Abstract
In force measurement applications, a piezoelectric force sensor is one of the most popular sensors due to its advantages of low cost, linear response, and high sensitivity. Piezoelectric sensors effectively convert dynamic forces to electrical signals by the direct piezoelectric effect, but their use has been limited in measuring static forces due to the easily neutralized surface charge. To overcome this shortcoming, several static (either pure static or quasistatic) force sensing techniques using piezoelectric materials have been developed utilizing several unique parameters rather than just the surface charge produced by an applied force. The parameters for static force measurement include the resonance frequency, electrical impedance, decay time constant, and capacitance. In this review, we discuss the detailed mechanism of these piezoelectric‐type, static force sensing methods that use more than the direct piezoelectric effect. We also highlight the challenges and potentials of each method for static force sensing applications.
Highlights
Force sensation as part of tactile information is an important feedback mechanism to perceive external stimuli in human explorations [1,2,3]
When a static force is applied to piezoelectric force sensors, the induced electrostatic charge begins to exponentially decrease according to the following equation, q = Qe−t/RC (q is the amount of charge after a certain time, Q is the original value of generated charge, R is the resistance of the feedback resistor, C is the total capacitance of the sensor system, and t is the measurement time)
The electrical impedance measurement method is one of the most promising techniques and is suitable especially for small force measurements because it presents a high sensitivity to small forces
Summary
Force sensation as part of tactile information is an important feedback mechanism to perceive external stimuli in human explorations [1,2,3]. In the last few decades, many electromechanical force sensing techniques have been developed to satisfy these requirements, including piezoresistive-, capacitive-, and piezoelectric-type sensors [12,13,14,15] Among these sensing methods, piezoelectric (PE) sensing is one of the most popular methods because it uses a direct piezoelectric effect that can efficiently measure dynamic forces [16,17,18,19]. For the sufficiently long DTC with adequate signal processing, quasistatic forces can be possibly measured, but there are still limitations in the time window for measuring static forces due to the current leakage [24] This characteristic makes typical piezoelectric force sensors only suitable for time-varying (dynamic) force measurements despite their advantages over other types of force sensors. Our review covers relatively recent literature (mainly from 2000 to 2020) with the keywords of “piezoelectricity” and “static force sensor”
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