Piezoelectric Film Sensor (Picoleaf™)Basics on piezoelectric film sensors (Picoleaf™)

Polylactic acid (PLA) is a biodegradable polymer that provides the same strength and formability as general-purpose petroleum-derived plastic. It began attracting attention around 1995, and is now widely known as an environmentally friendly polymer. The main ingredient of PLA is lactic acid, which is produced by using lactic acid bacteria to ferment starch obtained from plants. Starch can be obtained through photosynthesis, so this carbon neutral material can be produced without increasing the amount of CO₂ in the atmosphere (excluding energy using during manufacturing processes), throughout the entire life cycle from manufacturing to disposal and decomposition.

Unlike other biodegradable polymers, PLA is highly transparent and its light transmittance is comparable to that of acrylic (93%). PLA is used in many familiar products, including the packaging used for eggs and tomatoes sold in supermarkets. Although PLA is generally well-known for being a plant-derived polymer that is both environmentally friendly and economical, Murata was more interested in its piezoelectric performance.

The piezoelectric constant (piezoelectric constant d constant) of PLA is around seven to twelve pC/N, which is quite small compared with materials such as PZT. However, the relative permittivity of PLA is extremely low (approximately 2.5), which results in a large piezoelectric output constant (piezoelectric constant g constant, g=d/εT). This provides PLA with a high sensing sensitivity. When comparing by piezoelectric output constant, it is approximately the same as polyvinylidene fluoride (PVFD), which has a piezoelectric constant at least four times that of PLA.

Picoleaf is a thin and flexible sensor made from PLA. In addition to being able to be mounted in small spaces, it offers the following features.

Picoleaf can be used to obtain output based on the displacement speed of the piezoelectric film, when used in combination with a detection circuit. These output characteristics can be used to design various sensors for detecting pressing force, grip, biosignals, and more.