineering materials. The key objectives of this paper are to identify and rank optimal combinations of active materials and elastic substrates to deliver maximum performance against the functional requirements and to compare the performance of electrothermal and piezoelectric actuators in bimaterial architectures at microscales.…”

Tunable MEMS cantilever resonators electrothermally actuated and piezoelectrically sensed

“…When applying a voltage difference across the actuation electrode, the induced electrical current generates Joule heating thus resulting in thermal expansion and mechanical strain. The bilayer structure of materials with different thermal expansion coefficients (Pt and 3C-SiC) allows enhanced mechanical strain of the structure [18]. As the dissipated power depends on the squared value of actuation voltage, a device can be driven into resonance if the frequency f AC of an actuating voltage containing an AC component that is equal to half of the structure's natural frequency f 0 (f AC = f 0 /2) [14].…”

Modeling the distribution of phonon density for designing high quality thermal resonators

“…The tip of the beam is thermally insulated due to high surface to volume ratio of most thin film structures [8]. Neglecting the higher order terms (O(D 3 ) and O(D 5 )) equation (1) can be rewritten as…”