In order to fully mimic the human body**, there is a strong need for tactile sensors that can quantitatively detect pressure and temperature signals at the same time. Depending on the sensor unit and the conversion principle, pressure and temperature sensors are divided into two types: (1) dual-parameter sensors;(2) Integrated bimodal sensor. A biparameter sensor is a single sensor that can convert pressure and temperature bimodal stimuli into separate signals. An integrated bimodal sensor is defined as two separate sensors integrated into a pixel that can convert pressure and temperature bimodal stimuli into separate signals.
1) Dual-parameter sensor.
An easy way to achieve a bimodal pressure and temperature sensor is to develop a biparameter sensor that can respond to pressure and temperature stimuli as separate signals through a single sensor. The main advantages of this type of tactile sensor are the simple manufacturing process and readout mechanism. Two types of piezoresistive thermal resistance and piezoresistive thermoelectricity have been commonly reported in the previous literature. Only one active material is used to sense the pressure and temperature signals.
(2) Integrated bimodal sensor.
Another approach is to integrate two separate sensors into a single pixel, each in response to a specific stimulus. Theoretically, if the number of types of pressure sensors is multiplied by the number of temperature sensors, there can be many combinations of bimodal sensors. For example, piezoresistive and thermally resistive;Capacitive RTD;Piezoresistive thermoelectric;Piezoelectric thermoelectric pressure and temperature bimodal sensors.
Integration of tactile sensors: power supply, wireless communication, and signal processing circuits.
In addition to the above principles and classifications, it is also important to integrate pressure and temperature tactile sensors with other electrical components such as power supply, wireless communication, signal processing on readout circuits, etc., which will ensure accuracy and authenticity. Time signal processing and data transmission require even flexible tactile sensors to be self-powered without the need for batteries. In order to ensure the continuous monitoring and data transmission of signals, the integration of sensors and signal processing circuits and wireless communication has also been widely carried out.
Power Supply: Energy harvesting and energy storage technology.
Traditional tactile sensors are often powered by bulky lithium batteries that need to be recharged frequently. However, due to the urgent need for lightweighting, flexibility, and autonomous continuous operation, it severely limits the development of next-generation tactile sensors. Therefore, energy harvesting technologies that extract energy directly from the surrounding environment and convert it into electrical energy, as well as energy storage technologies, are necessary. Such as energy harvesting technologies: photovoltaic, thermoelectric, piezoelectric and triboelectric;Energy storage technology: batteries and supercapacitors.
Signal processing circuitry: Piezoresistive sensor arrays typically employ improved electrical grounding circuitry to eliminate crosstalk and parasitic effects. Piezoelectric sensor arrays use bias amplification circuitry to convert the signal. For capacitive sensor arrays, a differential circuit is required to detect low differences in capacitance.