The evolution of sensing technology and communication network contribute to the realization of an Autonomous driving society and its growth. Ultrasonic parking assistant is a key sensor for automated driving and parking functions. Ultrasonic parking sensors were in use in Europe long before debate on automated driving became active. TDK has for many years supplied Piezo Disks and ultrasonic driver transformers for use with ultrasonic parking sensors. TDK also developed a multilayer ceramic chip capacitor that exhibits attenuating capacitance (ZL characteristics) under high-temperature environments that is suitable for resonant circuits with Piezo Disk. This article presents Piezo Disk, ultrasonic driver transformers, and MLCC with ZL characteristics.
The Autonomous Driving society is coming to the reality in order to reduce the number of casualties caused by traffic accidents and improve the level of convenience of mobility services. Plans call for automated driving vehicles and vehicles with ADAS functions to be equipped with cameras, millimeter wave radar, LiDAR, telematics control units (TCU), and other new units. In Europe, where most parking is on roads or parallel parking on narrow private roads, ultrasonic parking assist has long been in use, even before the proliferation installation of ADAS functions. Ultrasonic sensors emit ultrasonic waves, and a receiver detects waves reflected from obstacles to confirm the presence of objects and measure to distance to obstacles. In the past, systems issued warnings to drivers so that vehicles could avoid colliding with obstacles such as walls and other vehicles, but now, adoption and use in automated parking systems that control the steering is increasing. Ultrasonic parking assist will continue to play a vital role in automated driving and automated parking functions.
Ultrasonic parking assist systems require a Piezo Disk that detects and measures the distance to an obstacle. A piezo device generates electricity from mechanical force according to the force between electrodes. In contrast, if voltage is applied between the electrodes, the device will undergo a mechanical change depending on the amount of voltage applied. The amount of electricity generated is used to detect whether an object is present and to measure the distance to the object. TDK brand piezo products are used in ultrasonic parking assist systems, but have also been used for many years in the automotive sector for injector piezoelectric devices. This means that TDK products have high-precision sensing performance and long-term reliability under harsh automotive environments, enabling custom designs according to customer requests.
|Thickness in mm||0.195～1.02|
|Diameter in mm||5～7|
|Frequency in kHz||285～2000|
|Wrap around metallization: Possible||Possible|
The component that supplies the stable voltage to the Piezo Disk described above is an ultrasonic parking assist transformer. TDK transformers have a long track record of use in automotive applications. Since they are manufactured on advanced, automated production lines, they are highly robust. In addition, we have established reference designs with TI and Elmos, makers of ICs for driving piezo components. TDK has products suitable for different configurations, inductance, and frequency bands, as shown in Table 4.
|Terminals||SMD, 5 U-shape|
|Max size / mm||L:8.8 x W：7.6 x H:7.1|
|Turn ratio||1 : 1 : 8.42||1 : 1 : 8.42||1 : 1 : 9||1 : 1 : 15||1 : 1 : 10.1|
|Operating temperature range||-40 ~ +85°C||-40 ~ +85°C||-40 ~ +85°C||-40 ~ +85°C||-40 ~ +85°C|
|Shielding||-||With connection to pin 6||-||-||-|
Piezo Disk has an electrostatic capacitance component, and the electrostatic capacitance with changes with operating temperature.
When the electrostatic capacitance component changes, the resonance frequency of the ultrasonic sensor deviates, and this has an impact on the measurement range or the measurement precision.
In order to resolve this problem, a capacitor with ZL characteristics has temperature characteristics whereby the capacitance decreases as the operating temperature increases, compensating for the change in the Piezo Disk’s electrostatic capacitance.
|Capacitance||1200 pF ± 5%||1300 pF ± 5%|
|Dimensions||Length(L)||2.00 ± 0.20 mm|
|Width(W)||1.25 ± 0.20 mm|
|Thickness(T)||0.85 ± 0.15 mm|
|Terminal Width(B)||0.20 mm Min.|
|Terminal Spacing(G)||0.50 mm Min.|
|Temperature Characteristic : ZL||-5350 ± 750ppm/℃ [ -40 ~ 20°C ]|
|-4500 ± 500ppm/℃ [ 20 ~ 85°C ]|
|Rated Voltage||250 VDC|
|Dissipation Factor ( DF )||0.025 Max.|
|Insulation Resistance ( IR )||10000 MΩ Min.|
Capacitance, DF : 1kHz/ 1Vrms
Insulation Resistance : 250V / 60sec.
To achieve a society with widespread, safe and comfortable automated driving, automobiles will be equipped with new sensors including cameras as well as wireless communication functions. In addition to new sensors, the functions of ultrasonic parking assist, which has been in use for some time, will change even as they continue to be used. TDK has long supplied components for ultrasonic parking assist and will continue its efforts to contribute to a modern, mobile and connected society while further refining its advanced technologies. Please take a look at the Product Center for detailed product data and for consultations regarding individual product specifications.